Nervous System Physiology Part 8

Question 1

Where are anterior motor neurons located?

Answer 1

In the anterior horns of the spinal cord gray matter.

Question 2

What are the two types of anterior motor neurons?

Answer 2

Alpha motor neurons and gamma motor neurons.

Question 3

What do alpha motor neurons innervate?

Answer 3

Extrafusal muscle fibers.

Question 4

What do gamma motor neurons innervate?

Answer 4

Intrafusal muscle fibers.

Question 5

What are muscle spindles?

Answer 5

Encapsulated muscle fibers scattered throughout striated muscle.

Question 6

How do anterior motor neurons compare in size to other neurons?

Answer 6

They are 50 to 100 percent larger.

Question 7

What is the function of the ventral horn in the spinal cord?

Answer 7

It contains motor neurons responsible for movement.

Question 8

What do alpha (α) motor neurons innervate?

Answer 8

Extrafusal skeletal muscle fibers.

Question 9

What is a motor unit?

Answer 9

An alpha motor neuron and the muscle fibers that it innervates.

Question 10

Why are alpha motor neurons called the “final common pathway” out of Central Nervous System ?

Answer 10

Because all neural influences on skeletal muscle converge on them, and they are the only route through which the CNS can affect skeletal muscle.

Question 11

What do gamma (γ) motor neurons innervate?

Answer 11

Specialized intrafusal muscle fibers, which are part of muscle spindles.

Question 12

What is the function of the muscle spindle?

Answer 12

To sense muscle length.

Question 13

What is the function of gamma motor neurons?

Answer 13

To adjust the sensitivity of the muscle spindles.

Question 14

What do gamma (γ) motor neurons innervate?

Answer 14

The polar regions of intrafusal fibers

Question 15

What happens when gamma motor neurons are activated?

Answer 15

The central receptor region of the intrafusal fibers is stretched.

Question 16

Where are muscle spindles located?

Answer 16

Throughout the belly of the muscle.

Question 17

What do muscle spindles do?

Answer 17

They send information to the nervous system about muscle length or rate of change of length.

Question 18

What is alpha-gamma coactivation

Answer 18

The simultaneous activation of gamma and alpha motor neurons to maintain tension in the muscle spindle during contraction.

Question 19

Why is alpha-gamma coactivation important?

Answer 19

: It prevents the central region of the muscle spindle from going slack during a shortening contraction, allowing continued sensory feedback.

Question 20

Where are Golgi tendon organs located?

Answer 20

: In the muscle tendons near their junction with the muscle.

Question 21

What do Golgi tendon organs detect?

Answer 21

Tendon tension or the rate of change of tension.

Question 22

What wraps around the collagen bundles in tendons?

Answer 22

Afferent nerve fibers from Golgi tendon organs.

Question 23

What activates the Golgi tendon organs?

Answer 23

Tension from muscle stretching or contraction that straightens collagen bundles and distorts receptor endings.

Question 24

When is the tendon stretched more: active contraction or passive stretch?

Answer 24

Tendon is stretched more during active contraction of the muscle.

Question 25

What are spinal reflexes?

Answer 25

Somatic reflexes mediated by the spinal cord, often without higher brain involvement.

Question 26

Name the three types of spinal reflexes.

Answer 26

1.The Stretch Reflex 2. The Tendon Reflex 3. The Withdrawal Reflex and Crossed-extensor Reflex

Question 27

How do Golgi tendon organs work?

Answer 27

Afferent nerve endings wrap around collagen bundles; when tension is applied, the collagen straightens and distorts the endings, activating the receptors.

Question 28

Does the brain play any role in spinal reflexes?

Answer 28

Yes, the brain is “advised” of most spinal reflex activity and can facilitate, inhibit, or adapt it.

Question 29

What triggers the stretch reflex?

Answer 29

Stretching of muscle spindles activates sensory neurons, which send signals to the spinal cord.

Question 30

What happens when sensory neurons of the stretch reflex reach the spinal cord?

Answer 30

They synapse with motor neurons that excite the extrafusal muscle fibers of the stretched muscle, causing contraction.

Question 31

What is the function of the stretch reflex?

Answer 31

: It causes reflexive muscle contraction to resist further stretching.

Question 32

What initiates the knee-jerk reflex?

Answer 32

Tapping the patellar ligament stretches the quadriceps and excites its muscle spindles.

Question 33

What does a positive knee-jerk reflex indicate?

Answer 33

That sensory and motor pathways between the muscle and spinal cord are intact and it shows spinal cord excitability.

Question 34

What happens during the knee-jerk reflex after the quadriceps are stretched?

Answer 34

Afferent impulses travel to the spinal cord. 2. Motor neurons send activating impulses to quadriceps (causing contraction). 3. Interneurons inhibit motor neurons to hamstrings (preventing resistance to movement).

Question 35

How does the state of spinal motor neurons affect the reflex response?

Answer 35

Highly facilitated neurons cause a strong reflex, while high inhibitory input may prevent the reflex entirely.