72 - Intro to the Autonomic Nervous System

Efferent Neurons

Neurons leaving the CNS

Types of efferent neurons

Somatic Neurons and Autonomic Neurons

Somatic Neurons

involved in controlling voluntary functions

Autonomic Neurons

involved in regulating bodily functions outside of conscious control

Structure of Somatic Neurons

• Has no ganglia

  • NT goes straight to a Nicotinic Receptor (N_m) in skeletal muscle

NT of Somatic Neurons

ACh

Strucutre of Autonomic Neurons

• Have preganglionic neuron → ganglia → postganglionic neuron → Effector organ

Ganglia

Aggregation of nerve cell bodies located in the peripheral nervous system that function as relay stations

Ganglionic receptor

Nicotinic Receptor N_n

Strucutre of Sympathetic Autonomic Neurons

Short preganglionic neuron, Long post ganglionic neuron

Terminal Receptor of Sympathetic Autonomic Neurons

Adrenergic (alpha or beta)

Neuroeffector NT of Sympathetic Autonomic Neurons

Norepinephronne

Strucutre of Parasympathetic Autonomic Neurons

Long preganglionic neuron, Short postganglionic neuron

Neuroeffector NT of Paraympathetic Autonomic Neurons

Acetylcholine

Terminal Receptor of Parasympathetic Autonomic Neurons

Muscarinic Receptors

Sympathetic

• FFF

  • increase HR

  • Decrease GI motility, secretions, sphincters contract

  • Bronchodilation, decreased secretions

  • Bladder relaxation

  • Pupil dilation

    • accomodation for far vision

Parasympathetic

• Rest and Digest

  • decrease HR

  • Increase GI motility, secretions, sphincters contract

  • Bronchoconstriction, increased secretions

  • Bladder constriction

  • Pupil constriciton

    • accomodation for short distance vision

Synthesis of ACh

Choline acetyltransferase catalyzes the synthesis of ACh from choline and acetyl-CoA

Uptake into Storage Vesicles

ACh is protected from degredation in the vesicle

Release of NT

• Release is blocked by botulinum toxin

• Spider venom causes the release of ACh

Binding to the Receptor

• Postsynaptic receptor is activated by binding of the NT ACh

Degredation of ACh

ACh is rapidly hydrolyzed by acetyl-cholinesterase in the synaptic cleft

Recycling of Choline

Choline is taken up by the neuron. This transport is inhibited by hemicholinium

N_m

found at skeletal muscle neuromuscular junctions

N_n

Found in the CNS, ganglia and adrenal gland

M₂

Found in cardiac tissue

M₃

Found in glands, smooth muscle, endothelium

Termination of ACh action caused by

breaking down ACh

Acetylcholinestetase

breaks down ACh → important drug target!

Termination of Norandrenergic Transmission (epinephrine)

Agonist removal and reuptake into the presynaptic neuron

Types of Adrenergic Receptors

Alpha and Beta

a₁ Adrenergic Receptor

blood vessels

a₂ Adrenergic Receptor

CNS

b₁ Adrenergic Receptor

Heart

b₂ Adrenergic Receptor

bronchial smooth muscle

b₃ Adrenergic Receptor

Bladder detrusor muscle