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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.
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