Chapter 16

  • Organization of Somatic and Autonomic Nervous System Neurons: The somatic nervous system controls skeletal muscle movement through somatic motor neurons, while the autonomic nervous system (ANS) regulates involuntary functions through autonomic motor neurons that innervate smooth muscle, cardiac muscle, and glands.

  • Comparison Between Somatic and Autonomic Nervous Systems:

    • Somatic: Controls voluntary movement; involved in reflex arcs.

    • Autonomic: Regulates involuntary functions; consists of sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) divisions.

  • Routes Taken by Sympathetic Axons:

    1. Spinal Nerves: Preganglionic axons synapse within the sympathetic chain.

    2. Sympathetic Nerves: Postganglionic neurons exit ganglia via sympathetic nerves.

    3. Collateral Ganglia via Splanchnic Nerves: Axons pass through chain ganglia without synapsing, synapsing in collateral ganglia instead.

    4. Innervation to the Adrenal Gland: Preganglionic axons synapse with adrenal medulla cells; secrete epinephrine and norepinephrine.

  • Adrenal Gland Sympathetic Innervation: Preganglionic axons synapse with adrenal medulla cells, which release epinephrine and norepinephrine into the bloodstream, enhancing sympathetic effects.

  • Enteric Nervous System Definition: A subdivision of the ANS that governs the function of the gastrointestinal system, capable of functioning independently via local reflexes.

  • Comparison of Sympathetic vs. Parasympathetic Activity:

    • Sympathetic: Prepares body for action, increasing heart rate, dilating air passages, and inhibiting digestion.

    • Parasympathetic: Promotes rest and recovery, reducing heart rate, constricting air passages, and stimulating digestion.

  • Locations of ANS Receptors: Located on effector organs innervated by the autonomic divisions, including adrenergic receptors (sympathetic) and cholinergic receptors (parasympathetic).

  • Clinical Impact: Influence of Drugs on the ANS: Certain drugs can mimic or block neurotransmitters, affecting how the sympathetic or parasympathetic systems operate, like beta-blockers which inhibit effects of norepinephrine.

  • Higher Parts of CNS Influencing Autonomic Functions: The hypothalamus plays a significant role in regulating the ANS by integrating signals from higher brain centers.

  • Representative Diseases and Disorders of the ANS: Disorders can include autonomic neuropathy, postural orthostatic tachycardia syndrome (POTS), and dysautonomia, affecting the functioning of autonomic control over bodily functions.