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?

<p>To break down acetylcholine into choline and acetate (A)</p> Signup and view all the answers

Which of the following would be classified as an anticholinergic?

<p>A substance that interferes with the action of acetylcholine (D)</p> Signup and view all the answers

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

<p>Glutamate (C)</p> Signup and view all the answers

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

<p>In the pre-synaptic neuron (B)</p> Signup and view all the answers

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

<p>Metabotropic receptor (D)</p> Signup and view all the answers

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

<p>Metabolizing glutamate back into glutamine (D)</p> Signup and view all the answers

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

<p>The postganglionic neurons of the sympathetic nervous system (B)</p> Signup and view all the answers

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

<p>Pons (B)</p> 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?

<p>Serotonin (A)</p> Signup and view all the answers

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

<p>Gastrointestinal (GI) tract (A)</p> Signup and view all the answers

Norepinephrine primarily binds with which type of receptors?

<p>Noradrenergic receptors (A)</p> Signup and view all the answers

What do nicotinic receptors primarily facilitate?

<p>Direct ion flow across the cell membrane (D)</p> Signup and view all the answers

The synthesis of norepinephrine directly involves which amino acid precursor?

<p>Tyrosine (D)</p> Signup and view all the answers

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

<p>Tryptophan (B)</p> 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?

<p>Nitric oxide (A)</p> Signup and view all the answers

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

<p>Dopamine monooxygenase (A)</p> Signup and view all the answers

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

<p>Methylation (D)</p> Signup and view all the answers

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

<p>Inhibition (D)</p> Signup and view all the answers

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

<p>Epinephrine (C)</p> Signup and view all the answers

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

<p>Substantia nigra (D)</p> Signup and view all the answers

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

<p>It increases its production (B)</p> Signup and view all the answers

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

<p>Norepinephrine (B)</p> Signup and view all the answers

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

<p>Glycine, via serine hydroxymethyltransferase (D)</p> Signup and view all the answers

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

<p>By causing hyperpolarization of the cell membrane. (D)</p> Signup and view all the answers

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

<p>To act as the primary inhibitory neurotransmitter. (A)</p> Signup and view all the answers

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

<p>Synthesizing GABA from glutamate (A)</p> Signup and view all the answers

What is a common pharmacological approach to increase GABA activity?

<p>Using drugs such as valium (diazepam) (D)</p> Signup and view all the answers

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

<p>May result in anxiety due to decreased inhibition. (A)</p> Signup and view all the answers

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

<p>Glutamate (A)</p> Signup and view all the answers

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

<p>They open to allow chloride ions to pass when GABA binds. (A)</p> Signup and view all the answers

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

<p>To keep neural signals organized and segmented. (D)</p> Signup and view all the answers

In which location is GABA secreted by nerve terminals?

<p>In the spinal cord, cerebellum, basal ganglia and cortex. (D)</p> 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?

<p>Active reuptake of NE back into the adrenergic nerve ending. (A)</p> 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)?

<p>Regulation of motor control and coordination within brain circuits (C)</p> 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?

<p>Receptors bind with NTMs outside of the cell membrane, leading to structural change in the protein molecule. (C)</p> Signup and view all the answers

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

<p>It works by opening chloride ion channels, causing hyperpolarization of the neuron. (A)</p> Signup and view all the answers

What is the impact of dopamine on the kidneys?

<p>It increases sodium excretion and urine output. (B)</p> 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?

<p>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. (A)</p> 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?

<p>MAO and COMT are tissue enzymes that destroy small amounts of NE after reuptake and diffusion. (B)</p> Signup and view all the answers

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

<p>Dopamine decreases gastrointestinal motility and protects the intestinal mucosa. (A)</p> 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?

<p>A change in membrane permeability to one or more ions. (B)</p> Signup and view all the answers

What best describes the effect of dopamine on the pancreas?

<p>Decreased insulin secretion. (C)</p> Signup and view all the answers

Flashcards

What is acetylcholine?

Acetylcholine (ACh) is a neurotransmitter found in various parts of the body, particularly at neuromuscular junctions and within the autonomic nervous system (ANS).

What are cholinergics?

Cholinergics are cells, tissues, or organs that utilize acetylcholine as their primary neurotransmitter. They are involved in various bodily functions like muscle contractions and autonomic responses.

What are anticholinergics?

Anticholinergics interfere with the action of acetylcholine. They can block or inhibit acetylcholine's effects on cholinergic receptors, leading to various physiological changes.

Where is acetylcholine secreted from?

Acetylcholine is secreted by various neurons, including the large pyramidal cells of the motor cortex, basal nuclei, motor neurons innervating skeletal muscles, preganglionic neurons of the autonomic nervous system, postganglionic neurons of the parasympathetic nervous system, and some postganglionic neurons of the sympathetic nervous system.

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What is acetylcholine's main effect?

Acetylcholine primarily has an excitatory effect on muscles, including those in the gastrointestinal tract, but can also have inhibitory effects like slowing heart rate via the vagus nerve.

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What is acetylcholine's role in the body?

Acetylcholine plays a crucial role in memory and learning. Its breakdown is associated with conditions like Alzheimer's disease, highlighting its importance in cognitive functions.

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What receptors does acetylcholine bind to?

Acetylcholine primarily binds to two types of receptors: nicotinic and muscarinic receptors.

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What are nicotinic receptors?

Nicotinic receptors are found on muscle cells, in the central nervous system (CNS), and the autonomic nervous system (ANS). They are ionotropic receptors, meaning they directly open ion channels, facilitating the passage of ions and influencing nerve impulse transmission.

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What are muscarinic receptors?

Muscarinic receptors are found throughout the central and peripheral nervous systems, including the heart, lungs, upper gastrointestinal tract, and sweat glands. They are metabotropic receptors, meaning they work indirectly through a G-protein to initiate cellular signaling pathways.

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Glutamate

The primary excitatory neurotransmitter in the central nervous system (CNS). Plays a crucial role in learning and memory by binding to glutaminergic receptors, altering synapses, and forming new connections.

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GABA

The counterpart of GABA, responsible for inhibiting neuronal activity.

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Serotonin

A neurotransmitter involved in mood regulation, sleep, and appetite. Low levels are linked to depression, anxiety, and other mood disorders.

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Nitric Oxide

A gaseous neurotransmitter associated with long-term behavior and memory. It plays a role in the complex processes of learning and remembering.

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Glutamate Synthesis

A process where glutamate is converted into glutamine, then taken up by presynaptic terminals, and finally metabolized back into glutamate.

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Tryptophan

A key amino acid needed for serotonin synthesis. It's obtained through diet and found in foods like milk, eggs, and nuts.

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Norepinephrine (NE)

A neurotransmitter (NT) crucial for the sympathetic nervous system (SNS), responsible for "fight or flight" responses, and plays a key role in attention and concentration.

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Dopamine

A neurotransmitter (NT) that is a precursor to norepinephrine (NE). It's mainly associated with the brain's reward system and movement.

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Hydroxylation

The process of adding a hydroxyl group (-OH) to a molecule, a crucial step in the synthesis of NE and dopamine.

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Decarboxylation

The process of removing a carboxyl group (-COOH) from a molecule, another crucial step in the synthesis of NE and dopamine.

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Noradrenergic Receptor

A type of receptor that binds with norepinephrine (NE), responsible for various physiological effects. It is subdivided into alpha-1, alpha-2, beta-1, beta-2, and beta-3.

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Methylation

The final step in the synthesis of epinephrine from norepinephrine. It involves the addition of a methyl group (-CH3).

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Epinephrine (EPI)

A neurotransmitter (NT) that acts as a "fight or flight" mediator. It is released by the adrenal medulla and some neurons and binds to adrenergic receptors.

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Striatum

A crucial region in the brain responsible for planning, movement, and reward. Dopamine neurons terminate primarily in this area.

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Pons

Referred to as the bridge, it functions in controlling the overall activity and mood of the brain.

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Sympathetic Nervous System (SNS)

The part of the autonomic nervous system (ANS) responsible for "fight or flight" responses, involving norepinephrine (NE) as its primary neurotransmitter.

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Dopamine: What is its effect on neuron firing?

A neurotransmitter that inhibits the firing of neurons. It binds to dopaminergic receptors and plays a role in various brain functions, including movement, motivation, and reward.

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Glycine

A neurotransmitter that binds to Glycinergic receptors, playing a role in the central nervous system (CNS).

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What is the main function of norepinephrine?

A neurotransmitter that primarily functions in the central nervous system (CNS). It is involved in the regulation of mood, attention, arousal, and sleep.

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Glycine Synthesis

A non-essential amino acid synthesized from serine, catalyzed by glycine synthase.

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How is norepinephrine removed from the synapse?

The process of removing norepinephrine from the synapse. It involves three main mechanisms: reuptake, diffusion, and enzymatic degradation.

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GABA's Role

A crucial player in regulating muscle tone and preventing anxiety.

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How long does norepinephrine remain active in the synapse and the bloodstream?

Norepinephrine is inactivated within seconds of being released in the tissue, while in the bloodstream, it remains active for about 10-30 seconds.

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GABA Receptors

GABA receptors are ligand-activated chloride channels, allowing chloride ions to flow across cell membranes when activated.

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What are receptors on effector organs?

A type of protein receptor found on effector organs. They bind to neurotransmitters, leading to activation or inhibition of the effector organ.

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What is glycine's primary function?

An inhibitory neurotransmitter that is primarily secreted in the spinal cord, brain stem, and retina.

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GABA Synthesis

GABA synthesis involves the conversion of glutamate into GABA through the action of the enzyme glutamate decarboxylase.

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What is Neurotransmitter Transmissions?

The process of releasing neurotransmitters from the presynaptic neuron into the synaptic cleft, where they can bind to receptors on the postsynaptic neuron.

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GABA Inhibition

The process of inhibiting nerve activity through GABA, which flows into a neuron, making it less likely to fire.

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How does neurotransmitter binding affect the postsynaptic neuron?

The binding of a neurotransmitter to its receptor can cause changes in the structure of the receptor protein, leading to either excitation or inhibition of the postsynaptic neuron.

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GABA's Importance

GABA's role is crucial in maintaining a balanced neural environment, preventing excessive excitation and facilitating communication.

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What is GABA?

Inhibitory neurotransmitter that plays a role in the central nervous system and is involved in regulating muscle tone and neuronal activity.

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What is serotonin?

A neurotransmitter that functions in the central nervous system. It plays a role in regulating mood, anxiety, and sleep and is associated with a range of mental health conditions.

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GABA & Anxiety

A common medication like Valium (Diazepam) for anxiety works by increasing GABA activity, promoting a calming effect.

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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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