Histology of Nervous Tissue

The human body comprises simultaneous functions carried out by numerous internal systems, each more intricate than the other, but equally important. One such system is the nervous system. This system comprises vital body organs such as the brain, spinal cord and the supporting network of nerves and nervous tissue. The nervous tissue controls and regulates body functions. It comprises the neurons or transmitters of impulses and the neuroglia, the propagators of nerve impulses and providers of neuron nutrients. The intricacy of the nervous tissue can be best understood by knowing that each time any part of the body is pinched, local nervous tissue is permanently damaged. The nervous tissue pervades the functions and structure of the entire nervous system and related functions, throughout the body.

Histology of Nervous Tissue:

Nervous tissue comprises various nerve cells, each characterized by a long stem like part called the axon. This feature of the tissue helps in sending 'action potential signals' to the adjacent cell, thus generating an awareness to stimulus. All living organisms display the ability to react to stimuli. This primary and distinct characteristic manifests due to the sensitivity of the nervous tissue. The tissue is designed to react to internal or external stimuli and respond to the same. The response is generated by the conduction of impulses within related body organs. Nerve tissue that encompasses the brain, peripheral nerves and spinal cord consists of special nerve cells called neurons. Neurons are classified structurally (multipolar, bipolar and unipolar) and functionally. The easily stimulated neurons transmit quick response-impulses across nerve cell fibers that are bound by connective tissue. Each nerve within the nervous system is covered by a sheath of epineurium, a dense connective tissue comprising blood vessels of various sizes. The epineurium penetrates individual nerves to form the perineurium.

The nerve cell body is held within a plasma membrane. Each cell has a central nucleus and Nissl body granules in the cytoplasm. There are fine neurofibrils that extend from the axon to the dendrites. The axon is enclosed in a myelin sheath, a non-cellular, fatty layer, beyond which lies the myelin sheath, a cellular covering. This cellular covering is referred to as the neurilemma. The myelin sheath and neurilemma together form the medullary sheath. This sheath is characterized by nodes of Ranvier at intervals. Neuronal communication takes place in a junction called the synapse. This is the region where the axon terminal branches meet the dendrites of another neuron. Information is transmitted within the region via chemical secretions, also referred to as neurotransmitters. The result is the activation of the post-synaptic cell and subsequent response to stimuli. The nervous system is characterized by rigid physiological control, to meet the thermo-regulatory and metabolic demands to response. The sensitivity of the system, to external and internal stimuli, is regulated by hormonal and neural mediators along peripheral and central sites. All multicellular organisms are naturally equipped with nervous tissue to increase sensitivity to the environment and move and react to stimuli. Thus, nervous tissue cells control behavior patterns, body structure and chemistry and intellectual capabilities. Diseases, like Parkinson's disease, that affect nervous tissue functions, have serious consequences on the quality of life. The health of the tissue is affected adversely by a deficiency of dopamine (a neurotransmitter) and progressive death of brain cells. Health issues resulting from nervous tissue damage manifest in the form of rigid and unstable posture, and even death.