BMS 108 Ch. 12 Skeletal Muscle Part 1

Question 0

What are the unique characteristics of a muscle fiber?

Answer 0

multinucleated, striated, and electrically excitable

Question 1

What is another name for a muscle cell?

Answer 1

Muscle fiber

Question 2

What is the specific name of a synapse that innervates a muscle fiber?

Answer 2

neuromuscular junction (NMJ)

Question 3

How many neurons are in the pathway from the brain to skeletal muscle?

Answer 3

2

Question 4

What is the terminal bouton of the neuromuscular junction called?

Answer 4

synaptic knob

Question 5

What is the place on the sarcolemma where the NMJ interfaces?

Answer 5

the Motor End Plate (MEP)

Question 6

What is an EPP and what does it cause?

Answer 6

End Plate Potential; causes Action Potentials

Question 7

What is a motor unit?

Answer 7

A motor neuron and all the fibers it innervates (20-2000 muscle fibers each)

Question 8

When a motor unit is activated, do all the muscle fibers it controls contract?

Answer 8

yes

Question 9

The number of muscle fibers in a motor unit vary according to ________________.

Answer 9

degree of fine motor control in the muscle.

Question 10

Are fine control motor units small or large?

Answer 10

small

Question 11

Since individual motor units fire “all-or-none”, how do skeletral muscles perform smooth movements?

Answer 11

Recruitment is used. The brain estimates the number of motor units to activate and stimulates them to contract.

Question 12

What is the smallest functional unit of a muscle fiber?

Answer 12

sarcomere

Question 13

What is a sarcomere composed of?

Answer 13

Thick filament (myosin) and thin filament (actin)

Question 14

What is an M-Line? A-Band? I-Band? H-Zone? Z-Line? Titin?

Answer 14

Structural proteins that anchor myosin during contraction;

Dark band of mostly myosin; light band, mostly actin;

light area in the center of an A-Band;

center of the I-Band where actins attach;

elastic protein that attaches the myosin to the z-line and contributes to elastic recoil of the muscle.

Question 15

Which bands shorten during contraction?

Answer 15

I-Band and H-Zone

Question 16

What is the Sliding Filament Theory of Muscle Contraction?

Answer 16

Muscle contracts because sarcomeres get shorter.

Occurs because thin filaments slide over thick filaments toward the center of a sarcomere without changing length - shortening the distance between z-lines

Question 17

List the steps involved in muscle contraction (assuming Ca++ is present).

Answer 17

1. ATP binds to myosin head and is hydrolyzed to ADP + P
2. Myosin head reaches back and binds to actin
3. Release of P causes the power stroke
4. The ADP is then released. Myosin head is stuck in the post-power stroke position until…
5. New ATP binds and allows the myosin to release the actin

Question 18

What are cross bridges?

Answer 18

Formed by heads of myosin molecules that extend toward and interact with actin

Question 19

Each myosin head contains an ATP-binding site which functions as _______.

Answer 19

ATPase (hydrolyzes ATP into ADP & P - exergonic reaction)

Question 20

Myosin can’t bind to actin unless it is ________ by hydrolysis of ATP.

Answer 20

cocked

Question 21

Why don’t our muscles contract continously?

Answer 21

Calcium control of the troponin-tropomyosin system

Question 22

What is tropomyosin? what is its function?

Answer 22

A filament that lies in a groove along thin filaments (actin); In relaxed muscle, tropomyosin blocks binding sites on actin so crossbridges can’t occur. Calcium binds to the troponin complex and moves the tropomyosin off the active sites allowing crossbridges.

Question 23

Calcium is very important to muscle contraction. Where does the calcium needed for crossbrides come from in the muscle fiber?

Answer 23

High stores of calcium in the sarcoplasmic reticulum.

Question 24

Describe the steps involved in muscle contraction.

Answer 24

1. NMJ releases ACh, causing depolarizing EPPs&raquo_space; APs in the muscle
2. APs race over the sarcolemma and down T-Tubules
3. VG Ca++ channels in the T-Tubules open (DHP receptors)
4. Nearby Ca++ channels in the SR (ryanodine receptors) open because they are mechanically linked to channels in the T-Tubules
5. RyR are 10x larger than VG Ca++ channels. Opening them causes a massive eflux of Ca++ into the cell

Question 25

What type of positive feedback do ryanodine receptors participate in?

Answer 25

Calcium Induced Calcium Release (CICR)

Question 26

What are the two things that cause a muscle to relax?

Answer 26

As long as Ca++ is elevated, contraction will continue. When APs cease, the muscle relaxes.

Question 27

Is ATP needed for muscle relaxation?

Answer 27

yes

Question 28

What two ways are ATP used in muscle relaxation?

Answer 28

1. Pumps Ca++ back into SR via Ca++ - ATPase pump

2. Required to release crossbridges

Question 29

What are two ways in which skeletal muscle generates ATP?

Answer 29

1. Cellular respiration

2. Phosphate groups donated by creatine phosphate

Question 30

What is the source of energy (ATP) for skeletal muscle in the first few seconds of powerful, explosive movement?

Answer 30

phosphocreatine

Question 31

What is the source of energy (ATP) for skeletal muscle in the first few minutes of high intensity exercise?

Answer 31

anaerobic respiration

Question 32

What is the source of energy (ATP) for skeletal muscle for sustained exercise?

Answer 32

aerobic respiration

Question 33

Why is phosphocreatine the perferred energy source for the first few seconds of movement?

Answer 33

ATP is used faster than it can be replaced by cellular respiration. Phosphocreatine helps regenerate ATP from ADP and Phosphate. It is so efficient that muscle ATP concentration decreases only slightly from rest to heavy exercise.

Question 34

During light exercise, most energy is derived from aerobic respiration of _______ _______.

Answer 34

fatty acids

Question 35

During moderate exercise, energy is derived equally from _______ _______ and ________.

Answer 35

fatty acids; glucose

Question 36

During heavy exercise, ________ supplies 2/3 of the energy.

Answer 36

glucose

Question 37

How are the three ways the body increases glucose availabily and use during exercise?

Answer 37

1. Liver increases glycogenesis
2. And gluconeogenesis
3. GLUT-4 carriers move into the muscle cell’s plasma membrane (increases facilitated diffusion of glucose into the cell)