Neuroscience Spinal Reflexes and EMG Demonstration Blair Calancie

Question 1

What is the purpose of the muscle spindle stretch receptor?

Answer 1

Senses changes in muscle length

Question 2

What is the only afferent receptor in the CNS that receives a nerve supply?

Answer 2

Muscle spindle stretch receptor

Question 3

How are muscle spindle stretch receptors arranged?

Answer 3

In parallel with extrafusal fibers

Question 4

What kind of MNs innervate intrafusal muscle fibers?

Answer 4

Gamma MNs

Question 5

Intrafusal fibers include two kinds of sensory zones:

Answer 5

1. Central (bag) region - 1a receptors

2. Distal regions - type 2 receptors

Question 6

Explain the perturbation part of the stretch reflex:

Answer 6

1. Increased load, as on elbow holding a filling glass, causes rotation
2. Spindle (intrafusal fibers) in biceps are stretched
3. Afferent signals sent to spinal cord, recruiting biceps and brachialis alpha LMNs, resulting in stretch reflex.

Question 7

Explain the restoration of equilibrium part of the stretch reflex:

Answer 7

1. Original muscle excited
2. Synergist (heteronymous) muscle also excited
3. Antagonist (triceps) inhibited (1a inhibitory interneuron) / reciprocal inhibition
4. Biceps contract and shortens, elbow flexes, resisting perturbation

Question 8

T or F: Muscle contraction will unload the spindle, eliminating further signaling of changes in muscle length to CNS.

Answer 8

True. A silent stretch receptor is of no use to the CNS

Question 9

How do intrafusal fibers maintain sensitivity to stretch?

Answer 9

They receive input from gamma MNs when extrafusal fibers are already “used” to maintain afferent information input to CNS.

Question 10

T or F: Alpha motor neurons can continue to receive and transmit progressive stretch input to the CNS during muscle contraction.

Answer 10

False. There are periods of silence that are filled in by the actions of gamma MNs

Question 11

What is the GTO?

Answer 11

Golgi tendon organ, located bewteen muscle fibers and tendon

Question 12

How are GTOs arranged?

Answer 12

In series with extrafusal fibers

Question 13

What kind of receptors do GTOs have?

Answer 13

1b receptors

Question 14

What is the purpose of GTOs?

Answer 14

It senses force generation. Passive stretch has little effect on GTOs, but active muscle contraction (active force) causes strong GTO firing.

Question 15

T or F: A-delta receptors (nocioceptors) have direct connections to motor neurons.

Answer 15

FALSE. They connect with interneurons in the intermediate gray.

Question 16

What is CPG?

Answer 16

Central Pattern Generator. A distributed network of neurons in the spinal cord that can produce coordinated movements in the absence of higher inputs. (cat experiment)

Question 17

T or F: CPG output can be modified by training.

Answer 17

True. Lends itself to potential for spinal cord plasticity and rehabilitation.