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신경계의 구조(Structure of the Nervous System)

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신경계를 해부학적으로 구분하는 것은 어떻게 보면 위험한 선택일지도 모른다. 실제로 신경계는 뇌.척수.말초신경계가 유기적으로 연결된 단일의 대형 정보처리체계로서 매우 정교하고 광범위하게 구축된 정보통신망에 비견될 것이다.

Anatomical references in the nervous system of a rat
Side view: Anterior(rostral), Posterior (caudal); Dorsal, Ventral
Top view: Lateral, Medial

Anatomical planes of section
Midsagittal, Horizontal, Coronal

체성계=뇌신경 12쌍+척수신경 13쌍
자율계=교감신경계 + 부교감신경계, 자율신경계 그림

Spinal cord(척수)
simplest & most caudally situated, evolutionally appears early
resembles embryonic "neural tube"
get sensory input from skin, joints, muscles, internal organs
send voluntary or reflexive motor outputs
has 31 pairs of spinal nerves
dorsal root receives input from muscle, skin & viscera
ventral root send outputs to muscles, preganglionic sympathetic & parasympathetic
grey matter: sensory neurons in the dorsal horn; motor neurons in the ventral horn
cross sectional appearance
white matter: ascending and descending fibers
individual dorsal root may have several types of central branches

Brainstem= medulla + pons + cerebellum + midbrain
has cranial nerves (sensory input & motor output)
has ascending & descending neural pathways
function: 1) sensory input & motor output at head, neck & face; 2) specialized senses (taste, hearing, balance); 3) arousal

where: rostral end of the spinal cord
structure is similar to the spinal cord
has ascending & descending neural pathways
medulla & pons control blood pressure & respiration

situated rostral to the medulla
has ascending & descending neural pathways
function: food intake, facial expression
connected to braistem, cerebellum & cerebral cortex

dorsal to pons & medulla
foliated surface, fissures, many lobes
input from skin (somatosensory), motor information from cerebral cortex & balance input from vestibular organs
function: 1) planning, timing, patterning of skeletal muscle; 2) posture & coordination of head & eye movements

function: direct control of eye movement
motor control of skeletal muscles
has auditory & visual relay nuclei
has ascending & descending neural pathways

diencephalon=thalamus + hypothalamus

function: 1) motor & sensory information의 distribution & processing; 2) control levels of awareness; 3) involved in the emotion aspects of sensory experiences

function: 1) control autonomic nervous system; 2) control of hormonal secretion via pituitary gland
connection: thalamus, midbrain, & cerebral cortex

Cerebral cortex(대뇌피질):
cytoarchitectonical area: Boradman area numbers
convolution (due to suci & gyri), folding (maximize volume within the limited space of the cranium)
has four lobes: frontal, parietal, temporal, occi[ital
has insular cortex at the medial wall of the lateral sulcus
has limbic lobe at the medial portion of the 3 lobes (fontal, parietal & temporal lobes)
limbic lobes are related to the learning, memory & emotions
primary motor cortex at the precentral gyrus
primary visual cortex at the occipital lobe
primary sensory cortex at the postcentral gyrus
input to output: primary sensory cortex---> higher order sensory cortex--->higher order motor cortex --->primary motor cortex
function of the 3 association cortex: perception, movement, motivation
parietal-temporal-occipital (p.f.t) association cortex: integrating somatic, auditory & visual informations
prefrontal association cortex: planning of voluntary movement
limbic association cortex: located at the medial & inferior surface of the cerebreal hemisphere & portions of the p.f.t lobes
has three deep nuclei: basal ganglia, hippocampus & amygdala
진화의 과정에서 가장 늦게 출현한 구조물인 대뇌피질은 감각입력의 종착지인 감각피질.운동출력의 시발점인 운동피질 그리고 아직 그 기능을 정확히 알지 못하는 훨씬 광범위한 연합피질로 구분된다.

인간의 경우 대뇌의 여타 모든 영역을 완전히 뒤덮고 있는 대뇌피질은 모든 감각입력을 분석하고 의사결정을 하며, 미래를 예측. 설계하고 정교한 운동 프로그램을 작성하는 등 고도로 발달된 정신기능의 산실이다.
인간이 다른 동물과 비교해 놀라운 정신능력을 가지게 된 것도 이 대뇌피질이 엄청나게 팽창한 결과이며, 300만년도 되지 않는 짧은 기간에 이러한 현상이 일어난 것은 다른 어떤 종진화에서도 발견되지 않는 일이다. 아마도 언어라는 상징체계를 사용하게 됨으로써 이러한 기능을 담당할 뇌 영역의 팽창을 가져온 것 같으며 앞으로도 인간의 대뇌피질은 더 팽창할 가능성이 있는 것으로 믿어진다.

basal ganglia: 3 components (caudate, putamen, globus pallidus)
---function: cognition & regulation of movements

hippocampus: memory storage
amygdala: autonomic, endocrine & emotional functions through the hypothalamus

Four Principles governing the organization of the major functional system

1) Each system contains synaptic relays
not one-to-one connection
modification of information in the relay nuclei or from the higher center
relay nuclei has local interneurons (excitatory, inhibitory) and projection neurons

2) Each system composed of several distinct pathways
each sensory modality
visual system (moving or nonmoving object)
in somatic system (pain, touch)
in motor system (pyramidal system for accurate voluntary movements & fine finger movements; extrapyramida system for overall body posture & spinal reflexes

3) Topographic organizations: from spinal cord to cortex
visuotopic, somatotopic, tonotopic, motor map

4) Crossing the midline
bilaterally symmetrical & cross over
pain sensation crossing at spinal cord
commissures, corpus callosum

Reference link: General overview of the Nervous System