BIO310H5 Lecture 7: BIO310 Lecture 7

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25 Mar 2020

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Bio310 lecture 7 organization of the nervous system: the nervous system and locomotion. Immediately after the opening of nicotinic receptors sodium will rush into the cell and create a wave of depolarization, this wave will be followed by repolarization because potassium leaves faster than sodium enters. This wave of depolarization will induce an opening of voltage gated sodium channels which are scattered all over the place on the cell membrane of the skeletal muscle. At the voltage-gated sodium channels there will be the generation of another action potential (not the neuron action potential anymore) it"s the skeletal muscle cell membrane ap. This ap will propagate will move through the cell membrane and spread; one motor neuron endplate can open many of these voltage- gated sodium channels. Excitation of the sarcolemma which induces contractions. Ap will be conducted through the presence of these voltage-gated sodium channels deep inside the muscle cell by the transverse tubules.

Related Questions

12.

Explain what happens to microfilaments within cells treated with cytochalasin D and why existing actin polymers eventually depolymerize. Fill in the blanks in the explanation below using words from the selections below.

Cytochalsin D _______ of monomers at ______ of existing filaments. When the concentration of G-actin in the cytosol is _______ the critical concentration, the loss of monomers at __________ of existing filaments eventually results in their shortening.

** Selections: prevents addition; equal to; plus ends; facilitates loss; above; below; both minus and plus ends; minus ends

18.

What effect does VX, a typical but potent acetylcholinesterase inhibitor, have on muscle function? Fill in the blanks in the explanation below. A word bank of choices follows.

Because the removal of acetylcholine is inhibited, the muscle membrane at the nueromuscular junction will remain _____ for an abnormally long period, causing the muscles to remain in a ______ state. The prolonged ______ in turn would be propagated via the T tubule system to ________ . The result would be prolonged release of calcium, resulting in sarcomere _______ via the effects of calcium on ________.

***Selections: polarized; depolarized; polarization; depolarization; shortening; relaxing; contracted; the sarcoplasmic reticulum; the troponin system; myosin; Z lines

1)Describe the directions in which the two motor proteins, kinesin and dynein, travel along a microtubule. Which of the two proteins moves materials towards the Golgi and which moves materials away from the Golgi? Lastly, what is the speed of kinesin dependent on?

2)What are microfilaments crucial for? How do they self-assemble? Which end do they prefer to elongate from?

3)Describe what types of filaments are in each of the bands of the sarcomere. As a muscle fiber is shortened, describe what happens to each of the bands in the sarcomere as the Z lines move inwards.

4)Describe the role of calcium ions in muscle contraction.

5)List the various types of actin-binding proteins

6) A. What are 3 functions of the cytoskeleton?

B.What are the three filaments that compose the cytoskeleton, and what are they composed?

7)How do they see the internal structures of cells in the microscope? What do proteins get labeled with?

8)Myosin II action (Figure 9.61) differs from that of kinesin (Figure 9.15) in that one of the kinesin heads is always in contact with a microtubule, whereas both myosin heads become completely detached from the actin filament. How are these differences correlated with the two types of motor activities in which these proteins engage?

9)If a myofibril were pulled so that the sarcomeres increased in length by approximately 50 percent, what effect would you expect this to have on the contractile ability of the myofibril? Why? What effects would this have on the H, A, and I bands?

10)Because cytoplasmic vesicles are seen to move in both directions within an axon, can you conclude that some microtubules are oriented with their plus end facing the axon terminus and others oriented with the opposite polarity? Why or why not?

1. Each muscle fiber is a bundle of myofibrils. Eachmyofibril is a series of sarcomeres. Thus, a muscle fiber contractswhen each sarcomere within a series contracts simultaneously. Suchcoincidence is mirrored by each myobril within the muscle fiber.What enables the extent to which molecular motors contractsimultaneously within an innervated muscle fiber?

a. the frequency of acetylcholine secretion within theneuromuscular synapse

b. the frequency of Ca²⁺ oscillations within themuscle fiber

2. A living muscle fiber experiences dynamic frequencies ofCa²⁺ oscillations. In effect, Ca²⁺ acts as asecond messenger when it disperses throughout the fluid-filledspaces between actin and myosin filaments. What is the source ofthis second message?

a. extracellular fluid b.sarcoplasmic reticulum

3. Why might a muscle fiber need an ample amount ofNa⁺,K⁺-ATPase on itssurface?

a. as evident by the value of the cellâs membrane potential,muscle fibers are leaky to Na⁺

b. to counter the effect of numerous action potentials persecond

4. Assume that you could âseeâ nicotinic acetylcholine receptorswithin the musculature. How would they be arranged spatially?

a. evenly distributed on the cellâs surface like voltage-gatedNa⁺ and K⁺ channels

b. in dense arrays within the motor end plate

5. Assume that you could âseeâ neurosecretion fromÎ±-motor neurons within the musculature of an animal standing still.What would this âlookâ like?

a. uniform, baseline secretion throughout the musculature

b. enhanced acetylcholine secretion within antigravity muscles,baseline secretion elsewhere

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BIO310H5 Lecture 7: BIO310 Lecture 7

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