What muscles and skeleton do?

Answer 1

The human skeleton is an endoskeleton (internal skeleton) made of bone and cartilage.

Major Functions

1. Support for the soft tissues and largely responsible for the shape of the human body.
2. Movement: the strong rigid bones function as levers moved by the contraction of muscles.
   1. The brain is protected by the skull.
   2. The heart and lungs are protected by the rib cage.
   3. The spinal cord is protected by the backbone
3. Protection: the tough bones protect delicate vital organs

Structure

The skeleton is divided into:

1. Axial Skeleton: skull, backbone, ribs and sternum.

2. Appendicular Skeleton: pectoral girdle, pelvic girdle and limbs.

2. Spine or Backbone: Also known as the vertebral column. It is composed of 33 small bones in a line - cervical (7), thoracic (12), lumbar (5), sacrum (5), coccyx (4).

The vertebrae of the sacrum and coccyx are fused together. The vertebrae of the other regions can move slightly giving flexibility to the backbone. There are cartilage discs between these that act as shock absorbers. They help to protect the vertebrae. The vertebrae are held in position by ligaments. Muscles attached to their surfaces also support the vertebrae. Spinal nerves emerge in pairs from the spinal cord between the vertebrae.

Muscles

There are 3 types of muscle: skeletal, smooth, and cardiac.

Skeletal Muscle

Skeletal muscle, as its name implies, is the muscle attached to the skeleton. It is also called striated muscle. The contraction of skeletal muscle is under voluntary control. These muscles are mainly responsible for movement of the body. Other purposes are posture maintenance, support of the joints, and heat production. While its contraction is fast and strong, skeletal muscle tires easily.

Smooth Muscle

Smooth muscle is found in the walls of all the hollow organs of the body (except the heart). Its contraction reduces the size of these structures. Thus it regulates the flow of blood in the arteries, moves your breakfast along through your gastrointestinal tract, expels urine from your urinary bladder, sends babies out into the world from the uterus, and regulates the flow of air through the lungs. The contraction of smooth muscle is not under voluntary control. It is called involuntary muscle. It contracts slowly and is slow to tire.

Cardiac Muscle

Your heart is made of cardiac muscle. This type of muscle only exists in your heart. Unlike other types of muscle, cardiac muscle never gets tired. It works automatically and constantly without ever pausing to rest. Cardiac muscle contracts to squeeze blood out of your heart, and relaxes to fill your heart with blood.

Antagonistic Skeletal Muscles

Antagonistic muscles are pairs of muscles. The action of one member is opposite to that of the other member. Muscles can contract but they do not have the ability to lengthen (stretch) themselves. They are arranged in pairs such that after one muscle or muscle group contracts, a skeleton transfers the movement to stretch another muscle or muscle group. The pairs of muscles that stretch each other are said to be antagonistic.

Example of an antagonistic muscle pairThe biceps and triceps muscles of the arm are an example of an antagonistic pair. Contraction of the biceps moves the arm toward the body and stretches the triceps. Contraction of the triceps extends the arm and stretches the biceps. In this example the bicep is said to be the flexor while the tricep is the extensor. Extensors are not as strong as flexors.

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