Autonomic Nervous System Overview

Autonomic Nervous System Overview

• Preganglionic neurons use class B axons to transmit signals from the CNS, synapsing with postganglionic neurons.
• Postganglionic neurons use class C axons.

Neurotransmitters

• Acetylcholine (ACh) is the neurotransmitter released by all parasympathetic neurons.
• Norepinephrine (NE) is the primary neurotransmitter of the sympathetic nervous system (fight-or-flight response).

Receptors

• Cholinergic receptors: bind to acetylcholine.

  • Nicotinic receptors: Found on all postganglionic neurons in both sympathetic and parasympathetic systems, the adrenal medulla, and skeletal muscle.
  • Muscarinic receptors: Found on muscles and glands innervated by the parasympathetic division, as well as sweat glands and some blood vessels.

• Adrenergic receptors: bind to norepinephrine and epinephrine (adrenaline).

  • Alpha receptors: Found on most cells, except cardiac muscle cells.
    • Alpha 1: Binding with NE leads to excitation.
    • Alpha 2: Binding with NE leads to inhibition.
  • Beta receptors: Found on cardiac, smooth, and skeletal muscle cells, as well as in the liver, kidneys, and adipose tissue.
    • Beta 1: Found in cardiac muscle, liver, and kidney cells; binding with epinephrine (E) leads to excitation.
    • Beta 2: Found in smooth muscle of blood vessels in the heart and skeletal muscles; binding with epinephrine leads to relaxation and inhibition.
    • Beta 3: Found on adipocytes; binding with epinephrine leads to excitation, stimulating lipolysis.

Nerve Plexuses

• Brachial plexus: Innervates the upper limbs.
• Sacral plexus: Innervates the lower limbs and some hip structures.
• Ventral rami combine to form nerve plexuses, from which peripheral nerves branch.