Movement And Locomotion Chapter Notes | Biology Class 9 ICSE PDF Download

Introduction

Most animals have a distinct shape and the ability to move various body parts. These movements facilitate locomotion, or movement from one place to another. The skeleton and muscles work together to enable these functions. Most animals have a distinct shape and the ability to move various body parts. These movements facilitate locomotion, or movement from one place to another. The skeleton and muscles work together to enable these functions.

Functions of the Human Skeleton

The human skeleton serves six primary functions:

1. Support and Shape: The skeleton acts as a framework, supporting soft tissues and giving the body and its parts a defined shape. For instance, without the phalanges in your fingers, grasping objects like a pen would be impossible. Consider the ear: you can fold it, but it returns to its original shape due to the flexible yet firm cartilage inside, which provides both support and shape.
2. Protection: Bones encase and shield vital organs. The skull safeguards the brain, the vertebral column protects the spinal cord, and the ribcage shields the heart and lungs.
3. Movement: Bones are connected at joints, allowing one bone to move relative to another. Muscles, attached to bones, drive these movements by originating on one bone and inserting on another.
4. Leverage: Certain bones and joints function as levers, amplifying the speed and range of muscle movements. For example, a small contraction of the biceps muscle can rapidly move the hand over a distance greater than a foot.
5. Blood Cell Formation: The bone marrow within the hollow spaces of some long bones produces red and white blood cells.
6. Mineral Storage: Bones store essential minerals like calcium and phosphorus, which can be released to meet the body’s needs.

Components of the Skeleton

The skeleton is made up of three main elements:

• Bones: Form the rigid framework of the body.
• Cartilages: Provide support and flexibility, as seen in structures like the external ears and the tip of the nose.
• Ligaments: Connect bones to one another, ensuring stability.

Bones

Composition and Structure

• Bone is the primary component of the human skeleton, made up of both organic and inorganic materials. The inorganic portion, which accounts for about two-thirds of the bone's composition, primarily consists of calcium and phosphorus compounds. 
• When a bone is soaked in weak hydrochloric acid, the mineral content dissolves, leaving behind a soft, flexible organic framework known as decalcified bone, which is pliable enough to be tied into a knot. 
• Conversely, when a bone is intensely heated, the organic matter is destroyed, leaving only the brittle mineral "ash," which easily breaks. As people age, the organic component of bones diminishes, making them more fragile and slower to heal after fractures.

Bone Classification by Shape
Bones are categorized by shape into long, short, flat, and irregular types.

Structure of a Long Bone

• A typical long bone, such as the thigh bone, is a highly mineralized, rigid, and strong connective tissue capable of withstanding significant stress. It contains osteocytes (bone cells) arranged in concentric rings within a matrix of collagen fibers and mineral salts (calcium and phosphorus). The bone's outer surface is covered by a membrane called the periosteum, which has an outer fibrous layer and an inner cellular layer, both richly supplied with blood vessels. 
• Long bones feature a central hollow cavity filled with bone marrow, which exists in two forms: (1) yellow marrow, composed of adipose tissue and blood vessels that produce white blood cells, and (2) red marrow, located at the bone ends, which generates red blood cells.

The Human Skeleton

• Consists of 206 bones, including three tiny bones in each ear.
• Divided into two main parts: axial skeleton (central framework) and appendicular skeleton (limbs and girdles).

Axial Skeleton

Includes the skull, vertebral column, ribs, and sternum.

Skull

• Consists of two parts: cranium (brain-box) and facial bones.
• Cranium: Made of eight fixed bones forming the brain-box.
• Facial bones: 14 bones forming the face, including upper and lower jaws.
• Foramen magnum: A large hole at the back of the cranium through which the spinal cord passes to connect with the backbone.

Vertebral Column

• Also called the backbone, made of 33 ring-like vertebrae.
• Divided into five regions: 7 cervical (neck), 12 thoracic, 5 lumbar, 1 sacrum (5 fused vertebrae), 1 coccyx (4 fused vertebrae).
• Curved to maintain balance in an erect position, absorbing pressure and shock during movement to prevent breaking.
• Structure of a vertebra: Includes a solid cylinder (centrum), neural canal (housing the spinal cord), neural spine (upward ridge), transverse processes (side projections), and articular facets (for joining vertebrae).
• Intervertebral disc: A cartilage pad acting as a cushion between vertebrae.
• Cervical vertebrae: First is the atlas, second is the axis; remaining five have no special names.
• Thoracic vertebrae: Have long, backward-directed neural spines and facets on transverse processes for rib articulation.
• Lumbar vertebrae: Have well-developed neural spines and transverse processes for back muscle attachment.
• Sacrum: Formed by five fused vertebrae, articulates with hip bones.
• Coccyx: Four fused vertebrae, representing a rudimentary tail; occasionally, babies are born with a small tail, which is surgically removed.

Ribs

• 12 pairs form the rib cage with thoracic vertebrae and sternum.
• True ribs: First seven pairs directly attached to the sternum via hyaline cartilage.
• False ribs: 8th, 9th, and 10th pairs join the seventh rib via hyaline cartilage.
• Floating ribs: 11th and 12th pairs are not attached to the sternum.

Sternum

• A long, flat bone in the middle of the chest’s front part.

Appendicular Skeleton

Includes bones of the limbs and girdles (shoulder and hip).

Bones of the Limbs

• Forelimbs: Humerus (upper arm), radius and ulna (lower arm), 8 carpals (wrist), 5 metacarpals (palm), 14 phalanges (2 in thumb, 3 in each finger).
• Hind-limbs: Femur (thigh, longest and strongest bone), tibia and fibula (shank), 7 tarsals (ankle), 5 metatarsals (foot), 14 phalanges (2 in great toe, 3 in each other toe), and patella (knee-cap, formed from a tendon).

Girdles

• Shoulder (pectoral) girdle: Two flat, triangular scapulae (shoulder blades) on upper ribs, with a glenoid cavity for humerus articulation and a clavicle (collar bone) connecting to the sternum.
• Hip (pelvic) girdle: Two hip bones (each made of ilium, ischium, and pubis) joined to the sacrum, with an acetabulum for femur articulation; supports and protects abdominal organs.
• Difference between male and female skeleton: Male skeleton is larger and heavier; female pelvis is wider and trough-shaped to accommodate pregnancy.

Joints

Points where two bones meet, classified into three types: immovable, partially movable, and freely movable.

• Immovable Joints: No movement possible; bones joined tightly by fibrous connective tissue, e.g., sutures in the skull.

Partially Movable Joints

• ​Allow limited movement; bones joined by cartilage, e.g., joints between ribs and sternum or between vertebrae.

Freely Movable Joints

Allow varying degrees of movement; include four types:

• Gliding joint: Bones glide over each other, e.g., wrist and ankle bones, vertebrae.
• Pivot joint: One bone rotates over a pivot-like end of another, e.g., skull on the axis vertebra.
• Hinge joint: Moves in one plane like a door hinge, e.g., elbow (humerus and ulna), finger, toe, and knee joints; provides sufficient power.
• Ball and socket joint: A ball-like bone end fits into a cup-like depression, allowing movement in all directions, e.g., shoulder (humerus in glenoid cavity) and hip (femur in acetabulum).

Synovial Joints

• Freely movable joints with synovial fluid for lubrication to reduce friction, e.g., shoulder and knee joints.
• Held firmly by strong ligaments and a fibrous capsule to prevent dislocation.
• Synovial fluid is contained in a thin synovial membrane sac, acting as a cushion between bones.

Muscles

• Enable all body movements, give shape to the body, and maintain posture during sitting, standing, or walking.
• Consist of long bundles of contractile tissue with a fixed end (origin) and a movable end attached to a bone via a tendon.
• Muscles contract to become shorter and thicker, pulling the bone at the movable end; they cannot lengthen.

Antagonistic Muscles

• Muscles causing opposite movements; one muscle moves a structure, another returns it to its original position.
• Example: Biceps (flexor) bends the lower arm; triceps (extensor) straightens it.

Types of Muscles

• Voluntary muscles: Controlled by will, e.g., arm muscles.
• Involuntary muscles: Not controlled by will, e.g., muscles in the digestive tract.
• Some muscles (e.g., eyelids, diaphragm) can be both voluntary and involuntary.
• Cardiac muscles: Found in heart walls, capable of rapid, tireless contractions.

Coordination of Muscles

• Actions like standing, walking, or running require coordinated action of multiple muscles.

Lever Mechanisms

• Skeletal lever actions make body movements easier.
• First-order lever: Fulcrum between power (P) and weight (W), e.g., triceps extending the arm at the elbow, skull resting on atlas and axis vertebrae.
• Second-order lever: Fulcrum at one end, power at the other, weight in between, e.g., gastrocnemius muscle raising the body on toes.
• Third-order lever: Fulcrum at one end, weight at the other, power in between, e.g., biceps flexing the arm.

Points to Remember

• Skeleton provides support, protection, movement, and leverage.
• Bones store calcium and phosphorus; hollow long bones produce blood cells.
• Skeleton includes axial (backbone, ribs) and appendicular (limbs, girdles) parts.
• Joints are immovable, partially movable, or freely movable (gliding, hinge, pivot, ball and socket).
• Most movable joints have synovial fluid for lubrication.
• Antagonistic muscles produce opposite movements.
• Skeleton demonstrates all three orders of levers.