Section 6: Motor functions of spinal cord

Question 1

What kind of reflex applies to putting your hand on a hot burner?

Answer 1

Withdrawal reflex

Question 2

Where are sensory neurons and their synapse located?

Answer 2

In the dorsal root ganglion and they synapse at the spinal cord level to elicit motor reflexes

Question 3

Tue or false: Sensory neurons transmit signals to higher centers

Answer 3

True

Question 4

Define motor neurons (anterior horn)

Answer 4

• Directly innervate skeletal muscle fibers
• Alpha MNs (a-alpha axons) excite extrafusal muscle fibers
• Gamma MNs (A-gamma axons) excite intrafusal fibers (muscle sensory receptors)

Question 5

What are interneurons?

Answer 5

Local neurons that have connections with sensory and motor neurons

Question 6

Are interneurons inhibitory or excitatory?

Answer 6

They can be both

Question 7

What are sensory receptors of the muscles?

Answer 7

Mechanoreceptors

Question 8

Define muscle spindle

Answer 8

• Mechanoreceptors
• Are distributed throughout the muscle belly
• Sense muscle length and rate of change of length
• Sensory signals are transmitted through 1a fibers and II fibers

Question 9

Golgi tendon organs are:

Answer 9

• Located in the muscle tendon
• Sense tendon tension and rate of change of tension
• Sensory signals are transmitted through 1b fibers

Question 10

What is the function of muscle spindles?

Answer 10

To provide information on the position of body parts (proprioception)

Question 11

What type of fibers terminate on the nuclear bag AND on the nuclear chain?

Answer 11

Type 1a fibers

Question 12

Type 1a fibers respond to what in the muscle spindle?

Answer 12

The rate of change in the muscle length (dynamic) and to the degree of stretch of the muscle

Question 13

Type II fibers terminate where?

Answer 13

Nuclear chain fibers

Question 14

Type II fibers respond to what?

Answer 14

The degree of stretch of the muscle (static)

Question 15

What is the purpose of Alpha-Gamma Coactivation?

Answer 15

To maintain the tension in the muscle spindles as the muscle shortens, the sensitivity to stretch is maintained

Question 16

True or false: Signals are still sent to the CNS even if the muscle spindles are not stretched

Answer 16

False: they must be stretched

Question 17

What are GTO’s?

Answer 17

Golgi tendon organs: they are encapsulated sensory receptors through which the muscle tendon fibers pass

Question 18

GTO’s are stimulated when?

Answer 18

When the muscle fibers are tensed by the contraction or the stretching of the muscle (sensitive to muscle tension)

Question 19

When do GOT’s react intensively?

Answer 19

when the muscle tension suddenly increases (dynamic) or when it settles down rapidly to a lower level of steady state tension (static)

Question 20

What is the role of Ib fibers in the GTO?

Answer 20

To inhibit indirectly, through interneurons, alpha motor neurons at the spinal cord to allow the muscle to relax and relieve tension in the tendon

Question 21

What are spinal cord reflexes?

Answer 21

A mechanism by which sensory impulses are automatically converted into a motor effect, a protective mechanism to the body

Question 22

Are reflexes voluntary?

Answer 22

No, they are rapid and controlled by the spinal cord integration center

Question 23

Define stretch reflex

Answer 23

• Sudden stretch of the muscle activates the muscle spindle
• Associated sensory fibers transmit impulses at the spinal cord level
• Type 1a and II fibers synapse directly with alpha motor neurons causing the muscle to contract to oppose the stretch
• Inhibitory interneurons sends efferent signal to antagonist

Question 24

Define the Golgi tendon reflex

Answer 24

• Serves to relieve excess tension on the muscle
• Sensory neurons synapse with inhibitory interneurons that inhibit alpha motor neurons and cause the contracted muscle to relax
• Sensory neurons synapse with excitatory neurons of antagonist muscles and cause the muscle to contract

Question 25

How is the Golgi tendon reflex activated?

Answer 25

By the contracting of a muscle that creates tension on the tendon attached to the same muscle and thus activates the GTO

Question 26

What is the flexion reflex?

Answer 26

• Also known as the withdrawal reflex

- Is initiated by a painful stimulus that causes an automatic withdrawal of the threatened body part

Question 27

Describe the process of the flexion reflex

Answer 27

Sensory neurons synapse with interneurons that:

• Excite motor neurons of the flexor muscle and cause muscle to contract
• Inhibit motor neurons of the extensor muscles and cause the muscle to relax