Muscle Physiology 1

Question 1

what types of muscle cells are striated?

Answer 1

cardiac and skeletal

Question 2

where are smooth muscle cells present?

Answer 2

vessels, tracts, bladder, GI, lungs

Question 3

what is the function of a muscle cell?

Answer 3

to contract and relax in order to create movement

Question 4

what muscle is under somatic control?

Answer 4

skeletal muscle

Question 5

what muscle is under autonomic control?

Answer 5

cardiac and smooth muscle

Question 6

what makes muscle cells contract?

Answer 6

excitation-contraction coupling

Question 7

what do the difference of electrical charges across the plasma membrane create?

Answer 7

chemical and electrical gradient until equilibrium is reached

Question 8

what is the resting membrane potential?

Answer 8

-90mv

Question 9

how is the resting membrane potential calculated?

Answer 9

the voltage in the cytoplasm (inside the cell) minus the voltage in the ECF (outside the cell)

Question 10

why is the inside of the cell -90mv?

Answer 10

the Na/K ATPase transports 3Na+ out for 2K+ in which causes a net transfer of + charge out of the cell so the inside is negative

Question 11

what are the different types of active (gated) channels?

Answer 11

chemically regulated channels, voltage-regulated channels and mechanically regulated channels

Question 12

what do active (gated) channels do?

Answer 12

facilitate the diffusion or even move (ATPase) ions against the electrochemical gradient

Question 13

what is the mechanism of the voltage-gated channels?

Answer 13

they have activation and inactivation gates

1. deactivated (closed)
2. activated Na+ channels (open) when the threshold is reached AKA depolarisation
3. inactivated Na+ channels (closed) when voltage-sensitive K+ channels open AKA repolarisation
4. return to the beginning

Question 14

what is the action potential?

Answer 14

a rapid change in the membrane potential that is propagated along the length of the cell followed by a return to the resting Em

Question 15

what is the action potential caused by?

Answer 15

movement of ions against the electrochemical gradient = depolarisation to threshold

Question 16

what does the action potential do?

Answer 16

elicit synchronous contraction/relaxation in muscle, in neurons it is the basis for communication

Question 17

when is the refractory period

Answer 17

from time action potential begins until normal resting potential returns (the hyperpolarisation bit in the graph)

Question 18

where is the action potential in the cardiac cycle generated?

Answer 18

in the SA node

Question 19

where is the action potential in a skeletal muscle generated?

Answer 19

motor unit through Ach

Question 20

where is the action potential in smooth muscle generated?

Answer 20

neurotransmitters from neuron varicosities

Question 21

what is the mechanism of AP and membrane depolarisation in muscle cells?

Answer 21

depolarisation (upstroke of AP) activates plasma membrane voltage-sensitive Ca2+ channels that activate inward Ca2+ current, in smooth muscle also agonist-sensitive Ca2+ channels, this gives a small Ca2+ entry into the cell

Question 22

what is the 1st step of excitation-contraction coupling?

Answer 22

depolarisation (AP) and/or agonists in smooth muscle

Question 23

what is the 2nd step of excitation-contraction coupling?

Answer 23

depolarisation activates inward Ca2+ channel current

Question 24

what is the 3rd step of excitation-contraction coupling?

Answer 24

inward Ca2+ entry activates release of Ca2+ from the sarcoplasmic reticulum. This Ca2+ release is mediated by the SR Ca2+ release channels

Question 25

what is the 4th step in excitation-contraction coupling?

Answer 25

intracellular Ca2+ contraction increased from ~0.2 to 1 nanometer

Question 26

what is the 5th step in the excitation-contraction coupling?

Answer 26

Ca2+ triggers myofilament contraction

Question 27

what is the 6th step in excitation-contraction coupling

Answer 27

Ca2+ re-sequestered into the SR via the SR Ca-pump and removed from the cell by the plasma membrane Na/Ca exchanger and Ca-ATPase

Question 28

what is the 7th step of excitation-contraction coupling?

Answer 28

Ca2+ is removed from myofilaments causing them to relax

Question 29

why does cytoplasmic Ca2+ bind to in cardiac and skeletal muscle?

Answer 29

troponin C

Question 30

what does the binding of cytoplasmic Ca2+ to troponin C induce?

Answer 30

a conformational change in the troponin/tropomyosin complex that exposes the myosin-binding sites on actin filaments to the myosin. Myosin heads can then attach to actin

Question 31

what induces contraction in smooth muscle cells?

Answer 31

voltage and receptor-mediated influx of Ca2+

Question 32

what is the role of the action of the ligand Ca2+ channel in skeletal and cardiac muscle?

Answer 32

to stimulate SR Ca2+ release through the RyR

Question 33

what does the influx of Ca2+ in smooth muscle cells do?

Answer 33

activates RyR and IP3 which stimulates IP3R both of which release SR Ca2+

Question 34

what are myosin heads charged by?

Answer 34

hydrolyzing ATP to ADP and Pi

Question 35

what does calcium bind to in smooth muscle cells?

Answer 35

calmodulin

Question 36

summarise muscle contraction in skeletal and cardiac muscle cells

Answer 36

Ca2+ binds to troponin C - conformational change of troponin-tropomyosin complex which exposes actin binding sites - myosin heads bind to these sites - Pi is released and myosin heads move to induce contraction - ADP released and binds to Pi to form ATP and myosin head then releases from binding site and relaxes

Question 37

summarise smooth muscle contraction

Answer 37

Ca2+ binds to calmodulin - myosin light chain kinase activated which phosphorylates myosin - myosin binds to actin and then moves to induce contraction (power stroke) - removal of cytoplasmic Ca2+ by SERCA, NCX and PMCA inactivates myosin-actin binding by blocking myosin binding site which causes relaxation