Spinal and Descending Control of Movement

Question 1

Where is the motor neuron cell body located?

Answer 1

The central gray matter of the spinal cord in the anterior ventral horn.

Question 2

Big motor neurons that transmit signals quickly are known as what?

Answer 2

Alpha motor neurons

Question 3

Alpha motor neurons are a synonym of what?

Answer 3

Lower motor neurons

Question 4

Smaller motor neurons that transmit signals more slowly are known as what?

Answer 4

Gamma motor neurons

Question 5

What is the fastest sensory nerve fibre?

Answer 5

Aalpha 1a fibres

Question 6

Describe the basic characteristics of C nerve fibres.

Answer 6

Unmyelinated nerve fibres that respond to pain

Question 7

What is meant by intrafusal?

Answer 7

Refers to fibres within the muscle spindle

Question 8

What is meant by extrafusal?

Answer 8

Refers to fibres outside of the muscle spindle

Question 9

Explain the stretch myotactic reflex in muscle.

Answer 9

1. Muscle is stretched by an unexpected weight.
2. 1a sensory afferent neurons of muscle spindle fibres increase tonic firing.
3. Synapses at one point in the gray matter of the spinal cord.
4. The synapse is to alpha motor neuron to the same muscle.
5. The muscle contracts to revert to it’s original length.

Question 10

What process maintains the position of muscle against unexpected forces?

Answer 10

Stretch reflex.

Question 11

What neurons are involved in the stretch reflex?

Answer 11

1a neurons (afferent)
Alpha motor neurons (efferent)

Question 12

What do the gamma motor neurons contract?

Answer 12

Intrafusal muscle fibres

Question 13

What does alpha-gamma coactivation do in the stretch reflex?

Answer 13

Maintains the shape of the muscle spindle as both the extrafusal and intrafusal muscle fibres contract.

Question 14

What is Renshaw cell?

Answer 14

Spinal inhibitory interneuron

Question 15

What do spinal inhibitory interneurons do?

Answer 15

The cause inhibition the antagonist muscle when the agonistic muscle is contracting.

Question 16

What forms the start of the corticospinal tract?

Answer 16

Pyramidal cells in the 5th layer of the primary motor cortex.

Question 17

What do giant pyramidal cells of the corticospinal tract synapse onto?

Answer 17

Giant pyramidal cells synapse directly onto alpha motor neurons.

Question 18

What are Betz cells?

Answer 18

Giant pyramidal cells

Question 19

What are the classic upper motor neurons?

Answer 19

Giant pyramidal cells

Question 20

What are the largest pyramidal cells?

Answer 20

Betz cells of the primary motor cortex.

Question 21

Explain the path of the corticospinal tract.

Answer 21

The corticospinal tract starts in the primary motor cortex, it then pass through the midbrain and the pons.
The CST then decussates across the medullary pyramids, and enters the spinal cord.

Question 22

Where is the upper motor neurons cell body located?

Answer 22

The primary motor cortex.

Question 23

Define ataxia.

Answer 23

Lack of co-ordination of voluntary muscles