Term
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Definition
| a single alpha motor neuron, and all branches of the axon, and all the muscle fibers innervated by that alpha motor neuron |
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Term
| What is the relationship between # of motor neurons and # of muscle fibers? |
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Definition
| each muscle fiber is innervated by one alpha motor neuron, but an alpha motor neuron innervates multiple muscle fibers |
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Term
| The size of a motor unit is dependent upon: |
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Definition
| the number of muscle fibers contained within that motor unit |
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Term
| Muscles involved in skilled movements requiring fine control will have: |
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Definition
| very low ratio of muscle fibers to motor neurons, thus small motor units |
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Term
| In one motor unit, all muscle fibers will be ____. |
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Definition
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Term
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Definition
small fibers
red
endurance activities
use aerobic metabolism
fatigue resistant, slow to contract |
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Term
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Definition
medium fibers
utilize both aerobic and anaerobic metabolism
between type I and type IIb |
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Term
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Definition
large fibers
white
have glycogen stored
use anaerobic metabolism
used for rapid, powerful activities
fatigue easily |
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Term
| What are the 3 types of motor units? |
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Definition
slow twitch
fast twitch, fatigable
fast twitch, fatigue resistant |
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Term
| What determines the type of motor unit? |
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Definition
| the neuron innervating the motor unit determines the type of motor unit and the muscle fiber type |
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Term
| Type S (slow twitch) motor units |
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Definition
slowly discharging motoneurons
innervate slow oxidative myofibers (type I)
involved in functions as maintaining posture |
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Term
| When activity requires only slight tension: |
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Definition
| varying numbers of slow myofibers are activated by the motoneuron |
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Term
| Type FR (fatigue resistant, fast twitch) motor units vs. Type FF (fatigable, fast twitch) |
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Definition
FR contain type IIa myofibers
FF contain type IIb myofibers |
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Term
| When a muscle is denervated, the muscle fibers: |
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Definition
| tend to convert to type IIb fibers |
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Term
| What happens when the innervation to one motor unit is lost? |
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Definition
remaining nerve fibers send collateral processes to the denervated unit
the number of muscle fibers in the motor unit increases
muscular function is retained by control is lost
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Term
| Increasing the number of motor units serves to: |
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Definition
increase the tension development
allow the muscle movement to be continuous and smooth |
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Term
| normal recruitment order of motor units begins with (1) and proceeds to (2) |
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Definition
1. motor units producing the lowest tension
2. those producing the highest tension as more force is needed |
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Term
| increased tension can be acheived by : |
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Definition
summation/recruitment of motor units
wave summation- increasing the firing requency of a single unit |
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Term
| If a second action potential is applied before the contraction-relaxation cycle is complete: |
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Definition
| a second contraction-relaxation cycle is immediately initiated and it's force is greater than that of the first action |
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Term
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Definition
| when a maximum developed force is reached and the contraction-relaxation cycles fuse to produce a single smooth curve |
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Term
| tetanus is possible in skeletal muscle because: |
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Definition
| the refractory period is short relative to the contraction time |
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Term
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Definition
| tetanus that still allows for some release of tension (vs. fused tetanus) |
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Term
| monosynaptic stretch reflex |
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Definition
aka - deep tendon reflex
simplest of all spinal cord reflexes
it's peripheral receptor is the muscle spindle |
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Term
| One muscle spindle consists of (1) muscle fibers enclosed in a connective tissue capsule. These fibers are called (2). Each spindle is attatched at both ends to (3), and lies in parallel with them. |
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Definition
1. 2-14
2. intrafusal muscle fibers
3. extrafusal muscle fibers |
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Term
| One end of the muscle spindle is attached to the (1) of the extrafusal fiber, and the other end is attatched to the (2). |
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Definition
1. endomysium
2. perimysium |
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Term
| Since the muscle spindle is attatched to and lies in parallel with the extrafusal muscle, a stretch to the extrafusal muscle will cause it to be stretched. Muscle spindles are sensitive to: |
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Definition
change in the length of extrafusal fibers
AND
rate of change in length |
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Term
| Each intrafusal muscle fiber is composed of two regions: |
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Definition
contractile region - striated muscle located on each end of the fiber
equatorial region - non-contractile region located at the center of each fiber, cell nuclei is located here |
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Term
| What are the two types of intrafusal muscle fibers? |
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Definition
nuclear bag fiber - bag shaped equatorial region
nuclear chain fiber - has a long slender equatorial region |
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Term
| sensory innervation of the muscle spindle is supplied by (2 types- what's the difference): |
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Definition
type Ia sensory neurons - which wrap around the center of the muscle spindle
type II sensory neurons- which terminate near the edges of the qeuatorial region of the intrafusal fibers |
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Term
| Type Ia sensory fibers are most responsive to ---- and activation causes -----. |
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Definition
a quick stretch of the extrafusal muscle
quick, strong contraction of the stretched muscle |
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Term
| Type II sensory neurons are most responsive to ----- and activation results in ----. |
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Definition
a slow stretch of the muscle near its physiological limits
maintained contraction of the stretched muscle |
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Term
| Each muscle spindle has its own efferent (motor) innervation. The motor neurons innervating the spindle are (1). The cell bodies of these are located (2) and the axons terminate (3). |
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Definition
1.gamma motor neurons (small, myelinated axons)
2.ventral horn of SC
3. on the contractile regions of the intrafusal muscle fibers |
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Term
| what are other names for the deep tendon reflex? |
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Definition
myotatic stretch reflex
muscle stretch relfex |
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Term
| Deep tendon reflexes are (1) reflexes. They are composed of a (2) and a (3), with a synapse between. The synapse is located (4). |
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Definition
1. monosynaptic
2. afferent limb
3. efferent limb
4. ventral horn of the SC |
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Term
| The afferent limb of the DTR is composed of --- neurons, which respond to ----. The quick contraction that results from the alpha motor neuron stimulation is called ----. |
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Definition
type Ia sensory neurons
quick stretch
autogenic facilitation |
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Term
| during activation of the monosynaptic stretch reflex, a second mechanism is activated. Explain. |
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Definition
Reciprocal inhibition
- mediated by collaterals of the Ia afferent and serves to protect the agonist muscles from being stretched and opposing the agonist
- Ia inhibitory neurons in the ventral horn are activated and inhibit alpha motor neurons to the antagonist |
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Term
|
Definition
sensory rectptor in the muscle
provides proprioceptive information from skeletal muscle and mediates a reflex
located at the musculotendinous junction |
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Term
| GTO conveys inhibitory information via ___. THese inhibitory interneurons inhibit the ____, resulting in inhibition of the muscle. THis meghanism is known as ____. |
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Definition
Ib afferents
alpha motor neurons of the same muscle
autogenic inhibition |
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Term
| Flexor Withrdrawl Reflex is initiated by cutaneous input that activates ____ fibers. These afferents transmit pain information to the ____, causing activation of excitatory interneurons which ____ and inhibitory neurons that ____. |
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Definition
a delta or c pain fibers
dorsal horn
synapse on motor neurons on the ipsilateral flexor muscles
synapse on motor neurons to the ipsilateral extensor muscles |
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Term
| Crossed Extension Reflex is activated if: |
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Definition
a flexor withdrawal reflex is activated in a weight bearing limb
results in extension of the contralateral limb |
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Term
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Definition
-viral infection which attacks the cell bodies of alpha motor neurons in the SC
-viral entry through the GI tract
- paralysis (if it occurs) develops 2-5 days after onset
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Term
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Definition
may occur 30-40 years after initial disease
progressive weakness in previously affected muscles |
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Term
| Amyotrophic Lateral Sclerosis (ALS) |
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Definition
aka- Lou Gehrig's disease
injury to the neuronal cell body
mixed upper and lower motor neuron lesions |
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Term
|
Definition
produced by the puffer fish
-blockage of Na+ channels in neuronal cell membrane
-failure of action potential with resutant paralysis
-starts with tingling and quickly progresses |
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Term
| What are some motor unit pathologies that affect the neuronal cell body? |
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Definition
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Term
| What motor unit pathology affects the ability to conduct an action potential? |
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Definition
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Term
| What motor unit pathologies are created by injury to the synaptic terminals? |
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Definition
alpha-latrotoxin
botulinum toxin
tetanus toxin |
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Term
|
Definition
-produced by black widow spider
-stimulates excessive release of ACH, depletes the terminal --> paralysis
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Term
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Definition
-orally injested (incompletely sterilized canned foods)
-produced by anaerobic bacterium
- most powerful biological poison known
fatal in nanogram quantities |
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Term
| How can botulinum toxin be used productively? |
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Definition
when injected into a muscle it can reduce spasticity
-used in 2-3 locations max
allows relaxation of the muscles and full ROM, give a chance to strengthen the antagonist |
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Term
|
Definition
-produced by anaerobic bacterium in puncture wounds
-carried to SC by retrograde transport
-binds to axonal terminals of glycine-secreting inhibitory neurons
-prevents glycine release -->unopposed excitatory input to motor neurons
-onset 3 days to 3 wks later
-50% mortality
-there is a vaccine |
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Term
| What is a motor unit pathology caused by injury to post synaptic receptors? |
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Definition
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Term
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Definition
-unknown etiology, autoimmune disorder
-antibodies produced against own ACh receptors which then block the receptors and lead to muscle weakness
-patient presents initially with weakness of ocular mucles
-may also have oropharyngeal weakness and limb and neck weakness
-weakness resolved by cholinesterase blockers |
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Term
| What are two types of ocular weakness? |
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Definition
ptosis - drooping of the eyelid
diplopia- double vision |
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Term
| What are two types of oropharyngeal weakness? |
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Definition
dysarthria- difficulty speaking
dysphagia - difficulty swallowing |
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Term
| What is a motor unit pathology that results from inury to the muscle cell membrane? |
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Definition
| Duchenne Muscular Dystrophy |
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Term
| Duchenne Muscular Dystrophy |
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Definition
-most common x-linked disorder known 1:3500
-lifespan into late teens/early 20s
-muscle cell destruction in DMD is due to abnormal or missing dystrophin protien and it's effect on the muscle cell membrane
-pt goals are to prevent contractures and preserve mobility |
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Term
| What motor unit pathology is the result of injury to myelin-forming cells? |
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Definition
|
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Term
| Diptheria toxin and Lead toxin |
|
Definition
-poison schwann cells
-cause demyelination of nerve fibers and loss of nerve function |
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Term
| What motor unit pathologies result from injury to the myelin? |
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Definition
Guillian-Barre Syndrome
Multiple Sclerosis |
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Term
|
Definition
-peripheral polyneuropathy
-autoimmune disease, unknown etiology
-demyelination of peripheral nerves
-symmetric limb weakness progressing to paralysis
-cognitive function remains intact
-prognosis varies, based on cranial nerve impairment and time on vent |
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Term
|
Definition
- multiple areas of demyelination and sclerosis in CNS
-onset usually bt 20-40 (females)
-unknown etiology, possibly environmental/genetic
-characterized by exacerbations and remissions
-symptoms vary according to location and number of lesions |
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Term
| What are the 3 classifications of peripheral nerve lesion? |
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Definition
neuropraxia
axonotmesis
neurotmesis |
|
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Term
|
Definition
temporary slowing or loss of axonal conduct
no disruption of axon or axonal degeneration
caused by compression, stretching, or inflammation
quick, complete recovery |
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Term
|
Definition
disruption of axon continuity
no damage to connective tissue surrounding the axon
degerneration of distal axonal segments
distal weakness or sensory loss
may have axon sprouting --> recovery |
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Term
|
Definition
axonal disruption and damage to connective tissue surrounding the nerve
degeneration of distal axonal segments
distal weakness or sensory loss
typically surgical repair is needed for full recovery
the nerve can reconnect to the wrong destination or get derailed all together |
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Term
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Definition
| after neurotmesis injury, the sprouting axon becomes severly tangled |
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Term
| The process of axonal degeneration and secondary myelin degeneration following axonotmesis or neurotmesis is: |
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Definition
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Term
| Process of Wallerian Degeneration |
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Definition
-axon degenerates since it is no longer supported by the neuronal cell body
-myelin sheath degenerates
-macrophages remove degraded myelin and axonal fragments
- process takes many weeks |
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Term
|
Definition
-primarily in PNS
-central chromatolysis of cell body
-cell body swells and nissl substance disappears
-altered metabolism to support regeneration of severed axon
-axonal stump sprouts new axons
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Term
| Axonal sprouts will grow at a rate of ---- if the nerve sheath is still intact. |
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Definition
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