→ Movement is an essential feature of all living beings.

→ Protoplasmic streaming, ciliary movements, movements of fin, limbs, wings, etc., are some forms exhibited by animals,

→ A voluntary movement that causes the animal to change its place is called locomotion.

→ Animals move generally in search of food, shelter, mate, breeding ground, a better climate or to protect themselves.

→ The cell of the human body exhibit amoeboid, ciliary, and muscular movements.

→ Locomotion and many other movements require coordinated muscular activities.

→ Three types of muscles are present in our body.

→ Skeletal muscles are attached to skeletal elements. They appear united and are voluntary in nature.

→ Visceral muscles, present in the inner walls of visceral organs are nonstriated and involuntary.

→ Cardiac muscles are the muscles of the heart. They are striated, branched, and involuntary.

→ Muscles possess excitability, contractility, extensibility, and elasticity.

→ A muscle fiber is the anatomical unit of muscle. Each muscle fiber has many parallelly arranged myofibrils. Each myofibril .contain many serially arranged units called sarcomere which is the functional unit.

→ Each sarcomere has a central A-bond made of thick myosin filaments, and two half I-bands made of thin actin filaments on either side of it marked by Z lines.

→ Actin and myosin are polymerized proteins with contractility, the active sites for myosin on resting actin filament are masked by a protein- troponin.

→ Myosin head contains ATP phase and has ATP binding sites and active sites for actin.

→ A motor neuron carries the signal to the muscle fiber which generates action potential in it. This causes the release of Ca⁺⁺ from the 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 myosin filaments and thereby causing contraction.

→ Ca are then returned to the sarcoplasmic reticulum which inactivates the actin. Cross bridges are broken and the muscles relax.

→ Repeated stimulation of muscle leads to fatigue. Muscles are classified as Red and White fibers based primarily on the amount of red-colored myoglobin pigment in them.

→ Bones and cartilages constitute our skeletal system. The skeletal system is divisible into axial and appendicular.

→ Skull, vertebral column, ribs, and sternum constitute the axial skeleton. Limb bones and girdles form the appendicular skeleton.

→ Three types of joints are formed between bones or between bone and cartilage:

1. Fibrous,
2. cartilaginous, and
3. synovial.

→ Synovial joints allow considerable movements and therefore, play a significant role in locomotion.

→ Locomotion: Such voluntary movements i.e., limbs, jaws, eyelids, tongue, etc. are called locomotion.

→ Striated muscles: Skeletal muscles have a striped appearance under the microscope and hence are called striated muscles.

→ Voluntary muscles: As striated muscle activities are under the voluntary control of the nervous system, they are known as voluntary muscles too.

→ Smooth muscles (nonstriated muscle): Visceral muscles do not exhibit any striation and are smooth in appearance. Hence, they are called smooth muscles (non-striated muscles).

→ Involuntary muscles: Smooth muscle activities are not under the voluntary control of the nervous system and are therefore known as in-voluntary muscles.

→ Fascia: Each organized skeletal muscle in our body is made of a number of muscle bundles or fascicles held together by a common collagenous connective tissue layer called fascia.

→ Myofilaments or myofibrils: A characteristic feature of the muscle fiber is the presence of a large number of parallelly arranged filaments in the sarcoplasm called myofilaments or myofibrils.

→ ‘I’ band and ‘A’ band: The light bands contain actin and are called T band or Isotropic band whereas the dark band called ‘A’ or Anisotropic band contain myosin.

→ Thin and thick filaments: Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively.

→ ‘M’ Line: The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called the ‘M’ line.

→ Sarcomere: The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere.

→ ‘H’ Zone: Central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone.

→ Meromyosins: Each myosin (thick) filament is also a polymerized protein. Many monomeric proteins called meromyosins constitute one thick filament.

→ Myoglobin: Muscle contains a red-colored oxygen storing pigment called myoglobin.

→ Red muscles: Myoglobin content is high in some of the muscles which give a reddish appearance. Such muscles are called the Red muscles.

→ Aerobic muscles: Red muscles also contain plenty of mitochondria that can utilize a large amount of oxygen stored in them for ATP production. These muscles, therefore, can also be called aerobic muscles.

→ Hyoid: A single ‘U’ shaped bone called hyoid is present at the base of the buccal cavity and it is also included in the skull.

→ Spine and Acromion: The posterior, flat, triangular body of the scapula has a slightly elevated ridge called the spine which projects as a flat, expanded process called the acromion.

→ Glenoid Cavity: Below the acromion is a depression called the glenoid cavity which articulates with the head of the humerus to form the shoulder joint.

→ Collar bone: Each clavicle is a long slender bone with two curvatures. This bone is commonly called the collar bone.