Principles - Function of the Nervous System

Question 1

What does efferent mean?

Answer 1

Motor

These nerves carry action potential towards the body wall, body cavity or organ

Question 2

What does afferent mean?

Answer 2

Sensory

These nerves carry action potential towards the brain from the organ, body wall or body cavity.

Question 3

What is the sensory/motor supply of the body wall?

Answer 3

Somatic sensory

Somatic Motor

Question 4

What is the sensory/motor supply of the organs?

Answer 4

Sensory - visceral afferent

Motor - sympathetic, parasympathetic

Question 5

What is in a nerve?

Answer 5

Bundles of axons wrapped in connective tissue, travelling to or from the same region or structure

Question 6

Describe what happens after somatic sensory mechanoreceptors in right L2 dermatome are stimulated.

Answer 6

1. Action potentials are conducted along axons within the L2 anterior ramus
2. The same L2 axons weave their way through the lumbar plexus to the L2 spinal nerve - once the AP goes through the spinal nerve it will only move posteriorly
3. APs conducted via the same axons, pass through the dorsal root ganglion, the posterior roots and posterior rootlets
4. APs arrive at the posterior horn of the L2 spinal cord segment
5. APs synapse in posterior (dorsal) horn onto 2nd sensory neurone (3 neurone chain)
6. APs cross over the midline then ascend towards the thalamus and cerebral cortex
7. Sensory APs synapse onto a 3rd neurone in the thalamus
8. AP’s finally arrive at location in left cerebral cortex specific to the part of the right body wall stimulated (detected in opposite side of the brain)

Question 7

What are the names of the three columns of grey matter in the spinal cord?

Answer 7

Dorsal/posterior horns - sensory neurones
Lateral horns - visceral neurones
Ventral/anterior horns - motor neurones

Question 8

What is the somatic pathway for touch?

Answer 8

A 3 neurone chain

Question 9

Where is the primary somatosensory area in the brain?

Answer 9

In the parietal lobe, left and right

Question 10

Where is the primary somatomotor area in the brain?

Answer 10

In the frontal lobe

Motor APs originate here

Question 11

How is contraction brought about in the right lower limb?

Answer 11

1. somatic motor axons from the left cerebral cortex cross over in the brainstem then descend to the right anterior horn
2. APs are conducted along axons within anterior rootlets, then anterior roots then into spinal nerves
3. APs are conducted along axons in right named nerves of the right lumbar plexus
4. synapse onto skeletal muscle of the right lower limb causing contraction

Question 12

Before the motor axon reaches the spinal nerve, how does it travel?

Answer 12

Only in anterior things (e.g. anterior roots, anterior rootlets)

Question 13

Once the sensory axon reaches the spinal nerve, how does it travel?

Answer 13

Only in posterior things (e.g. posterior rootlets, posterior roots)

Question 14

What organs does the sympathetic division supply that the parasympathetic division doesn’t?

Answer 14

Only body wall organs and arterioles - everything else has both sympathetic and parasympathetic supply