CVS 5 Autonomic Nervous System Flashcards
What does the autonomic nervous system control?
All involuntary actions
Divisions of the autonomic nervous system
Parasympathetic - rest + digest
Sympathetic - fight or flight
Describe the preganglionic nerve in the sympathetic nervous system
Short
Myelinated
Describe the postganglionic nerve in the sympathetic nervous system
Long
Non-myelinated
Describe the preganglionic nerve in the parasympathetic nervous system
Long
Myelinated
Describe the postganglionic nerve in the parasympathetic nervous system
Short
Non-myelinated
What is released from the preganglionic nerve in the sympathetic nervous system?
Acetylcholine
What is released from the postganglionic nerve in most sympathetic nervous system?
Noradrenaline
What is released from the preganglionic nerve in the some sympathetic nervous system?
Acetylcholine
What is released from the preganglionic nerve in the parasympathetic nervous system?
Acetylcholine
What is released from the postganglionic nerve in the parasympathetic nervous system?
Acetylcholine
What receptor does acetylcholine from the pregangionic nerve act on?
Nicotinic ACh receptors
What receptor does acetylcholine from the postganglionic nerve act on?
Muscarinic ACh receptors
What receptor does noradrenaline from the postganglionic nerve act on?
Adrenoreceptors
Origins of the sympathetic nervous system
Thoracic + lumbar regions of spine
Origins of parasympathetic nerves system
Cranial + sacral regions of spine
Describe the action of parasympathetic input into the heart
- Via the vagus nerve
- Innervate with epicardial surface or SAN + AVN
- Releases acetylcholine
- Act on M2 Muscarinic receptors
- negative chronotropic effect (slows HR)
- decreases AVN conduction velocity
Effect of acetylcholine on heart
Negative chronotropic effect (slows HR)
Decreases AVN conduction velocity
Describe the sympathetic input to the heart
- From sympathetic trunk
- Innervates with SAN, AVN + myocardium
- Releases noradrenaline
- Act on B1 adrenoreceptor
- positive chronotropic effect (^ HR)
- positive inotropic effect (increased force of contraction)
What does an positive or negative in chronotropic effect refer to?
Heart rate
Positive CE - increase
Negative CE - decrease
What does the positive or negative inotropic effect refer to?
Force of contraction of heart
Positive IE - increased force
Negative IE - decreased force
Effect of noradrenaline on heart
Positive chronotropic effect (^ HR)
Positive inotropic effect (^ force of contraction)
How does noradrenaline have a positive inotropic effect on the heart ?
positive inotropic effect = ^ force of contraction
1- act on B1 adrenoreceptors in myocardium
2- ^ CAMP - activates protein kinase A
3- PKA phosphorylates Ca2+ channels
4- ^ Ca2+ uptake in sarcoplasmic reticulum
5- more Ca2+ for contraction
How does noradrenaline have a positive chronotropic effect?
1- sympathetic nervous system speeds up relaxation (decreases diastole)
2- decreases time of 1 cardiac cycle
3- increase HR
Effect of sympathetic nervous system on SAN
Speeds up pacemaker potential
Steeper slope
Increases CAMP
Effect of parasympathetic nervous system on SAN
Slows down pacemaker potential
Shallower slope
Less CAMP
What happens to blood vessels and airways in anaphylaxis?
Blood vessels dilate
Airways constrict
What is used to treat anaphylaxis?
How does this work?
High does of adrenaline injection intramuscularly
- acts on a1 receptors in vessels - vasoconstriction
- increased BP
- acts on B2 receptors in bronchi - bronchodilation
- ^ airflow
What receptors do noradrealine act on in vessels?
a1 adrenoreceptors
What receptors do circulating (normal levels) adrenaline act on in vessels?
B2 adrenoreceptors
What receptors does high concentrations of adrenaline act on in vessels?
Example of when this may occur
a1 adrenoreceptors
e.g. adrenaline injection in anaphylaxis
What does activating B2 adrenoreceptors in vessels cause?
Explain why
Vasodilation Gs
1- Gs stimulates adenylate cyclase
2- ^ cAMP made
3- PKA activated
4- PKA phosphorylates MLCK
5- MLCK inhibition
5 - Smooth muscle contraction inhibited
6- vasodilation
Function of PKA in myocardium
Phosphorylates Ca2+ channels
Increase force of contraction
Function of PKA in vascular smooth muscle
Inhibits MLCK by phosphorlating it»_space; prevents vasoconstriction»_space; vasodilation occurs
Describe contraction of vascular smooth muscle
1- Ca2+ enter via VGCC or from sarcoplasmic reticulum
2- Ca2+ binds to calmodulin
3- Ca2+ CaM complex activates MLCK
4- MLCK phosphorylates myosin light chain
5- MLC interacts with actin > contraction
6- as Ca2+ levels fall, MLCP dephosphorylates MLC
What does activation of a1 adrenoreceptors in vascular smooth muscle cause?
Explain why
^ in intracellular Ca2+»_space; Contraction
1- IP3 production
2- release of Ca2+ from SR
3- Ca2+ CaM complex activates MLCK
4- MLCK phosphorylates MLC
5- contraction
1- DAG (diacylglycerol) activated
2- DAG inhibits MLCP
What does activation of B1 adrenoreceptors in vascular smooth muscle cause?
Explain why
promotes relaxation
1- adenylate cyclase activation
2- cAMP produced
3- PKA activated
4- PKA phosphorylates MLCK
5- MLCK inhibited
6 - decrease in MLC phosphorylation
7- relaxation + less contraction
Where are baroreceptors found?
Aortic arch
Carotid sinus
Explain how baroreceptors respond to an increase in arterial pressure
1- ^ arterial pressure causes stretch
2- stretch detected by baroreceptors
3- impulse sent to medulla oblongata
4- sends signal to decrease HR + contractility
5- BP decreases
What effect do local metabolites have on circulation?
Increase in metabolites leads to vasodilation which increases flow
