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Physiology > Spinal Mechanisms of motor control > Flashcards

Spinal Mechanisms of motor control Flashcards

1
Q

What is the route of innervation of the patellar tendon reflex?

A

Tapping stretches muscle spindles, causing reflex arc via Ia fibers to A motor neurons of extensors, and inhibitors of flexor muscles

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2
Q

What is a phasic stretch reflex?

A

very brief stretch usually elicited by tapping on a tendon

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3
Q

What is a tonic stretch reflex?

A

longer lasting stretch caused by stretching a muscle and holding it at its new longer length

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4
Q

What are the two fibers involved in a monosynaptic reflex?

A

Ia from muscle spindle

Alpha motor neuron

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5
Q

What are the two phases of the tonic stretch? What are each of these phases?

A
  1. Dynamic phase-period during which length is changing

2. Static/steady phase– when muscle has stabilized at its new length

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6
Q

Type Ia fibers carry static or dynamic information about stretch? How about type II?

A 
Ia = both
II = static
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7
Q

Which type of muscle fibers are sensitive to dynamic changes in stretch: nuclear bags or chains?

A

Bags

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8
Q

Muscle spindles lie parallel or perpendicular to muscle fibers?

A

Parallel

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9
Q

What are the three types of intrafusal muscle fibers?

A

a. Dynamic nuclear bag
b. Static nuclear bag
c. Nuclear chain

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10
Q

What type of fibers innervate muscle spindles?

A

Type Ia

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11
Q

Firing pattern of Group Ia afferent is related to what two factors?

A

both how fast the muscle length is changing and the current length of the muscle.

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12
Q

Group II fibers relay what information?

A

Firing rate gives information about muscle length but does not emphasize changes in muscle length

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13
Q

True or false: patellar tendon reflexes do not stimulate group II fibers

A

True –too fast for them to respond

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14
Q

What do gamma efferent fibers innervate?

A

Stretches the ends of the nuclear bag/chain fibers.

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15
Q

What is the role of coactivation of alpha and gamma neurons?

A

• To prevent unloading of the muscle spindle gamma motor neurons are activated and they make intrafusal fibers contract. Now a small lengthening of the muscle can be sensed immediately.

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16
Q

The firing rate of muscle spindle afferents depends on what two factors?

A

both
muscle length and the level of gamma activation of the
intrafusal muscle fibers

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17
Q

What are the three functions of muscle spindles?

A

a. sensory input for stretch reflexes
b. sensory input to cerebellum
c. Muscle spindle output relayed to cerebral cortex for
conscious proprioception.

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18
Q

What are the two ways in which muscle spindle fibers can be stretched?

A

gamma motor neuron activation

Alpha motor neuron activation of muscle

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19
Q

What is an “adequate stimulus” for a muscle spindle?

A

Stretch of the central portion of the intrafusal muscle fiber

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20
Q

True or false: there are usually more than one type Ia fiber per muscle spindle

A

False–usually 1-1

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21
Q

True or false: Ia fibers usually innervate all the intrafusal fibers, so innervates both nuclear bags and chain

A

true

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22
Q

Where are type II fibers found?

A

at the ends of the nuclear bags/chains

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23
Q

Review alpha-gamma coactivation.

A

Both are needed to maintain the muscle spindle sensitivity when a muscle contracts

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24
Q

Why is DTR a misnomer?

A

uses muscle spindles, not GTOs

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25
Q

What is the tonic stretch reflex used to measure?

A

measure muscle tone= the resistance of a relaxed muscle to passive stretch.

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26
Q

What is the route of innervation of the tonic stretch reflex?

A

type Ia fibers from bags/chains synapse directly of alpha motor neurons.

Group II fibers from muscle spindles also synapse on alpha motor neurons of homonymous muscles

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27
Q

Spastic limbs show a blank-dependent increase in tonic stretch reflexes

A

velocity

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28
Q

What type of reflexes are seen with parkinsons?

A

Rigidity

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29
Q

What is the MOA of spasticity of UMN lesions?

A

Loss of inhibitory signals from corticospinal tract

30
Q

What is reciprocal inhibition?

A

Inhibit antagonist muscle in a reflex arc

31
Q

What is co-contraction?

A

simultaneous activation of agonist and antagonists at a joint

32
Q

True or false: co-contraction is normal in neurologically intact adults

A

true

33
Q

When is co-contraction important?

A

When stabilization is important

34
Q

Inappropriate co-activation is implicated in what disease?

A

Thought that inappropriate coactivation contributes to the motor control problems found in children with cerebral palsy.

35
Q

What is the MOA of the stretch reflex?

A

Same as the patellar tendon reflex plus descending inhibition/facilitation

36
Q

What is the gain of stretch reflex?

A

how large a response you get for a stretch of a certain amount (e.g. large gain if small stretch caused strong contraction, small gain if large stretch caused weak muscle contraction)

37
Q

What is the stretch reflex dependent on? (3)

A
  1. level of activity in gamma motor neurons
  2. background inhibition/excitation of alpha motor neurons
  3. modified by presynaptic inhibition of Ia afferents onto motor neurons
38
Q

What is resting tone?

A

slight tension that can be felt in a relaxed muscle

39
Q

Clinically, how would you test resting tone?

A

measure muscle tone by testing the tonic stretch reflex.

40
Q

What causes muscle tone?

A

Passive (viscoelastic) properties of muscles and joints.

41
Q

What is atonia? When is it seen?

A

No muscle tone–spinal shock

42
Q

When is hypotonia seen? (2)

A

With pure pyramidal tract lesions and cerebellar lesions

43
Q

What is the most common type of hypertonia?

A

Spasticity

44
Q

Rigidity is another form of what tone? What disease is this classically found in?

A

Patients with Parkinson’s disease can have rigidity, another kind of hypertonia.

45
Q

Spasticity is usually found with what type of motor neuron lesion?

A

UMN

46
Q

What are the three major causes of spasticity?

A

Brain trauma
Spinal cord injury
MS

47
Q

Spasticity is what type of disorder? What is the tone like? What is the major variable that this depends on?

A

Motor disorder
Hypertonia
Velocity dependent (resistance to tonic stretch increases as speed of stretch increases)

48
Q

Spasticity is found particularly in which muscles?

A

Antigravity muscles

49
Q

The more severe the patient’s spasticity, the (faster or slower) you can test the tonic stretch reflex and still feel increased muscle tone.

A

Slower

50
Q

If a pt has spasticity in the LE, what other sign would you be likely to see?

A

Babinski sign

51
Q

What is clonus? How is it tested? What type of motor lesion is it seen in?

A

oscillation in muscle stretch reflexes

Pushing up on the foot.

UMN lesion

52
Q

What is the clasp-knife reflex? What type of motor lesion is it associated with?

A

The sudden decrease in resistance when flexing a knee

UMN lesion

53
Q

What causes the clasp-knife reflex?

A

Hyperactive stretch reflexes of the spastic patient

54
Q

Ia fibers innervate what? Ib?

A 
Ia = muscle spindle
Ib = GTO
55
Q

Do GTOs have a high or low threshold of activation with muscle stretch?

A

High

56
Q

What measures muscle length, and what measures muscle tension?

A

Length - muscle spindles

Tension - GTOs

57
Q

Where are GTOs found?

A

Between muscles and tendons

58
Q

Are GTO’s stimulated by stretch at all?

A

Yes, but high threshold

59
Q

What happens to muscle spindle fiber firing if you only stimulate alpha motor neurons?

A

muscle contraction and lower muscle spindle firing

60
Q

What are the three places the GTOs send their signals?

A

a. spinal cord (for reflex)
b. cerebellum
c. cerebral cortex

61
Q

What is the Ib circuit reflex?

A

Very similar to the stretch reflex, but GTOs send Ib fibers to INHIBIT homonymous muscle, while STIMULATING antagonist

62
Q

What is the result of the Ib reflex (hint, has to do with tension in a muscle since it’s GTOs involved)?

A

increased tension in muscle causes muscle to be inhibited. Decreased tension in muscle causes inhibition by Ib interneuron to decrease

63
Q

True or false: Ib reflexes are only innervated via Ib fibers.

A

False–Ib inhibitory neurons also receive input from cutaneous receptors, joint receptors, muscle spindles and descending pathways. The GTO reflex can thus be modified by higher centers and /or additional sensory receptors.

64
Q

True or false: the Ib reflex can protect its muscle from injury via excessive tension by reflexively inhibiting it when tension got too high

A

False-ish–the reflex is not strong enough to protect muscle by itself.

65
Q

The Ib reflex is also called what (like it was called in neuroanatomy)?

A

Autogenic inhibition

66
Q

What are the fibers that are involved in the flexion reflex afferents?

A

II, III, and IV

67
Q

What is the crossed extension reflex?

A

The withdrawal reflex on one side of the body is counteracted by increased extensor muscle activation on the other side (e.g. stepping on a tack)

68
Q

What is a renshaw cell?

A

A cell that receives innervation from the Alpha motor neuron that is stimulating a muscle, and has an inhibitor effect on that same alpha motor neuron (thus inhibits overactive neurons)

69
Q

What is the effect of the renshaw cells?

A

Recurrent inhibition to alpha motor neurons

70
Q

What is the most common inhibitory neurotransmitter in the spinal cord?

A

Glycine

71
Q

Inhibiting an inhibitor produces what?

A

Excitation

72
Q

What is the effect of Renshaw cells in the descending pathways?

A

Descending pathways can excite or inhibit Renshaw cells and thus adjust the excitability of all the motor neurons innervating muscles around a joint.

Physiology (75 decks)

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