Chapter 6 The Skeletal System
Bones and Cartilage
Factors that affect bone growth and maintenance
Types of bones
Divisions of the skeleton
There are a total of 206 bones in the human body.
The skeletal system contains both bone and cartilage – 2 types of connective tissue.
The appearance and texture of bone varies, depending on its location.
Outer layer of bone, very hard and dense.
Organized in structural units called Haversian systems.
Matrix is composed of Ca salts (Ca carbonate and Ca phosphate)
Osteocytes – living bone cells that live in matrix.
Porous (Spongy) bone
Located in the ends of long bones.
Many spaces that are filled with red bone marrow which produces blood cells.
Trabeculae – needle-like threads of spongy bone that surround the spaces. Add
strength to this portion of the bone.
Matrix is a firm gel with chondrocytes suspended in the matrix.
Provides framework that supports the body.
Provides movement with the help of the skeletal muscles.
**Storage of calcium
Produces blood cells
Embryonic Bone Growth
The skeleton is first made of cartilage and fibrous connective tissue. These are
gradually replaced by bone.
Bone matrix is produced by osteoblasts.
“Calcification” begins at 8 weeks gestation.
Process is not complete at birth.
Factors that Affect Bone Growth and Maintenance
Hormones – growth hormone, thyroxine, parathyroid hormone and insulin help
regulate cell division, protein synthesis, Ca metabolism and energy production.
Exercise or “stress” – “bearing weight” causes bones to thicken.
4 Types of Bones
Long bones – bones of the arms and legs. Structure:
Medullary cavity –
Composed of spongy bone which contains red bone marrow in children,
replaced with yellow marrow in adults.
Epiphyses are covered with compact bone which in turn is covered with
articular (hyaline) cartilage.
Short bones – carpels and tarsals (wrist and ankle).
Flat bones – skull bones.
Irregular bones – vertebrae.
Divisions of the Skeleton
Axial Skeleton – bones of the skull, spine, chest and the hyoid bone.
Skull – 8 bones that form the cranium, 14 that form the face and 6 in the middle
Frontal – forehead bone, also forms upper part of eye sockets.
Parietal – top/upper sides of the cranium behind the frontal bone
Temporal – forms the lower sides of the cranium; contains middle and inner
ear structures, external auditory canal, and mastoid process (behind the ear).
Occipital bone - forms the back of the skull, large hole (foramen magnum)
allows entry of spinal cord.
Sphenoid – forms central part of the floor of the cranium; pituitary gland is
located in a depression called the sella turcica (Turkish sadle).
Ethmoid bone – helps form floor of cranium, side walls and roof of nose.
Nasal bones form upper bridge of nose.
Maxilla – upper jawbones
Zygomatic bones – cheek bones; help form eye orbit.
Mandible – lower jawbone.
Lacrimal bones – form medial wall of the eye socket and side of nasal cavity.
Palatine – forms back part of the roof of the mouth, part of the orbit.
Vomer – forms lower, back part of nasal septum.
Axial - skull
Ear bones – from the outside in..
Malleus – hammer
Incus – anvil
Stapes – stirrup
Sinuses – spaces or cavities inside the cranium
Sutures – Immovable joints that join skull bones together
Lamboidal – between the parietal and occipital
Squamous – between the parietal and temporal
Coronal – between parietal and frontal
Sagittal – between parietal bones
**Fontanels – usually ossify by 2 years of age
Divisions of the Skeleton
Vertebral column consists of a series of separate bones or vertebrae connected such
that they form a flexible curved rod.
7 Cervical vertebrae - Atlas and axis are first two vertebrae
Axial – Vertebral column
Vertebral column has 4 curves that support the weight of the body and help with
Cervical curvature – curves anteriorly
Thoracic curvature curve posteriorly
Lumbar curvature – anteriorly
Sacral – posteriorly
Axial – Vertebral column
Kyphosis (thoracic) = exagerated curve =
Lodosis (lumbar) = exagerated curve =
Scoliosis – lateral curve.
Axial – Thorax
Includes manubrium, sternum, thoracic vertebrae and the ribs.
All 12 ribs are all attached posteriorly to the vertebrae:
“True ribs” - 1st 7 pair are attached to the sternum by the costal cartilage
beginning at the manubrium (upper part of the sternum).
False ribs – ribs 8, 9, and 10 are attached to the cartilage of the 7th ribs.
Floating ribs – last 2 pairs are not attached at the anterior end.
Appendicular skeleton – bones of the upper and lower extremities and their girdles.
Scapula – shoulder blade
Clavicle – collar bone
Humerus – long bone of the upper arm; 2nd longest bone in the body. The
humerus is attached to the scapula proximally and articulates with the radius and
ulna distally to form the elbow joint.
Radius and ulna – bones of the lower arm, articulate with each other distally and
with the carpals.
Carpals – 8 wrist bones
Metacarpals – palm of hand
Phalanges – 14 finger bones, 3 in each finger and 2 in each thumb.
Appendicular skeleton - Lower extremity
Pelvic (hip) girdle connects legs to the trunk. Consists of 2 large os coxae one
on each side of the pelvis. Each os coxae consists of 3 separate bones in the
Pubis These grow together
in the adult.
Femur – thigh bone, longest bone in the body. The femur fits into the
cup-shaped “socket” = acetabulum – in the pelvic girdle. Distally the femur
articulates with the patella (knee cap) and the…
Tibia (lower leg - shinbone).
Medial malleolus – inner anklebone, protuberance of the tibia.
Fibula – long slender, non-weight bearing bone located along the lateral border
of the lower leg.
Lateral Malleolus – rounded projection at the lower end of the fibula (outer
Tarsals – 7 ankle bones; the talus articulates with the tibia and the calcaneous,
the heel bone.
Metatarsals – 5 long bones of the foot.
Phalanges - toe bones, two in the “big” toe and 3 in each of the other toes.
Three types of joints – synarthroses, amphiarthroses and diarthroses
Diarthroses – freely moveable joints.
All have a joint capsule, a joint cavity and a layer of cartilage over the ends of the
Joint Capsule – made of tough fibrous connective tissue and lined with the
smooth slippery synovial membrane; fits over the ends of the bones like a
Ligaments – cords or bands of fibrous connective tissue that hold the bones
Articular cartilage – layer of cartilage over the end of the bones.
Synovial membrane – secretes a lubricating fluid (synovial fluid) that allows
easier movement with less friction.
Types of Diarthroses
Ball and Socket – ball like head on one bone fits into a socket of another. Ex –
shoulder and hip. Widest range of movement.
Hinge – allow movements in only 2 directions – flexion and extension. Ex –
elbow and knee, fingers.
Pivot – small projection of one bone pivots in an arch of another. Ex – atlas and
Saddle or saddle-shaped – allows for flexion, extension, abduction, adduction,
opposition. **Only example – metacarpal bone of thumb and a carpal bone of
Gliding – least moveable, flat articulating surfaces. Ex – carpals.
Condyloid – distal end of radius into the depressions in the carpals.