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Neuromuscular PT 1 > Motor Neurons > Flashcards

Motor Neurons Flashcards

1
Q

Describe UMN

-

A
  • Motor tracts
  • cell bodies in CNS
  • target/synapse in CNS
  • connect with LMN
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2
Q

Describe LMN

A
  • cell bodies in CNS/Spinal cord
  • target periphery
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3
Q

Describe what occurs when we decide to move

A
  1. Frontal lobe makes decision to move
  2. motor planning areas activated
  3. control circuits (basal ganglia/cerebellum) regulate activity of UMN
  4. UMN tracts deliver signals to interneurons and LMNs
  5. LMNs signal skeletal muscle
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4
Q

Where are the cell bodies of the LMN located

A
  • ventral horn
  • their axons leave the spinal cord via the ventral horn
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5
Q

Classification of UMNs (motor tracts)

A
  • postural/gross motor tracts: control automatic skeletal muscle activity
  • fine movement tracts: fractionated movements of limbs and face
  • nonspecific tracts: facilitate all other motor neurons
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6
Q

Multipolar neuron

describe look

A
  • cell bod with many dendrites
  • axon with multiple collaterals
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7
Q

Types of LMN

A
  • alpha motor neurons
  • gamma motor neurons
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8
Q

Alpha motor neurons

A
  • synpase with extrafusal muscle
  • innervate skeletal muscle
  • when we test when we do MMT
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9
Q

Gamma Motor neuron

A
  • medium myelination
  • synpase with intrafusal muscle fibers in the mucsle spindle
  • responsble for volume control of a muscle (reflex)
  • excited by the brainstem
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10
Q

muscle tone imbalance

is caused by?

A

is caused by an imbalance between alpha and gamma activation

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11
Q

What is the path of a lower motor neuron

A
  1. Axons leave spinal cord via ventral root
  2. Travel through the spinal nerve
  3. Travel through peripheral nerve
  4. Skeletal muscle
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12
Q

Coactivation

alpha-gamma

A
  • stretch on central region of the muscle is maintained while the extrafusal fibers contract
  • Alpha-gamma coactivation
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13
Q

what does alpha motor neuron synapse with

A
  • synpases with extrafusal muscle
  • extrafusal muscle is responsible for muscle action
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14
Q

What does gamma motor neurons synpase with

A
  • muscle spindle/intrafusal muscle fibers
  • montiors and controls muscle length
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15
Q

What is a motor unit

A
  • alpha motor neuron and the muscle fibers it innervates
  • when an alpha motor neuron ia activated ACh is released at all the neuromuscular junctions and all muscle fibers that are innervated by the neuron contract
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16
Q

Slow twitch muscle fibers

A
  • twitch-innervated by smaller diameter,
  • slower conducting alpha motor neurons
  • postural muscles/slower contracting muscles (Ex: soleus tonically active in standing, physically active with walking)
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17
Q

Fast Twitch muscle fibers

A
  • innervated by larger diameter, faster conducting alpha motor neurons
  • Ex: gastroc-sprinting
18
Q

Henneman’s principle

A
  • Slow twitch fibers continue to contribute during faster actions, as fast twitch units are recruited.
  • Order of recruitment known as Henneman’s. (LE)
  • Order of recruitment is modified depending on the task and phase during walking and running
19
Q

What gives sensory input to the LMN

A
  • Golgi tendon organs (GTO)
  • muscle spindle
20
Q

Muscle spindle

A
  • Provides information about and responds to muscle length
  • 3 components
  • The more delicate the movement, the higher the spindle count/More spindles in muscles that produce fine motor movement vs. larger muscles responsible for posture and gross movements
21
Q

what are the three components of a muscle spindle

A
  • Intrafusal muscle fibers
  • sensory endings (primary 1a and secondary type 2 afferents)
  • motor endings
22
Q

Describe the intrafusal muscle fibers of the muscle spindle

A
  • muscle fiber
  • found on the inside
23
Q

Describe the sensory endings fibers of the muscle spindle

A
  • Sensory endings respond to stretch
  • change in muscle length and velocity of length change
  • Stretch of the central region of intrafusal fibers is sensed by these primary and secondary endings
  • sensory info conveyes to the CNS by type 1a and type 2 afferents
24
Q

Primary 1a afferents in a muscle spindle

A
  • annulospiral
  • discharge is phasic and tonic
  • phasic = velocity of length change
  • tonic = stretch over time
  • responds partly to muscle length but more powerfully to changes in length
25
Q

Seconary type 2 afferent in a muscle spindle

A
  • discharge is tonic only
  • better at registering length alone (ie static stretch)
26
Q

Motor endings component of muscle spindle

A
  • intrafusal fibers provided by gamma motor neurons
27
Q

Gamma motor neuron activity

A
  • maintain sensitivity of spindle throughout normal range of muscle lengths
  • Gamma motor neurons fire, causing end of intrafusal fibers to contract and maintain sensory activity from spindle
  • 2 types of intrafusal fibers: Nuclear bag fibers and Nuclear chain fibers
28
Q

Nuclear bag fibers

A
  • clump of nuclei
  • contain info about length and velocity of length
  • 1a acts on both but mostly on bag fibers
29
Q

Nuclear Chain fibers

A
  • nuclei arranged single file
  • contains info about static length only
30
Q

What is the gamma loop

A
  • gamma motor neurons fire to maintain the sensitivity of the spindle throughout the normal rnage of the muscle lengths
  • no activation of gamma = flaccid and extrafusal cannot contract
31
Q

GTO

A
  • sensory organ of a tendon near musclotendinous junction
  • respond to tension in the tendons
  • contraction of a muscle pulls on the collagen strands which compressess the GTO and leads to action potential generation
  • info is transmitted from GTOs into the SC by type 1 b afferents
  • depending on the task GTO inputs either inhibits or facilitates LMN
32
Q

Stretch reflex

A
  • DTR
  • monosynpatic
  • stimulus: muscle stretch
  • stretches the spindle
  • primary afferents 1a activated
  • alpha motor neuron activated
  • response: muscle contracts
33
Q

Reciprocal inhibition

A
  • used to coordinate movement
  • during agonist contraction antagonist is inhibited
  • allows agonist to act unopposed/prevents unwanted activity
  • achieved by inhibitory interneurons in the spinal cord
34
Q

Tendon Organ reflex

A
  • Autogenic Inhibition?
  • muscle contracts; GTO detects tension and afferent activiated stimualtes interneuron
  • THEORY NO SUPPORTED BY RESEARCH
35
Q

Recurrent inhibition

A
  • opposite of reciprocal inhibition
  • inhibits agonist + disinhibition of antagonist
  • helps to isolate fine motor from gross motor
36
Q

Withdrawal/cross extension reflex

A
  • polysynpatic
  • cutaneous reflex
  • activation of muscles innervated at numerous spinal cord segments
  • noxious afferent stimulation => withdrawl of limb on ipsilateral side
  • activation of extensor muscles on contralateral side = crossed extension
37
Q

Spinal cord and movement coordination

A
  • muscle syergies: coordinated muscular action; type 2 affernet and interneurons to and from the spinal cord
  • proprioceptive body schema: used to plan and adapt movements,
  • reciprocal inhibition
  • GTO input
  • Stepping pattern generators

Joint capsule and ligament receptors, muscle spindle receptors, and Golgi tendon organs (GTOs) provide the proprioceptive input required to generate the body

38
Q

GTO and coordination

A
  • GTO contributes proprioception by registering tendon tension
  • information is conveyed by type Ib afferents to spinal cord and stimulate interneurons that either excite or inhibit motor neurons
  • Overally play a role in adjusting muscle contraciton
39
Q

Stepping Pattern Generators/Central Pattern Generators

A
  • adaptable networks of spinal interneurons (activate LMN)
  • each LE has its own SPG
  • SPGs recieve proprioceptive input
  • Descending signals from the brain required to activate and coordinate SPG
  • body weight support and SPGs
40
Q

UMN lesion symptoms

A

Location: brain, brainstem, corticospinal tracts, SC
Diagnosis: CVA, TBI, SCI, MS, CP
tone: hypertonia
reflexes: hyperreflexia
involuntary movemens: muscle spasms
strenght: weakness/paralysis
Muscle bulk: disuse atrophy
Voluntary movements: impaired or absent

41
Q

LMN lesion symptoms

A
  • Location: CN nuclei/nerves, ventral horn cells, spinal roots, peripheral nerve
  • Diagnosis: polio, guillain-barre, peripheral Neuropathy, radiculopathy
  • tone: hypotonia
  • reflexes: hyporeflexia
  • involuntary movemens: with denervation: fasciculations
  • strenght: ipsilateral weakness/paralysis
  • Muscle bulk: neurogenic atrophy
  • Voluntary movements: weak or absent

Neuromuscular PT 1 (32 decks)

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