Autonomic Nervous System Overview

  • Overview of the Autonomic Nervous System (ANS)

    • The ANS is divided into the Sympathetic and Parasympathetic nervous systems, each serving different functions in the body.
    • Sympathetic Nervous System (SNS):
      • Prepares the body for "fight or flight" response.
      • Increases heart rate, blood flow to muscles, and energy release.
      • Key neurotransmitter: Norepinephrine (Adrenaline)
      • Short preganglionic fibers; synapse occurs in ganglia that are often close to the spinal cord.
    • Parasympathetic Nervous System (PNS):
      • Responsible for "rest and digest" activities.
      • Decreases heart rate and promotes digestion and energy conservation.
      • Key neurotransmitter: Acetylcholine (ACh)
      • Long preganglionic fibers; synapse generally occurs near target organs.

  • Neurotransmitters and Receptors

    • Acetylcholine (ACh):
      • Released by cholinergic fibers in the PNS.
      • Affects target cells like glands, cardiac muscle, and smooth muscle.
    • Norepinephrine:
      • Released by adrenergic fibers in the SNS.
      • Contains two types of receptors:
      • Alpha receptors: Generally excitatory
      • Beta receptors: Generally inhibitory
    • Receptors determine whether the response will be excitatory or inhibitory depending on the target tissue.

  • Control Mechanisms in ANS

    • Vasoconstriction and Vasodilation:
      • SNS: Increases blood flow to essential organs and muscles during emergencies.
      • PNS: Promotes blood flow to digestive organs at rest.
    • Dual Innervation:
      • Many organs receive innervation from both SNS and PNS, often with antagonistic effects.
      • Example: Heart rate modulation—SNS increases heart rate while PNS decreases it.
    • Sympathetic Tone:
      • Constant low-level activation of the SNS to maintain blood pressure and readiness.

  • Neuropharmacology

    • Drugs can mimic or inhibit neurotransmitter actions:
      • Sympathomimetics: Enhance SNS activity (e.g., ephedrine)
      • Parasympathomimetics: Mimic or enhance PNS activity
      • Beta-blockers: Inhibit SNS activity and lower heart rate.

  • Role of the Brain in ANS Regulation

    • Hypothalamus: Central in the regulation of homeostasis and stress response.
    • Cerebral Cortex: Influences stress responses based on emotions and experiences.
    • Spinal Cord: Plays a role in triggering reflexes and autonomic motor responses.

  • Additional Concepts

    • Excitatory vs. Inhibitory Responses:
      • EPSP (Excitatory PostSynaptic Potential) and IPSP (Inhibitory PostSynaptic Potential) guide the overall response behavior of tissues.
    • Receptors: Different receptors respond differently to neurotransmitters, leading to varied physiological effects based on location and type of target cells.
    • Pain Perception:
      • Distinction between somatic pain (from skin, muscles) and visceral pain (from internal organs).
      • Referred Pain: Pain perceived in a different location other than its actual source due to overlapping neural pathways.

  • Taste and Smell Mechanisms

    • Taste Buds:
      • Different regions of the tongue detect different tastes: salty, sweet, sour, bitter, umami.
    • Chemical processes:
      • Gustation involves detection of chemical particles that stimulate taste cells, leading to interpretations of flavor.
    • Odor detection:
      • Chemical molecules enter the nasal cavity and stimulate olfactory receptors which send signals to the brain for smell recognition.

  • Final Tips for Exam Preparation

    • Focus on the key functions and differences between the SNS and PNS.
    • Understand neurotransmitter roles and their respective receptors.
    • Remember dual innervation and how it affects physiological responses.
    • Be familiar with pharmacological terms and concepts related to modulation of the ANS.