Chapter+14

Nervous System Overview

• The nervous system controls the body across various consciousness levels:

  • Consciousness: Defines thoughts, actions, and awareness.

  • Subconsciousness: Involves reactions and actions that can be modified by conscious thought.

    • Example: Breathing can be automatic but controlled if needed.

    • Includes subconscious memory and learned skills like typing or playing piano, which become automatic through repetition.

  • Unconsciousness: Processes that occur automatically without any need for thought.

Chapter 14: The Autonomic Nervous System

Peripheral Nervous System (PNS)

• Function: Transmits information between the Central Nervous System (CNS) and the body; regulates movement and internal environment.

• Components:

  • Afferent Neurons: Transmit sensory information to the CNS.

  • Efferent Neurons: Transmit motor information away from the CNS.

Efferent Components of PNS

• Two main motor pathways:

  • Somatic Nervous System (SNS):

    • Controls voluntary movement by sending signals to skeletal muscles.

  • Autonomic Nervous System (ANS):

    • Controls involuntary actions and regulates smooth muscles, cardiac muscles, and glands.

Divisions of the ANS

• Three divisions within the ANS:

  • Sympathetic Division:

    • Prepares the body for fight-or-flight response; regulates arousal and energy generation.

  • Parasympathetic Division:

    • Promotes rest-and-digest functions; counteracts sympathetic effects, calming the body.

  • Enteric Division:

    • Controls digestive tract operations; can function independently of CNS.

Functional Anatomy and Organization of ANS

• SNS vs. ANS Comparisons:

  • SNS uses lower motor neurons for voluntary control over skeletal muscles; reflexes operate within the spinal cord.

  • ANS operates through visceral motor neurons and ganglia:

    • Preganglionic Neurons: Arise from the CNS, take direct reflex responses.

    • Ganglionic Neurons: Found in autonomic ganglia, innervate effectors like smooth and cardiac muscles.

Autonomic Ganglia

• Sympathetic Division:

  • Short preganglionic fibers and long postganglionic fibers.

  • Ganglia located near the spinal cord (e.g., sympathetic chain, collateral ganglia).

• Parasympathetic Division:

  • Long preganglionic fibers and short postganglionic fibers, often in or near target organs.

Effects on Target Organs

• Parasympathetic Actions:

  • Constricts pupils, stimulates salivary glands, slows heart rate, and enhances digestive activity.

• Sympathetic Actions:

  • Dilates pupils, accelerates heart rate, inhibits digestive functions, stimulates glucose release.

Autonomic Stimulation Mechanisms

• Sympathetic Division Neurotransmitters:

  • Primary neurotransmitters: Acetylcholine (ACh), Epinephrine (E), and Norepinephrine (NE).

  • Two adrenergic receptor types: Alpha (sensitized by NE) and Beta (sensitized by E).

• Parasympathetic Division Neurotransmitter:

  • Primarily uses Acetylcholine (ACh); receptors include nicotinic and muscarinic types.

Autonomic Control and Regulation

• ANS maintains homeostasis and regulates functions autonomously.

• Visceral Reflexes:

  • Short reflexes bypass CNS; long reflexes involve CNS processing, controlling responses across multiple organs.

• Receptors for Monitoring Functions:

  • Baroreceptors (pressure changes), Chemoreceptors (chemical concentrations) play crucial roles in feedback loops regulating vital functions.

Functional Comparison: ANS Reflexes

• Visceral Reflexes:

  • Short Reflexes: Localized; involves structures within autonomic ganglia.

  • Long Reflexes: Integrates CNS, affecting entire organ systems.

• Examples of Visceral Reflexes:

  • Cardioacceleratory reflex (heart rate increase) and vasomotor reflexes (changes in blood vessel diameter).

Interaction of Brain Structures in ANS Control

• Key Structures:

  • Hypothalamus: Coordinates ANS and integrates with brain regions for autonomic responses based on emotion or stimuli.

  • Medulla Oblongata: Processes complex visceral reflexes signaling the body.

Summary & Key Takeaways

• The nervous system is a multi-layered entity capable of controlling both voluntary and involuntary functions. The relationship between the sympathetic and parasympathetic divisions is crucial for maintaining homeostasis and responding to environmental changes.