Somatosensory system

5 classical senses – sensory organs

• vision

• hearing

• touch

• smell

• taste

non-classical senses

• proprioception

• pain

• itch

• temperature

• balance

• visceral sensations

somatosensory system main functions

provides feedback for motor functions

protects against harmful stimuli

Types of receptors

• mechanoreceptor

• chemoreceptor

• photoreceptor

• thermoreceptor

Receptor categories

• exteroceptor

• interceptor

• proprioceptor

Information flow from sensory receptors to CNS: primary sensory neurons

1. Sensory endings in skin

2. Action potential in sensory axon

3. Sensory axon enters spinal cord and synapses w/ brain

4. Sensory pathway continues with second neuron projecting to the thalamus

5. Sensory pathway reaches the cerebral cortex for conscious perception

Aa receptors

Golgi tendon organs and muscle spindles – proprioception

AB receptor

Merkel, Meissner, Ruffini, Pacinian – pressure, texture, flutter, motion, stretch, vibratio

AG Receptor

free nerve ending – cold, sharp pain

C receptor

free nerve ending – warmth, burning pain

direct / lateral (neospinothalamic) pathway

• fast
• sharp
• discriminative
• protective

indirect / medial (paleospinothalamic) pathway

• slow
• burning
• punishing
• aversive

ACA stroke

contralateral leg and foot

MCA stroke

contralateral hand, face

Trigeminal lemniscus

a nerve pathway that transmits sensory information from the face to the main sensory trigeminal nucleus in the pons

• anterior trigemino-thalamic tract
• posterior trigemino-thalamic tract
• fibers from mesencephalic nucleus of V

spinal cord hemi section (Brown-Sequard syndrome)

At the level of injury:
• ipsilateral sensory loss
• no contralateral impairments

Down to injury:
• ipsilateral loss of touch and proprioception
• contralateral loss of pain and temperature