Introduction to Autonomic and Neuromuscular Pharmacology

Chapter 3 Introduction to Autonomic and Neuromuscular Pharmacology

I. Divisions of the Efferent Autonomic Nervous System (ANS) (Fig. 3-1)

A. Parasympathetic nervous system (PSNS): craniosacral division of the ANS

1. Origin from spinal cord

a. Cranial (midbrain, medulla oblongata)

2. Nerve fibers

a. Long preganglionic fibers

b. Short postganglionic fibers

3-1 Schematic representation of sympathetic, parasympathetic, and somatic efferent neurons. α, α-adrenoreceptor; β, β-adrenoreceptor; M, muscarinic receptor; N, nicotinic receptor; NM, neuromuscular.

PSNS = craniosacral origin

3. Neurotransmitters

a. Acetylcholine (ACh)

(1) Ganglia (nicotinic receptors)

(2) Somatic neuromuscular junction (nicotinic receptors)

(3) Neuroeffector junction (muscarinic receptors)

b. Actions terminated by acetylcholinesterase

ACh stimulates both nicotinic and muscarinic receptors.

c. All ganglia and adrenal medulla have nicotinic receptors.

4. Associated processes

b. Conservation of energy

c. Maintenance of organ function

PSNS conservation of energy at rest.

B. Sympathetic nervous system (SNS): thoracolumbar division of the ANS

1. Origin from spinal cord

b. Upper lumbar regions

2. Nerve fibers

a. Short preganglionic nerve fibers, which synapse in the paravertebral ganglionic chain or in the prevertebral ganglia

b. Long postganglionic nerve fibers

SNS = thoracolumbar origin

3. Neurotransmitters

a. ACh is the neurotransmitter at the ganglia (stimulates nicotinic receptors).

b. Norepinephrine (NE) is usually the neurotransmitter at the neuroeffector junction (stimulates α- or β-adrenergic receptors).

• Exception: ACh is the neurotransmitter found in sympathetic nerve endings at thermoregulatory sweat glands.

ACh is neurotransmitter at sympathetic thermoregulatory sweat glands

NE is neurotransmitter at sympathetic apocrine (stress) sweat glands

4. Associated processes

• Mobilizing the body’s resources to respond to fear and anxiety (“fight-or-flight” response)

II. Neurochemistry of the Autonomic Nervous System

A. Cholinergic pathways

1. Cholinergic fibers

a. Synthesis, storage, and release (Fig. 3-2A)

b. Receptor activation and signal transduction

(1) ACh activates nicotinic or muscarinic receptors (Table 3-1)

(2) All ganglia, adrenal medulla, and neuromuscular junction have nicotinic receptor

c. Inactivation

(1) ACh is metabolized to acetate and choline

3-2 Cholinergic and adrenergic neurotransmission and sites of drug action. A, Illustration of the synthesis, storage, release, inactivation, and postsynaptic receptor activation of cholinergic neurotransmission. B, Illustration of the synthesis, storage, release, termination of action, and postsynaptic action of adrenergic neurotransmission. Uptake I is a transporter that transports NE into the presynaptic neuron. Uptake II is a transporter that transports NE into the postsynaptic neuron. α, α-adrenoreceptor; β, β-adrenoreceptor; ACh, acetylcholine; COMT, catechol-O-methyltransferase; DA, dopamine; M, muscarinic receptor; MAO, monoamine oxidase; N, nicotinic receptor; NE, norepinephrine.

TABLE 3-1 Properties of Cholinergic Receptors

ACh action terminated by cholinesterases.

(2) Occurs by acetylcholinesterase (AChE) in the synapse

(3) Occurs by pseudocholinesterase in the blood and liver

2. Drugs that affect cholinergic pathways (Table 3-2)

a. Botulinum toxin

(1) Mechanism of action

• Blocks release of ACh by degrading the SNAP-25 protein, inhibiting neurotransmitter transmission

TABLE 3-2 Drugs that Affect Autonomic Neurotransmission

Mechanism	Drugs that Affect Cholinergic Neurotransmission	Drugs that Affect Adrenergic Neurotransmission
Inhibit synthesis of neurotransmitter	Hemicholinium*	Metyrosine
Prevent vesicular storage of neurotransmitter	Vesamicol*	Reserpine
Inhibit release of neurotransmitter	Botulinum toxin	Bretylium Guanethidine
Stimulate release of neurotransmitter	Black widow spider venom*	Amphetamine Tyramine
Inhibit reuptake of neurotransmitter	—	Tricyclic antidepressants Cocaine Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Like this: Like Loading... Related Related posts: Cholinergic Drugs Drugs Used in the Treatment of Bone and Calcium Disorders Antiarrhythmic Drugs Drugs Used in the Treatment of Hypothalamic, Pituitary, Thyroid, and Adrenal Disorders Stay updated, free articles. Join our Telegram channel Tags: Rapid Review Pharmacology Apr 8, 2017 \| Posted by admin in PHARMACY \| Comments Off on Introduction to Autonomic and Neuromuscular Pharmacology Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access