ANS Neurotransmitters and Receptors
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Questions and Answers

Which enzyme is responsible for hydrolyzing acetylcholine into acetate and choline?

  • Pseudo-cholinesterase
  • Calmodulin
  • Acetylcholinesterase (correct)
  • Vesicular transporter

    • What triggers the release of acetylcholine from nerve terminals?

  • Opening of sodium channels
  • Diffusion of calcium ions (correct)
  • Binding of acetylcholine to receptors
  • Diffusion of potassium ions

    • Which type of cholinergic receptor is primarily associated with smooth muscle contraction?

  • Nicotinic
  • M2
  • M5
  • M3 (correct)

    • What is the composition of nicotinic receptors found at the neuromuscular junction in adults?

    <p>2α1- β1-2δ</p> Signup and view all the answers

    Which receptor type does acetylcholine activate primarily in the heart to open K+ channels?

    <p>M2</p> Signup and view all the answers

    What is the role of the vesicular transporter (VAChT) in cholinergic fibers?

    <p>Transport acetylcholine for storage</p> Signup and view all the answers

    Which fiber type does norepinephrine NOT release to?

    <p>Vasodilator fibers to skeletal muscles BVs</p> Signup and view all the answers

    What effect does ACh have on muscarinic M2 receptors?

    <p>Decreases adenylyl cyclase activity</p> Signup and view all the answers

    What characterizes cholinergic fibers in the autonomic nervous system?

    <p>They are involved in all preganglionic autonomic fibers.</p> Signup and view all the answers

    Which of the following is a characteristic of synapses in the autonomic nervous system?

    <p>The chemical transmitter is released into a space called the cleft.</p> Signup and view all the answers

    Which neurotransmitter is primarily released by cholinergic fibers?

    <p>Acetylcholine</p> Signup and view all the answers

    Which of the following fibers is involved in the sympathetic nervous system?

    <p>Preganglionic sympathetic fibers can release acetylcholine.</p> Signup and view all the answers

    What is a function of choline acetyltransferase in cholinergic neurons?

    <p>It synthesizes acetylcholine from acetyl Co-A and choline.</p> Signup and view all the answers

    Which statement accurately describes the binding of neurotransmitters to receptors?

    <p>Chemical mediators act on receptors after being transmitted across a synaptic cleft.</p> Signup and view all the answers

    What is the primary action of drugs targeting the autonomic nervous system?

    <p>To modulate the effectiveness of neurotransmitters on their receptors.</p> Signup and view all the answers

    Which of the following statements about postganglionic sympathetic fibers is true?

    <p>They can release norepinephrine or acetylcholine.</p> Signup and view all the answers

    What is the primary source of tyrosine used in the synthesis of catecholamines?

    <p>Dietary intake</p> Signup and view all the answers

    Which enzyme is responsible for converting dopamine to noradrenaline (NE)?

    <p>β-Hydroxylase</p> Signup and view all the answers

    What mechanism primarily accounts for the removal of secreted noradrenaline from the synaptic cleft?

    <p>Re-uptake into nerve endings</p> Signup and view all the answers

    Which enzyme's activity is inhibited by cocaine and tricyclic antidepressants in the context of noradrenaline removal?

    <p>Monoamine oxidase (M.A.O.)</p> Signup and view all the answers

    How is dopamine primarily transported to the vesicles for storage?

    <p>Via vesicular monoamine transporters</p> Signup and view all the answers

    What is typically contained in the granulated vesicles alongside noradrenaline?

    <p>Chromogranin A</p> Signup and view all the answers

    Which of the following is a function of phenylethanolamine-N-methyltransferase?

    <p>Transforms noradrenaline into adrenaline</p> Signup and view all the answers

    What is the predominant mechanism by which catecholamines are released from nerve endings?

    <p>Exocytosis</p> Signup and view all the answers

    What is the primary mechanism by which drugs can manipulate autonomic activity?

    <p>They affect chemical transmission at junctions.</p> Signup and view all the answers

    Which of the following drug actions can occur at the efferent autonomic pathway?

    <p>Stimulation or inhibition of various neurotransmitter processes.</p> Signup and view all the answers

    What type of drugs primarily affect the Parasympathetic Nervous System?

    <p>Drugs that enhance cholinergic activity.</p> Signup and view all the answers

    Which statement is true regarding sympatholytic drugs?

    <p>They block adrenergic receptor activity.</p> Signup and view all the answers

    How can drugs influence the breakdown of neurotransmitters in the autonomic system?

    <p>By promoting enzyme activity that degrades neurotransmitters.</p> Signup and view all the answers

    What is the primary action of norepinephrine (NE) when stimulated through α2 presynaptic receptors?

    <p>Decrease the release of norepinephrine</p> Signup and view all the answers

    Which of the following receptors increases cAMP levels when stimulated?

    <p>β1 receptors</p> Signup and view all the answers

    Which neurotransmitter is most closely associated with the response of dilating pupils?

    <p>Adrenaline</p> Signup and view all the answers

    What physiological effect does clonidine exert on blood pressure?

    <p>Decreases blood pressure</p> Signup and view all the answers

    What is the function of catechol-O-methyl-transferase (C.O.M.T.)?

    <p>Deactivation of catecholamines</p> Signup and view all the answers

    Which of the following is NOT associated with the sympathetic nervous system's alarm response?

    <p>Increased digestion</p> Signup and view all the answers

    In terms of receptor distribution, where are β-receptors prominently located?

    <p>Postsynaptic neurons and glial cells</p> Signup and view all the answers

    What effect does stimulation of β2 receptors generally have?

    <p>Leads to bronchodilation</p> Signup and view all the answers

    Study Notes

    ANS neurotransmitters, fibers and receptors

    • Synapses are junctions between neurons where signals are transmitted.

    • Chemical transmission is involved in autonomic synapses.

    • Cholinergic fibers release acetylcholine (ACh) and activate cholinergic receptors.

    • Adrenergic fibers release norepinephrine (NE) and activate adrenergic receptors.

    • Acetylcholine (ACh)*

    • Synthesis: ACh is synthesized from acetate and choline through a series of enzymatic steps.

    • Choline transporter (3) is inhibited by hemicholinium.

    • Choline acetyltransferase (1) catalyzes the synthesis of ACh.

    • Vesicular acetylcholine transporter (VAChT) transports ACh into vesicles.

    • Release: ACh is released by exocytosis triggered by Ca+2 influx.

    • Removal: ACh is broken down by acetylcholinesterase.

    • Cholinergic receptors: ACh activates two different receptor types:

      • Muscarinic receptors (M1-5) are G protein-coupled receptors (GPCR).
      • Nicotinic receptors are ligand-gated ion channels found in autonomic ganglia, CNS, and neuromuscular junctions.

    • Norepinephrine (NE)*

    • Synthesis: NE is synthesized from tyrosine through a series of enzymatic steps.

    • Tyrosine is transported into catecholamine-secreting neurons by a carrier.

    • Dopamine is produced by a series of enzymatic steps.

    • Vesicular monoamine transporters (VMAT-1 & -2), inhibited by reserpine, transport dopamine into vesicles.

    • Release: NE is typically released by exocytosis, along with ATP, chromogranin A, and β-hydroxylase enzyme.

    • Removal: NE is removed from the synaptic cleft by:

      • Re-uptake: into the adrenergic nerve endings by an active transport process, inhibited by cocaine and tricyclic antidepressants.
      • Diffusion away: from the nerve endings into the bloodstream.
      • Destruction: by enzymes such as:
        • Monoamine oxidase (MAO)
        • Catechol-O-methyltransferase (COMT)

    • Adrenergic receptors*

    • Post-synaptic receptors:

      • α1 receptors: increase IP3 and DAG.
      • α2 receptors: decrease cAMP.
      • β1, β2, β3 receptors: increase cAMP.

    • Pre-synaptic receptors: located on postganglionic adrenergic nerve endings and regulate neurotransmitter release.

      • Stimulation of α2 receptors decreases NE release.
      • Stimulation of β1 receptors increases NE release.

    Alarm response

    • Sympathetic nervous system activates as a unit during emergencies.
    • Effects:
      • Dilates pupils
      • Accelerates heart rate, respiration, and blood pressure
      • Constricts blood vessels in the skin
      • Lowers threshold in the brain
      • Stimulates lipolysis & glycogenolysis

    Drugs that affect the autonomic activity

    • Drugs can manipulate neurotransmitter synthesis, storage, release, breakdown, reuptake or receptor binding.

    • Drugs that affect the Parasympathetic Nervous System:*

    • Parasympathomimetics: mimic or enhance parasympathetic activity.

      • Acetylcholinesterase inhibitors: enhance the effects of ACh.
      • Muscarinic agonists: directly activate muscarinic receptors.

    • Drugs that affect the Sympathetic Nervous System:*

    • Sympathomimetics: mimic or enhance sympathetic activity.

      • Adrenergic agonists: directly activate adrenergic receptors.
      • Indirect sympathomimetics: increase NE release or inhibit its reuptake.

    • Sympatholytics: block sympathetic activity.

      • Adrenergic antagonists: block adrenergic receptors.
      • Drugs that interfere with NE synthesis, storage, or release.

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    Autonomic Nervous System Lecture Notes PDF

    Description

    Explore the key components of the autonomic nervous system (ANS), including neurotransmitters, fibers, and receptors. This quiz covers the synthesis, release, and breakdown of acetylcholine, as well as the functions of cholinergic and adrenergic fibers. Test your knowledge on how synapses transmit signals in the nervous system.

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