The Autonomic Nervous System Flashcards
The ANS is a subdivision of the
PNS
controls autonomic visceral functions
works with rapidity
Three Divisions of the ANS:
- sympathetic
- parasympathetic
- enteric
PNS:
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Which division of the autonomic nervous system maximises the use of metabolic resources?
sympathetic division
Basic Map of ANS:
bilateral, paravertebral sympathetic trunk allows sympathetic region of spinal cord to affect other areas because sympathetic axons can enter sympathetic trunk and ascend or descend to synapse at sympathetic ganglia
Axons do not pass directly to the effector organs; they form
disynaptic pathway
What is the exception to axons not passing directly to effector organs?
sympathetic supply to the adrenal medulla
functional benefit = momentarily faster to initiate fight or flight pathway by monosynaptic pathway to trigger chromaffin cells to release adr and noradr
General Autonomic Activity: Sympathetic:
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Within autonomic sympathetic ganglia what is the main preganglionic neurotransmitter and its receptor?
ach
nicotinic receptors
ionotropic ligand -> results in depolarisation
Within autonomic sympathetic ganglia, what is the main postganglionic neurotransmitter and its receptor?
noradrenaline
adrenergic receptors
metabotropic GPCR (slow)
alpha 1 = blood vessels, antagonist for
hypertension
beta 1 = blood vessels/heart, antagonist for
hypertension
beta 2 = lungs/bronchi, agonist for asthma
Exception to autonomic postganglionic sympathetic neurons releasing noradrenaline?
Sweat glands use ach
The adrenal medulla is monosynaptic.
What is the main neurotransmitter used here?
Receptor?
Effect? -
- ach
- nicotinic receptors on chromaffin cells within
the adrenal medulla - causes release of adr/Nadr into circulation
- direct activation of sympathetic effector organs
What is the main neurotransmitter in autonomic preganglionic parasympathetic neurons?
- ach
- metabotropic GPCR (slow)
- muscarinic receptors
Sympathetic Trunk/Chain:
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Sympathetic Trunk/Chain:
interconnected paravertebral gangli close to vertebral bodies, extending from cervical to sacral lvels
preganglionic fibers enter sympathetic trunk through white rami communicantes
from T1-L2 spinal nerves only
Sympathetic Trunk: Preganglionic Fibers:
on entering the trunk, preganglionic fibers will either:
- synapse in ganglion (on same level or travel to another level) - pass through ganglion forming splanchnic nerves to synapse in prevertebral ganglia to innervate internal organs
Sympathetic Trunk: Post-ganglionic fibers:
Either:
- travel to periphery via grey rami
communicans back into spinal nerves
- travel to viscera via medial
branches/plexus; from prevertebral
ganglia, postganglionic fibers forming
plexus around viscera
Journey of Spinal Nerve into and out of sympathetic trunk:
- sympathetic axon sitting in lateral horn of
spinal cord - exits spinal cord via the ventral horn
- becomes ventral ganglionic root
- leaves the ventral root / r and merges with the
dorsal root to become the spinal nerve - sympathetic axon of spinal nerve can leave
spinal nerve via the White Rami
communicantes - now in sympathetic trunk
- can now either synapse with post ganglionic
neuron at same level or ascend and synapse
with post ganglionic neuron at higher level,
or descend and synapse with post ganglionic
neuron at lower level - if synapsed at same level now post-
ganglionic and is unmyelinated grey matter - leaves via grey rami communicantes back
into spinal nerve - will either go to dorsal or ventral primary
ramos, split off again and eventually get to
target organs
ORRRR instead of synapsing in sympathetic trunk, will pass through becoming a splanchnic nerve and synapse in the pre-vertebral ganglia located close to target organs
Cervical Sympathetic Ganglia supply the (3):
- heart
- upper limbs
- heart
Name the Cervical Sympathetic Ganglia:
- superior (largest)
- middle (smallest)
- inferior (intermediate size)
Cervical Sympathetic Post-Ganglionic Fibers:
- exit via the grey rami communicantes to
spinal nerves - piggyback along the common carotid artery
and existing vasculature to the heart - which then form an internal carotid plexus
- and an external carotid plexus
The Cervical Post-ganglionic fibers in the internal carotid plexus results in
- eye: dilation of pupil, raising of eye lid
- lacrimal gland: inhibits secretions
want to see more and cry less during fight and flight
The Cervical Post-ganglionic fibers in the external carotid plexus results in
- inhibition of submandibular and parotid
gland secretions
conserve unnecessary energy
Cervical Sympathetic Ganglia:
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Label carotid plexi:
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Thoracic Sympathetic Ganglia supply the
thorax, heart, lungs and abdominal viscera
Thoracic Sympathetic Ganglia: Post Gangliionic Fibers:
- exit via the grey rami communicantes to
spinal nerves - medially branches toward heart and lungs
- form two sympathetic plexi
- cardiac plexus
- pulmonary plexus
Lumbar Sympathetic Ganglia supply
the abdominal viscera and lower limbs
Lumbar Sympathetic Post Ganglionic Fibers:
- exit via the grey rami communicantes to
spinal nerves
Lumbar Sympathetic Pre-ganglionic fibers exit via
- lumbar splanchnic nerves to the abdomen
- synapse in prevertebral ganglia
- innervate the abdominal viscera including
the large intestine
Sacral Sympathetic Ganglia supply
the pelvis and lower limb
Sacral Sympathetic Post Ganglionic Fibers exit via
- grey rami communicantes to spinal nerves
supplying lower limbs - sacral splanchnic nerves to pelvic organs
- inferior hypogastric pelvic organs
Parasympathetic pregagnlionic neurons are found
- within the brainstem
- within S2-S4 spinal nerves
Parasympathetic ganglia are all located
close to target organs
Parasympathetic Ganglia:
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Parasympathetic ganglia lenght:
preganglionic fibers are longer
Within which cranial nerves do parasympathetic nerves arise?
- CN III = occulomotor nerve = edinger-
westphal nucleus - CN VII = facial nerve = superior salivatory
nucleus - CN IX = glossopharyngeal nerve = inferior
salivatory nucleus - CN X = vagus nerve = nucleus ambiguous,
dorsal motor nucleus
Cranial Parasympathetic:
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How do cranial parasympathetic preganglionic axons reach ganglia?
by passing through cranial nerves
Where does the preganglionic occulomotor branches synapse?
ciliary ganglion
Parasympathetic innervation of the occulomotor nerve (post-ganglionic branch) results in
pupil contriction = sphincter pupillae
Where do the preganglionic branches of the facial nerve synapse?
the pterygopalatine ganglion which are involved in lacrimation
the submandibular gland = saliva
Parasympathetic innervation of the facial nerve (post-ganglionic branch) results in
stimulation of the lacrimal gland
stimulation of submandibular gland in watery saliva
Where does the preganglionic branches of the glossopharyngeal nerve synapse?
otic ganglion
Parasympathetic innervation of post-ganglionic branches of the glossopharyngeal nerve results in
stimulation of the parotid gland (watery saliva)
Vagus nerve post-ganglionic synapses
multiple
lungs, heart, abdominal organs
Sacral Parasympathetic:
- S2,3,4
- from sacral spinal cord
- preganglionic fibers exit via pelvic splanchnic
nerves to pelvic organs - synapse near target organs
- pelvic plexus
- inferior hypogastric plexus
Sacral Parasympathetic:
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Sacral Parasympathetic Innervation results in:
- urination: contraction of bladder wall,
inhibition/relaxation of bladder sphincter - defecation: relaxation/inhibition of rectal
sphincter - sexual function: vasodilation in erectile
tissues
The Enteric Nervous System: Two Plexi:
- myenteric plexus = muscle layer =
motility/contraction - submucosal = glandular secretions/blood
flow
The enteric nervous system is truly autonomous hence can function after all central connections are severed.
What is this called?
intrinsic control mechanism
Enteric Nervous System:
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white and grey rami communicantes are
connections between the spinal nerve and sympathetic trunk
