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