Human body

Autonomic Nervous System Overview

Heart Rate and Oxygen Demand

  • Muscles undergo increased demand, leading to a rise in heart rate.
  • Example of autonomic response: heart rate increases to meet oxygen needs.
  • Increased oxygen is crucial under threat situations to support bodily functions.

Eye Muscles and Pupil Dilation

  • Different muscles in the eye are involved in pupil dilation.
    • Radial muscles: Allow pupil dilation to let in more light during dangerous situations.
    • Circular muscles: Lead to pupil constriction.
  • Knowledge of specific muscles may not be necessary: focus on the concept of dilation allowing more light entry.

Blood Flow and Digestive System During Stress

  • In threat situations, blood flow shifts from the digestive system to the muscles, enhancing physical readiness.
  • Example of blood flow diversion: blood vessels in lungs expand to increase airflow, while blood to intestines reduces.

Sympathetic vs Parasympathetic Responses

  • These systems are antagonistic:
    • Sympathetic: Activates during threats, increasing heart rate and blood flow to muscles.
    • Parasympathetic: Activates post-threat to restore body to calm state by decreasing heart rate and increasing digestion (vasodilation in intestines).

Autonomic Reflexes

  • Autonomic reflexes operate without conscious control; include heart rate regulation and digestion.
  • Example: Some individuals can control heart rate consciously.
  • Mind over Matter: Managing perceived threats can help control some autonomic functions.

Structure of Autonomic Reflexes

  • The sensory pathway for autonomic and somatic systems almost identical, featuring:
    • Receptor
    • Sensory neuron to the central nervous system
  • The message to the effector differs:
    • Autonomic: Involves two neurons with ganglia.
    • Somatic: Involves a single continuous neuron.

Definition of Ganglion

  • A ganglion functions as a junction box in electricity, connecting neurons in the autonomic nervous system for widespread signaling.

Sympathetic Nervous System

  • Definition: Subdivision of the autonomic nervous system controlling processes such as digestion, heart rate, and respiration; often related to energy expenditure and fight or flight responses.
  • Origin of Nerves: Arise from thoracic and lumbar spinal cord. Typically, they do not travel directly to targets but synapse at sympathetic ganglia.
  • Ganglia Types:
    • Sympathetic chain ganglia: Close to the spinal cord.
    • Prevertible ganglia: Closer to target organs.
  • Neurons:
    • Preganglionic neurons: Extend from spinal cord to ganglia; release acetylcholine.
    • Postganglionic neurons: Extend from ganglia to target organs; mainly release norepinephrine.

Parasympathetic Nervous System

  • Definition: Also a subdivision of the autonomic nervous system, it is focused on energy conservation and activities such as digestion; sometimes termed "rest and digest."
  • Origin of Nerves: Arise from brainstem and sacral spinal cord; synapse at ganglia near or within the target organs.
  • Neurons:
    • Like sympathetic system:
      • Preganglionic neurons: Release acetylcholine.
      • Postganglionic neurons: Also primarily release acetylcholine, providing innervation to the body.

Functional Differences between Somatic and Autonomic Systems

  • Somatic Reflexes:
    • Voluntary.
    • Fast, one long neuron to effector.
  • Autonomic Reflexes:
    • Involuntary.
    • Slower with two neurons and ganglia for more sustained responses.

Neurotransmitter Activity

  • Somatic:
    • Neurotransmitter: Acetylcholine released from the single neuron to the muscle.
  • Autonomic:
    • Sympathetic Nervous System: Pre-ganglionic releases acetylcholine; post-ganglionic typically releases norepinephrine.
    • Parasympathetic Nervous System: Both pre-ganglionic and post-ganglionic neurons release acetylcholine.

Receptor Types and Functions

  • Sympathetic Nervous System Receptors:
    • Postganglionic target receptors: Called adrenal receptors (alpha and beta forms for norepinephrine).
  • Parasympathetic Nervous System Receptors:
    • Target cell receptors are termed muscarinic for acetylcholine.
    • Receptor names origin: Derived from chemicals used in discovery.
      • Nicotinic receptors: Bind acetylcholine.
      • Muscarinic receptors: Bind acetylcholine for parasympathetic activity.

Duration of Neurotransmitter Effects

  • Acetylcholine in autonomic responses is quickly broken down by enzymes in the synaptic cleft, leading to rapid cessation of receptor activation.
  • Norepinephrine, associated with sympathetic responses, takes longer to clear from the synapse due to reuptake mechanisms and enzymatic breakdown, resulting in prolonged effects.

Hormonal Influence in Sympathetic Responses

  • During fight or flight, norepinephrine release is complemented by adrenaline from adrenal glands, enhancing sympathetic responses.

Differences in Receptor Functions

  • Vasodilation vs Constriction:
    • Receptors allow for diverse responses depending on the organ involved.
    • Example: In fight or flight, blood flow to skeletal muscles increases, while it decreases to the digestive organs.
  • Alpha receptors: Cause vasoconstriction in intestines to redirect blood.
  • Beta receptors: Cause dilation in heart tissues to increase oxygen supply.

Summary Tasks

  • Create visual representations (mind maps, diagrams, tables) to summarize somatic vs autonomic pathways and neurotransmitter differences.
  • Focus on understanding the primary neurotransmitters, their receptors, and their implications for bodily responses during various states (rest/digest vs. fight/flight).