Autonomic Nervous System Quiz

Adrenergic (Sympathetic) Nervous System

• The adrenergic system, a part of the autonomic nervous system, is crucial for responding to stress.
• Stress triggers a "fight or flight" response.
• Physical indicators of this include:
  • Dilated pupils
  • Pale or flushed skin
  • Trembling
  • Rapid heart beat and breathing

Nervous System Organization

• The nervous system is divided into:
  • Central Nervous System (CNS): Brain and spinal cord
  • Peripheral Nervous System (PNS):
    • Somatic Nervous System (controls voluntary movements)
    • Autonomic Nervous System (controls involuntary functions, further divided into):
      • Sympathetic Nervous System (fight or flight)
      • Parasympathetic Nervous System (rest and digest)

Autonomic Nervous System Response

• The sympathetic nervous system regulates heart and peripheral vasculature activity, crucial in stress responses like trauma, fear, hypoglycemia, cold, and exercise.
• The sympathetic nervous system's response is "fight or flight" (stress), while the parasympathetic response is "rest and digest" (peace).

Neuronal Communication

• Action Potential: Electrical signals along the neuron membrane.
• Neurotransmitter: Chemical signals between neurons and other cells.
• Neuron communication involves chemical synapses, synaptic vesicles, and receptors.

Autonomic Nervous System: Details

• Sympathetic Nervous System:
  • Preganglionic neuron uses acetylcholine.
  • Postganglionic neuron uses norepinephrine except in the case of the adrenal medulla where it uses epinephrine (adrenaline).
  • Uses various receptors on effector organs.
• Parasympathetic Nervous System:
  • Preganglionic and postganglionic neurons both use acetylcholine.
  • Uses different receptors on effector organs.
  • Responsible for "rest and digest" functions.

Adrenergic Neurotransmitters

• Norepinephrine (NE)/Noradrenaline: Postganglionic sympathetic fibers and some tracts within the central nervous system (CNS).
• Epinephrine (Ep)/Adrenaline: Major hormone of the adrenal medulla.
• Dopamine (DA): A central and peripheral neurotransmitter.

Regulation of Catecholamine Release

• Homotropic regulation: A transmitter regulates its own release.
• Heterotropic regulation: A transmitter regulates another transmitter's release.
• Norepinephrine release is modulated by presynaptic receptors (like α2 and β2).

Catecholamine Degradation

• Catecholamines (epinephrine, norepinephrine, and dopamine) and serotonin are degraded mainly by monoamine oxidase (MAO) and catechol-o-methyl transferase (COMT).
• The end product, vanillylmandelic acid (VMA), is excreted in the urine; elevated VMA levels can indicate pheochromocytoma.

Adrenergic Receptors

• Adrenergic receptors are G-protein coupled receptors.
  • α Adrenergic Receptors (Alpha):
    • α1: Linked to Gq protein. Primarily stimulates smooth muscles, including blood vessels, GI tract, and bladder.
    • α2: Linked to Gi protein. Primarily inhibits norepinephrine release and stimulates other functions like liver glycogenolysis.
  • β Adrenergic Receptors (Beta):
    • β1: Linked to Gs protein. Primarily stimulates the heart (increasing heart rate, contractility, and conduction velocity).
    • β2: Linked to Gs protein. Primarily inhibits smooth muscle contraction, causing vasodilation and bronchodilation.
    • β3: Linked to Gs protein. Primarily stimulates lipolysis in adipose tissue.
  • Other: Dopamine receptors (D1, D2)

Alpha₁ Adrenergic Receptor Effects

• Blood Vessels: Vasoconstriction increasing blood pressure.
• GI Tract & Urinary Bladder: Relaxation of the wall and contraction of sphincters.
• Prostate & Vas Deferens: Contraction
• Liver: Weak glycogenolysis, potassium release (hyperkalemia)
• Eye: Contraction of the dilator pupillae muscle causing mydriasis (pupil dilation).

Alpha₂ Adrenergic Receptor Effects

• Neuron sites: Inhibits norepinephrine release from sympathetic nerves; ACh release in the heart and intestine.
• Central sympathetic outflow: Decreases blood pressure.
• Lipolysis: Inhibition.
• Insulin secretion: Predominant inhibition.

Beta₁ Adrenergic Receptor Effects

• Heart: Increases heart rate, contractility, and conduction velocity, increasing cardiac output and blood pressure.
• Renin secretion: Increase
• Lipolysis: No effect.

Beta₂ Adrenergic Receptor Effects

• Vasoconstriction: Inhibits
• Bronchodilation & Mast Cells: Causes bronchodilation and mast cell stabilization.
• Insulin: Weak release.
• Liver & Muscle Glycogenolysis: Predominant effect increasing blood glucose.

Beta₃ Adrenergic Receptor Effects

• Lipolysis: Stimulation
• Detrusor Smooth Muscle (Urinary Bladder): Relaxation
• Other: Various effects depending on location.

Sympathomimetic Drugs

• Direct acting: Directly activate receptors (e.g., epinephrine).
• Indirect acting: Increase the release of norepinephrine (e.g., amphetamine).
• Mixed acting: Both directly and indirectly activate receptors (e.g., ephedrine).

Specific Sympathomimetic Drugs

• Direct Acting: Norepinephrine, Epinephrine, Isoprenaline, Dopamine, Dobutamine, Phenylephrine, Midodrine, Beta-2 agonist, Fenoldopam.
• Indirect Acting: Amphetamine, Methylphenidate, Tyramine.
• Mixed Acting: Ephedrine, Pseudoephedrine.

Therapeutic Uses of Epinephrine

• Anaphylactic shock
• Asthma
• Cardiac arrest
• Bleeding
• Local anesthetics
• Open angle glaucoma

Norepinephrine

• Cardiovascular effects: Marked vasoconstriction leading to increased blood pressure (α₁). Positive chronotropic and inotropic effect (β₁).
• Therapeutic uses: Shock associated with hypotension (e.g., septic shock)

Dopamine and Dobutamine

• Dopamine (low dose): Stimulates D₁ receptors increasing renal blood flow.
• Dopamine (moderate to high dose): Stimulates α₁ and β₁ receptors raising blood pressure and heart rate.
• Dobutamine: Selective β₁ agonist, preferred for shock with maintained blood pressure. Acts on β₁ receptors increasing heart contractility & rate.

Adverse Effects

• Palpitations, anginal pain, arrhythmias (less with dobutamine).
• Hypertension (with dopamine).
• Headache, nausea, vomiting.

Selective α₁-Agonists (Phenylephrine)

• Long lasting effects, therapeutic uses:
  • Hypotensive states
  • Mydriatic for fundus examination
  • Eye and nasal decongestant
  • Local treatment for hemorrhoids.

Selective α₂-Agonists (Midodrine)

• Prodrug to active form, therapeutic uses:
  • Postural hypotension
• Adverse effects: Hypertension and bradycardia; rebound nasal congestion and atrophic dermatitis.

Selective β₁-Agonists (Dobutamine)

• Significant advantages over non-selective β agonists.
  • No cardiac complications in regular doses
  • Longer lasting action (not affected by MAO or COMT)
  • Available in various administration routes (oral, inhalation, parenteral).

Selective β₂ Agonists

• Therapeutic Uses:
  • Bronchial asthma (inhalation)
  • Preventing premature labor and threatened abortion.

Selective D₁ Agonist (Fenoldopam)

• Peripheral vasodilation in some vessels.
• Therapeutic Use: Severe hypertension (emergency).

Indirectly Acting Sympathomimetics (Amphetamine, Methylphenidate, Tyramine)

• Non-catecholamines; not degraded by MAO in the GIT.
• Longer duration of action
• Strong CNS stimulation and a strong anorexigenic effect.
• Tyramine is associated with a hypertensive crisis when taken in combination with monoamine oxidase inhibitors (MAOIs).

Mixed-Acting Drugs (Ephedrine and Pseudoephedrine)

• Act through both norepinephrine release and direct receptor activation.
• Therapeutic uses:
  • Epistaxis (topical)
  • Nasal decongestion (oral)
  • Spinal shock
  • Nocturnal enuresis
  • Urine incontinence

Fight-Flight-Freeze-Fawn Response

• This section presents a brief summary of different stress response actions to environmental triggers.

Test your knowledge on the autonomic nervous system, including the effects of adrenergic receptor activation and the functions of the sympathetic nervous system. This quiz covers various receptors and neurotransmitters involved in physiological responses, making it ideal for students of physiology or medicine.