The Somatic Sensory System - Introduction touch

6 important questions on The Somatic Sensory System - Introduction touch

What is the route of primary afferent axons?

They bring informatio form the somatic sensory receptors to the spinal cord or brain stem.

How are axons from skin sensory receptors usually designated? And the axons innervating the muscles and tendons in relationship to this?

Which groups are unmyelinated?

As A(alpha), A(beta),  A(sigma), and C; axons of similar size, but innervating the muscles and tendons, are called groups I, II, III, and IV.

Group C (or IV) axons are, by definition, unmyelinated.

The 30 spinal segments (paired dorsal and ventral roots) are divided in four groups:

- cervical (C) 1 - 8
- thoracic (T) 1 - 12
- lumbar (L) 1 - 5
- sacral (S) 1 - 5
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What is a dermatome, and what is it related to?

The area of skin innervated by the right and left dorsal roots of a single spinal segment. Thus, there is one-to-one correspondence between dermatomes and spinal segments.
When mapped, the dermatomes delineate a set of bands on the body surface.

Information about touch and vibration of the skin takes a path to the brain that is entirely distinct from that taken by information about pain and temperature. What is this pathway called?

The dorsal column-medial lemniscal pathway or spino-cortical pathway

The sense of touch of the face obviously does not go via the spinal cord, what route does it follow?

Somatic sensation of the face is mostly supplied by the large trigeminal nerves (cranial nerve V) .

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