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Neurotransmitters and Receptors in the Autonomic Nervous System, Exams of Nursing

University of WestminsterNursing

The functioning of the autonomic nervous system, focusing on the neurotransmitters and receptors involved in the transmission of signals. It covers the role of acetylcholine (ach) and adrenergic receptors, as well as the effects of various drugs on these receptors.

Typology: Exams

2023/2024

Available from 03/19/2024

johnrays
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1. Somatic Nervous System The division of the peripheral nervous sys-
tem that controls the body's skeletal mus-
cles. In this system, a single myelinated
fiber carries signal from the CNS to skeletal
muscle to produce contraction. ACh is the
neurotransmitter.
2. Autonomic Nervous System the part of the peripheral nervous system
that controls the glands and the muscles of
the internal organs (such as the heart). Its
sympathetic division arouses; its parasym-
pathetic division calms. Two neurons are
in series, which synapse in ganglia, inner-
vate smooth muscle, heart, and glands.
Only the pre-ganglionic fiber is myelinat-
ed. ACh is neurotransmitter in all gan-
glia and post-ganglionic parasympathetic
fibers. Norepinephrine (NE) is neurotrans-
mitter in most postganglionic sympathetic
fibers.
3. Sympathetic Nervous System The division of the autonomic nervous sys-
tem that arouses the body, mobilizing its
energy in stressful situations. Preganglion-
ic fibers exit CNS in the thoracic and lumbar
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  1. Somatic Nervous System The division of the peripheral nervous sys- tem that controls the body's skeletal mus- cles. In this system, a single myelinated fiber carries signal from the CNS to skeletal muscle to produce contraction. ACh is the neurotransmitter.
  2. Autonomic Nervous System the part of the peripheral nervous system that controls the glands and the muscles of the internal organs (such as the heart). Its sympathetic division arouses; its parasym- pathetic division calms. Two neurons are in series, which synapse in ganglia, inner- vate smooth muscle, heart, and glands. Only the pre-ganglionic fiber is myelinat- ed. ACh is neurotransmitter in all gan- glia and post-ganglionic parasympathetic fibers. Norepinephrine (NE) is neurotrans- mitter in most postganglionic sympathetic fibers.
  3. Sympathetic Nervous System The division of the autonomic nervous sys- tem that arouses the body, mobilizing its energy in stressful situations. Preganglion- ic fibers exit CNS in the thoracic and lumbar

regions of the spinal cord. Most sympathet- ic ganglia are found in chains on each side of the spinal cord - "paravertebral ganglia".

ganglion. Innervated by preganglionic sym- pathetic fibers that release acetylcholine. Releases epinephrine (not NE) from chro-

maffin cells directly into the blood stream (Hence: epinephrine is a hormone not a neurotransmitter).

  1. Sweat Glands Glands involved in temperature control. Postganglionic sympathetic fibers release ACh not norepinephrine to activate "ec- crine" sweat glands.
  2. Cholinergic Terminals Terminals that release ACh. Steps of neu- rotransmission: storage of the transmitter. After synthesis in the cytosol, ACh is stored in vesicles where it accumulates to high concentration. Release of the transmitter. Arrival of the action potential depolarizes the membrane, which opens voltage-de- pendent Ca2+ channels. Influx of Ca2+ trig- gers exocytosis - ACh-containing vesicles fuse with the membrane and release their contents. This step is blocked by botulinum toxin. Empty vesicles are recycled. Activa- tion of œr2eceptors on the nerve terminal can inhibit further release of ACh - feed- back inhibition.

allows ACh to last longer in the synaptic cleft and exert its effects.

  1. Botulinum Toxin An acetylcholine antagonist; prevents re- lease by terminal buttons
  2. Adrenergic Receptors Receptor sites for the sympathetic neuro- transmitters norepinephrine and epineph- rine. Include ±1, ±2, ²1,a²n 2 d, ²3.They are all G-protein linked receptors. Their ago- nists are norepinephrine, epinephrine, and dopamine. Epinephrine binds to all adren- ergic receptors. Norepinephrine binds to all except ²2receptors. Dopamine not only binds to dopamine D receptors, but also to ²1and ±1adrenergic receptors. 15. Norepinephrine Transporter (NET) Neuronal uptake of noradrenaline; high affinity, selective, inhibited by cocaine, tri- cyclic antidepressants, amphetamines. It also transports dopamine and tyramine. It is a site of action of cocaine, whose pe- ripheral effects result from inhibition of NE reuptake by sympathetic neurons. Note: its CNS effects result from inhibition of dopamine reuptake by DAT in dopamin- ergic neurons. Cocaine, tri-cyclic antide- pressants and sibutramine inhibit reuptake of NE into the neuron by NET so effect of NE increases. Amphetamines and tyra- mine enter the nerve terminal and stimulate NE release via NET without needing neural stimulation.

back inhibition. Activation of M3 receptors on target leads to increase in cell Ca2+.

  1. Nicotinic Receptor Type of acetylcholine receptor protein that is characterized by also binding to nicotine and is an ionotropic receptor. Action po- tential going across preganglionic neuron causes opening of Ca2+ channels. Ca2+ triggers fusion of vesicles and release of ACh. Binding of two ACh opens the ion channel of this receptor (ligand-gated ion channel), and influx of Na+ triggers an action potential in the muscle. Agonists open the channel, and antagonists block the channel. They have 5 subunits. ACh is the only physiological agonist for these receptors.
  2. ±1Receptor An adrenergic receptor located at smooth muscles (causes contraction --> vasocon- striction), pupils (contracts radial muscle - mydriasis), pylorus, urinary sphincter, and prostate. It also causes ejaculation from pe- nis. Mechanism: Leads to constriction and results in an increase in cytosolic Ca2+ (cause contraction). 21. • They are located at smooth muscles (causes contraction --> vasoconstriction), pupils (contracts radial muscle -

sphincter, and prostate. It also causes ejaculation from penis.

- Mechanism: Leads to con- striction and results in an increase in cytosolic Ca2+ (cause contraction).

  1. ±2Receptor An inhibitory adrenergic receptor located at pre-synaptic nerve terminals that caus- es inhibition. Mechanism: results in a de- crease in cAMP (inhibition of signals).
  2. • Located at pre-synaptic nerve • Where are ±2receptors located? **terminals that causes inhibi- tion.
  • Mechanism: results in a de- crease in cAMP (inhibition of signals)**
  • What is their mechanism?
  1. ²1Receptor An adrenergic receptor located at the heart and the juxtaglomerular cells of the kidneys (release renin). Mechanism: results in an increase in cAMP. **25. • Located in the at the heart and the juxtaglomerular cells of the kidneys (release renin).
  • Mechanism: results in an in- crease in cAMP**
  • Where are ²1receptors located?
  • What is their mechanism?
  1. ²2Receptor An adrenergic receptor located in the lungs, blood vessels, GI tract, uterus, and liver. Causes smooth muscle relaxation. Mechanism: results in an increase in cAMP. Also to note, it is the only adrenergic recep- tor that norepinephrine is not sensitive to.

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27. • Located in lungs, blood ves- sels, GI tract, uterus, and liver. - Where are ²2receptors located? - What is their mechanism?

35. M2, ± 2 a, nd D2 Receptors

Which receptors cause a decrease in cAMP?

  1. ²2Receptor Which is the only adrenergic receptor that norepinephrine does not stimulate?
  2. Nicotinic N The type of nicotinic receptor found in gan- glia of both the sympathetic and parasym- pathetic nervous systems.
  3. Nicotinic M The type of nicotinic receptor found at the neuromuscular junction (NMJ).
  4. Acetylcholine A physiological agonist at both muscarinic and nicotinic receptors, therefore, will have many effects. It is a quaternary compound (limited distribution, poor GI absorption). Has a very short half life (ester bond cleaved very rapidly by BChE). Has virtu- ally no therapeutic uses. Only use: instilled into anterior chamber of the eye to induce miosis during ophthalmic surgery - effects last only for about ten minutes. 40. • Quaternary compound (poor distribution, poor absorption). Ester bond broken down rapid- ly after use (by BChE), so virtu- ally no therapeutic uses - Only use: instilled into ante- rior chamber of the eye to in- duce miosis during ophthalmic surgery - effects last only for about ten minutes.
    • What is the MOA of acetylcholine?
    • Therapeutic use?
  5. Nicotine A tertiary ammonium drug, very lipophilic so easily crosses mucosal membranes,

nicotinic N and nicotinic M receptors. Ef- fects: CNS effects - mild, alerting action. Tremor, emesis, stimulation of respiratory center, convulsion, respiratory failure, and fatal coma. It has sympathomimetic effects on cardiovascular system - causes vaso- constriction, increased HR --> increases BP. It has parasympathetic effects in GI and urinary tracts - cause nausea, vom- iting, diarrhea, and urination. In skeletal muscle, depolarization blockade results in flaccid paralysis including respiratory mus- cles - the channel is kept open! Treatment in overdose: give anticonvulsant (e.g. di- azepam) for CNS effects, give atropine to antagonize muscarinic effects, and provide mechanical respiration. It is used in treat- ment of nicotine withdrawal symptoms as an aid to smoking cessation. It is also used as an insecticide. The mechanism of ac- tion limits potential use of drugs on these receptors because both the sympathetic and parasympathetic nervous systems will be affected.

  1. • Tertiary ammonium drug, very • What is the MOA of nicotine? lipophilic so easily crosses mu- cosal membranes, BBB, skin, and kidney tubules. It accumu- lates in breast milk. It is an ag- onist at most nicotinic N and nicotinic M receptors. - CNS effects - mild, alerting action. Tremor, emesis, stimula- tion of respiratory center, con- vulsion, respiratory failure, and fatal coma. It has sympath- omimetic effects on cardiovas-cular system - causes vasocon-

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  • Effects?
  • How to reverse actions during overdose?
  • Why does the mechanism of action limit potential use of drugs on these receptors?