Introduction to Body Movements

Our bodies are constantly in motion. Even when we are sitting still, we can observe movements like the blinking of our eyes or the rhythmic movement of our chest as we breathe. We perform countless movements throughout the day, such as writing, turning to look at someone, walking, running, skipping, and jumping.

Movement is a characteristic of all living beings. The way animals move from one place to another (locomotion) varies greatly. Some walk, others run, fly, swim, crawl, or slither. This variety in movement is due to the differences in their body structures.

How Animals Move

Different animals use different body parts and methods for locomotion. The table below lists some examples.

Movement in Plants

While animals move from place to place, plants are generally fixed in one location. However, plants do show other kinds of movements. For example, a sunflower turns to face the sun, and the leaves of a 'touch-me-not' plant fold upon being touched. These are movements, but not locomotion.

Joints of the Human Body

We are able to bend, rotate, or lift parts of our body because of specific points where different parts are joined together. These places are called joints. If our body had no joints and was made of a single rigid structure, movement would be impossible.

At these joints, two or more bones meet. Bones are the hard structures that form the framework of our body. Since bones themselves cannot be bent, all our movements, like bending an elbow or a knee, happen at the joints where these bones are connected.

Types of Joints

There are different types of joints in our body, each allowing a different kind and range of movement.

1. Ball and Socket Joints

In a ball and socket joint, the rounded, ball-like end of one bone fits into the cup-like cavity (hollow space) of another bone. This structure allows for movement in all directions, including full circular rotation.

Examples: The joints at the shoulder (where the arm joins the shoulder) and the hip (where the thigh bone joins the hip bone).

2. Pivotal Joint

A pivotal joint allows for rotational movement. In this joint, a cylindrical bone rotates within a ring formed by another bone and ligaments.

Example: The joint where our neck joins the head. This joint allows us to bend our head forward and backward and turn it to the left and right.

3. Hinge Joints

Hinge joints work like the hinges on a door, allowing movement in only one plane (back and forth). They do not permit rotation.

Examples: The joints at the elbow and the knee. These joints allow us to bend and straighten our arms and legs but not twist them at the joint.

4. Fixed Joints

Fixed joints are joints where the bones are fused together and cannot move at all. These joints provide strength and protection to the structures they enclose.

Examples: The joints between the bones of the skull (except for the lower jaw). The joint between the upper jaw and the rest of the head is also a fixed joint.

The Human Skeleton

All the bones in our body come together to form a framework that gives shape and support to our body. This framework is called the skeleton. An adult human skeleton is composed of 206 bones.

We can get an idea of the shape of our bones by feeling them. For a more accurate view, doctors use X-ray images, which can show the shapes of the bones and help identify injuries like fractures.

Major Parts of the Skeleton

The Rib Cage

The ribs are curved bones in our chest. They are joined to the chest bone (sternum) in the front and the backbone at the back, forming a box-like structure called the rib cage. There are 12 pairs of ribs. The rib cage protects vital internal organs like the heart and lungs.

The Backbone (Vertebral Column)

The backbone runs down the back of our body from the neck. It is not a single long bone but is made up of 33 small, stacked bones called vertebrae. This segmented structure allows us to bend and twist our back. The rib cage is joined to the backbone.

Shoulder and Pelvic Bones

• Shoulder Bones: These bones are prominent on the back where the shoulders are located. They provide the attachment point for the arms.
• Pelvic Bones: This structure is made of several fused bones and is located below the stomach. It encloses this portion of the body and provides support. It is the part of the body we sit on.

The Skull

The skull is a bony structure made up of many bones joined together by fixed joints. Its primary function is to enclose and protect the most important part of our body, the brain. The only movable part of the skull is the lower jaw.

Cartilage

In addition to bones, the skeleton has some additional parts that are not as hard as bones and can be bent. These are called cartilage. Cartilage is a firm but flexible connective tissue.

Examples: It is found in the upper part of the ear and at the end of the nose. It is also found in the joints between bones, where it acts as a cushion to prevent them from rubbing against each other.

How Muscles Cause Movement

Bones and joints provide the framework and points of movement, but they cannot move on their own. The force required to move the bones is provided by muscles.

Muscle Contraction and Relaxation

Muscles are attached to bones. Movement is caused by the tightening (contraction) and loosening (relaxation) of muscles.

When a muscle contracts, it becomes shorter, stiffer, and thicker. This contraction pulls on the bone it is attached to, causing the bone to move at the joint. A muscle can only pull; it cannot push.

Muscles Work in Pairs

Because muscles can only pull, they must work in pairs to move a bone in opposite directions. These are called antagonistic pairs.

1. To move a bone in one direction, one muscle of the pair contracts (pulls), while the other muscle relaxes.
2. To move the bone back to its original position, the relaxed muscle contracts (pulls), and the first muscle relaxes.

For example, to bend your arm at the elbow, the bicep muscle (on the front of the upper arm) contracts, and the tricep muscle (on the back) relaxes. To straighten the arm, the tricep contracts, and the bicep relaxes.

Gait of Animals

The term "gait" refers to the manner or pattern of movement of an animal. Different animals have evolved unique gaits suited to their body structure and environment.

Earthworm

The earthworm's body is made up of many rings joined end to end. It does not have bones. Movement is achieved through the alternate expansion and contraction of its muscles.

Its body has tiny, hair-like bristles underneath, which are connected to muscles. These bristles help the earthworm get a good grip on the ground. To move, it extends its front part, grips the ground with bristles, and then pulls its rear end forward. Its body also secretes a slimy substance that helps in movement.

Snail

The snail carries a rounded structure on its back called the shell. This is the snail's outer skeleton (exoskeleton), but it is a single unit and does not help in movement; it has to be dragged along. The snail moves using a large, muscular foot. The foot produces a wavy motion that pushes the snail's body forward.

Cockroach

Cockroaches can walk, climb, and fly. They have a hard outer skeleton (exoskeleton) made of different plates joined together. They have three pairs of legs for walking and two pairs of wings for flying, which are moved by distinct sets of muscles.

Birds

Birds are well-adapted for flying. Their features include:

• Hollow and light bones: This reduces their body weight.
• Modified forelimbs: Their forelimbs are modified into wings.
• Strong muscles: Their breastbones are modified to hold large flight muscles that move the wings up and down.

Birds also use their hind limbs (legs) for walking and perching.

Fish

Fish have a streamlined body shape (tapering at both ends), which allows water to flow around it easily, reducing resistance. They swim by forming curves in their body. Strong muscles cause the front part of the body to curve to one side while the tail swings to the opposite side. This creates a jerk that pushes the fish forward. The fins on their body help maintain balance and direction.

Snake

Snakes move by slithering. They have a long backbone and many thin, interconnected muscles. The snake’s body curves into many loops. Each loop pushes against the ground, giving the snake a forward push. By forming multiple loops, the snake can move forward very fast, but not in a perfectly straight line.

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