Ch 16Skeleton and Movement — Class 11 Biology, concept-first.

Movements may be internal (e.g. protoplasmic streaming, peristalsis, heartbeat) or external (e.g. limb movement), and they may be voluntary or involuntary.

The muscle that moves a particular bone is usually not located on that same bone but on the bone lying just proximal to it — for example, the biceps and triceps that move the forearm are located in th…

Muscles generally work in pairs that produce opposite actions — for example, the biceps (a flexor) folds (flexes) the elbow while the triceps (an extensor) straightens (extends) it.

The sliding filament theory, proposed by H.E. Huxley and A.F. Huxley, is also known as the walk-along theory or ratchet theory.

In the resting (relaxed) muscle, the active (myosin-binding) sites on actin remain covered by the troponin-tropomyosin complex, so myosin cannot interact with actin and contraction cannot occur.

During relaxation, the events of contraction occur in reverse. Once nerve stimulation is terminated, the actomyosin complex is broken down and the myosin head detaches from the actin filament — a proc…

When a skeletal muscle is stimulated electrically, it displays several characteristic properties:

Multicellular animals need some form of support to maintain their body structure. Various groups of organisms show supportive skeletal structures either outside the body, inside the body, or both.

A point where two or more bones get articulated is called a joint, articulation, or arthrosis; the study of joints is called arthrology.

Muscular dystrophy is a gradual, wasting disease affecting various groups of muscles; these conditions are genetically inherited in families.

Arthritis is an inflammation of the joints — a painful disorder of bones, ligaments, tendons, etc., in which the joints become swollen, stiff and painful, and which can lead to disability.