INTRODUCTION :
most animals are characterized by a definite shape and the capacity for movement of the different parts of the body.these movements also help the animal in locomotion, that is movement from place to place. These functions are performed by the Skelton and the muscles together.
FUNCTIONS OF HUMAN SKELETON :
The skeleton in our body serves six main purposes :
1.support and shape : The skeleton provides a support or framework to all the soft parts and gives the body and it’s parts a definite shape.
2.protection : several delicate and important organs are well protected by a casing of bones.for example, the skull protects the brain,the vertebralcolumn (back bone) protects the spinal cord , the ribs protect the heart and lungs, and so on.
3.movement : many bones are joined to each other in a manner that one bone can be moved on another. These movements are brought about by muscles which originate on one bone and are inserted on another.
4.leverage : some bones and joints form levers that increase the speed and distance of movement by a muscle. For example : contraction of only few centimeters by the biceps muscle swings the hand swiftly through an arc of more than a foot.
5.Formation of blood cells : certain types of blood cells , including red and white blood cells formed in the tissue of the hollow space or the marrow of some of the long bones.
6. The bones are a storehouse of calcium and phosphorus for the rest of the body.
Locomotion is the voluntary movement of an individual from one place to another.
Walking, running, climbing, swimming are the examples of locomotion. All locomotion are
movement but all movements are not locomotion.
Types of Movement
Cells of the human body show three main types of movements:
1.Amoeboid, 2. Ciliary, 3.muscular.
- Macrophages and leucocytes in blood exhibit amoeboid movements. Coordinated
movement of cilia in trachea to remove dusts particles and passage of ova through
fallopian tube is example of Ciliary movements. - Movement of limbs, jaw, tongue, etc. need muscular movement. Contractile property of muscles is used in movement in higher organism including human beings.
Muscles are specialized tissues of mesodermal origin. They have property like excitability,contractility, extensibility and elasticity.
Based on their location, three types of muscles are identified :
SKELETAL MUSCLES :associated with skeletal system, alternative light and dark bands (striated) voluntary and locomotory change in body posture function.
VISCERAL MUSCLES : form inner wall of internal visceral organs, non – striaghted, involuntary muscle, assists in movement of food through digestive tract and gametes.
CARDIAC MUSCLE : muscles of heart, having branching pattern, alternative light and dark brands, involuntary in action.
- Skeletal Muscle is made up of muscles bundles (fascicles), held together by
collagenous connective tissue called fascia - Each muscle bundle contains a number of muscle fibres. Each muscle fibre is lined by plasma membrane called sarcolemma enclosing sarcoplasm. Partially arranged
myofibrils are present in muscle bundle having alternate light and dark bands due to
presence of protein- actin and myosin - Light bands contain actin and is called I-band (isotropic band) and dark band contains myosin, called A-band (anisotropic band). Both bands are present parallel to
each other in longitudinal fashion. - In centre of each I-band is elastic fibre called ‘Z’ line. In the middle of A-band is thin
fibrous ‘M’ line. The portion of myofibrils between two successive ‘Z’ lines is the
functional unit of contraction called a sarcomere. - At resting stage thin filament overlaps the thick filament. The part of thick filament
not overlapped is called ‘H’ zone.
Structure of contractile Protein :
Each thin filament (actin) is made of two ‘F’ actins helically wounded to each other. Two
filaments of another protein, tropomyosin runs close to it. A complex protein
Troponin is distributed at regular intervals on the tropomyosin.
Each myosin filament is made of many monomeric proteins called Meromyosins. Each
meromyosin has globular head with short arm and tails. Globular head has ATP binding
sites
Mechanism of muscle contraction :
- The mechanism of muscle contraction is explained by sliding mechanism theory in
which thin filament slide over thick filament. - Muscle contraction start with signal sent by CNS via motor neuron. Neural signal
release neurotransmitter ( Acetyl choline) to generate action potential in the sarcolemma. - This causes the release of Ca ++ from sarcoplasmic reticulum.
- Ca ++ activates actin which binds to the myosin head to form a cross bridge.
- These cross bridges pull the actin filaments causing them to slide over the myosinfilaments and thereby causing contraction.
- Ca ++ are then returned to sarcoplasmic reticulum which inactivate the actin. Cross bridges are broken and the muscles relax.
Muscles are classified as :
Red fibres (aerobic muscles-) contain myoglobin that has plenty of mitochondria to use large amount of oxygen stored in them.
White fibres-the muscle fibres containing less number of myoglobin are called white fibres.
Skeletal System
Framework of bones and cartilage forms the skeletal system. In human beings, it consists of
206 bones and some cartilages. The two principle division of skeletal system are:
1. Axial Skeleton (80 bones)- includes skull, vertebral column, sternum and ribs constitute
axial system.
- The skull (22 bones) is composed of cranial and facial bones. Cranial (8 bones) forms protective covering for brain (cranium). The facial region consists of 14 skeletal systems that form front part of skull. Hyoid bone (U-shaped) forms the base of buccal cavity.
- The middle ear bone (Malleus, Incus and Stapes) collectively called Ear Ossicles. Skull joins with vertebral column with two occipital condyle.
- Vertebral column consists of 26 serially arranged vertebrae. First vertebra is atlas
that combines with occipital condyle. Other includes Cervical-7, thoracic -12, lumbar
-5, sacral – 1 coccoygeal -1. - 12 pairs of ribs connected dorsally to vertebral column and ventrally to sternum. 11th and 12th rib bones are not connected with sternum and are called floating ribs.
APPENDICULAR SKELETON : includes bones of limbs and girdles. Each limb contains 30 bones.
Upper arm : Humerus, radius and ulna, 8-carpels,5-metacarpels, 14-phalanges
Lower limb : Femur, tibia and fibula, 7-tarsals, 5-metatarsals, 14- phalanges, cup shaped patella cover the knee.
Pectoral and Pelvic girdle bones help in the articulation of the upper and the lower limbs
respectively with the axial skeleton.
Pectoral girdle consists of a clavicle and a scapula.
Pelvic girdle consists of two coxal bones. Each coxal bone is formed by the fusion of three
bones – ilium, ischium and pubis
Joints – are points of contact between bones, or between bones and cartilage.
1. Fibrous joints- do not allow any movements. Present in flat skull bones to form cranium.
2. Cartilaginous joints- bones are held together with the help of cartilage present in
vertebrae. Permits limited movements.
3. Synovial joints- fluid filled synovial cavity, provide considerable movements. Ball and
socket joint, hinge joints, pivot joints, gliding joints etc.
Disorders of Muscular and Skeletal System
- Myasthenia gravis- auto immune disorder affecting neuromuscular junction causingfatigue, weakening and paralysis of skeletal system.
- Muscular Dystrophy- degeneration of skeletal muscles due to genetic disorder.
- Osteoporosis – decreased bone mass in old age leading to chance of fracture due to
decreased estrogen. - Arthritis– inflammation of joints.
- Gout– inflammation of joints due to accumulation of uric acid crystals.
- Tetany– Rapid spasms in muscle due to low Ca ++ in body fluid
