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