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Dental Neuroscience > segmental motor circuits > Flashcards

segmental motor circuits Flashcards

1
Q

classes of movement

A
  • reflex (stereotyped)
  • voluntary (motor cortex)
  • cyclical (programmed)
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2
Q

motor unit

A
  • basic lowest level
  • alpha motor neuron
  • in ventral horn
  • sends axon out into periphery
  • connects to skeletal muscle fibers
  • decides whether muscle will contract or not
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3
Q

lower motor neurons

A

ventral horn of gray matter of spinal cord

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4
Q

3 types of input to a LMN

A
  1. from local interneurons (neighboring neurons)
  2. from sensory afferents (pain, temp)
  3. from higher centers (descending tracts)
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5
Q

reflexes can be classified as

A
  1. monosynaptic (stretch)
  2. disynaptic (inverse stretch)
  3. polysynaptic (withdrawal/flexion)
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6
Q

monosynaptic (stretch) reflex

A
  • afferent and motor neurons
  • MOST IMPORTANT
  • ex: muscle spindle
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7
Q

muscle spindle

A
  • intrafusal muscle fibers
  • annulospiral fibers that
  • sensory fibers go to dorsal root and synapse with motor neuron
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8
Q

stretch reflex circuit (spindle)

A
  • muscles spindle senses stretch
  • spindle activated
  • signal to DRG
  • signal goes to alpha motor neuron to synapse
  • signal to same muscle
  • contraction
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9
Q

stretch reflex (AKA: myotatic, deep tendon)

A
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10
Q

another one

A
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11
Q

knee jerk reflex

A
  • tendon of quads is hit (stretched)
  • causes alpha motor neuron to fire
  • quad contracts
  • leg kicks
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12
Q

why is the reflex so important?

A
  • reflexes help muscles contract
  • keeps the horse from collapsing
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13
Q

stretch reflex functions

A
  • holds muscle length constant
  • maintenance of erect posture
  • responsible for muscle tone
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14
Q

what is muscle tone?

A

basal level of contraction of muscle
- only when you are wake

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15
Q

gamma motor system

A
  • A-gamma motor neurons come out of ventral horn
  • smaller motor neurons that go to the spindle
  • these can stretch the muscles spindle
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16
Q

alpha and gamma co-activation occurs during

A

voluntary movement

17
Q

disynaptic (inverse stretch) reflex

A
  • golgi tendon organ
  • senses muscle tension
  • 2 synapses, 3 neurons
18
Q

golgi tendons measure

A

muscle tension

19
Q

inverse stretch reflex

A
  • GTO measure tension
  • synapse with inhibitory interneuron
  • acts on alpha motor neuron
  • cause muscle to relax
20
Q

golgi tendon reflex is a

A

protective reflex

21
Q

polysynaptic (withdrawal flexion reflex)

A
  • response to painful stimuli
  • free nerve ending synapse in substantia gelatinosa
  • polysynaptic connection of interneurons to alpha motor neurons
  • ascending spinothalamic tract
  • synapse with interneurons which converge on alpha motor neuron
  • ex: touching hot stove
22
Q

antagonist muscles

A
  • with any movement there is an opposite movement
  • ex: contract bicep = relax tricep
  • both muscles in pair cannot contract at same time
  • one contracts, the other relaxes
23
Q

reciprocal (antagonist) inhibition

A
  1. muscle spindle reflex
  2. muscle spindle in extensor muscle branches and connect to inhibitory neurons
    - inhibitory neurons acts on the flexor muscle = relax
24
Q

jaw closing reflex

A
  • if you stretch masseter by tapping chin = reflex
  • under normal circumstances, reflex is ibhibited
  • if abnormality of central motor pathway, reflex is apparent
25
Q

jaw jerk reflex

A
  • spindle in masseter afferents to mesencephalic nucleus (pseudounipolar neuron)
  • spindle fiber synapses with alpha motor neuron in motor nucleus of V
  • masseter contracts and closes the jaw
26
Q

mesencephalic nucleus of V

A
27
Q

corneal reflex

A

touch cornea = blinking reflex
- unencapsulated receptors in cornea go thru V1
- synapse in brainstem @ chief nucleus of V
- interneuron goes to motor nucleus of V
- contract eye muscles
- blink!!

28
Q

central pattern generators

A

neuronal networks in spinal cord or brain stem that generate rhythmic alternative activity like
- walking
- swimming
- chewing
- breathing
- eye movements
- sneezing and coughing

29
Q

mastication

A
  • central pattern generator
  • stretch reflexes (in jaw closes muscles)
  • mandibular rest position (
  • periodontal reflexes
  • joint reflexes
30
Q

the masticatory system can

A

exert great forces

Dental Neuroscience (24 decks)

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