Pharmacology Chapter 12: Cholinergic Drugs Affecting the Autonomic Nervous System

Cholinergic Drugs
Affecting the
Autonomic Nervous
System

Basic Functions of the Nervous
System
• Recognizes the changes in the internal environment and the external environment.
• It processes and integrates environmental
changes that are perceived.
• It also reacts to environmental changes by
producing an action or response.

Two major divisions of the nervous system
The central nervous system is composed of the brain and the spinal cord.

The peripheral nervous system is all other tissues outside of the CNS, including sensory and motor neurons.

Functional Divisions of the Central Nervous System

Divisions of the Peripheral Nervous
System
• Somatic nervous system is the voluntary control over skeletal muscles.
•Autonomic nervous system is the Involuntary control over smooth and cardiac muscle and glands.

Autonomic Nervous System has 2 parts
• Sympathetic Nervous System activates under stress and is responsible for Fight-or-flight response.
It Readies the body for an immediate response to
a potential threat

Parasympathetic Nervous System
– Activated under nonstressful conditions.
– Rest-and-digest response.
– Digestive processes promoted; heart rate and
blood pressure decline.

Sympathetic and Parasympathetic
Divisions
• Branches produce mostly opposite effects
• Homeostasis
– Proper balance of the two branches
– Achieved by changing one or both branches
• Branches do not always produce opposite
effects (e.g., sweat glands only controlled
by sympathetic nerves)

Effects of the parasympathetic and sympathetic nervous systems

Synaptic Transmission
The Synapse is a junction of neurons
• Connection of two neurons outside CNS—
ganglionic synapse
– Preganglionic neuron
– Postganglionic neuron
• Many drugs affect autonomic function by
altering neurotransmitter activity at the
second synapse

Basic structure of the autonomic pathway

Drugs Not Intended to Correct
Autonomic Nervous System
• System relatively free of disease
• Drugs used to stimulate or inhibit target
organs of the autonomic nervous system

Primary Neurotransmitters of
Autonomic Nervous System
Primary Neurotransmitters of
Autonomic Nervous System
• Acetylcholine (Ach)
– Neurotransmitter of parasympathetic nervous
system
• Norepinephrine (NE)
– Neurotransmitter of sympathetic nervous
system

Acetylcholine and Cholinergic
Transmission
Acetylcholine and Cholinergic
Transmission
• Released by cholinergic nerves
• Two types of cholinergic receptors
– Nicotinic receptors (named this because nicotine
binds to these receptors)
– Muscarinic receptors (named this because
muscarine from poisonous mushrooms binds to
these receptors)

Nicotinic Receptors
Nicotinic Receptors
• Located at ganglionic synapse in both
sympathetic and parasympathetic divisions
• Response
– Stimulates smooth muscle
– Stimulates gland secretion

Muscarinic Receptors
Muscarinic Receptors
• Located in parasympathetic target organs
except the heart
– Response
Stimulates smooth muscle
Stimulates gland secretion
• In heart: decreases heart rate and force of
contraction

Physiology of Acetylcholine
• Several mechanisms by which drugs may
act
• Synthesized in presynaptic nerve terminal
from choline and acetyl coenzyme A
• Ach in the synaptic cleft is rapidly destroyed
by the enzyme acetylcholinesterase (AchE)

Classification and Naming of
Autonomic Drugs
• Based on two possible actions affecting the
parasympathetic nervous system
• Stimulation of parasympathetic nervous
system
– Cholinergic agents or parasympathomimetics
• Inhibition of parasympathetic nervous
system
– Cholinergic-blocking agents, anticholinergics,
parasympatholytics, or muscarinic blockers

Cholinergic Drugs
(Parasympathomimetic)
• Divided into two subclasses
– Direct acting
Bind to cholinergic receptors to produce the rest-and digest
response
– Indirect acting
Inhibit the action of AchE
High potential for serious adverse effects

Table 12.1 Cholinergic Drugs

Cholinergic Agents
(Parasympathomimetic)
• Prototype drug: bethanechol (Urecholine)
• Mechanism of action: to activate the
parasympathetic nervous system
directly/indirectly, induce rest/digest
response

Cholinergic Agents
(Parasympathomimetic)
• Uses: glaucoma, urinary retention,
myasthenia gravis, Alzheimer’s disease
• Adverse effects: profuse salivation,
sweating, increased muscle tone, urinary
frequency, bradycardia

Cholinergic-Blocking Drugs
• Drugs that inhibit parasympathetic impulses
• Suppression of parasympathetic division
induces fight-or-flight symptoms
• Uses are predictable extension of
parasympathetic-blocking effects

Cholinergic-Blocking Drugs
• Effects include
– Pupil dilation (mydriasis)
– Increasing heart rate
– Drying glandular secretions
– Relaxing bronchi (asthma)

Cholinergic-Blocking Drugs
• Uses include
– Peptic ulcer disease
– Ophthalmic procedures
– Heart rhythm abnormalities
– Anesthesia adjunct
– Asthma and COPD
– Overactive bladder
– Parkinson’s disease

Cholinergic-Blocking Agents
• Prototype drug: atropine (Atropair,
Atropisol)
• Mechanism of action: to inhibit the
parasympathetic nervous system
• Primary use: peptic ulcers, irritable bowel
syndrome, mydriasis and cycloplegia during
eye examination, bradycardia,
preanesthetic, asthma

Cholinergic-Blocking Agents
• Adverse effects: tachycardia, CNS
stimulation, dry mouth, constipation,
urinary retention, dry eyes, decreased
sweating, photophobia

Two divisions of the Nervous System Central Nervous System (brain and spinal cord) Peripheral Nervous System (outside of brain and spinal cord) Two divisions of the Peripheral NS Efferent Division (consists of the neurons that carry signals AWAY from the …

Sympathetic nervous system mobilize the body’s fight-or-flight response & constantly active at a basic level to maintain homeostasis. Parasympathetic nervous system responsible for stimulation of “rest-and-digest” or “feed and breed” WE WILL WRITE A CUSTOM ESSAY SAMPLE ON ANY TOPIC …

What components of the sympathetic nervous system are innervated by cholinergic fibers? adrenal medulla and sweat glands ACh acts are 2 types of receptors: nicotinic and muscarinic. What types of receptors are these? nicotinic ACh receptors are Na+/K+ channels muscarinic …

What does dual innervation mean? Dual innervation means that a body organ receives neural innervation from both sympathetic and parasympathetic neurons on the ANS. Which division, sympathetic or parasympathetic, has longer preganglionic axons? Why? Most parasympathetic preganglionic axons are longer …

parasympathethic nervous system decrease heart rate, nonvascular smooth muscle contracts (increase mobility of digestive muscles, increased bladder motility) sphincters relax eye ciliary muscles contract increase in exocrine gland secretion Sympathetic nervous system Fight or flight increase in HR increase in …

Cholinergic Drugs Drugs that stimulate the parasympathetic nervous system (PSNS) The PSNS is the opposing system to the SNS Also known as cholinergic agonists or parasympathomimetics Mimic the effects of the PSNS neurotransmitter acetylcholine (Ach) Cholinergic Receptors Two types, determined …

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