Phys.II Test One: Skeletal Muscle

Question 1

What is the sarcolemma?

Answer 1

Plasma membrane of skeletal muscle fiber

Question 2

What is the subunit of muscle composed of?

Answer 2

Fascicle

Question 3

What makes up a fascicle?

Answer 3

Muscle fibers

Question 4

What makes up a muscle fiber?

Answer 4

Myofibrils

Question 5

What is a sarcomere?

Answer 5

Functional unit of muscle, portion of myiofibril between two adjacent Z discs

Question 6

Thin filament?

Answer 6

Actin

Question 7

Thick filament?

Answer 7

Myosin

Question 8

Tropomyosin?

Answer 8

Protein on top of F-actin that covers up the binding site for myosin.

Question 9

Troponin?

Answer 9

On actin attached intermittently along tropomyosin. T troponin binds tropomyosin I troponin binds Actin C troponin binds calcium

Question 10

What makes up a sarcomere?

Answer 10

Complete A band and two halves of the I bands next to it

Question 11

What is titin?

Answer 11

Protein that maintains alignment between actin and myosin and acts like a spring between Z discs and end of myosin.

Question 12

What transmitter is released at a Neuromuscular Junction?

Answer 12

ACh

Question 13

Describe the steps to muscle contracting.

Answer 13

1. AP gets to the axon terminal and calcium voltage gates open allowing calcium in the synaptic bulb.
2. Calcium entering causes ACh to be released exocytosis
3. ACh diffuses across synaptic cleft and binds to ACh receptors on sarcolemma. Remaining is broken down by acetylcholinesterase.
4. In the muscle fiber cation channels open and they enter producing an EPP followed by an AP.
5. Action potential travels to the T tubules and causes calcium to be released from the SR.
6. Calcium binds to tropoin and removes tropomyosins inhibition of actin myosin binding site.
7. Myosin pulls on actin shortening the sarcomere producing the contraction.

Question 14

How many molecules of ACh does one synaptic vesicle contain, and how many vescicles are relased during one AP?

Answer 14

5,000 molecues of ACh and 300 are released

Question 15

How does Botuline Toxin impact skeletal muscle?

Answer 15

It blocks the releases of ACh leading to muscle weakness and paralysis

Question 16

How does Curare impact skeletal muscle?

Answer 16

It is a competitive inhibitor of ACh. It competes with ACh for binding sites on Sarcolemma, but when it binds it does not result in anything so no electrical signal is mproduced in the muslce fiber when an AP arrives at the axon terminal.

Question 18

What causes an mEPP?

Answer 18

spontaneous discharge of one synaptic vesicle

Question 19

In the T-tubule and SR what two proteins interact to release the calcium?

Answer 19

Dihydropyridine receptor in the t tubule senses the voltage change from the AP and interacts with Ryanodine receptor/Ca release channel in the SR.

Question 20

What causes the cocking of the myosin head in the sliding filament theory?

Answer 20

Hydrolysis of ATP to ADP and Pi causes the conformation change

Question 21

What does a cross bridge represent?

Answer 21

When the myosin head binds to actin

Question 22

What causes the springing of the myosin head?

Answer 22

Release of the phosphate group from the myosin head

Question 23

Does myosin shorten with contraction?

Answer 23

No, the sarcomere shortens and Z discs move towards each other but myosin does not shorten.

Question 24

How many motor neurons innervate one muscle fiber?

Answer 24

one motor neuron

* a motor neuron can innervate several muscle fibers but muscle fibers can only be innervated by one motor neuron*

Question 25

What is a motor unit?

Answer 25

One motor neuron plus all of the fibers it innervates

Question 26

What is multiple fiber summation?

Answer 26

Increased muscle tension caused by an increasing number of motor units contracting simultaneously

Question 27

What is tension?

Answer 27

Force exerted on an object by muscle

Question 28

What is load?

Answer 28

Force exerted on a muscle by the weight of an object

Question 29

For a fiber to shorten __ needs to exceed \_\_.

Answer 29

tension, load

Question 30

Isotonic contraction?

Answer 30

Muscle shortens while the load is constant

Question 31

Isometric contraction?

Answer 31

Muscle develops tension but it doesn't shorten

Question 32

What is a muscle twitch?

Answer 32

Contraction of a single muscle fiber in response to a single AP

Question 33

What is frequency summation?

Answer 33

Increase in muscle tension when successive AP occur rapidly enough that the fiber did not have time to completely relax from the prior twitch.

Question 34

What is Treppe?

Answer 34

Period of summation in which the strength of contraction rapidly increases as rate of stimulation rises

Question 35

What is unfused tetanus?

Answer 35

Maintained contraction at high rates of stimulation in which muscle tension oscillates due to slight relaxations between stimuli

Question 36

What is fused tetanus?

Answer 36

Maintained cotarction at even higher stimulation rates where no oscillations occur

Question 37

What can cause buckeling of myosin filaments?

Answer 37

When muscles are over contracted with very short sarcomere lengths. The Z lines can collide with the ends of myosin causing it to crumple.