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Neuroendocrine > Motor Reflexes > Flashcards

Motor Reflexes Flashcards

1
Q

What are the spinal reflexes?

A

Myotatic (stretch), Golgi tendon, crossed extensor

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2
Q

What are the brainstem/midbrain reflexes?

A

Vestibular, righting, suckle, yawn, eye/head movements

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3
Q

What are the cortical reflexes?

A

Placing reaction and hopping reaction

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4
Q

Which brainstem/midbrain reflexes occur even in the absence of a cortex?

A

Suckle, yawn, eye/head movements

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5
Q

What are some of the purposes of reflexes?

A

Protection, correct action without conscious thought, the need to respond quickly

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6
Q

How do you tell the difference between a reflex and volitional movement?

A

SPEED - reflexes are faster

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7
Q

What is volitional movement?

A

Conscious choice of a movement at your own will

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8
Q

Does a reflex require the cortical areas of the brain?

A

NO - only needs the CNS levels (spinal cord/brainstem)

Volitional movement requires the cortex

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9
Q

What initiates volitional movement?

A

Higher cognition and/or sensory stimuli

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10
Q

How is the specificity of a reflex?

A

Very high

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11
Q

How many synapses take place during the myotatic reflex?

A

1 - monosynaptic

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12
Q

During the myotatic reflex, is the muscle active or passive?

A

Passive

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13
Q

Provide a summary of the basic actions of the myotatic reflex?

A

Tap patellar tendon - which stretches the muscle
The muscle spindle initiates the reflex
The quads then contract and shorten to protect the muscle from damage by the stretching

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14
Q

Any fibers outside of the muscle spindle capsule

A

Extrafusal

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15
Q

Fibers within the muscle spindle capsule, that are a part of the muscle spindle

A

Intrafusal

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16
Q

What are the 3 components to a muscle spindle fiber?

A 
Motor component (efferent)
nuclear bag fiber and nuclear chain fiber (both afferent)
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17
Q

What are the afferent components of a muscle spindle fiber? (just sensory)

A

Nuclear bag fiber and nuclear chain fiber

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18
Q

What innervates both the nuclear bag and nuclear chain fibers?

A

Ia fiber innervation

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19
Q

What is the Ia afferent fiber sensitive to?

A

Length of a muscle AND
How fast the length is changing
(rapid change = Increased action potentials)

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20
Q

The Ia afferent fiber that innervates both the nuclear bag fiber and nuclear chain fiber has a fast conduction velocity. Describe the threshold, myelination and diameter?

A

The threshold is low, which makes it very sensitive

There is a lot of myelination and the fiber diameter is large

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21
Q

What innervates just the nuclear chain fibers?

A

Secondary afferent, made of group II fibers

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22
Q

What is the sensory afferent fiber that only innervates the nuclear chain sensitive to?

A

ONLY the length of the muscle

23
Q

The group II afferent innervation fiber of the nuclear chain has a slower conduction velocity than the Ia fiber. Describe its threshold and sensitivity?

A

Its sensitivity is lower than that of the Ia fiber, and thus its threshold is higher, making it harder to activate and fire an action potential

24
Q

What innervates the motor component (efferent) of the muscle spindle fibers?

A

Gamma motor neuron

25
Q

What does the gamma motor neuron control?

A

The muscle portion of the muscle spindle fiber, and thus it controls the length of the sensory portion and thus their sensitivity

26
Q

What innervates the extrafusal fibers and leads to motion of the muscle?

A

Alpha motor neuron

27
Q

Does a gamma motor neuron result in motion of the muscle?

A

No, not directly - it controls the SENSITIVITY of the intrafusal fibers which control the motor portion of the muscle

28
Q

Describe the pathway of the myotatic reflex

A
  • A Ia fiber senses the stimuli (stretch) and then synapses on to an Alpha motor neuron
  • It releases EAA
  • The Alpha motor neuron then contracts and thus shortens the muscle to relieve the stretch
29
Q

How are the hamstrings (Antagonists) relaxed during the myotatic reflex? As they are also stretched…

A

The Ia fiber branches and also activates an inhibitory neuron - which releases GABA or Glycine to the Alpha motor neuron of the hamstrings and relaxes it

30
Q

What reflex involves sudden relaxation of a CONTRACTED muscle?

A

Golgi tendon reflex

31
Q

What initiates the golgi tendon reflex?

A

Golgi tendon organ

32
Q

How many synapses are there for the golgitendon reflex?

A

Polysynaptic - multiple

33
Q

What innervates the tendons of the muscles?

A

Golgi tendon organ

34
Q

Describe the threshold for the Golgi tendon reflex?

A

The threshold must be high, because you do not want sudden relaxation if you are just holding a cup for example. You only want relaxation if there is a possibility for muscle damage!

35
Q

What is the afferent fiber for the golgi tendon reflex?

A

Ib from the golgi tendon organ

36
Q

Describe the golgi tendon reflex pathway

A
  • A Ib afferent fiber from the golgi tendon senses the extreme contraction of the muscle
  • It synapses on to an inhibitory neuron and releases EAA to activate
  • The inhibitory neuron releases GABA to inhibit the Alpha motor neuron of the contracted muscle
    • This causes sudden relaxation of the muscle that was contracting!
37
Q

What does the inhibitory neuron release in the golgi tendon pathway?

A

GABA only

38
Q

What does the inhibitory neuron release to the antagonist muscle in the myotatic reflex?

A

Either GABA or Glycine

39
Q

When there is a lesion of the spinal cord (transection) and the reflexes BELOW that transection fail to occur

A

Spinal shock

40
Q

Can you recover from spinal shock and regain reflexes below that spinal transection?

A

Yes

41
Q

What are 2 ways that you can recover from spinal shock?

A

Axonal sprouting or expression of self-activating receptors such as 5HTC

42
Q

What are the 2 regions in the brain that can alter the myotatic (stretch) reflex?

A

Brainstem facilitatory region and the Brainstem inhibitory region

43
Q

Which brainstem region is spontaneously active and activates gamma-MN?

A

Brainstem facilitatory region

44
Q

What does the Brainstem facilitatory region ultimately result in?

A

Over activation of the gamma MN causes the muscle spindle fibers to be stretched and thus more sensitive = hyperactive myotatic reflexes!!

45
Q

What does the Brainstem inhibitory region do?

A

Inhibits gamma-MN which causes muscle spindle fibers to be less sensitive

46
Q

With loss of the cortex and when the brainstem inhibitory region is not active, what results?

A

The brainstem facilitatory region dominates and there will be spasticity and hyperactive reflexes

47
Q

What is spasticity?

A

Resistance to motion in a certain direction due to continual activation of the gamma MNs

48
Q

What is rigidity?

A

Resistance to motion in ALL directions due to continual activation of the alpha MNs = maintained muscle contraction

49
Q

Describe how decerebrate posturing looks?

A

All muscles in EXTENSION bilaterally

50
Q

Describe how decorticate posturing looks?

A

Flexion of upper limbs, Extension of lower limbs that is dependent on head positioning

51
Q

Which posturing may be unilateral?

A

Decorticate

52
Q

What can cause decerebrate posturing?

A

Loss of all structures rostral to the pons

53
Q

What can cause decorticate posturing?

A

A stroke that affects the internal capsule

Neuroendocrine (47 decks)

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