Lecture on the Nervous System

Introduction

• The nervous system is essential for most bodily functions.
• Controls organs, physiological, and psychological reactions.
• Central theme of upcoming lectures: anatomy, organization, communication, and issues of the nervous system.

Overview of Nervous System Functions

• Three principal functions:
  1. Sensory Input: Detection of stimuli (e.g., feeling a spider on your skin).
  2. Integration: Processing and deciding on response (e.g., deciding whether to stay calm or react).
  3. Motor Output: Executing the response (e.g., swatting the spider).

Major Components

1. Central Nervous System (CNS): Brain and spinal cord - main control center.
2. Peripheral Nervous System (PNS): Nerves branching out from brain and spine - communication network.

Divisions of the PNS

• Sensory (Afferent) Division: Picks up sensory stimuli and sends to the brain.
• Motor (Efferent) Division: Sends instructions from brain to muscles and glands.
  • Somatic Nervous System: Voluntary control over muscle movements.
  • Autonomic Nervous System: Involuntary control over heart, lungs, etc.
    • Sympathetic Division: Prepares body for action (fight or flight).
    • Parasympathetic Division: Relaxes the body.

Nervous Tissue and Cells

• Nervous tissue is densely packed with cells (>80%).
• Two main types of cells:
  • Neurons: Transmit signals and respond to stimuli.
  • Neuroglia (Glial) Cells: Support and protect neurons.

Types of Neuroglia Cells

• Central Nervous System:
  • Astrocytes: Connect neurons to blood supply.
  • Microglial Cells: Provide immune defense.
  • Ependymal Cells: Circulate cerebrospinal fluid.
  • Oligodendrocytes: Create myelin sheath for insulation.
• Peripheral Nervous System:
  • Satellite Cells: Support neuron cell bodies.
  • Schwann Cells: Produce myelin sheath for insulation.

Characteristics of Neurons

• Long-lived cells (possibly last a lifetime).
• Irreplaceable (do not divide).
• High metabolic rate (consume lots of energy).

Neuron Structure

• Soma (Cell Body): Life support center with nucleus, DNA, etc.
• Dendrites: Receive messages from other cells.
• Axon: Sends electrical impulses away from the cell body.

Classification of Neurons

• By structure:
  • Multipolar Neurons: Many processes (one axon, many dendrites).
  • Bipolar Neurons: One axon and one dendrite.
  • Unipolar Neurons: Single process.
• By function:
  • Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS.
  • Motor (Efferent) Neurons: Transmit impulses from CNS to muscles/glands.
  • Interneurons: Transmit impulses within the CNS.

Example: Responding to a Spider

• Sensory input: Unipolar sensory neurons detect spider.
• Integration: Signal processed in spinal cord and brain by multipolar interneurons.
• Motor output: Multipolar motor neurons cause muscle reaction.

Closing

• Preview of next lesson: How neurons communicate using chemistry and electricity.
• Acknowledgments to contributors and supporters of the content.