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#pragma description The Somatosensory System: Receptors and Central Pathways;

= The Somatosensory System: Receptors and Central Pathways =

<<TableOfContents(3)>>

== 기본 개념 ==
[[WikiPedia:Charles Scott Sherrington]](1932 노벨상)의 분류
 1. 고유감각([[WikiPedia:proprioception]]): 관절의 꺽인 정도나 근육의 수축 상태 등 monitoring
 1. 외수용([[WikiPedia:exteroception]]): 온도, 촉각 등 통상적 의미의 감각. (후각, 시각, 미각은?)
 1. 내수용([[WikiPedia:interoception]]): visceral sensation?

== 일차감각신경세포 (Primary Sensory Neurons) ==
감각이 중추의 감각 피질까지 전달되려면 여러 단계의 neuron와 synapse를 거치게 된다.
 * 그 첫 번째 신경세포를 primary sensory neurons 혹은 primary afferent neurons 라고 한다.
  * Primary sensory neuron으로부터 신호를 받는 post-synaptic neuron을 second order neuron이라고 한다.
  * Primary & Secondary sensory neurons가 만나는 synapse는 척수의 뒤쪽, dorsal horn에 있다.

{{https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Periphery.png/1024px-Periphery.png||width=600}}

=== Dorsal Root Ganglion ===
Peripheral neurons의 세포체(soma)가 모여 있는 곳을 신경절(ganglion)이라 부른다.
 * Primary sensory neurons의 세포체는 spinal cord의 dorsal에 있어서 dorsal root ganglion (DRG)라고 부른다.
 * Primary sensory neurons는 pseudounipolar 형태이다. {{attachment:pseudounipolar.png|axon hilock은 어디?|height=75}}
  * Distal end는 피부, 근육, 관절 등의 감각기관에 innervated 되고,
  * Proximal end는 dorsal horn에서 2차 신경(second order neuron)과 synapse 한다.
  {{https://upload.wikimedia.org/wikipedia/commons/a/ad/Spinal_Cord_Sectional_Anatomy.png||width=500}}

=== Trigeminal Ganglion ===
목 보다 윗 부분(얼굴, 머리)을 담당하는 감각신경의 세포체가 모여있는 곳은 trigeminal ganglion (TG)라고 부른다.
 * 머리에는 척수 자리에 뇌간(brainstem)이 있다. 즉, brainstem에서 second order neuron과 만난다.
 * 세 가지 핵이 모여 있는 듯한 구조여서 trigeminal 이라 부른다 (사이즈가 DRG보다 크다)
{{https://upload.wikimedia.org/wikipedia/commons/8/84/Brain_human_normal_inferior_view_with_labels_en.svg||width=330}}
{{http://www.strokeeducation.info/images/brainstem%20and%20brain%20.jpg||width=350}}

==== Nerves vs. Neurons ====
{{https://upload.wikimedia.org/wikipedia/commons/5/5a/Nerve_Anatomy.jpeg}}

==== Conduction Velocity & Compound Action Potential ====
 {{https://faculty.washington.edu/chudler/axon.gif|그림 22-2|height=300}}
 {{https://instruct.uwo.ca/anatomy/530/comppot.gif|그림 22-3|height=300}}

== Sensory Receptors ==
{{https://upload.wikimedia.org/wikipedia/commons/thumb/b/be/Blausen_0809_Skin_TactileReceptors.png/768px-Blausen_0809_Skin_TactileReceptors.png||width=600}}

=== Mechanoreceptors ===
Proposed activation mechanism
 1. Direct membrane stretch
 1. Direct cytoskeleton stretch
 1. Indirect cytoskeleton stretch
 1. 기타 등등
[[DOI:10.1016/j.conb.2005.05.012|{{https://ars.els-cdn.com/content/image/1-s2.0-S0959438805000772-gr1.gif||width=330}}]]
[[DOI:10.1126/science.1193270|{{https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3062430/bin/nihms-257858-f0001.jpg||width=370}}]]

[[DOI:10.1126/science.1193270|Piezo1 and Piezo2 are essential components of distinct mechanically activated cation channels]] (Science 2010)
 * [[doi:10.1038/nature25453|Structure of the mechanically activated ion channel Piezo1]] (Nature 2017)
 * [[doi:10.1038/nature25743|Structure and mechanogating mechanism of the Piezo1 channel]] (Nature 2018)

=== Proprioceptive Receptors ===
 * Muscle Spindle
 * Golgi tendon organ
{{https://pocketdentistry.com/wp-content/uploads/285/F00002Xf02-05-9780323082204.jpg||height=400}}
{{https://3dprintingindustry.com/wp-content/uploads/2015/06/3D-printed-derby-dog-prosthetic.gif||height=200}}

참고: [[WikiPedia:Stretch reflex|Myotatic (Stretch) Reflex]]
 {{https://pocketdentistry.com/wp-content/uploads/285/F00002Xf02-06ab-9780323082204.jpg||width=600}}

번외편: [[WikiPedia:Withdrawal reflex]]
 {{https://pocketdentistry.com/wp-content/uploads/285/F00002Xf02-07-9780323082204.jpg||width=600}}
=== Pain Receptors ===
[[DOI:10.1016/j.cell.2009.09.028|{{https://ars.els-cdn.com/content/image/1-s2.0-S0092867409012434-gr3_lrg.jpg||width=600}}]]

=== Thermo Receptors ===
[[DOI:10.1016/S0959-4388(03)00101-6|{{https://ars.els-cdn.com/content/image/1-s2.0-S0959438803001016-gr1.jpg}}]]

=== Itch Sensation ===

=== Visceral Sensation ===

== Central Pathways ==

=== Dorsal Horn ===
[[doi:10.1038/nrn2947|{{https://media.nature.com/lw926/nature-assets/nrn/journal/v11/n12/images/nrn2947-f1.jpg|그림 22-10|}}]]

==== Dermatome ====
{{https://jcphysiotherapy.files.wordpress.com/2015/02/10872852_1515044748768756_3090295442741329178_o.jpg||width=750}}

{{http://what-when-how.com/wp-content/uploads/2012/04/tmp15F36_thumb.jpg||width=750}}

[[https://www.rfa.org/korean/weekly_program/ac74ac15d558ac8c-c0bdc2dcb2e4/healthylife-12162016141348.html|대상포진]] ([[WikiPedia:Herpes Zoster]]) {{http://www.dtnews24.com/news/photo/201601/60179_388576.jpg||height=200}}
{{https://www.researchgate.net/profile/Mehmet_Demirkol4/publication/266263308/figure/fig2/AS:392157086142465@1470508943041/Preoperative-extraoral-photograph-of-a-patient-with-herpes-zoster-rash-on-the-left-chin.png||height=200}}

==== 연관통 ====
{{https://pocketdentistry.com/wp-content/uploads/285/F00002Xf02-01-9780323082204.jpg||width=600}}

=== Dorsal Column System & Spinothalamic Tract ===

{{https://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/1417_Ascending_Pathways_of_Spinal_Cord.jpg/1000px-1417_Ascending_Pathways_of_Spinal_Cord.jpg}}

=== Thalamus ===
{{https://upload.wikimedia.org/wikipedia/commons/8/8c/Cortical_surface_with_an_overlay_of_the_basal_ganglia_and_thalamus.jpg||width=600}}

{{http://humanphysiology.academy/Neurosciences%202015/Images/3/thalconn%20www.glittra.JPG||width=600}}

=== Somatosensory Cortex ===
{{http://droualb.faculty.mjc.edu/Course%20Materials/Physiology%20101/Chapter%20Notes/Fall%202007/figure_10_04_labeled.jpg||width=450}}

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