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Block 5 Week 3 Meg > Kenyon: Motor Neurons > Flashcards

Kenyon: Motor Neurons Flashcards

1
Q

Cell bodies in the brainstem or spinal cord
The axons end in neuromuscular junctions with skeletal muscle fibers.
Excitatory

A

Lower motor neurons

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2
Q

Cell bodies in the brainstem or cerebral cortex
The axons end in synapses on other upper motor neurons, local circuit neurons, lower motor neurons, or some combination.
Excitatory or inhibitory or both!

A

Upper motor neurons

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3
Q

Describe the major pathway from upper motor neurons to skeletal muscles.

A

upper motor neurons in the motor cortex (for planning, initiating, directing voluntary movements) or in the brainstem (basic movements and posture) –> local circuit neurons (lower motor neurons) –> motor neuron pool (lower motor neurons)–> skeletal muscles

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4
Q

Describe the minor pathway from upper motor neurons to skeletal muscles.

A

upper motor neurons in the motor cortex or brainstem centers –> motor neuron pools (lower motor neurons) –> skeletal muscles

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5
Q

What is the final common pathway in the organization of motor control?

A

motor neuron pools –> skeletal muscles

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6
Q

Where is there sensory input in the organization of motor control?

A

to local circuit neurons
to motor neuron pools
to the cerebellum

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7
Q

Many spots along the motor control pathway may be excitatory or inhibitory. Which spot is only excitatory?

A

motor neuron pool –> skeletal muscle

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8
Q

Lower motor neurons can synapse in what two places?

A

spinal cord

brainstem

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9
Q

What do lower motor neurons that synapse in the ventral horn of the spinal cord do?

A

control the skeletal muscles of the body

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10
Q

What do lower motor neurons that synapse in the somatic and branchial motor nuclei do?

A

control the muscles of the head

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11
Q

What are the somatic motor nuclei that lower motor neurons may synapse in?

A

oculomotor
trochlear
abducens
hypoglossal

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12
Q

What are the branchiomotor nuclei that lower motor neurons can synapse in?

A

trigeminal
facial
ambiguus
spinal accessory

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13
Q

What are upper motor neurons in the primary motor cortex and premotor cortex for?

A

planning, initiating, and directing series of movements in limbs and eyes

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14
Q

What are upper motor neurons in the cingulate gyrus for?

A

expressions of emotions especially facial muscles

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15
Q

Where are upper motor neurons found in the brainstem?

A
  1. vestibular nuclei
  2. reticular formation
  3. superior colliculus
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16
Q

What do upper motor neurons in the brainstem do?

A

regulate muscle tone

orient eyes, head, and body with respect to vestibular, somatic, auditory, and visual sensory information

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17
Q

Compares actual movement (proprioceptive input) with intended movement and commands corrections. Modulates ongoing movements

A

cerebellum

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18
Q

The basal ganglia is made up of the forebrain nuclei. What are they?

A 
caudate 
putamen
globus pallidus
substantia nigra
subthalamic nucleus
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19
Q

What are the basal ganglia (forebrain nuclei) responsible for?

A

initiation of movements
suppressing unwanted movements
starting wanted movements

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20
Q

Receive input from upper motor neurons and sensory neurons.

Excite or inhibit lower motor neurons

A

local circuit neurons

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21
Q

In the spinal cord, the lower motor neurons for the axial (postural) muscles are located (blank), while the lower motor neurons for distal muscles (limbs) are located (blank)

A

medially; axially

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22
Q

In the spinal cord, where are local circuit neurons controlling POSTURE located? Are these projections long or short? What is unique about them?

A

medially; long; they contract OR relax muscles over a large part of the body as needed in posture

23
Q

In the spinal cord, where are local circuit neurons controlling LIMBS located? Are their projections long or short?

A

laterally (near the motor neurons); projections are short **local circuit neurons controlling limbs control a more limited set of muscles

24
Q

Each lower motor neuron innervates from 3 to 3000 muscle fibers. The motor neuron and its fibers are called a (blank). The lower motor neurons for a given muscle are clustered in (blank) in one or more spinal cord segments.

A

motor unit; ventral horns

25
Q

The muscle fibers innervated by a single motor neuron are spread throughout the muscle. Compare the lower motor neurons of the gastroc and the eye.

A

the gastroc has 1 motor neuron for about 2000 muscle fibers, while the eye muscles have 1 motor neuron for every 3 muscle fibers (more fine movement)

26
Q

What are the different types of motor units?

A

slow
fast fatigable
fast fatigue-resistant

27
Q

red muscle, resist fatigue

Tend to be continuously active (e.g. posture).

A

slow motor units

28
Q

paler

large forces for short bursts

A

fast fatigable motor units

29
Q

easier to depolarize to threshold (needs fewer EPSPs), slow and steady firing rate, good for slow postural muscles

A

small motor unit

30
Q

harder to depolarize to threshold (needs more EPSPs), fast firing rate, good for fast fatigable muscles

A

large motor unit

31
Q

As the synaptic activity driving muscle contraction increases, which units are activated first?

A

slow units, then fast fatigue resistant then fast fatigable (stand, walk/run, jump/gallop)

32
Q

help control muscle length (deep tendon reflex, a.k.a. stretch reflex, a.k.a. myotatic reflex)

A

muscle spindles

33
Q

help control muscle tension

A

golgi tendon organs

34
Q

moves you away from an unpleasant event in the periphery

A

flexion reflex

35
Q

Activate contraction of 8 – 10 specialized intrafusal muscle fibers (muscle spindles) in proprioception

A

gamma motor neurons

36
Q

Describe the role of 1a afferent fibers in keeping your beer from spilling when it’s heavy.

A

stretching of muscle causes 1a afferents to synapse on lower motor neurons which drive the activity in the homonymous muscle and inhibit the activity in the antagonist muscle

37
Q

stretching of the muscle spindle causes 1a afferents to activate the (blank) muscle, but inhibit the (blank) muscle

A

homonymous; antagonist

38
Q

Why must you activate gamma motor neurons as well as lower motor neurons in the muscle spindle reflex?

A

activation of lower motor neurons alone would cause the muscle to shorten and the 1a afferents would shut down *the cerebellum won’t know what is happening

39
Q

Why is co-activation of lower and gamma motor neurons necessary?

A

An effective control center needs to know the activity in both the gamma efferents and the Ia afferent to know what is going on in the muscle

40
Q

Sensitivity of muscle spindles is under constant adjustment. When you’re sitting or stretching is gamma activity high or low? When you’re standing on a moving bus or skiing, is gamma activity high or low?

A

low; high

41
Q

Gamma motor neurons are wrapped in (blank) afferent neurons that sense muscle length

A

1a primary

42
Q

Encapsulated afferent nerve endings between the muscle fibers and the tendon

A

golgi tendon organs

43
Q

Golgi tendon organs utilize (blank) fibers

A

Ib

44
Q

What are golgi tendon organs activated by?

A

tension

45
Q

Passive stretch increases activity in afferents from both muscle spindles and golgi tendon organs. Spindles respond to (blank) change, while golgi organs respond only slightly to passive increase in (blank)

A

length; muscle tension

46
Q

What does contraction do to activity in spindle afferents? What does it do to activity in Golgi afferents?

A

decreases; increases

47
Q

Golgi afferents synapse on local circuit neurons that inhibit a response in the (blank) muscle and activate the (blank) muscle

A

homonymous; antagonis

48
Q

If tension gets to big, what do golgi afferents cause the muscle to do?

A

relax to prevent damage

49
Q

How do primary afferent neurons for pain and temp link to lower motor neurons?

A

directly and via interneurons

50
Q

What happens when you step on something unpleasant?

A

a cutaneous afferent fiber from the a nociceptor in the foot will synapse in the dorsal horn on a lower motor neuron causing you to flex the ipsilateral leg and extend the contralateral leg

51
Q

Can the spinal cord organize and generate sequences of movement without input from the cortex?

A

yes

**pattern generators in the spinal cord

52
Q

What happens to a cat after sectioning the dorsal roots of the spinal cord?

A

it can still walk on a treadmill!

53
Q

What do deficits due to damage or loss of lower motor neurons result in?

A

specific loss of neuro-muscular transmission

54
Q

List some symptoms of lower motor syndrome

A 
paralysis
paresis
areflexia
loss of tone
atrophy
fibrillations
fasiculations

Block 5 Week 3 Meg (10 decks)

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