Heart

Question 1

Rest Cell Na

Answer 1

• High outside 140mM - membrane no so permeable - Both electrical and concentration gradients inward
• Low inside

Question 2

Resting Cell K

Answer 2

• High INSIDE - membrane more permeable to K the electrical gradient balances the chemical gradient - slow leakage bc chemical gradient a little bigger
• low outside
• concentration gradient OUT
• electrical gradient IN

Question 3

Resting Cell Ca

Answer 3

• Cardiac cells dont have as much SR but still need SOME flux of Ca across the membrane.
• Higher OUTSIDE
• Lower inside
• membrane relatively impermeable to Ca

Question 4

Resting Cell Cl

Answer 4

• High OUTSIDE- balance of chemical and electrical gradient keeps it balanced
• low inside
• membrane relatively permeable to Cl

Question 5

Phase 0

Answer 5

• Opening of fast Na channel = depolarization

- Na rushes in

Question 6

Phase 1

Answer 6

• opening of K or Cl channel

- potential startss going back toward 0

Question 7

Phase 2

Answer 7

• Plateau phase
• Opening of slow Ca channel
• K channels partially open - more closed than open
• letting Ca in so how is it flat? Same # positive charges coming in with Ca as with K positive charges leaving
• when fast channels opens the K channels start to close

Question 8

Phase 2 into Phase 3

Answer 8

Throughout phase 2 K permeability is increasing and at some point Ca channels close (right before Phase 3)

Question 9

Phase 3

Answer 9

Repolarization - K rushing out – high conducatnace and permeability

Question 10

Phase 4

Answer 10

• resting membrane potential

- balanqce between Na and K

Question 11

Resting Na gate

Answer 11

fast gate closed - M gate (activity gate)

slow gate open - H gate (inactivity gate)

Question 12

Active Na gate

Answer 12

both M and H gate open

Question 13

Na electrical vs chemical gradient

Answer 13

electrical&raquo_space; chemical

Question 14

Which gate starts to close first after active Na state?

Answer 14

H gate closes first ( electrical gradient is reversed but chemical gradient is same = not a lot of Na entered cell but enough to change the charge)

Question 15

Inactive Na gate

Answer 15

H gate (inactivity gate) closed
M gate (activity gate) Open
CELL CANNOT BE STIMULATED RIGHT NOW = REFRACTORY PERIOD

Question 16

Refractory period defined as:

Answer 16

H GATE CLOSED (INACTIVITY GATE)

Question 17

effective refractory period

Answer 17

• begins at depolarization (Phase 0-Opening of fast sodium channel (m-gate opens)) and ends during repolarization (phase 3) when enough H and M gate closed have been reset to Resting state
• cant stimulate the cell here - no propagation of action potential

Question 18

Relative refractory period

Answer 18

• A propagated action potential can be produced, but requires a stronger than normal stimulus. Action potential has abnormal characteristics.
• begins when ERP ends. Ends with normal action potential
• action potential that you get in relative refractory period is not normal –> DANGEROUS - screw up the rhythm

Question 19

what prevents tetany?

Answer 19

the effective refractory period is LONGER than in skeletal muscle- impossible to stimulate contraction again

Question 20

conductance is

Answer 20

actual movement of ion

Question 21

permeability is

Answer 21

potential to move

Question 22

stimulus comes during repolarization

Answer 22

• Low slope of phase O because many fast channels are in inactivated state.
• No plateau because PK+ and Conductance of K+ is very high resulting in repolarization.
• can ge tventricular fibrilation (ventricles out of sync) bc some cardiac muscles may still be in ERP so CANT fire while some in the RRP CAN fire.

Question 23

tetrodotoxin -

Answer 23

Blocks fast channels - makes a hump action potential

Question 24

prepotential phase

Answer 24

• not flat resting membrane protential that moves to threshold (Phase 4 with POSITIVE slope = slow depolarization)
• permeability to K DECREASING and Permeability to Ca and Na INCREASING

Question 25

ventricular cell haswhat permeability to the ions

Answer 25

LOW to Na and Ca

High to K

Question 26

POSITIVEChronotropic agents do what?

Answer 26

-Increase the rate of INFLUX of SODIUM and
CALCIUM (MOSTLY JUST CA)
-increases HR - reaches threshold faster
-ex) norepinephrine

Question 27

NEGATIVE Chronotropic agents do what?

Answer 27

• Increase PK.
• This results in repolarization to more negative values and in decreased rate of decay of the K+ efflux channel
• Decreases HR - reaches threshold slower
• ex) Ach

Question 28

Ectopic Foci

Answer 28

Areas outside the SA node that may spontaneously depolarize and are capable of pacing the heart. ORDER:

• SA node
• Junctional area of the AV node
• Bundle of His
• Purkinje fibers
• Ventricular muscle

Question 29

Sinous rhythm

Answer 29

paced by the SA node.

heart is paced by the SA node because it has the highest free potential slope

Question 30

Av node slows down impulse so that

Answer 30

the atria have time to fill the ventricles before ventricular stimulation

Question 31

R and L bundle branches

Answer 31

• bundle of Purkinje fibers
• depolarize the ventricle quickly
• do not Innervate every cell. terminate close to endocardium and gap junctions spread rest from muscle cell to muscle cell
• R is uniform
• L gives off septal branch, anterior fascicle, posterior fascicle