Peripheral Nervous System and Autonomic Nervous System

Peripheral Nervous System (PNS) and Reflex Activity

Overview of PNS

  • PNS: Involves nerves outside the brain and spinal cord.

  • Autonomic Nervous System (ANS) is a component of PNS.

Structure of the Nervous System

  • Figure Analysis: PNS placement within the overall nervous system structure.

Neuron Classification

Types of Neurons

  • Multipolar: Most common; typical in CNS.

  • Bipolar: Rare; found in special sensory organs (e.g., olfactory, visual).

  • Unipolar (Pseudounipolar): Mainly in PNS; found in sensory ganglia.

Structural Variations

  • Multipolar Variations: Purkinje and pyramidal cells.

  • Bipolar Variations: Olfactory and retinal cells.

  • Unipolar Variations: Dorsal root ganglion cells.

Nerves

General Structure

  • Nerve Definition: Combination of myelinated and nonmyelinated axons, encased in connective tissue.

  • Types: Spinal and cranial nerves based on origin.

Types of Nerves

  • Mixed Nerves: Contain both afferent and efferent fibers.

  • Sensory (Afferent) Nerves: Impulses toward CNS.

  • Motor (Efferent) Nerves: Impulses away from CNS.

Nerve Regeneration

PNS vs CNS

  • PNS Regeneration: Possible if soma is intact; involves Wallerian degeneration.

  • CNS: Generally does not regenerate due to inhibitory factors from oligodendrocytes.

Sensory Receptors

Types of Sensory Receptors

  • Classifications: By stimulus type, body location, and structural complexity.

By Stimulus Type

  • Mechanoreceptors: Touch, pressure.

  • Thermoreceptors: Temperature changes.

  • Photoreceptors: Light energy (retina).

  • Chemoreceptors: Chemical changes (taste, smell).

  • Nociceptors: Pain stimuli.

Reflexes and Reflex Arcs

Types of Reflexes

  • Inborn Reflexes: Predetermined responses.

  • Learned Reflexes: Result from practice.

Reflex Arc Components

  • Parts of Reflex Arc: Receptor, sensory neuron, integration center, motor neuron, effector.

  • Types: Somatic (skeletal muscles) vs autonomic (visceral effectors).

Autonomic Nervous System (ANS)

Overview

  • ANS: Controls involuntary body functions; divides into sympathetic and parasympathetic.

  • Operating subconsciously; responsible for homeostasis.

Divisions of ANS

  • Parasympathetic Division: Conserves energy; rest-and-digest.

  • Sympathetic Division: Mobilizes body; fight-or-flight.

Interaction and Tone

  • ANS maintains dynamic antagonism for homeostasis.

  • Sympathetic Tone: Controls blood pressure; continuous constriction.

  • Parasympathetic Tone: Involves digestive/urinary function; modulates heart rate.

Control of ANS Activity

Levels of Control

  • Higher Brain Centers: Include limbic system and hypothalamus.

  • Cerebral Influence: Voluntary control through biofeedback.

Summary of Specific Structures

  • Cranial Nerves: Control functions in head and neck.

  • Sympathetic Trunk: Contains ganglia influencing various organs.

  • Dual Innervation: Most organs receive input from both ANS divisions, allowing fine-tuned control.