Fundamentals of the Nervous System

Overview

• The nervous system is crucial for processing and executing all bodily functions through electrical and chemical signals.
• It controls physiological and psychological reactions and coordinates with the endocrine system.

Main Functions

• Sensory Input: Detects stimuli (e.g., feeling a spider on the knee).
• Integration: Processes input and decides on a reaction (e.g., deciding whether to stay calm or panic about the spider).
• Motor Output: Responds to processed information by activating body parts (e.g., removing the spider).

Levels of Organization

• Central Nervous System (CNS): Consists of the brain and spinal cord.
  • Main control center deciding actions and sending orders.
• Peripheral Nervous System (PNS): Includes all nerves branching from the CNS.
  • Sensory (Afferent) Division: Carries sensory stimuli to the brain.
  • Motor (Efferent) Division: Sends directions from the brain to muscles and glands.
    • Somatic Nervous System: Controls voluntary movements.
    • Autonomic Nervous System: Manages involuntary functions (heart, lungs).
      • Sympathetic Division: Triggers action.
      • Parasympathetic Division: Promotes relaxation.

Nervous Tissue Composition

• Neurons: Nerve cells responsible for transmitting signals.
  • Account for a small portion of nervous tissue.
• Glial Cells: Supportive cells outnumbering neurons 10 to 1.
  • Astrocytes: Anchor neurons to blood supply, exchange materials.
  • Microglial Cells: Provide immune defense in CNS.
  • Ependymal Cells: Circulate cerebrospinal fluid.
  • Oligodendrocytes (CNS) & Schwann Cells (PNS): Form myelin sheath around neurons.

Neuron Characteristics

• Long-lived, irreplaceable, high metabolic rate.
• Basic structure: Soma (cell body), Dendrites (listeners), Axon (talker).

Neuron Types

• Multipolar Neurons: Most common, multiple processes including one axon.
• Bipolar Neurons: Rare, found in sensory areas like the retina.
• Unipolar Neurons: Single process, found in sensory receptors.

Neuron Functional Classification

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

Application: Spider Example

• Unipolar sensory neurons detect the spider's legs.
• Signal travels via Schwann cell-wrapped axons to the spinal cord.
• Interneurons trigger immediate reaction or send signal to the brain for processing.

Upcoming Topics

• Next lesson will explore how neurons use chemistry and electricity for communication.