Locomotion and Movement
* Movement is one of the most important characteristics of all living beings.
* Movement resulting in a change of location is called locomotion.
* There are three main types of movement-amoeboid, ciliary and muscular.
* Amoeboid movement is the simplest form of movement and is due to protoplasmic streaming.
* Ciliary movement occurs in the internal tubular organs lined by ciliated epithelium.
* Muscular movement is brought about by contractile muscles, which help in body movements and locomotion.
* Locomotion is brought about by the coordination of the muscular, skeletal and neural systems in the body.
Muscles and Contractile Proteins
* Muscle tissue originates from the mesoderm and has special properties such as excitability, contractility, extensibility and elasticity.
* Based on their location, muscles are classified into three types, namely skeletal, visceral and cardiac.
* Skeletal muscles are striated and voluntary and help in locomotion and different body postures.
* Visceral muscles are unstriated and involuntary and are found in the inner walls of hollow visceral organs.
* The cardiac muscle is a contractile, involuntary muscle found only in the heart.
* The myofibrils in muscle fibre show alternate light and dark bands due to the alternate distribution of two important proteins- actin and myosin.
Mechanism of Muscle Contraction
* The sliding filament theory describes the mechanism used by muscles to contract.
* Muscle contraction is initated when a signal is sent to a motor neuron touching the sarcolemma of the muscle fibre.
* When a neuro signal reaches the neuromuscular junction, actyl choline is released, which generates an action potential in the sarcolemma.
* The action potential spreads to the muscle fibre, which causes the release of calcium ions in the sarcoplasm.
* The calcium ions further bind to a subunit of a troponin on actin filaments, thereby unmasking the active sites on actin for thick filaments.
* Myosin cross-bridges attached to the actin filament bring about a contraction.
* When calcium ions return to the sarcoplasmic reticulum, actin is deactivated.
* When myosin releases ADP and Pi, cross- bridges are broken and muscles relax.
* Repeated activation of muscles causes the accumulation of lactic acid due to the anaerobic breakdown of glycogen, causing muscle fatigue.
* Muscles can be of two types: one, those that undergo aerobic respiration and two, those that depend on anaerobic process for energy.
Skeletal System
* The adult skeletal system consists of 206 bones and a few cartilages, both of which are specialised connective tissues.
* The axial skeleton consists of 80 bones, which include the skull, vertebral column, ribs and sternum.
* The appendicular skeleton includes the bones of the limbs and their supporting girdles.
* The point at which two bones or a bone and a cartilage make contact is called a joint.
* Although the muscular and skeletal systems function in a coordinated manner, these systems may begin to wear and tear or exhibit some disorders.