Autonomic nervous system Flashcards
Features of the ANS
- part of the PNS
Involuntary control - - Regulates operation of the internal organs
- Maintains internal environment
- Innervates smooth muscle, cardiac muscle, glands
3 divisions of the ANS
- SYMPATHETIC
- PARASYMPATHETIC
- ENTERIC (The “Little Brain”)
Origins of sympathetic and parasymp innervation
Parasymp - brainstem
sym - T1-L2 region of spinal cord
parasymp - s2-s4 region of spinal cord
Path of axons in ANS
- Axons do not pass directly to the effector organs
- They form disynaptic pathways
- Except symp supply to adrenal medulla
What is the main type of neurotransmitter within the autonomic ganglia
- Acetylcholine is the main neurotransmitter
- Binds to nicotinic receptors on postganglionic neurons
- Ionotropic ligand-gated(fast)
- Acetylcholine opens pore and depolarises neuron
What is the main neurotransmitter in postganglionic sympathetic neurons
- Noradrenaline is the main neurotransmitter
- Except sweat glands use acetylcholine
- binds to adrenergic receptors on the effector organ
What are the type of adrenergic receptors on the effector organ
- Metabotropic g-protein coupled(slow)
- Multiple subtypes alpha1, alpha2, beta1, beta2 and beta3
Location of alpha1 adrenergic receptors
- On blood vessel smooth muscle
Use of prazosin
- alpha1 antagonists are used to treat hypertension
Location of beta1 adrenergic receptors
- On heart
Effect of atenolol on beta1 adrenergic receptors
- Atenolol - beta1 antagonists are used to treat hypertension
Location of beta2 adrenergic receptors
- On bronchial smooth muscle
Effect of salbutamol on beta2 adrenergic receptors
- Beta2 agonists are used to treat asthma
What is the main neurotransmitter within adrenal medulla
- Acetylcholine is the main neurotransmitter
What does acetylcholine bind to within adrenal medulla
- Binds to nicotinic receptors on chromaffin cells
Effect of acetylcholine on nicotinic receptors within adrenal medulla
- Causes release of adrenalin/noradrenalin into circulation
- Direct activation of sympathetic effector organs
Main neurotransmitter in postganglionic parasymp neurons
- Acetylcholine is the main neurotransmitter
What type of receptors does acetylcholine bind to in postganglionic parasympathetic neurons
- Binds to muscarinic receptors on the effector organ
- Metabotropic G-protein coupled(slow)
Effect of atropine on cholinergic-muscarinic receptors
- Cholinergic-muscarinic antagonist(lowers parasymp activity)
- Used to treat bradycardia, dilate pupils, reduce glandular secretions
Effect of sympathetic activity on the cardiac muscle
- increases pacemaker activity + contractile force
Effect of sympathetic activity on the bronchi of lungs
- Causes bronchodilation
Effect of sympathetic activity on the sweat glands
- Causes sweat secretion
Effect of sympathetic activity on hair follicles
- causes piloerection
Effect of sympathetic activity on blood vessels
- Vasoconstriction in skin and vasodilation in skeletal muscles
Effect of sympathetic activity on abdomino-pelvic viscera
- Inhibits peristalsis + gastric secretion
- Stimulates glucagon secretion
- Stimulates secretion of adrenaline from adrenal medulla
Location of paravertebral ganglia
- Interconnected paravertebral ganglia extends from cervical to sacral levels
How do preganglionic fibres enter sympathetic trunk
- Through white rami communications
- From T1-L2 spinal nerves only
What does the lateral horn contain
- Cell bodies of preganglionic neurons
What do white ramus communicans contain
- myelinated preganglionic neurons
What do grey ramus communicans contain
- Unmyelinated postganglionic neurons
Pathway of preganglionic fibres upon entering the trunk
- Synapse in ganglion(same level or travel to another level)
- Pass through ganglion into splanchnic nerves to synapse in prevertebral ganglia
What are mass responses
- Sympathetic responses are mass responses
- Allows coordinated activity at multiple levels
Path of postganglionic fibres in the symp system from the sympathetic trunk
- From sympathetic trunk, postganglionic fibres follow of two routes:
1) To the periphery(sweat glands, hair follicles, blood vessels) - via grey rami communications back into spinal nerves
2) To the viscera(heart, lungs, head) - via medial branches/plexus
Path from prevertebral ganglia in symp system
- From prevertebral ganglia, postganglionic fibres form plexus around viscera
What are the 3 cervical ganglia in cervical symp trunk
- Superior
- Middle
- Inferior
