Autonomic Nervous System

• The PSNS has craniosacral outflow
• The SNS has thoracolumbar outflow
• The vagus nerve controls the heart, lungs, and upper GI tract
• The sacral outflow controls the lower GI tract, bladder, and genitalia
• The thoracolumbar outflow has three major outflows:

  1. Prevertebral ganglia
  2. Paravertebral ganglia
  3. Adrenal medulla
• In the PSNS, the pre-ganglionic (spinal/cranial) nerve is very long
• The adrenal medulla is directly innervated from the thoracolumbar outflow
• The PSNS and SNS have opposing effects on target organs, with the salivary glands being the only exception
• Three major classes of neurotransmitters:

  1. Amino acid transmitters
  2. Monoamines
  3. Quaternary amines
• Examples of amino acid transmitters

  GABA, glutamate, glycine
• Examples of monoamines

  Catecholamines, indoleamines, histamine
• Examples of catecholamines

  noradrenaline, adrenaline, dopamine
• Example of Indoleamines

  Serotonin
• Example of quaternary amine

  acetylcholine
• noradrenaline and adrenaline are central to the SNS
• acetylcholine is involved in both the SNS and PSNS
• In the somatic efferent system, post-ganglionic nerves release acetyl choline onto skeletal muscle synapses
• In the SNS, pre-ganglionic nerves are always cholinergic and all post-ganglionic nerves are adrenergic
• The only exception for the SNS is that acetyl choline acts on the muscarinic acetyl choline receptors on the sweat glands
• Adrenergic

  Releases noradrenaline
• Cholinergic

  Releases acetylcholine
• In the PSNS, pre-ganglionic nerves are cholinergic and post-ganglionic nerves are cholinergic
• In the pre-synaptic neuron, acetyl CoA and choline combine to form acetylcholine which is stored in vesicles
• Acetylcholine is broken down by acetylcholine esterase into choline and acetic acid
• What is the selective agonist for mAChRs?

  Muscarine
• mAChRs are metabotropic receptors
• muscarinic acetyl choline receptor = mAChR
• nicotinic acetyl choline receptor = nAChR
• What is the selective agonist of nAChRs?

  Nicotine
• nAChRs are ionotropic receptors
• When activated, nAChRs become permeable to cations
• M1 receptors are neural
• M2 receptors are cardiac
• M3 receptors are glandular/smooth muscle
• M1 receptors are excitatory
• M2 receptors are inhibitory
• M3 receptors are excitatory
• In the pre-synaptic neuron, dopamine is converted to noradrenaline via DA beta-hydroxylase
• Noradrenaline is taken back into the neuron and repackaged or broken down by MAO-A
• Adrenoceptors are metabotropic