PNS Handout

Overview of the Nervous System

• Nervous System Components:

  • Brain

  • Spinal Cord

• Divisions:

  • Central Nervous System (CNS)

    • Comprises the brain and spinal cord

  • Peripheral Nervous System (PNS)

    • Encompasses all other nervous structures

Central Nervous System (CNS)

• Major Regions of the Brain:

  • Cerebrum

  • Diencephalon

  • Midbrain

  • Pons

  • Cerebellum

  • Medulla

• Spinal Cord Regions:

  • Cervical Enlargement

  • Lumbar Enlargement

  • Cauda Equina

Peripheral Nervous System (PNS)

• Cranial Nerves

• Spinal Nerves

• Peripheral Ganglia

Objectives for Understanding the Nervous System

• Functions of Nervous Systems:

  • Contrast functions between the somatic and autonomic nervous systems

  • Describe the structure & function of spinal nerves

• Reflex Arcs:

  • Explain reflex arcs and their function

• Dermatomes:

  • Positioning and roles in pain perception

• Nerve Plexus:

  • Define and provide examples

• Somatic vs. Autonomic Motor Systems:

  • Key differences in structure and function

Components of the PNS

• Types of Nervous Systems:

  • Motor:

    • Somatic

    • Autonomic (Visceral)

  • Sensory:

    • Corresponding sensory systems for somatic and autonomic

Somatic Nervous System

• Supplies:

  • Structures: Skin, muscle, bone, parietal membranes

• Motor Functions:

  • Controls skeletal muscle (voluntary)

  • Reflex Arc Exception: Reflex arc operates outside voluntary control

• Sensory Functions:

  • Pain: Direct, localized perception

  • Temperature, Touch, Proprioception

Autonomic Nervous System

• Supplies:

  • Viscera: Includes glands, smooth muscle, cardiac muscle

• Control Type:

  • Involuntary Control

• Functions:

  • Motor: Sympathetic and Parasympathetic

  • Sensory: Vague, ill-defined pain; often referred pain linked to dermatomes

Classification of Nerves

• Spinal Nerves:

  • Emerge from the spinal cord

  • 31 pairs:

    • 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

• Cranial Nerves:

  • Emerge from brainstem

General Classification of Spinal Nerves

• Afferent Nerves:

  • General Somatic Afferents (GSA): Pain, temperature, touch, proprioception

  • General Visceral Afferents (GVA): Pain and distension from visceral structures

• Efferent Nerves:

  • General Somatic Efferents (GSE): Motor neurons to skeletal muscles

  • General Visceral Efferents (GVE): Autonomic fibers to smooth muscles, cardiac muscles, and glands

Reflex Arc Overview

• Step 1: Arrival of stimulus and activation of receptor

• Step 2: Activation of sensory neuron

• Step 3: Information processing in CNS

• Step 4: Activation of motor neuron

• Step 5: Response by effector

Dermatomes

• Diagram and Segmentation:

  • Description of dermatomes and their positioning in relation to the body wall

  • Role in the perception of referred pain

Nerve Plexuses

• Types of Plexuses:

  • Brachial Plexus: Upper extremities

  • Lumbar Plexus: Supplies lower abdomen and thigh

  • Lumbosacral Plexus: Lower extremities and pelvic region

Autonomic Nervous System Classifications

• Sympathetic Division (Thoracolumbar):

  • Functions related to fight or flight responses

• Parasympathetic Division (Craniosacral):

  • Functions related to rest and digestive activities

Functions of Autonomic Nervous System

• Sympathetic Actions:

  • Increases heart rate, dilates pupils, inhibits digestion

• Parasympathetic Actions:

  • Decreases heart rate, stimulates digestion, constricts pupils

Conclusion and Summary

• Important Topics Covered:

  • Organization and functions of the nervous system

  • Comparison of somatic and visceral components of the PNS

  • Overview of spinal nerves, reflex arcs, dermatomes, nerve plexuses, and autonomic divisions

• Key Associations:

  • Understanding how these systems interconnect and function collectively within the body.