Electrical Activity in the heart Flashcards
What else happens as calcium moves in during ECC?
calcium moves out of cell via Na/Cl pump to ensure a steady state stability over time
What are the two challenges in relation to contraction?
- contraction must be synchronised
2. atria must contract before ventricles
What enables the synchronicity of contraction?
gap junctions
what regulate the strength of contraction?
number of gap junctions, also the more gap junctions the faster the contraction
What initiates the contraction of the heart?
an intrinsic electrical system composed of specialised myocytes
Specifically, the sino atrial node
What is the SAN and where is it located?
strip of myocytes roughly 20mm long and 4mm wide , located on the posterior wall of the right atrium, close to the superior vena cava
Why is SAN deemed the pacemaker of the cell?
The group of cells discharge spontaneously in regular intervals to initiate a heart beat
nerves linked to SAN
does not depend on extrinsic nerve supplies, however the rate of depolarisation can be altered parasympathetically of sympathetically
Why are the SAN cells best suited for their role?
the small myocytes have scanty myofibrils and an unstable membrane potential which is capable of spontaneous depolarisation
unstable membrane potential due to the lower number of inwardly delayed rectifying potassium channels
Function of AV node
allows conduction of electricity through the otherwise non-conductive annulus fibrosus
delays the impulse by around 0.1s at resting heart rates
How does the AVN delay the impulses?
complex local circuitry and the small diameter of nodal cells
Explain structure and function of ventricular conducting system
bundle of His- bundle of fast conducting muscle fibres convey the electrical impulse from the AVN to the fibrous part of the interventricular septum . This then splits off into two branches, the left and right into both ventricle bases. End in subendocardial myocytes
purkinje fibres- distribute the impulse rapidly to the subendocardial myocytes
relative conduction velocities at each stage
SAN- medium - 1m/s
AVN- low- 0.005m/s
bundle of His- fast
Purkinje- fastest- 3-5/s -
why are purkinje fibres the fastest?
have the widest cells in the heart
Experiment to prove the myogenic contractility of the heart
place the heart in ringer solution- will contract on its own