Control of heart rate Flashcards
What does myogenic mean?
Where the heart can initiate its own contraction
Describe the heart beat
The SAN (sino atrial node) in the wall of the right atrium initiates an electrical impulse that spreads through conductive tissue through the Atria.
This causes the atria to contract, forcing blood into the ventricles.
The wave of exicitation is then detected by the AVN (atrio ventricular node) in the wall of the right atrium, which adds a short delay allowing the atria to empty.
The impulse then passes through the septum in the bundle of His to the apex of the heart.
Here the purkyne fibres carry the impulse up the outer walls of the ventricles causing the ventricle muscle to contract from the apex upwards.
What are chemoreceptors?
These are found in the aorta, the cartiod artery an the medulla.
They detect changes in blood pH.
How do chemoreceptors detect changes in blood pH?
When we aerobically respire the CO2 produced diffuses into blood plasma. Here it reacts with water, catalysed by carbonic anhydrase to produce carbonic acid.
CO2+H20. —-> H2 CO3
When the carbonic acid dissociated it forms H ion and CO3. The hydrogen ion will then diffuse into the red blood cells, bind to the haemoglobin forming haemoglobinic acid. This slightly alters the binding sites for oxygen, forcing the release of more oxygen- the Bohr effect.
What makes up the central nervous system?
Brain
Spinal cord
What makes up the peripheral nervous system?
Somatic (voluntary)
Autonomic (Involuntary)
Splitting off from autonomic:
Sympathetic (fight or flight)
parasympathetic (rest and digest)
What happens when blood pH falls?
The chemoreceptors send more frequent action potentials to the cardio-regulatory centre in the medulla.
The medulla responds by sending more frequent action potentials along the sympathetic nervous system to the SAN.
This leads to more neurotransmitter to be released onto the SAN, which increases heart rate.
What happens when blood pH increases?
Less frequent action potentials are sent to the medulla which then sends more frequent action potentials via the parasympathetic system, slowing the heart rate.
What are Baroreceptors?
They are found in the carotid artery and aorta, and detect blood pressure.
In response to an increase in blood pressure they cause the medulla to increase the frequency of action potentials via the parasympathetic system, slowing the heart rate.
