Chapter 14: Autonomic Nervous System Overview

Overview of Autonomic Nervous System (ANS)

  • The ANS is responsible for involuntary control of bodily functions, distinct from the somatic nervous system which controls voluntary movements.

Somatic Nervous System

  • Involves control over skeletal muscles.
  • Uses direct pathways from the central nervous system (CNS) to the effectors (skeletal muscles).
  • Relies on motor neurons with long, heavily myelinated axons, facilitating rapid transmission of impulses.
  • Neurotransmitter: Acetylcholine, which stimulates muscle contraction.
  • Example: Reacting to a red traffic light by stopping the car.

Autonomic Nervous System (ANS)

  • Operates involuntarily and controls smooth muscle, cardiac muscle, and glands.
  • Divided into two branches:
    • Sympathetic Division: Prepares the body for high energy, stressful activities (fight or flight).
    • Parasympathetic Division: Promotes relaxation and conserves energy (rest and digest).

Key Differences between Somatic and Autonomic Nervous Systems

  • Effectors:
    • Somatic: Skeletal muscles.
    • ANS: Cardiac muscle, smooth muscle, and glands.
  • Efferent Pathway:
    • Somatic: Single, long myelinated motor neuron.
    • ANS: Two neurons (preganglionic and postganglionic), with connections at ganglia.
  • Neurotransmitters:
    • Somatic: Always acetylcholine at neuromuscular junctions.
    • ANS: Preganglionic fibers release acetylcholine; postganglionic fibers may release acetylcholine or norepinephrine.
  • Response:
    • Somatic: Voluntary muscle contraction.
    • ANS: Involuntary adjustments of organ function, such as heart rate.

Sympathetic Division

  • Prepares the body for "emergency situations."
  • Related to high-energy activities and stress (E-related activities).
    • Examples include excitement, emergency, embarrassment, exercise.
  • Increased heart rate, blood flow to muscles, pupil dilation, and decreased salivation.
  • Example: Recognizing danger (e.g., a bear approaching) triggers physiological responses for action.

Parasympathetic Division

  • Restores the body to resting state and conserves energy.
  • Promotes digestion, lowering heart rate and increase salivation.
  • D-related activities include digestion, defecation, and diuresis (urination).
  • Example: After the danger has passed, the heart rate decreases, and digestive functions resume.

Control of the ANS

  • The hypothalamus acts as a central regulatory organ for the autonomic nervous system.
    • Processes information from various body systems and coordinates responses.
    • Controls functions such as blood pressure, heart rate, digestion, and thermoregulation.

Homeostasis and Balance

  • Importance of balance between sympathetic and parasympathetic activity for maintaining homeostasis.
  • Chronic sympathetic activation can lead to stress-related health issues, while overly dominant parasympathetic activity can hinder necessary responses to danger.
  • Conclusion: A healthy balance of both systems is vital for overall well-being and effective functioning in various environments.