Organization of the Nervous System

Overview of Nervous System Structure

The nervous system is a complex network responsible for communication and control throughout the body. It is divided into central and peripheral components, each with specialized functions.

• Neurons are cells with processes that secrete neurotransmitters, enabling communication.

• Emergent properties refer to complex behaviors and functions arising from neural networks.

Central Nervous System (CNS)

• Consists of the brain and spinal cord.

• Responsible for processing and integrating information.

Peripheral Nervous System (PNS)

• Includes all neural tissue outside the CNS.

• Sensory (afferent) neurons transmit information to the CNS.

• Efferent neurons carry signals from the CNS to effectors (muscles and glands).

• Efferent division is further subdivided into:

  • Somatic motor division (controls voluntary muscles)

  • Autonomic division (controls involuntary functions)

    • Sympathetic branch (fight or flight)

    • Parasympathetic branch (rest and digest)

Enteric Nervous System

• Network of neurons in the walls of the digestive tract.

• Controlled by the autonomic nervous system but can function independently.

Cells of the Nervous System

Neurons: Structure and Function

Neurons are the functional units of the nervous system, specialized for carrying electrical signals.

• Neuron classification is based on structure and function:

  • Structure (number of processes):

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

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

    • Bipolar neurons: One dendrite, one axon (retina, olfactory epithelium).

    • Anaxonic neurons: No apparent axon (interneurons in CNS).

  • Function:

    • Sensory (afferent) neurons: Carry information to CNS.

    • Efferent neurons: Carry commands from CNS to effectors.

    • Interneurons: Connect neurons within CNS.

• Neuron structure includes:

  • Cell body (soma): Contains nucleus and organelles; control center.

  • Dendrites: Receive incoming signals; may have dendritic spines for increased surface area.

  • Axons: Carry outgoing signals; originate at axon hillock.

  • Collaterals: Branches of axon.

  • Axon terminals: Release neurotransmitters.

  • Varicosities: Swellings along axon for neurotransmitter release.

Nerves and Signal Transmission

• Nerves are bundles of axons with connective tissue.

• Types of nerves:

  • Sensory nerves: Carry sensory information.

  • Motor nerves: Carry motor commands.

  • Mixed nerves: Contain both sensory and motor fibers.

Key Points

• The cell body is the metabolic and genetic center of the neuron.

• Dendrites receive signals; axons transmit signals away from the cell body.

• Axon hillock is the site where action potentials are initiated.

Example

• A multipolar neuron in the spinal cord receives sensory input via dendrites and sends motor output via its axon to a muscle.

*Additional info: The above notes are expanded from textbook slides and include standard definitions and examples for clarity and completeness.*