Autonomic cardiac control Flashcards
Where do the preganglionic fibres of the parasympathetic nervous system arise
Either in the brainstem of the sacral region of the spinal cord.
From brainstem they exit as carinal nerves III, VII, IX, X. From the sacral region they leave through the 3rd or fourth sacral spinal nerve roots.
Where do the preganglionic fibres of the sympathetic nervous system arise
In the spinal cord between the first thoracic segment (T1) and the second or third lumbar segment (L2-L3).
What is the neurotransmitter for preganglionic fibres for both the parasympathetic and sympathetic nervous systems
Acetylcholine
What does preganglionic NT ACh bind with on postganglionic fibres
Nicotinic Ach receptors
Where do the ganglia of the parasympathetic nervous system lie
Close to the organ which they innervate
Where do the ganglia for the sympathetic nervous system lie
Close to the spinal cord either para or prevertebrally
What do the postganglionic fibres of the parasympathetic nervous system release and where does it bind
Acetylcholine
Muscarinic ACh receptors on the target organs
What do the postganglionic sympathetic fibres release and where do they bind
Mostly noradrenaline
Acts on adrenergic receptors on target organs
How is acetylcholine synthesised
In the cytoplasm from acetyl-CoA and choline by the actions of choline acetyltransferase
What is the enzyme that inactivates acetylcholine and what does it do
Acetylcholinesterase
Splits Ach into acetate and choline
Two classes of cholinergic receptors
Nicotinic and muscarinic
Two classes of nicotinic receptors
Nn (found in autonomic ganglia)
Nm (found in endplates of skeletal muscle)
What do ‘ganglion blockers’ do
They are antagonists for Nn receptors. So they inhibit parasympathetic activity adverse effects include postural hypotension, flushing, impotence.
Where are muscarinic receptors located
On cell membranes of organs innervated by postganglionic parasympathetic fibres
What is the result of ACh acting on muscarinic fibres in the cardiovascular system
Heart rate is slowed by direct action on the SA node and by slowing conduction to the AV node.
Contractility of the heart is reduced
Dilates blood vessels (through infusion of ACh into the bloodstream as there are few cholinergic nerves on blood vessels)
What is the action of atropine and what is its effects
It is a muscarinic antagonist so blocks the physiological effect of parasympathetic activity thus increases heart rate. Also reduces salivation.
What is the main neurotransmitter released by the sympathetic post-ganglionic nerve
Noadrenaline.
Two exceptions- post ganglionic nerves that innervate sweat glands (these release ACh)
The adrenal medulla releases primarily adrenaline
What are the receptors for catecholamines
Adrenergic receptors. Include alpha 1 and 2, beta 1, 2, & 3
What are the main effects of receptor activation of alpha 1 receptors
Vasoconstriction, relaxation of GI smooth muscle, salivary secretion, and hepatic gycogenolysis
What are the main effects of receptor activation of alpha 2 receptors
Inhibition of transmitter release (located on presynaptic cell), platelet aggregation, contraction of vascular smooth muscle, inhibition of insulin release.
What are the main effects of activation of beta 1 receptors
Increased cardiac rate and force
What are the main effects of activation of beta 2 receptors
Bronchodilation, vasodilation, relaxation of visceral smooth muscle, hepatic glycogenolyis, and muscle tremor
What are the main effects of activation of beta 3 receptors
Lipolysis
Example of alpha 1 agonist
phenylephrine (vasoconstrictors useful in treating nasal congestion)
