Structure and Function of Neurons

Nerve Tissue Components

• Nerve tissue consists of two principal types of cells: neurons and supporting cells.
• The human brain contains approximately 100 billion neurons.

Neuron Types

• Neurons are classified based on their anatomic structure and function as:
• Sensory neurons
• Motor neurons
• Interneurons

Neuron Structure

• A neuron consists of:
• Dendrites (to receive signals)
• Cell body (to drive cellular activities)
• Axon (to conduct impulses to target cells)
• Synaptic junctions (specialized junctions between neurons that facilitate the transmission of impulses)

Supporting Cells

• Supporting cells are called neuroglial cells and are located close to the neurons.
• In the CNS, there are four types of glial cells:
• Oligodendrocytes
• Astrocytes
• Microglia
• Ependymal cells
• Each glial cell has a different function.
• In the PNS, supporting cells are called peripheral neuroglia and include:
• Schwann cells
• Satellite cells
• Various other cells with specific structures and functions.

Schwann Cells

• Schwann cells surround the processes of nerve cells and isolate them from adjacent cells and the extracellular matrix by producing a lipid-rich myelin sheath.
• This ensures the rapid conduction of nerve impulses.

Satellite Cells

• Satellite cells are similar to Schwann cells, but they surround the nerve cell bodies.

Oligodendrocytes

• Oligodendrocytes produce and maintain the myelin sheath in the CNS.

Nerve Composition

• A nerve is composed of a collection of bundles of nerve fibers.
• Within the CNS, the brain and spinal cord tissue can be classified as:
• Gray matter (made up of neuronal cell bodies)
• White matter (composed of myelinated nerve fibers)

Cell Body Components

• The cell body contains:
• Mitochondria (participate in the regulation of cell respiratory mechanisms, metabolic processes, and energy homeostasis)
• Golgi apparatus (functions as a factory in which proteins are further processed and sorted for transport)
• Nissl's granules (rough endoplasmic reticulum with rosettes of free ribosomes, site of protein synthesis)
• Lysosomes (contain digestive enzymes and devour foreign particles that enter the cell body)
• Nucleus (contains DNA and controls the formation of RNA, synthesis, and composition of cellular protein substances)

Axon Structure

• The axon is the primary appendage that emerges from the body of the nerve cell.
• The axon is cylindrical in shape, with a constant diameter throughout its length.
• The axon is either branched or single and ends with the final branches that form the synapse area.
• The axon is surrounded by the myelin sheath, which is secreted by Schwann cells, and contains Ranvier's nodes.
• Axons can be classified as:
• Myelinated fibers (surrounded by the myelin sheath)
• Non-myelinated fibers (not covered by the myelin sheath)