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AHN 568 UNIT 1 EXAM
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AHN 568 UNIT 1 EXAM 2024-2025Sinoatrial Node (SA)
Rate?
What are the location and area of intervention?
EKG? - ANSWER: Natural pacemaker of the heart
Rate: 60–100 bpm
Location: Upper posterior section of the Right Atrium, near the superior vena
cava.
EKG is depicted as the P wave.
The atrioventricular (AV) node
Rate?
Location? - ANSWER A specialized mass of conducting cells found at the
atrioventricular junction of the heart. (backup pacer for the heart)
Rate: 40-60 bpm.
Location: at the tricuspid valve.
Bundle of His
Rate?
ANSWER: route for electrical signals to be transferred to the v
entricles.
Rate: 40–45 b
pm
,Location: partly in the right atrium and upper portion of interventricular septum
that joins the AV node and two bundle branches.
Purkinjie fibres.
Rate? - ANSWER hair-like fibres that stretch out from bundle branches into the
ventricles; directly innervate cardiac cells; induce ventricular depolarization
Rate: 20–40 bpm.
Normal Conduction Pathway through the Heart: ANSWER SA Node
Interatrial Tracts
AV Node
Bundle of His
Bundle branches
Purkinje Fibers
resting membrane potential is the electrical charge that cardiac muscle cells
have at rest.
Depolarization is the change in the electrical charge of a stimulated cell from
negative to positive caused by the passage of ions; Na+ allows for
depolarization, except in the AV node, which is dependent on the slow-moving
Ca2+.
,Repolarization is the recharging of a cell to its usual polarity; K+ enables
repolarization.
action potential - ANSWER When cardiac cells change polarity, the electrical
impulse created generates an energy stimulation that goes across the cell
membrane
Which ion promotes contraction? - ANSWER: Calcium
ANSWER Phase 4: Resting State.
Closed Na+ and Ca2+ channels; increased K+ permeability allows for a new
cycle.
ANSWER Phase 0: Rapid depolarization.
Opening of voltage-gated fast Na+ channels; cell fires to commence
transmission of an electrical impulse.
Phase 1 - Answer: Depolarization.
Peak positive charge: K+ closes, Cl- enters slow channels, and slow Ca2+
channels open.
Phase 2: Plateau
The membrane potential is maintained or plateaued by opening voltage-gated
slow Ca2+ channels and closing certain K+ and Na+ channels.
ANSWER Phase 3: Re-polarization
, Voltage-gated K+ channels open, Ca2+ channels close, and K+ flows from ICF
to ECF.
Refractory periods - ANSWER time from phase 0 till myocyte repolarization or
when enough Na+ has recovered.
Absolute refractory periods - ANSWER occurs during the early part of the T-
wave, when the majority of the ventricle is depolarized and "refractory" to fresh
stimuli.
Relative refractory periods - ANSWER occurs toward the end of the T-wave
when most ventricular cells are repolarized and sensitive to new stimuli; can
lead to VT if PVC lands during this time.
Refractory means resistive.
Normal P Wave - ANSWER Measures: 0.5 to 2.5mm high
< 0.12 seconds in width.
Every QRS complex has one P wave, which represents depolarization of the SA
node, implying atrial depolarization (and contraction). It is smooth and rounded,
with an upright position in lead II.
Normal QRS - The normal measurement/duration is less than 0.12 seconds, or
three boxes. Contains the Q wave, R wave, and S wave. Denotes ventricular
depolarization (and contraction) and atrial repolarization.
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