Microsoft word - autonom_notes_bf_rev.docx

AUTONOMIC NEURONES
SOMATIC vs. AUTONOMIC
somatic (afferent & efferent)
autonomic (efferent only)
structures innervated by
neurites
homeostasis of ‘vegetative’ vital
functions – la vie organique
peripheral ganglia in
usually one – cranial or terminal efferent path*
ganglia (parasym.); paravertebral or prevertebral ganglia (symp.) neurone(s) of efferent path 1 – in motor nuclei of cranial nn. 2 – 1st in brain & s. cord, 2nd in
PARASYMPATHETIC (Langley, 1905) vs. SYMPATHETIC (Winslow, 1732)
parasympathetic
sympathetic
general distribution
input from CNS
craniosacral (Langley, 1900)
thoracolumbar spinal cord
central soma
brainstem nuclei of 4 cranial nn.; lateral horn of spinal cord from grey matter of sacral spinal cord (C8)T1–L2 (L3) ganglia*
ciliary – CN III; pterygopalatine sympathetic trunk (22–23 & fibres
& submandibular – CN VII; otic paravertebral ganglia, etc.) & – CN IX; ganglia in walls of long postganglionic (grey ramus communicans) general effects
conserve & restore; anabolism; rapid catabolism for energy to NB. extreme terror: parasymp.
extent, duration of effect
transmitter at ganglion
transmitter at organ
‘adrenergic’; except ACh in
sweat glands^ & penile vv.; also NPY, ATP NB: * Peripheral sympathetic neurones are not confined to ganglia: they are embedded in sympathetic
nn., i.e., in grey & white rami communicantes, splanchnic nn., etc. (Pick, 1970).
^ Sympathetic nn. are generally vasoconstrictor; sympathetic vasodilation in coronary aa. is mostly due to
inhibition of parasympathetic nn.
Afferent nn. for autonomic reflexes are found in somatic nn.; visceral afferent fibres accompany autonomic
nn. (rami communicantes, splanchnic nn., vagus, etc.)
SPECIFIC PHYSIOLOGICAL EFFECTS
parasympathetic stimulation
sympathetic stimulation
ciliary body
stiffens causing lens to thicken = accommodation for near vision blood vessels
vasoconstriction (generally, e.g.,
intestines
++ motility (peristalsis);
defecation (relaxes sphincter m.) excitatory to anal sphincter suprarenal glands*
salivary & lacrimal glands
? more viscous secretion due to vasoconstriction lacrimal gland
sex organs
dilates blood vessels of penis & ejaculation; vasoconstriction;
clitoris, testis & ovary; secretion vasodilation of penile vx. (ACh)
of sex glands
sweat glands
stimulates (= sudomotion; ACh)
NB. Terror may activate parasympathetic nn. to inhibit sphincters of stomach, bladder & rectum, with
decrease in heart rate (vasovagal syncope).
Stimulation of parasympathetic nn. has little effect on liver, adrenal glands, sweat glands, skeletal mm.,
skin, or hair. Vasodilation in skeletal mm. in exercise is due to local release of NO from endothelium.
* Cells of suprarenal medulla are considered to represent postganglionic sympathetic neurons.
ENTERIC NERVOUS ‘SYSTEM’ (Remark, 1847; Langley, 1900)
• a neuronal network within GIT (as distinct from sympathetic nerves and parasympathetic ganglia). • comprises sensory & motor neurones, interneurones (excitatory, inhibitory), neurites, dendrites & glial cells in alimentary canal (oesophagus to anus), pancreas & gall bladder, i.e., intrinsic to viscera. • in alimentary canal, is usually found in 2 annular plexuses in different layers: larger myenteric (Auerbach’s) plexus; smaller submucosal (Meissner’s) plexus. • involved in reflex peristalsis and secretion from intestinal mucosa, hormone release, etc. • functions reflexly in absence of extrinsic autonomic input, but modified by extrinsic input. • transmitters include nitric oxide (NO), vasoactive intest. peptide (VIP), substance P, ATP, GABA, etc. • co-transmitters: ACh & SP in excitatory cells; ATP, NO, VIP in inhibitory cells.
References
Jänig W (2006) Integrative Action of the Autonomic Nervous System. Cambridge Univ. Press
Langley JN (1921) Autonomic Nervous System. www.archive.org/details/autonomicnervous01languoft
Moore KL et al (2006) Clinically Oriented Anatomy. Philadelphia: Lippincott
Pick J (1970) The Autonomic Nervous System. Philadelphia: Lippincott
Remark R (1847) Ueber ein selbständiges Darmnervensystem. Berlin: Reimer

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