The Autonomic Nervous System and Cholinergic Drugs

Flashcards covering the divisions of the nervous system, cholinergic transmission, receptor subtypes, and key autonomic drugs.

Central Nervous System (CNS)

Considered the body's master control unit, consisting of the brain and spinal cord.

Peripheral Nervous System (PNS)

The body's link to the outside world, connecting the CNS to the rest of the body.

Autonomic Nervous System (ANS)

Regulates involuntary bodily processes such as heart rate, respiration, digestion, and pupil contraction without conscious direction.

Somatic Nervous System

Carries sensory information from sensory organs to the CNS and relays motor commands to muscles to control voluntary movements.

Sympathetic Nervous System (SANS)

Prepares the body for action and stress, commonly referred to as the "fight or flight" response.

Parasympathetic Nervous System (PANS)

Calms the body and helps conserve energy, often associated with "rest and digest" functions.

Preganglionic fiber

A nerve fiber that leaves the CNS and connects to a ganglion.

Postganglionic fiber

A nerve fiber that leaves the ganglion and innervates the effector organ.

Craniosacral Division

Another name for the Parasympathetic Nervous System, involving cranial nerves $3$, $7$, $9$, and $10$.

Dorsolumbar Division

Another name for the Sympathetic Nervous System, where ganglia are closed to the spinal cord and away from the supplied organ.

Preganglionic to postganglionic ratio (SANS)

The numerical ratio of fibers in the Sympathetic system, which is $1:20$.

Preganglionic to postganglionic ratio (PANS)

The numerical ratio of fibers in the Parasympathetic system, which is $1:1$.

Miosis

The contraction of the circular fibers of the Iris, resulting in pupil constriction.

Mydriasis

The dilation of the pupil, a typical response of the Sympathetic Nervous System.

Parasympathomimetics

Drugs that produce actions similar to the parasympathetic system, also known as Cholinergic drugs.

Parasympatholytic

Drugs that oppose the action of the parasympathetic system, also known as Anticholinergic drugs.

Acetylcholine (ACh)

A major neurohumoral transmitter in the cholinergic system used by the PANS and at neuromuscular junctions.

Nicotinic Receptors

Cholinergic receptors found on motor end plates, all ganglionic neurons, and the adrenal medulla; their effect is always stimulatory.

Muscarinic Receptors

Cholinergic receptors occurring on all effector cells stimulated by postganglionic cholinergic fibers; their effect can be inhibitory or excitatory.

$M_1$ Receptor

Located in autonomic ganglia, gastric glands, and the CNS; associated with depolarization and acid secretion.

$M_2$ Receptor

Located in the SA node and Atrium; its stimulation leads to hyperpolarization and decreased heart rate.

$M_3$ Receptor

Located in visceral smooth muscle, exocrine glands, and vascular endothelium; causes contraction, secretion, and vasodilation via NO release.

$N_M$ (Muscle type) Receptor

Nicotinic receptor located at skeletal muscle end plates responsible for muscle contraction.

$N_N$ (Ganglion type) Receptor

Nicotinic receptor located in autonomic ganglia and the adrenal medulla responsible for postganglionic impulses.

Pilocarpine

A natural alkaloid and direct-acting muscarinic agonist ($M_3$) used to treat glaucoma and xerostomia (dry mouth).

Anticholinesterases (Anti-ChEs)

Indirect-acting cholinergic drugs that inhibit the enzyme cholinesterase, protecting ACh from hydrolysis and causing it to accumulate.

Physostigmine

A reversible carbamate anticholinesterase and tertiary amine that crosses the blood-brain barrier; used for glaucoma and atropine poisoning.

Neostigmine

A synthetic quaternary ammonium reversible anticholinesterase that does not cross the BBB well; used to treat myasthenia gravis.

Negative Inotropy

A decrease in the contractility of the heart, produced by the action of Acetylcholine on $M_2$ receptors.

Negative Chronotropy

A decrease in the heart rate caused by Acetylcholine depressing the sinoauricular (SA) node.