Lecture on Animal Nervous Systems

Introduction

• This lecture marks the transition from plant and fungus studies to animal studies.
• Focus on the nervous system, which is unique to animals (excluding sponges).
• Nervous system enables rapid response to environmental stimuli and movement.
• All animals except sponges have a network of nerves for rapid communication within the body.

Diversity of Nervous Systems

• Cephalization: Concentration of nervous and sensory systems in the head region.
  • Common in vertebrates and many invertebrates like arthropods and mollusks.
• Nerve Net: Found in cnidarians (jellyfish, corals, sea anemones) without a centralized nervous system.
• Echinoderms: Have a central nerve ring with radiating patterns.

Structure of Nerves

• Basic structure: Cell body, dendrites, axon.
  • Cell body: Contains nucleus and other cellular structures.
  • Dendrites: Receive signals, tend to be short.
  • Axon: Sends signals to other nerves or cells, e.g., muscle cells.
  • Directional flow: Dendrites → Cell body → Axon.
• Myelin Sheath: Insulates axons, formed by neuroglial cells.
  • Enhances signal transmission and protection.

Types of Neurons

• Sensory Neurons: Detect stimuli from sensory cells and send to the central nervous system.
• Motor Neurons: Carry signals from the central nervous system to cause effects in target cells, e.g., muscles.
• Interneurons: Connect neurons, involved in reflexes, memory, and language. Predominant in the brain.

Signal Transmission

• Neurons have a charge across the cell membrane (polarized state).
• Stimulation causes depolarization (change in charge), enabling signal transmission.
• Signals are passed along neurons through rapid polarization and depolarization, occurring in milliseconds.
• Neurotransmitters released at synapses to transfer signals between neurons across synaptic clefts.

Nervous System Structure

• Central Nervous System (CNS): Brain and spinal cord, responsible for data processing and decision-making.
• Peripheral Nervous System (PNS): All other nerves, consists of:
  • Somatic Nervous System: Under conscious control.
  • Autonomic Nervous System: Under unconscious control.
    • Sympathetic: Manages fight or flight response.
    • Parasympathetic: Manages rest and digest functions.

Spinal Cord and Reflexes

• Part of CNS, encased in vertebral column for protection.
• Functions as an information superhighway and reflex center.
• Reflexes (e.g., knee-jerk) are processed by the spinal cord for quick responses.

Peripheral Nervous System

• Comprises nerves (bundles of axons) and ganglia (clusters of neuron cell bodies).
• Gathers environmental information and sends it to the body.

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Key Functions of Sympathetic vs Parasympathetic Systems

• Sympathetic: Prepares body for stress.
  • Dilates eyes, increases heart rate and breathing, inhibits digestion.
• Parasympathetic: Manages relaxation and regular bodily functions post-stress.
  • Constricts eyes, slows heart rate and breathing, stimulates digestion.

Conclusion

• The nervous system is a complex and essential feature of animal life, facilitating rapid response and adaptation to the environment.
• Next lecture will delve into the sensory system.