week 3- reflexes Flashcards

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1
Q

what are 2 other names for deep tendon reflex

A

muscle stretch reflex myotatic reflex

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2
Q

outline what occurs during a muscle reflex

A

the muscle spindle detects muscle stretch and sends information to the dorsal horn via II and 1a afferents, which then sends information to alpha motor neurons (LMN) in the ventral horn to contract in response to the stretch. This is modified by the Y motor neurons (gain control which innervates the contractile ends of the intramural fiber). This is controlled at the level of the reticular formation in the brainstem.

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3
Q

differentiate between the two types of muscle spindle afferents

A

1a- dynamic, cares about the changing situation II- static -increases with total Length, only cares about the total

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4
Q

what occurs in the antagonist and synergistic muscles during a DTR

A

Spindle afferents indirectly contact motor neurons of antagonist muscle by synapsing on inhibitory interneurons [multi-synaptic pathway!] … which decreases contraction of the antagonist muscle Spindle afferents also synapse directly on motor neurons to synergistic muscles …and cause those muscles to contract, too

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5
Q

describe alpha-gamma co-activation

A

regulates how tightly the feedback needs to be regulated depending on situation and posture

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6
Q

what aspects need to be intact to ensure a reflex

A

sensory, motor output pathway, brainstem do not need UMN to reflex, but since the UMN does modulate you can see hyperrflexia with damage

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7
Q

what is the grading for DTR

A

dynamic portion 0 = none + = hyporeflexive (1+) ++ = normal (2+) +++ = generally considered brisk, but normal (3+) ++++ = hyperactive (with clonus) (4+) can also look at muscle tone for static portion

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8
Q

what does a change in muscle tone indicate

A

If muscle tone changes (decrease or increase) Sensory limb has changed, Motor limb has changed, or UMN modulation of reflex has changed

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9
Q

name the two ways in which sensory neurons can detect duration

A

1- constant input coding- good for pressure detection 2- on and off coding (beginning and end) good for vibration

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10
Q

explain the difference in receptive fields

A

can vary throughout the body determined by somatosensory cortex pinpricks only 2 mm apart can be detected separately on the fingertips while pinpricks 0.5 cm apart may be perceived as a single touch in the middle of the back.

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11
Q

differentiate between small and large fiber axons

A

Large

A- beta- fine touch, vibration

type 1a, 1b, II- proprioception

Expect peripheral demyelinatingdisorders to affect these modalities disproportio

small

a delta- small myelinated, 12-37C, sharp fast localized pain

C fibers- smaller unmyelinated, 25-45 C, delayed aching burning, diffuse pain

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12
Q
A
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13
Q

what is the difference between deep and superficial reflexes

A

superficial- decrease with UMN damage

deep- does not need, but they assist in modulation so may see hyperreflexia

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14
Q

what tract is damaged with if there is a + babinksi sign

A

If the corticospinal tract is damaged, we see “up-going toes” (i.e. the Babinski sign)

superficial reflex (others include abdominal and cremaster scrotum)

which is actually the re-emergence of the primitive extensor plantar reflex

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15
Q

how does a chronic versus a acute UMN lesion present

A
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16
Q

what is indicative of LMN damage

A

fasciculation and denervation

hyporeflexia or areflexia if there is sensory loss

Each LMN innervates many muscle fibers (definition of motor unit), but each muscle fiber is innervated by only one LMN.If some LMNs die, those muscle fibers are denervated

17
Q

presynaptic versus post synaptic disorder of neuromuscular transmission

A

pre-

  • decrease in ability to release neurotransmitter
  • uncontrolled release of neurotransmitter until the terminal is depleted

larger response with repeated stimulation

Lambert-Eaton Myasthenic Syndrome

Black Widow Spider venom

post-

Frequently the result of decrease in availability of ACh receptor on motor endplate

  • AChRdesensitization.
  • weakness or even paralysis, cramps, bronchospasm, and cardiovascular perturbations.

Myasthenia Gravis

organophosphates

snake venom