Organization of the Nervous System

Overview of Nervous System Structure

The nervous system is a complex network responsible for coordinating body functions and enabling communication between different body parts. It is divided into central and peripheral components, each with specialized roles.

• Central Nervous System (CNS): Consists of the brain and spinal cord. It processes information and is the main control center.

• Peripheral Nervous System (PNS): Composed of all neural tissue outside the CNS. It connects the CNS to limbs and organs.

• Sensory (Afferent) Neurons: Transmit sensory information from receptors to the CNS.

• Efferent Neurons: Carry commands from the CNS to effectors (muscles and glands). Subdivided into:

  • Somatic Motor Division: Controls voluntary movements (skeletal muscles).

  • Autonomic Division: Regulates involuntary functions (smooth muscle, cardiac muscle, glands). Further divided into:

    • Sympathetic Branch: Prepares the body for 'fight or flight' responses.

    • Parasympathetic Branch: Promotes 'rest and digest' activities.

• Enteric Nervous System: A network of neurons in the digestive tract walls. It is regulated by the autonomic nervous system but can function independently.

Emergent Properties: The nervous system exhibits properties that arise from the complex interactions of its components, such as consciousness and learning.

Cells of the Nervous System

Neurons: Structure and Function

Neurons are the primary functional units of the nervous system, specialized for the transmission of electrical and chemical signals.

• Neuron Classification by Structure:

  • Multipolar Neurons: Many dendrites, one axon (most common in CNS).

  • Pseudounipolar Neurons: Single process that splits into two branches (sensory neurons).

  • Bipolar Neurons: One dendrite and one axon (sensory organs).

  • Anaxonic Neurons: No apparent axon (found in CNS).

• Neuron Classification by Function:

  • Sensory (Afferent) Neurons: Carry information to the CNS.

  • Efferent Neurons: Transmit commands from the CNS to effectors.

  • Interneurons: Connect neurons within the CNS.

• Neuron Structure:

  • Cell Body (Soma): Contains the nucleus and organelles; metabolic center.

  • Dendrites: Receive incoming signals; may have dendritic spines to increase surface area.

  • Axon: Conducts outgoing signals; may branch into collaterals and end in axon terminals or varicosities.

  • Axon Hillock: The initial segment where action potentials are generated.

Nerves: Bundles of axons in the PNS, classified as sensory, motor, or mixed nerves based on the types of fibers they contain.

Example:

A multipolar motor neuron in the spinal cord receives input from interneurons via its dendrites and sends an action potential down its axon to stimulate a muscle fiber.

Additional info: Dendritic spines are dynamic structures that can change in response to learning and experience, contributing to synaptic plasticity.