Introduction to the Nervous System - Notes (Adelaide)

Acknowledgments and Purpose

  • Acknowledgment of Kaurna people, the traditional custodians whose ancestral lands we gather on.
  • Acknowledge the deep feelings of attachment and relationship of the Kaurna people to country.
  • Respect and value their past, present and ongoing connection to the land and cultural beliefs.

Learning Objectives

  • Describe the general organisation of the nervous system, with regard to its two major subdivisions (includes online revision).
  • Define the term “neural pathway” and draw a simple sensory and motor neural pathway in relation to components of the nervous system.
  • Describe the structure of a typical neuron, including:
    • cell body;
    • dendrites;
    • axon (nerve fibre);
    • myelin sheath;
    • axon terminal (online revision).
  • Describe the structural and functional classifications of neurons (online revision).
  • Describe the structure of a typical peripheral nerve and provide a brief explanation of the function of each component.
  • Classify types of nerve stimuli and name the sensory receptors that detect each of these stimuli (online revision).

Self-Directed Online Learning

  • Complete/watch the following online interactives & videos to recap and build knowledge:
    • Interactive Books: The Nervous System + additional interactives
    • Videos: Nerves & Neurons; Peripheral Nervous System & its Branches

Live Interactions in the Lecture

  • Use your laptop/tablet/phone to open up the lecture within the Echo360 tab in MyUni.
  • Every lecture contains interactive elements to check understanding in real-time.
  • All answers are anonymous.

Divisions of the Nervous System

  • (See following sections for detailed CNS vs PNS content)

Recap: Central vs Peripheral Nervous System

  • Central Nervous System (CNS):
    • Brain
    • Spinal cord
    • Lined by meninges
    • Surrounded by cerebrospinal fluid (CSF)
  • Peripheral Nervous System (PNS):
    • All nervous tissue outside of the CNS
    • Examples: (Most) Cranial/Spinal nerves; Ganglia (groups of nerve cell bodies); Nerve endings (innervating tissues and organs)

Functional Organisation of the Nervous System

  • Nervous System is divided into:
    • Central Nervous System (CNS) – Brain; Spinal Cord
    • Peripheral Nervous System (PNS)
  • Sensory (afferent) division: PNS → CNS
    • Somatic sensory division: info from skin, fascia, joints, skeletal muscles, special senses to CNS
    • Visceral sensory division: info from internal organs to CNS
  • Motor (efferent) division: CNS → PNS
    • Somatic (voluntary) motor division: innervates skeletal muscle
    • Autonomic (involuntary) motor division: innervates cardiac & smooth muscle and glands
  • Autonomic divisions:
    • Sympathetic division: fight or flight
    • Parasympathetic division: rest & digest

Sensory & Motor Divisions of the PNS

  • Sensory (afferent): information coming in from PNS to be processed in CNS
    • Somatic subdivision: sensory information from skin, fascia, joints, skeletal muscles, and special senses to CNS for integration/processing
    • Visceral subdivision: sensory information from internal organs to CNS for integration/processing
  • Motor (efferent): information going out from CNS to effectors in PNS
    • Somatic subdivision: motor information from CNS to skeletal muscle, i.e., conscious movements
    • Autonomic (visceral) subdivision: motor information from CNS to cardiac muscle, smooth muscle and glands, i.e., motor impulses to muscles/glands not under conscious control

Activity 1: Organisation of the Nervous System

  • PART 1: Each group collects 1x ‘Organisation of the Nervous System’ document and places structures into boxes:
    • A) Active Thermoreceptor
    • B) Contraction of thigh muscle
    • C) Control centre
    • D) Vasoconstriction of blood vessels
  • PART 2: Facilitator reads out physiological tasks; groups decide whether task is automated/involuntary or controlled voluntarily

Neural Pathways

  • What is a Neural Pathway?
    • Brain cortex has functional areas (e.g., primary motor cortex) – spinal cord has similar organisation (explored next week).
    • It makes sense to organise neurons coming from the SAME place, carrying the SAME type of information, to the SAME brain region, together.
    • Putting these neurons together creates a pathway.

Ascending (Sensory) Neural Pathways

  • Ascending pathways travel from the body, up into the spinal cord (via spinal nerves) and up to the brain.
  • They carry sensory information that requires brain processing (e.g., touch).
  • Pathway involves three (3) neurons:
    • First order neuron (sensory neuron): cell body in DRG of spinal nerve
    • Second order neuron (interneuron): cell body in spinal cord or brainstem
    • Third order neuron (interneuron): cell body in brain
  • 33 neurons total

Descending (Motor) Neural Pathways

  • Descending pathways travel from the brain, down the spinal cord and out to the body via spinal nerves.
  • They carry motor information to muscles.
  • Pathway involves two (2) neurons:
    • Upper motor neuron: cell body in brain
    • Lower motor neuron: cell body in spinal cord
  • 22 neurons total

Drawing Simple Neural Pathways

  • Visual elements to include in drawings:
    • nerve cell body
    • nerve fibre
    • synapse
  • Pathways:
    • Ascending – Sensory
    • Descending – Motor

Activity 2: Thinking About Pathways

  • PART 1: Imagine the hard drive is the central nervous system (CNS). Draw an arrow between the hard drive and each component to indicate the direction messages travel and label them as ‘motor’ or ‘sensory’.
  • PART 2: Draw a SIMPLIFIED diagram to show the relationship between a sensory neuron, an interneuron and a motor neuron (each labelled).
  • BONUS: Represent the structural classification of the three neurons.

Overview of Peripheral Nerves

  • Peripheral nerves consist of axons bundled together with connective tissue coverings (endoneurium, perineurium, epineurium).
  • The typical nerve organization is: endoneurium around individual axons (superior to any myelin), fascicles wrapped in perineurium, nerve wrapped in epineurium.

Structure of Spinal Nerves

  • Anterior/Ventral roots contain motor neurons (CNS → PNS → effector muscles).
  • Posterior/Dorsal roots contain sensory neurons (PNS receptors → CNS).
  • Spinal nerves form where the anterior and posterior roots come together as they exit the spinal cord (contain both motor and sensory neurons).

Structure of Spinal Nerves (Continued)

  • Spinal nerves branch into anterior and posterior rami (pl.).
  • Posterior ramus: innervates and receives sensory input from posterior structures of the body.
  • Anterior ramus: innervates and receives sensory input from the anterior structures of the body.

Spinal Nerve Positioning

  • Spinal nerves exit the vertebral column in line with their vertebral counterpart:
    • Cervical nerves C1-C7 exit above their corresponding vertebrae; C8 exits below the seventh cervical vertebra.
    • Thoracic nerves T1-T12 exit below their corresponding vertebrae.
  • The spinal cord ends at approximately L1 (lumbar nerve level), and from there, nerves form a bundle called the Cauda Equina.
  • Lumbar nerves L1-L5 exit below their corresponding vertebrae.
  • Sacral nerves S1-S5 exit through the sacral foramina.

Peripheral Nerve Branches

  • A typical nerve will have branches to supply:
    • Skin (cutaneous branch)
    • Skeletal muscle (muscular branch)
    • Blood vessels (vascular branch)
    • Joints (articular branch)
  • Each branch may contain both motor and sensory fibres:
    • Somatic (efferent) motor fibres controlling contraction of skeletal muscle
    • Somatic (afferent) sensory fibres feeding sensory information back to CNS
    • Autonomic (efferent) motor fibres controlling smooth muscle of blood vessels located within the muscle

Activity 3: Peripheral Nerve Crossword

  • Task: Each group collects 1x ‘Peripheral Nerve Crossword’ and completes the crossword using Brains Trust

Speech Pathology / Clinical Connection

  • Occupational Therapy; Physiotherapy; Peripheral Nerve Compression (Not Examinable)

What is Peripheral Nerve Compression?

  • Peripheral nerve compression refers to dysfunction of a nerve due to localised microvascular interference and structural changes in the nerve or adjacent tissues.
  • Compression interferes with the nerve’s ability to conduct both afferent and efferent impulses (causing both motor and sensory changes).
  • Pain can be generated by compression at the site of compression and distal to it in the nerve’s sensory distribution.
  • Compression may be very transient or last for significant periods, but is not usually permanent.

Transient Peripheral Nerve Compression

  • Example: Knocking your ‘funny bone’ (compression of the ulnar nerve against the humerus).
  • Leads to pain, tingling and numbness down the medial forearm and into the little finger and medial side of the ring finger (innervated by the ulnar nerve).
  • Resolution occurs when blood flow is restored to the nerve (e.g., shaking the arm until symptoms cease).

Carpal Tunnel Syndrome

  • Involves compression of the median nerve as it passes through the carpal tunnel on the anterior (palmar) side of the wrist.
  • Tunnel formed by the carpal bones and the transverse carpal ligament.
  • Motor and sensory functions associated with the median nerve at sites distal to the carpal tunnel are affected, e.g.:
    • Skin over the palm, thumb, index finger, middle finger and lateral side of the ring finger
    • Motor input to muscles that flex the thumb and the index finger
  • Effects of carpal tunnel usually last for an extended period.

Carpal Tunnel Syndrome Clinical Presentation

  • A patient will present with pain, tingling or numbness in the sensory distribution of the median nerve.
  • May present with weakness when performing a ‘pincer grip’ (thumb to index finger).
  • Causes:
    • Often associated with poor ergonomics or increased time working at a computer/device (sustained wrist extension).
    • Arthritis and other joint/connective tissue disorders.

Activity 4: IPL Huddle – Meet Dave

  • (Placeholder note: referenced as part of the session activities)

End Notes

  • The slide deck includes “make history.” and institutional branding for The University of Adelaide.
  • CRICOS and related information are included in the footer for context.