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Skull, vertebral column, sternum and ribs.

Hyoid is a U- shaped bone present at the base of the buccal cavity.

The bones of the limbs and their girdles.

Ribs contain two articulation surface on its dorsal end and hence called bicephalic.

(a) True

(b) False; H – zone represents thick filaments.

(c) True

(d) False; There are 12 pairs of ribs.

(e) True.

(a) TRUE

(b) FALSE, H-zone represents thick filaments

(c) TRUE

(d) FALSE, There are 12 pairs of ribs in man

(e) TRUE 

Mechanism of muscle contraction is best explained by the sliding filament theory which states that contraction of a muscle fiber takes place by the sliding of the thin filaments over the thick filaments.

Muscle contraction is initiated by a signal sent by the central nervous system (CNS) via a motor neuron. A motor neuron alongwith the muscle fibres connected to it constitute a motor unit. The junction between a motor neuron and the sarcolemma of the muscle fibre is called the neuromuscular junction or motor-end plate. A neural signal reaching this junction releases a neurotransmitter (Acetyl choline) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions into the sarcoplasm. Increase in Ca⁺⁺ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby remove the masking of active sites for myosin.

Utilising the energy from ATP hydrolysis, the myosin head now binds to the exposed active sites on actin to form a cross bridge. This 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 the sarcomere, i.e., contraction. It is clear from the above steps, that during shortening of the muscle, i.e., contraction, the ‘I’ bands get reduced, whereas the ‘A’ bands retain the length. The myosin, releasing the ADP and P₁ goes back to its relaxed state. 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 and breakage is repeated causing further sliding. The process continues till the Ca⁺⁺ ions are pumped back to the sarcoplasmic cisternae resulting in the masking of actin filaments. This causes the return of ‘Z’ lines back to their original position, i.e., relaxation. 

• Calcium ions bind to specific sites on the troponin component of thin (actin) filaments.
• As a result, conformational change occurs in the troponin molecules and the active sites of F- actin are exposed. These are the sites Specific to myosin head that shows Mg dependent ATPase activity.
• When calcium ions are pumped back into the sarcoplasmic reticulum, the troponin component becomes free to mask the active sites for myosin head. This leads to breakage of cross bridges and the actin filaments slide out of A – band.

Fascia connective tissue layer of muscle bundles.

Synovial joints are characterised by the presence of a fluid filled synovial cavity between the articulating surfaces of the two bones. Such an arrangement allows considerable movement. These joints help in locomotion and many other movements.

Ex: Ball and socket joint, Pivot joint.

Synovial joints are characterised by the presence of a fluid filled synovial cavity between the articulating surfaces of the two bones.

Glenoid cavity.

• Ball and Socket joint. Eg: between humerus and pectoral girdle.
• Hinge joint. Eg: Knee joint and Elbow joint.
• Pivot joint. Eg: between atlas and axis
• Gliding joint. Eg: between the carpals
• Saddle joint Eg: between carpal and metacarpal of thumb.

(a)  7

(b)  14

(c)  Troponin and Tropomyosin

(d)  Sarcoplasmic reticulum

(e)  11 and 12

(f)  8

A portion of myofibril between two successive ‘Z’ lines.

The dorsal, flat, triangular body of scapula has a spine which projects as a flat, expanded process called the acromion.

The portion of the myofibril between two successive ‘z’ lines is called as sarcomere. It is the functional unit of muscle contraction. A sarcomere consists of a dark band in the centre and light bands on either side. The dark band or Anisotropic band (A band) is made of myosin and the light band on Isotropic band (I- band) is made of actin filaments.

Along the centre of the I- band is an elastic fibre called z – line, that bisects the band. Their filaments are attached firmly to the z – line. The myosin filaments are also held together in the centre by a thin fibrous membrane called M – Line. The central part of A band, not over lapped by thin filaments (I- band) is called a H – zone.

30 bones present in each limb.

We have a total of 26 vertebrae in our body.

• Cervical vertebrae (7) in the neck region.
• Thoracic vertebrae (12) present in the thoracic region of the trunk.
• Lumbar vertebrae (5) present in the abdominal region.
• Sacrum (1) is the triangular bone at the end of vertebral column.
• Coccygeal (1) which is vestigial tail bone in human being.

Associated with the skeletal components of body.

Striated muscles -They have a striped appearance under the microscope.

Voluntary muscles - As their activities are under the voluntary control of the nervous system.

They are primarily involved in locomotory actions and changes of body postures.

Muscle - specialised tissue of mesodermal origin.

They have special properties like excitability, contractility, extensibility and elasticity.

Based on their location, three types of muscles are identified : 

(i) Skeletal 

(ii) Visceral 

(iii) Cardiac. 

Types of movement in human body :

Amoeboid Movement :

macrophages leucocytes in blood is effected by pseudopodia formed by the streaming of protoplasm (as in Amoeba). 

Ciliary Movement : 

Occurs in most of our internal tubular organs which are lined by ciliated epithelium. 

Coordinated movements of cilia in the trachea help us in removing dust particles and some of the foreign substances inhaled along with the atmospheric air. 

Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.

Muscular Movement : 

Eg.- Movement of our limbs, jaws, tongue, etc. 

Contractile property of muscles are effectively used for locomotion and other movements by human beings and majority of multicellular organisms. 

Meromyosin contains two parts:

• Globular head with a short arm called heavy meromyosin (HMM)
• A tail called Light meromyosin (LMM)

Meromyosins is monomers of myosin filament.

In the resting state a subunit of troponin masks the active binding sites for myosin on the actin filaments.

Central part of the A- band not overlapped by the thin filaments is called H – zone.

Troponin is distributed at regular intervals on the tropomyosin.

Joints are points of contact between bones, or between bones and cartilages.

Public symphysis is the cartilaginous joint between the two halves of the pelvic girdle on the ventral side.

• Contractility
• Excitability
• Extensibility
• Elasticity

Repeated activation of the muscles lead to the accumulation of lactic acid due to anaerobic breakdown of glycogen causing fatigue.

Fibrous, cartilaginous and synovial.

Synovial fluid

Actin and myosin

(a) (iv)

(b) (ii)

(c) (i)

(d) (iii)

The endoplasmic reticulum of striated muscle fibres is called sarcoplasmic reticulum. It is the storehouse of calcium ions.

Cells of the human body exhibit three main types of movements, namely, amoeboid, ciliary and muscular.Some specialised cells in our body like macrophages and leucocytes in blood exhibit amoeboid movement. It is effected by pseudopodia formed by the streaming of protoplasm.

Ciliary movement occurs in most of our internal tubular organs which are lined by ciliated epithelium. The movement of cilia in the trachea help in removing dust particles and some of the foreign substances. Passage of ova through the female reproductive tract is also facilitated by the ciliary movement. Movement of our limbs, jaws, tongue etc. requires muscular movement. The contractile property of muscles are effectively used for locomotion and other movements by human beings.

Cells of the human body exhibit three main types of movements, namely, amoeboid, ciliary and muscular.

Amoeboid Movement: Some specialised cells in our body like macrophages and leucocytes in blood exhibit amoeboid movement. It is effected by pseudopodia formed by the streaming of protoplasm (as in Amoeba). Cytoskeletal elements like microfilaments are also involved in amoeboid movement.

Ciliary Movement: Ciliary movement occurs in most of our internal tubular organs which are lined by ciliated epithelium. The coordinated movements of cilia in the trachea help us in removing dust particles and some of the foreign substances inhaled alongwith the atmospheric air. Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.

Muscular Movement: Movement of our limbs, jaws, tongue, etc, require muscular movement. The contractile property of muscles are effectively used for locomotion and other movements by human beings and majority of multicellular organisms. Locomotion requires a perfect coordinated activity of muscular, skeletal and neural systems.

Movement of limbs, jaw, tongue etc.

• The coordinated movements of cilia in the trachea help in removal of dust particles and foreign substances inhaled along with atmospheric air.
• Passage of ova through the female reproductive tract is also facilitated by the ciliary movement.

Limbs and tongue.

Located in the inner walls of hollow visceral organs of the body like the alimentary canal, reproductive tract, etc.

Non-striated muscle - do not exhibit any striation.

Smooth muscles - are smooth in appearance.

Involuntary muscles - Their activities are not under the voluntary control of the nervous system.

They assist in transportation of food through the digestive tract and gametes through the genital tract.

Structure of a skeletal muscle:

Muscle bundles or fascicles- Many such fascicles are held together by a common collagenous connective tissue layer called fascia to form a skeletal muscle in our body.

Sarcolemma – Plasma membrane lining each muscle fibre which encloses sarcoplasm.

Sarcoplasm – Cytoplasm of a muscle cell. Muscle fibre is a syncitium as the sarcoplasm contains many nuclei.

Sarcoplasmic reticulum -Endoplasmic reticulum of the muscle fibres which is the store house of calcium ions.

Myofilaments or Myofibrils - a large number of parallel arranged filaments in the sarcoplasm. 

• Each myofibril has alternate dark and light bands on it.
• Striated appearance of myofibril is due to the distribution pattern of two important proteins – Actin and Myosin. 

Light band contains actin and is called I-band or Isotropic band. 

Dark band called ‘A’ or Anisotropic band contains myosin. 

Both proteins are arranged as rod-like structures, parallel to each other and also to longitudinal axis of the myofibrils. 

Actin filaments are thinner as compared to myosin filaments, hence are commonly called thin filaments. 

Myosin filaments are thick filaments.

Sarcomere - Portion of myofibril between two successive "Z" lines. - is the functional unit of contraction.

Malleus, Incus and Stapes

Longest bone of human body is Femur. 

80 bones axial skeleton

Striated appearance of myofibril is due to the distribution pattern of two proteins, actin and myosin.