2.24 Motor SC 3 Flashcards Preview

7303 Neuroanatomy > 2.24 Motor SC 3 > Flashcards

Flashcards in 2.24 Motor SC 3 Deck (38):
1

reflexes

involuntary, relatively short-latency, and stereotyped response set into motion by an environmental stimulus

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components of a reflex arc

- receptor
- afferent fiber
- reflex center in CNS
- efferent fiber
- effector

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polysynaptic reflex

if there's an interneuron in the reflex arc (doesn't have to be)

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monosynaptic reflex

no interneuron

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What are the 3 major reflexes?

- Stretch (myotatic) reflex
- Inverse myotatic reflex
- Flexion and Crossed Extension Reflex

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simplest and best studied reflex

stretch (myotatic)

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stretch reflex (overall)

- elicited by tapping tendon of the muscle with a reflex hammer
- brief and brisk contraction of the stretched muscle

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stretch reflex mediated by

muscle spindle

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stretch reflex is (mono/poly)synaptic

monosynaptic

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reciprocal inhibition

- agonist contracts
- antagonist relaxes

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What would happen without reciprocal inhibition?

the antagonist muscle would prevent the reflex from happening

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process of reciprocal inhibition

- tapping tendon stretches muscle
- monosynaptic reflex sends out positive signal to quad to contract
- polysynaptic mechanism sends negative signal to hamstring muscle telling it to relax

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At agonist, the reflex is (mono/poly)synaptic

monosynaptic

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At antagonist, the reflex is (mono/poly)synaptic

polysynaptic

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purpose of stretch reflex

controls muscle directly by causing agonist contraction

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inverse myotatic reflex is mediated by

Golgi Tendon Organs (GTOs) located in tendons that respond to muscle tension

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autogenic inhibition generally results in

relaxation of the agonist and contraction of the antagonist

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inverse myotatic reflex: mechanism

- polysynaptic reflex (with interneuron) between afferent and efferent
- targeted muscle gets a negative (relaxation) signal
- antagonist gets a positive signal

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function of GTO

- cause relaxation of the muscles
- GTO helps with proprioception during movement
- measures the amount of tension on the tendons
- helps create proprioceptive schema so we know where all body parts are at any point in time

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Flexion and Crossed Extension Reflex is a response to

a suddenly applied noxious stimulus

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In the flexion and crossed extension reflex, adaptive withdrawal of limb from offending stimulus causes an excitatory discharge that spreads through many segments via

spinospinal system

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flexion and crossed extension reflex: ipsilateral limb

- reciprocal inhibition of the antagonists
- flexion

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flexion and crossed extension reflex: contralateral limb

extends

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flexion and crossed extension reflex mediated by

interneurons that decussate

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flexion and crossed extension reflex: inteneuron activity

- crossing pathways
- inhibit extensors, activating flexors

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Why do pathways cross for the flexion/crossed extension reflex?

- opposite thing happens on the other side
- need to stabilize and bear weight on the other leg

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What are the other reflexes we talked about?

- somatomotor reflex
- viscerovisceral reflex
- somatovisceral reflex
- viscerosomatic reflex

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somatomor reflex

works via long descending tracts (pyramidal tracts)

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viscerovisceral reflex

- ANS only
- contribute to muscle tone of bladder, etc.
- monosynaptic

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somatovisceral reflex

- skin cooling: reflex activates muscles that give you chill bumps
- monosynaptic

31

viscerosomatic reflex

- noxious stimulus activates muscle guarding
- primal reflex of movement
- works similarly to stretch reflex, except it's polysynaptic

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clinical connection: evaluation

- Is the reflex present?
- If present, is status altered (grading)?
- Are pathological reflexes present?

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hyporeflexia indicates damage to:

What happens?

- LMN
- LMN isn't adequately stimulating the muscle

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hyporeflexia is a (PNS/CNS) problem

PNS

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hyperreflexia is a (PNS/CNS) problem

CNS

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hyperreflexia indicates

UMN is not properly modulating activity of LMN in long descending motor tracts

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UMN is typically (excitatory/inhibitory) in reflexes

inhibitory

38

reflexes and knee stability if knee is moderately hyperextended

hamstring stretch reflexes will cause contraction of hamstrings and relieve strain on ACL