Nerve Tissue

Parts of a Neuron

Neurons are the fundamental units of the nervous system, responsible for transmitting electrical and chemical signals throughout the body. Each neuron consists of several distinct parts, each with specialized functions.

• Cell Body (Soma): The central part of the neuron containing the nucleus and most organelles. It integrates incoming signals and generates outgoing signals to the axon.

• Cell Processes:

  • Dendrites: Branch-like extensions that receive signals from other neurons and convey this information to the cell body.

  • Axon: A long, singular process that transmits electrical impulses away from the cell body to other neurons or effector cells.

• Nissl Bodies: Granular structures in the cell body composed of rough endoplasmic reticulum and ribosomes, involved in protein synthesis.

• Neurotransmitter Junction (Motor Nerve Endings) on Skeletal Muscle: The synapse where a motor neuron communicates with a skeletal muscle fiber to initiate contraction.

Neuroglial Cells

Neuroglial cells, or glia, provide support, protection, and nutrition to neurons. In peripheral nerves, Schwann cells are the primary glial cells.

Peripheral Nerve Fiber in Longitudinal Section (Myelinated Nerve)

When viewing a myelinated peripheral nerve in longitudinal section, several key structures can be identified:

• Nodes of Ranvier: Gaps in the myelin sheath along the axon that facilitate rapid conduction of nerve impulses via saltatory conduction.

• Axon (Nerve Fiber): The elongated projection that carries electrical signals.

• Myelin Sheath: A multilayered covering formed by Schwann cells, which insulates the axon and increases the speed of impulse transmission.

• Schwann Cell (Neurolemmocyte): A type of glial cell in the peripheral nervous system that produces the myelin sheath around axons.

Peripheral Nerve Fiber in Cross-Section

In cross-section, the following structures are visible:

• Axon (Nerve Fiber): Appears as a central circular structure within the myelin sheath.

• Myelin Sheath: Surrounds the axon, appearing as a clear ring due to the lipid content.

• Schwann Cell (Neurolemmocyte): The cell body may be seen adjacent to the myelin sheath.

Locate Neuron Cell Bodies in Spinal Cord Gray Matter, Sensory (Dorsal Root) Ganglia, and the Cerebellar Cortex Slides

Neuron cell bodies are found in specific regions of the nervous system, each with distinct structural and functional characteristics.

• Gray Matter in Spinal Cord: Contains neuron cell bodies, dendrites, and unmyelinated axons. It is involved in processing and integrating information.

• White Matter in Spinal Cord: Composed mainly of myelinated axons, responsible for transmitting signals to and from the brain.

• Sensory Neurons in Dorsal Root Ganglia of Spinal Cord: The dorsal root ganglia contain the cell bodies of sensory neurons that transmit sensory information from the periphery to the central nervous system.

Table: Comparison of Gray Matter, White Matter, and Dorsal Root Ganglia

Additional info:

• Saltatory Conduction: The process by which action potentials "jump" from one node of Ranvier to the next, greatly increasing conduction velocity in myelinated axons.

• Myelin Sheath Disorders: Diseases such as multiple sclerosis involve the degradation of myelin, leading to impaired nerve function.