Midterm 1 - Cardiac Function and Control Flashcards
what are the 2 types of muscle cells that compose the myocardium
contractile cells
auto rhythmic cells
what percentage of cells in myocardium physically contract
99%
what is require for contraction
action potential
what are autorhythmic cells
modified non-contractile cells
where are autorhytmic cells
concentrated in specific regions of the heart
what do autorhytmic cells do
spontaneously generate action potential - pacemaker
what are gap junctions
water-filled pores that form open connections between adjacent cells
what do gap junctions allow
for ion to move freely from one cell to another - electrical activity can pass from cell to cell
what do the gap junctions have no need for
no need for synapse - allow AP to jump rapidly through cells
what is the electrical conduction system generated by
pacemaker cells - auto rhythmic
what is the Sino-Atrial (SA) node
the command centre (determine heart contraction)
what does the SA node do
rhythmical self excitation
what is the difference between SA and AV nodes
AV nodes have slower pace, therefore under SA control
do both AV and SA nodes have auto rhythmic activity
yes
what is AV node a gateway for
electrical conduction between atria and ventricle
what does the bundle of His and Purkinje fibers help
to quickly propagate electrical activity from the AV node to the rest of the ventricles
what is the role of the electrical system
maintain appropriate heart rate
coordinate contraction of atria and ventricles
coordinate contraction of each chamber
what is the clinical relevance of the electrical system
use ECG to determine heart rhythm
problems with conduction - abnormal rhythm (arrhythmia)
during contraction, where do APs from auto rhythmic cells propagate to
the contractile cells
what is responsible for muscle contraction
action potentials in contractile cells
due to the gap junction, what can the heart be considered
a functional syncytium
do to the gap junction, what rule does contraction follow
all or none rule
how does the action potential of contractile cells differ from auto rhythmic
stable resting membrane potential (no drift)
how does the action potential of contractile cells differ from skeletal muscle AP
duration
length of refractory period
duration of skeletal muscle AP
very short, milliseconds
duration of contractile muscle AP
long, 100s of milliseconds
does skeletal muscle have a shorter or longer refractory period than cardiac muscle
shorter
what is the effect of the sympathetic nervous system
stimulates heart rate
increases contractile force
reduces the contraction time
how does the SNS stimulate the heart rate
stimulates the firing of the SA node and the velocity of the AV node conduction (shorter delay)
how does the SNS increase contraction force
increase release of Ca2+ from sarcoplasmic store, which increases strength
how does the SNS reduce contraction time
increases speed of Ca2+ transport (reduces plateau length)
what is present in all cardiac cells associated with SNS
actions mediated by epinephrine/norepinephrine on B-adrenegic receptors
effect of the parasympathetic nervous system (vagus nerve)
decreases heart rate
how does the PSNS decrease heart rate
reduce SA node firing and decreases the velocity of the AV node conduction (longer delay)
what occurs in auto rhythmic cells due to PSNS
actions mediated by binding of acetylcholine on muscarinic receptors - increase in K+ permeability and hyper polarization increase time required to reach the AP threshold
where is the current conducted from heart cells firing AP simultaneously
through body fluid to skin
what does an ECG do
measure heart membrane potential throughout cardiac cycle
what do electrodes do in ECG
they are placed at different location on skin to read progression of the electric current wave
how many waves does a standard ECG have
3
what are the 3 waves of an ECG
P wave
QRS wave
T wave
what does the P wave on an ECG show
depolarization of atria
what does the QRS wave show on ECG
depolarization of the ventricles
what does the T wave on an ECG show
depolarization of the ventricles
what is the base-apex lead configuration
one lead on left chest, second lead over the neck in jugular groove
what does the shape of an ECG depend on
where electrodes are placed
2 uses of an ECG
assessment of heart rate and rhythm
detection of abnormalities
how does an ECG measure heart rate
measure intervals between cycles
how does an ECG measure contraction force
measure amplitude of waves
how does an ECG measure rhythm
measure intervals between each waves
how does an ECG detect abnormalities
by measuring heart rate under resting conditions
rhythm
what is bradycardia
slower rate
what is tachycardia
faster rate
what are problems with rate generally associated with
the SA node… pacemaker is an artificial SA node
how does an ECG detect rhythm
abnorally long P-Q interval
ectopic beats (extrasystole)
what does an abnormally long P-Q interval mean
AV conduction problem
what do ectopic beats (extrasystole) mean
action potential generated independently of the SA node which results in ventricular extracontraction
