Autonomic Nervous System Overview

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Questions and Answers

What is the primary function of alpha-2 adrenergic receptors in the sympathetic nervous system?

Stimulating norepinephrine release

Increasing heart rate

Inhibiting presynaptic norepinephrine release (correct)

Causing contraction of smooth muscles

Which physiological effect is primarily associated with beta-1 adrenergic receptors?

Relaxation of the GI tract

Increased heart rate and contractility (correct)

Vasodilation in skeletal muscles

Bronchodilation

What effect do beta-2 adrenergic receptors have on smooth muscles?

Inhibition of heart rate

Contraction of the bladder

Increase in blood pressure

Bronchodilation and relaxation of walls in various organs (correct)

Which of the following statements is true regarding beta-1 adrenergic receptors in the kidney?

They stimulate renin release. Signup and view all the answers

What second messenger system is activated by beta-1 adrenergic receptors?

cAMP Signup and view all the answers

What effect does a muscarinic agonist have on the heart?

Decreased heart rate and contraction Signup and view all the answers

What happens to the sphincters under a parasympathetic response?

They relax Signup and view all the answers

What is the effect of stimulating M3 receptors in the bladder wall?

Contraction of the bladder wall Signup and view all the answers

Which of the following statements about irreversible cholinesterase inhibitors is true?

They can be used as poisonous gases in warfare Signup and view all the answers

What is the outcome of an excessive cholinergic response regarding secretions?

Increased secretions including salivary and respiratory Signup and view all the answers

How does a muscarinic agonist affect the lungs?

Bronchoconstriction Signup and view all the answers

What is the role of M receptors in the CNS?

They are involved in cognitive function Signup and view all the answers

Which process is characterized by no recovery when cholinesterase is bound?

Phosphorylation Signup and view all the answers

Which receptors are classified as cholinergic?

Nicotinic and Muscarinic Signup and view all the answers

What is the primary neurotransmitter released at the ganglia in both the sympathetic and parasympathetic nervous systems?

Acetylcholine Signup and view all the answers

What regions of the spinal cord do the parasympathetic nerves originate from?

Craniosacral Signup and view all the answers

Which neurotransmitter is synthesized from tyrosine?

Norepinephrine Signup and view all the answers

The two types of adrenergic receptors are categorized into which subtypes?

Alpha and Beta Signup and view all the answers

Which muscarinic receptors are G-protein coupled to Gi and influence heart rate?

M2 and M4 Signup and view all the answers

What is the dominant neurotransmitter released by the adrenal medulla?

Epinephrine Signup and view all the answers

How many subdivisions are there for muscarinic receptors?

Five Signup and view all the answers

Which of the following statements about the PSNS is incorrect?

Receptors are referred to as adrenergic. Signup and view all the answers

Which action characterizes the effects of a muscarinic agonist?

Opposes adrenergic agonist effects Signup and view all the answers

What is the primary effect of beta-2 adrenergic receptors in the bladder wall?

Relaxation of the bladder wall Signup and view all the answers

Which of the following processes are mediated by beta-2 receptors in the liver?

Gluconeogenesis Signup and view all the answers

How do sympathomimetics primarily act on adrenergic receptors?

By directly activating adrenergic receptors or increasing neurotransmitter levels Signup and view all the answers

What is the effect of alpha-1 adrenergic receptors in the sphincter?

Induce contraction Signup and view all the answers

What happens when neurotransmitter reuptake is inhibited in the synapse?

Increased neurotransmitter concentration Signup and view all the answers

Which of the following actions is NOT a method to increase neurotransmitter levels in the synapse?

Decreasing synaptic cleft size Signup and view all the answers

What role does adenylate cyclase play in G-protein coupled receptor signaling?

Converts ATP to cAMP Signup and view all the answers

What type of receptor does the new compound act as an agonist for regarding skeletal muscle blood vessel relaxation?

Beta-2 receptor Signup and view all the answers

Which organ systems are primarily innervated by the sympathetic nervous system?

Liver, kidney, and uterus Signup and view all the answers

Which physiological effect is associated with the activation of M3 receptors in the bladder wall?

Contraction of the bladder wall Signup and view all the answers

What physiological response does the compound produce in bronchodilation?

Activation of beta-2 receptors Signup and view all the answers

What receptor mediation causes relaxation of the bladder wall according to the autonomic nervous system?

M3 receptors Signup and view all the answers

Which type of receptor is minimally involved in the relaxation of skeletal muscle vessels?

Alpha-2 receptors Signup and view all the answers

What is the net effect of the sympathetic nervous system on the bladder?

Inhibits urination Signup and view all the answers

Which receptor type causes vasoconstriction in the circulatory system?

Alpha-1 receptors Signup and view all the answers

What receptor does the sympathetic nervous system primarily activate to achieve relaxation of the bladder wall?

Beta-2 receptors Signup and view all the answers

Study Notes

Nomenclature

The Parasympathetic Nervous System (PSNS) is also called:
- Cholinergic
- Muscarinic
The Sympathetic Nervous System (SNS) is also called:
- Adrenergic

Anatomy

PSNS Nerves (Craniosacral):
- Originate from the top and bottom of the spinal cord
SNS Nerves (Thoracolumbar):
- Originate from the middle of the spinal cord

ANS Anatomy

The SNS and PSNS both have ganglia
The neurotransmitter released at the ganglia is acetylcholine (ACh)
The receptors in the ganglia are nicotinic receptors

Neurotransmitters (NT)

Acetylcholine is synthesized from Acetyl CoA and Choline
Acetylcholine is stored in synaptic vesicles

ANS Anatomy - The Adrenal Medulla:

The adrenal medulla is source of NT, releasing 80% epinephrine (Epi) and 20% norepinephrine (NE)

Neurotransmitters (NT): Synthesis

Key NT like dopamine, norepinephrine, and epinephrine are synthesized from tyrosine
The catecholamines (dopamine, norepinephrine, epinephrine) are a type of NT synthesized from tyrosine

Receptor Distribution: Cholinergic

There are two types of cholinergic receptors: Nicotinic and Muscarinic
Nicotinic receptors are found in:
- Muscle
- Ganglia
- Adrenal Medulla
- Central Nervous System (CNS)
- Immune System
Muscarinic receptors are divided into 5 subtypes:
- M1, M3, M5: G-protein coupled (Gq)
- M2, M4: G-protein coupled (Gi)

PSNS-Receptors

PSNS Receptors are referred to as Muscarinic (M)
Most drugs targeting M receptors are not classified by subtype
Fewer drugs target M receptors than adrenergic receptors
M receptors play an important role in drug side effects

M1, M3, M5 Receptors

G-protein coupled (Gq)
Found in:
- Smooth Muscle:
  - Contraction
- Bladder:
  - Contraction

M2, M4 Receptors

G-protein coupled (Gi)
Found in:
- Heart:
  - Decreased rate, contraction
  - Decreased heart rate

PSNS-Receptors

The effects of muscarinic agonists oppose the effects of adrenergic agonists
Effects of muscarinic agonists:
- Heart:
  - Decreased rate
  - Decreased contraction
- Lungs:
  - Bronchoconstriction
- Sphincters (GI and bladder):
  - Relaxation
- Walls:
  - Contraction of bladder and GI tract walls

To Pee or Not to Pee - Bladder and Urination

PSNS response in the bladder:
- M3 in bladder wall: contracts
- M3 in sphincter: relaxes
- This results in urination

PSNS-Receptors

Increased secretion:
- Salivary
- Respiratory
- Tears
Eye: (more on this later)

PSNS-Receptors

M receptors play an important role in CNS
M Receptors are important for cognitive function

Ligands for Muscarinic Receptors

Direct stimulation:
- Use of an agonist
Indirect stimulation:
- Acetylcholinesterase inhibitors increase the concentration of acetylcholine

Indirect-Acting Cholinergic Drugs

Cholinesterase can bind to 3 types:
- Acetylation:
  - Rapid Recovery
  - Physiological
- Carbamylation:
  - Slower Recovery
  - Reversible drugs (e.g., neostigmine)
- Phosphorylation:
  - No recovery
  - Irreversible drugs (e.g., "nerve gases")

Indirect-Acting Cholinergic Drugs:

Irreversible cholinesterase inhibitors have been used in chemical warfare

Excess Cholinergic Response

Excessive cholinergic response can cause:
- Excessive secretion
- Other related side-effects

Alpha-1 Adrenergic Receptors

G-protein coupled (Gq)
Causes contraction

Sympathetic Nervous System (SNS)

Alpha-2 (α-2)
- Function: inhibits the release of norepinephrine

Alpha-2 Agonists

Binding of alpha-2 receptor agonist:
- Inhibits the release of norepinephrine

Beta-1 (β-1)
- Function: stimulates the heart
- Location:
  - Heart:
    - Increased heart rate
    - Increased atrioventricular conduction
    - Increased contractility

Beta-1 Adrenergic Receptors

G-protein coupled (Gs)
Found in:
- Heart:
  - Increased heart rate
  - Increased contractility

Beta-1 Adrenergic Receptors

Liver, kidney, and uterus are innervated by the SNS
Kidney:
- Beta-1 receptors stimulate renin release
- Renin causes increased blood pressure

Beta-2 Adrenergic Receptors

Function: relaxation of smooth muscle
Location:
- Lungs: Bronchodilation
- Blood vessels in skeletal muscle: Vasodilation
- GI tract, bladder, uterus: relaxation of walls

Beta-2 Adrenergic Receptors

G-protein coupled (Gs)
Found in:
- Lungs: Bronchodilation

To Pee or Not to Pee - Bladder & Urination

SNS response in the bladder:
- β-2 in bladder wall: relaxes
- α-1 in sphincter: contracts
- This results in not urinating

Beta-2 Adrenergic Receptors

Liver, kidney, and uterus innervated by the SNS
Liver:
- Beta-2 receptors mediate glucose release by:
  - Gluconeogenesis: formation of new glucose
  - Glycogenolysis: breakdown of glycogen to glucose

Ligands for Adrenergic Receptors

Sympathomimetics mimic stimulation of the SNS:
- Direct activation of adrenergic receptors
- Increased NT in the synapse

Sympathomimetics

Increasing NT in the synapse by:
- Increasing neurotransmitter release
- Inhibiting reuptake of neurotransmitter

Fate of Neurotransmitters

Reuptake pumps sit presynaptically, remove neurotransmitters from the synapse

Sympathomimetics

Inhibiting neurotransmitter reuptake increases the amount of NT in the synapse

Sympathomimetics

Increasing NT in the synapse:
- Inhibiting neurotransmitter reuptake is more effective
- Muscarinic antagonists can also be used
- Beta-2 agonists can also be used, but have minimal effect

Case #2

A compound causes the following:
- Skeletal muscle vessels to relax
- Uterus relaxation
- Bronchodilation
This compound is likely a beta-2 agonist

ANS effects in the circulation (Summary/Review)

SNS:
- β-2 receptors (skeletal muscle): Vasodilation
- α-1 receptors: Vasoconstriction
PSNS:
- Minimal contribution to circulation
- Stimulation of M3 causes nitric oxide release, leading to vasodilation

Case #2

A compound causes the following:
- Skeletal muscle vessels to relax
- Bladder wall relaxation
- Bronchodilation
This compound is likely a beta-2 agonist

ANS Effects in the Bladder (Summary/Review)

SNS:
- β-2 receptors (bladder wall): Relaxation
- a-1 receptors (sphincter): Contraction
- Result: Do not pee
PSNS:
- M3 in bladder wall: Contraction
- M3 in sphincter: Relaxation
- Result: Pee

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Description

Test your knowledge on the anatomy and functions of the Autonomic Nervous System, including the Parasympathetic and Sympathetic Nervous Systems. This quiz covers nomenclature, neurotransmitter synthesis, and the roles of various receptors and ganglia. Challenge yourself to see how well you understand these complex systems.