Efferent Peripheral NS The Autonomic Somatic Motor Divisions

Efferent Peripheral NS: The Autonomic & Somatic Motor Divisions

Homeostasis and the Autonomic Division • BP, HR, Resp. , H 2 O 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 (T 1 to L 2) ® 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 & S 2 - S 4 ® 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 & parasympathetic 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 and β

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

Varicosity of Sympathetic Neuron Fig 11 -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 Amanita muscaria • Found in neuro-effector junctions of parasympathetic branch • G-protein coupled mechanisms • Atropine = antagonist

Muscarinic ACh Receptors are G-protein Mediated Example: Sweat Glands Other examples have more complex with 2 nd 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 2 nd mess. mech. Receptors: NE > E (most common) Excitation [Ca 2+]in muscle contraction or secretion by exocytosis. Inhibition of GI tract and pancreas

- Receptors Clinically more important – Excitation heart (E = NE) – 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 Fig 8 -22 • Catecholamine reuptake �repackaging �degradation (MAO) 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 �Curare muscarinic nicotinic �Propranolol �Metoprolol 1 and 2 1

Indirect (Ant)agonists See Table 11 -3 • Botulinum toxin inhibits Ach release • Neostigmine inhibits Ach. E (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