Chapter 20

Bones and Muscles

The Skeletal System

The skeletal system consists of two broad divisions:

1. The axial skeleton

2. The appendicular skeleton

Axial Skeleton

The eighty bones that make up the head and spine:

Bones of the skullHyroid – bone of neckVertebrae – bones of

neck and backboneSternum – breastboneRibs

Appendicular Skeleton

Bones on the appendages (arms and legs)

Bones of the hips and shoulders.

Bones of the Head

The skull is divided into two parts:

1. Cranium

2. Facial bones

Cranial Bones

The cranium is made of eight bones tightly formed:

Frontal bone (forehead)

Parietal bone (top of head)

Temporal Bone (sides of head)

Occipital Bone (back of head)

Facial Bones

Includes 14 Bones:

Serve as the framework of the face and jaw

Two maxillary bones – serve as attachment for upper teeth

Palatine bones – form the roof of the mouth

Mandible – ONLY MOVABLE bone of skull

Facial Bones

The smallest bones of your body are found in your ears…

The Malleus (hammer)

The Stapes (stirrup)

The Incus (anvil)

Bones of the Spine

Regions of the vertebral column:

1. Cervical vertebrae (top 7)2. Thoracic vertebrae (next 12)3. Lumbar vertebrae (next 5)4. Sacral vertebrae

a) (next 5, fused in adults - sacrum)b) (last 4, fused in adults – coccyx)

Bones of the Chest

Thoracic Cage:

includes ribs and sternum

Classification of Bones

Bones are classified into four categories:

1. Long bones

2. Short bones

3. Flat bones

4. Irregular bones

Design of the Bone

A long bone (like a femur) has a shaft known as the diaphysis and bulged ends known as epiphysis.

The bone is enclosed in a protective sheath called periosteum (has blood vessels in it).

Engineered for Strength

• Outer shell is strong and dense –compact bone

• Inside is lightweight, porous tissue – spongy bone

it looks “spongy”, but it is hard• Inside the porous spongy bone is the red

marrow (produces blood cells)• Inside the center is the medullary cavity – has

red marrow in young children and yellow marrow in adults.

Maintenance and Restoration

• Bones are self repairing, self maintaining, self modifying.

• Two types of cells maintain the bones:

1. osteoclasts – remove old material to make room for new in the Haversian canals

2. osteoblasts – construct new fibers and crystals

Muscles

There are two major types of muscles:

1. Voluntary Muscle You have

control of these muscles.

2. Involuntary MuscleYou do not have

conscience control of these muscles.

Skeletal Muscle

• You have voluntary control over skeletal muscle

• The primary function of these over 600 muscles is to move the skeleton.

• These muscles are made up of individual cells known as muscle fibers.

• Each skeletal muscle is composed of thousands of these muscle fibers.

Skeletal Muscle

• These muscle fibers give skeletal muscle a striped, or striated appearance….

• Because of this, skeletal muscle is also called striated muscle.

• Most skeletal muscle is attached to bone with tendons.

Skeletal Muscle

• Muscle on the face is attached directly to the bone.

• Skeletal muscle is designed to move quickly and powerfully.

Smooth/Visceral Muscle

• Smooth muscle consist of shorter, wider cells in a looser arrangement.

• Smooth muscle is specialized for relatively slow, powerful, and prolonged contractions.

• It adjusts the tension in the walls of blood vessels.

• It controls the organs of the digestive system.

• It controls the lens of your eye.

Cardiac Muscle

• Cardiac muscle is found only in the heart.

• It is designed to contract over and over without tiring.

The Design of Skeletal Muscle

Fiber bundles and connective tissue:

The skeletal muscle is encased in a tough, translucent sheath called the fascia. It functions to bind the muscle together.

At the end the fascia tapers into strong tendons that hold the muscle to bone.

The Design of Skeletal Muscle

• The muscle cells are called muscle fibers.

Structure of Muscle Cells

• A muscle cell is just like other cells with a cell membrane.

• However, they have more than one nuclei and more than the usual number of mitochondria.

• Myofibrils extend the length of the muscle cells.

• A single muscle cell has dozens or hundreds of myofibrils.

Structure of Muscle Cells

• Each myofibril is composed of millions of overlapping protein fibers arranged in repeating units called sarcomeres.

• The sarcomeres give the skeletal muscle their striated appearance.

• They are composed of thick Myosin filaments and thin actin filaments.

Structure of Muscle Cells

• When the muscle contracts, the myosin and actin work to shorten the cell.

• Each myofibril is surrounded by an extensive network of pipes and reservoirs called sarcoplasmic reticulum.

Structure of Muscle Cells

• Addition pipes called transverse tubules connect the sarcoplasmic reticulum to the cell membrane.

• Both of these trigger the myofibril to contract.

Nerve Impulse Reception

• Muscle contractions are triggered by your nervous system.

• The point at which the nerve attaches to a muscle cell is called neuromuscular junction.

The End