Physiology of the heart (non-timetabled)

Question 1

Describe cardiac muscle

Answer 1

Muscle cells branch and are connected together by desmosomes (cell-cell adhesion molecules) at the junction between cells (intercalated discs). These intercalated discs also contain gap junctions that directly connect the cytoplasm and permit the easy transfer of ions between cells

Electrical connection through gap junctions - allow passage of ions permitting APs to spread

Question 2

Describe the conduction in cardiac muscle

Answer 2

Functional syncitum

• Cells of atrial myocardium are all electrically connected
• Depolarise and contract in sync
• Ventricles are similar but separate functional unit

Conduction network - 1% fibres don’t contract but form excitatory and conductive muscle fibres

Pacemaker - SAN but other areas have pacemaker ability

Autonomic innervation - symp increase rate of SAN depolarisation and parasymp decerase rate of SAN depolarisation

Co-ordinated electrical activity - pacemaker SAN starts the process and depolarisation spreads around atria first and then ventricles