Power Point 18 & 19

Question 1

Under the boutons lies specialized portion of muscle membrane termed

Answer 1

end plate

Question 2

Motor axon branches at its terminal, each branch terminates in a

Answer 2

synaptic bouton

Question 3

Neuromuscular synapses are

Answer 3

cholinergic (ACh)

Question 4

One action potential fired by motor neuron produces one ________ in the muscle fiber

Answer 4

twitch

Question 5

The time it takes the twitch to reach its peak force is termed the

Answer 5

contraction time

Question 6

Depending on biochemical properties, there are ______ twitch motor units

Answer 6

slow and fast

Question 7

A rapid series of action potentials (resulting in temporal summation) elicits superimposed twitches, resulting in sustained contraction is known as

Answer 7

tetanus

Question 8

Biochemical properties of a muscle fiber influence what?

Answer 8

contraction speed, force, and fatigability

Question 9

Type I muscle fibers are what type of twitch muscles

Answer 9

slow twitch - produce small forces but can sustain contraction longer

Question 10

Type II muscle fibers are what type of twitch muscles

Answer 10

fast twitch - produce large forces but are easy to fatigue

Question 11

The _________ is defined as a single motor neuron and the group of muscle fibers which it innervates.

Answer 11

motor unit

Question 12

one muscle fiber is innervated by one ______

Answer 12

motor neuron

Question 13

fine control = few muscle fibers per neuron – type _______ fibers (motor units of less than 100 for control of eye movements)

Answer 13

1

Question 14

large force = many muscle fibers per neuron – type _______ fibers (>1000 for single motor unit controlling leg muscles)

Answer 14

2

Question 15

all the muscle fibers innervated by the (Same/Different) motor neuron are of the same type

Answer 15

same

Question 16

muscle fibers in one muscle work in parallel and are subdivided into _______

Answer 16

motor units

Question 17

motor neurons in the ventral horn of the spinal cord that control one muscle are clustered into a column termed the __________________

Answer 17

motor nucleous

Question 18

one motor nucleus = one _______

Answer 18

muscle

Question 19

axons from a motor nucleus exit the spinal cord in several ____________, but cluster into one nerve bundle en rout to the target muscle.

Answer 19

ventral roots

Question 20

the force exerted by a muscle depends on:

Answer 20

• the number of motor units activated during contraction

* the rate at which motor neurons discharge action potentials

Question 21

Force is increased during a muscle contraction by the activation of additional motor units which are recruited progressively from the __________ to the __________.

Answer 21

weakest, strongest

Question 22

the force during the contraction at which the motor unit is activated.

Answer 22

Motor unit recruitment threshold

Question 23

Size Principle Of Motor Neuron Recruitment

Answer 23

recruitment proceeds in ascending order of motor neuron size

smaller motor neurons get recruited first

Question 24

sequence of motor unit recruitment is determined by spinal mechanisms (brain cannot selectively activate specific motor units)

Answer 24

motor units are activated in order of increasing fatigability

Question 25

Charles Sherrington recognized the importance of ________ in regulating movements.

Answer 25

sensory information

Question 26

In 1906 he proposed that simple reflexes, elicited by activation of receptors in skin or muscle, are the ____________

Answer 26

basic units of movement.

Question 27

Ibeta proprioceptive fibers (activated by muscle tension) synapse on Ibeta ________ interneurons in the spinal cord

Answer 27

inhibitory

Question 28

the __________ slows muscle contraction as muscle tension increases, limiting the time muscles stay contracted in stationary animal. In the moving animals (when limbs are moving and muscle length is changing) inputs from other types of proprioceptive fibers modulate activity of Ibeta interneurons

Answer 28

reverse myotactic reflex

Question 29

Ialpha proprioceptor is activated by muscle stretch, activates motor neuron that excites the same muscle, causing it to contract.

Answer 29

monosynaptic feed-forward excitation:

Question 30

at the same time Ia also synapses on inhibitory interneurons that inhibit the motor neurons innervating antagonist muscles. This inhibition prevents muscle contraction that might otherwise resist the movement produced by stretch reflex

Answer 30

disynaptic feed-forward inhibition:

Question 31

what reflex ark is controlled entirely by spinal cord circuitry, since it remains intact even if spinal cord has been transected from the brain.

Answer 31

stretch reflex

Question 32

sensory feedback is required: if _____________

Answer 32

dorsal roots are transected reflex is abolished

Question 33

Divergent Innervation

Answer 33

Opposite effect in the opposite leg: to support the body weight

Question 34

Sensory afferent fibers excite both:

Answer 34

• motor neurons innervating the same (homonymous) muscle,• and motor neurons innervating other (heteronymous) muscles with a similar action

Question 35

In all reflex spinal cord circuits sensory neurons form extensive divergent connections, allowing to produce a widely distributed, ___________

Answer 35

coordinated motor pattern.

Question 36

Both the spatial extent and the force of muscle contraction depends on stimulus intensity. Diversity of sensory information – from Golgi tendon organ, muscle spindles, cutaneous receptors, and joints converges on interneurons in the spinal cord. In addition, they receive both excitatory and inhibitory inputs from descending pathways

Answer 36

Reflex adaptability:

Question 37

Reflex Adaptability

Answer 37

Both the spatial extent and the force of muscle contraction depends on stimulus intensity.
Diversity of sensory information – from Golgi tendon organ, muscle spindles, cutaneous receptors, and joints converges on interneurons in the spinal cord.
Both excitatory and inhibitory inputs from descending pathways converge on interneurons in the spinal cord.

Question 38

however the neural mechanism that produces stepping involves a set of spinal cord ________ that do not require any sensory feedback to produce activity

Answer 38

pacemaking circuits

Question 39

for baseline activity spinal pattern-generating networks do not require sensory input, however their activity ________________ by both the inputs from the proprioceptors and by the descending signals from the brain

Answer 39

can be modulated

Question 40

Properties of motor neurons are strongly influenced by ____________, so the excitability of motor neurons innervating a single muscle is under control of the brainstem.

Answer 40

monoamines