Skeletal System

Bones are classified according to shape◦ Long bones◦ Short bones◦ Flat bones◦ Irregular bones◦ Sesamoid bones (round)

Bone Classification

Long bones – longer than they are wide. They consist of a long shaft with two bulky ends.

Examples: Thigh, leg, arm, and forearm bones.

The walls of the shaft of a long bone are made of compact bone and the ends (epiphyses) are made of spongy bone.

Long Bones

Long bones Diaphysis – shaft of long

bone. Medullary cavity – hollow

space – A thin layer of cells called the endosteum lines the cavity, and marrow fills it.

Epiphysis – At the end of the diaphysis.

End of the epiphysis is covered by cartilage which allows smooth movement against other bones.

Epiphyseal plate – in growing bones – it is a plate of hyaline cartilage between the epiphysis and diaphysis. This is where growth takes place.

It is gradually replaced by bone tissue. Growth stops when the bone has completely taken the place of cartilage.

Periosteum – a tough, fibrous connective tissue that covers long bones.

Periosteum has many nerves, blood vessels and osteoblasts (cells that create new bone)

Nutrient foramina are small openings through which blood vessels enter into the bone.

Roughly cube-shaped Primarily made of spongy bone, covered by

a thin layer of compact bone. Bones of the wrist and ankle

Short bones

Thin, flattened, and often curved. Usually arranged like a sandwich. They

have a middle layer of spongy bone, covered on each side by a later of compact bone.

Examples: bones of the skull

Flat bones

Don’t fit in any of the other categories. Primarily spongy bone, covered with a thin

layer of compact bone. Examples: vertebrae and some skull bones.

Irregular bones

Sesamoid Bones Small and nodular

bones. Usually embedded

within a tendon adjacent to a joint

Example: patella and sesamoid bones of foot

General structure

General bone structure

Structure of bone 2 types of bone

a) compactb) spongy (cancellous)

These 2 types differ in how tightly tissue is packed together.

Compact and Spongy bone

Compact bone Spongy bone

Bone cells are called osteocytes The Haversian system – consists of a central

canal surrounded by lamellae (rings) of matrix. Between the rings the osteocytes are located in spaces called lacunae.

Small channels called canaliculi radiate from the lacunae to the Haversian canal and connect the osteocytes.

This cylindrical shaped unit is called an osteon.

Compact bone

Cross section of compact bone

Spongy Bone Composed of

osteocytes and extracellular matrix. Bone cells here do not surround a central canal.

Cells lie within the trabeculae (bony spaces) and get nutrients through diffusion

Osteogenesis/ossification – either term is used to indicate the process of bone formation.

Parts of the skeleton form in the first few weeks after conception. Bone development continues throughout adulthood.

Bone development may continue for repair of fractures or to remodel bone to meet changing lifestyles.

Bone development and growth

Osteoblasts – bone forming cells

Osteocytes – mature bone cells

Osteoclasts – break down and reabsorb bone.

Cells involved in bone development

The replacement of sheet-like connective tissue membranes with bony tissue.

Bones formed in this way are called intramembranous bones.

Examples: Flat bones of the skull, and some irregular bones.

Intramembranous Ossification

Endochondral ossification – replacement of hyaline cartilage with bony tissues.

Most bones of the skeleton formed this way.

Bones called endochondral bones.

Endochondral ossification

Long bones continue to grow (lengthen) while the cartilaginous cells of the epiphyseal plates are active.

Once the ossification centers meet and the epiphyseal plates ossify – no further growth occurs.

An injury to an epiphyseal plate may cause uneven growth. For this reason injuries to the epiphysis are treated very carefully.

Growth

Throughout life, osteoclasts resorb bone matrix, and osteoblasts replace it.

Hormones that regulate bone calcium control these opposing processes.

So in an adult, total bone mass stays about the same throughout life.

Vitamin D, calcium, and physical exercise are necessary for bone development, growth, and repair.

Homeostasis of bone

Support – a rigid framework Protection – of the soft body parts. Movement – Sites for muscle attachment. Bones

and muscles work as a lever system. Storage – Intercellular matrix of bone contains

calcium salts. Bone also contains sodium, magnesium, potassium, and stores fat.

Blood cell formation – takes place mostly in bone marrow. This process is called hematopoiesis. Red marrow helps form RBCs, WBCs, & platelets.

Yellow marrow stores fat.

Functions of the Skeletal System

Skeleton 206 named bones Other bones:

◦ Wormian bones – small bones in the joints between certain cranial bones.

◦ Sesamoid bones – small bones that grow in certain tendons.

Axial skeleton – 80 bones◦ Head, vertebral column,

ribs, sternum, and hyoid

Appendicular skeleton – 126 bonesUpper and lower limbs, and their attachments

Axial Skeleton

Axial Skeleton

Anterior skull

Skull – 28 bones Bones in the skull

are tightly interlocked along irregular lines called sutures.

Some skull bones contains sinuses – air filled cavities lined with mucous membranes.

Numerous openings or foramina to allow blood vessels and nerves to enter.

Lateral view of skull

Cranium – 8 bones interlocked to enclose the brain.◦ Frontal◦ Parietal bones (2)◦ Occipital bone◦ Temporal bones (2)◦ Sphenoid◦ Ethmoid

Skull Frontal bone

◦ Anterior portion of the skull above the eyes, part of the nose, and the upper eye socket

◦ Supraorbital foramen or notch – blood vessels and nerves pass to forehead.

◦ Frontal sinuses – above the eyes – cavity.

Skull Parietal bones – 2 of

them. Joined to each other in

the midline by the sagittal suture and to the frontal bone by the coronal suture

Skull Occipital bone

◦ Most of the dorsal part of the skull.

◦ Lambdoid suture joined to the parietal bones.

◦ Foramen magnum is the large opening on the lower surface of the occipital bone- spinal cord passes through foramen magnum

Foramen magnum in the occipital bone

Skull Temporal bones – the

sides and base of the cranium◦ External auditory meatus

– opening to the middle ear.

◦ Mastoid process – a knob that contains air cells

◦ Styloid process◦ Zygomatic process

Skull Sphenoid – crosses

the cranial floor Forms the sides of the

skull and base of the cranium

The pituitary gland sits in the sella turcica, a part of the sphenoid bone.

Skull Ethmoid bone – forms

most of the bony area between the nasal cavity and orbits.

Newborn skull Skull of newborns not

completely joined together.

There are areas called fontanels or soft spots.

14 bones 13 are interlocked 1 movable mandible – the lower jawbone

◦ Maxillary◦ Palatine◦ Nasal◦ Lacrimal◦ Zygomatic◦ Inferior Nasal conchae◦ Vomer◦ Mandible

Axial Skeleton – Facial bones

Maxillary bones form the upper jaw.

Hard palate – roof of the mouth is the palatine process

Has a large maxillary sinus

Palatine bones

Behind the maxillae

Bones are roughly L shaped

Form the hard palate and side walls of the nasal cavity.

Palatine bones

Facial bones Nasal bones Small rectangular

bones that form the bridge of the nose.

Lacrimal bones Located in the medial

wall of the orbits. Each one has a

lacrimal groove – the pathway for a tube that carries tears from the eyes to the nasal cavity.

Zygomatic bones Form the prominences

of the cheeks (cheekbones)

Temporal processes form the zygomatic arch.

Nasal conchae Thin curved bones

attached to the lateral walls of the nasal cavity.

Vomer The inferior part of the

midline in the nasal cavity.

Part of it forms the nasal septum.

Mandible The lower jaw Horseshoe shaped

body that forms the chin.

The ramus projects upward at each end.

Forms the temporomandibular joint.

Auditory ossicles 3 tiny bones Malleus – hammer Incus – anvil Stapes – stirrup

Transmit sound from the eardrum to the inner ear.

Hyoid bone

Base for the tongue

Not part of the skull U shaped bone in the

neck. It is unique because it

is the ONLY bone in the body that does not articulate with another bone.

Anchored by ligaments to the temporal bone.

Part of the axial skeleton

Vertebral Column

Extends from skull to pelvis. Contains 26 bones called vertebrae. Separated by pads of fibrocartilage called

intervertebral disks. Disks act as shock absorbers Four curvatures that increase strength and

resilience of the column.◦ Thoracic curvature◦ Sacral curvature◦ Cervical curvature◦ Lumbar curvature

Vertebral column

General vertebra anatomy All vertebrae have

common structure Foramen – opening for

the spinal cord Spinous process –

what protrudes near the skin of the back

7 cervical vertebrae – designated C1 through C7.

Have transverse foramina in the transverse processes.

Spinous processes are forked. Atlas – another name for C1 Axis – another name for C2 Atlas and axis pivot to rotate the neck.

Cervical vertebrae

Thoracic vertebrae 12 thoracic vertebrae,

designated T1-T12. They have facets to

articulate with the ribs.

Long pointed spinous processes.

Lumbar vertebrae 5 lumbar vertebrae,

designated L1-L5 Large heavy bodies to

support body weight. Many back muscles

attached.

Sacrum and coccyx Sacrum – triangle

shaped bone below lumbar vertebrae.

Coccyx – tailbone. Some muscles attach to coccyx.

Protects the heart, lungs and large vessels.

Supports the bones of the shoulder

Thoracic vertebrae, ribs, and sternum

Thoracic cage

Sternum Also called the

breastbone 3 parts

◦ Manubrium – upper triangle part

◦ Body – middle slender part

◦ Xiphoid process – very small end.

Ribs 12 pairs- each attached

to thoracic vertebra Upper 7 pairs are true

ribs – they attach to sternum

Lower 5 pairs – false ribs – cartilage does not reach sternum.

Of the lower 5 pairs, the last 2 pairs are called “floating”

Appendicular Skeleton

126 bones

This part of the skeleton is designed for movement.

The two girdles (pelvic and pectoral) are attached to the abdomen.

Appendicular Skeleton

Pectoral Girdle

Pectoral Girdle

Scapula

Each half consists of 2 bones:◦ The clavicle (collar bone)◦ Scapula (shoulder blade)

◦ Scapula has numerous muscles that attach.

◦ The acromion process articulates with the clavicle

Pectoral Girdle

Broken Clavicle

Upper Extremity (arm, forearm, and hand) Humerus – single long

bone of the upper arm.

Head of the humerus fits into the scapula.

The tuberosities and epicondyles are places where muscles attach.

The olecranon fossa – where the ulna fits to form the elbow.

Humeral cross sections

Forearm 2 bones radius and

ulna When the forearm

rotates, the radius crosses over the ulna

Radius has a disc-like head which articulates with the humerus.

Ulnar head articulates with the wrist.

Wrist and Hand

Wrist and hand 8 bones in the wrist –

tightly bound by ligaments – called carpals.

5 metacarpals in the hand (numbered 1-5 starting at the thumb)

Phalanges – 14 bones of the fingers. 3 bones in each finger, 2 in each thumb

Attaches the lower extremities to the axial skeleton.

Provides support for the weight of the body. Consists of 2 coxal bones (hip bones) In childhood, each coxal bone has 3

separate parts – ilium, ischium, and pubis. In an adult, these are fused to form a single

bone. The acetabulum on each side is a

depression where the femur articulates

Pelvic Girdle

Pelvic Girdle Acetabulum – where

the femur articulates with the pelvis.

Greater sciatic notch is where the sciatic nerve passes through and down the leg.

True pelvis

True pelvis

This is the important passage in childbirth.

This large opening is called the pelvic outlet.

Lower extremity Bones of the thigh,

lower leg, ankle, and foot.

Support entire weight of the body when we are upright.

Bones are larger and stronger than upper extremity.

Thigh One single long bone –

the femur. Largest, longest, and

strongest bone in body.

Top of the femur is called the femoral head.

Muscles attach at the trochanters.

Lower leg Tibia is the weight-

bearing bone. Tibia articulates with

the femur to form the knee joint.

Lateral and medial malleoli form the ankle joint (these are the bumps you feel on your ankle)

Lower leg Anterior crest of the

tibia is what forms your shinbone.

Head of the fibula is at the proximal portion of the bone.

Foot Foot is composed of

the ankle, instep and 5 toes.

There are 7 tarsal bones in the ankle. The largest one is the heel or calcaneus.

The 5 metatarsals make up the instep.

Foot Phalanges – the 14 toe

bones. Three phalanges in

each toe except the big toe where there are only 2.

Patella The patella is

enclosed within the patellar tendon.

It provides a smooth surface for the tendon.

It protects the knee joint from the front

Another name for joint – where 2 bones come together.

3 types◦ Fibrous◦ Cartilaginous◦ Synovial

Articulations

Articulations Immovable joints are

called fibrous joints. The bones are in very

close contact, separated only by a thin layer of fibrous connective tissue.

Sutures of the skull are an example

Cartilaginous Bones are connected

by hyaline or fibrocartiliage.

Examples: ribs and sternum.

These types separate the vertebrae

Symphysis pubis

Synovial joints Most joints in the

body. Freely movable Ends of opposing

bones are covered with hyaline cartilage and are separated by a space called the joint cavity.

Synovial joints The joint capsule

encloses the bones. The inner layer of this

capsule is the synovial membrane.

Some synovial joints have pads of fibrocartilage called menisci.

These joints may also have fluid-filled sacs called bursae.

Are classified by the types of movement they allow◦ Ball and socket – oval or round head that articulates within

a cup-shaped cavity. Examples: hip, shoulder◦ Ellipsoidal – oval shaped condyle fits into elliptical shaped

cavity – Examples: btw. Metacarpals and phalanges◦ Gliding joints – nearly flat. Examples: joints within the

wrist and ankle◦ Hinge – Movement in 1 plane only: Examples: elbow,

knee◦ Pivot – rotation – Example: joint btw first vertebra and

skull◦ Saddle: Both concave and convex. Example: joint

between carpal and metacarpal bones of thumb

Synovial joints

Skeletal System Diseases

Trauma Metabolic Endocrine Infections Inflammatory Nutritional Malignant tumors (cancer)

Categories of skeletal system diseases

Fractures

Dislocations and subluxations

Sprains and strains

Severe injuries (amputations, etc)

Trauma

A fracture is any break in the continuity of bone.

Most commonly caused by trauma. BUT, aging and metabolic disease may

weaken bones so that they break easily. Children’s bones tend to heal more quickly

than adults.

Fractures

Typical fractures

Greenstick fracture Spiral fracture

Comminuted fracture Transverse fracture

Compound fracture

Closed reduction – moving fractured pieces back into place by physical manipulation.

Open reduction – Using surgical techniques to move fractured pieces into place. This may include the use of hardware either internally (internal fixation) or externally (external fixation)

Fracture treatment and healing

Internal fixation External fixation

Bone healing is a slow process. Tissue is usually destroyed during the injury, and bone cells reproduce slowly.

The first stage of fracture healing is the formation of a fracture hematoma (a blood clot at the fracture site). This plugs the gap between the broken ends of bones)

Fracture healing

Second step in healing – capillaries grow into the hematoma. Phagocytic cells come to the area to clean up dead tissue. This process may take several weeks.

This organization is called a procallus.

Third step – fibrocartilage tissue forms at the site of the fracture. This also lasts about 3 weeks.

Fracture healing

Bony callus forms next – it is usually made of spongy bone. This callus lasts for 3-4 months before the bones remodel.

Remodeling is the final step in repair. Osteoblasts lay down new compact bone and osteoclasts reabsorb spongy bone.

Once healing is complete, full bone strength is restored.

Fracture healing

Dislocations and subluxations

Finger dislocation

A subluxation is a partial dislocation

Dislocations – 1 bone has slipped out of joint.

Dislocations

Sprains

Normal ankle anatomy Ankle sprain

Metabolic

gout

Gout is a disease caused by accumulation of uric acid crystals within the joint.

The most commonly affected joint is the great toe.

Treated with medications and diet change.

Endocrine - osteoporosis Osteoporosis is a

result of calcium loss from bones.

It occurs in both men and women, but usually starts earlier and is more severe in women.

Estrogen decrease plays a role.

Infections

Left x ray is normal Right x-ray is infected tibia

Osteomyelitis – is the clinical term for an infection in the bone itself.

This can be very severe and result in loss of a limb.

Osteomyelitis in a 9 yr old

Inflammatory Diseases

Achilles tendinitis

Includes◦ Tendinitis◦ Bursitis◦ Arthritis (either

Rheumatoid or Osteoarthritis)

Bursitis

Normal olecranon bursa

A bursa is a fluid filled sac that acts as a cushion.

It usually is located between tendons and ligaments.

Olecranon bursitis

Arthritis There are 2 types of

arthritis: Osteoarthritis – the

wearing out of joint cartilage due to aging and or overuse

Rheumatoid arthritis – the inflammation of joints due to an autoimmune response.

Osteoarthritis

Rheumatoid Arthritis

Nutritional Rickets is a deficiency

in vitamin D. Not common in the US

at this time. More common in third

world countries. Causes the bones to

bow – legs will not be able to support weight.

The most common type of primary bone tumor is osteosarcoma.

It can be a disease of any age. Other tumors (lung, breast, or other

cancers) may metastasize (spread) to the bone as well.

Symptoms may not be present until the bone breaks.

Malignant tumors (cancer)

Osteosarcoma Malignant hand tumor