3.4 Muscle Tissue

. Muscle Tissue Each muscle is made of many long, cylindrical fibres arranged in parallel arrays. These fibres are composed of numerous fine fibrils, called myofibrils . Muscle fibres contract (shorten) in response to stimulation, then relax (lengthen) and return to their uncontracted state in a coordinated fashion. In general muscles play an active role in all the movements of the body. Muscles are of three types, skeletal, smooth and cardiac. Skeletal Muscle tissue is closely attached to skeletal bones. In a typical muscle such as the biceps, the striated (striped) skeletal muscle fibres are bundled together in a parallel fashion. A sheath of tough connective tissue encloses several bundles of muscle fibres (You will learn more about this in Chapter ). The smooth muscle fibres taper at both ends (fusiform) and do not show striations XI Std Biology-Zoology Chapter- conditions. Neurons, the unit of neural system are excitable cells (Figure . ). The neuroglial cells which constitute the rest of the neural system protect and support the neurons. Neuroglia makes up more than one-half of the volume of neural tissue in our body. When a neuron is suitably stimulated, an electrical disturbance is generated which swiftly travels along its plasma membrane. Arrival of the disturbance at the neuron’s endings, or output zone, triggers events that may cause stimulation or inhibition of adjacent neurons and other cells (You will study in detail in Chapter ) Diseases of Nervous System: . Parkinson’s disease: A degenerative disorder of the nervous system that affects movement, often including tremors. . Alzheimer’s Disease: It is a chronic neurodegenerative disease which includes the symptoms of difficulty in remembering recent events, problems with language, disorientation and mood swings. Biopsy is an examination of tissue or liquid removed from a living body to discover the presence, cause or extent of a disease. Autopsy is a post-mortem (dissection of a dead body) examination to discover the cause of death or the extent of disease. The field of Forensic science effectively uses the histological techniques to trace out crimes.