Control of Heart Rate Flashcards
(11 cards)
What is meant by the heart being described as myogenic?
The cardiac (heart) muscle is myogenic meaning contraction is initiated by the muscle itself, without receiving signals from nerves.
How are the heart’s contractions controlled?
The sinoatrial node (SAN) sets the frequency of the contractions. It sends out regular electrical impulses to the atrial walls, causing the atria to contract.
What is the process of a contraction?
1) SAN generates an electrical impulse.
2) Electrical impulse spreads from SAN across both atria, causing them to contract simultaneously.
3) The septum prevents the impulse from crossing to the ventricles.
4) The impulse reaches the atrioventricular node (AVN).
5) After a short delay, the AVN passes on the impulse to the bundle of His fibres, which conduct the impulse down to the Purkyne fibres.
6) Impulse reaches the Purkyne fibres at the heart apex, which carry the impulse up to the walls of the ventricles, causing them to contract simultaneously, from bottom up.
What is the reason for the short delay at the atrioventricular node (AVN)?
The short delay is to allow the atria to be emptied before the ventricles contract.
How is heart rate controlled?
The autonomic nervous system controls heart rate. The rate at which the SAN generates impulses is controlled by the Medulla Oblongata in the brain.
Electrical impulses from the receptors are sent to the Medulla via sensory neurons, which processes info and sends impulses to SAN via sympathetic or parasympathetic neurons.
Which neurotransmitter is released if an impulse is sent by a parasympathetic neuron?
Acetylcholine
Which neurotransmitter is released if an impulse is sent by a sympathetic neuron?
Noradrenaline
What are some possible stimuli which would trigger a parasympathetic response?
High blood pressure, high O2, or low CO2 and high pH.
What would happen if these stimuli are detected?
Chemoreceptors detect the stimulus and send more impulses to the medulla which processes the info and sends impulses to the SAN via a parasympathetic neuron. This releases acetylcholine which binds to receptors on the SAN which sends impulses at a lower frequency.
This results in a decreased heart hate which decreases blood pressure, decreases O2, or increases CO2 and decreases pH.
What are some possible stimuli which would trigger a parasympathetic response?
Low blood pressure, low O2, or high CO2 and low pH.
What would happen if these stimuli are detected?
Chemoreceptors detect the stimulus and send more impulses to the medulla which processes the info and sends impulses to the SAN via a sympathetic neuron. This releases noradrenaline which binds to receptors on the SAN which sends impulses at a higher frequency.
This results in an increased heart hate which increases blood pressure, increases O2, or decreases CO2 and increases pH.
