The Nervous System - Lecture by Professor Dave

Introduction

• Human body as a finely tuned machine
• Sentience commands bodily actions
• The nervous system carries signals from the brain to the body
• Nervous system cells: fourth type of tissue

Nervous Tissue

• Main cell: Neuron
  • Unique structure with branching cytoplasmic extensions
  • Amitotic: do not divide, can live a lifetime
• Supporting cells: Neuroglia or Glial cells

Neuron Structure

• Cell Body
  • Contains nucleus and nucleolus
  • Surrounded by organelles
• Dendrites
  • Many projections for receiving signals
• Axon
  • Initiates from axon hillock
  • Can extend long distances (nerve fibers)
  • Terminates in axon terminals forming neuromuscular junctions
  • Generates electrical signals
• Myelin Sheath
  • Protects axon, increases impulse transmission speed
  • Schwann cells form sheath in peripheral nervous system
  • Nodes of Ranvier: gaps between Schwann cells

Classification of Neurons

• By Structure
  • Unipolar: single axon
  • Bipolar: one axon, one dendrite
  • Multipolar: one axon, multiple dendrites
• By Function
  • Sensory (Afferent): towards CNS
  • Motor (Efferent): from CNS to muscles/glands
  • Interneurons: shuttle signals within CNS

Neuron Function

• Regions
  • Receptive region: receives stimulus
  • Trigger zone: initiates signal
  • Conducting region: transmits signal
  • Secretory region: releases neurotransmitters
• Membrane Potential
  • Opposite charges attract, separated charges create potential
  • Ion channels in membrane allow ions to pass
  • Resting membrane potential maintained by sodium-potassium pumps
  • Action potential: depolarization exceeds threshold
  • Repolarization and hyperpolarization reset levels

Synapses

• Junctions between neurons or neurons and effector cells
• Types:
  • Axodendritic
  • Axosomatic
  • Axoaxonal

Nervous System Overview

• Functions
  • Receives sensory input
  • Integrates information
  • Generates motor output
• Divisions
  • Central Nervous System (CNS): Brain and spinal cord
  • Peripheral Nervous System (PNS): Nerves extending from CNS
  • PNS Sub-Divisions
    • Sensory (Afferent) division: Signals from receptors to CNS
    • Motor (Efferent) division: Signals from CNS to muscles/glands
      • Somatic Nervous System: Controls skeletal muscles
      • Autonomic Nervous System: Controls smooth and cardiac muscles
        • Sympathetic division
        • Parasympathetic division

Conclusion

• Detailed structure and function of neurons
• Overview of nervous system components and their roles
• Further detailed discussions to follow on central nervous system