Neurotransmission and Acetylcholine Effects

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Questions and Answers

Which of the following best describes the primary effect of acetylcholine on skeletal muscle?

Inhibition, leading to muscle relaxation

Excitation, leading to muscle contraction (correct)

Modulation of muscle sensitivity to pain

Regulation of muscle glycogen storage

Where are muscarinic receptors typically found in the body?

Only in the parasympathetic ganglia

Primarily in the central nervous system, heart, lungs, upper GI tract, and sweat glands (correct)

Exclusively on preganglionic neurons

Exclusively on skeletal muscle cells

Which of the following statements regarding the role of Vagus cranial nerve with acetylcholine is accurate?

It has an inhibitory effect on the heart. (correct)

It activates muscarinic receptors in the skeletal muscles.

It regulates acetylcholine synthesis in the heart.

It has an excitatory effect on the heart.

What is the function of acetylcholinesterase in the cholinergic synapse?

To break down acetylcholine into choline and acetate Signup and view all the answers

Which of the following would be classified as an anticholinergic?

A substance that interferes with the action of acetylcholine Signup and view all the answers

Which neurotransmitter, when found in excessive amounts, is associated with neurodegenerative conditions like Amyotrophic Lateral Sclerosis (ALS)?

Glutamate Signup and view all the answers

Where in the neuron does the resynthesis of acetylcholine primarily take place?

In the pre-synaptic neuron Signup and view all the answers

Which type of receptor uses a G-protein causing a change in shape when acetylcholine binds?

Metabotropic receptor Signup and view all the answers

What is the primary role of glutamine synthetase in glutamate neurotransmission?

Metabolizing glutamate back into glutamine Signup and view all the answers

Which of the following is NOT a location where acetylcholine is secreted?

The postganglionic neurons of the sympathetic nervous system Signup and view all the answers

Which neurotransmitter is MOST associated with overall wakefulness and mood control?

Pons Signup and view all the answers

A deficiency in which neurotransmitter is most associated with symptoms such as increased carbohydrate cravings, sleep disturbances, and feelings of depression?

Serotonin Signup and view all the answers

Where is the majority (90%) of the body's total serotonin found?

Gastrointestinal (GI) tract Signup and view all the answers

Norepinephrine primarily binds with which type of receptors?

Noradrenergic receptors Signup and view all the answers

What do nicotinic receptors primarily facilitate?

Direct ion flow across the cell membrane Signup and view all the answers

The synthesis of norepinephrine directly involves which amino acid precursor?

Tyrosine Signup and view all the answers

Which essential amino acid is the direct precursor to the synthesis of serotonin?

Tryptophan Signup and view all the answers

Which of the following neurotransmitters is a gas, released by nerve terminals, that is particularly connected with long-term behavior and memory processes?

Nitric oxide Signup and view all the answers

What enzyme is responsible for the conversion of dopamine to norepinephrine?

Dopamine monooxygenase Signup and view all the answers

Which process is directly involved in the synthesis of epinephrine from norepinephrine?

Methylation Signup and view all the answers

What is a primary effect of dopamine secreted by neurons originating in the substantia nigra?

Inhibition Signup and view all the answers

Which neurotransmitter is primarily responsible for the 'fight or flight' response?

Epinephrine Signup and view all the answers

In which area of the brain do dopaminergic neurons primarily originate?

Substantia nigra Signup and view all the answers

What is the primary effect of exercise on the source of adrenaline?

It increases its production Signup and view all the answers

Which of the following directly activates both excitatory and in a few cases inhibitory receptors?

Norepinephrine Signup and view all the answers

Which neurotransmitter is primarily synthesized from serine via a specific enzyme?

Glycine, via serine hydroxymethyltransferase Signup and view all the answers

How does GABA primarily exert its inhibitory effect when chloride ions flow into the cell?

By causing hyperpolarization of the cell membrane. Signup and view all the answers

Which of the following best describes the primary function of GABA in the central nervous system?

To act as the primary inhibitory neurotransmitter. Signup and view all the answers

What key role does the enzyme glutamate decarboxylase play in neurotransmission?

Synthesizing GABA from glutamate Signup and view all the answers

What is a common pharmacological approach to increase GABA activity?

Using drugs such as valium (diazepam) Signup and view all the answers

Which statement accurately describes the effect of a decrease in GABA levels?

May result in anxiety due to decreased inhibition. Signup and view all the answers

Which neurotransmitter is often released in sensory pathways entering the CNS and generally causes excitation?

Glutamate Signup and view all the answers

How do GABAergic receptors function as ligand-activated chloride channels?

They open to allow chloride ions to pass when GABA binds. Signup and view all the answers

What is a crucial function of inhibitory neurotransmission in the brain?

To keep neural signals organized and segmented. Signup and view all the answers

In which location is GABA secreted by nerve terminals?

In the spinal cord, cerebellum, basal ganglia and cortex. Signup and view all the answers

What is the primary mechanism by which released norepinephrine (NE) is removed from the synaptic cleft, within a few seconds after the initial release?

Active reuptake of NE back into the adrenergic nerve ending. Signup and view all the answers

Which effect of dopamine is NOT considered to be a direct action OUTSIDE of the central nervous system (CNS)?

Regulation of motor control and coordination within brain circuits Signup and view all the answers

Which of the following best describes the function of receptors on effector organs in the context of neurotransmitter (NTM) action?

Receptors bind with NTMs outside of the cell membrane, leading to structural change in the protein molecule. Signup and view all the answers

In what way does glycine predominantly function as a neurotransmitter in the central nervous system (CNS)?

It works by opening chloride ion channels, causing hyperpolarization of the neuron. Signup and view all the answers

What is the impact of dopamine on the kidneys?

It increases sodium excretion and urine output. Signup and view all the answers

How does the duration of norepinephrine's activity differ outside of the nervous system after being released directly into the tissue versus being released into the bloodstream from adrenal medullae?

Tissue-released NE acts for only a few seconds due to rapid reuptake and diffusion, whereas bloodstream-released NE can remain active for up to several minutes. Signup and view all the answers

What is the primary role of monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) in the context of norepinephrine (NE) degradation?

MAO and COMT are tissue enzymes that destroy small amounts of NE after reuptake and diffusion. Signup and view all the answers

Which statement about the effect of dopamine on the digestive system is most accurate?

Dopamine decreases gastrointestinal motility and protects the intestinal mucosa. Signup and view all the answers

When a neurotransmitter binds to a receptor on an effector organ, what primary mechanism can lead to either the excitation or inhibition of that organ?

A change in membrane permeability to one or more ions. Signup and view all the answers

What best describes the effect of dopamine on the pancreas?

Decreased insulin secretion. Signup and view all the answers

Study Notes

Small Molecule Neurotransmitters (NTM)

Small molecule NTM are rapidly acting chemical messengers
Classified into four classes based on structure and function

Class I: Acetylcholine (ACh)

Organic chemical found in parts of the body, especially neuromuscular junctions and the autonomic nervous system (ANS)
Parts of the body using Ach are called cholinergic
Parts of the body that block ACh are called anticholinergic
Secreted by:
- Terminals of large pyramidal cells in the motor cortex
- Basal nuclei
- Motor neurons innervating skeletal muscles
- Preganglionic neurons of the ANS
- Postganglionic neurons of the parasympathetic nervous system
- Some postganglionic neurons of the sympathetic nervous system (less common)
Primarily excitatory, affecting muscles. Also exhibits inhibitory effects, like slowing the heart via the vagus nerve.
Critical for memory and learning
Associated with Alzheimer's disease, linked to its breakdown in neurons.
Commonly binds to nicotinic and muscarinic receptors
These receptors are collectively known as cholinergic receptors.
Nicotinic receptors are integral to movement and are ionotropic
Muscarinic receptors are metabotropic, using G-proteins to affect intracellular second messengers.
Post-synaptic: broken down by acetylcholinesterase
Choline is transported back to the presynaptic neuron for recycling
Acetate is either secreted or reused as acetyl CoA (important for metabolism)

Class II: Amines

Norepinephrine (NE)
- Secreted by: the brain stem and hypothalamus, pons (influencing wakefulness and moods), and most postganglionic neurons of the sympathetic nervous system (some excitatory, some inhibitory)
- It activates excitatory receptors but sometimes activates inhibitory receptors.
- Another name: noradrenaline (NA)
- Binds to alpha 1,2; beta 1,2,3 receptors
- Stress decreases its source; exercise increases it
- Associated with alertness and high alert states, as well as cardiovascular tone. Important for the autonomic nervous system (SNS),
- Synthesized from phenylalanine (an essential amino acid)
- Degradation:
  - Reuptake into adrenergic nerve endings: removing 50–80%
  - Diffusion into surrounding body fluids and blood
  - Destruction by tissue enzymes (monoamine oxidase [MAO] and catechol-O-methyltransferase [COMT])
  - NE secreted directly into the tissue, active for a few seconds; then reabsorbed or destroyed.
  - When released into the blood, NE stays active for 10–30 seconds before becoming inactive.
Epinephrine (EPI)
- Also known as adrenaline.
- Produced by adrenal glands and some neurons
- Binds to adrenergic receptors.
- Responsible for the fight-or-flight response in the ANS.
  - Highly responsive to metabolic or global challenges to homeostasis.
  - Used to treat cardiac arrest, anaphylaxis, hypoglycemia, and bronchospasm (e.g., using an EpiPen).
- Synthesized from norepinephrine (NE) by methylation.
Dopamine
- Secreted by neurons originating in the substantia nigra, terminating primarily in the striatal region of the basal nuclei.
- Primarily inhibitory in effect, preventing neuron firing.
- Binds to dopaminergic receptors.
- Levels have a correlation with parkinson’s disease and schizophrenia.
- Outside the CNS:
  - Dilates blood vessels by inhibiting norepinephrine release
  - Increases sodium excretion and urine output (kidneys)
  - Decreases insulin production (pancreas)
  - Decreases motility and protects intestinal mucosa (digestive system)
  - Decreases activity of lymphocytes (immune system)

Class III: Amino Acids

Glycine
- Secreted mainly at synapses in the spinal cord, brain stem, and retina.
- In some areas of the CNS, released with GABA.
- Contributes to motor, sensory, and auditory processing.
- Acts as an inhibitory neurotransmitter,
- Binds to Glycinergic receptors.
- Biosynthesized from the amino acid serine
GABA (Gamma-aminobutyric acid)
- Secreted by nerve terminals in the spinal cord, cerebellum, basal ganglia, and parts of the cortex.
- Believed to always cause inhibition.
- Primary inhibitory NTM in the central nervous system (CNS)
- Regulates muscle tone.
- Acts as a "brake" on excitatory neurotransmitters, reducing anxiety by increasing GABA activity.
- Binds to GABAergic receptors. The receptors are chloride channels that alter the flow of chloride ions in the cell. The inward or outward flow of these ions hyperpolarizes or depolarizes the cell
- Synthesized from glutamate.
Glutamate
- Secreted by presynaptic terminals in sensory pathways entering the CNS and many areas of the cerebral cortex.
- Probably always causes excitation.
- Toxic if in abundance as it leads to excessive cell activity resulting in cell death.
- GABA's counterpart.
- Primarily excitatory in the CNS.
- Important for learning and memory.
  - Binds to glutaminergic receptors. This action allows for changes in neural synapses, and the formation of new connections, which is essential to the creation of memories.
- Synthesized from glutamine.

Class IV: Nitric Oxide (NO)

Gaseous NTM.
Secreted by nerve terminals in brain regions associated with long-term behavior and memory.
Different synthesis than other NTMs: synthesized as needed in the presynaptic terminal, not preformed, and not stored in vesicles.
Diffuses into the postsynaptic terminal after being produced, affecting intracellular metabolism to change neuron excitability for longer than a few seconds.

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Test your knowledge on the effects of acetylcholine and its role in neurotransmission. This quiz covers various aspects including receptor types, neurotransmitter functions, and related neurodegenerative conditions. Dive into the significance of acetylcholine and other neurotransmitters in the nervous system.