Lecture Exam 3: Muscles and Movement

When the action potential arrives at the axon terminal of a motor neuron which ion channels open?

Voltage-gated calcium channels

Which of the following would cause the cross bridge to transition from a high force state to a low force state?

Decreasing intracellular calcium

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions

What is the role of calcium in the crossbridge cycle?

Calcium binds to troponin, altering its shape

The action potential traveling along the t-tubule is detected by the

Dihydropyridine (DHP) receptor (L-type calcium channel)

A myogenic contraction describes the opening of ____ channels in smooth muscle cells in response to a distortion of the cell in response to a distortion of the cell membrane that is commonly observed in _____

Stretch activated, blood vessels

Asynchronous activation of motor units is important because it functions to prevent

Fatigue

What is the role of calcium in skeletal muscle contraction?

Calcium binds to troponin. This moves tropomyosin away from the the myosin binding sites on actin, allowing myosin head to attach to actin and initiate contraction

What is the role of calcium in smooth muscle contraction?

Calcium binds to calmodulin. This activates myosin light chain kinase, which phosphorylates myosin light chains, enabling myosin to interact with actin and initiate a contraction

A muscle moving a load goes through two phases of contraction. What is the first phase that occurs prior to moving the load, and what happens inside the muscle during this phase?

Isometric; elastic elements stretch

What is the response of a muscle stretch reflux?

Contraction of the agonist mucle

The reflux that prevents a muscle from exerting too much tension is the

Tendon reflux

The tension maintained in a muscle at rest is known as muscle

Tone

When does the crossbridge cycling end?

When sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium Ions diffuse inward along favorable chemical and electrical gradients

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape

ATP is regenerated by ___?

Direct phosphorylation, anaerobic pathways, aerobic respiration

What are the three phases of muscle twitch?

Latent period, period of contraction, and period of relaxation

Light and dark muscle striation are due to ___?

The organization of the proteins of the thin and the thick filaments

What are the three connective tissue sheaths in skeletal muscle?

Endomysium, perimysium, and epimysium

Where is the sarcomere located?

Within the muscle fiber

What are the characteristics of skeletal muscle?

Excitability, contractility, extensibility, and elasticity

What are three things that can cause fatigue?

Ionic imbalance, prolonged exercise, and lack of ATP

Alpha-gamma coactivation causes___

The muscle spindle to remain active during skeletal muscle contraction

The target of the gamma motor neuron is ____

The intrafusal fibers of a muscle

How is calcium removed from the skeletal muscle?

Calcium ATPase (pump) cytosol → SR

How is calcium removed from the smooth muscle?

Calcium ATPase (SR), calcium ATPase (PM), or sodium/calcium ATPase antiporter (PM)

What is muscle tonus?

Constant, slightly contracted state of all muscles. Keeps muscles firm, healthy, and ready to respond

After the power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin

What happens when calcium binds to troponin?

Tropomyosin is pulled away from the actin active site

Which of the following would cause the crossbridge to transition from high force state to a low force state?

Decreasing intracellular calcium

What of the following is most directly responsible for the coupling of excitation of skeletal muscle fibers?

Calcium ions

What role does tropomyosin play in the crossbridge cycle?

The displacement of tropomyosin exposes the active sites of actin, allowing cross bridges to form