Skeletal System

D.R. Scarbrough

Five Functions• Supports the body

– Framework for body

– Without it, the body

would collapse

• Protects internal organs

– Skull protects brain

– Ribs protect heart and lungs

• Provides for movement

– Act as a system of levers for

muscles to produce movement

Five Functions (cont’d)

• Store minerals [matrix storehouse] and fat [internal cavities]– Crystalline salts deposited in the matrix of

bone – mainly calcium and phosphate [combined to form hydroxyapatite crystals]

– Matrix is composed primarily of collagen fibers and calcium salts

Five Functions (cont’d)• Make blood cells [hematopoiesis]

– 3.7X1011 blood cells per day– Prenatally, hematopoiesis occurs in the yolk

sack, then liver, and eventually the bone marrow.

– In normal adults, it occurs in marrow and lymphatic tissues.

Bone Marrow and Hematopoiesis

Structures

• Periosteum—tough layer of connective tissue; carries O2 and nutrients to bone– Periosteum is attached to bone by

strong collagenous fibers [Sharpey’s fibers]

– http://kidshealth.org/misc/movie/bodybasics/bone.html

Structures

Compact Bone--surrounds the

shaft [diaphysis] and the ends [epiphysis]

– --dense, thick layer containing Haversian canals

StructuresSpongy [Cancellous]

Bone

* located at the ends beyond epiphyseal plate

* less dense

* latticework structure adds strength but not mass

StructuresBone Marrow—soft tissue in center

Yellow Marrow —primarily storage of fat cells; can convert to redRed Marrow —produces blood cells—WBCs, RBCs, and platelets

Structures• Endosteum – medullary cavity (marrow);

contains osteoblasts and osteoclasts

• Diaphysis – shaft contains medullary cavity

• Epiphysis – ends of the bone (spongy)

• Epiphyseal line – epiphyseal (growth) plate remnant

• Articular (hyaline) cartilage – at long bone junctions

Structures

• http://www.innerbody.com/image_skel09/skel01.html

Bone Cells

• Osteocytes—mature bone cells

• Osteoclasts—break down bone

• Osteoblasts—produce bone

Bone markings are:

• Sites of muscle attachment – Tendon attaches to bone

• Sites of ligament attachment– Bone to bone connection

• Conduits [routes] for blood vessels and nerve

Microscopic Structure of Bone

• Compact bone– Haversian systems

• Osteon – structural unit

• Spongy bone– Composed of trabeculae (“little beams”)– No osteons present

Compact Bone and Spongy Bone

Classification of Bones

• Shape

– Long: longer than they are wide; shaft with heads at each end; mostly compact bone

• Limbs, except wrist and ankle bones

– Short: cube-shaped; mostly spongy bones

• Wrist and ankle

• Sesamoid bones [form within tendons]

–Patella [knee cap]

Classification of Bones

– Flat: thin, flattened, usually curved• Two thin layers of compact bone sandwiched

around spongy bone layer

– Irregular: misfits category• Vertebrae [spinal column]• Hip bones

Two Divisions of the Human Skeleton

• THE AXIAL SKELETON - CONSIST OF THE SKULL, VERTEBRAL COLUMN, AND THE RIB CAGE.

• THE APPENDICULAR SKELETON - CONSIST OF THE BONES OF THE ARMS AND LEGS, SHOULDER, AND THE PELVIC GIRDLE.

Axial Skeleton:Green

AppendicularSkeleton:Purple

Human Skeleton

Bones to Know

• Cranium• Clavicle• Scapula• Humerus• Ribs• Femur• Coxal bones

– Ilium, ischium, pubis

• Radius• Ulna• Carpals• Metacarpals• Phalanges• Tarsals• Metatarsals

Bones to Know• Calcaneus• Talus• Glenoid cavity• Vomer• Tibia• Fibula• Lacrimals• Palatine bones

• Nasal bones• Zygomatic arch & bone• Maxilla• Mandible• Occipital• Parietal• Temporal• Frontal

Bones to Know

• Orbits – seven bones– Frontal,– Sphenoid– Zygomatic– Maxilla– Palatine– Lacrimal– Ethmoid

• Paranasal sinuses – five bones– Frontal– Ethmoid– Sphenoid– Paired maxillary bones

Bones to Know

• Hyoid bone*• Sternum

– Manubrium– Body– Xiphoid process

* Only bone that does not articulate with any other bone; base for tongue and neck muscle attachments

• Vertebral column– Atlas– Axis– Cervical vertebrae– Thoracic vertebrae– Lumbar vertebrae– Sacrum– Coccyx

Structure of Joints

• Cartilage covers the surfaces of bones where they articulate [come together].

• Joints are surrounded by a joint capsule.

• Ligaments hold bones together in a joint.

• Some joints have bursa, fluid-filled sacs that reduce friction.

Types of Joints• Immovable-example skull

• Slightly movable-adjacent vertebrae

• Freely movable [most]– Ball and socket (movement in many

directions)– Hinge Joints (back and forth movement)– Pivot (rotate around another)– Saddle (one bone slides in two directions)– Gliding (one surface over the other without

rotation)

Plane or Gliding Joints—slide past each other. [midcarpal and midtarsal

joints]

Plane or Gliding Joints

• The articular surfaces are essentially flat

• Only short slipping or gliding movements are allowed

• Nonaxial movements—gliding does not involve rotation around any axis

• Example—intercarpal joints of the wrist

Hinge Joint--allows extension and retraction of an appendage

Hinge Joints

• The cylindrical end of one bone fits into a trough-shaped surface on another--like a mechanical hinge

• Examples—elbow joint, ankle joints, joints between phalanges and fingers

Ball and Socket Joints—allows radial movement in almost any direction. [hips

and shoulders]

Ball and Socket Joints

• The spherical head of one bone fits into a round socket in another

• Multi-axial joints allow movement in all axes, including rotation

• These are the most freely moving synovial joints

• Examples—shoulder joints [head of humerus into scapula]; hip joints

Saddle Joint--allows back and forth and up and down movements, but not

rotation like ball and socket joints.

Saddle Joints

• Each articular surface has both convex and concave areas (saddle-like).

• Biaxial joints allow the same movements as condyloid joints

• Example—carpometarcarpal joints in the thumb—”twiddling the thumbs”

Ellipsoid or Condyloid Joints

• Ellipsoid joints are similar to a ball and socket joint.

• The egg-shaped articular surface of one bone fits into an oval concavity in another.

• They allow the same type of movement to a lesser magnitude.

• The wrist is an ellipsoid or condyloid joint.

Pivot Joints

• Pivot joints allow rotation around an axis.

• The neck and forearms have pivot joints.

• In the neck, the occipital bone spins over the top of the axis.

• In the forearms, the radius and ulna twist around each other.

Formation of bones

• By the end of the eighth week after conception, the skeletal pattern is formed in cartilage

• Then, ossification begins

Ossification

• Bone formation; cartilage is replaced by bone

Ossification

• Formation of bony skeleton– Begins at about 6 weeks– Intramembranous ossificationBone forms from

fibrous tissue – Bone called membrane bone

• Endochondral ossification – Begins in third month of development– Bone called cartilage bone– Most bones form this way

Ossification

Bone Growth

• Growth in width = appositional growth

• Growth in length occurs at the epiphyseal plate [growth plate]

• The growth plate is the area of growing tissue near the end of the long bones in children and adolescents.

• Each long bone has at least two growth plates, one at each end.

Bone Growth

• The growth plate determines the future length and shape of the mature bone.

• When growth is complete - sometime during adolescence - the growth plates close and are replaced by solid bone.

Bone Growth & Injuries

• Growth plate injuries occur in children and adolescents.

• The growth plate is the weakest area of the growing skeleton, weaker than the nearby ligaments and tendons that connect bones to other bones and muscles.

Growth Plate Injury

• In a growing child, a serious injury to a joint is more likely to damage a growth plate than the ligaments that stabilize the joint.

• An injury that would cause a sprain in an adult can be associated with a growth plate injury in a child.

Growth Plate Injuries

• Most injuries to the growth plate are fractures; they make up 15% of all childhood fractures.

• They occur twice as often in boys as in girls, with the greatest incidence among 14- to 16-year-old boys and 11- to 13-year-old girls.

Growth Plate Injuries

• Older girls experience these fractures less often because their bodies mature at an earlier age than boys.

• As a result, their bones finish growing sooner, and their growth plates are replaced by stronger, solid bone.

Growth Plate Injuries

• Approximately half of all growth plate injuries occur in the lower end of the outer bone of the forearm (radius) at the wrist.

• These injuries also occur frequently in the lower bones of the leg (tibia and fibula).

• They can also occur in the upper leg bone (femur) or in the ankle, foot, or hip bone.

Causes of Growth Plate Injuries

• Many growth plate injuries are caused by an acute event such as a fall or a blow to a limb

• Chronic injuries can also result from overuse. – A gymnast who practices for hours on the

uneven bars, a long-distance runner, or a baseball pitcher perfecting a curve ball can all have growth plate injuries.

Growth Plate Injuries

• Research has show that the majority resulted from a fall, usually while running or playing on furniture or playground equipment.

• Competitive sports such as football, basketball, softball, track and field, and gymnastics accounted for one-third of all injuries.

Growth Plate Injuries

• Recreational activities such as biking, sledding, skiing, and skateboarding accounted for one-fifth of all growth plate fractures.

• Car, motorcycle, and all-terrain-vehicle accidents accounted for only a small percentage of fractures involving the growth plate.

Growth Plate Injuries

• Whether acute or due to overuse, a child who has persistent pain that affects athletic performance or the ability to move or put pressure on a limb should be examined by a doctor.

• A child should never be allowed or expected to "work through the pain."

Growth Plate Injuries

• Children who participate in athletic activity often experience some discomfort as they practice new movements.

• A child’s complaints always deserve careful attention to prevent permanent damage which will interfere with proper growth of the involved limb if left untreated.

Growth Plate Injuries

• Accidents during play or athletic activity cause most of these injuries.

• Growth plates are also susceptible to other disorders, such as bone infection, that can alter their normal growth and development.

Additional Causes: Growth Plate Injuries

• Child abuse can be a cause of skeletal injuries, especially in very young children, who still have years of bone growth remaining.

• Half of all fractures due to child abuse were found in children younger than age 1, whereas only 2% of accidental fractures occurred in this age group.

Additional Causes (cont’d)• Injury from extreme cold (frostbite) -

damage the growth plate in children.

• Result--short, stubby fingers or premature degenerative arthritis.

• Radiation, cancer treatment, can damage the growth plate.

• Chemotherapy [cancers] may also negatively affect bone growth, likewise with prolonged use of steroids for rheumatoid arthritis.

Additional Causes

• The growth plates are the site of many inherited disorders that affect the musculoskeletal system.

• Future discoveries regarding the genes and gene mutations involved in skeletal formation, growth, and development will improve treatment of children who are born with poorly formed or improperly functioning growth plates.

X-RAYS & TX

• Epiphyseal plates don’t show up on x-rays

• Gaps indicate the presences of the plates

• Both sides of the body may be x-rayed and the two compared to assess damage.

• Manipulation, strengthening exercises, surgery, immobilization

Number of Bones

• When you were born, you had over 300 bones.

• As you grew, some bones fused together.

• An adult has only 206 bones

Bone Remodeling

• Bone remodeling units

• Osteoblasts and osteoclasts

• Bone deposition – sites of injury or strength [osteoblasts]

• Bone reabsorption [osteoclasts]

• Remodeling control– Hormonal feedback

Types of Fractures• Comminuted – broken into fragments

• Compression - crushed

• Depressed – bone portion pressed inward

• Impacted – bone ends are forced into each other

• Spiral – ragged break occurs w/excessive twisting forces applied

• Greenstick – bone breaks incompletely; more common in children [increased flexibility of bone]

Types of Fractures

Repair of Fractures

• Reductions – setting the bone

[realignment]

• Phases of repair– Hematoma formation [bruise]– Fibrocartilaginous callus formation [splints the

bone] – Bony callus formation – Remodeling [removes excess material –

osteoclasts – and replaces with compact bone

Homeostatic Imbalances of Bone

• Osteomalacia – softening of the bones; inaequate mineralization

• Paget’s disease – excessive bone reabsorption and formation

• Osteoporosis – bone reabsorption outpaces bone deposition

Osteoporosis

• Cause = the loss of calcium, leads to weakening of the bones.

• The elderly and astronauts are at greatest risk.

Human Space Travel• International Space Station crew members were

studied for effects of microgravity on their bones. • On average, they lost roughly 11 percent of their

total hip bone mass over the course of their mission.

• A year after their return, much of their lost bone mass was replaced.

• The bone structure and density had not returned to normal and signs of hip strength had not recovered at one year.

Bone Mass Loss

• It may take longer than a year to replace strength in their bones.

• On average, crewmembers lost as much bone mass in one month in orbit as an elderly woman loses in an entire year.