lecture 17,18-

Question 1

What are cardiomyocytes ?

Answer 1

cardiac muscle cells
striated appearance
regularly repeating sarcomeres composed of thick and thin myofilaments arranged in orderly parrallel manner
small + nucleus
adjacent cells are joined via intercalculated disks hold these cells together ;contain gap junctions

Question 2

What is the function of the cardiomyocytes ?

Answer 2

adjacent cells electrically coupled via gap junctions cells form
synctium: permit the electrical aactivity to spread from 1 cell to another
1% -conducting cells

Cardiac muscle: cells are cylindrical and striated;
single central nucleus; intercalated disks.

Question 3

What is heart beat coordination ?

Answer 3

both sides of heart contract in unison
The atria contract together first; then, the ventricles contract.
* This coordinated (atrial, then ventricular) contraction is essential for
effective blood pumping.
* The heartbeat originates in cardiac muscle:
o Depolarisation is initiated in the sinoatrial node (SA node):
o Located in right atrium, near entrance of superior vena cava.
o SA node is the heart’s pacemaker → determines heart rate.

Question 4

process of conduction ?

Answer 4

1. atrial muscle cells depoalrise due to spread of spontaneous depolarisation from SA node –> atria contract in unison
2. depolarisation quickly reaches AV node but AP propagation through AV node is quite slow
   Why? No gap junctions between atria & ventricles → AP cannot spread directly:
   o Atria and ventricles are electrically separate, except at
   AV node and Bundle of His .
   o AV node is responsible for the sequencing of contraction
3. depolarisation of AV node enables AP to propagate through
   the interventricular septum via the Bundle of His:
   o Bundle of His divides into right and left bundle branches.
   o Branches enter ventricular walls and spread through them; they
   are composed of Purkinje fibres connected by gap junctions:
   o Purkinje fibres of the conducting system rapidly spread the
   wave of depolarisation through the ventricular myocardium.
   o Result: the ventricles contract simultaneously:

Question 5

What is pacemaker potential and what are the ion channels involved ?

Answer 5

Note: SA node cell’s ‘unsteady’ RMP → cell undergoes a slow, gradual depolarisation known as the pacemaker potential:i. …Progressive reduction in K+
permeability: voltage-gated
K+ channels gradually close…
ii. F-type (‘funny’) Na+ channel:
open at negative membrane
potentials → conduct inward,
depolarising Na+ current (#1).
iii. Also, open (briefly; are T-type,
‘transient’) Ca2+ channels:
inward Ca2+ current (#1)

Question 6

ion channels involve what ?

Answer 6

Once threshold has been reached
once pacemaker mechanisms have brought a SA nodal cell threshold ,an AP occurs
Voltage-gated K+ channels then open (slowly) → K+ exits the cell → Thus, SA node cell membrane repolarises