Skeletal & Smooth Muscle (TEST 2)

Question 1

What are the 3 types of human muscle tissue?

Answer 1

1. Skeletal Muscle
2. Cardiac Muscle
3. Smooth Muscle

Question 2

Light Bands

Answer 2

Thin actin filaments

Question 3

Dark Bands

Answer 3

Thick myosin filaments

Question 4

Skeletal muscle is responsible for what?

Answer 4

• Controls body movement

Question 5

What is a fascicle?

Answer 5

Bundled groups of adjacent muscle fibres

Question 6

True or False, Skeletal muscles are the largest cells in the body?

Answer 6

True

Question 7

Sarcolemma

Answer 7

cell membrane of muscle fibers

Question 8

sarcoplasm

Answer 8

the cytoplasm of muscle cells

Question 9

sarcoplasmic reticulum

Answer 9

modified endoplasmic reticulum that wraps around each myofibril

Question 10

What is a triad?

Answer 10

1 T tubule and 2 adjacent cisternae

Question 11

What is a T-tubule?

Answer 11

extensions of the cell membrane that penetrate into the centre of skeletal and cardiac muscle cells.

Question 12

What are myofibrils?

Answer 12

Are highly organized bundles of contractile and elastic proteins, and the myofibrils are contractile structures within a muscle fiber

Question 13

What does a myofibril consist of?

Answer 13

1. Contractile Proteins (myosin & actin)
2. Regulatory Proteins (tropomyosin & troponin)
3. Accessory Proteins (titin & nebulin)

Question 14

Sarcomere

Answer 14

one repeat of the pattern

Question 15

What are the 3 major steps in muscle fibre contraction?

Answer 15

1. Events at the neuromuscular junction
2. Excitation - contraction Coupling
3. Contraction-relaxation cycle

Question 16

What are the events at the neuromuscular junction?

Answer 16

a. ACh is always excitatory and always causes a muscle to contract
b. ACh released from motor neuron is converted to an electrical signal in the muscle fiber (Na+ entry)
c. In order prevent muscle contraction, we have to prevent the release of acetylcholine at the neuromuscular junction

Question 17

What are the 4 major events that happen during EC coupling?

Answer 17

1. Acetylcholine is released from somatic motor neurons
2. ACh initiates action potential in the muscle fibre
3. Action Potential causes Ca 2+ to release from SR
4. Ca 2+ combines with troponin to initiate contraction

Question 18

What are the steps that occur during muscle fiber relaxation?

Answer 18

• SR pumps Ca 2+ back into its lumen
• decrease in Ca 2+ causes unbinding of Ca 2+ from troponin
• tropomyosin slides back to block actin’s myosin binding site
• cross bridges release; muscle fiber relaxes

Question 19

Explain muscle fibre tension?

Answer 19

maximum tension is proportional to a number of cross bridges formed between thick and thin filaments

Question 20

Explain the timing of EC coupling?

Answer 20

One full cycle consists of:

1. Somatic neuron action potential
2. Skeletal Muscle Action Potential
3. Contraction
4. Relaxation

Question 21

Define latent period:

Answer 21

Delay between muscle AP & start of muscle tension

- time required for Ca 2+ build up and binding to troponin

Question 22

Define Summation:

Answer 22

high frequency of action potentials increase force generated by a single muscle fiber

Question 23

Define Tetanus:

Answer 23

occurs when stimulation have very high frequency (muscle is unable to relax)

Question 24

What is ATP needed for during a fibre contraction?

Answer 24

• cross bridge movement & release
• pump Ca 2+ back into SR during relaxation
• Restore Na + and K+ in the extracellular and intracellular compartments

Question 25

What are the sources of energy for muscle contraction?

Answer 25

1. Transfer high energy phosphate from phosphocreatine to ADP to make ATP
2. When the creatine phosphate stores run out we will resort to metabolism to transfer energy in the chemical bonds of nutrients to ATP
3. If we have adequate oxygen supply we can also obtain energy from fatty acids, where fatty acids are converted to acetyl coa through that beta oxidation process so that they can enter aerobic metabolism

Question 26

type I muscle fibers

Answer 26

slow twitch (red muscle, known as the dark meat)

Question 27

type II-A muscle fibres

Answer 27

fast-twitch oxidative glycolytic fibres (known as white meat)

Question 28

type II-B/type II-X

Answer 28

fast twitch glycolytic fibers

• type IIB found in other animals
• type IIX found in humans

Question 29

What is a motor unit?

Answer 29

One motor Neuron and all the muscle fibers it innervates

Question 30

How does motor unit recruitment work?

Answer 30

• weak stimulus recruits neurons with lowest thresholds (usually fatigue resistance type I)
• increases stimulus, motor neurons with higher thresholds will fire
• order of recruitment: type I, type IIA, type IIB/IIX