Control of heart function Flashcards
- What can the 3 main anatomical components of the heart be broadly categorised as?
- Muscle cells (cardio-myocytes): can contract and relax in response to electrical stimuli. Essential for pumping blood around the body
- Specialised electrical cells: cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes
- Vessels: the major blood vessels are responsible for transporting blood in and out of the heart, whilst the coronary blood vessels are responsible for supplying blood to the heart
- What is the pacemaker of the heart?
- Where is the pacemaker of the heart located?
.
Sinoatrial node - usually beats at around 60-100bpm.
Junction of the crista terminalis; upper wall of right atrium and opening of the superior vena cava
- Where is the AV node located?
- What tract connects the SAN and AV nodes?
Triangle of Koch at the base of the right atrium.
(Has pacemaker activity with a slow calcium mediated action potential: but it is usually the SAN that controls the heart beat).
Internodal tracts, which are specialised myocytes.
- What is the pathway of the bundle of His in the heart?
From the atria
on to the bundle of His
down through the intraventricular septum
to the bundle branches
then through to the actual Purkinje fibres
which propagate the electrical current along the ventricles.
- How many phases does nodal AP have and name each of them?
3
Phase 4 - Pre-potential Phase 0 - Upstroke Phase 3 - Re-polarisation
- Outline the process of a nodal AP
Pre-potential (phase 4) → Na+ influx through a ‘funny channel’- Increase in membrane potential from -60 to -40 mV
Upstroke (phase 0) → Increase in membrane potential -40 to 0 mV due to Ca2+ influx Re-polarisation (phase 3) decrease in membrane potential due to K+ efflux
- What causes the different action potential profiles in the different parts of the heart?
Different ion currents flowing and different ion channel expression in the cell membrane
so different parts of heart have different action potential shapes
- Is a cardiac muscle AP longer than a nervous AP? How long is a cardiac muscle AP?
- What does duration of a cardiac muscle AP control?
Yes
Cardiac muscle AP - 200-300 ms
(Nervous - 2-3ms)
Duration of contraction of the heart
- How many phases are present in a cardiac muscle AP and name each phase?
5
Phase 0 - Upstroke (-90 mV up to ~20-30 mV) → Na+ influx Phase 1 - Early re-polarisation → Decrease in Na+ permeability Phase 2 - Plateau (maintains cell at a level of depolarisation at value of 0mV) → Due to Ca2+ influx Phase 3 - Re-polarisation → Happens at ~270ms after stark of upstroke → K+ efflux Phase 4 - Resting Membrane Potential - Na+/K+ ATPase pump
- What is the absolute refractory period of a cardiac muscle AP?
- What is the relative refractory period of a cardiac muscle AP?
- What 2 components are important for control of the heart via the CNS?
Time during which no other AP can be initiated regardless of stimulus intensity
First 200ms
Period after ARP where an AP can be elicited, but only with larger stimulus strength. Cardio-regulatory centre and vasomotor centres in medulla.
- What affect do the 2 different components of the ANS have on the heart and how they affect action potential curve
Parasympathetic (goes via vagus nerve to the heart)
When activated it causes a decrease in HR
decreases the slope of phase 4 OF SAN potential (pre-potential nodal AP phase)
Therefore reduces HR
Sympathetic
increased HR
by increasing the slope of phase 4 of SAN potential (decrease in time of phase 4)
increase in force of contraction, increases Ca2+ dynamics.
- What is chronotrophy?
- what is ionotrophy?
factors changing speed of heart rate
factors changing force of heart rate
- Where do parasympathetic nerves arise from?
- Describe the design of the parasympathetic response in terms of what is released at the pre and post-ganglionic nerve fibres
Craniosacral outflow (cranial and sacral part of the spinal cord).
Pre-ganglionic fibres use ACh as NT. Use nicotinic receptors Post-ganglionic fibres also use ACh as a NT. Use muscarinic receptors,
- Where do sympathetic nerves arise from?
- Describe the design of the sympathetic response in terms of what is released at the pre and post-ganglionic nerve fibres
Thoracolumbar outflow.
Pre-ganglionic fibres use ACh as their NT; use nicotinic receptors. Synapse at sympathetic ganglia. Post-ganglionic fibres use noradrenaline, use adrenergic receptors (where post-ganglionic fibres are longer than pre-ganglionic fibres).
- Where is the vasomotor centre located?
- What is the vasomotor centre composed of?
Bilaterally in reticular substance of medulla and lower third of pons.
Vasoconstrictor (pressor) area Vasodilator (depressor) area Cardio-regulatory inhibitory area