What is normal membrane resting potential range?
-60 to -90 mv
What is the resting membrane potential dependent on?
1. Transmembrane distribution of electrolytes 2. Increased permeability to K+ 3. The Na+/K+ pump
What is the ICF and ECF Na+ levels in mEq
ICF= 10 mEq; ECF= 144 mEq
What is the intracellular concentration and electrical gradient for Na+?
Concentration gradient is inward, electrical gradient is inward
What is the normal ICF and ECF K+ levels in mEq?
ICF = 150 mEq; ECF = 5 mEq
What is the concentration and electrical gradient for K+?
Concentration gradient is outward and electrical gradient is in
What is the cellular membrane permeability for Na+ and K+?
Na+= low; K+= high
What is the normal ICF and ECF Cl levels in mEq?
ICF = 4 mEq; ECF = 107 mEq
What is the cellular membrane permeability for Cl-?
What is the normal ICF and ECF Ca+ levels in mEq?
ICF = Low; ECF = 1.2 mmol
What is the cellular membrane permeability for Ca+-?
What is the concentration and electrical gradient for Cl-?
Concentration gradient is inward and electrical gradient is outward
What is the concentration and electrical gradient for Ca?
Inward concentration, inward electrical
What is the normal ICF for anions in mEq?
What is the concentration and electrical gradient for anions?
Concentration outward; electrial outward
What is the cellular membrane permeability for anions?
Which has greater permeability, K+ or Na+?
K+ permeability is 50-100 greater than Na+.
What is an action potential?
Depolarization initiated by changes in cell permeability
to Na+ and Ca++.
Explain the difference between fast and slow channels during the action potential?
FAST: threshold potential -65 mV, allows rapid
entry of Na+; SLOW threshold potential -30 mV, allows
slow entry of Ca++.
Explan Phase O of the AP.
Na+ influx via fast channels, + 20mV
P wave & QRS complex.
initial rapid repolarization, Na+ channels close,
plateau, -0 mV, Ca++ influx & start of K+
What represents Phase 1-2 on the ECG?
K+ efflux (Ca+ gates closed), return to
RMP T wave.
RMP reestablished via Na+/K+ pump.
Absolute Refractory Period
(ARP) - Phase 0,
1,2 and initial phase 3 (+20 to -50 mV).
- membrane unexcitable.
Relative Refractory Period (RPP)
3 and early phase 4 (-50 to -90 mV).
- membrane responsive to strong stimulus .
Effective Refractory Period (ERP):
ARP and RRP
End of RPP (phase 3/4).
membrane unstable, responsive to weak stimulus.
T wave on EKG.
What does increased automaticity show on the AP phases?
increased slope phase 4; decreased RMP (less neg); decreased threshold (more neg)
What does decreased automaticity show on the AP phases?
decreased slope phase 4; increased RMP (more neg); increased threshold (less
What does the sympathetic NS do to automaticity?
increases Na+ and Ca+ permeability increases
slope of phase 4.
What does the parasympathetic NS do to automaticity?
increases K+ permeability (hyperpolarization) decreases
slope of phase 4, increases threshold
What does increased excitability result in?
shortened ERP; prolonged SNP; decreased threshold (more neg)
What does decreased excitability result in?
prolonged ERP; shortened SNS; increased threshold (less neg)
ability to respond to an impulse
ability to transmit an impulse
Conduction is velocity dependent upon:
Rate of rise of AP
Both amplitude & rate of rise are related to the
Increased conductivity results in...
increased RMP (more neg); increased amplitude
Decreased conductivity results in...
decreased RMP (les neg); decreased amplitude
What does the impulse of the heart travel the slowest through
The purkinje fibers
Where is conduction time between structures the slowest?
From the AV node to the bundle of his (interval is .11 seconds) accounts for p-r interval
What is conduction time between all of the other structures?
About 0.03 to .04 seconds
What is AV node delay
conduction slowest in
fibers that connect atrial fibers with AV node
What factors influence the AV node delay?
small size of fibers.
small # tight junctions at intercalated disks.
embroyonically less well differentiated.
What differentiates the AV node from the purkinje fiber system?
Purkinje fibers - larger with large # tight
junctions immediate transmission of
impulses throughout ventricles
What is the rate of the SA node?
What is the rate of the AV node?
What is the rate generated from the bundle of his?
What is the rate generated by the bundle branches?
What rate is generated by the purkinje fibers?