Key words

• Flexor• Extensor• Smooth muscle• Skeletal muscle• Cardiac muscle

Chapter 20 Support and Movement

Formation of Bones• As a developing baby,

your skeleton was made mostly of cartilage.– During the 2nd and 3rd

months of development bones begin to form.

– Bone cells replace cartilage and calcium compounds were deposited

Formation of Bones cont.• Growth in height from infancy to adulthood takes

place because new bone tissue was produced in the round ends of your bones.– Bone growth continues until the cartilage is replaced

by bone.– The replacement of cartilage into bone is a long

process that will not be completed until you are about 20 years old.

Skeletal problems• Have you ever fractured a

bone?• A fracture is a break in a

bone, which may be partial or complete.

• Some skeletal problems arise from injury while others can arise from birth, disease, or unknown sources.– Ex: Arthritis, scoliosis,

osteoporosis

The Muscular System• Your body contains more than 600 muscles.

Types of Muscles

• Skeletal muscles (voluntary muscles)• Smooth muscles (involuntary muscles)• Cardiac muscles

Skeletal muscles (voluntary muscles)• This type of muscle is attached to bones, and

make movement possible.• You can make skeletal muscles move whenever

you want, therefore they can also be called voluntary muscles.

• Skeletal muscles are attached to bones by tendons, which are tough elastic bands of tissue.

Smooth muscles (involuntary muscles)

• This type of muscle is found in the walls of blood vessels, the stomach, and other organs.

• Involuntary muscles are muscles that you can not control.

Cardiac muscles• This type of muscle makes up the heart.• It pumps blood through the heart and the rest

of the body.• Is the cardiac muscle voluntary or involuntary

muscle? How do you know?

Muscle actions• Muscle cells can change their length.– When a muscle does its job, the cells in the muscle

contract, or shorten.– When a skeletal muscle contracts, the muscle pulls on

the bone to which it is attached causing that body part to move.

– Skeletal muscles always work in pairs.• Ex: biceps and triceps

Muscle actions cont.

• A muscle that bends a joint is called a flexor.• A muscle that straightens a joint is called an

extensor.

Muscle problems• Have you ever had a muscle cramp?• Do your muscles get sore after you exercise?• Cramps occur when muscles spasm by

contracting suddenly and strongly.• Sore muscles are caused by overuse or small

tears in muscle.• A muscle strain is caused by a large tear that

requires rest and time to heal.• What are some other muscle problems?

Skin• Skin is the largest organ

of the human body.• Dead skin cells form

much of the outer layer of skin, which is called the epidermis.

• The main function for skin is to support and protect the body.

Careers in Biology

• X-Ray Technician• Physical Therapist• Chiropractor

X-Ray Technician• They make x-ray films of parts of the human

body for in use of diagnosing medical problems. They work in hospitals, clinics, medical laboratories, nursing homes, and in private practice.

Physical Therapist• They plan and treat people who have suffered

disabling accidents or who have permanent physical disabilities. They work in hospitals, doctors’ offices, and rehabilitation centers.

Chiropractor• They treat based on the principle that a

person’s health is determined largely by the nervous system.