The Skeletal System

Fun Facts• A giraffe has the same # of bones in the neck as

humans do• Bones are 14% of your body weight• Bone is 5x as strong as steel• Most women and girls have smaller and lighter

skeletons than men and boys• The female pelvis is wider than males• Male’s growth plates harden at 18-21 years of

age• Female’s growth plates harden at 16-18 years of

age

How many bones does an adult body have?

206How many bones are babies born with?

350

Largest bone?

Femur: thigh bone

Shortest Bone?

Stirrup: located in the ear

Functions of the Skeletal system

1. Support

2. Protection

3. Movement

4. Mineral storage

5. Hematopoiesis (blood cell formation)

What’s in a bone?

• Bones, Muscles, and Joints

Classification of BonesBones are identified by:

1. ShapeA. Long bonesB. Short bonesC. Flat bonesD. Irregular bones

2. Internal tissuesA. Compact B. Spongy

3. Bone markings

Osteogenesis (Bone Formation)

Ossification - the process of replacing other

tissues with bone• The growth of the skeleton determines the

size and proportions of your body• The bony skeleton begins to form about 6

weeks after fertilization• Bone growth continues through adolescence,

and portions of the skeleton do not stop growing until approx. the age of 25

Shape: Long Bones

• Are typically longer than they are wide

• As a rule they have a shaft with heads at both ends

• Mostly compact bone

• All of the limbs (femur, tibia, humerus), except the wrist and ankle bones.

Shape: Long BonesDiaphysis (long part):

– Covered by periosteum– Sharpey’s Fibers secure the

periosteum to the underlying bone

Epiphysis (ends): – Articulate with other bones– Covered by Articular cartilage

Metaphysis: – Location where diaphysis and

epiphysis meet

Shape: Flat Bones

• Are thin, flattened and usually curved

• Have two thin layers of compact bone sandwiching a layer of spongy bone between them

• Found in the skull, sternum, ribs, and scapula

Shape: Irregular Bones

• Have complex shapes

• Examples: Vertebrae, Mandible, Sacrum, Pelvis

Shape: Short Bones• Are small and thick

• Cube-shaped and contain mostly spongy bone

• Examples: Carpals, Tarsals,

Calcaneus

Shape: Sesamoid (ses’ah-moyd) Bones

Special type of short bone

- Form within tendons

- Best known example is the patella

- Develop inside tendons near joints of knees, hands, and feet

Check Point

1. Approximately how many bones are there in the human body?

2. What is hematopoiesis?

3. What are the five functions of the bones?

4. What is the difference between compact bone and spongy bone?

5. Name the parts of a long bone.

BONE MARKINGS (Surface Features)

• Each bone in the body has characteristic external and internal features.

• Every bump, groove, and hole has a name on your bones.

• Detailed examination can yield an abundance of anatomical information.

Bone Markings

• Two types of bone markings:– Projections (aka processes) that grow out

from the bone

– Depressions (cavities) that indent the bone

The Axial Skeleton

• Includes 80 bones

• 40% of the bones in the human body

Axial Skeleton

• Three Regions:1. Skull (8 cranial & 14 facial)

** bones associated with skull (6 auditory ossicles and hyoid)

2. Vertebral column (24 vertebrae, the sacrum & coccyx)

3. Thoracic cage (sternum & 24 ribs)

The Skull• The bones of the skull protect the brain and guard

the entrances to the digestive & respiratory systems

• The skull (22 bones), the body’s most complex bony structure, is formed by the cranium (8 bones) and facial bones (14 bones)

• 6 auditory ossicles (tiny bones) are situated within the temporal bones of the cranium (smallest bones in the body that are contained in the middle ear space; hammer, anvil, stirrup)

• Hyoid bone (connected to the inferior surfaces of the temporal bones)

The Skull

• Cranium – protects the brain and is the site of attachment for head and neck muscles

• Facial bones– Supply the framework of the face, the sense organs,

and the teeth– Provide openings for the passage of air and food– Anchor the facial muscles of expression

Anatomy of the CraniumEight cranial bones:

1. 2 parietal2. 2 temporal3. Frontal4. Occipital5. Sphenoid6. Ethmoid

• The cranial bones enclose the cranial cavity, a fluid-filled chamber that cushions and supports the brain

• Cranial bones are thin and remarkably strong for their weight

Skull – Anterior View

Figure 7.2a

Frontal Bone

• Forms the anterior portion of the cranium & the roof of the orbits (eye sockets)

Parietal Bones

• Forms most of the superior and lateral aspects of the skull

Figure 7.3a

Parietal Bones & Major Associated Sutures

• Four sutures mark the articulations of the parietal bones

1. Coronal suture – articulation between parietal bones and frontal bone anteriorly

2. Sagittal suture – where right and left parietal bones meet superiorly

3. Lambdoid suture – where parietal bones meet the occipital bone (posterior)

Parietal Bones & Major Associated Sutures

4. Squamosal or squamous suture – where parietal and temporal bones meet

Occipital Bone

• Located at the back and lower part of the cranium

Temporal Bones

Form part of both the lateral walls of the cranium

Figure 7.5

Sphenoid Bone• Butterfly-shaped bone that forms part of the

floor of the cranium, unites the cranial and facial bones, and acts as a cross brace that strengthens the sides of the skull

• Forms the central wedge that articulates with all other cranial bones

Ethmoid Bone• Most deep of the skull bones; lies between

the sphenoid and nasal bones

Figure 7.7

Facial Bones

• Fourteen bones of which only the mandible and vomer are unpaired

• The paired bones are the maxillae, zygomatics, nasals, lacrimals, palatines, and inferior conchae

Mandible

• The mandible (lower jawbone) is the strongest bone of the face

Figure 7.8a

Maxillary Bones• Medially fused bones that make up the upper jaw and the

central portion of the facial skeleton (largest facial bones)

Figure 7.8b

Zygomatic Bones• Irregularly shaped bones (cheekbones)

that form the prominences of the cheeks and the inferolateral margins of the orbits

Other Facial Bones• Nasal bones – thin medially fused bones that

form the bridge of the nose• Lacrimal bones – contribute to the medial walls of

the orbit and contain a deep groove that house the tear ducts

Facial Bones

• Palatine bones – two bone plates that form portions of the hard palate and contribute to the floor of each orbit

Other Facial Bones• Vomer – forms part of the nasal septum

• Inferior nasal conchae – paired, curved bones in the nasal cavity that form part of the lateral walls of the nasal cavity

Hyoid Bone• Lies just inferior to the mandible in the anterior neck

• Only bone of the body that does not articulate directly with another bone

• Attachment point for neck muscles that raise and lower the larynx during swallowing and speech

Figure 7.12

Vertebral Column

• 26 irregular bones (vertebrae)

• Provide a column of support, bearing the weight of the head, neck, and trunk.

• Transfers weight to the appendicular skeleton of the lower limbs

• Protects spinal cord

• Helps maintain an upright body position

• Approx. length of an adult column is 71cm

Vertebral Column

Cervical vertebrae

7 bones of the neck

Thoracic vertebrae

12 bones of the torso

Lumbar vertebrae

5 bones of the lower back

Figure 7.13

Vertebral Column

Sacrum - 5 fused vertebrae

Coccyx – 4 fused vertebrae

Figure 7.13

Disks are small shock absorbers between the vertebrae (gel-like interior)

General Structure of Vertebrae:1. Vertebral body (centrum) – disc-shaped, weight-

bearing region

2. Vertebral arch – composed of pedicles (walls) and flat layers called laminae (roof)

** forms the posterior margin of each vertebral foramen (together they form the vertebral canal which encloses the spinal cord)

3. Articular processes– projections on each vertebra

Cervical Vertebrae

Table 7.2

Cervical Vertebrae

• Most mammals have 7 cervical vertebrae (giraffes, whales, mice & humans)

• Seven vertebrae (C1-C7) are the smallest, lightest vertebrae

Cervical Vertebrae: The Atlas (C1)

– Holds up the head– The superior surface articulates with the

occipital condyles of the skull (permits you to nod)

»Has no body and no spinous process

Cervical Vertebrae: The Axis (C2)

• The axis has a body, spine, and vertebral arches as do other cervical vertebrae

• Articulates with the atlas to permit rotation

Figure 7.16c

Thoracic Vertebrae• There are twelve vertebrae (T1-T12)

• Distinctive heart-shaped body (more massive than that of a cervical vertebra)

• Each thoracic vertebra articulate with ribs

Lumbar Vertebrae

• The five lumbar vertebrae (L1-L5) are located in the small of the back and have an enhanced weight-bearing function

• Largest vertebrae

Tip: Mealtimes

Breakfast: 7 a.m. (7 cervical)

Lunch: 12 p.m. (12 thoracic)

Dinner: 5 p.m. (5 lumbar)

Sacrum and Coccyx• The sacrum

– Consists of five fused vertebrae (S1-S5), which shape the posterior wall of the pelvis

– Begin fusing after puberty and are completely fused at age 25-30

– Protects reproductive, digestive, and urinary organs

– It articulates with L5 superiorly, and with the auricular surfaces of the hip bones

Coccyx

• Coccyx (Tailbone)– The coccyx is made up of four (in some cases

three to five) fused vertebrae that articulate superiorly with the sacrum

– Generally begun fusing by age 26

Sacrum and Coccyx

Figure 7.18a

Sacrum and Coccyx

Figure 7.18b

Bony Thorax (Thoracic Cage)Bony Thorax (Thoracic Cage)Functions:

– Forms a protective cage around the heart, lungs, and great blood vessels

– Supports the shoulder girdles and upper limbs

– Provides attachment for many neck, back, chest, and shoulder muscles

Sternum (Breastbone)

• A dagger-shaped, flat bone that lies in the anterior midline of the thorax

• Fusion is not complete until at least age 25 (until this age the sternal body consist of four separate bones)

Ribs• There are twelve pair of ribs

• All ribs attach posteriorly to the thoracic vertebrae

• The superior 7 pair (true, or vertebrosternal ribs) attach directly to the sternum via costal cartilages

• Ribs 8-10 (false, or vertebrocondral ribs) attach indirectly to the sternum via costal cartilage

• Ribs 11-12 (floating, or vertebral ribs) have no

anterior attachment

Ribs

Figure 7.19a

Appendicular Skeleton

• The appendicular skeleton is made up of the bones of the limbs and their supporting elements (girdles) that connect them to the trunk

• Pectoral girdles attach the upper limbs to the body trunk

• Pelvic girdle secures the lower limbs

Clavicles (Collarbones)

• S-shaped bones

• Small, fragile

• Smooth superior surface lies just beneath the skin

Figure 7.22b, c

Scapulae (Shoulder Blades)

• The scapulae are triangular, flat bones lying on the dorsal surface of the rib cage, between the second and seventh ribs

• Have three sides or borders (superior, medial, and lateral) and three angles (superior, inferior, and lateral)

Scapulae (Shoulder Blades)

Figure 7.22d, e

The Upper Limb

• Consists of the bones of the arms, forearms, wrists, and hands

Arm (Brachium)

• The humerus is the sole bone of the arm• It articulates with the scapula at the

shoulder, and the radius and ulna at the elbow

Arm

Figure 7.23 a, b

Ulna

• In anatomical position, the ulna lies medial to the radius

• Slightly longer than the radius

• Forms the major portion of the elbow joint with the humerus

Radius

• Lateral bone (to the ulna) of the forearm

• Thin at its proximal end, widened distally

• The superior surface of the head articulates with the humerus

Ulna & Radius

Figure 7.24 a, b

Carpus (Wrist)

• Consists of eight carpal bones:– Scaphoid– Lunate– Triquetrum– Pisiform– Trapezium– Trapezoid– Capitate– Hamate“Sam Likes To Push The Toy Car Hard”

Metacarpus (Palm)

• Five numbered (1-5) metacarpal bones radiate from the wrist to form the palm

– Their bases articulate with the carpals proximally, and with each other medially and laterally

– Heads articulate with the phalanges

Phalanges (Fingers)• Each hand contains 14 miniature long bones called phalanges

• Fingers (digits) are numbered 1-5, beginning with the thumb (pollex)

• Each finger (except the thumb) has three phalanges – distal, middle, and proximal

• The thumb has no middle phalanx

Wrist & Hand

Pelvic Girdle (Hip)

• The hip is formed by a pair of hip bones (coxal)• Together with the sacrum and the coccyx, these

bones form the bony pelvis

• The pelvis– Attaches the lower limbs to the axial skeleton

with the strongest ligaments of the body– Transmits weight of the upper body to the

lower limbs– Supports the visceral organs of the pelvis– Forms by the fusion of 3 bones: ilium, ischium,

and pubis

Pelvic Girdle (Hip)

Figure 7.27a

Illium

Figure 7.27b

Comparison of Male and Female Pelvic Structure

• Female pelvis– Tilted forward, adapted for childbearing– True pelvis defines birth canal– Cavity of the true pelvis is broad, shallow, and

has greater capacity

• Male pelvis– Tilted less forward– Adapted for support of heavier male build and

stronger muscles– Cavity of true pelvis is narrow and deep

Comparison of Male and Female Pelvic Structure

Table 7.4

Lower Limbs

• Each lower limb consists of a femur (thigh), patella (knee cap), tibia & fibula (lower leg), tarsal bones (ankle), metatarsal (foot), and phalanges (toes)

• They carry the weight of the erect body, and are subjected to exceptional forces when one jumps or runs

Femur (Thigh)• The sole bone of

the thigh

• Longest and heaviest bone in the body

• Articulates proximally with the hip and distally with the tibia and fibula

Figure 7.28b

Patella (Knee cap)

• Large sesamoid bone

Tibia (Shinbone)

• Large medial bone of the leg• Receives the weight of the body from the

femur and transmits it to the foot

• Slender bone of the leg• Site for attachment of muscles that move

the foot and toes

Fibula

Fibula

• Sticklike bone with slightly expanded ends located laterally to the tibia

• Major markings include the head and lateral malleolus

Tibia & Fibula

Figure 7.29a, b

Tarsus (Ankle)• Composed of seven tarsal bones:

1.Talus

2.Calcaneus (heel bone)

3.Cuboid

4.Navicular

5.Medial Cuneiform

6.Intermediate Cuneiform

7.Lateral Cuneiform

“Tom Can Control Not Much In Life”

Tarsus

Figure 7.31b, c

Metatarsal Bones & Phalanges• Metatarsals

– Five (I - V) long bones

• Phalanges– The 14 bones of the

toes– Each digit has three

phalanges except the hallux, which has no middle phalanx

Figure 7.31a

Clinical Disorders and Diseases of the Skeletal System

Cleft Palate• Occurs when the roof of a baby's mouth

doesn't fully develop (palatine bones fail to fuse) leaving an opening (cleft) in the palate that may go through to the nasal cavity.

• It is a birth defect that happens during pregnancy and can affect either the soft or hard palate.

• Cleft palate is treatable, and surgery is usually recommended.

Cleft Palate

Vertebral Column: CurvaturesScoliosis: abnormal lateral curvature of the spine– Occurs most often in the thoracic region

• Most common during adolescence and girls are more prone to developing the condition

• If muscles on one side of the body are not functioning properly, those on the opposite side tug on the spine and force it out of alignment

Scoliosis

Clinical Conditions

• Osteomalacia– Literally “soft bones.”– Includes many disorders in which

osteoid is produced but inadequately mineralized.

• Causes can include insufficient dietary calcium

• Insufficient vitamin D fortification or insufficient exposure to sun light.

• Rickets– Children's form of osteomalacia– More detrimental due to the fact that

their bones are still growing.– Signs include bowed legs, and

deformities of the pelvis, ribs, and skull.

Age and Age and BonesBones

• Bone loss outpaces bone regeneration

• Bones weaken and lose mass

• Bones become brittle and fractures occur more often

• Found most often in women

Osteoporosis

Osteoarthritis

• Degenerative joint disease• Most common type of arthritis (21 million)• Breakdown of cartilage in joints • Mostly occurs in the weight bearing joints, but

it can occur anywhere• Causes cartilage to become stiff and lose its

elasticity• As cartilage deteriorates, tendons and

ligaments stretch, causing pain

Osteoarthritis

Symptoms:•Joint aching and soreness•Pain after overuse or long periods of inactivity•Joint swellingFluid accumulation

Fractures• A crack or break in a bone

• Despite its mineral strength, bone can crack or even break if subjected to extreme loads, sudden impacts, or stresses from unusual directions

Types of Fractures

• Named according to their external appearance, their location, and the nature of the crack or break in the bone.

• Two general categories:

1.Closed (simple) – fracture is internal

2.Open (compound) – fracture projects through the skin

Common fracture types (cont’d)

Common fracture types

• Comminuted fractures

• Spiral fractures

Figure 6–16 (4 of 9)

Figure 6–16 (7 of 9)

• Greenstick fracture

Figure 6–16 (9 of 9)

• Compression fractures

Depression fracture of the skull

X-ray & MRI

How do they work???

Steps in the Repair of a FractureStep 1 – • Immediately after the fracture, extensive

bleeding occurs (blood vessels are broken). • A large blood clot, or fracture hematoma, soon

closes off the injured vessels and leaves a fibrous meshwork in the damaged area.

• The disruption of the circulation kills osteocytes (mature bone cells) around the fracture.

• Dead bone soon extends along the shaft.

Steps in the Repair of a FractureStep 2 – • The cells of the endosteum (cellular layer) and

periosteum undergo cell division and the daughter cells migrate into the fracture zone.

• An external callus (hard skin) forms and encircles fracture

• An internal callus organizes within the cavity and between the broken ends of the shaft

• The broken ends have been temporarily stabilized

Steps in the Repair of a FractureStep 3 – • Osteoblasts (bone building cells) replace the

central cartilage of the external callus with spongy bone

• Calluses form a brace at the fracture site• Spongy bone now unites the broken ends• Fragments of dead bone are removed and

replaced• If the fracture required a cast, it can be removed

at this stage

Steps in the Repair of a FractureStep 4 – • Osteoclasts (remove and recycle bone matrix)

and osteoblasts continue to remodel the region of the fracture (4 months to 1 year)

• When remodeling is complete, the bone of the calluses is gone and only living compact bone remains.

• The bone could be slightly thicker and stronger than normal at the fracture site

Fracture repair

Fracture repair (cont’d)

Casts

• Holds a broken bone in place as it heals

• Help to prevent or decrease muscle contractions

• Provide immobilization (the joints above and below the area)

• Casts are made of plaster and fiberglass

• Typically worn for 6-8 weeks

Treatment of a Fracture

• Initial treatment for fractures of arms, legs, hands, and feet include splinting the extremity in the position it is found, elevation, and ice.

• Edema (what does this have to do with splinting and casting?)

• Closed Reduction – manual realignment

• Open Reduction – surgically realignment

Joints (Articulations)• Where two bones interconnect

• The structure of a joint determines the type and amount of movement that may occur

• Functions– Give the skeleton mobility– Hold the skeleton together

Joint Facts

• 400 + joints• Approximately 230 movable and semi-

movable joints• Muscles span joints, crossing from 1 bone

to another• When muscles contract, they tug on the

bones, producing movement at the joint

Classification of Joints: Structural/Functional

• The three structural classifications are:– Immovable (synarthrosis)– Slightly movable (amphiarthrosis)– Freely movable (diarthrosis) or synovial joint

lmmovable Joints• The bones are close together and may interlock• Extremely strong joints• There is no joint movement

Figure 8.1a

Examples:

1. Suture – skull2. Binds the teeth to bony

sockets in jaw3. Bridge between two

articulating bones (first pair of ribs and the sternum)

Immovable Joints

Figure 8.2b

Slightly Movable Joints• Permits movement• Stronger than a freely

movable joint• Articulating bones are

connected by cartilage or collagen fibers

• Example: articulation between the two pubic bones

Figure 8.2a

Synovial (Freely Movable) Joints

• Permit a wider range of motion

• Typically located at the ends of long bones

• Examples: upper and lower limbs

Synovial Joints: General Structure

• Synovial joints all have the following:– Articular cartilage– Joint (synovial)

cavity– Articular capsule– Synovial fluid– Reinforcing

ligaments

Figure 8.3a

Synovial Joints: General Structure

• The surfaces of the articular cartilage are slick and smooth

• Articular cartilages are separated by a thin film of synovial fluid

• How are these two features important when it comes to movement?

Synovial Joints: Accessory Structures

• Synovial Fluid – lubrication, nutrient distribution, shock absorption

• Cartilage – shock absorption, subdivide• Fat Pads – protection, packing material• Ligaments – support, strength• Tendons – limit ROM, support• Bursae – reduce friction, shock absorption

Synovial Joints: Movement/ROM• Muscle attachment across a joint

– Origin – attachment to the immovable bone– Insertion – attachment to the movable bone

•Nonaxial – slipping movements only

•Uniaxial (monaxial) – movement in one plane

•Biaxial – movement in two planes

•Multiaxial – movement in or around all three planes

Types of Synovial Joints• Based on the shapes of the articular surfaces

• Each type of joint permits a different type and range of motion

Types:• Gliding• Hinge• Pivot• Condylar• Saddle• Ball and socket

Types of Synovial Joints

• Gliding (Plane) joints– Articular surfaces

are essentially flat– Allow only slipping

or gliding movements

– Examples: clavicle, carpals, tarsals, sacrum-iliac

Figure 8.7a

Types of Synovial Joints

• Hinge joints– Cylindrical projections of

one bone fits into a trough-shaped surface on another

– Motion is along a single plane

– Examples: elbow, knee, ankle, and interphalangeal joints

Figure 8.7b

Pivot Joints

• Rounded end of one bone protrudes into a “sleeve,” or ring, composed of bone (and possibly ligaments) of another

• Permit only rotation

• Examples: joint between the axis and the dens (neck), and the proximal radioulnar joint

Figure 8.7c

Condyloid (Ellipsoid) Joints• Oval articular surface of

one bone fits into a complementary depression in another

• Biaxial joints permit movement around two axes (flexion/extension and abduction/adduction)

• Examples: radiocarpal (wrist) joints, and metacarpophalangeal (knuckle) joints

Figure 8.7d

Saddle Joints• Similar to condyloid

joints but with greater movement

• Each articular surface has both a concave and a convex surface

• Allows circumduction but prevents rotation

• Example: carpometacarpal joint of the thumb

Figure 8.7e

Ball-and-Socket Joints• A spherical or

hemispherical head of one bone articulates with a cuplike socket of another

• Multiaxial joints permit the most freely moving synovial joints

• Examples: shoulder and hip joints

Figure 8.7f

Bone Bingo

Frontal Zygomatic Nasal

Lacrimal Mandible Maxilla

Clavicle Scapula Ribs

Sternum Vertebrae Ulna

Humerus Radius Carpals

Phalanges Femur Tibia

Patella Fibula Tarsals

Metatarsals Metacarpals Sacrum

Coccyx Occipital Parietal