Electrophysio Of Heart

Question 1

IONIC CURRENTS IN
CARDIAC TISSUES

1. The largest current in cardiac tissues, especially in ventricular muscles, atrial muscle and Purkinje fibers.
2. INa current is not present in
   ______ or _______
3. The ion channel responsible
   for INa is a _______-gated ______ channel, they are always fast sodium channels.

Answer 1

Na+ Current (INa)
SA or AV nodal cells.
3. Voltage, Na+

Question 2

Activation of Na+ Channels

1. The Na+ channels are ______ at RMP of the ventricular muscle cells but rapidly activated in response to stimulation by impulses from the _______.
2. Activation of Na+ channels results in the opening of the ________
   gate which produces a massive
   inward flow of Na+ that results in rapid upstroke of the fast response action potential.
3. The ________ gate closes
   at the end of ________ that stops Na+ influx (inactivation of Na+ channel).

Answer 2

1. Closed, pacemaker
2. outer (activation) gate
3. inner (inactivation) gate, depolarization

Question 3

Inactivation of Na+ Channels

1. If the membrane potential
   becomes ________, these
   channels close automatically, the process known as _________.
2. Partly responsible for *the rapid
   repolarization of the action
   potential in phase ____.

Answer 3

1. Positive, autoinactivation
2. Phase 1

Question 4

Importance of INa

The action potential is produced
by the ________.

This Na+ current also
activates other membrane
currents like calcium (ICa) and
potassium (IK) currents.

2. _________ drugs, such as
   lidocaine, exert their effect by
   partly blocking INa

Answer 4

1. Na+ current
2. Antiarrhythmic

Question 5

The calcium current exists in all cardiac tissues due to the presence of calcium channels.

There are two types of voltage-gated calcium channels:
1. __________
The long-lasting voltage-gated Ca2+ channel, not a fast channel.
Present in all cardiac tissues including cardiac myocytes, SA node, AV node, and His-Purkinje system. It contributes to the action potential of pacemaker tissues, myocytes, and other tissues

Answer 5

1. Ca++ Currents (ICa)
2. L-type Ca2+ Channels (ICaL)

Question 6

In ventricular and atrial muscles
and the Purkinje fibers, ICaL is
responsible for state of _________ ___________that results in the
prolonged _______ phase.

2. The Ca2+ that enters via _______
   _______ channels activates the release
   of Ca2+ from the sarcoplasmic
   reticulum by stimulating calcium induced Ca2+ release.
3. _____________ like
   verapamil, diltiazem, and nifedipine
   act by inhibiting L-type Ca2+
   channels

Answer 6

1. sustained depolarization, plateau
2. L-type Ca2+ channels
3. Calcium channel blockers

Question 7

In the pacemakers, ICaL is responsible for the _______ or ________ of the SA and AV nodal action potentials.

The slower and less steep upstroke contributes to the ______ of the conducted action potential, which is much slower than that of any other cardiac tissue

Answer 7

1 upstrokes or depolarization
2. speed

Question 8

Transient type voltage gated Ca2+ channel

Present only in SA node and AV node.

They are responsible for later part of the _______ (gradual depolarization) or
_______ potential.

Answer 8

1 T-type Ca2+ Channel (ICaT)
2 prepotential, pacemaker

Question 9

K+ currents (IK)
Voltage-gated K+ channels

Voltage-gated channels
that maintain resting membrane potential (phase 4) of cardiac muscle by
allowing at highly _______ membrane potential

Answer 9

1. Inward Rectifying K+ Channels, outflux of
   K+, negative