The structure of nervous tissue, composed of neurons and glial cells, directly reflects its primary function of rapid communication via electrical and chemical signals.
Neuron Structure and Function
Neurons, the fundamental units of the nervous system, are uniquely structured to receive, process, and transmit information. This specialization is evident in their distinct components:
- Cell Body (Soma): Contains the nucleus and other organelles necessary for cell function. It's the neuron's control center.
- Dendrites: Branch-like extensions that receive signals from other neurons. Their extensive surface area maximizes signal reception.
- Axon: A single, long extension that transmits signals away from the cell body. The axon's length enables long-distance communication.
- Myelin Sheath: A fatty insulation layer surrounding the axon, formed by glial cells (specifically, oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system). Myelin increases the speed of signal transmission by allowing action potentials to "jump" between Nodes of Ranvier (see below).
- Nodes of Ranvier: Gaps in the myelin sheath where the axon membrane is exposed. These gaps allow for saltatory conduction, where the action potential jumps from node to node, greatly increasing the speed of transmission.
- Axon Terminals (Synaptic Terminals): Branched endings of the axon that release neurotransmitters to communicate with other neurons, muscle cells, or glands at synapses.
The polarized structure of the neuron – with dendrites receiving signals and the axon transmitting them – is crucial for unidirectional signal flow. The neuron's shape, though variable, is always structured to facilitate this flow.
Glial Cell Structure and Function
Glial cells provide structural and functional support to neurons. Their diverse shapes and functions contribute to nervous tissue function:
- Astrocytes: Star-shaped cells that provide structural support, regulate the chemical environment around neurons, and form the blood-brain barrier, protecting neurons from harmful substances in the blood.
- Oligodendrocytes: Form the myelin sheath around axons in the central nervous system. Their multiple processes can myelinate portions of several axons, increasing the efficiency of signal transmission in the brain and spinal cord.
- Schwann Cells: Form the myelin sheath around axons in the peripheral nervous system. Each Schwann cell myelinates only one segment of one axon.
- Microglia: Act as immune cells in the nervous system, removing cellular debris and pathogens. Their small size and ability to migrate allow them to quickly respond to injury or infection.
- Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord, producing and circulating cerebrospinal fluid.
The arrangement and specialization of these glial cells directly support neuronal function, contributing to the overall efficiency and stability of the nervous system.
Summary
The structure of nervous tissue is intrinsically linked to its function. The polarized shape of neurons facilitates rapid signal transmission, while glial cells provide support, insulation, and protection, ensuring the optimal functioning of the nervous system. The arrangement and morphology of both cell types are crucial for efficient communication and information processing.
