PHYSIOEX Lab 6 Exercises 1-5 Flashcards
skeletal muslce is unique in that
it requires depolarizing signals from the NS to contract
Define autorhymicity
the heart’s ability to trigger its own contraction
autorthymicity occurs because the plasma membrane in cardiac pacemaker muscle cells has
reduced permeability to potassium ions but still allows sodium and calcium ions to slowly leak into the cells
leakage from autorthymicity causes the muscles to….
slowly depolarize until the action potentional threshold is reached and L-type calcium channels open, allows Ca+ entry from the extracellular fluid
what are the five phases of membrane polarization in cardiac action potential
PHASE 0 PHASE 1 PHASE 2 PHASE 3 PHASE 4
describe Phase 0
depolarization causes voltage-gated sodim channels in the cell membrane to open, increasing the flow of sodium ions into the cell and increasing the membrane potential
describe Phase 1
the open sodium channels begin to inactivate, decreasing the flow of sodium ions into the cell and causing themembrane potential to fall slightly. voltage-gated potassium channels close and voltage-gated calcium channels open. decrease in potassium out of cell and increase of calcium into cell act to depolarize the membrane and curb the fall in membrane potential caused by the inactivation of sodim channels
describe Phase 2 aka plateau phase
membrane remains in a depolarized state. potassium channels stay closed, and long lasting (L-type) calcium channels stay open.
describe Phase 3
membrane potential gradually falls to more negative values when 2nd set of potassium channels begin opening. phase 1 and 2 allows significant amounts of potassium to flow out of the cell. this falling membrane potential causes calcium channels to close, reducing flow of calcium into the cell and repolarizing the membrane until resting potential is reached.
describe Phase 4
resting membrane potential is again established in cardiac muscle cells and is maintained until the depolarization arrives from neighboring cardiac pacekmaker cells
how long does total cardiac action potential last
250-300 milliseconds
wave summation occurs when
a skeletal muscle is stimulated with such frequency that muscle twitches overlap and result in a stronger contracting than a single muscle twitch
define absolute refractory period
action potentials cannot be generated no matter how strong the stimulus
T/F: cardiac muscle has a relatively long refractory period and is thus INCAPABLE of wave summation
TRUE
the cardiac muscle is INCAPABLE of reacting to any stimulus before the middoe of Phase ____ and will not respond to a normal cardiac stimulus before Phase _____
3
4
the period of time between the beginning of the cardiac action potential and the approximate middle of phase 3 is
the absolute refractory period
the period of time between the absolute refractory period and Phase 4 is the
relative refractory period
Q: the cardiac muscle is capable of which of the following
autorhymicity
Q: Phase 2 of the cardiac action potential, when the calcium channels remain open and potassium channels are closed, is called
plateau phase
Q: which of the following is true of cardiac action potential
the cardiac actionpotential is longer than the skeletal muscle action potential
Q: the main anatomical difference between the frog heart and the human heart is that the frog heart has
single fused ventricle
at rest both sympathetic and parasympathetic NS are working bu the ____________ branch is more active
parasympathetic
what nerve carries signal to heart
vagus
T/F: if stimulation is excessive the heart will stop beating?
TRUE
define Vagal escape
the resumption of the heartbeat
Vagal escape can be the result of sympathetic reflexes or initiation of a rhythm by the
Purkinje fibers
define Sinoatrial (SA) nodes
cluser of autorhythmic cardiac cells found in the right atrial wall in the human heart.
why is the SA node referred to as the heart’s pacemaker
it has the fastest rate of spontaneous depolarization, for that reason, it determines the heart rate.
in the absence of what will the SA node generate action potentials 100 times per minute
abence of
parasympathetic stimulation
sympathetic stimulation
hormonal controls
Q: the effect of the parasympathetic NS on the heart is to
decrease the heart rate
the branch of the autonomic NS that dominates during exercise is the
sympathetic
Q: parasympathetic stimulation reaches the heart through
vagus nerves, which are cranial nerves
Q: the usual pacemaker of the heart is
sinoatrial node
define homeothermic
the human body’s internal temp within 35.8 - 38.2 degree C even though external temp is changing
when temp is elevated, what signals to active heat-releasing mechanisms?
hypothalamus
define Poikilothermic
internal body temp changes depending on the temp of its external environment because it lacks internal homeostatic regulatory mechanisms (frog)
Define Ringer’s solution
consists of essential electrolytes in a physiological solution and is required to keep the isolated, intact heart viable.
Q: organisms that usually maintain the same internal body temp in spite of environmental temp changes
homeothermic
Q: the general name for the process that maintains the internal body temp in humans is
homeostasis
Q: the electrolytes in a Ringer’s solution are required
prodvide for autorhythmicity
Q; an internal body temp that is above the normal is
hyperthermic
when the sympathetic NS is activated in times of flight or fight the nerve fibers release what at their cardiac synapses
norepinepherine and epinephrine
what do norepinephrine and epinephrine increase the frequency of what and how
action potentials by binding the B1 adregenic receptors embedded in the plasma membrane of the SA node
what does the parasympathetic nerve fibers release
acetylcholine at their cardiac synapses
what does acetylcholine decrease the frequency of what and how
action potentials by binding the muscarinic cholinergic receptors embedded in the plasma membrane of the SA node cells.
define cholinergic
chemical modifiers that inhibit, mimic or enhance the action of acetycholine in th ebody
define adrenergic
chemical modifiers that inhibit, mimic, or enhance the action of epinephrine in body
define agonist
the modifier works in the same fasion as the neurtransmitter
define antagonist
the modifier works in opposition to the neurotransmitter
Q: the parasympathetic NS releases ______ to affect heart rate:
acetylcholine
Q: a cholinergic drug that worked the same as acetylcholine would be an
agonist and decrease heart rate
Q: norepinephrine affects the heart rate by
increasing the rate of depolarization and increasing the frequency of action potentials
Q: the ______ receptor binds norepinephrine and epinephrine
B1 adrenergic
permeability changes that occur for the cardiac muscle cell involve
potassium
sodium
calcium ions
concentration of potassium is greater ______ the cardiac muscle cell than _________ the cell
inside the cell
than outside the cell
sodium and calcium are present in larger quantities _________ the cell than ___________
outside the cell
than inside the cell
resting cell membrane favors the movement of ____________ more than ________ or ______________
potassium
sodium or calcium
defgien chronotropic
modifiers that affect heart rate
define inotropic
modifiers that affect the force of concentration
modifiers that lower heart are called
negative chronotropic
modifiers that increase the heart rate are called
positive chronotropic
negative inotropic drugs __________ the force of contraction of the heart
decrease
positive inotropic drugs ___________ the force of contraction of the heart
increase
Q: which organelle in the cardiac muscle stores calcium
sarcoplasmic reticulum
verapamil is a calcium-channel blocker. its effects could be described as
negative chronotropic and negative inotropic
Q: when the cardiac muscle cell is at rest, where is the most potassium found
in the sarcoplasmic reticulum
Q: resting cardiac muscle cells are most permeable to
potassium
