What is the autonomic nervous system (ANS)?
The part of the nervous system that conveys CNS output to the rest of the body except for skeletal muscles; it controls involuntary processes.
What are the main processes regulated by the ANS?
Smooth muscle contraction, gland secretion (exocrine and endocrine), heartbeat, and energy metabolism.
What are the three divisions of the ANS?
Sympathetic, parasympathetic, and enteric.
Which two ANS divisions are the primary focus in pharmacology?
The sympathetic and parasympathetic systems.
What is the basic neural pattern of the ANS?
A two-neuron chain: a preganglionic neuron from the CNS synapses in a ganglion with a postganglionic neuron projecting to the target organ.
Where are parasympathetic ganglia located?
Close to or within the target organ.
Where are sympathetic ganglia located?
In paravertebral chains or midline ganglia.
What are the two main neurotransmitters in the ANS?
Acetylcholine (ACh) and noradrenaline (norepinephrine).
What neurotransmitter is released by all neurons leaving the CNS?
Acetylcholine (ACh).
What type of receptor does ACh from preganglionic neurons act on?
Nicotinic acetylcholine receptors (nAChRs).
What neurotransmitter is released by parasympathetic postganglionic neurons?
Acetylcholine (ACh), acting on muscarinic acetylcholine receptors (mAChRs).
What neurotransmitter is released by sympathetic postganglionic neurons?
Noradrenaline (norepinephrine), acting on α- and β-adrenoceptors.
What is the main exception to sympathetic neurotransmission?
Sweat glands, which use acetylcholine acting on muscarinic receptors.
What is unique about the adrenal medulla?
It functions as a modified sympathetic ganglion releasing adrenaline into the bloodstream.
What are the three main classes of nicotinic acetylcholine receptors?
Muscle, ganglionic, and CNS types.
Where are muscle nicotinic receptors located?
At skeletal neuromuscular junctions.
Where are ganglionic nicotinic receptors located?
At autonomic ganglia of both sympathetic and parasympathetic systems.
Where are CNS nicotinic receptors found?
Widely distributed in the brain.
What type of ion channel are nicotinic receptors?
Ligand-gated ion channels that increase Na+ permeability and depolarize the membrane.
What is the effect of nicotinic agonists on ganglia?
They excite both sympathetic and parasympathetic neurons, producing widespread and complex effects.
Give examples of nicotinic receptor agonists.
Nicotine and dimethylphenylpiperazinium (DMPP).
List some effects of nicotinic receptor agonists.
Tachycardia, increased blood pressure, variable GI motility, and increased secretions.
Give examples of nicotinic receptor antagonists.
Hexamethonium, trimetaphan, and tubocurarine.
What are the main effects of nicotinic antagonists?
Hypotension, loss of cardiovascular reflexes, inhibition of secretions, GI paralysis, and impaired urination.
