Neurotransmitters and Receptors Study Quiz

Neurotransmitters and Receptors

• Receptors are integral membrane proteins in the post-synaptic cell's plasma membrane.

Cholinergic Neurons

• Release acetylcholine (ACh).
• Types of cholinergic neurons include: all preganglionic neurons, all parasympathetic postganglionic neurons, and sympathetic postganglionic neurons innervating sweat glands.
• ACh is stored in synaptic vesicles and released via exocytosis.
• Two types of cholinergic receptors:
  • Nicotinic receptors:
    • Located on sympathetic & parasympathetic postganglionic neurons, chromaffin cells, motor end plates, and neuromuscular junctions (NMJs).
    • Stimulated by acetylcholine and nicotine.
  • Muscarinic receptors:
    • Located on all effectors innervated by parasympathetic postganglionic neurons, and sweat glands.
    • Stimulated by acetylcholine.

Adrenergic Neurons

• Release norepinephrine (NE), also known as noradrenaline.
• Primarily found on most sympathetic postganglionic neurons.
• NE is stored in synaptic vesicles and released by exocytosis.
• Adrenergic receptors bind to both NE and epinephrine (adrenaline).
• NE can act as a neurotransmitter or a hormone released by chromaffin cells.
• Epinephrine is a hormone released by chromaffin cells.
• Adrenergic effects are typically longer lasting compared to cholinergic effects.
• NE is either reabsorbed by the axon that released it, or inactivated by enzymes (COMT and MAO).
• Two main types of adrenergic receptors:
  • Alpha: further sub-classified into α1, α2 subtypes.
  • Beta: further sub-classified into β1, β2, β3 subtypes.
  • Alpha1 and Beta1 receptors generally produce excitation.
  • Alpha2 and Beta2 receptors generally cause inhibition.
  • Beta3 receptors are only found in brown adipose tissue, and their activation stimulates thermogenesis (heat production).

Receptor Agonists and Antagonists

• Agonist: A substance that binds to and activates a receptor, mimicking the effect of a natural neurotransmitter or hormone.
• Antagonist: A substance that binds to and blocks a receptor, preventing a natural neurotransmitter or hormone from exerting its effect.

Effects of Sympathetic Stimulation (vs. Parasympathetic)

• Effects are longer lasting and more widespread due to greater divergence of sympathetic postganglionic axons activating multiple tissues simultaneously.
• Acetylcholinesterase quickly inactivates ACh, while NE lingers in the synaptic cleft.
• NE and epinephrine secreted into the blood from the adrenal medullae amplify and prolong responses caused by the neurotransmitter norepinephrine.

Nervous System Diseases

• Charcot-Marie-Tooth Disease (CMT):
  • Most common inherited disorder affecting motor and sensory nerves.
  • Initially involves the fibular nerve leading to foot and lower leg muscle impairment, then progresses to forearms and hands.
  • Characterized by:
    • Bilateral distal limb wasting and weakness.
    • Skeletal deformities.
    • Distal sensory loss and abnormal deep tendon reflexes (DTRs).
• Diabetic Neuropathy:
  • A common complication of diabetes mellitus due to long-term hyperglycemia impairing vasculature and nerve function.
  • Symptoms are typically distal, bilateral, and symmetrical.
  • Primarily affects sensory nerves but can affect motor or autonomic nerves.
• Alcoholic Neuropathy:
  • Caused by chronic alcohol abuse, with lesions affecting peripheral nerves attributed both to the toxin's direct effect and nutritional deficiencies.
  • Symptoms appear distally and symmetrically in a progressive pattern, affecting both motor and sensory nerves.
• Chronic Renal Failure:
  • Peripheral neuropathy generally symmetrical, progressive, and more common in the lower extremities (sensory & motor nerve atrophy and demyelination).
• Anemia:
  • Neuropathy patterns are usually distal and symmetrical, impacting motor and sensory function. Sensory loss, such as proprioception issues, can cause issues with walking.
• Guillain-Barré Syndrome (GBS):
  • Most common cause of rapidly progressive evolving motor and sensory problems, often peaking within 2-3 weeks.
  • Immune-mediated disorder potentially triggered by infections or vaccinations, resulting in demyelination (of Schwann cell myelin) and axonal degeneration.
  • Characterized by rapidly ascending symmetrical weakness and sensory impairments. Initially appearing in the toes, weakness progresses to arms, trunk, and facial muscles.
  • Recovery progresses from proximal to distal areas, and may take months or years.
• Poliomyelitis:
  • A viral infection damaging motor cell bodies, leading to asymmetrical paralysis.
• Post-Polio Syndrome:
  • Characterized by new muscle symptoms decades after recovering from paralytic polio, often featuring pain, muscle atrophy, and fatigue.
• Myasthenia Gravis:
  • Most common disorder of neuromuscular transmission with fluctuating weakness and fatigability of skeletal muscles. Caused by auto-antibodies antagonistically binding to ACh receptors and causing their destruction.
• Botulism:
  • Caused by the botulinum toxin produced by Clostridium botulinum, resulting in flaccid paralysis due to the toxin interfering with Ach release at motor endplates. Symptoms typically include malaise, weakness, blurred vision, and other gastrointestinal distress; progressing to dysphagia, dysarthria, and photophobia.

Test your knowledge of neurotransmitters and their receptors with this quiz. Focus on cholinergic and adrenergic neurons, including the roles of acetylcholine and norepinephrine. Understand the functions of nicotinic and muscarinic receptors to strengthen your grasp of neurobiology.