Flashcards in CVS 4 ANS and the CVS and Cellular and Molecular events Deck (58):
How do neurones exert actions?
Via smooth muscle, viscera and secretory glands
What are the relative nerve lengths in the sympathetic nervous system?
Where are cell bodies in sympathetic outflow?
Nerve fibres have cell bodies in all 12 thoracic sections and in the first 2 lumbar sections
What neurotransmitter do pre-ganglionic nerves in the sympathetic nervous system use?
What type of receptor do post-ganglionic sympathetic neurones express?
What neurotransmitter do post-ganglionic sympathetic neurones express?
What receptors do sympathetic effectors express?
adreno receptors: alpha 1 & 2, beta 1 & 2
Which sympathetic postganglionic synapses are an exception being cholinergic?
perspiration and ejaculation pathways
What does the ANS exert control over?
smooth muscle (vascular and visceral)
rate and force of contraction in the heart
What is the origin of the parasympathetic division
What is the relative length of parasympathetic neurones?
What neurotransmitter do pre-ganglionic parasympathetic neurones use?
What receptors do post ganglionic parasympathetic neurones express?
What neurotransmitter do postganglionic parasympathetic neurones us?
What receptors to parasympathetic effectors express?
muscarinic, g protein coupled
What type of receptors are present in the heart?
Sympathetic- b1 adrenoreceptor- increases rate/force of contraction
Parasympathetic- M2- decreases rate
What type of receptors are present in the airways?
Sympathetic- b2 adrenoreceptor- relax
Parasympathetic- M3- contract
What type of receptors are in the pupil?
Parasympathetic- M3- contraction
What type of receptors are in sweat glands?
Sympathetic- a1 localised secretion
How do nicotinic receptors work?
They have an ion channel and allow sodium influx
What are chromaffin cells?
Like special postganglionic sympathetic neurones that release adrenaline into the bloodstream
What is the origin of the pregangionic parasympathetic fibres to the heart?
10th cranial nerve- vagus nerve
Where do parasympathetic fibres to heart synapse with postganglionic fibres?
epicardial surface or within walls of heart at SAN and AVN
What do M2 receptors in the heart do?
decrease heart rate (-ve chronotropic effect)
decrease AVN conduction velocity
Where are the ganglions for the smpathetic input to the heart?
Where do the sympathetic fibres innervate the heart?
SAN, AVN and myocardium
What do the b1 receptors do in the heart?
positive chronotropic effect
positive inotropic effect
How does depolarisation in the SA node occur?
slow depolarising pacemaker potential towards threshold, If- funny current, once above threshold causes opening of fast Ca2+ channels.
How does the ANS effect pacemaker potentials?
Sympathetic- increases slope gradient, g-protein receptors increasing cAMP speeding up pacemaker potential
Parasympathetic- decrease slope gradient, g protein receptors increasing K+ conductance and decrease cAMP
How does noradrenaline increase force of contraction?
acts of b1 receptors in myocardium, increasing cAMP
Ca2+ channels phosphorylated increasing Ca2+ entry during AP
increased uptake of Ca2+ in SR
increased sensitivity of contractile machinery to Ca2+
so increased force of contraction
What innervation do most blood vessels receive?
sympathetic (except some specialised tissue like erectile)
most arteries have a1 adrenoreceptors, coronary and skeletal muscle vasculature also have B2 receptors
How do changes in sympathetic output affect size or arteries?
normal- vasomotor tone
What blood vessels have B2 adrenoreceptors?
What binds to B2 receptors in blood vessels and why?
circulating adrenaline as has higher affinity for b2 adrenoreceptors
What does activating B2 adrenoreceptors in blood vessels cause and how?
Vasodilation by increasing cAMP which opens a type of K channel which relaxes smooth muscle
What does activating a1 receptors in blood vessels do and how?
Vasoconstriction by increasing [Ca2+]in from stores and via influx of extracellular Ca2+ causing contraction of smooth muscle
What effect do local metabolites have?
vasodilator effect. More important dilator effect than B2
Give examples of local metabolites made by active tissues
adenosine, K+, H+, increase in pCO2
What two types of receptors are afferent nerves feeding back from the heart?
baroreceptors (high pressure side of system)
Atrial receptors (low pressure side of system)
Where are baroreceptors located?
carotid sinus and aortic arch.
What are baroreceptors sensitive to?
stretch by increased arterial pressure
What is the resting membrane potential largely due to?
K+ permeability of the cell membrane at rest due to open leak K+ channels and a small permeability to other ions
How does excitation of cardiac myocytes cause contraction?
action potential causes increase in cytosolic Ca2+ conc which allows actin and myosin interaction
Summarise the cardiac action potential in words
RMP due to background K+ channels
Upstroke due to opening of voltage gated Na+ channel- influx of Na+
Initial repolarisation due to transient outward K+ channels (V-gated ito)
Plateau due to opening to voltage gated Ca2+ channels (L-type)- Ca2+ influx that balances with K+ efflux
Repolarisation due to efflux of K+ through voltage gated K+ channels and others
What is the initial slope to threshold called in the pacemaker potential?
If- funny current
What channels are involved in the funny current?
HCN channels (Hyperpolarisation-activated Cyclic Nucleotide-gated channels) which allow sodium influx. These channels are activated by membrane potentials more negative than -50mv. The more negative, the more activation.
What causes the upstroke in SAN potential?
voltage gated Ca2+ channel opening causing calcium influx
What causes the downstroke in SAN potential?
Opening of voltage gated K+ channels causing K+ efflux
Which part of heart depolarises fastest?
SA node as sets the rhythm being pacemaker. Other parts of heart do also have automaticity but slower
What do desmosomes do?
Mechanically tether cadiac myocytes together
What do gap junctions do?
Gap junctions permit ion movement and electrically couple cells
Where is the nucleus in cardiac myocytes?
Centre of cell
Will cardiac muscle contract in Ca2+ free solution?
No but skeletal muscle will
How does cytosolic calcium increase?
Depolarisation opens L-type Ca2+ channels in t-tubule system
Localised Ca2+ entry opens Calcium-Induced Calcium Release (CICR) channels in the SR
25% entry across sarcolemma 75% released from SR
How does calcium effect sliding filament mechanism?
binds to troponin C, conformational change shifts tropomyosin to reveal mysosin binding site on actin filament
How is Ca2+ conc returned to resting levels in relaxation of cardiac myocytes?
Most pumped back into SR by SERCA
Some exits via cell membrane: Sarcolemmal Ca2+ATPase, Na+/Ca2+ exchanger
How does calcium affect contraction in vascular smooth muscle?
Ca2+ binds to calmodulin
Activates Myosin Light Chain Knase MLCK
Phosphorylates the myosin light chain to permit interaction with actin.
Relaxation as Ca2+ levels decline