Control of Heart Function Flashcards
What three categories can the main anatomical components of the heart be categorized into?
- Muscle cells - cardiomyocytes
- Specialised electrical cells
- Vessels
Which cell type in the heart is most prominent in controlling heart function?
Electric cells
What is the pacemaker of the heart?
The Sinoatrial Node
What limits does the SAN work to keep the heart rate between?
60-100 bpm
Where is the SAN found?
At the junction of the cristae terminalis, upper wall of right atrium and opening of superior vena cava
What is the name given to the tracts between the SAN and the AV Node?
Internodal tracts
What is the tract which runs down the intraventricular septum?
Bundle of His
What are the fibres which project upwards around the ventricles from the apex of the heart?
The Purknje Fibres
Where is the AVN found?
At the triangle of Koch at the base of the right atrium
What are purkinje fibres?
Specialised conducting fibres
Does the AVN have pacemaker activity?
Yes - slow calcium mediated action potentials
What are the three main souces of control of the heart?
The kidneys, the central nervous system and the blood vessels
Which three phases does a nodal action potential have?
0, 3 and 4
What is phase 0?
The upstroke phase
What is Phase 1?
early repolarisation
What is phase 2?
Plateau phase
What is phase 3?
repolrisation
What is phase 4?
Resting in cardiac tissue, pre-potential in SAN
What causes the upstroke (Phase 0) in nodal cells?
The influx of calcium from outside the nodal cell into the nodal cell
What causes the repolarisation seen in nodal cells?
Due to K+ efflux
What causes the pre-potential seen in SAN?
The slow flow of Na+ through a funny channel
How does the length of a cardiac muscle action potential differ from a nerve action potential?
Cardiac muscle action potential is much longer - 200-300ms compared with 2-3ms
What does the duration of the cardiac muscle action potential control?
The duration of the contraction of the heart
What type of contraction is required to produce an effective pump?
Long and slow contraction
How may phases does the Cardiac Muscle action potential have?
5
What are the 5 phases of the cardiac muscle action potential?
Phase 0 - Upstroke Phase 1 - Early Repolarisation Phase 2 - Plateau Phase 3 - Repolarisation Phase 4 - Resting Membrane potential
What is meant by the absolute refractory period?
The period in which no Action Potential can be initiated regardless of stimulus intensity - this limits the rate at which the heart can beat at
What is the relative refractory period?
Period of time after the absolute refractory period in which the heart can elicit another action potential if a large enough stimuli is provided
Why is the plateau phase of the cardiac muscle cell action potential so important?
L type Ca2+ Channels open slowly resulting in Ca2+ influx, which maintains the cell at the level of depolarisation - this is essential for generating a large force of contraction
What triggers the repolarisation phase in cardiac muscle cells?
The efflux of K+ from the cell
What happens when the Cardiac muscle has been sufficiently repolarised?
The K+ channels close, returning the muscle cell to resting membrane potential
Why is Ca2+ influx essential for contraction?
heart muscle contracts through Ca2+ enduced Ca2+ release - this means Ca2+ is needed for the release of Ca2+ from the sarcoplasmic reticulum which then binds to troponin on muscle to shorten the fibres and contract it
Which ion is the upstroke more reliant on?
Na+
What does the autonomic nervous system that controls the heart comprise of?
The cardio-regulatory center and the vasomotor centers in the medulla
What nerve is responsible for the parasympathetic changes which are seen in the heart (decrease in heart rate)
Vagus nerve
What happens to the slope of Phase 4 (Pre-Potential) of the SAN Action potential during the parasympathetic response?
Decreases the slope
Which nerves are involved in the sympathetic control of the heart to increase heart rate?
Cardiac nerves from the lower cervical and thoracic ganglia
What affect does the sympathetic response have on the slope of Phase 4 in the sympathetic nervous system?
It increases the slope