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neuro exam 3 > segmental motor circuits > Flashcards

segmental motor circuits Flashcards

1
Q

what are the classes of movement

A
  1. Reflex (stereotyped)
  2. Voluntary (motor cortex)
  3. Cyclical (programed)
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2
Q

what is a motor unit

A

alpha motor neuron and the skeletal muscle fibers that it controls and has
NMJs with.

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3
Q

how many fibers do alpha motor neurons innervate

A

Each alpha motor neuron will innervate a few skeletal muscle fibers. Some neurons control more
skeletal muscle fibers than others.

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4
Q

what are the 3 types of inputs of a LMN

A
  1. From local interneurons
  2. From sensory afferents (periphery)
  3. From higher centers (descending
    tracts)
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5
Q

what are the segmental reflexes

A
  • Monosynaptic, disynaptic, polysynaptic
  • Reciprocal inhibition
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6
Q

what is the monosynaptic reflex

A
  • 2 neurons and 1 synapse in between
  • stretch reflex
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7
Q

what is a disynaptic reflex

A

inverse stretch reflex

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8
Q

what are are polysynaptic reflexes

A
  • Withdrawal (flexion) reflex
  • Reciprocal (antagonist) inhibition
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9
Q

what does the stretch reflex involve

A
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10
Q

Muscle spindle pathway

A
  • Sensory axons from the muscle spindle goes to the dorsal root ganglion,
  • synapses to the motor
    neuron in the ventral horn of grey matter, and causes the alpha motor neuron to fire and contract
    the muscle that was stretched.
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11
Q

what is the stretch reflex also called

A

Stretch reflex has other names: myotatic reflex or deep tendon
reflex.

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12
Q

steps of muscle stretch

A

step 1) stretching of the muscle stimulates muscle spindles
step2) activation of sensory neuron
step 3) information processing at motor neuron
step4) activation of motor neuron
step5) contraction of the muscle

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13
Q

what happens when during the knee jerk reflex test

A
  • when Dr taps the tendon you stretch the muscle which stretches the spindle and reflex goes through spinal cord which causes alphamotor neuron to fire and contraction of quads and jerk of the leg
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14
Q

what are the functions of the stretch reflex

A

 Holds muscle length constant
 Maintenance of erect posture
 Responsible for muscle tone

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15
Q

what is muscle tone

A
  • the basal level of contraction of a muscle due to gravity
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16
Q

what is the gamma motor system

A
  • it adds to the reflex story
  • controls the spindle itself, its sensitivity
  • stetch the muscle spindle itself
17
Q

what is the gamma motor neuron pathway

A

-CNS stimulates gamma motor neuron to stretch the muscle spindle
 muscle
spindle axon enters the DRG to the spinal cord, where it synapses with the alpha motor
neuron that innervates the muscle  alpha motor neuron fires, and the muscle in
contracted
 this low level contraction adds to muscle tone

18
Q

intrafusal vs extrfusal muscle fibers

A
  • extrafusal - bulk of the muscle
  • intrafusal - muscle spindle
19
Q

what does the inverse stretch reflex involve ( Disynaptic reflex)

A

 Golgi tendon organ
 Senses muscle tension
- 3 neurons 2 synapses

20
Q

what is the inverse stretch reflex pathway

A

GTO measures muscle tension. It synapses with an inhibitory interneuron in the segmental pool
of neurons within the spinal cord. The inhibitory interneuron acts on the alpha motor neuron,
causing the muscle to relax.
- overall decresases contraction of EXTRAFUSAL muscle fibers

21
Q

example of inverse stretch

A
  • overloading muscle with a weight if its too heavy the inverse stretch reflex inhibits and drop the weight
22
Q

what does the flexor ( withdrawl) reflex respond to

A
  • respond to painful stimulus
23
Q

what is the pathway of the flexor reflex

A
  • Free nerve ending in the skin synapse in the gelatinosa.
  • Polysynapstic connections of interneurons to the alpha motor neuron.
  • There’s also the ascending spinothalamic tract, which goes through the anterior
    commissure and up the spinothalamic tract.
  • Pain afferents synapse with interneurons which converge on an alpha motor neuron
    and typically cause reflexive flexion withdrawal.
24
Q

what is a example of a flexor reflex

A
  • touching a hot stove
  • remove the hand even before you feel the pain
25
Q

what are antagonist muscles

A
  • biceps - reflexer
  • tricpes - extencer
  • there needs to be reciprocal inhibition
26
Q

what is reciprocal inhibiton

A
  • if you reflex biceps alpha motor neurons of triceps need to be inhibited and vice versa
27
Q

what are the 2 routed of reciprocal inhibiton

A
  1. Classic muscle spindle reflex. Muscle spindle in the extensor muscle excites the alpha motor
    neuron, which goes back to the same muscle and causes it to contract.
  2. Muscle spindle in the extensor muscle branches and connects with an inhibitory interneuron.
    This inhibitory interneuron acts on the flexor muscle and causes it to relax.
28
Q

what are the cranial nerve reflexes

A
  • jaw jerk
  • corneal reflex
29
Q

what is the jaw closing reflex

A
  • If you stretch the masseter muscle by tapping the chin, there’s a reflex that contract
    the masseter
  • usually, this reflex is inhibited
  • But if there is some abnormality of the central motor pathway, this reflex may become
    apparent.
30
Q

jaw closing reflex pathway

A
  • masseter muscle has muscle spindle
  • spindle afferent goes to mesencephalic nicleus
  • The muscle spindle fiber synapses with the alpha motor neuron in the
    motor nucleus of V and causes the masseter to contract, closing the jaw.
31
Q

where is the mesecephalic nucleus of V in the pons

A
32
Q

what is the cornal refelx

A
  • if you touch the cornea you blink
33
Q

what is the corneal reflex pathway

A
  • receptors in the cornea go through V1 and synapse in the brainstem at the chief
    sensory nucleus of V.
  • There is an interneuron that goes to the motor nucleus of 7 (facial muscles), which causes a
    contraction of the eye muscles
     blinking reflexively
34
Q

what are central pattern gernators

A

Neuronal networks in spinal cord or brain stem that generate,
rhythmic alternating activity.
-

35
Q

examples of central pattern gerneators

A

 Walking
 Swimming
 Chewing
 Breathing
 Eye movements
 Sneezing & coughing

36
Q

mastication

A
  • exerts huge forces
  • also can execute precise movements such as for speech with speed
  • mandible moves rapidly
37
Q

what reflexes are included in mastication

A

 Central Pattern Generator
 Stretch reflexes (spindles in jaw
closing muscles)
 Mandibular rest position
 Periodontal reflexes
 Joint reflexes

neuro exam 3 (10 decks)

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