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The Skeletal System

Bones (skeleton)

Joints

Cartilage

Ligaments

The Bones The skeleton has 206 bones

Infants have 270 bones

Two basic types of bone tissue

Compact bone

Spongy bone

Functions of the Bones

Support the body

Protect soft organs

Movement due to attached skeletal muscles

Storage of minerals and fats – Ca & P

Blood cell formation -hematopoiesis

Compact vs. Spongy Bone Compact bone –

• Mostly found in shaft (diaphysis) of long bones

• Cylinders of bone growth around a central canal

• Appears organized: dense and rigid

• Provides a strong external layer in all bones

Spongy bone –

• Mostly found in short bones, irregular bones, flat bones and ends (epiphysis) of long bones

• Small needle-like pieces of bone – Trabeculae

• Filled with red marrow; softer hematopoietic tissue

Spongy bone Compact bone

Spongy

bone

Compact

bone

Spongy

bone Compact

bone

Gross Anatomy of a Long Bone Diaphysis

Shaft; Composed of compact bone

Epiphysis

Ends of the bone; Composed mostly of spongy bone

Periosteum

Outside membrane of the diaphysis

Endosteum

Membrane that lines canals of compact bone; covers trabeculae of spongy bone

Sharpey’s fibers

Secure periosteum to underlying bone

Arteries

Supply bone cells with nutrients

Structures of a Long Bone Articular cartilage

Covers the external surface of the epiphyses

Made of hyaline cartilage

Decreases friction at joint

Medullary cavity

Cavity of the shaft

Contains yellow marrow (mostly fat) in adults

Contains red marrow (for blood cell formation) in infants

Microscopic Anatomy of Bone Osteon (Haversian System)

A unit of bone

Central (Haversian) canal

Opening in the center of an osteon

Carries blood vessels and nerves

Perforating (Volkman’s) canal

Carries blood vessels and nerves

Lacunae

Cavities containing bone cells (osteocytes)

Arranged in concentric rings

Lamellae

Rings around the central canal; Sites of lacunae

Canaliculi

Tiny canals that form a transport system

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Bone Formation and Growth In embryos, the skeleton is primarily hyaline cartilage

During development, much of this cartilage is completely replaced by bone by 2 years of age

Cartilage remains in isolated areas

Bridge of the nose

Parts of ribs

Joints

Epiphyseal (growth) Plates aide growth of long bones during childhood

New cartilage is continuously formed

Older cartilage becomes ossified

Cartilage is broken down, then bone replaces cartilage

Bones are remodeled and lengthened until growth stops

Bones change shape somewhat AND grow in width

Long Bone Formation and Growth

Long Bone Formation and Growth Types and Composition of Bone Cells

Osteocytes

Mature bone cells

Osteoblasts

Bone-forming cells

Osteoclasts

Bone-destroying cells

Break down bone matrix for remodeling and release of calcium

Bone remodeling is a process by both osteoblasts and osteoclasts

Organic matrix – soft living tissue made of osteocytes and collagen

• Provides flexibility: tensile strength – resists twisting and stretching

Inorganic material – hard non-living material of mostly calcium salts

• Provides Hardness: compression strength – incredibly durable and strong without being brittle

Bone Fractures Types of bone fractures

Closed (simple) fracture – break that does not penetrate the skin

Open (compound) fracture – broken bone penetrates through the skin

Bone fractures are treated by reduction and immobilization; realignment of the bone

Repair of Bone Fractures 1. Hematoma (blood-filled swelling) is formed

2. Break is splinted by fibrocartilage to form a callus

3. Fibrocartilage callus is replaced by a bony callus of spongy bone

4. Bony callus is remodeled to form a permanent patch

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Classification of Bones on the Basis of Shape

Classification of Bones – Long

Long bones

Typically longer than wide

Have a single shaft with 2 distinct ends

Contain mostly compact bone

• Femur, humerus, all bones in arms and legs

Classification of Bones - Short Short bones

Generally cube-shape; contain mostly spongy bone

Sesamoid bones that form with tendons

Examples: Carpals, tarsals, and knee cap (patella)

Classification of Bones - Flat Flat bones

Thin and flattened

Usually curved

Spongy bone between 2 layers of compact bone

Skull, ribs, sternum, collar bone and shoulder blades Sandwich like

Classification of Bones - Irregular

Irregular bones

Irregular shape

Do not fit into other bone classification categories

Example: Vertebrae and hips

The Axial Skeleton

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Axial Skeleton Skull (8)

Frontal

Parietal (2)

Occipital

Temporal (2)

Sphenoid

Ethmoid

Facial (14)

Nasal (2)

Maxilla (2)

Zygomatic (2)

Mandible

Lacrimal (2)

Nasal Concha (2)

Palatine (2)

Volmer

Skull bones are joined by sutures

Only the mandible is attached by a freely movable joint

Sutures (4)

Coronal

Squamosal

Sagittal

Lambdoidal

Fontanelles (4)

Anterior

Posterior

Sphenoid

Mastoid

Ribs

True (7)

False (3)

Floating Ribs (2)

The Hyoid Bone

The only bone that does not articulate with another bone

Serves as a moveable base for the tongue

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The Fetal Skull and Fontanelles The fetal skull is

large compared to the infants total body length

Fontanelles (soft spots) – fibrous membranes connecting the cranial bones

Allow the brain to grow

Convert to bone within 24 months after birth

The Vertebral Column

Vertebrae separated by intervertebral discs

The spine has a normal curvature

Each vertebrae is given a name according to its location

Structure of a Typical Vertebrae Regional Characteristics –

Cervical Vertebrae

Regional Characteristics –

Lumbar & Thoracic Vertebrae

The Bony Thorax

Forms a cage to protect major organs

Made-up of three parts

Sternum

Ribs

Thoracic vertebrae

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The Appendicular Skeleton Appendicular Skeleton

Pectoral (Shoulder) Girdle

Clavicle

Scapula

Pelvic Girdle

Ilium

Ischium

Pubis

Pubic Symphysis

Lower Limb

Femur

Tibia

Fibula Hand:

• Carpals (8)

Scaphoid

Trapezium

Trapezoid

Lunate

Triquetral

Pisiform

Capitate

Hamate

Metacarpals

Phalanges

Upper Limb

Humerous

Ulna

Radius

Foot:

Tarsals (7)

Calcaneous

Cuboid

Talus

Navicular

First (medial) cuneiform

Second (intermediate) cuneiform

Third (lateral) cuneiform

Metatarsals

Phalanges

Bones of the Shoulder Girdle Bones of the Shoulder Girdle

Bones of the Upper Limb Bones of the Pelvis

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Sacrum & Coccyx

• 4-5 fused segments • Median sacral crest • Posterior sacral foramina • Posterior wall of pelvic cavity • Sacral promontory aka base • Area toward coccyx is the apex

Gender Differences of the Pelvis

Females • all about bearing

children • false pelvis (hips)

wider to support weight in pregnancy

• pelvic brim larger • pubic arch wider • sacrum coccyx less

curved • pelvic outlet larger

Males • all about bearing

weight

Bones of the Lower Limb Bones of the Hand

The Aging Hand

Newborn 1 Year 13 Years 18 Years

• Note the bones missing at birth • Observe the spaces between the bones on the 1 year old – this is the space

where the growth plate is found • An ossification center (epiphysis) is visible on the 13 year old at the ends of the

bone. These are cartilage plates that will turn to bone • By 18 years old the ossification centers will fuse with the bone, leaving only the

epiphysial line

Bones of the Foot

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Arches of the Foot

Bones of the foot are arranged to form three strong arches

Two longitudinal

One transverse

Common Bony Landmarks • Condyle - round, smooth knob that allows joint movement • Crest - narrow ridge of bone • Epicondyle - projection found superior to a condyle • Fissure – small slit through a bone • Foramen - unusually large, naturally occurring hole

completely through a bone • Fossa - shallow, elongated depression in a bone • Line - thin, elongated and often slightly raised ridge of bone • Meatus - naturally occurring canal within the bone • Notch – indentation at the end of a bone • Process - any bony prominence, projection or prolongation • Sinus - cavity found within the bone • Sulcus - specialized groove for a nerve, tendon, vessel • Trochanter - large process found on superior end of femur • Tubercle - small, rounded projection from the bone • Tuberosity - rough projection of bone from the skeleton

Joints Hold bones together; Allow for mobility

Functional Classification:

Synarthroses – immovable joints

Amphiarthroses – slightly moveable joints

Diarthroses – freely moveable joints

Structural Classification:

Fibrous joints - Generally immovable (i.e. sutures)

Cartilaginous joints - Immovable or slightly moveable (i.e. pubic symphysis, intervertebral joints)

Synovial joints –

Freely moveable; Ligaments reinforce the joint

Articular cartilage (hyaline cartilage) covers the ends of bones

Joint surfaces are enclosed by a fibrous articular capsule

Have a joint cavity filled with synovial fluid

Fibrous Joints Cartilaginous Joints

Synovial Joints

The Synovial Joint

Bursae – flattened fibrous sacs

Lined with synovial membranes

Filled with synovial fluid

Not actually part of the joint

Tendon sheath

Elongated bursa that wraps around a tendon

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Movements by Synovial Joints

Movements by Synovial Joints WHAT

CAUSES … ?

What Causes Bone Imbalances? Rickets

In children, bones fail to calcify and are too weak to bear weight – bow and buckle from the child’s weight

Lack of calcium or vitamin D in diet

Osteoporosis

Bone reabsorption outpaces bone deposit – more “clast” than “blast”

Bone mass is reduced and becomes more porous

Leads to deformities and fractures

Spine and femur especially vulnerable

Possible Causes

Estrogen levels decrease after menopause; dietary deficiencies; malabsorption; genetic propensity

Paget’s Disease

Excessive reabsorption and formation

Initially- too much spongy bone - soft, weak bones

Later in the disease- osteoclasts weaken (not enough breaking down), but osteoblasts keep going (too much formation)

Irregular thickenings, and eventually cavities fill in with Pagetic bone

Unknown Cause - possible latent virus?

Scoliosis

A musculoskeletal sideways curvature of the spine, or backbone.

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What Causes Joint Conditions? • Bursitis – inflammation of a bursa usually caused by a

blow or friction

Tendonitis – inflammation of tendon sheaths

Arthritis – inflammatory/degenerative diseases of joints

The most widespread crippling disease in the United States; Over 100 different types

Osteoarthritis

Most common chronic arthritis; normal aging processes

Rheumatoid arthritis

Autoimmune disease – immune system attacks the joints

Symptoms begin with bilateral inflammation of joints

Often leads to deformities

What Causes Lifespan & Disc Problems?

Examples of Lifespan Changes

•Decrease in height beginning at about age 30 • Calcium levels fall • Bones become brittle • Osteoclasts outnumber osteoblasts • Spongy bone weakens before compact bone • Bone loss rapid in menopausal women • Hip fractures common • Vertebral compression fractures common

What Causes the Noise When You Crack A Joint?

• Escaping gases Scientists explain that synovial fluid present in your joints acts as a lubricant. The fluid contains the gases oxygen, nitrogen, and carbon dioxide. When you pop or crack a joint, you stretch the joint capsule. Gas is rapidly released, which forms bubbles. In order to crack the same knuckle again, you have to wait until the gases return to the synovial fluid.

• Movement of joints, tendons and ligaments When a joint moves, the tendon’s position changes and moves slightly out of place. You may hear a snapping sound as the tendon returns to its original position. In addition, your ligaments may tighten as you move your joints. This commonly occurs in your knee or ankle, and can make a cracking sound.

• Rough surfaces Arthritic joints make sounds caused by the loss of smooth cartilage and the roughness of the joint surface.

If you feel pain when joints pop, seek a health care professional. Some studies show that knuckle cracking does not cause serious harm. Other

studies show that repetitive knuckle cracking can do damage to the soft tissue of the joint. It may also lead to a weak grip and a swelling hand.

• True bow legged-ness comes from malformed femurs and tibias that arc laterally. It is normal for babies to have bowed legs before the bones ossify and are still cartiligenous, because of internal tibial torsion (inward twist of the tibia caused by intrauterine positioning.) Eventually, the knees knock a bit and then straighten out, remaining slightly knock kneed in normal knees with the femurs tilting inwards/medially.

• Healthy people with bowed legs get it from activities that demand the bones to grow outwardly like horse-riding/jockey, or because of weak adductor muscles. Often times, people who press back in their knees while standing in their youth develop imbalances that can cause a bit of bowing of the bone.

What Causes Bowleggedness and Knock Knees?

What Causes Double-Jointedness?

• People with more than normal flexibility of their joints are considered to have hypermobility — which simply means their joints (and surrounding structures, including ligaments and tendons) are able to bend farther than "normal," or, more accurately, farther than average. In most cases, the reason for the extra mobility is not known.

• Most people with hypermobility are otherwise normal and healthy. It's also possible that they have an as-yet-undiscovered gene mutation, especially when others in the family have hypermobility as well. They may be able to bend forward and touch their palms on the floor, extend their elbows well past straight, or bend their fingers back toward the back of the hand farther than would be comfortable for others.

What Causes Pigeon Toe (metatarsus adductus)?

• In children under 2 years the most common cause is a shin bone that is twisted. Even with the twisted shin bone, the knees point straight ahead. It may result from the baby's position in the mother's womb before being born. This problem usually gets better as the baby starts pulling up to stand and walk. It may take another 6 to 12 months.

• The most common cause of pigeon toes in girls over 2 years old is a hip that turns in causing the thigh bone to twist. When the thigh bone twists, the knees and toes point in. This condition usually clears up by itself, but it may take 1 to 3 years for the thigh bone to straighten.

• When the front part of the foot turns in, it can also cause pigeon toes. Some children may need to wear special shoes. If the foot is rigid and cannot be straightened, it may be necessary to put casts on the feet and lower legs. Most children outgrow pigeon-toes and do not need treatment.