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Autonomic Nervous System - Anatomy & Physiology

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  • What is the primary function of the Autonomic Nervous System (ANS)?

    The ANS helps stabilize our internal environment and controls involuntary functions by innervating smooth muscle, cardiac muscle, and glands.

  • What are the main differences between the somatic and autonomic nervous systems in terms of effectors?

    Somatic nervous system controls skeletal muscle, while the autonomic nervous system controls smooth muscle, cardiac muscle, and glands.

  • Describe the neuron pathways in the somatic vs. autonomic nervous systems.

    Somatic: single motor neuron from CNS to muscle, heavily myelinated. Autonomic: two-neuron chain with lightly myelinated preganglionic and nonmyelinated postganglionic neurons.

  • What neurotransmitters are released by somatic and autonomic motor neurons?

    Somatic motor neurons release acetylcholine (ACh) and are always excitatory. Autonomic postganglionic fibers release either ACh or norepinephrine (NE), which can be excitatory or inhibitory depending on receptors.

  • What are the two main divisions of the autonomic nervous system and their general functions?

    Parasympathetic division calms the body (rest and digest). Sympathetic division arouses the body for action (fight or flight).

  • Where do parasympathetic and sympathetic fibers originate anatomically?

    Parasympathetic fibers originate from the craniosacral regions, while sympathetic fibers originate from the thoracolumbar regions of the spinal cord.

  • Compare the relative lengths of preganglionic and postganglionic fibers in parasympathetic vs. sympathetic divisions.

    Parasympathetic: long preganglionic and short postganglionic fibers. Sympathetic: short preganglionic and long postganglionic fibers.

  • Where are parasympathetic and sympathetic ganglia located?

    Parasympathetic ganglia are located in or near the target organs. Sympathetic ganglia are located close to the spinal cord in the sympathetic trunk.

  • Which cranial nerves carry parasympathetic preganglionic fibers?

    Cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal), and X (vagus) carry parasympathetic preganglionic fibers.

  • What is the role of the vagus nerve in the parasympathetic division?

    The vagus nerve (cranial nerve X) serves most thoracic and abdominal organs, providing parasympathetic innervation to the heart, lungs, digestive organs, and more.

  • What is the function of the sympathetic trunk ganglia?

    Sympathetic trunk ganglia form a chain alongside the vertebral column, allowing sympathetic fibers to synapse and distribute to various body regions.

  • Describe the three synapse options for sympathetic preganglionic fibers in the trunk ganglia.

    They can synapse at the same level, at a higher or lower level, or pass through to synapse in distant collateral ganglia.

  • What neurotransmitters do cholinergic and adrenergic fibers release?

    Cholinergic fibers release acetylcholine (ACh). Adrenergic fibers release norepinephrine (NE).

  • What types of receptors bind acetylcholine in the ANS and their effects?

    Nicotinic receptors are always stimulatory and found on postganglionic neurons. Muscarinic receptors can be excitatory or inhibitory depending on the target organ.

  • What are the main adrenergic receptor subtypes and their general effects?

    Alpha and Beta receptors bind norepinephrine. For example, B1 receptors increase heart rate, while B2 receptors relax bronchiole smooth muscle.

  • What is dual innervation in the autonomic nervous system?

    Most visceral organs receive input from both sympathetic and parasympathetic divisions, which usually have opposing effects to maintain balance.

  • How does sympathetic tone regulate blood vessel diameter?

    Sympathetic fibers maintain partial constriction of blood vessels. Increased firing causes vasoconstriction; decreased firing causes vasodilation.

  • What are the unique roles of the sympathetic nervous system beyond fight or flight?

    It regulates thermoregulatory responses, releases renin from kidneys, and influences metabolic effects.

  • How do parasympathetic and sympathetic effects differ in duration and localization?

    Parasympathetic effects are short-lived and localized due to one-to-one neuron connections and rapid ACh breakdown. Sympathetic effects are diffuse and longer-lasting due to branching fibers and circulating catecholamines.

  • What brain region acts as the integrative center for autonomic nervous system control?

    The hypothalamus is the main integrative center, coordinating autonomic functions and influencing lower CNS centers.