Autonomic nervous system - Saint Louis Universitystarklab.slu.edu/Physio/Autonomic.pdf · Autonomic nervous system ... • Beta-1 in heart, why beta blockers like ... • ->parasympathetic

Autonomic nervous system

•  motor system for smooth muscle and glands

•  contrasted with somatic system innervating striated (skeletal) muscle

•  Autonomic has preganglionic and postganglionic output

Function

•  Parasympathetic •  = "rest and digest” •  Sympathetic •  = "fight or flight"

Anatomy & Pharmacology

•  Parasympathetic, cranio-sacral •  ACh (nicotinic and muscarinic) •  ganglion near target •  Sympathetic, thoraco-lumbar •  ACh (nicotinic) then NE •  ganglion near spinal cord

Adrenergic

•  For NE (adrenergic), all receptors are G-protein-coupled-receptors

•  Alpha (vasoconstriction) phenylephrine (Neosynephrine, nasal decongestant) is agonist

•  Beta-1 in heart, why beta blockers like propranalol were given for high blood pressure

•  Beta-2 bronchioles, why asthma inhalers had epinephrine

Push-Pull vs Unique

•  Many targets are "push-pull" like heart •  Some are unique like arterioles

(sympathetic only) •  -- close in peripheral vascular beds

(make hands cold) •  open in muscle (hyperemia).

anatomy

•  sympathetic output from lateral horn neuron •  -> white ramus -> sympathetic ganglion •  -> gray ramus •  Simpler for parasympathetic •  from brain stem nucleus or lateral horn in

sacral cord •  ->parasympathetic ganglion called enteric for

gut.

Enteric nervous system

•  Contribution of neural network (plexus) •  to circular and longitudinal muscles to

mediate peristalsis. •  Parasympathetic allows digestion, •  sympathetic puts it on hold. •  Atropine blocks muscarinic synapses and is

in anti-diarrhea medications to slow motility.

Beautiful women

•  Atropine muscarinic antagonist •  Atropa belladonna (beautiful woman) •  [deadly nightshade] •  SLIDE (Hess, Scientific American, Nov.

1975, p.111) •  Women are more beautiful with dilated

pupils

Heart as an example

•  Automaticity at SA and AV nodes •  (spread from myocardial cell to next

myocardial cell). •  Sympathetic speeds heart, •  parasympathetic (via vagus, X) slows, •  relaxed heart rate is slower than

automatic rate.

Male sexual function

•  Furchgott, Ignarro, Mura 1998 Nobel •  parasympathetic dilates arterioles in

corpus cavernosum for erection •  Sympathetic contributes to ejaculation. •  This is too simple

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•  adrenergic (via alpha 1 receptors) contracts smooth muscle,

•  cholinergic (via muscarinic receptors) inhibits adrenergic-induced-contraction (resulting in relaxation)

•  more than cholinergic and adrenergic, a little mentioned autonomic component, the NANC (nonadrenergic noncholinergic) system, mediates relaxation.

Nitric oxide

•  Nitric Oxide (NO) •  endothelial nitric oxide synthase (eNOS), •  unusual in that it diffuses across

"postsynaptic" membrane •  affects guanylyl cyclase (GC) involved in

making cGMP •  NO = endothelial derived relaxation factor

(EDRF)

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•  mediator of parasympathetic nervous system's dilation of arterioles in corpus cavernosum.

•  Viagra (sildenafil) inhibits the PDE that breaks down cGMP

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•  2003 Something's gotta give, Jack Nicholson •  Viagra contraindicated w/ nitroglycerine. •  (also listed in advertisements for ED (erectile

dysfunction) medications because of interaction and resulting low blood pressure)

•  People take nitroglycerine for angina (chest pain), and it releases NO (nitric oxide) and relaxes the coronary arteries