CVS 7 - The Sympathetic Nervous System and the Renin-Angiotensin System Flashcards
Where does the parasympathetic nervous system originate? What about the sympathetic?
Parasympathetic = craniosacral region
Sympathetic = thoracolumbar region
What does increased baroreceptor firing lead to?
A decrease in sympathetic activity - reducing BP and HR
What 2 places are baroreceptors found?
- Aortic arch
2. Carotid arteries
Which neurotransmitter is always used in parasympathetic ?
What about sympathetic?
Ach
Ach, but noradrenaline is used at the effector end of the sympathetic arm.
Where does noradrenaline synthesis occur?
Terminal varicosity - small nodule at the end of sympathetic nerve.
In the sympathetic nervous system, the transmitter is noradrenaline, except in which case?
In the adrenal medulla
Explain the release and reuptake of NA.
Stored in granular vesicles and exocytosed (ACTIVE PROCESS).
NA then reuptaken and removed through 2 mechanisms:
1. Neuronal uptake - goes back to neurone that released it
- Extraneuronal uptake - taken up by extraneuronal cells (effector cell - often VSMC)
In extraneuronal uptake, COMT and MAO are 2 enzymes responsible for subsequent transmitter breakdown.
How are adrenoreceptors subdivided?
They can have 2 effects.
- Excitatory effects on smooth muscle.
- Alpha adrenoreceptor mediates - Relaxant effects on smooth muscle and stimulatory effect on heart
- Beta adrenoreceptor mediated
(Stimulatory means increases force of contraction and HR)
How can Beta-receptors be subdivided?
- Beta 1 = cardiomyocytes, GI tract SMC (stimulates heart)
- Beta 2 = vasculature, bronchi, uterine SMC (relaxes VSMC)
- Beta 3 = Fat cells, potentially GI tract SMC. Involved in thermogenesis (but low in humans as few brown fat cells.) Important in bladder function.
How can Alpha-receptors be subdivided?
- Alpha 1 receptors = post synaptic (many on effector cells). Important mediators of constriction of vessels in response to sympathomimetic amines.
- Alpha 2 = pre synaptic nerve terminal membrane. Activation through released transmitter causes Negative feedback inhibition of further transmitter release. Some Alpha 2 receptors are on VSMC and cause vasoconstriction (like Alpha 1)
Explain coupling of Alpha 1 adrenoreceptors.
- Done via G proteins.
- Receptor activated, which causes PLC activation.
- PIP2 to IP3.
- Leads to Ca influx into cytosol. Contraction ensues.
What is unique about cAMP and the heart?
cAMP is generally a relaxant in Smooth muscle.
In the heart, cAMP is a stimulant.
IF ALPHA 2 RECEPTOR, MUST(!) BE COUPLED WITH BETA 2 RECEPTOR
T
cAMP and Calcium are?
Antagonistic, except in cardiac muscle.
Explain alpha 2 and beta 2 receptor coupling.
- Beta receptors are coupled with adenylyl cyclase - increases cAMP levels
- cAMP is a relaxant in smooth muscle, and prevents platelet aggregation.
- Alpha 2 receptors inhibit adenylyl cyclase. This decreases intracellular cAMP and causes contraction in smooth muscle.