Efferent Peripheral NS: The Autonomic & Somatic Motor Divisions

Ch 11: Efferent Peripheral NS: The Autonomic & Somatic Motor Divisions

Homeostasis and theAutonomic Division • BP, HR, Resp., H2O balance, Temp. . . • Mostly dual reciprocal innervation • Sympathetic: flight-or-fight • Parasympathetic: rest and digest

Autonomic pathway: 2 Efferent Neurons in Series Preganglionic neuron cell body in CNS Synapsis in autonomic ganglion outside CNS  divergence Postganglionic neurons target cells?

= Thoracolumbar • division (T1 to L2) • Preganglionic neurons from thoracolumbar region of spinal cord • Pre and paravertebral ganglia • Long postganglionic axons secrete NE onto adrenergic receptors

= Craniosacral Division • Long preganglionic axons from brain & S2- S4 • Intramural ganglia • Postganglionic neurons secrete Ach onto cholinergic muscarinic receptors

Most Common Autonomic NTs: • Acetylcholine (ACh) ACh neurons & ACh receptors are called cholinergic(nicotinic or muscarinic).Located at autonomic preganglionic & para-sympathetic postganglionic synapses • Norepinephrine (NE) NE neurons & receptors are called (nor) adrenergic ( and ). Located at sympathetic postganglionic synapses Fig 11-7

NTs of Autonomic NS Compare to Fig 11-7  andβ

Neuroeffector Junction of ANS = Synapse between postganglionic cell and target organ Most are different from model synapse: Axon has varicositiescontaining neurotransmitter (compare to Fig 8-20, p. 270) Fig 11-8

Varicosity of Sympathetic Neuron Fig11-9

Two Types of Cholinergic Receptors: 1) Nicotinic cholinergic receptor • Nicotine = agonist • In autonomic ganglia & somatic NS • Directly opens a Na+ / K+ channel:  ? • Curare = antagonist

2) Muscarinic cholinergic receptor • Muscarine = agonist • Found in neuro-effector junctions of parasympathetic branch • G-protein coupled mechanisms • Atropine = antagonist Amanita muscaria

MuscarinicACh Receptors are G-protein Mediated Example: Sweat Glands Other examples have more complex with 2nd messenger mechanisms

Summary: Pre- & Postganglionic Parasympathetic Neurons Release ACh nicotinic muscarinic Receptors

Adrenergic Receptors Found in neuroeffector junctions of sympathetic branch G protein linked, with various 2nd mess. mech. Receptors:NE > E (most common) Excitation [Ca2+]in  muscle contraction or secretion by exocytosis.  Inhibition of GI tract and pancreas

 - Receptors Clinically more important • 1 Excitation heart (E = NE) • 2 usually inhibitory: smooth muscle relaxation of some blood vessels and bronchioles(E > NE!) • “ -blockers” = Antagonists (e.g.: Propranolol and metoprololToprol-XL)

Termination of NT Activity • ACh esterase • Catecholamine reuptake • repackaging • degradation (MAO) Fig 8-22 Fig 11-9

Somatic Motor Division • Pathway consists of single neuron from CNS to target • Neuromuscular junction: nicotinic cholinergic receptors • Always excitatory  muscle contracts

Somatic Neuromuscular Junction Fig 11-13

Agonists and Antagonist of ANS Direct Antagonists • Atropin muscarinic • Curare  nicotinic • Propranolol  1 and 2 • Metoprolol  1

See Table 11-3 Indirect (Ant)agonists • Botulinum toxin  inhibits Ach release • Neostigmine inhibits AchE(organophosphate insecticides, such as para-, malathion) Therapy for MG • Cocaine prevents NE reuptake • Amphetamines stimulate NE release

Also review Tables 11-1 11-4 11-5 A Powerful Addiction

Review Fig 11-11 The End

Efferent Peripheral NS: The Autonomic & Somatic Motor Divisions