Muscle Physiology Quiz

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Questions and Answers

What is the main function of the fusion of separate muscle cells early in development to form a single muscle fibre?

  • To facilitate efficient muscle contraction and enhance overall muscle strength. (correct)
  • To reduce the number of nuclei present in the muscle fibre.
  • To prevent the formation of myofibrils within the muscle fibre.
  • To decrease the concentration of mitochondria within the sarcoplasm.

Which protein filament is composed of two strands twisted around one another?

  • Myosin
  • Tropomyosin
  • Troponin
  • Actin (correct)

What causes the striated appearance of myofibrils?

  • Consistent distribution of actin filaments.
  • Alternating light and dark bands due to the arrangement of actin and myosin filaments. (correct)
  • The uniform arrangement of sarcoplasm.
  • The random organization of mitochondria.

Which region within the sarcomere corresponds to the distance between two adjacent Z-lines?

<p>Sarcomere (C)</p> Signup and view all the answers

What happens to the sarcomeres during muscle contraction?

<p>They shorten, changing the pattern of light and dark bands. (A)</p> Signup and view all the answers

What is the direct consequence of calcium ions ($Ca^{2+}$) entering the synaptic knob of a presynaptic neuron?

<p>Fusion of synaptic vesicles with the presynaptic membrane, releasing acetylcholine. (A)</p> Signup and view all the answers

Which process is directly responsible for the removal of acetylcholine from the synaptic cleft?

<p>Hydrolysis of acetylcholine by acetylcholinesterase. (A)</p> Signup and view all the answers

What is the ultimate effect of acetylcholine binding to receptor sites on the postsynaptic membrane?

<p>Opening of sodium channels and subsequent depolarization of the postsynaptic membrane. (A)</p> Signup and view all the answers

Which event occurs after the influx of sodium ions ($Na^{+}$) into the postsynaptic neuron?

<p>Generation of an action potential (EPSP). (C)</p> Signup and view all the answers

What is the role of ATP in the cholinergic synapse specifically mentioned?

<p>ATP is used to recombine choline and acetate into acetylcholine in the presynaptic neuron. (B)</p> Signup and view all the answers

According to the sliding filament mechanism, what happens to the I-band during muscle contraction?

<p>It becomes narrower as actin and myosin overlap more. (B)</p> Signup and view all the answers

What is the primary role of tropomyosin in muscle contraction?

<p>To block the myosin-binding sites on actin filaments in relaxed muscle. (A)</p> Signup and view all the answers

Which region of the sarcomere remains the same width during muscle contraction?

<p>A-band (B)</p> Signup and view all the answers

What is the function of troponin in muscle contraction?

<p>It binds to calcium ions and moves tropomyosin away from the myosin-binding sites on actin. (C)</p> Signup and view all the answers

What structural change occurs to the Z-lines during muscle contraction?

<p>They move closer together, shortening the sarcomere. (A)</p> Signup and view all the answers

What happens to the H-zone during muscle contraction?

<p>It disappears if actin filaments meet in the middle. (B)</p> Signup and view all the answers

Which protein is a globular protein that assembles into long chains that are twisted around one another to form a helical strand?

<p>Actin (D)</p> Signup and view all the answers

Why is it essential for rapid muscle contraction to occur?

<p>Frequently essential for survival. (D)</p> Signup and view all the answers

What is a motor unit?

<p>All muscle fibres supplied by a single motor neurone acting together as a functional unit. (D)</p> Signup and view all the answers

How does the body control the amount of force a muscle exerts?

<p>By stimulating differing numbers of motor units. (C)</p> Signup and view all the answers

What happens when a nerve impulse reaches the neuromuscular junction?

<p>The synaptic vesicles fuse with the presynaptic membrane and release acetylcholine. (A)</p> Signup and view all the answers

What is the role of acetylcholinesterase at the neuromuscular junction?

<p>To ensure that the muscle is not over-stimulated by breaking down acetylcholine. (B)</p> Signup and view all the answers

What happens to the choline and acetate resulting from the breakdown of acetylcholine?

<p>They diffuse back into the neurone and are recombined to form acetylcholine . (B)</p> Signup and view all the answers

Why are there many neuromuscular junctions spread throughout the muscle?

<p>To ensure that contraction of a muscle is rapid and powerful when it is stimulated by action potentials. (D)</p> Signup and view all the answers

What is the function of the sodium ions entering the postsynaptic membrane at the neuromuscular junction?

<p>To alter the resting potential, leading to the depolarisation of the membrane. (C)</p> Signup and view all the answers

Flashcards

Cholinergic synapse

A synapse that uses acetylcholine as a neurotransmitter for communication between neurons.

Calcium ions role

Calcium ions ($Ca^{2+}$) trigger the release of neurotransmitters in response to an action potential.

Excitatory postsynaptic potential (EPSP)

A change in the postsynaptic neurone that makes it more likely to fire an action potential after sodium influx.

Acetylcholinesterase function

An enzyme that breaks down acetylcholine into choline and acetate, facilitating recycling.

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Striated muscle

Muscle tissue characterized by its striped appearance, responsible for voluntary movement in vertebrates.

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Myofibrils

Structures within muscle fibers made of actin and myosin filaments.

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Sarcomere

The distance between adjacent Z-lines where muscle contraction occurs.

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A-band and I-band

Dark bands (A-band) where actin and myosin overlap, and light bands (I-band) where they don't.

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Neuromuscular Junction

The connection point between a motor neuron and a striated muscle fiber.

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Motor Unit

A group of muscle fibers innervated by a single motor neuron, acting together as one unit.

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Acetylcholine

A neurotransmitter released at neuromuscular junctions to induce muscle contraction.

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Acetylcholinesterase

An enzyme that breaks down acetylcholine to prevent over-stimulation of muscles.

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Action Potential

An electrical impulse along a neuron that triggers muscle fiber stimulation.

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Depolarization

The process of the postsynaptic membrane becoming less negative due to sodium influx.

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Force Control in Muscles

The ability to regulate muscle strength by adjusting the number of stimulated motor units.

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Sliding filament mechanism

Process where actin and myosin filaments slide past each other during muscle contraction.

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Sarcoplasmic reticulum

Organelle that stores calcium ions and releases them during muscle contraction.

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Troponin

Globular protein that interacts with tropomyosin to regulate muscle contraction.

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Tropomyosin

Protein that wraps around actin filaments, blocking myosin binding sites when muscle is relaxed.

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Z-lines

Boundaries of a sarcomere that move closer together during muscle contraction.

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I-band

Region of the sarcomere that becomes narrower during contraction, only containing actin.

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A-band

Region of the sarcomere that remains constant in width during contraction, containing myosin.

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Study Notes

Synaptic Transmission

  • A chemical synapse involves neurotransmitters, specifically acetylcholine in this case
  • Action potential arrives at presynaptic neuron, triggering voltage-gated calcium channels to open
  • Calcium ions (Ca2+) enter the synaptic knob
  • Influx of calcium ions causes synaptic vesicles to fuse with the presynaptic membrane
  • Acetylcholine is released into the synaptic cleft by exocytosis
  • Acetylcholine diffuses across the synaptic cleft to the postsynaptic neuron
  • Acetylcholine binds to receptor sites on sodium channels on the postsynaptic membrane
  • Binding of acetylcholine opens sodium channels
  • Sodium ions (Na+) diffuse rapidly into the postsynaptic neuron
  • Influx of sodium ions generates a new action potential in the postsynaptic neuron, called Excitatory Postsynaptic Potential (EPSP)
  • The enzyme acetylcholinesterase hydrolyzes acetylcholine into choline and acetate
  • Choline and acetate diffuse back into the presynaptic neuron for recycling
  • ATP released by mitochondria combines choline and acetate to reform acetylcholine.
  • Sodium channels close when acetylcholine is absent

Striated Muscle

  • Striated muscle is the major muscle type in vertebrates, attached to bones and under voluntary control

  • Muscles are composed of thousands of muscle fibers bundled together; they run parallel to the length of the muscle

  • Fibers consist of many parallel myofibrils

  • Myofibrils contain two protein filaments called actin and myosin

  • Actin consists of two strands twisted around one another(thinner)

  • Myosin consists of long rod-shaped fibers with bulbous heads projecting sideways(thicker)

  • Myofibrils appear striped due to alternating light (Isotropic, I-bands) and dark (Anisotropic, A-bands) bands. I-bands have no overlap, A-bands have an overlap.

  • The distance between Z-lines is called a sarcomere. Z-lines move closer during contraction.

  • The H-zone is a lighter region in the center of the A-band. The H-zone also shortens during contraction.

  • Sarcomeres shorten when actin and myosin filaments slide past each other

  • Muscle contraction also involves the proteins tropomyosin(fibrous) and troponin(globular).

  • Neuromuscular Junction: The point where a motor neuron connects to a muscle fiber, crucial for triggering muscle contraction.

  • Neuromuscular Junction Neurotransmitters (acetylcholine) are released into the synapse when an action potential reaches the axon terminal.

  • Neuromuscular Junction Acetylcholine causes the muscle cell membrane to become permeable to sodium ions.

  • Neuromuscular Junction The influx of sodium ions initiates an action potential, causing muscle contraction.

  • Neuromuscular Junction Calcium ions entering the synaptic knob trigger the release of acetylcholine, initiating the process.

Muscle Contraction

  • Sliding Filament Model: actin and myosin filaments slide past each other, resulting in sarcomere shortening.
  • Actin Filament: Thin filaments.
  • Myosin Filament: Thick filaments.
  • Proteins involved: troponin, tropomyosin, calcium ions, ATP play crucial roles
  • ATP enables cross-bridges to detach
  • The process repeats, causing filaments to slide, and muscle fiber to contract

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Related Documents

15.8-15.11 PDF: Synaptic Transmission and Striated Muscle

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