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Neuro Exam 2 > Motor Control: Reflexes > Flashcards

Motor Control: Reflexes Flashcards

1
Q

Reflexes do not have to be just spinal. Where else can they come from?

A
  1. Brainstem/midbrain
  2. Cortical.
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2
Q

What are examples of brainstem reflexes?

A

1. Suckling

2. Yawning

3. Eye and head movements

4. Vestibular

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3
Q

What are examples of cortical reactions?

A
  1. Placing reacting (arm placement when we fall)
  2. Hopping reacting (move out of the way if we feel like we are going to be pushed)
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4
Q

What is the purpose of a reflex?

A
    1. Protection
    1. Correct action without a conscious though
    1. Allows us to respond quickly to thing
    1. Infants: need them for survive because they do not the voluntarily ability to
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5
Q

What are some characteristics of reflexes?

A
    1. Involuntary
    1. Fast
    1. Short-acting
    1. MUST be precise.
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6
Q

Reflexes, in order to be effective, must be very “precise”. What is a consequence of this precision?

A

This “precision“ can make reflexes look like volitional movement

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7
Q

How to tell the difference between a volitional movement a reflex?

A

Speed! A reflex is faster than the fastest volitional movement.

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8
Q

What levels of orgnizaion does a reflex and volitional movement require?

A
  1. Reflexes can occur at any CNS level; does not require cortex for most.
  2. Volitional movement requires cortical and subcortical structures
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9
Q

What is a the purpose of a volitional movement?

A

Our resonse to a stimuli or need for someting.

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10
Q

Purpose of reflex:

A

Direct and rapid response to a sensory stimuli

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11
Q

What iniates a reflex and volitional movement?

A
  • Reflex: sensory input
  • Volitional movement: Higher cognition or a sensory input
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12
Q

Describe the circuity and specificity of a reflex and Volitional movement.

A

Reflex:

  • Circuitry: fixed
  • Specificity: high

Volitional movement

  • Circuitary: can change depending on the motion
  • Specificity: high
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13
Q

What is the myotactic (Stretch reflex) and why does it occur?

A

A monosynaptic, segmental (doesnt ascend or descend) reflex that is iniated by stretch of the muscle spindle fibers. It occurs to protect our muscle from tearing d/t stretch

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14
Q

myotatic reflex is also called what?

A

monosynpatic reflex

deep tendon reflex

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15
Q

What is the appearance of the mytoactic reflex?

A

we will contract (shorten) a stretched muscle

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16
Q

The sensory signal for the myotactic reflex originates where?

describe it.

A

At the muscle spindle, found in a fusiform capsule in the belly of skeletal muscles, between extrafusal muscle fibers.

Contrains both afferent (Sensory) components and efferent (contractile) components.

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17
Q

Because the capsule is “fusiform”, the fibers within the capsule are called ______ fibers.

The muscle fibers that make up the bulk of the muscle are called the ______ fibers

A

intrafusal

extrafusal

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18
Q

The intrafusal fibers of the muscle spindle have ______________ components

A

motor and sensory

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19
Q

The intrafusal fibers of the muscle spindle have motor and sensory components.

Describe the sensory components of a muscle spindle.

A

Sensory portion is made up of two sensors with different afferent: nuclear bag fiber and nuclear chain fiber.

  • do not contract
  • sensitive to changes in LENGTH.
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20
Q

What sensory afferent fibers innervate our intrafusal fibers?

A

1. Ia fiber

2. II fiber

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21
Q

Describe the sensory afferent innervations of the muscle spindle.

A
  • Ia (large and myelinated) fibers innervate both the nuclear bag and nuclear chain.
    • It responds to: length of the muscle (stretch) and how fast its changing.
  • II (smaller and myelinated) fibers innervates the nuclear chain fibers.
    • It responds to: the level sustained stretch by firing tonically in proportion to degree of stretch.
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22
Q

The speed of length change (change in stretch) will affect APs how?

A

Number of AP depends on how fast the length changed.

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23
Q

Intrafusal fibers have a motor and a sensory component.

Sensory component is made up of the nuclear bag and chain fibers.

Describe the motor component.

A

Intrafusal muscle fibers (motor portion) has the same histology as skeletal muscle and is innervated by a gamma motor neuron, which controls the length of the sensory portion.

24
Q

How do the sensory components of the detect stretch?

A
  • Y motor neurons contract the intrafusal muscles ->
  • we stretch the sensory portion ->
  • causing sensory portion more sensitive to stretch.
25
Q

When we contract our intrafusal muscle fibers, does this change the overal length of the muscle spindle?

A

No; it remains the same.

The Ia and II fibers just become more sensitive to stretch.

26
Q

Extrafusal fibers make up the bulk of the muscle. Describe its innervation.

A

Innervated by a alpha motor neuron, which is large and heavily mylinated. It activates the muscle and DIRECTLY leads to motion.

27
Q

Gamma motor neuron innervates __________

When activated:

A

Contractile component (intrafusal fibers) of the muscle spindle.

When activated: contracts the intrafusal muscle fibers -> stretch sensory portion of the muscle spindle.

28
Q

Does the activity of the gamma motor neuron lead directly to motion?

A

NO. that is the alpha motor neuron.

29
Q

How does sensitivity detected by the muscle spindle cause the muscle to contract?

A
  1. Within the spinal cord (ventral horn), the Ia afferent from the muscle spindle synapses directly onto the alpha-motoneuron innervating the stretched muscle AND an inhibitory inteneuron that synapses with the alpha-motor neuron of the antagonistic muscle.
  2. Ia neuron excites the agonist alpha motor neuron -> causing contraction, to relieve the stretch (increase AP)
  3. Ia discharge rate goes to normal
  4. HOWEVER; antagonistic muscle gets stretched!
  5. Thus Ia afferent + the inhibitory interneuron -> releases GABA onto alpha motor neuron of antagonist muscle
  6. Antagonist muscle relaxes (decreases APs).
30
Q

There is a _____ in the activity of the αmotoneuron innervating the antagonist muscle… allowing it to _________

A

decrease

relax and lengthen

31
Q

Golgi Tendon reflex is also called

A

Inverse myotactic

Autogenic inhibition

32
Q

What is the Golgi Tendon reflex

A

A polysynpatic, segmental reflex that occurs to protect muscle from damage d/t too much force.

33
Q

What is the appearance of the GTR?

A

Sudden relation of contracted muscle

34
Q

What are golgi tendon organs?

A

Golgi tendon organs are bare nerve endings with many branches that innervate tendons.

They fire AP d/t increase tension (force) via a Ib fiber -> spinal cord.

35
Q

Golgi tendon organs fire AP d/t increase tension (force) via a ____ fiber -> spinal cord.

A

Ib

36
Q

How does the GTO work?

A
  1. When too much force is generated by a muscle, the GTO are activated.
  2. Send signals via Ib afferents to SC and synapse on inhibitory interneuron (which synapses on alpha- motor neuron of the contracting muscle)
  3. Inhibitory interneuron releases GABA
  4. Contracted muscle abruptly relaxes and force (tension) decreases (decrease AP) -> prevents damage
  5. GTO firing rate -> normal
37
Q

Myotactic reflex is a involved in a ___________ stretch of the muscle.

GTO is involved in a ______ contraction of muscle.

A

Myotactic reflex is ainvolved in a passive stretch of the muscle.

GTO is involved in active contraction of muscle.

38
Q

The GTO reflex is known to have a HIGH THRESHOLD. Why?

A

Because the muscle that is contracting is a generating alot of force and getting alot of outside stimuli; thus, we must release enough GABA to completely inhibit muscle and make it abruptly relax

39
Q

How can we modify our reflexes?

A

Higher centers of the brain are often seen to be inhibitory to the reflexes, but certain regions do provide an excitatory input.

  • Nociceptors and mechanoreceptors inhibit
  • For example; we will exhibit less of a DTR if we are focusing and watching.
40
Q

What is a spinal shock?

A

Transection of the spinal cord causes `loss of function below level of injury, even though ALL neurons that produced the reflex are intact.

41
Q

What is the cause of reflex loss below level of injury in spinal shock?

A
    1. alpha-motor neurons hyperpolarlize because there is a loss of excitatory input from the CTX.
    1. Thus, when a reflex is initiated, the alpha motor neuron is so hyperpolarized that even though the afferent neuron is still releasing EAA, it cannot reach threshold
42
Q

Recovery of reflexes in spinal shock is believed to result from:

A
    1. Increase in number of axons (sprouting) below the level of the transection.
    1. Self-activating receptors are expressed (5HTC receptor)
43
Q

What is decerebrate posturing?

A

Contraction (extension) of all anti-gravity muscles that indicates severe brain injury.

44
Q

Decerebrate posturing is caused by a lesion …

A

Below the red nucleus-> structures rostral to the pons.

45
Q

In decerebrate posturing, what 2 motions can we see

A

1. Rigidity

2. Spasticity

46
Q

What is rigidity?

A

Rigdity (consistant stiffness) is when a person resists motion in all directions d/t to maintained muscle contraction: alpha motor neurons are being continually activated because there is a of info from cortex that inhibits medullary input.

47
Q

What is spasticity?

A

When a person resists passive force in a given direction (stiff in flexion but not extension) that begins when the stretch occurs. They will have stiffness, but at end of ROM, release tightness. It caused by a hyperactive myotactic reflex d/t

  • increased gamma motor neuron firing by the brainstem facilitory region
  • inactivation of the brainstem inhibitory region.
48
Q

Spasticity occurs when a person resists motion in a give direction (stiff in flexion but not extension) because the myotactic reflex is hyperactive. How is does it become hyperactive?

A

Brainstem facilitary region -> + Gamma-motor neurons continually -> muscle spindle becomes more sensitive -> contracting intrafusal muscle -> lengething bag/chain fibers.

49
Q

Brainstem facilitory region

A

Spontaneously active region that activates the gamma-motoneurons, making muscle spindle more sensitive.

50
Q

What is the brainstem inhibitory region?

A

Inhibits gamma motoneurons, making muscle spindle less sensitive. Cortical regions must activate it.

51
Q

What is the overarching reason for spacitisty in decerebrate posturing?

A

Loss of CTX -> the brainstem (-) region is not activated, leaving the (+) region to dominate.-> stretch reflexes that fight any type of passive movment.

52
Q

What is decorticate posturing?

A
  • Red nucleus in intact
  • RIGIDITY
    • Flexion of the UE limb (disinhibition of red nucleus & its control of UE flexors). •
    • Extension of the lower limbs (disinhibition of reticulospinal and vestibulospinal pathways)
    • IR of legs
    • That is dependent on head position (release of postural reflexes)
53
Q

Decorticate posturing is due to?

A

Lesions above the red nucleus, leaving intact.

There is a loss of cortical inputs, often d/t damage from a stroke near the internal capsule

54
Q

What is more common: unilateral or bilateral decorticate posturing?

A

UNILATERAL

55
Q

__________ is speed dependent. The faster you try to move someones arm, the more resistane you feel.

A

SPASTICITY

56
Q

RIGIDITY: is the limb weak?

A

no. It is very stiff in all directions.

it is not dependent on velocity

Neuro Exam 2 (12 decks)

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