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. Merkelís disks: touch

2. encapsulated endings

††††††††††††††††††††††† a. Meissnerís 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 ŗ Medial Lemniscal Pathway: fine touch, proprioception, vibration, (shape, size, weight)


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