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Neuroanatomy Exam II > Spinal Cord Reflexes > Flashcards

Spinal Cord Reflexes Flashcards

1
Q

What specific neural structures do spinal reflexes require?

A

An afferent limb (sensory) and efferent limb (motor)

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2
Q

What supplies the lower motor neurons of lamina IX?

A

the efferent/motor limb

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3
Q

What are the afferent/sensory limb provided by?

A

primary sensory neurons that enter the cord through the dorsal roots of spinal nerves

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4
Q

What tpe of receptor is a neuromuscular spindles?

A

enscapsulated receptors

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5
Q

What do neuromuscular spindles in skeletal muscle monitor?

A

1) stretch/tension/length of skeletal muscle (flexing vs extending a muscle)
2) velocity of tension/length/stretch changes of skeletal muscle (slow stretch vs reflex stretch)

Also known as proprioception

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6
Q

Where is the greatest distribution of neuromuscular spindles found?

A

Greatest in muscles near where it joins its tendon and in muscles that perform skilled moevemnts

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7
Q

What is the shape of neuromuscular tendons?

A

Fusiform shaped

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8
Q

How are neuromuscular spindles attached in regards to skeletal muscles?

A

They are attached in parallel therefore the capsule of connective tissue of the spindle is attached to the CT that encloses the extrafusal fiber (spindle lies side beside the extrafusal fibers)

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9
Q

Where are intrafusal muscle fibers enclosed?

A

Enclosed in capsular tissue

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10
Q

What happens when extrafusal muscle fibers do when they are stretched?

A

When extrafusal muscle fibers are stretched it should increase the tension of a neuromuscular spindle

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11
Q

What happens when extrafusal muscle fibers do when relaxed?

A

When extrafusal muscle fibers relax it decreases tension of neuromuscular spindle

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12
Q

How many fibers are found in each spindle?

A

2-14 fibers per spindle

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13
Q

Which are smaller, extrafusal or intrafusal fibers?

A

Intrafusal muscle fibers

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14
Q

What are the two types of intrafusal fibers?

A

nuclear chain fibers

nuclear bag fibers

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15
Q

When tension in neuromuscular spindles increase what happens to the firing of fibers?

A

Increases firing of type Ia and type II fibers

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16
Q

When tension in neuromuscular spindles decrease what happens to the firing of fibers?

A

Decreased firing of the type Ia and type II fibers

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17
Q

How many types of fibers supply sensory innervation t neuromuscular spindles?

A

2 types of fibers:
Group A alpha fibers
Group A beta fibers

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18
Q

What is another name for group A alpha fibers?

A

Type Ia fibers

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19
Q

What do type Ia fibers spiral around and form?

A

These endings spiral around intrafusal fibers forming annulospiral endings of the muscle spindle

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20
Q

What is another name for Group A beta fibers?

A

Type II fibers

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21
Q

What do type II fibers form?

A

flower spray endings of the spindle

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22
Q

When are type Ia and II fibers activated?

A

When a muscle is stretched at an appropriate rate.

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23
Q

What does the activation of type Ia and II fibers do?

A

Stretch leads to lengthening (increased tension) in neuromuscular spindles and the endings are stimulated and generating proprioceptive data that travels to the CNS/spinal cord via primary afferents

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24
Q

What is the motor innervation of neuromuscular spindles achieved by?

A

Gamma motor neurons

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25
Q

What do gamma motor neurons control?

A

The length and tension of neuromuscular spindles and determines the sensitivity of the nm spindle to stretch

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26
Q

What does an increasing in firing of gamma motor neurons result in?

A

Contraction of intrafusal fibers and increases the sensitivity (lowers the threshold) of the nm spindle to a stretch stimulus

27
Q

What can intense gamma motor neuron activity initiate?

A

Initiates spindle discharge and results in an increase in firing of type Ia and II fibers

28
Q

What is a stretch reflex also known as?

A

a deep tendon reflex

29
Q

What are the 2 neurons required for a stretch reflex to occur?

A

Afferent limb

Efferent limb

30
Q

What is the afferent limb of a deep tendon reflex?

A

Sensory fibers from a nm spindle (Ia and II fibers)

31
Q

What is the efferent limb of a deep tendon reflex?

A

Alpha motor neurons

32
Q

What is an example of a stretch reflex that only requires 2 neurons?

A

Monosynaptic reflex

33
Q

What is required to initiate the stretch reflex of a muscle?

A

High velocity stretch

34
Q

In the stretch reflex, what occurs with spindle activation and afferent information?

A

Enter into the spinal cord visa type Ia and II fibers

35
Q

In the stretch reflex, where do central processes of primary afferents travel?

A

Primary afferents enter cord and send collaterals in the ascending conscious proprioceptive pathway

36
Q

Where do collaterals in the stretch reflex terminate?

A

Directly on alpha motor neurons and facilitate them

37
Q

What do the pool of alpha motor neurons activated in the stretch reflex supply?

A

Supply extrafusal muscle fibers of the homonymous (same) muscle that was stretched

38
Q

What happens to the muscle after the pool of alpha motor neurons activate?

A

The muscle contracts or shortens

39
Q

What happens to spindles when the muscle contracts?

A

Tension in the spindle decreases resulting in: decreased firing of Ia and II fibers -> loss of facilitation on alpha motor neurons -> decreased activity of alpha motor neurons and muscle reflexes

40
Q

What other receptors help to monitor tension generated in muscle tendon units?

A

Golgi tendon organs (neurotendinous spindles)

41
Q

What are Golgi tendon organs?

A

Encapsulated receptor in the tendon, positioned in series with the muscle tendon

42
Q

Where are golgi tendon organs found?

A

In tendons mostly near muscle

43
Q

What afferent fibers supply golgi tendon organs?

A

Ib (A beta fibers)

44
Q

What occurs in golgi tendon organs when a muscle contracts?

A

Muscle contracts -> increased tension of golgi tendon organs -> increased firing of Ib fibers

45
Q

What effect does golgi tendon organs have on alpha motor neurons?

A

Afferent information of golgi tendon organs is projected along ascending conscious pathways and onto interneurons in the spinal cord gray that have an inhibitory effect on alpha motor neurons that supply the homonymous muscle

46
Q

What components are included in the gamma reflex loop?

A 
Gamma motor neurons
Intrafusal muscle fibers of nm spindles
Type Ia, II fibers
Alpha motor neurons
Extrafusal muscle fibers
47
Q

What is important about the gamma reflex loop?

A

This loop of neurons and contractile fibers plays an important role in the control of muscular activity, including - involved in maintaining general tone and in control of active movement

48
Q

How is the gamma reflex loop interrupted?

A

De-afference of a muscle

49
Q

What does the de- afference of a muscle do?

A

1) Loss of muscle tone but no paralysis

2) movements lack precision and lack control of force of contraction

50
Q

Since many descending motor control fibers from higher centers influence lower motor neurons that terminate on gamma motor neurons, what would the result after de-afference of these muscles

A

Increase sensitivity of the nm spindle to increase firing of Ia, II fibers and this directly influences alpha motor neurons which increase firing and it causes extrafusal muscle fibers to contract and move the joint

51
Q

How do upper motor neurons exert control on muscular activity via alpha motor neurons?

A

Directly, by terminating on alpha motor neurons

52
Q

How do upper motor neurons exert control on muscular activity via gamma motor neurons?

A

Indirectly, by terminating on gamma motor neurons

53
Q

What is the flexor reflex?

A

Protective reflex that results in a removal of a body part from the source of noxious stimulus

54
Q

What type of reflex is a flexor reflex?

A

Polysynaptic (more than 2 neurons required)

55
Q

What do noxious stimulus activate nad how does it travel up the cord?

A

primary pain afferents (group A delta and C fibers) that enter the cord and tract cells relay the the pain data along the ascending conscious pathway

56
Q

Where do collaterals of the primary pain afferents synapse and where do they project fibers?

A

synapse on interneurons in the dorsal horn that project fibers to alpha motor neurons in the ventral horn

57
Q

Are flexor muscles innervated with the facilitation of alpha motor neurons?

A

Yes facilitation of alpha motor neurons innervate flexor muscles

58
Q

Are extensor muscles innervated with the facilitation of alpha motor neurons?

A

no, Inhibition of alpha motor neurons innervate extensor muscles

59
Q

What is reciprocal innervation?

A

When inhibition of neurons innervate antagonist muscles

60
Q

Is a single or multiple cord levels of motor neurons required for an effective flexor response?

A

multiple cord levels

61
Q

How does pain that might enter only at 1 cord segment activate an effective flexor response?

A

1) via collaterals in Lissauer’s tract that share the noxious info to adjacent cord segments
2) by neurons in the spinal cord gray that send axons through the fasciculus proprius

62
Q

What is the fasciculus proprius?

A

Made up of spinospinalis neurons and its axons can travel upstream or downstream for short and long distances

63
Q

What is a flexion - crossed extension reflex?

A

Some interneurons send collaterals to the contralateral side of the cord and they activate motor neurons that innervate extensor muscles of the extremity on the opposite side

Neuroanatomy Exam II (11 decks)

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