9. Somatosensory System
exteroreceptors: skin
proprioceptors:
muscles, tendons, joints
interoceptors:
viscera
Types of nerve-endings
1. non-encapsulated
endings
a. free nerve
endings: pain and temperature
b. Merkel’s disks: touch
2. encapsulated
endings
a. Meissner’s
corpuscles: two-point
discrimination, texture
b. Pacinian
corpuscles: touch, joints: proprioception
Spinal Cord Organization
1. White matter
a. posterior/dorsal
column
b. lateral column
c. anterior/ventral
column
2. Gray matter
a. dorsal horn
b. intermediate zone
c. anterior horn
Zones
a. Marginal zone
b. Substantia
gelatinosa
c. Nucleus proprius
Classification of somatosensory system
1. Spinothalamic
Pathway
a. Lateral division: pain and temperature: test sharp/dull touch with paperclip
b. Anterior division: simple touch
2. Dorsal Column à Medial Lemniscal Pathway: fine touch, proprioception,
vibration, (shape, size, weight)
tests:
1. two-point
discrimination
2. vibration (128 Hz fork on bony areas)
3. Romberg sign (close eyes
with feet together)
4. test fasciculus gracilis by moving finger and asking direction