Autonomic Nervous System Overview

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Questions and Answers

Which enzyme directly facilitates the conversion of tyrosine to DOPA in the synthesis of noradrenaline?

Phenylalanine hydroxylase

Monoamine oxidase

Dopamine β-hydroxylase

Tyrosine hydroxylase (correct)

What is the primary mechanism for the removal of secreted noradrenaline from the synaptic cleft, according to the text?

Diffusion into the bloodstream and subsequent removal

Destruction by MAO located on the outer surface of the mitochondria

Re-uptake into the adrenergic nerve endings via active transport (correct)

Metabolic breakdown by COMT in the surrounding tissues

Which statement accurately describes the location of the enzyme MAO (monoamine oxidase) in relation to noradrenaline removal?

It is mainly present in blood plasma.

It is found on the outer surface of mitochondria. (correct)

It is located in the surrounding body fluids.

It is found within the adrenergic nerve endings.

Which of the following enzymes is NOT directly involved in the synthesis of noradrenaline?

Catechol-O-methyltransferase (B) Signup and view all the answers

In contrast to MAO, where is COMT (catechol-O-methyl-transferase) primarily located with regards to adrenergic nerve terminals?

Present diffusely in all tissues but not found in adrenergic nerve endings (B) Signup and view all the answers

Which of the following best describes the distribution of cholinergic fibers in the autonomic nervous system?

All preganglionic fibers, all postganglionic parasympathetic fibers, and some postganglionic sympathetic fibers (C) Signup and view all the answers

The complex mechanism that maintains the internal environment's temperature is primarily controlled by which brain structure?

Hypothalamus (C) Signup and view all the answers

What is the immediate precursor of acetylcholine in the synthesis pathway?

Choline and Acetyl-CoA (C) Signup and view all the answers

Stimulation of the preoptic area within the anterior hypothalamus would likely result in which physiological response?

Decreased heart rate and vasodilation (C) Signup and view all the answers

Where is the enzyme choline acetyltransferase primarily located?

In the axoplasm of cholinergic nerve endings (A) Signup and view all the answers

Which of the following best describes the origin of simple reflexes like micturition and defecation?

Sacral segments of the spinal cord (D) Signup and view all the answers

What is the functional role of mitochondria within the synaptic knobs of cholinergic fibers?

To provide ATP for the synthesis of the chemical transmitter (A) Signup and view all the answers

Which of the following is a specific function of some postganglionic sympathetic cholinergic fibers?

Causing secretion in sweat glands (C) Signup and view all the answers

Which neurotransmitter is most associated with the chemical transmission between pre- and postganglionic neurons, as well as between postganglionic neurons and autonomic effectors within the autonomic nervous system?

Acetylcholine (D) Signup and view all the answers

Which brain region primarily controls reflexes related to light and accommodation?

Midbrain (C) Signup and view all the answers

If a drug inhibits the reuptake of choline into cholinergic neurons, what would be the most immediate and direct result?

A decrease in the ability to synthesize acetylcholine (C) Signup and view all the answers

Stimulation of the posterior and lateral nuclei of the hypothalamus would most likely cause which of the following?

Increased heart rate and vasoconstriction (D) Signup and view all the answers

What is the role of the suprarenal medulla in response to the stimulation of acetylcholine?

Releases adrenaline and noradrenaline (D) Signup and view all the answers

Where is the majority of stored acetylcholine found in cholinergic nerve fibers?

In clear vesicles (C) Signup and view all the answers

What term best describes a chemical substance that binds to a specific site on a receptor, potentially mimicking or blocking the action of a neurotransmitter?

Ligand (C) Signup and view all the answers

Which of the following does not act as a center of the autonomic reflexes?

Cerebellum (A) Signup and view all the answers

What is the primary mechanism by which acetylcholine is released from nerve terminals?

Exocytosis triggered by calcium ion influx (A) Signup and view all the answers

Which enzyme is primarily responsible for the rapid breakdown of acetylcholine in the synaptic cleft?

Acetylcholinesterase (AChE) (B) Signup and view all the answers

Where is the enzyme acetylcholinesterase (AChE) NOT found in high concentrations?

Plasma (A) Signup and view all the answers

What happens to the choline molecules after acetylcholine is broken down?

They are transported back into the nerve terminal to be used again for synthesizing new acetylcholine (B) Signup and view all the answers

What type of fibers release noradrenaline (norepinephrine) as their primary chemical transmitter?

Postganglionic sympathetic fibers (except for sweat gland secretory fibers and skeletal vasodilator fibers) (D) Signup and view all the answers

Where is noradrenaline (norepinephrine) primarily synthesized?

In the terminal endings of adrenergic nerve fibers (A) Signup and view all the answers

In what form is noradrenaline (norepinephrine) stored within the granulated dark vesicles?

Bound to ATP and the protein chromogranin (A) Signup and view all the answers

Which of the following statements is correct regarding the comparison between AChE and PsChE?

AChE has a greater affinity for acetylcholine and is located in the membranes of cholinergic nerve endings. (C) Signup and view all the answers

Study Notes

Autonomic Nervous System: Centers & Chemical Transmission

The autonomic nervous system (ANS) regulates involuntary functions like heart rate, digestion, and breathing.
The ANS has centers for various reflexes, including simple ones (like micturition and defecation) and more complex ones (regulating respiration and blood pressure).
Centers are located in the spinal cord, medulla, midbrain, hypothalamus, and limbic system, and cerebral cortex.
The center in the body coordinating various reflexes is the Hypothalmus.

Chemical Transmission at Autonomic Junctions

Neurotransmitters transmit nerve impulses across synapses (junctions).
A ligand is a molecule that binds to a specific receptor site on a protein molecule, the ligand could be an agonist, antagonist, or a neurotransmitter itself.
More than 50 chemicals act as neurotransmitters.

Autonomic Function of the Hypothalamus

The hypothalamus plays a crucial role in autonomic functions.
It is considered the main regulatory center for the ANS (autonomic nervous system).
The anterior hypothalamus is involved in parasympathetic functions, decreases heart rate, blood pressure, and produces cutaneous vasodilation.
The posterior hypothalamus is involved in sympathetic functions, increases heart rate, blood pressure, and produces cutaneous vasoconstriction.
Lateral and posterior regions in relation to the hypothalamus have function related to feeding, hunger, satiety, blood pressure, and temperature regulation

Chemical Transmitters

Acetylcholine (ACh) is a neurotransmitter released by cholinergic fibers.
These fibers are crucial in both the parasympathetic and sympathetic systems
- All preganglionic fibers are cholinergic.
- Some postganglionic fibers (e.g., those to sweat glands and blood vessels) are also cholinergic.
Norepinephrine (NE) is released by adrenergic fibers.
- Most postganglionic sympathetic fibers are adrenergic.
- Adrenal medulla also releases NE and epinephrine into the bloodstream

Synthesis and Release of Acetylcholine:

Acetylcholine (ACh) is synthesized from choline and acetyl-CoA in the terminal nerve endings of cholinergic fibers.
Choline acetyltransferase is the enzyme that catalyzes this reaction.
When a nerve impulse reaches the axon terminals, voltage-gated calcium channels open.
This influx of calcium causes the release of ACh from synaptic vesicles into the synaptic cleft.

Removal of Acetylcholine:

Acetylcholinesterase (AChE) is an enzyme present in the synaptic cleft, rapidly breaks down ACh into choline and acetate, terminating its signal.
The breakdown products are taken back into the nerve terminal for reuse, completing the cycle.

Synthesis and Release of Norepinephrine

Norepinephrine (NE) is synthesized from tyrosine in the terminal nerve endings of adrenergic fibers and the adrenal medulla.
Tyrosine hydroxylase, DOPA decarboxylase, and dopamine β-hydroxylase are the enzymes involved in the synthetic pathway.
When a nerve impulse reaches the terminal endings, NE is released by exocytosis into the synaptic cleft.

Removal of Norepinephrine

Norepinephrine is removed from the synapse by reuptake into the presynaptic terminal, diffusion into the blood, and enzymatic degradation (by monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT)).

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Description

Explore the fundamentals of the autonomic nervous system (ANS), including its centers, roles in reflexes, and chemical transmission at autonomic junctions. This quiz delves into the functions of neurotransmitters and the crucial contributions of the hypothalamus in autonomic regulation.