Action Potentials (Wed 18th) Flashcards
How does the heart contract?
The heart has intrinsic ability to contract, it does not need any external input to work, unlike muscle contraction. This is due to the Sino Atrial Node on right atria made of pacemaker cells.
How does the spread of electrical activity happen in the heart?
The spread of excitation happens in two ways:
- cell to cell using gap junctions
- conducting fibres
Why is there no fibrous electrical communication between the atria and ventricles?
There is a fibrous, non-conducting, layer between atria and ventricles which electrically insulates the chambers from each other
What are the steps that cause contraction in the heart?
First depolarisation spreads, then contraction, then re-polarisation.
Neurotransmitters in neural stimulation are?
The parasympathetic nerve uses acetylcholine. The sympathetic nerve uses nor-adrenaline.
What are chronotropic effects?
The affect of the ANS on heart rate.
How does sympathetic stimulation affect the heart rate?
Sympathetic stimulation causes the RMM to be higher, and steeper. Makes the funny calcium channels to be active.???
Tachycardia
Heart rate above 100
How does parasympathetic stimulation affect the heart rate?
The slope is less steep, and starts from more hyper-polarised, so takes longer to reach threshold. Uses potassium, which opposes sodium movement.
Bradycardia?
Heart rate less than 60 BPM
What is vagal tone?
The constant release of small amounts of acetylcholine slows HR via SAN cells and improves dynamic range.
What is the refractory period?
The period of time another action can’t be generated.
Tetany?
The sustained contraction of a muscle, like holding a heavy weight for a long time.
What happens to the heart under sustained tetany?
If only have one release of blood/ stroke volume, there is no flow of blood, no pressure gradient and die. There is a mechanism to prevent sustained tetany in the heart.
What is calcium induced calcium release?
More calcium released, equals more contraction.
