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Motor Reflexes Flashcards

1
Q

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

A

Speed

Reflex will be faster

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2
Q

What is the level of organization for a reflex?

A

Any CNS level

Does not require cortex for most

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3
Q

What is the level of organization needed for volitional motion?

A

Requires cortical and subcortical involvement

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4
Q

What is the purpose of a reflex?

A

Direct and rapid response to sensory stimuli. Often protective

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5
Q

What s the purpose of volitional movements

A

Response to stimuli; need; desire

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6
Q

What initiates a reflex?

A

Sensory input

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7
Q

What initiates volitional motion?

A

Higher cognition

Sensory input

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8
Q

What describe the circuitry of a reflex?

Versus volitional motion circuitry?

A

Fixed

Variable depending on motion

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9
Q

What is the specificity of reflexes and volitional motion?

A

Both have high specificity

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10
Q

What is an example of a monosynaptic reflex?

A

Myotatic reflex

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11
Q

What is the pathway of a monosynaptic reflex?

A

Afferent —> alpha motor neuron —> excitatory contraction of m.

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12
Q

What is a polysynaptic reflex?

Pathway?

Example?

A

More than one synpase

Afferent —> interneuron —> another interneon —> alpha MN.

Golgi tendon relfex

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13
Q

What are the reflexes produced at the level of the spinal cord ?

A

Myotatic

Golgi tendon
Crossed extensor reflex

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14
Q

What are the reflexes produced at the brainstem/midbrian?

A

Vestibular reflex

Suckling

Pushing food out of move
Sucking on fibers
Yawning
Stretching
Cry 
Following objects w/ head and eye movements
Turn head and eyes to sound
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15
Q

What are cortical reflexes?

A

Placing response

Hopping response

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16
Q

What innervates the intrafusal muscle fibers of a muscle spindle?

A

Efferent innervation By gamma MNs

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17
Q

What do intrafusal muscle fibers contain?

A

Contractile components (actin, myosin etc.)

Similar to sk. M.

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18
Q

What does the sensory portion of the muscle spindle consist of?

A

Nuclear bag fiber

Nuclear chain fiber

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19
Q

Is the sensory portion of a muscle spindle contractile?

A

No

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20
Q

What innervates the sensory portion of a muscle spindle?

A

2 afferent neurons

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21
Q

What is the primary afferent of the muscle spindle?

A

1a fiber to both nuclear bag and chain fibers

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22
Q

What characterizes the 1a primary afferent fiber?

A

Large
Myelinated
Fast

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23
Q

What is the primary afferent sensitive to?

A

Length of muscle

Rate of muscle length change

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24
Q

When is the primary afferent fiber discharged?

A

Discharged even at normal resting muscle length

And sensitive to length and rate of length change

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25
Q

What is the secondary afferent fiber to muscle spindle?

What characterizes this fiber?

A

Group 2 fiber

Myelinated, smaller, slower

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26
Q

What does the secondary afferent to the sensory portion of the muscle spindle innervate?

A

Only the nuclear chain fiber

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27
Q

What doe the secondary afferent fiber respond to?

A

Responds only to changes in length

28
Q

What is the purpose of having 2 types of afferent fibers?

A

Allows the cns to get 2 kind of info

Static and dynamic

29
Q

What is the efferent innervation of Extrafsusal fiber?

A

alpha MN via NMJ

30
Q

Where do Gamma MNs work on the muscle spindle? Using what?

What does this initiate?

A

On intrafusal fibers on the neds of m. Spindles using NMF

Contraction of intrafusal and stretching of muscle spindle

31
Q

What does the contraction of the intrafusal fibers by gamma MNs do?

A

Stretches muscle spindles thus sensitizes nuclear bag and chain fibers to further stretches

32
Q

Does the activity of Gamma MN lead to motion?

A

No

33
Q

Where do Alpha MNs work on the muscle spindle? Using what?

What does this initiate?

A

Extrafusal fibers via NMJ

Releases EAA to non-NMDA receptors

Excited skeletal muscles and contracts it

34
Q

What does the contraction of skeletal muscle by alpha MNs cause?

A

Shortening of intrafusal fibers and stops their increased signaling

35
Q

Will activation of alpha MNs lead to motion?

A

Yes

36
Q

What do gamma MNs controL?

A

Length of sensory portion and thus sensitivity of muscle spindle

37
Q

What is the myotatic reflex initiated by?

What is the result of this?

A

Initiated by muscle spindle in response to passive stretch of muscle

Contracts stretched muscle back to normal length

38
Q

What is the golgi tendon reflex caused by?

Result of the reflex?

A

Initiated by active contraction muscle felt by golgi tendon organ

Leads to abrupt relaxation of contracted muscle to prevent damage

39
Q

What is the muscle spindle enclosed by? Embedded where?

A

Enclosed in capsule in sk. Muscle

Embedded in fusiform capsule

40
Q

How is the muscle spindle orientation in comparison to skeletal muscle?

A

Parallel to sk. M. Proper

41
Q

What makes up the bulk of msucle, extrafusal or intrafusal?

A

Extrafusal

42
Q

What is the stimulus for muscle spindle?

A

Stretching/lengthening of muscle

43
Q

What does the full myotatic reflex contain?

A

Seance efferent limb for reciprocal inhibition of antagonist m.

44
Q

How does the second efferent limb of the myotatic reflex work?

A

The 1a afferent goes to alpha MNs —> contract agonist

ALSO goes to interneuron in SC that releases GABA —> Alpha MN of antagonist —> relax m.

45
Q

What is the golgi tendon organ?

A

Bare nerve ending w/ lots of branches

46
Q

Where do you find the golgi tendon organ?

What innervates it?

A

In tendon

Innervated by 1b fiber

47
Q

What is the golgi tendon reflex pathway? (Does abrupt relaxation of contracted msucle)

A

1b —> release EAA to non NMDA to interneuron in SC

Interneuron active —> releases GABA to alpha MN

Allows Cl in, hyperpolarizes alpha MNs —> muscle relaxes abruptly

48
Q

What is the difference between 1a and 1b fibers?

A

1a afferents are involved in msucle spindle reflex; myelinated, faster

1b afferents are afferents for golgi tendon reflex; less myelinated; slower

49
Q

What is the presentation of spasticity?

Why does this happen?

A

Patient RESIST IN A GIVEN DIRECTION a passive stretch of their muscles c their antagonists don’t relax

Hyperactive myotatic reflex increases gamma motor neuron firing(efferent to intrafusal m. Fiber)

50
Q

What is the cause of spasticity?

A

Damage to cortex that abolishes activation of the brainstem inhibition region (can’t inhibit antagonist)

51
Q

What is rigidity?

A

Contraction of muscles in absence of other stimuli causing resistance of motion in ALL DIRECTIONS

52
Q

What is the mechanism of rigidity?

A

Continual activation of alpha-MNs that causes contraction of Ms. w/o stimuli

53
Q

What causes rigidity?

A

Loss of cortical influence that inhibits a medullary input to alpha motor neurons

54
Q

What is altered in spasticity?

A

Alter stretch reflexes by changing gamma motor neuron firing rate

55
Q

What is continual active during spasticity?

What does this cause?

A

Gamma MNs

Contracts intrafusal and lengthens nuclear bag/chain fibers making spindle more sensitive and spontaneously active

56
Q

What is spinal shock?

Symptoms?

A

Transection of the SC that causes LMNs to lose input

LMNs signs, no reflexes

57
Q

What is the recovery of reflexes after spinal shock thought to be due to?

A

Axonal sprouting below level of transection

Expression of receptor phenotypes that are self-activating (5HTC Rs.)

58
Q

What are 5HTC receptors?

A

Self-exciting

Opens sodium channels

59
Q

What is Decerebrate posturing a result of?

A

Loss of all strucutre below and including red nucleus

60
Q

How is the myotatic reflex in spasticity?

A

Hyperactive

61
Q

What is continually active in

Rigidity vs. spasticity?

A

Rigidity: alpha MNs

Spasticity: gamma MNs

62
Q

What is decorticate posturing from?

A

Loss of structure above red nucleus resulting in flexion of upper limb and extension of lower limbs

63
Q

What can Decorticate posturing result from/

A

Strokes in vicinity of internal capsule

64
Q

What is clonus?

A

Beats of alternating agonist and antagonist contraction

65
Q

What happens when a muscle is stretched?

A

Increased AP in 1a fiber
EAA released to Alpha MN via NMJ
increased Muscle contraction

Decreases stretch
Stops 1a from firing

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