Autonomic nervous system Flashcards
Three divisions of the ANS
Sympathetic
Parasympathetic
Enteric
Sympathetic function
Fight, flight, fright
Maximises use of metabolic resources
Parasympathetic function
Opposite to sympathetic division
Switched on during resting
Increases/ conserves metabolic resources
Map of the ANS
Parasympathetic: brainstem
Sympathetic: T1-L2 spinal cord
Parasympathetic: S2- S4 spinal cord
Autonomic nervous system
Axons do not pass directly to the effector organs
Form disynaptic pathways
Neurotransmission within autonomic ganglia
Acetylcholine is the main neurotransmitter
Binds to nicotinic receptors on postganglionic neurones
Ionotropic ligand gated:
- acetylcholine opens pore
- depolarises neurone
Neurotransmission of postganglionic sympathetic neurones
Noradrenaline is the main neurotransmitter
Binds to adrenergic receptors on the effector organ
- metabotropoc G-protein coupled
Neurotransmission within adrenal medulla
Acetylcholine is main neurotransmitter
Binds to nicotinic receptors on chromaffin cells
Causes release of adrenaline/ noradrenaline into circulation
Direct activation of sympathetic effector organs
Neurotransmission within postganglionic parasympathetic neurones
Acetylcholine is the main neurotransmitter
Binds to muscarinic receptors on the effector organ
Metabotropic G protein coupled
Sympathetic trunk/ chain
Interconnected paravertebral ganglia
Extends from cervical to sacral levels
Preganglionic fibres enter sympathetic trunk through white rami communications
Preganglionic fibres
On entering the trunk, preganglionic fibres either
- synapse in ganglion
- pass through ganglion into splanchnic nerves to synapse in prevertebral ganglia
Postganglionic fibres
Much more numerous than preganglionic
Sympathetic responses are mass responses for coordinated activity
From sympaethtic trunk, two routes
- to the periphery
- to the viscera
From prevertebral ganglia, form plexus around viscera
Cervical sympathetic postganglionic fibres
Exit via grey rami communications to spinal nerves
Piggy back down common carotid artery to heart
Piggy back up internal/ external carotid artery to head
Horner’s syndrome
Disruption of the sympathetic supply to head
Any part of pathway- hypothalamus to preganglionic neurones
Pupils- miosis (constricted)
Eyelids- ptosis (drooping) Skin of face- anhydrosis (dry)
Thoracic sympathetic postganglionic fibres
Exit via
- grey rami communicans to spinal nerves
- medial branches to heart and lungs
- thoracic splanchnic nerves to abdomen
Thoracic splanchnic nerves
Synapse in prevertebral ganglia
Ganglia close to abdominal aorta
Postganglionic fibres form prevertebral plexus around viscera
Lumbar sympathetic
4 lumbar sympathetic trunk ganglia
Post ganglionic fibres exit via
- grey rami communicans to spinal nerves
Preganglionic fibres exit via
- lumbar splanchnic nerves to pelvis
Sacral sympathetic
4 sacral sympathetic trunk ganglia
Postganglionic fibres exit via
- grey rami communicans to spinal nerves
- sacral splanchnic nerves to pelvic organs
Parasympathetic preganglionic fibres
Preganglionic neurones within
- brainstem
- grey matter spinal cord
All ganglia located close to target organ
Cranial parasympethic
Preganglionic neuronal cell bodes in cranial nerve nuclei
Preganglionic axons pass though cranial nerves to ganglia
Vagus nerve pass to heart, lungs and abdominal viscera
Sacral parasympethetic
From sacral spinal cord
Preganglionic fibres exit via
- pelvic splanchnic nerves to pelvic organs
Form pelvic plexus over viscera
Preganglionic fibres synapse in walls of target organs
Sacral parasympathetic function on bladder
Contraction of bladder wall
Inhibition to bladder sphincter
Sacral parasympathetic function of rectum
Inhibition of rectal sphincter
Sacral parasympathetic function on sexual function
Vasodilation in erectule tissues
Enteric nervous system
In walls of GI tract
Auerbach’s- regulates muscle contraction
Meissner’s- regulates glandular secretions
Contains 10-100 billion neurones
Truly autonomic
