Lecture 10: Control Of Motor Function

Question 1

What fibers give rise to A(delta) fibers?

Answer 1

• alpha motor neurons

Question 2

What is a single motor neuron of extramural fibers that act on specific muscle fibers?

Answer 2

• motor unit

Question 3

What is the purpose of the motor neuron pool?

Answer 3

• this group of motor neurons innervate fibers writhing the same muscle

Question 4

When multiple motor units are activated to increase the tension of muscle tension refers to what?

Answer 4

• recruitment

Question 5

What is recruitment?

Answer 5

• increasing the tension of muscle contractions by activating additional motor units

Question 6

What is the difference of how many fibers a small motor neuron and a large motor neuron innervate?

Answer 6

• small= few fibers

- large= multiple fibers

Question 7

Small and large motor neurons have different thresholds. What is the difference?

Answer 7

• small= lowest threshold

- large= highest threshold

Question 8

Large and small motor neurons differ in which fire. How do they differ?

Answer 8

• the small neurons fire first, while the larger neurons fire last.

Question 9

How do small and large motor neurons differ in relation to force generated?

Answer 9

• small neurons generate smallest forces while the largest generated much larger forces.

Question 10

What are Renshaw cells?

Answer 10

• inhibitory cells of anterior horns of spinal cord, that receive collateral branches from alpha motor neurons

Question 11

What signals to Renshaw cells release?

Answer 11

• release an inhibitory signal to other motor neurons.

- this results in lateral inhibition and enhances the fluidity of limb movement.

Question 12

What type of signaling and from what structure will recurrent inhibition be generated?

Answer 12

• inhibitory signals are generated by the Renshaw cells, acting on the same motor neuron to produce recurrent inhibition

Question 13

Renshaw cells are able to transmit inhibitory signals to the same motor neuron, resulting in:_________

Answer 13

• recurrent inhibition

Question 14

What are the different kinds of muscle sensors?

Answer 14

• muscle spindle ( Ia, II afferent)
• Golgi tendon organ (Ib afferent)
• pacinian corpuscle (II afferent)
• free nerve endings (III, IV afferent)

Question 15

The muscle spindle muscle sensors are arranged how, and produce what function?

Answer 15

• parallel with the extramural fibers

- these detect both dynamic and static changes in muscle length

Question 16

The Golgi tendon muscle sensor is primarily responsible to what?

Answer 16

• detects the muscle tension and therefore should be arranged in series with extrafusal fibers

Question 17

What do pacinian corpuscles most likely detect?

Answer 17

• vibration

Question 18

Describe the components that form the muscle spindle.

Answer 18

• innervation by small gamma motor neurons, that are encapsulated within a sheath. This sheath will then run parallel with muscular fibers

Question 19

Where are no contractile fibers contained that act as a sensory receptor for the muscle?

Answer 19

• the muscle spindle

Question 20

How is the muscle spindle able to function as a sensory receptor?

Answer 20

• the stretching of the central region of the intrafusal fibers generates a response.
• therefore this structure (muscle spindle) functions to detect muscle length changes

Question 21

What type of function will consist of increased muscle spindle numbers?

Answer 21

• finer movement require more spindles

Question 22

What are the types of intrafusal fibers?

Answer 22

• nuclear bag fibers

- nuclear chain fibers

Question 23

What is the function of nuclear bag fibers?

Answer 23

• detect the rate a muscle length changes
• innervated by Ia afferent and dynamic gamma efferent
• bag like configuration

Question 24

What do nuclear chain fibers do to function as an intrafusal fiber in the muscle spindle?

Answer 24

• detect static changes in muscle length
• group II (afferent) gamma (efferent) fibers
• more numerous and contain multiple nuclei in a single row

Question 25

What happens when the sensory fibers from the central region of intrafusal fibers are stimulated?

Answer 25

- stimulation occurs when the muscle lengthens and activates the alpha motor neurons, which will cause contraction and shortening of the muscle.

Question 26

What are spindle gamma motor neurons?

Answer 26

- fibers that innervate intrafusal fibers and adjust the sensitivity of the muscle spindle. - these are coactivated with alpha motor neurons that are stimulated from a muscle being stretched.

Question 27

What are the different gamma motor neurons taht are stimulated?

Answer 27

- gamma dynamic stimulate nuclear bag intrafusal fibers | - gamma static stimulate nuclear chain intrafusal fibers

Question 28

What is in control of the gamma motor neurons?

Answer 28

- bulboreticular region of brain stem - cerebellum - basal nuclei - cerebral cortex

Question 29

What role does the muscle spindle play within dynamic stretch?

Answer 29

- signals are transmitted to primary nerve endings, that are elicited by rapid stretch or unstretch - this will oppose sudden muscle length changes

Question 30

What is the function of static reflex of the muscle spindle?

Answer 30

- this reflex is stimulated by primary and secondary endings that allow for degrees of contraction to remain constant

Question 31

The combination of dynamic stretch reflex, and static reflex of the muscle spindle provide what function?

Answer 31

- provides damping which prevents jerkiness with body movements.

Question 32

What are the nerve fibers that play a significant role in the Golgi tendon organ?

Answer 32

- Ib afferent synapse with an inhibitory interneuron, that synapse with an anterior motor neuron

Question 33

Why is a person unable to inhibit the knee-jerk reflex?

Answer 33

- this consists of a Monosynaptic reflex, which prevents a inhibition from other neurons, that would occur in Polysynaptic reflexes.

Question 34

Understand the flexor and crossed extensor reflexes on figure 55-9

Answer 34

.

Question 35

What is after discharge?

Answer 35

- the results of persistent neural activity in Polysynaptic circuits. Therefore it will prevent muscle from relaxing for some amount of time.

Question 36

What are the functions of the premotor and supplementary motor areas?

Answer 36

- generate plan for movement - premotor cortex develops a "motor image" of the muscle movement that will be performed - supplementary cortex mentally rehearses a movement

Question 37

What does the supplementary motor cortex do?

Answer 37

- provides sequence for complex motor sequences and is responsible for mental rehearsal of a movement

Question 38

What does the premotor cortex do?

Answer 38

- develop a diagram of what the total movement will look like with respect to the muscle.

Question 39

Where will more complex patterns of movement be generated? More complex than what the primary motor cortex could form.

Answer 39

Premotor and supplementary motor areas.

Question 40

Where does the posterior motor cortex send its signal sequence?

Answer 40

- primary motor cortex into the basal nuclei and thalamus and then into the primary motor cortex.

Question 41

What is an interneuron?

Answer 41

- responsible to spinal cord integrative function that is small, highly excitable, and reacts spontaneously