Nervous System Overview

Introduction

• Nervous system controls all physiological and psychological reactions.
• Essential for all animals, especially humans.
• Three key functions: Sensory Input, Integration, Motor Output.

Sensory Input, Integration, and Motor Output

• Sensory Input: Receptors detect stimuli (e.g., spider on skin).
• Integration: Brain processes input and decides response.
• Motor Output: Response executed (e.g., removing spider).

Organization of the Nervous System

Central Nervous System (CNS)

• Composed of brain and spinal cord.
• Main control center.

Peripheral Nervous System (PNS)

• All nerves branching off from CNS.
• Sensory (Afferent) Division: Sends stimuli to brain.
• Motor (Efferent) Division: Sends responses from brain to muscles/glands.
  • Somatic (Voluntary) Nervous System: Controls skeletal muscle movement.
  • Autonomic (Involuntary) Nervous System: Controls heart, lungs, digestion.
    • Sympathetic Division: Mobilizes body for action.
    • Parasympathetic Division: Relaxes body.

Nervous Tissue

• Neurons: Nerve cells that respond to stimuli and transmit signals.
• Neuroglia (Glial Cells): Support and protect neurons; outnumber neurons 10:1.

Types of Glial Cells

Central Nervous System (CNS)

• Astrocytes: Anchor neurons to blood supply, exchange materials.
• Microglial Cells: Immune defense in brain/spinal cord.
• Ependymal Cells: Create, secrete, and circulate cerebrospinal fluid.
• Oligodendrocytes: Produce myelin sheath.

Peripheral Nervous System (PNS)

• Satellite Cells: Surround/support neuron cell bodies.
• Schwann Cells: Produce myelin sheath around axons.

Neuron Structure and Function

• Soma (Cell Body): Life support of neuron.
• Dendrites: Receive messages from other cells.
• Axon: Transmits impulses away from cell body.

Neuron Characteristics

1. Longest-lived cells in body.
2. Irreplaceable (amitotic).
3. High metabolic rate, require abundant glucose and oxygen.

Neuron Classification

Structural Classification

• Multipolar Neurons: Multiple processes (1 axon, many dendrites).
• Bipolar Neurons: Two processes (1 axon, 1 dendrite).
• Unipolar Neurons: Single process, mostly in sensory receptors.

Functional Classification

• Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to CNS.
• Motor (Efferent) Neurons: Transmit impulses from CNS to muscles/glands.
• Interneurons (Association Neurons): Transmit impulses between sensory and motor neurons.

Applied Example: Spider on Knee

• Sensory neurons detect spider.
• Signal sent to spinal cord and brain via interneurons.
• Motor neurons trigger response (e.g., moving leg, screaming).

Conclusion

• Nervous system's sensory input, integration, and motor output are crucial.
• Covered CNS and PNS organization, glial cell roles, neuron structure and function.
• Next lesson: How neurons communicate using chemistry and electricity.