UMN&LMN Flashcards by Lisa Ho

What is feed forward?

Anticipatory use of sensory info to prepare for mvmt

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Feedback?

Use of sensory info during or after mvmt to make corrections

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Mvmt decomposition

Loss of synchronization and speed of skilled mvmts; segmented mvmt by single jts rather than coordinated mvmt of multiple jts.

Ex: lose sequence of mvmt is cerebellar

NEED feed forward and feedback mechanisms for most purposeful mvmt

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What are the 3 general types of mvmts?

Reflexive, rhythmic mvmts (CPGs), voluntary mvmts

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What is reflexive mvmt?

Involuntary, coordinated patterns of mvmt
Elicited by peripheral stim
EX-stretch, withdrawal

Proprioceptive info used to fine tune complex mvmts (fxn of muscle spindle and GTO reflexes)

Used in clinic to assess integrity of afferent and efferent pathways

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What are rhythmic mvmts? (CPGs)

Central pattern generators
Walking chewing breathing
Neuronal circuits in SC and brainstem
Triggered by peripheral stim
Humans- require control from higher centers

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Voluntary mvmts

Mvmts initiated to accomplish goal

Can be internally generated or in response to external

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How do you accomplish goal directed actions that are driven by motivational states?

Goal to action: ant-post gradient

Prefrontal association cx receives inputs from amygdala, hypothalamus, ventral striatum to code for primary impulses like fear, hunger, reward etc

Involved in planning actions/mvmt and abstract thought

*basic bodily needs**
decide how youre gonna accomplish your goal-

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What 2 cx work together to make decisions about what action to take to achieve a goal?

Posterior parietal and prefrontal areas

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What is the function of post parietal?

Assess context in which mvmts are made

Receives SS, proprioceptive, visual inputs then uses them to determine things like position of body and target in space

Produces internal models of the mvmt to be made PRIOR to involvement of premotor and motor cx.

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What does the prefrontal cx do?

Plans the mvmt to achieve goal

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What does the ppremotor area consist of?

Premotor cx, SMA frontal eye field, Brocas, cingulate motor area

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What does the premotor area do?

Use info from other cortical areas to SELECT MVMTS appropriate to context of action

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What does the primary motor cx do?

Control and modulate lower motor circuits/LMNs in brainstem and SC

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WHere are the LMN located ?

Brainstem and SC (in ventral horn and motor nuclei of CN)

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Where does decency go input from cortical and brainstem areas synapse mostly onto?

Local interneuron circuits in SC and brainstem nuclei

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What does the local circuits do?

Organize mvmts by coordinating activity of LMNs

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Can UMN synapse directly onto alpha mn?

Yes

Pyramidal from the primary motor cx- fine finger control

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Damage to what structures will cause LMN sx?

Cell body in CNS, axons in VENTRAL roots, spinal nerve, cranial or peripheral nerve in PNS

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Do LMN innervate a single muscle?

Yes

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The somatotopicc organization of proximal muscles are located where?

Reed lamina IX and more medially.

Received input from tracts in anterior and medial white matter

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What are Type I (S) fibers?

Slow motor units- contract slowly/sustained

Impt for posture***
Smaller motor neuron, fewer muscle fibers

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What are type I rich in?

Myoglobin, mitochondria, capillary beds

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What are Type IIa (FR)?

Fast fatigue resistant- intermediate

2x force of small units, not as fatigable as FF

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Type IIb (FF)?

Fast fatigable, brief but large forces-power jump Large motor neurons more fibers larger PALE fibers Not as much capillary supply so fatigues faster Every muscle has a combo of these types bc you want efficiency

What is the relationship between a motor unit and its firing rate>

Proportional- motor unit recruited, firing rate increases

What are the 3 main spinal reflexes?

``` Myotactic (stretch) GTO (autogenicc inhibition/inverse stretch) Withdrawal reflex (nociceptive or flexor withdrawal) ```

What does descending influences affect in terms of reflexes?

Affects all spinal reflexes - ccontrol state of readiness

What are the 2 types of LMN?

Extrafusal (innervated by alpha MN)- MUSCLE CONTRACTION Intramural (gamma MN)- regulate stretch of muscle spindle

What is alpha-gamma co-activation?

Gamma- medium sized myelinated axons (innervates contractile ends of muscle spindles) CNS co contracts AandG -gamma activation does not produce force- keeps spindle taut at all levels of length

What happens if there is a deviation from desired length in the stretch reflex

Muscle spindles detect it and corrected via connections to AMN

WHat is gain of this reflex?

Amount of force generated by a given amt of stretch to muscle

What is a high gain?

Small amt o stretch leads to activation of AMN Ex- standing on moving bus

When do you want high gain?

When youre doing mvmts when it requires high PRECISION

What is low gain?

Large stretch needed to activate AMN Ex: slow stretch ex

When do you want low gain?

You dont want it to stretch too much - descending motor control

What is gain controlled by?

Descending motor paths

What does gain play a major factor for?

Spasticity (high gain here)

What happens when you have an absent or decreased stretch reflex?

Pathology to sensory neurons, LMN, or SC connection, muscle , NMS jxn, acute UMN lesions

What happens when you have an increased (abn brisk) reflex?

Chronic UMN lesions

WHat is GTO?

autogenic inhibition reflex | Monitors and maintains muscle force at steady level

GTO- what happens when large forces are generated?

Decreased muscle activation

GTO- what happens when fatigue occurs?

Lessens inhibition

GTO: | _____ interneuron to _____ muscle

Inhibitory, agonist

GTO: | _____ interneuron to ____muscles

Excitatory, antagonist

Are GTOs active under normal conditions?

Yes

What is the main role of GTOs during locomotion?

Enhance muscular contraction of extensors during stance and swing

What is the withdrawal reflex?

Stim by nociceptors- Same side flexion, opp side extension

What happens when damage to descending pathways to the withdrawal reflex?

Non-noxious stim evoking this response

Which reflex can you suppress?

Withdrawal

What is reciprocal inhibition?

One muscle contracts, antagonist inhibited

What are the signs of UMN lesion?

Weakness, increased reflexes, increased tone

Lesion to LMN?

Weakness, atrophy, fasciculatonis, decreased reflex and tone

What is a myotome?

Group of muscles that a single spinal nerve root innervates. Most muscles are innervated by more than 1 spinal nerve.

What is indicative of denervated muscle on an EMG

Fibrillation | -short duration, spontaneous biphasic or triphasic potentials by single muscle fiber

What does a fibrillation on an EMG represent?

Unstable muscle fiber cell membrane

Where do fibrillation occur?

Peripheral nerve injuries, atonal neurophathies, motor neuron disorders and some myopathies.

What are fasciculations?

Large potentials cause by spontaneous activity in motor unit or several.

What is a fasciculation caused by?

LMN lesions, usually ANTERIOR horn cell disease (ALS).

What causes hypotonia?

LMN lesions, acute UMN lesion, developmental disorders

What is velocity dependent hypertonia?

Due to myoplasticity- changes the muscle due to abn activation and position (INCREASED bonds)

What causes vel-dependent hypertonia?

Lesions to corticospinal and corticoreticular tracts diminish inhibition of reticulospinal and vestibulospinal tract= there excitatory reticulo/vestibulo onto LMN of SC (hyperactivity) & increased gain of stretch reflex

What is rigidity?

BG disorders, brainstem lesions Increased tone that persists throughout PROM. “Lead pipe” Common in PD

WHat part is affected with polio?

Anterior horn- LMN syndrome Recovery due to sprouting neighboring MN

SMA affects what?

Degeneration fo ant horns Progressive Abn chromosome 5

What does the primary motor cx receive?

Parietal sensory input, input from premotor, regulatory input from cerebellum and BG

What are the important principles of primary motor cx?

Muscle field-muscles controlled by a given UMN Ex- wrist area 2-3 muscles per UMN Force of muscle change as a function of the firing rate of UMN UMN codes direction of mvmt POPULATIONS OF NEURONS THAT DISCHARGE TOGETHER TO PRODUCE A MVMT IN SPECIFIC DIRECTION- TAKE INTO ACCT TRAJECTORY AND FINAL POS

UMN&LMN Flashcards

(67 cards)