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https://en.wikipedia.org/wiki/Nervous_system
https://en.wikipedia.org/wiki/Memory
https://en.wikipedia.org/wiki/Soul
https://originalnature.co.nz/
신경 (NERVE) (in Korean and English)
위키백과, 우리 모두의 백과사전.
신경(神經)은 생물이 주위의 환경과 자극을 감지하고 이에 대처하는 기관이다.
신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다:
• 척수신경
• 뇌신경
• 신경계통 위키백과
신경계(神經系, 영어: nervous system)는 동물이 자신을 둘러싼 환경으로부터 자극을 받아들이고 반응을 일으키는 것과 관련된 계통이다. 해파리나 말미잘과 같은 자포동물은 단순한 신경망으로 촉수와 위수강을 움직인다. 척추동물과 같은 보다 복잡한 동물들은 신경원이라
• 중추신경계통
중추신경계통(中樞神經系統, 영어: central nervous system; CNS)은 중추신경계라고도 부르며 두개골에 싸여있는 뇌와 척수를 포함하는 신경계로 말초신경계통(Peripheral Nervous System; PNS)과 함께 동물의 행동이나 신체 기작을 제어한다
• 말초신경계통
말초신경계통(末梢神經系統, 영어: Peripheral Nervous System; PNS)은 척추동물의 뇌나 척수의 중추 신경계에서 나와 온몸에 나뭇가지 모양으로 분포하는 신경계를 말한다. 말초신경계라고도 부른다. 말초신경계는 동물의 신경계 일부로서 중추 신경 계통으로부터 피부, 근육, 샘 따위로 연결되는 신경의 모든 경로.
• 교감신경계통
교감신경계통(영어: sympathetic nerve system, SNS)은 교감신경이라고도 불리며 부교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경이다. 교감신경은 부교감신경과는 길항작용의 관계에 있어 교감신경이 흥분하면 맥박 증가, 혈압 상승, 소화 억제
• 몸신경계통
체성신경계(Somatic nervous system, SNS)는 자율신경계통과 함께 말초신경계통을 이루는 신경계통로 골격근의 운동과 외부 자극에 대한 반응을 조절한다. 체성신경계는 원심성인 운동신경과 구심성인 감각신경으로 구분되는데 운동신경은 중추신경계통에서 생긴 흥분(반응
• 부교감신경계통
부교감신경계통(Parasympathetic nervous system, PSNS)은 부교감신경이라고도 불리며 교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경계통이다. 부교감 신경은 교감 신경과는 길항작용의 관계에 있다. 부교감 신경이 흥분하면 맥박 감소, 혈압
• 자율신경계통
자율신경계(自律神經系統,autonomic nervous system, ANS)는 말초신경계통에 속하는 신경계로 평활근과 심근, 외분비샘과 일부 내분비샘을 통제하여 동물 내부의 환경을 일정하게 유지하는 역할을 한다. 자율신경이란 이름은 대뇌의 직접적인 지배를 받지 않는다는
• 신경
신경(afferent nerve, 구심성 신경) 원심 신경(efferent nerves, 원심성 신경) 혼합 신경(mixed nerves) 신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다: 척수신경 뇌신경 신경계통 (영어) 신경 목록
• 근육계통
근육계통(Muscular system, 筋肉系統)은 골격근, 평활근, 심장근으로 구성된 기관계이다. 몸을 움직이거나 자세를 유지하고, 전신에 혈액을 순환시키는 역할을 한다. 척추동물의 근육계통은 신경계통의 통제를 받고, 일부(심장근과 내장근육 등)는 자율적으로 움직인다
• 내분비계통
이동하며, 표적 기관에 도달해 적절한 작용을 일으킨다. 이러한 내분비계통의 이상은, 전반적 생리기능의 저하와 이상현상을 야기한다. 척추동물의 내분비기관 뇌하수체 솔방울샘 갑상샘 부갑상샘 가슴샘 부신 곁신경절 췌장 랑게르한스섬 정소의 간세포 난소 난소의 황체 태반 무척추동물의
• SNS
교감신경계(sympathetic nerve system): 부교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경 SNS (방송사): 케이블 TV 채널의 이름 체성 신경계(Somatic nervous system): 자율신경계통과 함께 말초신경계통을 이루는 신경계통
• 피부계통
피부계통(皮膚系統, 영어: Integumentary System)은 동물의 외부 부분을 덮고 있는 기관을 말한다. 이 부분은 특별한 도구를 쓰지 않고도 볼 수 있으며 다양한 기능을 가지고 있다. 피부, 머리카락, 손톱 등이 있다. 피부와 그 부속 구조물로 나눌 수 있다
• 순환계통
산소, 에너지 등을 공급하고, 생명 활동으로 생기는 이산화탄소, 노폐물 등을 호흡계통이나 비뇨계통으로 전달하여 몸 밖으로 배출하도록 하는 혈액이나 림프액 같은 체액의 흐름을 담당하는 계통이다. 혈액의 순환은 심장의 운동에 의해 이루어진다. 순환 중인 혈액은 산소의 운반
• 척삭동물
6만여 종 이상의 동물이 속해있다. 피낭동물아문은 유충일 때 척색과 신경관을 가지고 있다가 성충이 되면 없어진다. 두삭동물아문은 일생 동안 척색과 신경관이 있지만 뇌와 같은 특별한 신경절은 없으며 순환계통 역시 매우 단순하다. 두삭동물아문 가운데 유두동물만이 두개골을 갖고
• 해부학
석회에서 손을 씻었을 때 산모의 산욕 발열이 극적으로 감소될 수 있음을 보였다. 골격계통 근육계통 내분비계통 림프계통 비뇨계통 생식계통 소화계통 순환계통 신경계통 피부계통 호흡계통 두뇌 척추 간 콩팥 폐 심장 성기관: 남자의 성기, 여자의 성기 혈액 해부학 용어 인체
• 척수신경
앞가지의 제2가슴신경(T2)부터 제11가슴신경(T11)까지는 그대로 갈비사이신경이 되지만, 그 이외의 신경들은 목신경얼기, 팔신경얼기, 허리엉치신경얼기 등의 복잡한 구조물을 형성한다. 목신경얼기는 상지로 가는 신경(근육피부신경, 노신경, 자신경, 정중신경) 등을 내보내고
• 신경 조직
신경 조직(영어: nervous tissue)은 신경계통을 구성하는 주된 조직으로, 상피 조직, 결합 조직, 근육 조직과 더불어 동물의 네 가지 기본 조직에 속한다. 신경조직을 이루는 세포를 신경세포(neuron)와 신경아교세포(neuroglia, glia)로 분류할
• 각성 (분류 신경심리학)
상태이다. 이는 증가된 심박수 및 혈압과 감각 각성, 이동성 및 응답할 준비의 상태에 이어지는, 뇌줄기의 망상 활성계, 자율신경계통과 내분비계통의 활성화를 수반한다. 낮은 각성 접근 낮은 각성 이론 성적 각성 정서 Csikszentmihalyi, M., Finding
• 교감신경작용제
교감신경작용제(交感神經作用劑)는 교감신경계통에 작용하여 흥분했을 때와 같은 작용을 나타내게 하는 물질이다. 이를테면 카테콜아민, 에피네프린 (아드레날린), 노르에피네프린(노르아드레날린), 도파민 등이 있다. 이러한 약제들은 심정지와 저혈압을 치료하고, 심지어는 조기 분만을
뇌 BRAIN
위키백과, 우리 모두의 백과사전.
뇌(腦, 영어: Brain) 또는 골은 신경 세포가 하나의 큰 덩어리를 이루고 있으면서 동물의 중추 신경계를 관장하는 기관을 말한다. 뇌는 본능적인 생명활동에 있어서 중요한 역할을 담당하는데, 여러 기관의 거의 모든 정보가 일단 뇌에 모이고, 뇌에서 여러 기관으로 활동이나 조정 명령을 내린다. 또한 고등 척추동물의 뇌는 학습의 중추이다. 대부분의 척추동물, 특히 유두동물의 뇌는 머리에 위치하며 머리뼈로 보호된다.
인간의 경우 성인의 뇌 무게는 약 1,400g~1,600g 정도이며 이는 1000억 개 정도의 뉴런을 포함한다. 가로 15cm, 너비 15cm, 깊이 20cm로 평균 1350cc 정도의 부피를 가진다.
뇌는 대부분의 움직임, 행동을 관장하고, 신체의 항상성을 유지시킨다. 즉 심장의 박동, 혈압, 혈액 내의 농도, 체온 등을 일정하게 유지시킨다. 뇌는 인지, 감정, 기억, 학습 등을 담당한다.
신경 (NERVE)
위키백과, 우리 모두의 백과사전.
신경(神經)은 생물이 주위의 환경과 자극을 감지하고 이에 대처하는 기관이다.
신경은 신호의 활동 방향에 따라 다음과 같이 3가지 그룹으로 분류할 수 있다.
• 구심 신경(afferent nerve, 구심성 신경)
• 원심 신경(efferent nerves, 원심성 신경)
• 혼합 신경(mixed nerves)
신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다:
• 척수신경
• 뇌신경
신경 세포
위키백과, 우리 모두의 백과사전.
신경 세포(神經細胞, neuron) 또는 뉴런은 신경계를 구성하는 세포이다. 신경세포는 나트륨 통로, 칼륨 통로등의 이온 통로를 발현하여 다른 세포와는 달리 전기적인 방법으로 신호를 전달할 수 있다. 또한 인접한 다른 신경세포와는 시냅스라는 구조를 통해 (화학적)신호를 주고 받음으로써 다양한 정보를 받아들이고, 저장하는 기능을 한다. 인간의 두뇌에는 대뇌피질에만 약 100억개의 신경세포가 존재하는 것으로 추산되고 있다. 신경계에는 뉴런보다 많은 숫자의 신경 아교 세포가 존재한다.
세포체
세포체 (soma, cell body)는 신경세포의 중심이 되는 부분으로 세포의 핵과 세포소기관들이 있다. 크게 신경원섬유 (neurofibril)와 니슬소체(Nissl body)를 포함한다. 신경원섬유는 세포체를 지지하는 역할을 담당한다. 니슬 소체는 과립형태의 RNA로 단백질을 만들고 세포체에 영양을 공급하며 외부물질에 대한 식세포 작용을 수행한다.
가지돌기
가지돌기 (dendrite)는 수많은 가지로 뻗어나가 있으며, 주로 신경세포가 신호를 받아들이는 부분이다. 여러방향으로 뻗어나와있어 많은 다른 자극들을 수용 할 수 있다.
축삭
축삭 (axon)은 세포체로부터 아주 길게 뻗어나가는 부분으로 가지돌기와 세포체를 거쳐 전달된 신호를 다른 신경세포나 세포에 전달하는 부분이다. 세포체로부터 축삭이 시작되는 부분인 축삭둔덕 (axon hillock)에는 전압 개폐 나트륨 통로가 다량 분포하여 전달된 신호에 의해 활동전위를 발생시켜 축삭을 통해 전달한다.
수초
수초화(髓鞘化) Myelinated
는 신경 세포의 축삭(축색)을 수초라는 덮개에 의해 마디를 이루면서 둘러싸이는 과정으로 수초화가 진행되어 수초가 형성되면 이를 통해 정보전달속도가 보다 더 빨라지는것으로 알려져있다.
시냅스
시냅스(synapse)는 인접한 두 신경 세포가 연접하면서 만드는 구조이다. 전기적인 신호로 전달된 신호는 신경전달물질이라는 화학적 신호로 바뀌어 시냅스를 통과한다. 시냅스를 기준으로 신호를 주는 신경 세포를 시냅스 전 신경 세포(presynaptic neuron), 신호를 받는 신경 세포를 시냅스 후 신경 세포(postsynaptic neuron)라고 한다. 한 신경세포가 만들어내는 시냅스는 대략 1000여개 이상으로 신경 세포의 신경말을 이루는데 근간이 되며, 시냅스 신호전달의 강화 현상은 학습 및 기억의 기전으로 받아들여지고 있다.
뉴론종류
뉴런에는 크게 세 가지 종류가 있는데, 겉모습과 역할에 따라 분류한다. 감각신경을 구성하는 감각 뉴런은 축삭이 크게 발달해 있고 세포체의 크기가 작은 특징이 있다. 뇌와 척수 등 중추 신경계를 구성하는 연합 뉴런은 가지 돌기가 발달하였다. 그리고 연합 뉴런의 명령을 근육 등 기관에 전달해 운동을 하게 하는 운동신경을 구성하는 운동 뉴런. 이렇게 세 가지 종류가 있는데, 흔히 '뉴런'하면 떠올리는 모습은 대부분 운동 뉴런이다.
생각(Thought) - 위키백과, 우리 모두의 백과사전
생각은 결론을 얻으려는 관념 과정이다. 목표에 이르는 방법을 찾으려고 하는 정신 활동을 말한다. 사상(思想), 사유(思惟)라고도 한다. 지각이나 기억의 활동만으로는 충분하지 않은 경우에, 어떻게 이해하고 또 행동해야 할 것인가를 헤아리는 활동을 생각이라고 말한다.
기억(記憶) 또는 메모리(Memory)는 과거의 경험이나 학습을 통해 획득한 정보 또는 정보를 저장하는 능력을 의미한다. 또한 이렇게 저장된 기억이 환경과의 상호작용을 위해 인출되는 과정은 회상이 된다. 인간은 정보를 기억하는 능력과 더불어 망각하는 능력 역시 가지고 있다. 기억 과정은 학습, 사고, 추론을 하기 위한 필수적인 단계이다. 인간의 기억은 단기적 작업기억과 장시간 기억되는 장기 기억이 있다. 정보 처리 측면에서 기억은 부호화(Encoding), 저장(Storage), 재생(Retrieval)의 단계로 이루어진다.
정신(精神) |(Mental)은 육체나 물질에 대립되는 영혼이나 마음, 사물을 느끼고 생각하며 판단하는 능력 또는 그런 작용, 마음의 자세나 태도, 사물의 근본적인 의의나 목적 또는 이념이나 사상 등을 가리키는 말이다.[1]
영혼(靈魂, Soul )은 육체로부터 독립적인 정신체를 의미한다.
본성(本性, Nature)은 개별 존재가 본래 갖추고 있는 성품 또는 성질을 말한다.[1] 본성을 줄여서 간단히 성(性)이라고도 하고 다른 말로는 성품(性品)이라고도 한다. 한자어 성(性)은 마음[心]과 태어남[生]의 두 낱말이 합성하여 이루어진 글자로, 문자 그대로의 뜻으로는 '태어나면서 갖추고 있는 마음'을 뜻한다.
사물에 대하여는 본성은 개개의 사물이 가지고 있는 고유한 성질 또는 근본 성질을 말하며, 사람에 대하여서는 모든 사람이 본래 갖추고 있는 덕(德)과 능력(能力)을 말한다.[1][4]
Nervous system - Wikipedia
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In biology, the nervous system is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from ...
Latin: systema nervosum
Central nervous system
Spinal cord - Olfactory epithelium - Radiata - ... Sympathetic nervous system
The sympathetic nervous system (SNS) is one of the two main ...
Outline of the human nervous ...
The following Diagram is provided as an overview of and topical ... Nerve
A nerve is an enclosed, cable-like bundle of nerve fibres called ...
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The following Diagram is provided as an overview of and topical guide to the human nervous system:
Human nervous system
Human nervous system – the part of the human body that coordinates a person's voluntary and involuntary actions and transmits signals between different parts of the body. The human nervous system consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. The PNS consists mainly of nerves, which are long fibers that connect the CNS to every other part of the body. The PNS includes motor neurons, mediating voluntary movement; the autonomic nervous system, comprising the sympathetic nervous system and the parasympathetic nervous system and regulating involuntary functions; and the enteric nervous system, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.
, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.
Evolution of the human nervous system
• Evolution of nervous systems
• Evolution of human intelligence
• Evolution of the human brain
• Paleoneurology
Some branches of science that study the human nervous system[edit]
• Neuroscience
o Neurology
Paleoneurology
Central nervous system
The central nervous system (CNS) is the largest part of the nervous system and includes the brain and spinal cord.
• Spinal cord
Brain
Brain – center of the nervous system.
• Outline of the human brain
• List of regions of the human brain
Principal regions of the vertebrate brain:
Peripheral nervous system
Peripheral nervous system (PNS) – nervous system structures that do not lie within the CNS.
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception.
• List of sensory systems
• Sensory neuron
• Perception
• Visual system
• Auditory system
• Somatosensory system
• Vestibular system
• Olfactory system
• Taste
• Pain
Components of the nervous system
• Neuron
• Interneuron
• Ganglion (PNS) vs Nucleus (neuroanatomy) (CNS) except basal ganglia (CNS)
• Nerve(PNS) vs Tract (neuroanatomy) (CNS)
• White matter (more myelinated) vs Grey matter
Glial cells
Glial cells, commonly called neuroglia or glia, are supportive cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons.
• Microglia
• Astrocyte
• Oligodendrocyte (CNS) vs Schwann cell (PNS)
Neuron (also known as a neurone or nerve cell) is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, spinal cord, and peripheral nerves.
• Soma
• Axon
• Myelin
• Dendrite
• Dendritic spine
Action potential
An action potential (or nerve impulse) is a transient alteration of the transmembrane voltage (or membrane potential) across the membrane in an excitable cell generated by the activity of voltage-gated ion channels embedded in the membrane. The best known action potentials are pulse-like waves that travel along the axons of neurons.
• Membrane potential
• Ion channel
• Voltage-gated ion channels
Synapse
Synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.
• Chemical synapse
• Gap junction
• Synaptic plasticity
• Long-term potentiation
Neurotransmitter
Neurotransmitter – endogenous chemical that relays, amplifies, and modulates signals between neurons and other cells to which they are synaptically connected.
• List of neurotransmitters
• Neuromodulator
• Monoamine neurotransmitter
• Neuropeptide
Neurotransmitter receptor
Neurotransmitter receptor – membrane receptor that can be activated by a neurotransmitter. Interactions between neurotransmitters and neurotransmitter receptors can evoke a wide range of differing responses from the cell receiving the signal, including excitation, inhibition, and various types of modulation.
• Category:Receptors
Nerve
From Wikipedia, the free encyclopedia
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve transmits electrical impulses and is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium.
In the central nervous system, the analogous structures are known as nerve tracts.[1][2]
Cross-section of a nerve
Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres.[2] Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.
Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier.[3] Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.
Central nervous system
From Wikipedia, the free encyclopedia
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because it integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric animals—i.e., all multicellular animals except sponges and radially symmetric animals such as jellyfish—and it contains the majority of the nervous system. The CNS also includes the retina[2] and the optic nerve (cranial nerve II),[3][4] as well as the olfactory nerves (cranial nerve I) and olfactory epithelium[5] as parts of the CNS, synapsing directly on brain tissue without intermediate ganglia. As such, the olfactory epithelium is the only central nervous tissue in direct contact with the environment, which opens up for therapeutic treatments. [5] The CNS is contained within the dorsal body cavity, with the brain housed in the cranial cavity and the spinal cord in the spinal canal. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae.[6] The brain and spinal cord are both enclosed in the meninges.[6] Within the CNS, the interneuronal space is filled with a large amount of supporting non-nervous cells called neuroglia or glia from the Greek for "glue".[7]
Main article: Neuroanatomy
The CNS consists of the two major structures: the brain and spinal cord. The brain is encased in the skull, and protected by the cranium.[8] The spinal cord is continuous with the brain and lies caudally to the brain.[9] It is protected by the vertebrae.[8] The spinal cord reaches from the base of the skull, continues through[8] or starting below[10] the foramen magnum,[8] and terminates roughly level with the first or second lumbar vertebra,[9][10] occupying the upper sections of the vertebral canal.[4]
White and gray matter
Main articles: Gray matter and White matter
Dissection of a brain with labels showing the clear division between white and gray matter.
Microscopically, there are differences between the neurons and tissue of the CNS and the peripheral nervous system (PNS). [11] The CNS is composed of white and gray matter.[9] This can also be seen macroscopically on brain tissue. The white matter consists of axons and oligodendrocytes, while the gray matter consists of neurons and unmyelinated fibers. Both tissues include a number of glial cells (although the white matter contains more), which are often referred to as supporting cells of the CNS. Different forms of glial cells have different functions, some acting almost as scaffolding for neuroblasts to climb during neurogenesis such as bergmann glia, while others such as microglia are a specialized form of macrophage, involved in the immune system of the brain as well as the clearance of various metabolites from the brain tissue.[4] Astrocytes may be involved with both clearance of metabolites as well as transport of fuel and various beneficial substances to neurons from the capillaries of the brain. Upon CNS injury astrocytes will proliferate, causing gliosis, a form of neuronal scar tissue, lacking in functional neurons.[4]
The brain (cerebrum as well as midbrain and hindbrain) consists of a cortex, composed of neuron-bodies constituting gray matter, while internally there is more white matter that form tracts and commissures. Apart from cortical gray matter there is also subcortical gray matter making up a large number of different nuclei.[9]
Spinal cord
Main article: Spinal cord
Diagram of the columns and of the course of the fibers in the spinal cord. Sensory synapses occur in the dorsal spinal cord (above in this image), and motor nerves leave through the ventral (as well as lateral) horns of the spinal cord as seen below in the image.
Different ways in which the CNS can be activated without engaging the cortex, and making us aware of the actions. The above example shows the process in which the pupil dilates during dim light, activating neurons in the spinal cord. The second example shows the constriction of the pupil as a result of the activation of the Eddinger-Westphal nucleus (a cerebral ganglion).
From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves (sometimes segmental nerves[8]). The nerves connect the spinal cord to skin, joints, muscles etc. and allow for the transmission of efferent motor as well as afferent sensory signals and stimuli.[9] This allows for voluntary and involuntary motions of muscles, as well as the perception of senses. All in all 31 spinal nerves project from the brain stem,[9] some forming plexa as they branch out, such as the brachial plexa, sacral plexa etc.[8] Each spinal nerve will carry both sensory and motor signals, but the nerves synapse at different regions of the spinal cord, either from the periphery to sensory relay neurons that relay the information to the CNS or from the CNS to motor neurons, which relay the information out.[9]
The spinal cord relays information up to the brain through spinal tracts through the "final common pathway"[9] to the thalamus and ultimately to the cortex.
•
Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex.
Cranial nerves
Apart from the spinal cord, there are also peripheral nerves of the PNS that synapse through intermediaries or ganglia directly on the CNS. These 12 nerves exist in the head and neck region and are called cranial nerves. Cranial nerves bring information to the CNS to and from the face, as well as to certain muscles (such as the trapezius muscle, which is innervated by accessory nerves[8] as well as certain cervical spinal nerves).[8]
Two pairs of cranial nerves; the olfactory nerves and the optic nerves[2] are often considered structures of the CNS. This is because they do not synapse first on peripheral ganglia, but directly on CNS neurons. The olfactory epithelium is significant in that it consists of CNS tissue expressed in direct contact to the environment, allowing for administration of certain pharmaceuticals and drugs. [5]
A peripheral nerve myelinated by Schwann cells (left) and a CNS neuron myelinated by an oligodendrocyte (right)
BRAIN
Main article: Brain
Rostrally to the spinal cord lies the brain.[9] The brain makes up the largest portion of the CNS. It is often the main structure referred to when speaking of the nervous system in general. The brain is the major functional unit of the CNS. While the spinal cord has certain processing ability such as that of spinal locomotion and can process reflexes, the brain is the major processing unit of the nervous system.[12][13][citation needed]
Brainstem
Main article: Brainstem
The brainstem consists of the medulla, the pons and the midbrain. The medulla can be referred to as an extension of the spinal cord, which both have similar organization and functional properties.[9] The tracts passing from the spinal cord to the brain pass through here.[9]
Regulatory functions of the medulla nuclei include control of blood pressure and breathing. Other nuclei are involved in balance, taste, hearing, and control of muscles of the face and neck.[9]
The next structure rostral to the medulla is the pons, which lies on the ventral anterior side of the brainstem. Nuclei in the pons include pontine nuclei which work with the cerebellum and transmit information between the cerebellum and the cerebral cortex.[9] In the dorsal posterior pons lie nuclei that are involved in the functions of breathing, sleep, and taste.[9]
The midbrain, or mesencephalon, is situated above and rostral to the pons. It includes nuclei linking distinct parts of the motor system, including the cerebellum, the basal ganglia and both cerebral hemispheres, among others. Additionally, parts of the visual and auditory systems are located in the midbrain, including control of automatic eye movements.[9]
The brainstem at large provides entry and exit to the brain for a number of pathways for motor and autonomic control of the face and neck through cranial nerves,[9] Autonomic control of the organs is mediated by the tenth cranial nerve.[4] A large portion of the brainstem is involved in such autonomic control of the body. Such functions may engage the heart, blood vessels, and pupils, among others.[9]
The brainstem also holds the reticular formation, a group of nuclei involved in both arousal and alertness.[9]
Cerebellum
Main article: Cerebellum
The cerebellum lies behind the pons. The cerebellum is composed of several dividing fissures and lobes. Its function includes the control of posture and the coordination of movements of parts of the body, including the eyes and head, as well as the limbs. Further, it is involved in motion that has been learned and perfected through practice, and it will adapt to new learned movements.[9] Despite its previous classification as a motor structure, the cerebellum also displays connections to areas of the cerebral cortex involved in language and cognition. These connections have been shown by the use of medical imaging techniques, such as functional MRI and Positron emission tomography.[9]
The body of the cerebellum holds more neurons than any other structure of the brain, including that of the larger cerebrum, but is also more extensively understood than other structures of the brain, as it includes fewer types of different neurons.[9] It handles and processes sensory stimuli, motor information, as well as balance information from the vestibular organ.[9]
Diencephalon
Main articles: Diencephalon, Thalamus, and Hypothalamus
The two structures of the diencephalon worth noting are the thalamus and the hypothalamus. The thalamus acts as a linkage between incoming pathways from the peripheral nervous system as well as the optical nerve (though it does not receive input from the olfactory nerve) to the cerebral hemispheres. Previously it was considered only a "relay station", but it is engaged in the sorting of information that will reach cerebral hemispheres (neocortex).[9]
Apart from its function of sorting information from the periphery, the thalamus also connects the cerebellum and basal ganglia with the cerebrum. In common with the aforementioned reticular system the thalamus is involved in wakefullness and consciousness, such as though the SCN.[9]
The hypothalamus engages in functions of a number of primitive emotions or feelings such as hunger, thirst and maternal bonding. This is regulated partly through control of secretion of hormones from the pituitary gland. Additionally the hypothalamus plays a role in motivation and many other behaviors of the individual.[9]
Cerebrum
Main articles: Cerebrum, Cerebral cortex, Basal ganglia, Amygdala, and Hippocampus
The cerebrum of cerebral hemispheres make up the largest visual portion of the human brain. Various structures combine to form the cerebral hemispheres, among others: the cortex, basal ganglia, amygdala and hippocampus. The hemispheres together control a large portion of the functions of the human brain such as emotion, memory, perception and motor functions. Apart from this the cerebral hemispheres stand for the cognitive capabilities of the brain.[9]
Connecting each of the hemispheres is the corpus callosum as well as several additional commissures.[9] One of the most important parts of the cerebral hemispheres is the cortex, made up of gray matter covering the surface of the brain. Functionally, the cerebral cortex is involved in planning and carrying out of everyday tasks.[9]
The hippocampus is involved in storage of memories, the amygdala plays a role in perception and communication of emotion, while the basal ganglia play a major role in the coordination of voluntary movement.[9]
Difference from the peripheral nervous system
This differentiates the CNS from the PNS, which consists of neurons, axons, and Schwann cells. Oligodendrocytes and Schwann cells have similar functions in the CNS and PNS, respectively. Both act to add myelin sheaths to the axons, which acts as a form of insulation allowing for better and faster proliferation of electrical signals along the nerves. Axons in the CNS are often very short, barely a few millimeters, and do not need the same degree of isolation as peripheral nerves. Some peripheral nerves can be over 1 meter in length, such as the nerves to the big toe. To ensure signals move at sufficient speed, myelination is needed.
The way in which the Schwann cells and oligodendrocytes myelinate nerves differ. A Schwann cell usually myelinates a single axon, completely surrounding it. Sometimes, they may myelinate many axons, especially when in areas of short axons.[8] Oligodendrocytes usually myelinate several axons. They do this by sending out thin projections of their cell membrane, which envelop and enclose the axon.
Main article: Neural development
During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove (the neural folds) become elevated, and ultimately meet, transforming the groove into a closed tube called the neural tube.[14] The formation of the neural tube is called neurulation. At this stage, the walls of the neural tube contain proliferating neural stem cells in a region called the ventricular zone. The neural stem cells, principally radial glial cells, multiply and generate neurons through the process of neurogenesis, forming the rudiment of the CNS.[15]
The neural tube gives rise to both brain and spinal cord. The anterior (or 'rostral') portion of the neural tube initially differentiates into three brain vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon. The spinal cord is derived from the posterior or 'caudal' portion of the neural tube.
As a vertebrate grows, these vesicles differentiate further still. The telencephalon differentiates into, among other things, the striatum, the hippocampus and the neocortex, and its cavity becomes the first and second ventricles. Diencephalon elaborations include the subthalamus, hypothalamus, thalamus and epithalamus, and its cavity forms the third ventricle. The tectum, pretectum, cerebral peduncle and other structures develop out of the mesencephalon, and its cavity grows into the mesencephalic duct (cerebral aqueduct). The metencephalon becomes, among other things, the pons and the cerebellum, the myelencephalon forms the medulla oblongata, and their cavities develop into the fourth ventricle.[9]
Planaria
Planarians, members of the phylum Platyhelminthes (flatworms), have the simplest, clearly defined delineation of a nervous system into a CNS and a PNS.[16][17] Their primitive brains, consisting of two fused anterior ganglia, and longitudinal nerve cords form the CNS; the laterally projecting nerves form the PNS. A molecular study found that more than 95% of the 116 genes involved in the nervous system of planarians, which includes genes related to the CNS, also exist in humans.[18] Like planarians, vertebrates have a distinct CNS and PNS, though more complex than those of planarians.
Arthropoda
In arthropods, the ventral nerve cord, the subesophageal ganglia and the supraesophageal ganglia are usually seen as making up the CNS. Arthropoda, unlike vertebrates, have inhibitory motor neurons due to their small size. [19]
See also: Lateral horn of insect brain
Chordata
The CNS of chordates differs from that of other animals in being placed dorsally in the body, above the gut and notochord/spine.[20] The basic pattern of the CNS is highly conserved throughout the different species of vertebrates and during evolution. The major trend that can be observed is towards a progressive telencephalisation: the telencephalon of reptiles is only an appendix to the large olfactory bulb, while in mammals it makes up most of the volume of the CNS. In the human brain, the telencephalon covers most of the diencephalon and the mesencephalon. Indeed, the allometric study of brain size among different species shows a striking continuity from rats to whales, and allows us to complete the knowledge about the evolution of the CNS obtained through cranial endocasts.
Mammals – which appear in the fossil record after the first fishes, amphibians, and reptiles – are the only vertebrates to possess the evolutionarily recent, outermost part of the cerebral cortex known as the neocortex.[21] The neocortex of monotremes (the duck-billed platypus and several species of spiny anteaters) and of marsupials (such as kangaroos, koalas, opossums, wombats, and Tasmanian devils) lack the convolutions – gyri and sulci – found in the neocortex of most placental mammals (eutherians).[22] Within placental mammals, the size and complexity of the neocortex increased over time. The area of the neocortex of mice is only about 1/100 that of monkeys, and that of monkeys is only about 1/10 that of humans.[21] In addition, rats lack convolutions in their neocortex (possibly also because rats are small mammals), whereas cats have a moderate degree of convolutions, and humans have quite extensive convolutions.[21] Extreme convolution of the neocortex is found in dolphins, possibly related to their complex echolocation.
Clinical significance
Diseases
Main article: Central nervous system disease
There are many CNS diseases and conditions, including infections such as encephalitis and poliomyelitis, early-onset neurological disorders including ADHD and autism, late-onset neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and essential tremor, autoimmune and inflammatory diseases such as multiple sclerosis and acute disseminated encephalomyelitis, genetic disorders such as Krabbe's disease and Huntington's disease, as well as amyotrophic lateral sclerosis and adrenoleukodystrophy. Lastly, cancers of the central nervous system can cause severe illness and, when malignant, can have very high mortality rates. Symptoms depend on the size, growth rate, location and malignancy of tumors and can include alterations in motor control, hearing loss, headaches and changes in cognitive ability and autonomic functioning.
Specialty professional organizations recommend that neurological imaging of the brain be done only to answer a specific clinical question and not as routine screening.[23]
Sympathetic nervous system
From Wikipedia, the free encyclopedia
The sympathetic nervous system (SNS) is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system. (The enteric nervous system (ENS) is now usually referred to as separate from the autonomic nervous system since it has its own independent reflex activity.)[1][2]
The autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's fight or flight response. It is, however, constantly active at a basic level to maintain homeostasis homeodynamics.[3] The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest-and-digest".
Structure
There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate in the thoracolumbar division of the spinal cord specifically at T1 to L2~L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body.[4]
At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus, the postganglionic neurons release norepinephrine, which activates adrenergic receptors that are present on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system. However, there are three important exceptions:[5]
1. Postganglionic neurons of sweat glands release acetylcholine for the activation of muscarinic receptors, except for areas of thick skin, the palms and the plantar surfaces of the feet, where norepinephrine is released and acts on adrenergic receptors.
2. Chromaffin cells of the adrenal medulla are analogous to post-ganglionic neurons; the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion. Within this endocrine gland, pre-ganglionic neurons synapse with chromaffin cells, triggering the release of two transmitters: a small proportion of norepinephrine, and more substantially, epinephrine. The synthesis and release of epinephrine as opposed to norepinephrine is another distinguishing feature of chromaffin cells compared to postganglionic sympathetic neurons.[6]
3. Postganglionic sympathetic nerves terminating in the kidney release dopamine, which acts on dopamine D1 receptors of blood vessels to control how much blood the kidney filters. Dopamine is the immediate metabolic precursor to norepinephrine, but is nonetheless a distinct signaling molecule.[7]
Organization
The sympathetic nervous system extends from the thoracic to lumbar vertebrae and has connections with the thoracic, abdominal, and pelvic plexuses.
Sympathetic nerves arise from near the middle of the spinal cord in the intermediolateral nucleus of the lateral grey column, beginning at the first thoracic vertebra of the vertebral column and are thought to extend to the second or third lumbar vertebra. Because its cells begin in the thoracolumbar division – the thoracic and lumbar regions of the spinal cord - the sympathetic nervous system is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
Presynaptic nerves' axons terminate in either the paravertebral ganglia or prevertebral ganglia. There are four different paths an axon can take before reaching its terminal. In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve. After this, it can then either synapse in this ganglion, ascend to a more superior or descend to a more inferior paravertebral ganglion and synapse there, or it can descend to a prevertebral ganglion and synapse there with the postsynaptic cell.
The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) medulla. In this case, presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the bloodstream.
In the sympathetic nervous system and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the sympathetic nervous system are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.
The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which send sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia, which send sympathetic fibers to the gut.
Sensation
The afferent fibers of the autonomic nervous system, which transmit sensory information from the internal organs of the body back to the central nervous system (or CNS), are not divided into parasympathetic and sympathetic fibers as the efferent fibers are.[14] Instead, autonomic sensory information is conducted by general visceral afferent fibers.
General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain sensations to the CNS masked as referred pain. If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as somatic in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.[citation needed]
https://en.wikipedia.org/wiki/Nervous_system
https://en.wikipedia.org/wiki/Memory
https://en.wikipedia.org/wiki/Soul
https://originalnature.co.nz/
신경 (NERVE) (in Korean and English)
위키백과, 우리 모두의 백과사전.
신경(神經)은 생물이 주위의 환경과 자극을 감지하고 이에 대처하는 기관이다.
신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다:
• 척수신경
• 뇌신경
• 신경계통 위키백과
신경계(神經系, 영어: nervous system)는 동물이 자신을 둘러싼 환경으로부터 자극을 받아들이고 반응을 일으키는 것과 관련된 계통이다. 해파리나 말미잘과 같은 자포동물은 단순한 신경망으로 촉수와 위수강을 움직인다. 척추동물과 같은 보다 복잡한 동물들은 신경원이라
• 중추신경계통
중추신경계통(中樞神經系統, 영어: central nervous system; CNS)은 중추신경계라고도 부르며 두개골에 싸여있는 뇌와 척수를 포함하는 신경계로 말초신경계통(Peripheral Nervous System; PNS)과 함께 동물의 행동이나 신체 기작을 제어한다
• 말초신경계통
말초신경계통(末梢神經系統, 영어: Peripheral Nervous System; PNS)은 척추동물의 뇌나 척수의 중추 신경계에서 나와 온몸에 나뭇가지 모양으로 분포하는 신경계를 말한다. 말초신경계라고도 부른다. 말초신경계는 동물의 신경계 일부로서 중추 신경 계통으로부터 피부, 근육, 샘 따위로 연결되는 신경의 모든 경로.
• 교감신경계통
교감신경계통(영어: sympathetic nerve system, SNS)은 교감신경이라고도 불리며 부교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경이다. 교감신경은 부교감신경과는 길항작용의 관계에 있어 교감신경이 흥분하면 맥박 증가, 혈압 상승, 소화 억제
• 몸신경계통
체성신경계(Somatic nervous system, SNS)는 자율신경계통과 함께 말초신경계통을 이루는 신경계통로 골격근의 운동과 외부 자극에 대한 반응을 조절한다. 체성신경계는 원심성인 운동신경과 구심성인 감각신경으로 구분되는데 운동신경은 중추신경계통에서 생긴 흥분(반응
• 부교감신경계통
부교감신경계통(Parasympathetic nervous system, PSNS)은 부교감신경이라고도 불리며 교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경계통이다. 부교감 신경은 교감 신경과는 길항작용의 관계에 있다. 부교감 신경이 흥분하면 맥박 감소, 혈압
• 자율신경계통
자율신경계(自律神經系統,autonomic nervous system, ANS)는 말초신경계통에 속하는 신경계로 평활근과 심근, 외분비샘과 일부 내분비샘을 통제하여 동물 내부의 환경을 일정하게 유지하는 역할을 한다. 자율신경이란 이름은 대뇌의 직접적인 지배를 받지 않는다는
• 신경
신경(afferent nerve, 구심성 신경) 원심 신경(efferent nerves, 원심성 신경) 혼합 신경(mixed nerves) 신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다: 척수신경 뇌신경 신경계통 (영어) 신경 목록
• 근육계통
근육계통(Muscular system, 筋肉系統)은 골격근, 평활근, 심장근으로 구성된 기관계이다. 몸을 움직이거나 자세를 유지하고, 전신에 혈액을 순환시키는 역할을 한다. 척추동물의 근육계통은 신경계통의 통제를 받고, 일부(심장근과 내장근육 등)는 자율적으로 움직인다
• 내분비계통
이동하며, 표적 기관에 도달해 적절한 작용을 일으킨다. 이러한 내분비계통의 이상은, 전반적 생리기능의 저하와 이상현상을 야기한다. 척추동물의 내분비기관 뇌하수체 솔방울샘 갑상샘 부갑상샘 가슴샘 부신 곁신경절 췌장 랑게르한스섬 정소의 간세포 난소 난소의 황체 태반 무척추동물의
• SNS
교감신경계(sympathetic nerve system): 부교감신경계통과 함께 자율신경계통을 이루는 원심성 말초신경 SNS (방송사): 케이블 TV 채널의 이름 체성 신경계(Somatic nervous system): 자율신경계통과 함께 말초신경계통을 이루는 신경계통
• 피부계통
피부계통(皮膚系統, 영어: Integumentary System)은 동물의 외부 부분을 덮고 있는 기관을 말한다. 이 부분은 특별한 도구를 쓰지 않고도 볼 수 있으며 다양한 기능을 가지고 있다. 피부, 머리카락, 손톱 등이 있다. 피부와 그 부속 구조물로 나눌 수 있다
• 순환계통
산소, 에너지 등을 공급하고, 생명 활동으로 생기는 이산화탄소, 노폐물 등을 호흡계통이나 비뇨계통으로 전달하여 몸 밖으로 배출하도록 하는 혈액이나 림프액 같은 체액의 흐름을 담당하는 계통이다. 혈액의 순환은 심장의 운동에 의해 이루어진다. 순환 중인 혈액은 산소의 운반
• 척삭동물
6만여 종 이상의 동물이 속해있다. 피낭동물아문은 유충일 때 척색과 신경관을 가지고 있다가 성충이 되면 없어진다. 두삭동물아문은 일생 동안 척색과 신경관이 있지만 뇌와 같은 특별한 신경절은 없으며 순환계통 역시 매우 단순하다. 두삭동물아문 가운데 유두동물만이 두개골을 갖고
• 해부학
석회에서 손을 씻었을 때 산모의 산욕 발열이 극적으로 감소될 수 있음을 보였다. 골격계통 근육계통 내분비계통 림프계통 비뇨계통 생식계통 소화계통 순환계통 신경계통 피부계통 호흡계통 두뇌 척추 간 콩팥 폐 심장 성기관: 남자의 성기, 여자의 성기 혈액 해부학 용어 인체
• 척수신경
앞가지의 제2가슴신경(T2)부터 제11가슴신경(T11)까지는 그대로 갈비사이신경이 되지만, 그 이외의 신경들은 목신경얼기, 팔신경얼기, 허리엉치신경얼기 등의 복잡한 구조물을 형성한다. 목신경얼기는 상지로 가는 신경(근육피부신경, 노신경, 자신경, 정중신경) 등을 내보내고
• 신경 조직
신경 조직(영어: nervous tissue)은 신경계통을 구성하는 주된 조직으로, 상피 조직, 결합 조직, 근육 조직과 더불어 동물의 네 가지 기본 조직에 속한다. 신경조직을 이루는 세포를 신경세포(neuron)와 신경아교세포(neuroglia, glia)로 분류할
• 각성 (분류 신경심리학)
상태이다. 이는 증가된 심박수 및 혈압과 감각 각성, 이동성 및 응답할 준비의 상태에 이어지는, 뇌줄기의 망상 활성계, 자율신경계통과 내분비계통의 활성화를 수반한다. 낮은 각성 접근 낮은 각성 이론 성적 각성 정서 Csikszentmihalyi, M., Finding
• 교감신경작용제
교감신경작용제(交感神經作用劑)는 교감신경계통에 작용하여 흥분했을 때와 같은 작용을 나타내게 하는 물질이다. 이를테면 카테콜아민, 에피네프린 (아드레날린), 노르에피네프린(노르아드레날린), 도파민 등이 있다. 이러한 약제들은 심정지와 저혈압을 치료하고, 심지어는 조기 분만을
뇌 BRAIN
위키백과, 우리 모두의 백과사전.
뇌(腦, 영어: Brain) 또는 골은 신경 세포가 하나의 큰 덩어리를 이루고 있으면서 동물의 중추 신경계를 관장하는 기관을 말한다. 뇌는 본능적인 생명활동에 있어서 중요한 역할을 담당하는데, 여러 기관의 거의 모든 정보가 일단 뇌에 모이고, 뇌에서 여러 기관으로 활동이나 조정 명령을 내린다. 또한 고등 척추동물의 뇌는 학습의 중추이다. 대부분의 척추동물, 특히 유두동물의 뇌는 머리에 위치하며 머리뼈로 보호된다.
인간의 경우 성인의 뇌 무게는 약 1,400g~1,600g 정도이며 이는 1000억 개 정도의 뉴런을 포함한다. 가로 15cm, 너비 15cm, 깊이 20cm로 평균 1350cc 정도의 부피를 가진다.
뇌는 대부분의 움직임, 행동을 관장하고, 신체의 항상성을 유지시킨다. 즉 심장의 박동, 혈압, 혈액 내의 농도, 체온 등을 일정하게 유지시킨다. 뇌는 인지, 감정, 기억, 학습 등을 담당한다.
신경 (NERVE)
위키백과, 우리 모두의 백과사전.
신경(神經)은 생물이 주위의 환경과 자극을 감지하고 이에 대처하는 기관이다.
신경은 신호의 활동 방향에 따라 다음과 같이 3가지 그룹으로 분류할 수 있다.
• 구심 신경(afferent nerve, 구심성 신경)
• 원심 신경(efferent nerves, 원심성 신경)
• 혼합 신경(mixed nerves)
신경은 중추신경계에 어떻게 연결되었는지에 따라 다음과 같이 2가지 그룹으로 분류할 수 있다:
• 척수신경
• 뇌신경
신경 세포
위키백과, 우리 모두의 백과사전.
신경 세포(神經細胞, neuron) 또는 뉴런은 신경계를 구성하는 세포이다. 신경세포는 나트륨 통로, 칼륨 통로등의 이온 통로를 발현하여 다른 세포와는 달리 전기적인 방법으로 신호를 전달할 수 있다. 또한 인접한 다른 신경세포와는 시냅스라는 구조를 통해 (화학적)신호를 주고 받음으로써 다양한 정보를 받아들이고, 저장하는 기능을 한다. 인간의 두뇌에는 대뇌피질에만 약 100억개의 신경세포가 존재하는 것으로 추산되고 있다. 신경계에는 뉴런보다 많은 숫자의 신경 아교 세포가 존재한다.
세포체
세포체 (soma, cell body)는 신경세포의 중심이 되는 부분으로 세포의 핵과 세포소기관들이 있다. 크게 신경원섬유 (neurofibril)와 니슬소체(Nissl body)를 포함한다. 신경원섬유는 세포체를 지지하는 역할을 담당한다. 니슬 소체는 과립형태의 RNA로 단백질을 만들고 세포체에 영양을 공급하며 외부물질에 대한 식세포 작용을 수행한다.
가지돌기
가지돌기 (dendrite)는 수많은 가지로 뻗어나가 있으며, 주로 신경세포가 신호를 받아들이는 부분이다. 여러방향으로 뻗어나와있어 많은 다른 자극들을 수용 할 수 있다.
축삭
축삭 (axon)은 세포체로부터 아주 길게 뻗어나가는 부분으로 가지돌기와 세포체를 거쳐 전달된 신호를 다른 신경세포나 세포에 전달하는 부분이다. 세포체로부터 축삭이 시작되는 부분인 축삭둔덕 (axon hillock)에는 전압 개폐 나트륨 통로가 다량 분포하여 전달된 신호에 의해 활동전위를 발생시켜 축삭을 통해 전달한다.
수초
수초화(髓鞘化) Myelinated
는 신경 세포의 축삭(축색)을 수초라는 덮개에 의해 마디를 이루면서 둘러싸이는 과정으로 수초화가 진행되어 수초가 형성되면 이를 통해 정보전달속도가 보다 더 빨라지는것으로 알려져있다.
시냅스
시냅스(synapse)는 인접한 두 신경 세포가 연접하면서 만드는 구조이다. 전기적인 신호로 전달된 신호는 신경전달물질이라는 화학적 신호로 바뀌어 시냅스를 통과한다. 시냅스를 기준으로 신호를 주는 신경 세포를 시냅스 전 신경 세포(presynaptic neuron), 신호를 받는 신경 세포를 시냅스 후 신경 세포(postsynaptic neuron)라고 한다. 한 신경세포가 만들어내는 시냅스는 대략 1000여개 이상으로 신경 세포의 신경말을 이루는데 근간이 되며, 시냅스 신호전달의 강화 현상은 학습 및 기억의 기전으로 받아들여지고 있다.
뉴론종류
뉴런에는 크게 세 가지 종류가 있는데, 겉모습과 역할에 따라 분류한다. 감각신경을 구성하는 감각 뉴런은 축삭이 크게 발달해 있고 세포체의 크기가 작은 특징이 있다. 뇌와 척수 등 중추 신경계를 구성하는 연합 뉴런은 가지 돌기가 발달하였다. 그리고 연합 뉴런의 명령을 근육 등 기관에 전달해 운동을 하게 하는 운동신경을 구성하는 운동 뉴런. 이렇게 세 가지 종류가 있는데, 흔히 '뉴런'하면 떠올리는 모습은 대부분 운동 뉴런이다.
생각(Thought) - 위키백과, 우리 모두의 백과사전
생각은 결론을 얻으려는 관념 과정이다. 목표에 이르는 방법을 찾으려고 하는 정신 활동을 말한다. 사상(思想), 사유(思惟)라고도 한다. 지각이나 기억의 활동만으로는 충분하지 않은 경우에, 어떻게 이해하고 또 행동해야 할 것인가를 헤아리는 활동을 생각이라고 말한다.
기억(記憶) 또는 메모리(Memory)는 과거의 경험이나 학습을 통해 획득한 정보 또는 정보를 저장하는 능력을 의미한다. 또한 이렇게 저장된 기억이 환경과의 상호작용을 위해 인출되는 과정은 회상이 된다. 인간은 정보를 기억하는 능력과 더불어 망각하는 능력 역시 가지고 있다. 기억 과정은 학습, 사고, 추론을 하기 위한 필수적인 단계이다. 인간의 기억은 단기적 작업기억과 장시간 기억되는 장기 기억이 있다. 정보 처리 측면에서 기억은 부호화(Encoding), 저장(Storage), 재생(Retrieval)의 단계로 이루어진다.
정신(精神) |(Mental)은 육체나 물질에 대립되는 영혼이나 마음, 사물을 느끼고 생각하며 판단하는 능력 또는 그런 작용, 마음의 자세나 태도, 사물의 근본적인 의의나 목적 또는 이념이나 사상 등을 가리키는 말이다.[1]
영혼(靈魂, Soul )은 육체로부터 독립적인 정신체를 의미한다.
본성(本性, Nature)은 개별 존재가 본래 갖추고 있는 성품 또는 성질을 말한다.[1] 본성을 줄여서 간단히 성(性)이라고도 하고 다른 말로는 성품(性品)이라고도 한다. 한자어 성(性)은 마음[心]과 태어남[生]의 두 낱말이 합성하여 이루어진 글자로, 문자 그대로의 뜻으로는 '태어나면서 갖추고 있는 마음'을 뜻한다.
사물에 대하여는 본성은 개개의 사물이 가지고 있는 고유한 성질 또는 근본 성질을 말하며, 사람에 대하여서는 모든 사람이 본래 갖추고 있는 덕(德)과 능력(能力)을 말한다.[1][4]
Nervous system - Wikipedia
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In biology, the nervous system is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from ...
Latin: systema nervosum
Central nervous system
Spinal cord - Olfactory epithelium - Radiata - ... Sympathetic nervous system
The sympathetic nervous system (SNS) is one of the two main ...
Outline of the human nervous ...
The following Diagram is provided as an overview of and topical ... Nerve
A nerve is an enclosed, cable-like bundle of nerve fibres called ...
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The following Diagram is provided as an overview of and topical guide to the human nervous system:
Human nervous system
Human nervous system – the part of the human body that coordinates a person's voluntary and involuntary actions and transmits signals between different parts of the body. The human nervous system consists of two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. The PNS consists mainly of nerves, which are long fibers that connect the CNS to every other part of the body. The PNS includes motor neurons, mediating voluntary movement; the autonomic nervous system, comprising the sympathetic nervous system and the parasympathetic nervous system and regulating involuntary functions; and the enteric nervous system, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.
, a semi-independent part of the nervous system whose function is to control the gastrointestinal system.
Evolution of the human nervous system
• Evolution of nervous systems
• Evolution of human intelligence
• Evolution of the human brain
• Paleoneurology
Some branches of science that study the human nervous system[edit]
• Neuroscience
o Neurology
Paleoneurology
Central nervous system
The central nervous system (CNS) is the largest part of the nervous system and includes the brain and spinal cord.
• Spinal cord
Brain
Brain – center of the nervous system.
• Outline of the human brain
• List of regions of the human brain
Principal regions of the vertebrate brain:
Peripheral nervous system
Peripheral nervous system (PNS) – nervous system structures that do not lie within the CNS.
Sensory system
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception.
• List of sensory systems
• Sensory neuron
• Perception
• Visual system
• Auditory system
• Somatosensory system
• Vestibular system
• Olfactory system
• Taste
• Pain
Components of the nervous system
• Neuron
• Interneuron
• Ganglion (PNS) vs Nucleus (neuroanatomy) (CNS) except basal ganglia (CNS)
• Nerve(PNS) vs Tract (neuroanatomy) (CNS)
• White matter (more myelinated) vs Grey matter
Glial cells
Glial cells, commonly called neuroglia or glia, are supportive cells that maintain homeostasis, form myelin, and provide support and protection for the brain's neurons.
• Microglia
• Astrocyte
• Oligodendrocyte (CNS) vs Schwann cell (PNS)
Neuron (also known as a neurone or nerve cell) is an excitable cell in the nervous system that processes and transmits information by electrochemical signaling. Neurons are the core components of the brain, spinal cord, and peripheral nerves.
• Soma
• Axon
• Myelin
• Dendrite
• Dendritic spine
Action potential
An action potential (or nerve impulse) is a transient alteration of the transmembrane voltage (or membrane potential) across the membrane in an excitable cell generated by the activity of voltage-gated ion channels embedded in the membrane. The best known action potentials are pulse-like waves that travel along the axons of neurons.
• Membrane potential
• Ion channel
• Voltage-gated ion channels
Synapse
Synapses are specialized junctions through which neurons signal to each other and to non-neuronal cells such as those in muscles or glands.
• Chemical synapse
• Gap junction
• Synaptic plasticity
• Long-term potentiation
Neurotransmitter
Neurotransmitter – endogenous chemical that relays, amplifies, and modulates signals between neurons and other cells to which they are synaptically connected.
• List of neurotransmitters
• Neuromodulator
• Monoamine neurotransmitter
• Neuropeptide
Neurotransmitter receptor
Neurotransmitter receptor – membrane receptor that can be activated by a neurotransmitter. Interactions between neurotransmitters and neurotransmitter receptors can evoke a wide range of differing responses from the cell receiving the signal, including excitation, inhibition, and various types of modulation.
• Category:Receptors
Nerve
From Wikipedia, the free encyclopedia
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve transmits electrical impulses and is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system. Each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as some Schwann cells that coat the axons in myelin.
Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles, and each fascicle is wrapped in a layer of connective tissue called the perineurium. Finally, the entire nerve is wrapped in a layer of connective tissue called the epineurium.
In the central nervous system, the analogous structures are known as nerve tracts.[1][2]
Cross-section of a nerve
Each nerve is covered on the outside by a dense sheath of connective tissue, the epineurium. Beneath this is a layer of fat cells, the perineurium, which forms a complete sleeve around a bundle of axons. Perineurial septae extend into the nerve and subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium. This forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, delicate, meshwork of collagen fibres.[2] Nerves are bundled and often travel along with blood vessels, since the neurons of a nerve have fairly high energy requirements.
Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid. This acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier.[3] Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation (or injury), the amount of endoneurial fluid may increase at the site of irritation. This increase in fluid can be visualized using magnetic resonance neurography, and thus MR neurography can identify nerve irritation and/or injury.
Central nervous system
From Wikipedia, the free encyclopedia
The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because it integrates the received information and coordinates and influences the activity of all parts of the bodies of bilaterally symmetric animals—i.e., all multicellular animals except sponges and radially symmetric animals such as jellyfish—and it contains the majority of the nervous system. The CNS also includes the retina[2] and the optic nerve (cranial nerve II),[3][4] as well as the olfactory nerves (cranial nerve I) and olfactory epithelium[5] as parts of the CNS, synapsing directly on brain tissue without intermediate ganglia. As such, the olfactory epithelium is the only central nervous tissue in direct contact with the environment, which opens up for therapeutic treatments. [5] The CNS is contained within the dorsal body cavity, with the brain housed in the cranial cavity and the spinal cord in the spinal canal. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae.[6] The brain and spinal cord are both enclosed in the meninges.[6] Within the CNS, the interneuronal space is filled with a large amount of supporting non-nervous cells called neuroglia or glia from the Greek for "glue".[7]
Main article: Neuroanatomy
The CNS consists of the two major structures: the brain and spinal cord. The brain is encased in the skull, and protected by the cranium.[8] The spinal cord is continuous with the brain and lies caudally to the brain.[9] It is protected by the vertebrae.[8] The spinal cord reaches from the base of the skull, continues through[8] or starting below[10] the foramen magnum,[8] and terminates roughly level with the first or second lumbar vertebra,[9][10] occupying the upper sections of the vertebral canal.[4]
White and gray matter
Main articles: Gray matter and White matter
Dissection of a brain with labels showing the clear division between white and gray matter.
Microscopically, there are differences between the neurons and tissue of the CNS and the peripheral nervous system (PNS). [11] The CNS is composed of white and gray matter.[9] This can also be seen macroscopically on brain tissue. The white matter consists of axons and oligodendrocytes, while the gray matter consists of neurons and unmyelinated fibers. Both tissues include a number of glial cells (although the white matter contains more), which are often referred to as supporting cells of the CNS. Different forms of glial cells have different functions, some acting almost as scaffolding for neuroblasts to climb during neurogenesis such as bergmann glia, while others such as microglia are a specialized form of macrophage, involved in the immune system of the brain as well as the clearance of various metabolites from the brain tissue.[4] Astrocytes may be involved with both clearance of metabolites as well as transport of fuel and various beneficial substances to neurons from the capillaries of the brain. Upon CNS injury astrocytes will proliferate, causing gliosis, a form of neuronal scar tissue, lacking in functional neurons.[4]
The brain (cerebrum as well as midbrain and hindbrain) consists of a cortex, composed of neuron-bodies constituting gray matter, while internally there is more white matter that form tracts and commissures. Apart from cortical gray matter there is also subcortical gray matter making up a large number of different nuclei.[9]
Spinal cord
Main article: Spinal cord
Diagram of the columns and of the course of the fibers in the spinal cord. Sensory synapses occur in the dorsal spinal cord (above in this image), and motor nerves leave through the ventral (as well as lateral) horns of the spinal cord as seen below in the image.
Different ways in which the CNS can be activated without engaging the cortex, and making us aware of the actions. The above example shows the process in which the pupil dilates during dim light, activating neurons in the spinal cord. The second example shows the constriction of the pupil as a result of the activation of the Eddinger-Westphal nucleus (a cerebral ganglion).
From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves (sometimes segmental nerves[8]). The nerves connect the spinal cord to skin, joints, muscles etc. and allow for the transmission of efferent motor as well as afferent sensory signals and stimuli.[9] This allows for voluntary and involuntary motions of muscles, as well as the perception of senses. All in all 31 spinal nerves project from the brain stem,[9] some forming plexa as they branch out, such as the brachial plexa, sacral plexa etc.[8] Each spinal nerve will carry both sensory and motor signals, but the nerves synapse at different regions of the spinal cord, either from the periphery to sensory relay neurons that relay the information to the CNS or from the CNS to motor neurons, which relay the information out.[9]
The spinal cord relays information up to the brain through spinal tracts through the "final common pathway"[9] to the thalamus and ultimately to the cortex.
•
Reflexes may also occur without engaging more than one neuron of the CNS as in the below example of a short reflex.
Cranial nerves
Apart from the spinal cord, there are also peripheral nerves of the PNS that synapse through intermediaries or ganglia directly on the CNS. These 12 nerves exist in the head and neck region and are called cranial nerves. Cranial nerves bring information to the CNS to and from the face, as well as to certain muscles (such as the trapezius muscle, which is innervated by accessory nerves[8] as well as certain cervical spinal nerves).[8]
Two pairs of cranial nerves; the olfactory nerves and the optic nerves[2] are often considered structures of the CNS. This is because they do not synapse first on peripheral ganglia, but directly on CNS neurons. The olfactory epithelium is significant in that it consists of CNS tissue expressed in direct contact to the environment, allowing for administration of certain pharmaceuticals and drugs. [5]
A peripheral nerve myelinated by Schwann cells (left) and a CNS neuron myelinated by an oligodendrocyte (right)
BRAIN
Main article: Brain
Rostrally to the spinal cord lies the brain.[9] The brain makes up the largest portion of the CNS. It is often the main structure referred to when speaking of the nervous system in general. The brain is the major functional unit of the CNS. While the spinal cord has certain processing ability such as that of spinal locomotion and can process reflexes, the brain is the major processing unit of the nervous system.[12][13][citation needed]
Brainstem
Main article: Brainstem
The brainstem consists of the medulla, the pons and the midbrain. The medulla can be referred to as an extension of the spinal cord, which both have similar organization and functional properties.[9] The tracts passing from the spinal cord to the brain pass through here.[9]
Regulatory functions of the medulla nuclei include control of blood pressure and breathing. Other nuclei are involved in balance, taste, hearing, and control of muscles of the face and neck.[9]
The next structure rostral to the medulla is the pons, which lies on the ventral anterior side of the brainstem. Nuclei in the pons include pontine nuclei which work with the cerebellum and transmit information between the cerebellum and the cerebral cortex.[9] In the dorsal posterior pons lie nuclei that are involved in the functions of breathing, sleep, and taste.[9]
The midbrain, or mesencephalon, is situated above and rostral to the pons. It includes nuclei linking distinct parts of the motor system, including the cerebellum, the basal ganglia and both cerebral hemispheres, among others. Additionally, parts of the visual and auditory systems are located in the midbrain, including control of automatic eye movements.[9]
The brainstem at large provides entry and exit to the brain for a number of pathways for motor and autonomic control of the face and neck through cranial nerves,[9] Autonomic control of the organs is mediated by the tenth cranial nerve.[4] A large portion of the brainstem is involved in such autonomic control of the body. Such functions may engage the heart, blood vessels, and pupils, among others.[9]
The brainstem also holds the reticular formation, a group of nuclei involved in both arousal and alertness.[9]
Cerebellum
Main article: Cerebellum
The cerebellum lies behind the pons. The cerebellum is composed of several dividing fissures and lobes. Its function includes the control of posture and the coordination of movements of parts of the body, including the eyes and head, as well as the limbs. Further, it is involved in motion that has been learned and perfected through practice, and it will adapt to new learned movements.[9] Despite its previous classification as a motor structure, the cerebellum also displays connections to areas of the cerebral cortex involved in language and cognition. These connections have been shown by the use of medical imaging techniques, such as functional MRI and Positron emission tomography.[9]
The body of the cerebellum holds more neurons than any other structure of the brain, including that of the larger cerebrum, but is also more extensively understood than other structures of the brain, as it includes fewer types of different neurons.[9] It handles and processes sensory stimuli, motor information, as well as balance information from the vestibular organ.[9]
Diencephalon
Main articles: Diencephalon, Thalamus, and Hypothalamus
The two structures of the diencephalon worth noting are the thalamus and the hypothalamus. The thalamus acts as a linkage between incoming pathways from the peripheral nervous system as well as the optical nerve (though it does not receive input from the olfactory nerve) to the cerebral hemispheres. Previously it was considered only a "relay station", but it is engaged in the sorting of information that will reach cerebral hemispheres (neocortex).[9]
Apart from its function of sorting information from the periphery, the thalamus also connects the cerebellum and basal ganglia with the cerebrum. In common with the aforementioned reticular system the thalamus is involved in wakefullness and consciousness, such as though the SCN.[9]
The hypothalamus engages in functions of a number of primitive emotions or feelings such as hunger, thirst and maternal bonding. This is regulated partly through control of secretion of hormones from the pituitary gland. Additionally the hypothalamus plays a role in motivation and many other behaviors of the individual.[9]
Cerebrum
Main articles: Cerebrum, Cerebral cortex, Basal ganglia, Amygdala, and Hippocampus
The cerebrum of cerebral hemispheres make up the largest visual portion of the human brain. Various structures combine to form the cerebral hemispheres, among others: the cortex, basal ganglia, amygdala and hippocampus. The hemispheres together control a large portion of the functions of the human brain such as emotion, memory, perception and motor functions. Apart from this the cerebral hemispheres stand for the cognitive capabilities of the brain.[9]
Connecting each of the hemispheres is the corpus callosum as well as several additional commissures.[9] One of the most important parts of the cerebral hemispheres is the cortex, made up of gray matter covering the surface of the brain. Functionally, the cerebral cortex is involved in planning and carrying out of everyday tasks.[9]
The hippocampus is involved in storage of memories, the amygdala plays a role in perception and communication of emotion, while the basal ganglia play a major role in the coordination of voluntary movement.[9]
Difference from the peripheral nervous system
This differentiates the CNS from the PNS, which consists of neurons, axons, and Schwann cells. Oligodendrocytes and Schwann cells have similar functions in the CNS and PNS, respectively. Both act to add myelin sheaths to the axons, which acts as a form of insulation allowing for better and faster proliferation of electrical signals along the nerves. Axons in the CNS are often very short, barely a few millimeters, and do not need the same degree of isolation as peripheral nerves. Some peripheral nerves can be over 1 meter in length, such as the nerves to the big toe. To ensure signals move at sufficient speed, myelination is needed.
The way in which the Schwann cells and oligodendrocytes myelinate nerves differ. A Schwann cell usually myelinates a single axon, completely surrounding it. Sometimes, they may myelinate many axons, especially when in areas of short axons.[8] Oligodendrocytes usually myelinate several axons. They do this by sending out thin projections of their cell membrane, which envelop and enclose the axon.
Main article: Neural development
During early development of the vertebrate embryo, a longitudinal groove on the neural plate gradually deepens and the ridges on either side of the groove (the neural folds) become elevated, and ultimately meet, transforming the groove into a closed tube called the neural tube.[14] The formation of the neural tube is called neurulation. At this stage, the walls of the neural tube contain proliferating neural stem cells in a region called the ventricular zone. The neural stem cells, principally radial glial cells, multiply and generate neurons through the process of neurogenesis, forming the rudiment of the CNS.[15]
The neural tube gives rise to both brain and spinal cord. The anterior (or 'rostral') portion of the neural tube initially differentiates into three brain vesicles (pockets): the prosencephalon at the front, the mesencephalon, and, between the mesencephalon and the spinal cord, the rhombencephalon. (By six weeks in the human embryo) the prosencephalon then divides further into the telencephalon and diencephalon; and the rhombencephalon divides into the metencephalon and myelencephalon. The spinal cord is derived from the posterior or 'caudal' portion of the neural tube.
As a vertebrate grows, these vesicles differentiate further still. The telencephalon differentiates into, among other things, the striatum, the hippocampus and the neocortex, and its cavity becomes the first and second ventricles. Diencephalon elaborations include the subthalamus, hypothalamus, thalamus and epithalamus, and its cavity forms the third ventricle. The tectum, pretectum, cerebral peduncle and other structures develop out of the mesencephalon, and its cavity grows into the mesencephalic duct (cerebral aqueduct). The metencephalon becomes, among other things, the pons and the cerebellum, the myelencephalon forms the medulla oblongata, and their cavities develop into the fourth ventricle.[9]
Planaria
Planarians, members of the phylum Platyhelminthes (flatworms), have the simplest, clearly defined delineation of a nervous system into a CNS and a PNS.[16][17] Their primitive brains, consisting of two fused anterior ganglia, and longitudinal nerve cords form the CNS; the laterally projecting nerves form the PNS. A molecular study found that more than 95% of the 116 genes involved in the nervous system of planarians, which includes genes related to the CNS, also exist in humans.[18] Like planarians, vertebrates have a distinct CNS and PNS, though more complex than those of planarians.
Arthropoda
In arthropods, the ventral nerve cord, the subesophageal ganglia and the supraesophageal ganglia are usually seen as making up the CNS. Arthropoda, unlike vertebrates, have inhibitory motor neurons due to their small size. [19]
See also: Lateral horn of insect brain
Chordata
The CNS of chordates differs from that of other animals in being placed dorsally in the body, above the gut and notochord/spine.[20] The basic pattern of the CNS is highly conserved throughout the different species of vertebrates and during evolution. The major trend that can be observed is towards a progressive telencephalisation: the telencephalon of reptiles is only an appendix to the large olfactory bulb, while in mammals it makes up most of the volume of the CNS. In the human brain, the telencephalon covers most of the diencephalon and the mesencephalon. Indeed, the allometric study of brain size among different species shows a striking continuity from rats to whales, and allows us to complete the knowledge about the evolution of the CNS obtained through cranial endocasts.
Mammals – which appear in the fossil record after the first fishes, amphibians, and reptiles – are the only vertebrates to possess the evolutionarily recent, outermost part of the cerebral cortex known as the neocortex.[21] The neocortex of monotremes (the duck-billed platypus and several species of spiny anteaters) and of marsupials (such as kangaroos, koalas, opossums, wombats, and Tasmanian devils) lack the convolutions – gyri and sulci – found in the neocortex of most placental mammals (eutherians).[22] Within placental mammals, the size and complexity of the neocortex increased over time. The area of the neocortex of mice is only about 1/100 that of monkeys, and that of monkeys is only about 1/10 that of humans.[21] In addition, rats lack convolutions in their neocortex (possibly also because rats are small mammals), whereas cats have a moderate degree of convolutions, and humans have quite extensive convolutions.[21] Extreme convolution of the neocortex is found in dolphins, possibly related to their complex echolocation.
Clinical significance
Diseases
Main article: Central nervous system disease
There are many CNS diseases and conditions, including infections such as encephalitis and poliomyelitis, early-onset neurological disorders including ADHD and autism, late-onset neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and essential tremor, autoimmune and inflammatory diseases such as multiple sclerosis and acute disseminated encephalomyelitis, genetic disorders such as Krabbe's disease and Huntington's disease, as well as amyotrophic lateral sclerosis and adrenoleukodystrophy. Lastly, cancers of the central nervous system can cause severe illness and, when malignant, can have very high mortality rates. Symptoms depend on the size, growth rate, location and malignancy of tumors and can include alterations in motor control, hearing loss, headaches and changes in cognitive ability and autonomic functioning.
Specialty professional organizations recommend that neurological imaging of the brain be done only to answer a specific clinical question and not as routine screening.[23]
Sympathetic nervous system
From Wikipedia, the free encyclopedia
The sympathetic nervous system (SNS) is one of the two main divisions of the autonomic nervous system, the other being the parasympathetic nervous system. (The enteric nervous system (ENS) is now usually referred to as separate from the autonomic nervous system since it has its own independent reflex activity.)[1][2]
The autonomic nervous system functions to regulate the body's unconscious actions. The sympathetic nervous system's primary process is to stimulate the body's fight or flight response. It is, however, constantly active at a basic level to maintain homeostasis homeodynamics.[3] The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system which stimulates the body to "feed and breed" and to (then) "rest-and-digest".
Structure
There are two kinds of neurons involved in the transmission of any signal through the sympathetic system: pre-ganglionic and post-ganglionic. The shorter preganglionic neurons originate in the thoracolumbar division of the spinal cord specifically at T1 to L2~L3, and travel to a ganglion, often one of the paravertebral ganglia, where they synapse with a postganglionic neuron. From there, the long postganglionic neurons extend across most of the body.[4]
At the synapses within the ganglia, preganglionic neurons release acetylcholine, a neurotransmitter that activates nicotinic acetylcholine receptors on postganglionic neurons. In response to this stimulus, the postganglionic neurons release norepinephrine, which activates adrenergic receptors that are present on the peripheral target tissues. The activation of target tissue receptors causes the effects associated with the sympathetic system. However, there are three important exceptions:[5]
1. Postganglionic neurons of sweat glands release acetylcholine for the activation of muscarinic receptors, except for areas of thick skin, the palms and the plantar surfaces of the feet, where norepinephrine is released and acts on adrenergic receptors.
2. Chromaffin cells of the adrenal medulla are analogous to post-ganglionic neurons; the adrenal medulla develops in tandem with the sympathetic nervous system and acts as a modified sympathetic ganglion. Within this endocrine gland, pre-ganglionic neurons synapse with chromaffin cells, triggering the release of two transmitters: a small proportion of norepinephrine, and more substantially, epinephrine. The synthesis and release of epinephrine as opposed to norepinephrine is another distinguishing feature of chromaffin cells compared to postganglionic sympathetic neurons.[6]
3. Postganglionic sympathetic nerves terminating in the kidney release dopamine, which acts on dopamine D1 receptors of blood vessels to control how much blood the kidney filters. Dopamine is the immediate metabolic precursor to norepinephrine, but is nonetheless a distinct signaling molecule.[7]
Organization
The sympathetic nervous system extends from the thoracic to lumbar vertebrae and has connections with the thoracic, abdominal, and pelvic plexuses.
Sympathetic nerves arise from near the middle of the spinal cord in the intermediolateral nucleus of the lateral grey column, beginning at the first thoracic vertebra of the vertebral column and are thought to extend to the second or third lumbar vertebra. Because its cells begin in the thoracolumbar division – the thoracic and lumbar regions of the spinal cord - the sympathetic nervous system is said to have a thoracolumbar outflow. Axons of these nerves leave the spinal cord through the anterior root. They pass near the spinal (sensory) ganglion, where they enter the anterior rami of the spinal nerves. However, unlike somatic innervation, they quickly separate out through white rami connectors (so called from the shiny white sheaths of myelin around each axon) that connect to either the paravertebral (which lie near the vertebral column) or prevertebral (which lie near the aortic bifurcation) ganglia extending alongside the spinal column.
To reach target organs and glands, the axons must travel long distances in the body, and, to accomplish this, many axons relay their message to a second cell through synaptic transmission. The ends of the axons link across a space, the synapse, to the dendrites of the second cell. The first cell (the presynaptic cell) sends a neurotransmitter across the synaptic cleft where it activates the second cell (the postsynaptic cell). The message is then carried to the final destination.
Presynaptic nerves' axons terminate in either the paravertebral ganglia or prevertebral ganglia. There are four different paths an axon can take before reaching its terminal. In all cases, the axon enters the paravertebral ganglion at the level of its originating spinal nerve. After this, it can then either synapse in this ganglion, ascend to a more superior or descend to a more inferior paravertebral ganglion and synapse there, or it can descend to a prevertebral ganglion and synapse there with the postsynaptic cell.
The postsynaptic cell then goes on to innervate the targeted end effector (i.e. gland, smooth muscle, etc.). Because paravertebral and prevertebral ganglia are relatively close to the spinal cord, presynaptic neurons are generally much shorter than their postsynaptic counterparts, which must extend throughout the body to reach their destinations.
A notable exception to the routes mentioned above is the sympathetic innervation of the suprarenal (adrenal) medulla. In this case, presynaptic neurons pass through paravertebral ganglia, on through prevertebral ganglia and then synapse directly with suprarenal tissue. This tissue consists of cells that have pseudo-neuron like qualities in that when activated by the presynaptic neuron, they will release their neurotransmitter (epinephrine) directly into the bloodstream.
In the sympathetic nervous system and other components of the peripheral nervous system, these synapses are made at sites called ganglia. The cell that sends its fiber is called a preganglionic cell, while the cell whose fiber leaves the ganglion is called a postganglionic cell. As mentioned previously, the preganglionic cells of the sympathetic nervous system are located between the first thoracic segment and third lumbar segments of the spinal cord. Postganglionic cells have their cell bodies in the ganglia and send their axons to target organs or glands.
The ganglia include not just the sympathetic trunks but also the cervical ganglia (superior, middle and inferior), which send sympathetic nerve fibers to the head and thorax organs, and the celiac and mesenteric ganglia, which send sympathetic fibers to the gut.
Sensation
The afferent fibers of the autonomic nervous system, which transmit sensory information from the internal organs of the body back to the central nervous system (or CNS), are not divided into parasympathetic and sympathetic fibers as the efferent fibers are.[14] Instead, autonomic sensory information is conducted by general visceral afferent fibers.
General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain sensations to the CNS masked as referred pain. If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as somatic in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.[citation needed]
- 이전글심장 HEART 심혈관질환 BYPASS SURGERY STENT삽입 20.12.06
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