Copy of NEUROII-SOMATOSENSORY-SYSTEM.pdf - NEUROSCIENCE 2...

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SANTOS, C., VILLANUEVA, C., VILLASERAN [SANTOS, M. A.]
NEUROSCIENCE 2
SOMATOSENSORY SYSTEM
ROSALES, M.D.
1 st SHIFT, August 14, 2017
Topic Outline
I. Somatosensory System
A. Introduction
B. Bell-Magendie Law
C. Broadmann’s Area
D. Rexed Lamina
II. Sensory Modalities: Overview
A. Touch
B. Pain and Temperature
1. Types of pain
C. Proprioception
III. Sensory Nerve Fibers
IV. Sensory Modalities: Pathways
A. Somatosensory Pathway (Generalities)
B. Dorsal Column
1. Fasciculus Gracilis
2. Fasciculus Cuneatus
C. Anterolateral System
1. Lateral Spinothalamic Tract
2. Anterior Spinothalamic Tract
Some information were lifted from Haines and the Sensory
Physiology handout. Photos from Haines textbook (4 th ed),
Haines atlas (6 th ed), and internet.
SOMATOSENSORY SYSTEM
 Somato- body
 Sensory- consciousness
Introduction
 Central Sulcus of Rolando- separates the frontal and the
parietal lobes
 Frontal- Motor (precentral gyrus)
o Primary motor cortex (BA 4)
 Parietal- Sensory (postcentral gyrus)
o Primary somatosensory cortex (BA 3-1-2)
 Homonculus- grotesque inverted figure (H-A-L)
Figure 1. Homonculus
 Pain in body area is not perceived unless it reaches its
specific section in the homunculus
 Sensory pathways- ascending pathways
 Cerebellum- also involves ascending pathways
“ All sensory pathways are
ascending pathways but not all
ascending pathways are sensory
pathways”
 Axon - where nerve impulse travels
o Only myelinated segment of the neuron, making the
propagation faster = saltatory conduction
o High density of Na+ channels
 Opens Ca+ channels -> exocytosis -> Ach -> receptor
 Synapse - presynaptic + postsynaptic neuron
o No myelin, all gray
Bell-Magendie Law
 Dorsal – sensory
 Ventral – motor
o The line that demarcates each area is the central canal
o The impulse for pain is conveyed in the centripetal
direction towards the post-central gyrus via the spinal
cord’s dorsal half, in the white matter where the axons
are located
 Centripetal: towards the nervous system
1811- Ch arles Bell
 Function of the spinal cord
 Anesthetized ventral SC, then dorsal SC (rat is in comatose)
o Stimulated ventral (motor) = rat moved
o Stimulated dorsal (sensory) = no response
 First to distinguish between motor and sensory nerves
1822- Francois Magendie
 Twilight anesthesia is now available (rat is conscious)
o Stimulated ventral (motor) = rat moved
o Stimulated dorsal (sensory) = rat grimaced in pain
Broadmann’s Area
1902- Korbinian Broadmann
 Mapped out 52 areas in the cerebral cortex
 Each area has the same nerve cell bodies
Rexed Lamina
1952- Bror Rexed
 Rexed Lamina- 10 areas mapped out in the central gray of
the spinal cord
o Laminae I-VI: in the dorsal horn
o Lamina VII: in the intermediate zone
o Lamina VIII: occupies much of the ventral horn
o Lamina IX: interspersed in and alongside VIII
o Lamina X: area surrounding the central canal

Neuroscience 2: Somatosensory System
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SANTOS, C., VILLANUEVA, C., VILLASERAN [SANTOS, M. A.]
 Lamina I
o aka posterior marginal nucleus or zone
 Lamina II
o aka substantia gelatinosa
o where pain impulses travel through, to be projected to the