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Bmsc 207 > Muscle II > Flashcards

Muscle II Flashcards

1
Q

What is a neuromuscular junction?

A

Point of synaptic contact between somatic motor neuron (lower motor neuron) to a individual fibre

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2
Q

What is excitation-contraction coupling

A

An action potential initiated in the skeletal muscle fibre results in an increase in intracellular (Sarcoplasmic) Ca2+

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3
Q

What is the process of initiation of skeletal muscle contraction

A

Events in CNS -> events in neuromuscular junction ->excitation-contraction coupling ->Ca2+ signal -> contraction-relaxation cycle -> muscle twitch or sliding filament theory

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4
Q

What is brain region involved in voluntary movement

A

Primary motor cortex

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5
Q

What are parts of primary motor cortex?

A

Corticospinal tract, upper motor neuron, alpha (lower) motor neuron

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6
Q

What is the corticospinal tract

A

Descending tract (ventral and interior lateral white matter
- upper motor neuron goes down

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7
Q

What is upper motor neuron

A

Brain to brainstem or spinal cord (descending)
- from primary motor cortex down to spinal cord where it synapses with alpha motor neuron

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8
Q

what is alpha (lower) motor neuron

A

Spinal cord (or brainstem) to muscle
- exits spinal cord through ventral root, goes through nerve to muscle

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9
Q

What is a motor unit

A

Single motor neuron and all the muscle fibers it innervates

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10
Q

What happens to alpha motor neuron when approaching a muscle?

A

Axon splits into multiple collaterals
- each collateral will make contact with one muscle fiber
- axon with collaterals and muscle fibers is motor unit

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11
Q

Properties of alpha motor neuron

A
  • Large, myelinated axon, 15-120 m/sec
  • each axons branches and innervates several muscle fibers
  • all muscle fibers respond simultaneously
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12
Q

How many motor units for delicate precise work or for powerful less precise contractions?

A

<10
>100

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13
Q

What is amyotrophic lateral sclerosis (ALS)?

A

Neurodegenerative motor neuron disease
- upper and lower motor neurons degenerate leading to muscle atrophy and weakness from disuse

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14
Q

How many cases of ALS are genetic?

A

10%
2.5% due to gene mutation producing superoxide dismutase

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15
Q

What are the three components of a neuromuscular junction?

A
  1. Presynaptic motor neuron (axon terminal) filled with synaptic vesicles
  2. Synaptic cleft (space between)
  3. Postsynaptic membrane of skeletal muscle fiber
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16
Q

What is a motor end plate

A

Region of sarcolemma at the neuromuscular junction (underneath axon terminal)

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17
Q

Where are junctional folds

A

On sarcolemma and increase surface area
- squeeze as many receptors as possible

18
Q

What do motor neuron vesicles contain

A

Acetylcholine

19
Q

What does the muscle sarcolemma contain

A

Nicotinic acetylcholine receptors

20
Q

What is in the synaptic cleft

A

Extracellular matrix
- mesh work of proteins and preoteoglycans

21
Q

What happens to an AP when it arrives at the axon terminal of a skeletal muscle?

A

Causes voltage gated Ca2+ channels to open
Ca entry causes synaptic vesicles to fuse with presynaptic membrane and release ACh by calcium mediated exocytosis into synaptic cleft for nicotinic receptors

22
Q

What are nicotinic acetylcholine receptors

A

Member of cys-loop receptor family of ligand gated ion-channels
- monovalent cation channel (permeable to Na+ and K+)

23
Q

How many acetylcholine molecules does the ACh receptor require to open

A

Two

24
Q

What occurs when the nicotinic ACh receptor opens?

A

Massive influx of Na+ because large concentration and electrical gradient
Na+ influx depolarizes muscle fiber
Little K+ eflux

25
Q

What does entry of Na+ through nACh generate?

A

Excitatory end-plate potential (EPP) (wave of depolarization)
- Spreads to adjacent voltage gated Na+channels on sarcolemma and initiates AP
-

26
Q

How are APs stopped in muscle cells?

A

Have to stop firing in alpha motor neuron
- no inhibitory input

27
Q

What happens to ACh when alpha motor neurons stop firing APs?

A

-ACh in synaptic cleft will diffuse away
- or broken down to acetate and choline by enzyme acetylcholinesterase

28
Q

What happens to choline when ACh is broken down?

A

Choline transported back into motor neuron and combined with acetylcholine CoA (produced by mitochondria) by enzyme choline acetyltransferase to make acetylcholine at terminal

29
Q

What is myasthenia gravis?

A
  • severe weakness of muscle
  • autoimmune disorder of neuromuscular transmission
30
Q

How do action potentials propagate from sarcolemma into muscle fiber?

A

Along transverse tubule network
- t-tubules wrap around each myofibril

31
Q

What are the specialized Ca2+ storage organelles and where are they located?

A
  • Sarcoplasmic reticulum
  • strategically organized with the t-tubules
32
Q

What intracellular signal triggers contraction in all muscle types?

A
  • rise in intracellular calcium
33
Q

What are ways Calcium can enter the sarcoplasm?

A
  • from Extracellular space via voltage gated Ca channels
  • released from intracellular Ca storage reservoir of the Sarcoplasmic reticulum
  • or combination of both
34
Q

What is the excitation-contraction coupling process?

A

Process by which electrical excitation of the surface membrane triggers an increase of calcium in muscle

35
Q

Where do t-tubules surround after penetrating muscle fibre?

A

Surround myofibrils at two points in each sarcomere, at the A and I band junctions

36
Q

What is a triad

A

Tubule associated with two terminal cisternae (regions of SR)

37
Q

What does AP in t-tubule do?

A

Alters conformation of DHP receptor and DHP receptor opens RyR Ca2+ release channels in SR and Ca enters cytoplasm

38
Q

What is a DHP receptor

A

L-type Ca2+ channel
Voltage sensitive
On membrane of t-tubule

39
Q

What is a ryanodine receptor (RyR)

A

Ca2+ release channel on SR

40
Q

What is not vital in skeletal muscle?

A

Ca2+ induced Ca2+ release and Ca2+ entry from ECF

Bmsc 207 (35 decks)

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