Introduction to Nervous Tissue
Nervous tissue is a specialized tissue involved in transmitting and processing information via electrical and chemical signals. It is a critical component of the
central nervous system (CNS) and the
peripheral nervous system (PNS), playing a pivotal role in coordinating body functions and responding to external and internal stimuli.
Neurons: Also known as nerve cells, neurons are the fundamental units of the nervous system responsible for conducting impulses. They have a unique structure comprising the
cell body (soma),
dendrites, and an
axon.
Neuroglia: Also known as glial cells, neuroglia provide support, nutrition, and protection to neurons. Types of glial cells include
astrocytes,
oligodendrocytes,
microglia, and
ependymal cells in the CNS, and
Schwann cells and
satellite cells in the PNS.
Cell Body (Soma): The cell body contains the nucleus and other organelles necessary for the metabolic activities of the neuron.
Dendrites: These are branching extensions that receive signals from other neurons and convey them towards the cell body.
Axon: A long, slender projection that transmits impulses away from the cell body to other neurons, muscles, or glands. The axon may be covered by a
myelin sheath formed by oligodendrocytes in the CNS and Schwann cells in the PNS, which increases the speed of impulse conduction.
How Do Neurons Communicate?
Neurons communicate with each other through
synapses, which are specialized junctions where the axon terminal of one neuron comes into close proximity with the dendrite or cell body of another neuron. Communication occurs via chemical messengers known as
neurotransmitters, which are released from synaptic vesicles in the presynaptic neuron and bind to receptors on the postsynaptic neuron, initiating a new electrical impulse.
Astrocytes: Provide structural support, regulate the extracellular ion and neurotransmitter concentrations, and maintain the blood-brain barrier.
Oligodendrocytes: Produce the myelin sheath in the CNS, which insulates axons and enhances the speed of electrical impulses.
Microglia: Act as the immune cells of the CNS, phagocytosing debris and protecting against pathogens.
Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord, involved in the production and circulation of cerebrospinal fluid.
Schwann Cells: Form the myelin sheath in the PNS and assist in the regeneration of damaged axons.
Satellite Cells: Provide support and nutrition to the neurons in the PNS ganglia.
What is the Blood-Brain Barrier?
The
blood-brain barrier (BBB) is a selective permeability barrier formed by endothelial cells of the brain capillaries, astrocyte end-feet, and pericytes. It protects the CNS by restricting the entry of potentially harmful substances while allowing essential nutrients to pass through.
Conclusion
Nervous tissue, with its unique cellular components and specialized structures, is integral to the functioning of the nervous system. Understanding the histological features of neurons and neuroglia, as well as their roles in communication and support, provides essential insights into the complex workings of the brain and nervous system.
