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Nervous tissue

life science Maturity 9-11 Next article →

Nervous tissue, also called neural tissue, is the primary component of the nervous system. This specialized tissue allows the body to regulate and control various functions and activities. The nervous system is divided into two main parts. The central nervous system (CNS) includes the brain and the spinal cord. The peripheral nervous system (PNS) consists of branching peripheral nerves.

Peripheral nerve, cross section
Peripheral nerve, cross section

Nervous tissue is essential for sensory input, integration, and the control of muscles and glands. It also maintains homeostasis and supports mental activity throughout the body.

The tissue functions as a communication network by conducting electrical signals. These signals are known as action potentials. The process begins when a neuron receives an electrochemical signal called a neurotransmitter. This happens at the dendrites, which are thin, branching projections on the cell. The signal creates a change in voltage across the cell membrane. This change travels through the soma, or cell body, and moves down the axon. The axon is a long, stem-like projection that carries the action potential away from the cell body.

Saltatory Conduction
Saltatory Conduction

When the action potential reaches the end of the axon, it hits the axon terminal. This terminal is separated from the next neuron by a tiny gap called a synaptic cleft. To bridge this gap, the neuron releases neurotransmitters across the synapse. These chemicals bind to receptors on the next neuron to continue the impulse. This step-by-step chain allows messages to move rapidly through the body. The speed of these messages can be increased by a lipid-based insulation called myelin.

Saltatory Conduction
Saltatory Conduction

Neurons are classified in two ways: by their function and by their structure. Functionally, sensory neurons, or afferent neurons, relay information from the PNS to the CNS. Motor neurons, or efferent neurons, carry action potentials from the CNS to muscles and glands. Interneurons form connections between other neurons within a local area. Structurally, multipolar neurons have three or more processes and are common in the CNS. Bipolar neurons have only two processes: one dendrite and one axon. Pseudounipolar neurons have a single process that splits into two branches. There are also unipolar brush cells, which are excitatory interneurons found in the cerebellum.

Neuroglia, or glial cells, are non-neural cells that support the neurons. They are smaller than neurons and perform many crucial tasks. In the CNS, astrocytes are the most abundant cell type and are vital for a healthy system. Microglial cells are the smallest neuroglia and act as the primary immune system for the CNS. Oligodendrocytes in the CNS form myelin sheaths to increase the speed of action potentials. In the PNS, Schwann cells perform a similar role by maintaining axons and forming myelin. Other types include satellite glial cells, which line neuron cell bodies in ganglia, and enteric glia found in the gastrointestinal tract.

Nervous tissue is organized into specific types depending on its location. In the CNS, there is grey matter and white matter. Grey matter contains cell bodies, dendrites, and unmyelinated axons, making it important for information processing. White matter consists of myelinated axons and oligodendrocytes, which facilitate impulses between grey matter areas. In the PNS, ganglion tissue contains cell bodies and dendrites to act as relay points. Nerves in the PNS are bundles of axons wrapped in protective connective tissue.

Peripheral nerve, cross section
Peripheral nerve, cross section

Each nerve in the PNS is protected by three distinct layers of connective tissue. The innermost layer is the endoneurium, a thin, delicate sheath surrounding each individual axon. The next layer is the perineurium, which encloses bundles of axons called fascicles. The perineurium has seven or eight concentric layers and prevents large molecules from entering the fascicle. The outermost layer is the epineurium, which is a dense layer of connective tissue. These layers work together to provide structural support and protection for the nerve fibers.

Understanding nervous tissue is also important for medicine because of various tumors, or neoplasms. Gliomas are tumors that arise from glial cells. There are many specific types of these, such as astrocytoma, oligodendroglioma, and medulloblastoma. Other tumors can affect the nerve sheaths, including neurofibroma and Schwannoma. Because nervous tissue controls so many vital body systems, these growths can significantly impact how the body functions.

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File:Peripheral nerve, cross section.jpg
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Saltatory Conduction.gif
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