Vegetative Nervous System Quiz

Bases of Vegetative Nervous System. Nomenclature

• The Autonomic Nervous System regulates visceral functions without conscious control.
• Neuron communication occurs through synapses, involving the conversion of electrical signals to chemical signals (neurotransmitters) and back.
• Synapse is a junction between neurons, with presynaptic neurons carrying signals into the synapse and postsynaptic neurons carrying signals out.
• Ganglion is a group of nerve cells outside the brain or spinal cord.
• Preganglionic neurons carry signals into a ganglion, while postganglionic neurons carry signals out.
• Efferent fibers transmit signals from the CNS to the periphery, while afferent fibers transmit signals from the periphery to the CNS.
• Somatic nerves control voluntary movements.
• The ANS is divided into the sympathetic (adrenergic) and parasympathetic (cholinergic) systems, as well as the enteric system.

ANS Functions

• The autonomic system controls smooth muscle, exocrine and endocrine secretions, heart rate, and metabolic processes.
• Sympathetic and parasympathetic systems have opposing actions in some cases (e.g., heart rate, gastrointestinal smooth muscle), but not others (e.g., salivary glands, ciliary muscle).
• Sympathetic activity increases in stress (fight-or-flight response).
• Parasympathetic activity predominates during satiation and sleep.
• Both systems exert continuous physiological control of organs under normal conditions.

Chemical Transmission

• Autonomic efferent pathways consist of two neurons: preganglionic and postganglionic.
• Sympathetic ganglia are located outside the CNS, containing the nerve endings of preganglionic fibers and the cell bodies of postganglionic neurons.
• Parasympathetic postganglionic cells are mainly found in the target organs.

Main Transmitters

• Neurotransmitters are chemical molecules released from nerve terminals that bind to receptors on postsynaptic cells, triggering excitatory or inhibitory responses.
• The main neurotransmitters in the peripheral nervous system:
  • Sympathetic: acetylcholine (preganglionic), norepinephrine (postganglionic)
  • Parasympathetic: acetylcholine (preganglionic and postganglionic)
  • Somatic: acetylcholine (neuromuscular junction)
• Other transmitters, like nitric oxide, vasoactive intestinal peptide, ATP, neuropeptide Y, 5-hydroxytryptamine, GABA, and dopamine, also play roles.

Drugs Affecting Neurotransmission

• Autonomic Nervous System Drugs:

  • Agonists: mimic the action of ANS neurotransmitters (parasympathomimetics/cholinergics, sympathomimetics/adrenergics).
  • Antagonists: inhibit the action of ANS neurotransmitters (parasympatholytics/anticholinergics, sympatholytics/anti-adrenergics).
  • Indirect methods: interfere with neurotransmitter synthesis, storage, or metabolization.

• Sympathetic (Adrenergic) System:

  • Neurotransmitters: norepinephrine (NA), acetylcholine (Ach).
  • Adrenergic receptors (α1, α2; β1, β2, β3).

• Parasympathetic (Cholinergic) System:

  • Neurotransmitter: acetylcholine (Ach).
  • Receptor types: nicotinic, muscarinic (M1-M5).
  • Parasympathomimetic drugs reproduce parasympathetic stimulation.
  • Parasympatholytic drugs block parasympathetic stimulation effects.

• Neuromuscular Junction:

  • Motor plate: specialized area of skeletal muscle fiber rich in cholinergic receptors, part of the neuromuscular junction.
  • Motor nerves stimulate muscle by releasing Ach at the motor plate.
  • Nicotinic receptor antagonists block the motor plate, causing complete muscle relaxation and apnea.

Neurotransmission Blockers

• Tetrodotoxin, batrachotoxin, and snake venom interfere with neuromuscular function:
  • Tetrodotoxin: blocks sodium channels, preventing action potentials and leading to paralysis.
  • Batrachotoxin: keeps sodium channels open, causing continuous depolarization and muscle spasms.
  • Snake venom: blocks acetylcholine receptors or degrades acetylcholine, leading to paralysis.

Test your knowledge on the structures and functions of the Autonomic Nervous System (ANS). This quiz covers the nomenclature, including neuron communication, synapses, and the division of the ANS. Understand the roles of somatic, sympathetic, parasympathetic, and enteric systems.