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Muscular and Nervous Tissues
1.0Muscular Tissue
Muscular tissue is distinguished from other tissues by its unique ability to contract & relax and thereby perform mechanical work. It is responsible for movement of body organs and locomotion of the body.
The structural unit of muscular tissue is the muscle cells and because of its elongated shape is also called muscle fibre. The contractility is due to the presence of contractile proteins (actin & myosin) in the muscle fibre.
Functions of Muscular Tissue
(i) It supports the bones and other organs of the body.
(ii) Muscles cause peristalsis of gut, heart beat, production of sound, etc.
(iii) Muscles cause movements of body parts and locomotion of the animals.
(iv) Facial expression also depends on muscles.
(v) Contraction of muscles causes delivery of a baby.
Note: Muscle that contracts without conscious control and found in walls of organs like stomach, intestine, etc are called involuntary muscles.
Muscles present in our limbs move when we want them to and stop when we so decide. Such muscles are called voluntary muscles.
Differences Between Skeletal Muscle Tissue, Cardiac Muscle Tissue, Smooth Muscle Tissue
Presence of intercalated discs and oblique bridges are unique features of cardiac muscles. These help the muscles in faster conduction of wave of contraction.
2.0Nervous Tissue
The nervous tissue, contains densely packed cells called nerve cells or neurons, is present in the brain, spinal cord and nerves. They have least power of regeneration. The neurons are specialised for conduction of nerve impulses. They receive stimuli from within or outside the body and conduct impulses (signals) which travel from one neuron to another neuron. Nerve impulse allow us to move our muscles when we want to. The functional combination of nerve and muscle tissue is fundamental to most animals. This combination enables animals to move rapidly in response to stimulus.
Stimulus: An agent or a change in the external or internal environment that induces reaction in the body.
Each neuron has the following 2 parts.
Cyton or Cell Body
Contains a central nucleus and cytoplasm with characteristic deeply stained particles called Nissl's granules (i.e. clumps of ribosomes and rough endoplasmic reticulum).
Cell Processes
(a) Dendrites: These may be one to many, generally short and branched cytoplasmic processes. Dendrites are afferent processes because they receive impulse from receptor or other neuron and bring it to cyton.
(b) Axon: It is single generally long efferent process which conducts impulse away from cyton to other neuron.
Longest cell in body is neuron (upto 1 m) because axon can be more than one meter long. Axon has uniform thickness, but it has terminal thin branches called telodendria. Terminal end buttons or synaptic knobs occur at the end of telodendria. Nodes of Ranvier are gaps in the myelin sheath coating on the axon.