Samacheer Class 8 Science - Movements

The axial skeleton and appendicular skeleton are two main divisions of the skeletal system with distinct structures and functions. The axial skeleton consists of the bones along the central axis of the human body and includes the skull, facial bones, sternum, ribs, and vertebral column. These bones form the core framework of the body and protect vital organs such as the brain, heart, and lungs. The appendicular skeleton, on the other hand, contains the bones of the appendages and the structures that attach them to the axial skeleton. It comprises the shoulder girdle, the arm bones, wrist bones, and hand bones, as well as the pelvic girdle, leg bones, ankle bones, and foot bones. While the axial skeleton provides the central support and protection, the appendicular skeleton enables movement and locomotion through its connection to muscles and joints.

Tendon:
They are made of elastic tissue.
They attach muscle to a bone
Ligament:
They are short bands of tough fibrous connective tissues.
They connect one bone to another

1. Movement and Locomotion
Movement:
Movement is the act of changing the place or position by one or more parts of the body.
It can either be voluntary or involuntary.
A movement takes place at the biological level.
Movement requires energy.
Locomotion:
Locomotion is the movement of an organism from one place to another.
It is always voluntary.
Locomotion takes place at the organism level.
Locomotion doesn’t necessarily require energy.
2. Endoskeleton and Exoskleton
Endoskeleton:
It is the skeleton found inside the body.
It originals from mesoderm.
Example: Human beings.
Exoskleton:
It is the skeleton found on the exterior layer of the body.
It originals from embryonic ectoderm or mesoderm.
Example: Scales of fish feathers of birds
3. Pectoral and Pelvic girdle
Pectroal girdle:
It is situated in the shoulder region.
It gives articulation to forelimbs.
The shoulder blade and collar bone remain separate.
They are comparatively lighter.
Pelvic girdle:
It is situated in the hip region.
It gives articulation to legs or hind limb.
Three bones (ilium, ischium and pubis) are fused to form a single hip bone.
They are strong to take upto lot of stress
4. Ball and socket Joint and Hinge Joint
Ball and socket Joint:
A ball shaped head of one bone articulates with a cup like socket of j an adjacent bone.
Movement can occur in three planes. This joint allows the greatest range of movement.
Example: Shoulder, Hip
Hinge Joint:
A cylindrical protrusion of one bone articulates with a trough-shaped depression of an adjacent bone.
Movement is restricted to one plane. This joint allows bending and straightening only.
Example: Elbow Knee Ankle
5. Voluntary and Involuntary muscle:
Voluntary muscle:
They are striated (Multinucleate muscles and unbranched) muscles.
They are attached to bones.
Example: found in arms, legs
They are used as per our will.
Involuntary muscle:
They are non – striated (Single muscle, central nucleus) muscles.
They are attached to soft parts of the body like blood vessels, Iris, Skin etc.
They are not under our control.

Antagonistic muscles are muscles that work in pairs and function in opposition to each other, with one muscle contracting while the other relaxes to produce coordinated movement. A prime example is the biceps and triceps muscles in the upper arm. The biceps is a flexor muscle located on the front of the upper arm that contracts to bend the arm at the elbow, raising the forearm. When the biceps contracts, the triceps, which is located on the back of the upper arm, relaxes. To straighten the arm, the reverse action occurs: the triceps contracts to extend the arm while the biceps relaxes. This antagonistic relationship allows for smooth, controlled movement of the arm in both directions and is essential for precise muscular control throughout the body.

The skeleton of a bird is remarkably well-suited for flying due to several specialized adaptations. Birds have a streamlined body shape that reduces air resistance during flight. Their bones are light and strong, with hollow structures containing air spaces that reduce overall body weight without compromising strength. The hind limbs are modified as claws that help birds walk and perch on branches. The breast bone is enlarged and modified to accommodate massive flight muscles that power the wings during flight. The forelimbs are transformed into wings with long feathers that provide the surface area necessary for generating lift and thrust. The tail also bears long feathers that aid in steering and balance during flight. Additionally, birds possess specialized flight muscles and demonstrate two types of flight: gliding, where they use air currents to stay aloft with minimal effort, and flapping, where they actively beat their wings to generate propulsion and maintain altitude.

The skeleton serves multiple critical functions in the human body. First, it provides structure and shape to the body, forming the framework that gives the body its characteristic form. Second, it supports and protects the internal organs, with the skull protecting the brain, the rib cage protecting the heart and lungs, and the vertebral column protecting the spinal cord. Third, bones serve as storage sites for essential minerals, particularly calcium and phosphorus, which are vital for various regulatory functions in the body. Fourth, bone marrow, the soft tissue inside bones, produces red blood cells that carry oxygen throughout the body and white blood cells that fight infections. Fifth, the bones act as levers for muscular action, working in conjunction with muscles to produce movement. Muscular movement would not be possible without tendons, which are fibrous cords of tissue that attach muscles to bones and transmit the force of muscle contraction, and ligaments, which are fibrous cords that attach bone to bone and provide stability to joints.

Joint
Examples
Ball and Socket
Shoulder Hip
Hinge
Elbow Knee Ankle
Pivot
Spine (Atlas / Axis joint at the top)
Condyloid
Wrist
Gliding
Spine (between the bony processes of the vertebrae)
Saddle
Thumb, shoulder and inner ear.

The axial skeleton consists of the bones along the axis or central line of the human body. It consists of the skull, facial bones sternum, ribs and vertebral column.
Skull:
It is a hard structure made of 22 bones.
8 bones are fixed together to form the cranium and 14 hones fuse to form the face.
The lower jaw is the only movable bone of the skull.
Vertebral column:
It is called the backbone and runs of the back of the body.
It is made of 33 individual bones called vertebrae as follows :
7 Cervical vertebrae
12 Thoracic vertebrae
5 Lumbar vertebrae
5 Fused sacral vertebrae
4 Fused coccygeal vertebrae
The hollow tube of the vertebral column contains the spinal cord.
Vertebrae are joined by gliding points which allow the body to be bent back, front or side – wards.
Function of vertebral column:
It protects the spinal cord
It supports the head
It serves as an attachment for ribs
Helps in walking, standing erect and posture.
Sternum or Ribcage:It is a cone shaped structure in the chest region and made up of 12 pairs of ribs.
The ribs attached to the vertebral column at the back and the breast bone in the front.
There are 12 pairs of ribs.
First 10 pairs are attached to breast bone.
2 pairs are called free floating ribs and are free in the front.
Rib cage can contract and expand during breathing.
It protects the lungs, hearts and a part to the liver.

There are three types of movements:
1. Amoeboid movement:
It is brought about by pseudopodia which are appendages which move with movement of protoplasm within a cell.
2. Ciliary movement:
This movement is brought about by appendages called as cilia which are the hair-like extensions of the epithelium. Both these kinds of movements are seen with cells of the lymphatic system.
3. Muscular movement:
It is a more complex movement which is brought about by the musculoskeletal system. This type of movement is seen in the higher vertebrates.
Example: Human beings.
The movements brought about by the musculoskeletal system, comprising of the joints, skeleton and types of muscles.
Some of the movements in body parts of human are:
Movement of eyelids.
Movement of the heart muscles.
Movement of teeth and jaw.
Movement of arms and legs.
Movements of head.
Movements of neck.

1. A streamlined body is one which is pointed at the ends and broad in the middle. When such a body travels through a fluid or gaseous medium it exhibits minimum friction or resistance. A body shape which is streamlined helps cut against the friction created by the medium around the moving body.
2. Streamlined body lowers the friction drag between a fluid, air or water and an object moving trough that fluid. Drag is a force that slows down motion. Streamlining reduces the surface area of the moving object.
3. Streamlining reduces friction of movement to a minimum thus decreasing overall drag. Fishes can save energy while swimming because of the streamlined body.

Muscles found in higher vertebrates, including humans, are classified into three distinct types based on their structure and function. Striated or skeletal muscles, also called voluntary muscles, are under conscious control and are attached to bones by tendons. They appear striped under a microscope due to the organized arrangement of contractile filaments and enable purposeful movements such as walking, running, and lifting. Unstriated or smooth muscles, also called involuntary muscles, lack the striped appearance and are not under conscious control. They are found in the walls of internal organs such as the stomach, intestines, and blood vessels, where they perform automatic functions like digestion and blood circulation. Cardiac muscles are specialized muscles found only in the heart and are also involuntary. They have a striated appearance similar to skeletal muscles but function automatically to pump blood throughout the body continuously. Each muscle type is uniquely adapted to its specific function and location in the body.