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NYCC Neuro 2 > Reflexes > Flashcards

Reflexes Flashcards

1
Q

define motor unit

A

motor neuron and all fibers it innervates

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2
Q

define motor neuron pool

A

all axons that innervate a muscle

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3
Q

what are lower motor neurons, and what do they include?

A

motor neurons of the brainstem & spinal cord that innervate skeletal muscle:
- ventral horn cells & processes
- motor nuclei of CNs & processes

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4
Q

name the 2 types of ventral horn cells

A

alpha motor neurons
gamma motor neurons

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5
Q

what do alpha (a) motor neurons innervate?

A

extrafusal skeletal muscle fibers

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6
Q

what do gamma (y) motor neurons innervate?

A

intrafusal fibers (specialized skeletal muscle fibers enclosed in a fibrous capsule called a muscle spindle)

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7
Q

symptoms of LMN lesion

A
  • paresis/paralysis/plegia
  • atrophy
  • fasciculations
  • hypotonia and hyporeflexia
  • fibrillations
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8
Q

what are fasciculations?

A

visible muscle twitching resulting from involuntary synchronous contraction of all muscle fibers in a motor unit

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9
Q

fasciculations are characteristic of…

A

slowly progressive diseases of the motor unit

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10
Q

what are fibrillations?

A

spontaneous activity of one muscle fiber detected only with electromyography

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11
Q

fibrillations are a sign of…

A

progressed muscle denervation or myopathy

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12
Q

what is a muscle spindle?

A
  • specialized skeletal muscle fibers in fibrous capsule situated in parallel with the extrafusal muscle fibers
  • composed of intrafusal m fibers, sensory (afferent) axons, and motor axons (efferents which regulate sensitivity)
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13
Q

what is the motor innervation of muscle spindles?

A

gamma (y) motor neurons

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14
Q

describe alpha and gamma co-activation

A
  • stretch-> 1a proprioceptors in muscle spindle send info in spinal cord about stretch
  • contraction-> intrafusal fibers become slack
  • y-motor neurons cause them to tighten back up so sensitivity is not lost
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15
Q

why is alpha and gamma co-activation important?

A

ensures extrafusal and intrafusal fibers are in sync

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16
Q

what is the sensory innervation of muscle spindles?

A

Ia (annulospiral endings) fibers and II (flower spray) fibers that detect muscle stretch

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17
Q

name the 3 types of intrafusal fibers

A
  • nuclear chain fibers
  • nuclear bag fibers: dynamic & static
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18
Q

what are nuclear chain fibers?

A
  • thin intrafusal fibers, with nuclei arranged in a single file
  • afferents include group Ia and II
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19
Q

what are nuclear bag fibers?

A

thicker intrafusal fibers, with nuclei grouped in the central region

20
Q

what are dynamic nuclear bag fibers?

A
  • sensitive to rate of change (rapidly adapting)
  • afferents include group Ia only
21
Q

what are static nuclear bag fibers?

A
  • slowly adapting stretch receptors
  • afferents include both group Ia and II
22
Q

what is the stretch (deep tendon) reflex?

A

monosynaptic (no interneuron) connection between central axon of Ia fiber and the a-motor neuron, causing muscle contraction in response to stretch

23
Q

in the stretch reflex, the ____ muscle is excited via the ____ neuron

A

agonist
alpha motor

24
Q

what is the sensory receptor of the stretch reflex?

A

muscle spindle

25
Q

what is the Ia inhibitory reflex?

A

central Ia axon –< Ia inhibitory interneuron –< alpha motor neuron innervating antagonist muscle

26
Q

when testing the biceps deep tendon reflex, the biceps muscle is excited by the ____, while the triceps are inhibited by the ____

A

stretch reflex: alpha motor neuron
Ia inhibitory reflex: Ia inhibitory interneuron

27
Q

what is the function of recurrent (renshaw cell) inhibition?

A
  • to avoid overexcitation of agonist motor neuron pool
  • negative feedback system allows for control of excitability of all muscles around a joint
28
Q

explain recurrent (renshaw cell) inhibition

A
  • agonist a-motor neuron (or descending tracts) –< renshaw inhibitory cell
  • renshaw cell withdraws inhibition of Ia interneuron so that antagonist is excited while agonist is inhibited
29
Q

what is the overall effect of renshaw cell reflex?

A
  • directly inhibits agonist
  • withdraws inhibition of antagonist (inhibits Ia inhibitory interneuron)
30
Q

what is a golgi tendon organ?

A

encapsulated sensory receptors located in the junction between muscle & tendon, in series with the extrafusal muscle fibers

31
Q

what is the sensory innervation of golgi tendon organs?

A

Ib proprioceptors sensitive to muscle tension

32
Q

explain the Ib reflex

A

in response to tension in the muscle:
central axons of Ib fibers from golgi tendon organ, cutaneous receptors, & joint receptors –< Ib inhibitory interneuron inhibits a-motor neuron pool of agonist

33
Q

what is the overall effect of the Ib reflex?

A

inhibition of the agonist muscle

34
Q

what is the pain withdrawal reflex called?

A

flexion & crossed extension reflex

35
Q

what is the flexion & crossed extension reflex?

A

polysynaptic pathways where central axons of A-delta nociceptors facilitate flexion (withdrawal) of the hurt lower limb, while facilitating extension of the contralateral lower limb for support

36
Q

explain the flexion & crossed extension reflex

A

A-delta central axons synapse on:
- inhibitory interneurons inhibit a-motor neuron pool of ipsilateral extensors
- excitatory interneurons that facilitate a-motor neuron pool of ipsilateral flexors
- inhibitory interneurons that inhibit a-motor neuron pool of contralateral flexors
- excitatory interneurons that facilitate a-motor neuron pool of contralateral extensors

37
Q

what information do fasciculus gracilis & cuneatus carry?

A

ipsilateral:
proprioception
vibration
2-point discrimination
pressure
touch

38
Q

nucleus gracilis and cuneatus give rise to ____ that decussate to form the ____ which ends in the ____

A

internal arcuate fibers
medial lemniscus
ventral posterior lateral thalamic nucleus

39
Q

from the thalamus, fibers of the DCML then run through the ____ and end in the ____

A

internal capsule
somatosensory cortex (3,1,2)

40
Q

examination of DCML lesion

A
  • vibration tuning fork on dermatomes
  • position sense mainly of upper extremities
  • romberg’s test
41
Q

what tract is responsible for proprioception from the lower extremity?

A

spinocerebellar tract

42
Q

what tracts make up the anterolateral system, and what is their function?

A

spinothalamic
spinoreticular
spinomesencephalic

pain & temperature perception

43
Q

pain & temperature fibers enter the tract of ____ and end in the ____

A

Lissauer
dorsal horn

44
Q

when pain and temperature fiber cross at the ____, they form the ____ and end in the ____

A

ventral white commissure
spinothalamic tract
ventral posterior lateral thalamic nucleus

45
Q

spinothalamic fibers that end in the thalamus then travel through the ____ to end in the ____

A

internal capsule
somatosensory cortex (3,1,2)

46
Q

examination of spinothalamic tract lesion

A

pinwheel (prick) over dermatomes

NYCC Neuro 2 (28 decks)

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