Lecture 2: Conduction and ECG

Question 1

Cardiac Muscle Cells

Answer 1

*branched! (unique to only them)
striated, centrally located nucleus (or 2)
actin and myosin in myofibrils

Question 2

Why branching in CM cells?

Answer 2

allows for communication between 1 cell and every cell it touches
transmit electrical impulses and pull in all directions, so no tearing

Question 3

Gap Junctions

Answer 3

small tubes where ions travel from cell to cell
(electrical impulses) (sodium in first, depol., leaks into new cell, causing its depol
*** In intercalated discs between neighbors
spans 1 membrane, int. cell space, next membrane

Question 4

Intercalated discs house

Answer 4

Gap Junctions

desmosomes

Question 5

desmosomes

Answer 5

hold adj. cells together so they can pull w/o tearing

Question 6

folds (in what)

Answer 6

inc SA, so more desmosomes and gap junctions

for more pulling

Question 7

How cardiac muscle differs from skeletal

Answer 7

much reduced
     fewer t tubules
     lessened SR extensive network
       1 triad per sarcomere
       extracellular calcium also plays role (never in skeletal)

Question 8

purkinje

Answer 8

lots of extensive branching

carry signal to many places

Question 9

Pacemaker

Answer 9

In cell wall of R atrium, always sending sequence
cells spontaneously discharge APs: 100-120/minute by themselves
When inbody, ANS regulate speed, more like 70 bpm (resting)
SA node, depol here first

Question 10

Bundle of His

Answer 10

R & L bundles connected by it

Transmits AP to bundle branches, Purkinje fibers, and muscles of ventricles (lower parts first, blood pushes up.)

Question 11

atria and ventricles

Answer 11

contract separate from each other

Question 12

EKG/ECG

Answer 12

APs of all active cells that are detected and recorded

Question 13

P wave

Answer 13

atrial depol (influx Na+)

Question 14

PQ interval

Answer 14

time between initiation and ending of contraction of atria, ventricle excitation

Question 15

QRS complex

Answer 15

repol of atria, deopl of ventricles

Question 16

ST

Answer 16

period of time when vents contract

Question 17

T wave

Answer 17

repolarization of ventricles (relaxation)

Question 18

sarcomere

Answer 18

thick and thin filaments overlap

Question 19

triad

Answer 19

terminal cisternae: lots of calcium

Question 20

t-tubule

Answer 20

fluid inside, where the release of calcium is ordered

Question 21

Conduction 1

Answer 21

AP starts at SA, impulse travels down acorss atria, causes more contraction

Question 22

Conduction 2

Answer 22

AV node
AV border: cells (not PM) make a maze for AP to slow down impulse by 0.1 sec so the atria can fully empty and the vents can fill

Question 23

3 AV bundles (bundle of His)

Answer 23

signal is traveling and insulated.

contraction begins at apex, goes toward base

Question 24

Cardiac Muscle APs

Answer 24

polarize, plateau, repolarize, return to resting potential

Question 25

Plateau

Answer 25

not in skeletal
LONG time (100 to 300 X longer break than skeletal)
in contracting state, due to Ca influx

Question 26

Don’t want tetnus in heart!

Answer 26

avoided by long contraction period and a longer refractory period

Question 27

Depolarization:

Answer 27

sodium influx

Question 28

Repolarization

Answer 28

close Ca gates, open K+ gates

Question 29

Refractory period

Answer 29

when muscle cell is unresponsive to stimulatin

Question 30

absolute refractory period

Answer 30

cell won’t respond regardles of stimulus strength

very ling, about as long as AP (250 ms)

Question 31

relative refractory period

Answer 31

cell will respond only if stim reaches suprathreshold

Question 32

Pacemaker potentials

Answer 32

autorhytmic
innitiate APs
Unstable resting potentials = pacemaker potentials
Calcium influx used to raise phase of AP (not sodium)
Threshold: -60 mV (unstable)
depol then imediate repol (no waiting)

Question 33

Pacemaker Gate opening

Answer 33

Voltage gated Ca+ ;ead to increased depol

Na, Ca, K (as opposed to cardiac muscle: Na, K, done only)

Question 34

start-P

Answer 34

atrial systole

Question 35

Q-T

Answer 35

ventricle systole

Question 36

T- end

Answer 36

relaxation of ventricles

this gets shorter as heart speeds up