Muscle Physiology

Question 1

Skeletal muscle (tendon, body)

Answer 1

tendon: connective tissue to bone
body: generate force by contracting

Question 2

Skeletal muscle anatomy

Answer 2

bundle of fascicles encased in epimysium (CT)

Question 3

Fascicles

Answer 3

bundle of muscle fibers encased in perimysium (CT)

Question 4

muscle fiber

Answer 4

muscle cell surrounded by endomysium (CT)

Question 5

Muscle fiber (cell) (size, surrounded by, T-tubules, composed of)

Answer 5

size: long, length of muscle

surrounded by: sarcolemma (cell membrane) containing T-tubules

T-tubules: continuous with sarcolemma, dips into cell interior

-composed of myofibrils

Question 6

Myofibrils (what they are like, surrounded by, what can change, composed of)

Answer 6

-Rod-like structure

-Surrounded by:
        Sarcoplasmic reticulum (SR): ER, stores and releases        Ca2+ into cytosol

• # can change with cell use
  • Composed of contractile filaments

Question 7

Contractile filaments (arranged to form, types)

Answer 7

-Arranged to form:
Sarcomere: repeating functional contractile units

-Types:
Thick
Thin

Question 8

Thin filament (composed of)

Answer 8

• G-actin
• Tropomyosin
• Troponin

Question 9

Tropomyosin (what it is, how it works)

Answer 9

• Protein that controls interactions with thick filaments

- How? Blocking binding sites

Question 10

G-actin

Answer 10

-protein with myosin binding sites (bind to thick filaments)

Question 11

troponin (what it is, how it works)

Answer 11

• Moves tropomyosin off myosin binding sites during muscle stimulus
• How? Ca2+ binds to troponin → moves with tropomyosin

Question 12

Thick filaments (composed of)

Answer 12

• Myosin proteins
  
  1. Heads
  2. Tails

Titin: elastic protein allowing for stretch/ recoil

Question 13

Heads (thick filament)

Answer 13

-crossbridge

• sites
  
  • actin binding site
  • ATPase site

Question 14

tails

Answer 14

• no binding sites

- compose bare zone

Question 15

what is a sarcomere?

Answer 15

functional contractile unit

Question 16

A band

Answer 16

length of thick filament (remains the same)

Question 17

H zone

Answer 17

region of only thick filament

Question 18

I zone

Answer 18

region of only thin filament

Question 19

Z line

Answer 19

ends of sarcomere

Question 20

M line

Answer 20

middle of sarcomere

Question 21

muscle fiber contraction

Answer 21

• excitation: contraction coupling

- releasing NT at neuromuscular junction cell –> contraction of the cell

Question 22

Muscle fiber contraction (steps)

Answer 22

1. Act released from axon terminal at neuromuscular junction
2. Ach binds to receptors on motor end plate –> AP
3. AP propagates down sarcolemma down T-tubules
4. AP triggers calcium to be released from SR
5. Ca2+ binds to troponin –> moves tropomyosin to expose myosin binding sites
6. cross bridge forms with actin (cross bridge cycle) –> contraction
7. Ca2+ actively pumped back into SR following AP
8. Ca2+ no longer bound to troponin –> tropomyosin block myosin binding sites

Question 23

Sarcoplasmic reticulum gating

Answer 23

• Sarcolemma and SR connect through 2 receptors
  - DHP receptors: on sarcolemma
  - Ryanodine Receptors: on SR

AP down T-tubule changes DHP receptor shape
→ cause ryanodine receptor channels to open,
Ca2+ into cytoplasm

Question 24

Crossbridge cycle (steps)

Answer 24

1ATP binds to myosin head → cocking it back (ATP → ADP + Pi)

2. Myosin binds to actin, Pi released
3. Power stroke moves thin filaments, ADP released
4. New ATP binds, myosin releases actin

Question 25

Muscle fiber contraction

Answer 25

cross-bridge cycle repeats –> shortening each sarcomere

Question 26

muscle fiber relaxation

Answer 26

• Stimuli to muscle cells removed
• Ca2+ actively pumped back into SR
• Ca2+ no longer bound to troponin
• Tropomyosin block myosin binding sites
• Sarcomeres relax → back to normal length

Question 27

motor unit

Answer 27

• arrangement of skeletal muscles controlled by 1 ,motor neuron
• when stimulated –> all contract

Question 28

contractile force

Answer 28

change number of motor units stimulated to change force