Topic 2: Module 1 - Introduction to the Nervous System

Overview of the Nervous System

• Focuses on types of cells in the nervous system, specifically nerve cells (neurons) and glial cells.
• Distinguishes between nervous system cells and those with other functions (e.g., immune cells).
• Next module will cover how neurons signal events and transmit information.

Module Objectives

1. Understand organization of the nervous system:

• Central Nervous System (CNS): Spinal Cord and Brain.
• Peripheral Nervous System (PNS): Somatic and Autonomic Nervous Systems.

1. Identify the general functions of neurons and glial cells.
2. Differentiate between functional classes of neurons: sensory, motor, and interneurons.
3. Learn about neuron components: dendrites, cell body, axon hillock, axon, and terminals.
4. Understand anterograde vs retrograde transport.
5. Know myelin sheath production: oligodendrocytes (CNS) and Schwann cells (PNS).
6. Grasp the concept and types of ion channels, their properties, and factors regulating ion movement.

Cells of the Nervous System

Neurons

• Main nerve cells that transmit and integrate information, coordinating body activity.
• Structure includes:
• Cell Body: Contains nucleus and organelles.
• Dendrites: Receive inputs from other cells, branching from the cell body.
• Axon: Transmits information, extends from the cell body often ending in terminals that contact other cells.

Glial Cells

• Comprise about 90% of the CNS.
• Functions:
• Provide structural support and nutrients to neurons.
• Scavenge debris, and create blood-brain barrier.
• Insulate neurons with myelin and maintain extracellular environment.
• Types of glial cells include astrocytes, oligodendrocytes, Schwann cells, microglia, and ependymal cells.

Overview of Glial Functions

1. Astrocytes: Nutrient supply to neurons, manage extracellular environment, important in blood-brain barrier formation.
2. Oligodendrocytes: Myelination in CNS.
3. Schwann Cells: Myelination in PNS.
4. Microglia: Immune function in CNS, acting as macrophages.
5. Ependymal Cells: Line brain ventricles, may generate neurons.

General Organization of the Nervous System

• CNS: Brain and spinal cord.
• PNS: Consists of nerves throughout the body, including:
• Autonomic Nervous System: Internal structures (viscera).
• Somatic Nervous System: Superficial structures (skeletal muscles).
• Neuronal paths connect CNS to PNS through afferent (sensory) and efferent (motor) neurons.

Nuclei and Nerve Tracts

• CNS Structures: Cell bodies in nuclei or fields (e.g., Thalamus, Substantia Nigra).
• PNS Structures: Cell bodies in ganglia (e.g., Superior Cervical Ganglion).
• Nerves or nerve tracts refer to axons bundled together conducting information to and from the CNS.

Functional Classification of Neurons

1. Sensory Neurons: Transmit signals from sensory receptors to CNS.
2. Motor Neurons: Convey signals from CNS to effectors (muscles/glands).
3. Interneurons: Relay information between sensory and motor pathways.

• Local interneurons operate on short distances.
• Projection interneurons travel longer distances, including to the brain.

Neuronal Structure

• Major components:

1. Dendrites: Receive inputs.
2. Cell Body: Processes information.
3. Axon: Transmits output, often myelinated by Schwann cells or oligodendrocytes.
4. Axon Hillock: Integrates inputs and decides whether to transmit information.
5. Cytoskeleton: Provides structure and support, facilitates transport.
6. Axon Terminals: Output regions contacting other cells.

Ion Channels and Neuronal Function

• Ion channels regulate ionic movement, critical for neuronal signaling.
• Channel Selectivity: Based on size and charge of ions.
• Factors affecting ionic movement:
• Concentration gradient.
• Electrical gradient.
• Channel gating (open vs. closed state).
• Types of gating include: chemical, voltage, and mechanical.

Synapse and Chemical Transmission

• Neurons connect with other cells through synapses, separated by synaptic clefts.
• Chemical transmission occurs via neurotransmitters that cross the synaptic cleft to bind receptors on neighboring cells.

Summary

• Understanding neurons' structure and function is crucial for grasping physiological processes within the nervous system. Their organization and interaction with glial cells create the basis for neural communication and response mechanisms.