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63 Cards in this Set
- Front
- Back
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The large myelinated nerve fibers that innervate skeletal muscle arise from: |
The large motoneurons in the anterior/ventral horns of the spinal cord |
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How many neuromuscular junctions are on the vast majority of skeletal muscle fibers? |
One |
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What are the branches of the nerve fiber that innervate the skeletal muscle fibers called? |
Branching nerve terminals |
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What is the structure at the end of the axon that forms the nerve half of the neuromuscular junction? |
Motor end plate |
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What is the invagination of the muscle membrane to accommodate an axon terminal called? |
Synaptic gutter or trough |
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What is the space between the axon terminal and the fiber membrane called? |
Synaptic space or cleft |
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What are the folds of the muscle membrane in the neuromuscular junction called? |
Subneural clefts |
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Where is ACh stored in the axon terminal? |
Synaptic vesicles in the end plate |
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What enzyme rapidly destroys ACh? |
Acetylcholinesterase |
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What triggers the axon terminal to release ACh? |
When an action potential spreads across the nerve membrane, voltage-gated Ca2+ channels open and allow diffusion; Ca2+ ions attract ACh vesicles and draw them to the neural membrane to fuse/empty. |
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What receptors does ACh affect? |
ACh-gated ion channels in the subneural clefts, right below where the ACh is released |
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What is the protein composition of the ACh receptors? |
Two alpha proteins One beta, one delta, one gamma protein |
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How much ACh does it take to open the ACh-gated ion channel? |
Two molecules |
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What type of ions pass through the open ACh-gated channel? |
Positive ones (K+, Ca++, Na+) |
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Why do negatively charged ions not pass through the ACh-gated channel? |
Strong negative charges in the mouth of the channel |
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Which specific ion primarily diffuses through the ACh-gated channel? |
Sodium |
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What is the fate of most of the ACh released into the synaptic cleft? |
Destroyed within a few milliseconds by acetylcholinesterase |
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What causes the action potential on the muscle fiber side of the neuromuscular junction? |
The influx of Na+ through the ACh-gated channel |
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How does curare work? |
It competes with ACh & blocks ACh receptor sites |
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How does botulinum toxin work? |
It decreases the quantity of ACh released by the nerve terminals |
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What does it mean when it is said that the neuromuscular junction has a high safety factor? |
Normally, each impulse that arrives at the junction causes several times as much potential as is required to stimulate the muscle. |
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What is fatigue of the neuromuscular junction? |
Repeated stimulation decreases the number of ACh vesicles and weakens the attempts to stimulate the fiber |
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Where are the vesicles that will hold ACh formed? |
In the Golgi apparatus of the cell body |
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Where in the cell is ACh synthesized? |
In the cytosol |
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How many ACh vesicles rupture with each action potential? |
125 |
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What does ACh get split into, and what happens to those products? |
Acetate ion - diffuses out of synapse Choline - gets reabsorbed/reused |
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What contractile protein helps produce new vesicles for ACh after an action potential passes the neuromuscular junction? |
Clathrin |
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What are a few drugs that have the same effect on muscle fibers as ACh? |
Methacholine Carbachol Nicotine |
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What is the effect of drugs that have the same effect as ACh? |
Stimulate the muscle fiber but aren't destroyed by enzymatic activity, thus leading to muscle spasm |
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What group of drugs prevents passage of impulses from the nerve ending to the muscle by blocking ACh receptors? |
Curariform drugs |
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What is the basic process by which myasthenia gravis causes muscle weakness/paralysis? |
Autoimmune attack on the ACh receptors |
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What is the pharmacological treatment for myasthenia gravis? |
Neostigmine or another anticholinesterase drug |
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What is the resting membrane potential of skeletal muscle fibers? |
-80 to -90mV |
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What is the duration of the action potential in a skeletal muscle fiber? |
1 to 5 milliseconds |
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How does the duration of the action potential in a muscle fiber compare to that of a nerve fiber? |
It's 5x as long as the large myelinated nerves |
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What is the velocity of conduction of a muscle fiber? |
3 to 5 m/s |
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How does the velocity of the conduction of a muscle fiber compare to that of a nerve fiber? |
About 1/13th the velocity of the large myelinated nerves |
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What membranous structure enables deep muscle fibers recieve action potentials and contract? |
Transverse (T) tubules |
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What is the name of the process by which myofibrils' contraction is coordinated by the extensive membrane tubule system? |
Excitation-contraction coupling |
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What fluid does the lumen of the T tubule contain? |
Extracellular fluid (it communicates with the exterior of the cell) |
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What are the two components of the sarcoplasmic reticulum? |
Terminal cisternae (large chambers up against the T tubules) Longitudinal tubules that surround the myofibrils |
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What ion does the sarcoplasmic reticulum contain in large quantities? |
Ca2+ |
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What two receptors link the T tubules to the sarcoplasmic reticulum cisternae? |
DHP (dihydropyridine) receptors on T tubules Ryanodine receptors on cisternae |
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What 'gating' does the DHP receptor have? |
Voltage |
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What 'gating' does the ryanodine receptor have? |
None; linked to the DHP |
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How does the muscle deal with the released Ca2+ outside the sarcoplasmic reticulum? |
Returned to the sarcoplasmic reticulum by an ATP-dependent Ca2+ pump |
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What does calsequestrin do? |
Binds calcium inside the sarcoplasmic reticulum to reduce the gradient |
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How long is the calcium "pulse" in usual skeletal fibers? |
1/20 sec |
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How are motor units recruited? |
Small ones first (3-4 fibers/nerve), then progressively larger ones as more power is needed |
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What are EPSPs and are they found in skeletal neuromuscular junctions? |
Excitatory Post-Synaptic Potential; factors that increase cell potential; yes, absolutely |
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What are IPSPs and are they found in skeletal neuromuscular junctions? |
Inhibitory Post-Synaptic Potentials; factors that decrease cell potential; no, not in skeletal muscle (but many in the brain!!) |
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What is a MEPP and how does it relate to skeletal muscle excitation? |
Miniature End-Plate Potential; the -0.5 mV depolarization caused by a single ACh vesicle |
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What is proprioception? |
Body's sense of self - knowing where everything is and where it's going |
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What two structures give us proprioception? |
Intrafusal fibers and Golgi tendon organs |
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Describe the physical structure and means of functioning of intrafusal fibers: |
Run parallel to other muscle fibers and detect changes in muscle length (during contraction they send signals of slackness and vice versa) |
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Describe the location and means of functioning of the Golgi tendon organs: |
On the muscle tendons; detects total force placed on tendon |
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Describe the path of the corticospinal tract: |
Starts in the cortex, crosses over in the medulla, travels down to the lumbar enlargement where it synapses with the upper and lower motor neurons |
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What is the corticospinal tract involved in? |
Voluntary muscle movement |
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Describe the path of the dorsal column medial lemniscus: |
From the peripheral end, axon runs through the dorsal root ganglion, up the ipsilateral side of the spinal cord, synapses and crosses over at the medulla, synapses again at the thalamus, and into the sensory area of the cortex |
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What is the dorsal column medial lemniscus involved in? |
Transmitting fine touch, kinesthetic and proprioceptive sensory information to the brain |
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Describe the path of the spinothalamic tract: |
From the peripheral end, axon travels through dorsal root ganglion, immediately synapses and crosses over, runs up the contralateral side of the spinal cord, synapses again at the thalamus, then to the sensory area of the cortex |
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What is the spinothalamic tract involved in? |
Transmitting pain and temperature sensory information to the brain |
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How do opiate painkillers work (related to the spinal cord pathways)? |
Block the pain signal from the spinothalamic pathway but allows a signal from the DCML kinesis/fine touch pathway; blocks the cross-over junction in the spinal cord |
