Skeletal Muscle Physiology I

Question 1

sliding filament mechanism

Answer 1

a) Muscle relaxed
b) Partially contracted muscle
- actin move toward each other, sarcomere shortens
- I band and H zone narrow
c) Maximally contracted muscle
- actin ends overlapp
- H zone disappears

Question 2

Cross Bridge Cycle

Answer 2

1. Exposure: Ca2+ binds to troponin, exposes active site. Myosin heads in active state (ADP energy stored, ADP+phosphate bound)
2. Cross bridge forms: myosin binds to active sites, phosphate released
3. Power stroke: myosin head toward M line, pulls actin. When bent, ADP released.
4. Release: ATP binds to head, releases myosin from actin
5. Re-energize: ATPase on head turns ATP to ADP and phosphate, cycle starts again

Question 3

rigor mortis

Answer 3

Stiff muscles in dead bodies
Myosin head stays bound to actin because no ATP being produced to release it

Question 4

difference between skeletal muscle and nervous resting membrane potential

Answer 4

membrane potential larger in skeletal muscles
- greater K leak channels in

Question 5

what is a branch of a somatic motor neuron called

Answer 5

branch from somatic motor neuron

Question 6

neurtotransmitter released in somatic motor neurons

Answer 6

Acetylcholine

Question 7

portion of sarcolemma that contains neuromuscular junction

Answer 7

motor end plate

Question 8

function of neuromuscular junction

Answer 8

• AP arrives at presynaptic terminal, opens VG Ca2+ channels
• Ca2+ releases Ach from synaptic vesicles into synaptic cleft via exocytosis
• Ach diffuses across cleft, binds to ligand gated Na+ channels on motor end plate
• chanels open, Na+ into cell
• depolarization
• VG channels right beside continue AP

Question 9

EPSP or IPSP in muscles?

Answer 9

alwasy EPSP

Question 10

difference between neuron and skeletal muslce

Answer 10

In muscle ligand gated channels located close to VG channels on postsynaptic membrane

Question 11

how to stop muscle contraction from continually occuring

Answer 11

• Ach constantly broken down by ACETYLCHOLINEESTERASE into choline and acetic acid
• choline recycled (paired with acetic acid in presynatpic terminal), acetic acid reused by other cells

Question 12

excitation-contraction coupling

Answer 12

1. muscle AP propagated along sarcolemma and into t-tubules
2. Ca+ channels in the SR open and calcium is released into sarcoplasm
3. Ca+ binds to troponin, movement of tropomyosin off of myosin binding site
4. Heads of myosin can bind active sites on actin, cross-bridge forms

Question 13

how does calcium release from troponin?

Answer 13

via SERCA pumps
- an ATPase

Question 14

3 places where ATP is needed for skeletal muscle contraction

Answer 14

1. Na+ K to reestablish resting membrane potential
2. for myosin heads: stored energy and to detach from actin
3. calcium pumps