NEET Biology Notes Movement and Locomotion Muscle Contraction
Muscle Contraction
Muscle Contraction
It is initiated by a signal sent by the Central Nervous System (CNS) via a motor neuron. The mechanism of muscle contraction is best explained by sliding-filament theory.
The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate. At junction, a neurotransmitter- acetylcholine generates an action potential in the sarcolemma. Utilising the energy
from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. This L pulls the attached actin filaments towards the centre of A-band.
The Z-line attached to these actins are also pulled inwards thereby causing a shortening of sarcomere, i. e. contraction, the I-bands get reduced, whereas A-band retains the length. A new ATP binds and the cross-bridge is broken. The ATP is again hydrolysed by the myosin head and the cycle of cross-bridge formation 1 and breakage is repeated causing further sliding. The process continues till the Ca2+ ions are pumped back to I the sarcoplasmic cisternae resulting in the masking of actin filaments. This causes the return of Z-lines back to the original position, i.e. relaxation. Repeated activation ! of muscles can lead to the accumulation of lactic acid due to the anaerobic breakdown of glycogen in them, causing fatigue.
Muscle contains a red-coloured pigment called myoglobin. The myoglobin content is high in some muscles, which gives them reddish appearance and they are called as red fibres or aerobic muscles. Some of the muscles possess very less myoglobin, hence are pale in appearance or white. These are called white fibres. They depend on anaerobic process of respiration.
Human Skeletal System
The total number of bones in adult human is 206. The axial skeleton of human consists of 80 bones. The appendicular skeleton of human consists of 126 bones. The skull bones fit together by sutures. Cheek bones are called zygomatics. The vertebral column of human consists of 33 vertebrae. There are 12 pairs of ribs in human skeleton. The first seven pairs of ribs are known as true ribs, while 8, 9 and 10 pairs are false ribs and last two pairs (11 and 12) are known as floating ribs.
Different Type of Bones of Skeleton
- Long bones, e.g. humerus, radius, femur, etc.
- Short bones, e.g. metacarpals of palm and metatarsals, phalanges
- Flat bones, e.g. scapula, sternum, cranial bones.
- Irregular bones, e.g. vertebrae, carpals, tarsals.
- Femur is longest bone, while stapes is smallest bone.
- Fibula is the thinnest bone.
- Tibia is skin bone. Tibia-fibula is the longest bone of frog.
- Sternum is absent in fishes.
- Funny bone is found in the bend of elbow.
- Synovities is an inflammation leading to swelling at joints.
- Chondrology is the study of cartilages.
- Fibro-cartilage is the shortest cartilage.
Functions of Skeletal System
- It provides support to the body.
- It provides delicate support to internal organs, such as heart, brain and lungs.
- It provides surface for muscles attachment.
- It helps in blood cells formation.
- It acts as the storehouse of minerals such as calcium and phosphorus.
- It also helps in breathing and hearing.
Protection Function of Skeleton
- The skeleton protects many vital organs.
- The skull protects the brain, ayes, and middle and inner ears.
- The vertebrae protect the spinal cord.
- The rib cage, spine, and sternum protect the lungs, heart and major blood vessels.
- The clavicle and scapula protect the shoulder.
- The ilium and spine protect the digestive and urogenital systems and the hip.
- The patella and the ulna protect the knee and the elbow respectively.
