Question

describe the characteristics and functions of the nervous and muscle tissue

Answer 1

Nervous tissue is the main tissue component of the nervous system. They consist of two parts- the central nervous system [CNS] and the peripheral nervous system [PNS]. The CNS comprises the brain and the spinal cord, and the PNS comprises the branching peripheral nerves which reach out to all the body parts.

The nervous tissue consists of two categories of cells- neurons and neuroglia.

Neurons are long cells and are also called Nerve fibers. Each neuron has two distinct parts- a cell body called cyton, and a long tail like cylindrical process with fine branches at the end, called axon.

The cyton contain the cytoplasm, nucleus and the other cell organelles. It gives out short, hair like extentions called dendrons. The dendrons, in turn, branch into thin dendrites.

The axons may or may not be covered with a protein sheath made of myeline. If the axons have the myeline sheath, they are called 'myelinated nerve fibers' and if the sheath is absent, they are called 'non-myelinated nerve fibers'.

The neurons are arranged in such a way that the nerve endings of one neuron are in contact with the dendrites of the other. This is called a synapse. Nerve impulses travel from one neuron to another through the synapse with the help of neurotransmitters.

The neurons are of two types- sensory and motor neurons. Sensory neurons carry impulse from the sense organs to the brain and the spinal cord while motor neurons carry impulse from the CNS to the muscles.

Neuroglia or glial cells are non-neuronal cells and are mainly supprtive in nature. They maintain homeostasis, form myelin and provide support and protection to the neurons. They are of six types, namely - Schwann cells, Satellite cells, Oligodendrocytes, Astrocytes, Ependymal cells and Microglia.

Function- Nervous tissues play vital functions in our body. They control and coordinate every body function and cause reaction to external and internal stimuli. The neurons spread all over our body and maintain a rhythm and complete balance between the different body functions.

Neuroglia are the supportive cells which surround neurons and hold them in place, supply nutrients and oxygen to the neurons, insulate one neuron from another and also destroy and remove disfunctional neurons, if any.

Muscular Tissue

Muscles are found all over the body- around bones and make our organs. They contract and expand to make movement possible. There are three types of muscular tissues based on their structure and functuions--

[a] Striated or Voluntary muscles- These are made up of long, cylindrical muscle cells, called muscle fibers. They are multinucleated and unbranched. Each muscle fiber is enclosed within a thin delicate membrane called the sarcolemma. The cytoplasm is known as sarcoplasm. There are contractile structures within the sarcoplasm which are called myofibrils. The myofibrils help the muscles fibers to contract upon recieving a stimulus. The most distinguishing feature of the striated muscles is the alternating light and dark bands appear throughout the muscle fibers.

Functions- Striated muscles are also called Voluntary muscles because they are under the control of our will. They are also called Skeletal muscles because they are founf around the bones.

The main function of these muscles is to help in body movement. They fatigue or 'tire' after some time.

[b] Non-striated or Involuntary muscles-- The muscle fibers are spindle shaped with pointed ends and are uninucleate. Sometimes their ends may be branched. Many fibers are joined together in bundles by loose connective tissue. Myofibrils are present and run longitudinally through the entire length of the muscle fibers. They do not have striations or the light and dark bands which are present on Voluntary muscle fibers. For this reason, they are also called Smooth muscles.

Functions- They are involuntary, i.e., they are not under our will. They make up several organs of our body like the alimentary canal, blood vessels, iris of the eye and are even found in the skin. They do not fatigue or 'tire'.

[c] Cardiac muscles- These muscles only make up the heart. Structurally they are similar to Voluntary muscles, i.e., they are cylindrical and striated but functionally they are like Involuntary muscles. The cardiac muscle fibers are branched and the branches of the adjacent muscle fibers are attached by special structures called Intercalated disc. There are cross striations of myofibrils and the nucleus is located centrally.

Functions- The cardiac muscles contract rapidly and rhythmically throughout life without any external stimulation. They never get tired and continually pump blood throughout the life of an individual.