Spinal cord: info in-and-out of the spinal cord

Question 1

What is a dermatome?

Answer 1

An area of skin supplied by nerves from a single spinal root

Question 2

What is a ‘motor pool’?

Answer 2

All motor neurones that innervate a single muscle

Muscles are controlled by a ‘motor pool’ of neurones

Question 3

What is a motor unit

Answer 3

The motor neurone and all the muscle fibres it contacts

Question 4

Why do spinal enlargements occur?

Answer 4

The arms and legs (in particular hands and feet) have many highly innervated muscles and have a high density of sensory receptors. Because of this, portions of spinal cords that provide spinal nerves to arms and legs are enlarged.

Question 5

What are the 3 parts of the spinal segment which are involved in information flow?

Answer 5

1) Dorsal horn – contains sensory neurones which receive sensory info and send this up to the brain
2) Ventral horn – contain neurones that send messages directly to the muscles
3) Intermediate zone – contain interneurons which integrate information (e.g., inhibition)

Question 6

What is a ‘tetanic contraction’?

Answer 6

When multiple action potentials occur in quick succession, force in the muscle builds up. At certain rates muscle will be unable to contract further (maximal contraction). This is a tetanic contraction - occurs when input is at a frequency that is so fast that the muscle can’t relax between APs

Question 7

Rate coding in the motor system - recruitment principle

Answer 7

For small forces, small motor units are recruited first as the required force increases, larger motor units are recruited

Question 8

Rate coding in the motor system - size principle

Answer 8

With increasing strength of input onto motor neurons, smaller motor neurons are recruited and fire APs before larger motor neurons are recruited