Muscles are specialized tissues found in animals which have properties like excitability, contractibility. Muscles contract is initiated by CNS through motor neuron signalling. The motor neuron and muscle firbre connect and form a motor unit for movement. The junction between the sarcolemma (membrane) of muscle and the motor neuron is called as neuromuscular junction. The muscles after contraction, relax where the Calcium ions are pumped into the cisternae of the sarcoplasmic reticulum from the sarcoplasm. Muscles contain oxygen carrying red colour protein called myoglobin similar to haemoglobin. Muscles having higher content of myoglobin appear red in colour and are called red muscles. Muscles with lower concentration of myoglobin are called white muscles. Muscles contain large number of mitochondria to utilize the high amount of oxygen stored and provide high concentration of ATP as energy. Hence, such muscles are also referred as aerobic muscles.