Muscle Physiology

Question 1

Properties of Muscle

Answer 1

1. electrically excitable
2. contractability-can shorten and contract in response to stimuli
3. extensibility-flexibility
4. elasticity-can return to normal shape

Question 2

Superficial Fascia
Deep Fascia (+3 extensions)

Answer 2

-separates skin from muscle
-holds similar muscles together
1. epimysium covers entire muscle
2. perimysium covers facicles-groups of 10-100 mm fibers
3. endomysium-covers individual mm fibers
skeletal muscle-facicle-mm fibers-myofibrils

Question 3

titin

Answer 3

spring-like protein that connects Z-disks and M-line

adds flexibility and elasticity to sarcomere

Question 4

What happens to the components of a sarcomere during contraction?

Answer 4

H-zone, Z-disks, and I-band get smaller, A-band and M-line do nothing, and zone of overlap increases

Question 5

Events @ NMJ from nerve impulse to exocytosis

Answer 5

1. nerve impulse travels down axon and arrives at axon terminal
2. voltage-sensitive channels in axon terminal release Ca into the synaptic end bulb, Ca moves with the concentration gradient
3. Ca triggers vesicles to move to membrane and release ACh through exocytosis

Question 6

Events @ NMJ from exocytosis to contraction

Answer 6

4. ACh binds to nicotinic cholinergic receptors on motor end plate and cause cation channels to open and Na to flow into the sarcoplasm
5. T-tubules (extensions of sarcolemma) spread electrical charge through cell (depolarization
6. T-tubules and 2 terminal cisternae (bulges of SR)=triad, depolarization causes voltage sensitive channels to open causing release of Ca into sarcoplasm—->contraction

Question 7

Relaxation

Answer 7

• AChE-acetyl cholinesterase breaks down ACh and recycles contents back into synaptic end bulb
• Ca active transport channels pump Ca from sarcoplasm back into sarcoplasmic reticulum

Question 8

4 step contraction cycle

Answer 8

1. ATP hydrolysis-myosin heads contain ATPase, which breaks down ATP into ADP, Pi, and energy
2. Binding-myosin head binds to actin and forms cross bridge, Pi is release, triggering power stroke
3. Power stroke-myosin head swivels towards M-line, ADP is released
4. Detachment-new ATP binds to myosin head and causes detachment

Question 9

Creatine Phosphate

Answer 9

• stable storage form of ATP
• from liver, pancreas, and kidneys, unique to mm cells
• creatine+ATP—>creatine phosphate+ADP

Question 10

Sources of ATP

Answer 10

• creatine phosphate
• anaerobic respiration
• aerobic respiration

Question 11

fatigue

Answer 11

• central (brain): psychological feeling of tiredness
• NMJ-disease usually
• excitation-contraction coupling-increased exercise leads to more ATP hydrolysis and Pi (which can interfere with Ca release from SR and tends to bind to Ca
• Contraction cycle-lots of exercise leads to lots of pyruvic acid, which interferes with the power stroke and depletes nutrients

Question 12

what does speed of contraction depend on?

Answer 12

-load and type of fiber (speed of ATPase and power stroke)

Question 13

what neural components effect muscle tension?

Answer 13

• frequency of firing
• number of mm fibers recruited
• number of motor units recruited
• number of neurons

Question 14

Muscle tone

Answer 14

background level of motor unit activity, can be enhanced by resistance training (hypertrophy or neural adaptions)

Question 15

What factors affect muscle force

Answer 15

• length (length tension relationship)
• stimulus frequency
• number of fibers
• -metabolic properties
• -type of fiber