Nervous System Organization

Nervous System Layout

  • Overview of the nervous system's organization.
  • Flowchart illustrating the nervous system's structure and neuron types in its different sections.

Divisions of the Nervous System

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Everything outside the brain and spinal cord, including cranial nerves and spinal nerves.
    • Cranial nerves: Nerves coming off the brainstem.
    • Spinal nerves: 31 pairs coming off the spinal cord.

Neurons in the CNS

  • Multipolar Neurons: The only type of neuron found in the CNS.
    • Defined as neurons with more than one cell extension (pole).
    • Structure: Axon, soma (cell body), and multiple dendrites.
  • Functional Role: Integration.
    • Integrating neurons: They receive various signals and process them to decide whether to propagate a response.
    • Analogy: Similar to a computer in a thermostat that assesses incoming sensory signals (afferent) and sends out signals (efferent) to control an effector organ.
    • Examples of effector organs: Skeletal muscle, smooth muscle, cardiac muscle, and glands.

Neurons in the PNS

  • Contains multiple neuron types: Multipolar, bipolar, and unipolar (or pseudo-unipolar).
  • Bipolar Neurons: Found especially in the special senses (e.g., in the eye).
    • Defined as neurons with two poles.
  • Unipolar (Pseudo-Unipolar) Neurons: Functionally have two poles but only one extension from the cell body.
    • Carry signals into the CNS.
  • Multipolar neurons are also present in the PNS.
    • Can carry information out of the CNS to skeletal muscle, smooth muscle, cardiac muscle, or glands.

Further Division of the PNS

  • Divided into sensory and motor components.
Sensory Division
  • Further divided into visceral and somatic sensory.
    • Somatic Sensory: Sensation from the body wall (joints, muscle, skin).
      • Often involves general sensation (touch, body position).
    • Visceral Sensory: Sensation from organs.
      • Includes general senses like pain from the viscera.
    • Special Senses: Discrete structures perceiving specific stimuli (sight, taste, sound, smell).
  • Sensory information enters the CNS, where integration neurons process it.
  • Typical Neuron Locations:
    • Bipolar neurons: Usually in the special senses.
    • Unipolar/Pseudo-unipolar neurons: Usually in general body senses; cell bodies are found in the dorsal root ganglia of spinal nerves.
Motor Division
  • Divided into visceral and somatic motor.
    • Somatic Motor: Multipolar neurons innervating skeletal muscle (body wall).
      • Output (Efferent).
    • Visceral (Autonomic) Nervous System: Controls cardiac muscle, smooth muscle, and glands.
      • Further divided into:
        • Sympathetic: Fight or flight response (stress response).
        • Parasympathetic: Rest and digest activities (relaxation, digestion).
      • Applies only to motor function (control of cardiac muscle, smooth muscle, and glands). There is no autonomic component to sensory functions.

Autonomic Nervous System

  • Controls motor function of cardiac muscle, smooth muscle, and glands.
  • Broken down into sympathetic (fight or flight) and parasympathetic (rest and digest) responses.

Textbook Organization

  • Typical textbook layout often follows the organization of the nervous system:
    • Fundamentals.
    • CNS.
    • PNS (sensory and motor).
    • Autonomic Nervous System.
    • Special Senses.

Key Concepts

  • Afferent: Signals coming into the CNS.
  • Efferent: Signals going out of the CNS.
  • Integration: Processing of signals within the CNS.
  • Understanding this layout should make learning about the nervous system more manageable.