Nervous System Overview

 

Nervous System Overview

1. Neurons: The primary excitable cells of the nervous system that generate and propagate electrical signals.

• Parts of a Neuron:
  • Cell Body (Soma): Contains the nucleus and organelles; responsible for the synthesis of proteins and other cellular components.
  • Dendrites: Short, branched extensions that receive signals from other neurons.
  • Axon: A long extension that transmits electrical impulses away from the cell body. Axons can vary in length from a few millimeters to over a meter.
• Neurites: Collective term for dendrites and axons.

 

 

2. Glial Cells (Glia): Non-neuronal cells that provide support and protection for neurons.

• Types of Glial Cells:
  • Astrocytes: Provide structural support, form the blood-brain barrier (BBB), and regulate neurotransmitter levels.
  • Oligodendrocytes: Form the myelin sheath in the central nervous system (CNS).
  • Microglia: Act as immune cells in the CNS, clearing debris and dead cells.
  • Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord, producing cerebrospinal fluid (CSF).
• In the Peripheral Nervous System (PNS):
  • Schwann Cells: Form the myelin sheath around peripheral nerves.
  • Satellite Cells: Support neuron cell bodies in ganglia.

Neuronal Morphology and Function

• Excitability: Neurons are excitable cells that generate action potentials to communicate signals.
• Signal Transmission:
  • Dendrites receive incoming signals.
  • Cell Body integrates these signals.
  • Axon transmits the integrated signal to other neurons or muscles.

Staining Techniques

• Nissl Stain: Visualizes cell bodies by staining the nucleus and surrounding material.
• Golgi Stain: Fills the entire neuron with a dark color, allowing visualization of the entire structure, including dendrites and axons.

Cytoskeleton of Neurons

• Microtubules: Provide structural support and are involved in axonal transport.
• Neurofilaments: Provide tensile strength.
• Microfilaments (Actin Filaments): Involved in changing the shape of the neuron.

Axonal Transport

• Fast Axonal Transport: Moves materials (like neurotransmitter-filled vesicles) quickly along the axon (up to 400 mm/day).
• Slow Axonal Transport: Moves cytoskeletal components and enzymes more slowly (1-2.5 mm/day).

Synaptic Transmission

• Synapse: Junction between neurons where neurotransmitters are released from one neuron and received by another.
• Pre-Synaptic Terminal: The end of the axon where neurotransmitters are released.
• Post-Synaptic Dendrite: Receives the neurotransmitter signal via specific receptors.

Types of Neurons

• Sensory Neurons: Carry information from sensory receptors to the CNS.
• Motor Neurons: Transmit signals from the CNS to effectors like muscles.
• Interneurons: Connect neurons within the CNS.

Classifications of Neurons

• Based on structure:
  • Unipolar, Bipolar, Multipolar, Anaxonic.
• Based on function:
  • Sensory, Motor, Interneurons.

Glial Cells in Detail

• Astrocytes: Structural support, BBB formation, and ion balance.
• Oligodendrocytes: Myelination in the CNS.
• Microglia: Immune response in the CNS.
• Ependymal Cells: Line ventricles and produce CSF.
• Schwann Cells (PNS): Myelination in the PNS.
• Satellite Cells (PNS): Support neuron cell bodies in peripheral ganglia.