Ch 9Locomotion and Movement — Class 11 Zoology, concept-first.

Living organisms show an enormous range of movement — from a fly's escape reflex to the gentle blink of a human eyelid to a marathon runner covering 20 km.

Not every kind of biological movement uses the same machinery. Four distinct types occur in and around the cells of the human body:

Muscle is a specialised tissue that develops from the middle embryonic germ layer, the mesoderm. It is built from elongated, contractile cells called myocytes (muscle cells/fibres), which are bound to…

Skeletal muscle (also called voluntary muscle) is the muscle type directly responsible for locomotion.

A skeletal muscle fibre is a single, highly specialised cell — thin, elongated, and usually tapering at one or both ends. Several features distinguish it from a typical cell:

Contraction depends on two contractile proteins organised into the thick and thin myofilaments of the sarcomere, plus two regulatory proteins that control when contraction can occur.

In 1954, Andrew F. Huxley and Rolf Niedergerke proposed the sliding filament theory: actin and myosin filaments, each of fixed, unchanging length, slide past one another during contraction rather than…

Skeletal muscle contraction is classified into two primary types based on how the muscle's length and tension change during the contraction:

Beyond the isotonic/isometric distinction, individual skeletal muscle fibres also differ physiologically along two independent axes: how fast they shorten, and how they generate ATP.

Skeletal muscle owes its ability to move the body to four fundamental physiological properties:

The skeletal system — the framework of bones and cartilages — is, like muscle, derived from the embryonic mesoderm.

The axial skeleton forms the central, vertical axis of the body and consists of 80 bones across four regions: the skull, the hyoid bone, the vertebral column, and the thoracic cage (sternum + ribs).

The skull is composed of two sets of bones totalling 22: 8 cranial bones and 14 facial bones (Figure 9.7).

The vertebral column, or backbone (Figure 9.8), is made of 33 serially arranged vertebrae, each pair interconnected by a cartilaginous pad, the intervertebral disc, which cushions and permits limited…

The sternum, or chest bone, is a single flat bone lying along the mid-ventral (front, midline) surface of the thorax.

There are 12 pairs of ribs (Figure 9.9). Each individual rib is a thin, flat, curved bone that connects dorsally (at the back) to the vertebral column and, in most cases, ventrally (at the front) to t…

The appendicular skeleton is composed of 126 bones: the bones of the upper and lower limbs together with the girdles that anchor each limb to the axial skeleton.

The pectoral girdle is formed of two halves, each consisting of a clavicle (collar bone) and a scapula (Figure 9.10).

The pelvic girdle is a heavy structure specialised for bearing the body's weight (Figure 9.11), composed of two coxal (hip) bones that anchor the lower limbs to the axial skeleton.

A typical long bone (Figure 9.12) is built from a diaphysis, two epiphyses (singular epiphysis) and surrounding membranes.

The table below reconciles every bone count given in the preceding sections into the textbook's own summary, confirming that the axial skeleton's 4 regions add up to 80 bones and the appendicular skel…

A joint is any point of contact between two bones (Figure 9.13). Joints are essential for every movement performed by the bony skeleton, sometimes also playing a protective role, and — because the for…

Because muscles and bones function together as one system, a disorder affecting either one can impair the body's ability to move.

- Myasthenia gravis — an autoimmune disorder in which antibodies block the acetylcholine receptors on the sarcolemma at the neuromuscular junction, disrupting the normal signal for contraction.

The two major disorders of the skeletal system are arthritis and osteoporosis.

Physical activity and exercise fall into four broad categories, each targeting a different aspect of fitness:

Despite their considerable strength, bones remain susceptible to fractures (breaks) when subjected to sufficient force.

Bone is a living, cellular tissue capable of growth, self-repair and continuous remodeling in response to physical stress — in the adult skeleton, bone deposition and bone resorption occur side by sid…

A dislocation is the total displacement of a bone's articular end out of its joint cavity, altering the normal alignment of the joint's bones.

Physiotherapy is the therapeutic use of graded, structured exercise to restore near-normal function to the limbs, delivered by trained physiotherapists as a recognised rehabilitation profession presen…

This section presents the chapter's complete Evaluation exercise as printed in the textbook: 20 multiple-choice questions (Q1-20) testing recall of muscle and bone terminology, followed by 20 short-an…