Exam 1 Flashcards by Angie Broga

Na+

Iout, Iin, Keq

Iout: 145
Iin: 10
Keq: 70mV

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K+

Iout, Iin, Keq

Iout: 4
Iin: 135
Keq: -94mV

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Ca2+

Iout, Iin, Keq

Iout: 2
Iin: 10^-4
Keq: 132

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goldmann field equation

each permeable ion attempts to drive Emem toward its own Ex (Nernst potential)
-many ions - total permeable ions dictate membrane potential

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resting membrane potential

membrane potential is stable at this time

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nodal tissue

pacemaker cells

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how are cardiac cells myogenic

the electrical impulse starts in the same muscle causing it to contract

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pacemakers

SA node, AV node, PBH system

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provides electricity that generates heart beat by action potentials

pacemakers

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what is the sinus rhythm

pace from the SA node

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characteristics of nodal tissue action potential

sinusoidal curve (wave like)
no true RMP - never stable
diastolic depolarization (graded potential)

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Funny current

activated at a negative voltage!!

cation nonspecific!! - allows Na, Ca, and K to pass through

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diastolic depolarization

sum of 3 currents that flow through funny channel
-each ion that passes drives the membrane potential to its own Nernst potential
-graded potential - slope shows rate of flux slow
current not strong bc slope is gradual

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characteristics of cardiac muscle

myogenic
Ca dependent
involuntary, striated
no true RMP
intercalated discs
muscle fibers parallel and in series
30% is mitochondria!! - requires lots of energy
T tubule and sarcoplasmic reticulum not as extensive as skeletal

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physical places with high density of gap junctions

intercalated discs

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gap junctions

proteins imbedded in cell membrane of myocytes
allow low resistance of current flow
allow cell to cell communication and current flow between ICF
protein composition with hydrophillic core - aqueous pore

what is the dominant pacemaker in a healthy heart

SA node triggers myocyte to have an action potential

phase 0 nodal tissue/pacemaker cell action potential

depolarization

once threshold is hit, Ca channels open

phase 3 nodal tissue action potential

repolarization

K channels activated

phase 4 nodal tissue action potential

diastolic depolarization (pacemaker potential)
gives heart automaticity 
caused by activation of funny channels

myocyte action potential

square waves
like a light switch - needs to be hit to turn on and needs to be hit to turn off
MP: -90mV more neg than nodal tissue

phase 0 of myocyte-cardiac muscle action potential

depolarization
main ion moving is Na

Na fast channels - resistance to Na is low

phase 1 myocyte action potential

at peak of action potential
opening of K+ slow channels - this new current is why the line slopes down
inactivation of Na+ channels

phase 2 myocyte action potential

plateau
Ca, K, and Na lead to the plateau - all involved bc they are cancelling eachother out
time in the action potential when nothing is changing - parallel to x-axis
heart muscle does not do tetany

phase 3 myocyte action potential

membrane potential plumeting toward negative (K+) fast K+ channels repolarization does NOT extend beyond x-axis

in all muscle types, _____ precedes ______

electrical activity precedes mechanical

How does the PNS lower heart rate?

- interbeat interval | - inc maximum diastolic potential

what happens when the interbeat interval increases?

it gets longer between heart beats takes a longer amount of time to reach threshold lowers HR

how does NE effect the heart

increases heart rate

NADR

lowest point, maximum diastolic depolarization - most negative point

cardiac control center | cell bodies here travel to thoracic region when they synapse at ganglion

medulla

interganglionic commisural fibers

nerve fibers connecting superior and inferior ganglion together all target tissues stimulated at same time, low R junctions

what responses do you get when you activate the medulla

indiscrete, systemic, not specific - sympathetic indiscrete bc of the impulse by the interganglionic comisural fibers - conduct electricity get massive ganglion activation

arenaline is second contributer to SNS response

released fom adrenal medulla | - adrenal gland has tissue that can then secrete epinephrine

effective refractory period

can't get another action potential

why are there effective refractory periods?

1. all Na channels inactivated 2. in order to get them ready for another action potential the cell has to be negative need phase 0 to get anther action potential

what fraction of Na channels are closed at phase 4?

100%