Somatosensory system

The somatosensory system deals with sensation. It's not localized; its receptors can be found all over the body.

Reception
There are three kinds of somatosensory perception.

Nocioception
Deals with pain and temperature. Irritation to free nerve endings releases chemicals that produce action potentials.

Hapsis
Deals with fine touch and pressure. Pressure on the skin or movement of hairs produce action potentials.

Proprioception
Deals with body awareness; movement of muscles, joints, bones (Olaf has no proprioception). Movement stretches receptors, which produces action potentials.

Balance
Only localized part; the Vestibular system. Movement of the head or body creates an action potential.

Dorsal spinothalamic tract

 * The haptic and proprioceptive axons go this way, on the dorsal side of the spinal cord, ipsilaterally.
 * They switch to the other side of the body in the Medial Lemniscus (Brainstem).
 * They synapse in the ventrolateral thalamus.
 * They continue to the somatosensory cortex.

Ventral spinothalamic tract

 * Nocioceptive axons go this way. They synapse on the dorsal side of the spinal cord, then go to the ventral side, on the contralateral side.
 * They join the medial lemniscus pathway.
 * They synapse in the ventrolateral thalamus.
 * They continue to the somatosensory cortex.

Vestibular nerve
The vestibular nerve joins with the cochlear nerve, forming the auditory vestibular nerve (See: auditory pathway).

Processing
Somatosensory cortex.

Projects to

 * The ventrolateral thalamus sends information to the primary motor and premotor cortex.
 * The SS2 contributes to the visual ventral stream by providing (conscious) information about object size, shape, and texture. It contributes to the visual dorsal stream by specifying (unconscious) the movement used for grasping a target.
 * The spinal cord initiates reflexes based on somatosensory information.