muscle physiology

Question 1

what makes muscles contact?

Answer 1

excitation-contraction coupling

Question 2

what is excitation-contraction coupling?

Answer 2

series of events that produce an electrical stimulus that triggers the release of Ca from the sarcoplasmic reticulum, initiating the mechanism of muscle contraction by sarcomere shortening

Question 3

what are positively charged ions referred to as?

Answer 3

cations

Question 4

what are negatively charged ions referred to as?

Answer 4

anions

Question 5

is the inside of the cell negative or positive in comparison the the extracellular area?

Answer 5

negative

Question 6

what charge does the extracellular area of the cell have?

Answer 6

neutral

Question 7

what is the the potential difference in voltage across a cell called?

Answer 7

resting membrane potential (Em)

Question 8

what is the calculation used to calculate Em?

Answer 8

voltage in cytoplasm - voltage in ECF

Question 9

what structure maintains Em?

Answer 9

Na/K-ATPase

Question 10

which ions pass in and out of the cell via passive leak channels?

Answer 10

Na and K

Question 11

how many sodium ions enter the cell by the Na/K-ATPase?

Answer 11

3

Question 12

how many potassium ions leave cell by the Na/K-ATPase?

Answer 12

2

Question 13

what is the Em of a neutron?

Answer 13

-70mV

Question 14

what is the Em of a muscle cell?

Answer 14

-90mV

Question 15

name the 3 types of active (gated) channels?

Answer 15

. chemically-regulated channels (ligand gated)
. Voltage-regulatd channels
. mechanically-regulated channels

Question 16

describe the series of events that lead to an AP in a muscle cell

Answer 16

. voltage-sensitive Na channels are activated when voltage threshold is reached
. this causes depolarisation
. as membrane potential increases to a positive number, the threshold for voltage-dependant K channels is reached, and K enters the cell
. K influx quickly decreases Em, depolarising cell

Question 17

what is an action potential?

Answer 17

rapid change in Em caused by rapid activation and fluxes of ion currents, followed by a return to resting em

Question 18

what is the term used for sustained muscle contractions?

Answer 18

tetanic contaction

Question 19

what do action potentials allow?

Answer 19

synchronous contraction/relaxation in muscle and communication in neutrons

Question 20

what is the refractory period?

Answer 20

a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation

Question 21

what propagates action potentials in the heart?

Answer 21

SA node

Question 22

what propagates action potentials in skeletal muscles?

Answer 22

ACh binding to motor unit on skeletal muscle

Question 23

describe the series of events by which an AP leads to muscle contraction?

Answer 23

. depolarisation activates plasma membrane voltage-sensitive Ca channels that allow Ca to enter cell
. inward entry of Ca activates release of Ca from sarcoplasmic reticulum
. intracellular Ca conc increases trigering myofilamnet contraction

Question 24

describe the series of events by which cytoplasmic Ca exposes myosin binding sites

Answer 24

. cytoplasmic Ca bins to troponin C, inducing a conformational change that exposes myosin-binding sites on actin filament
. this allows myosin head to bind to actin

Question 25

how does the release of Ca differ in smooth muscle?

Answer 25

receptors also contribute by activating agonist-mediated Ca channels

Question 26

which channels stimulate SR Ca release through RyR receptors in cardiac/skeletal muscle?

Answer 26

L-type Ca channels

Question 27

Ca is released from the SR through which channels in smooth muscle?

Answer 27

RyR and IP3R

Question 28

which molecule blocks myosin binding sites on actin filaments?

Answer 28

tropomyosin

Question 29

tropomyosin contains which 3 proteins?

Answer 29

troponin C, troponin I and troponin T

Question 30

where on the actin filament does cytoplasmic Ca bind?

Answer 30

troponin C

Question 31

describe myosin chains?

Answer 31

2 myosin heavy chains and 4 myosin light chains

Question 32

describe the series of events that lead to smooth muscle contraction?

Answer 32

. Ca binds to cytoplasmic calmodium changing its conformation . Ca-calmodium complex activates myosin light chain kinase (MLCK) . MLCK phosphorylates myosin light chain to catalyse cross-bridge activation

Question 33

what is ATP most important for in terms of ECC?

Answer 33

relaxation

Question 34

at which stage of ECC id ATP broken down to ADP + Pi? ?

Answer 34

cocking of myosin head

Question 35

when during ECC is an inorganic phosphate released?

Answer 35

when myosin head binds to actin

Question 36

when is ADP released during ECC?

Answer 36

power stroke

Question 37

at which point during ECC is ATP supply depleted?

Answer 37

when the muscle has contacted

Question 38

how is the myosin head released from actin?

Answer 38

by the binding of ATP to the myosin head

Question 39

what happens to Ca release as a result of RyR dysfunction?

Answer 39

Ca sparks, abberent Ca release, loss of SR Ca

Question 40

which muscles types is RyR dysfunction most severe in?

Answer 40

cardiac and skeletal

Question 41

what may a consequence of RyR dysfunction in cardiac muscle be?

Answer 41

Heart failure

Question 42

what may a consequence of RyR dysfunction in skeletal muscle be?

Answer 42

muscular dystrophy

Question 43

what does muscular dystrophy cause?

Answer 43

muscle weakness, loss of skeletal muscle function and control, muscle degeneration, paralysis

Question 44

what type of mutation is muscular dystrophy?

Answer 44

X-linked recessive

Question 45

what is a possible way of treating RyR dysfunction?

Answer 45

increasing SERCA

Question 46

how may SERCA be increased?

Answer 46

gene therapy, exercise training