Gap junction One gap junction channel is composed of two connexons or hemichannels) which connect across the intercellular space 11)
Gap junction One gap junction channel is composed of two connexons (or hemichannels), which connect across the intercellular space. 11
Sequence of cardiac excitation Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Atrial excitation Ventricular excitation Ventricular relaxation Complete Begins Complete SA node AV node Atrial relaxation Time Ti Time Time Time Electrocardi
Sequence of cardiac excitation 12
Sinoatrial node (Sa node Located in the right artium Fire off action potentials at a regular and intrinsic rate Both parasympathetic and sympathetic neural input can modulate its pacemaker activity, or automaticity The existence of discrete conducting pathways in the atria is still disputed. The signal arrives to th left atrium and atrioventricular node(av node)
Sinoatrial node (SA node) • Located in the right artium. • Fire off action potentials at a regular and intrinsic rate. • Both parasympathetic and sympathetic neural input can modulate its pacemaker activity, or automaticity. • The existence of discrete conducting pathways in the atria is still disputed. The signal arrives to the left atrium and atrioventricular node (AV node). 13
Transmembrane SAN potentials recorded in AM different heart AVN regions BH PF TPF 300600ms
Transmembrane potentials recorded in different heart regions 14
The membrane currents underlying cardiac action potentials The Nat current(INa): is responsible for the rapid depolarizing phase of the action potential in cardiac muscle cells and in Purkinje fibers The Ca current(ca): is responsible for the rapid depolarizing phase of the action potential in the sa node and av node; also triggers contraction in all cardiomyocytes The k* current (k): is responsible for the repolarizing phase of the action potential in all cardiomyocytes The pacemaker(Funny) current(f): is responsible, in part, for pacemaker activity in SA nodal cells, av nodal cells and purkinju fibers; is mediated by a nonselective cation channel
The membrane currents underlying cardiac action potentials • The Na+ current (INa): is responsible for the rapid depolarizing phase of the action potential in cardiac muscle cells and in Purkinje fibers. • The Ca2+ current (ICa): is responsible for the rapid depolarizing phase of the action potential in the SA node and AV node; also triggers contraction in all cardiomyocytes. • The K+ current (IK ): is responsible for the repolarizing phase of the action potential in all cardiomyocytes. • The pacemaker (Funny) current (If ): is responsible, in part, for pacemaker activity in SA nodal cells, AV nodal cells and Purkinju fibers; is mediated by a nonselective cation channel. 15