CS - Heart part 2

• Return by way of the:
• great cardiac vein
• posterior interventricular (middle cardiac) vein
• left marginal vein
• coronary sinus - collects from other veins and dumps into the right atrium
• anterior cardiac veins - also directly into the cardiac vein

around 75 beats per minute in an adult

It means that the signal originates with the heart itself. So if its cut up it will still beat.

The sympathetic are the cardiac nerves and they go to the ventricle. These increase the force of contraction and help to dilate the coronary vessels during excersize. Can increase HR up to 230 beats/min.

The parasympathetic are the vagus nerves. They help to give the heart it vagus tone, which helps keep the heart at its normal HR. So it slows the heart down. If the vagus is cut the heart rate will increase to about 100 beats/minute.

• 1. Startes at the SA node in the right atrium where it spreads through the atria
• 2. It then goes the the AV node that is near the right AV valve - this is the electrical gateway to the ventricles
• 3. From the AV node the signal goes to the AV bundle - there are 2 branches the right and left that go towards the apex of the heart
• 4. From the bundle the signal travels to the purkinje fibers which are at the end of the AV bundle branches and go tot the myeocytes of the ventricles
• 5. From the fibers the signal finally ends in the individual myocytes (the heart cells) where the signal is passed from one cell to another.

• - short and thick
• - have large T tubules that allow Ca ++ enter which is key to the HR
• - large mitochondria
• - joined together by intercalaated discs

1. Interdigitating folds that help to increase the contact area

2. Mechanical junctions that enable myocytes to pull on each other without pulling apart

3. Electrical junctions that have gap junctions that allow the flow of ions from one cell to another. This allows the myocardium to contract as one, helps for maintaining heart pump.

Cardiac muscle

Systole is contraction

Diastole is relaxation

between 70 to 80 bpm but can range from 60 to 100 bpm

Its when the system fires before the SA node.

is any region that is firing other than the SA node

Most common is the AV node

Its when the HR is slower at around 40 to 50 bpm anything lower than that requires a pacemaker

Is any abnormal cardiac rhythm like:

• Atrial flutter - 200 to 400 bpm in the atria
• PVC's
• Ventricular fibrillation - a strong electrical shock that is deadly if not corrected and is treated with
• AED

A heart block which happens when any part of the conduction system does diliver its signal

A bundle branch block and a total heart clock which happens when damage to the AV node occurs.

Pacemaker physiology

ITs that gradual depolarization of the SA node.

Na+ goes slowly in until it reaches the threshold of -40mV. Ca++ goes in threw Ca+ channels from ECF. It then reaches action potential and K+ starts to flow out cause repolarization until the K+ gate close and the cycle starts over again.

***Ca++ allows for longer contration verses skeletal muscle so a longer platau***