Skeletal System
Introduction
 Bone is made up of several types of
tissues (bone, cartilage, dense
connective, blood, nerve)
Bone Structure
 Epiphyses – expanded ends of bones that
form joints
 Hyaline cartilage cover the epiphyses
 Diaphysis – the shaft of the bone
 Periosteum (tough layer of connective
tissue) covers the bone
 Compact bone (tightly packed tissue)
makes up the wall of the diaphysis
 The epiphyses is filled with spongy bone
(branching bony plates) that reduces the
weight of the skeleton
 The diaphysis contains a hollow cavity
that is filled with marrow (soft
connective tissue)
 Bone cells (osteocytes) are located
within lacunae (small bony chambers)
that lie in circles around osteonic canals
 These canals contain blood vessels and
nerve fibers
Bone Development and Growth
 Bones form by replacing connective
tissue in the fetus
 Some form within sheet like layers of
connective tissues (intramembranous
bones) ex. – flat bones of the skull
 Others replace masses of cartilage
(endochondral bones) ex. Most of the
bones of the skeleton
Bone Function
1.Support and protection
2.Body movement
3.Blood cell formation
o Two kinds of marrow
 Red marrow – functions in the
formation of red blood cells,
white blood cells and platelets
and is found in the spongy bone
skull, ribs, sternum, clavicles,
vertebrae, and pelvis
 Yellow marrow – stores fat and
occupies the cavities of most
bones
4.Storage of Inorganic Salts
o Calcium in bone is a reservoir for
body calcium; when blood levels are
low, osteoclasts release calcium from
bone.
o Bone also stores magnesium,
sodium, potassium, and carbonate
ions
o Bones can accumulate harmful
elements such as lead and radium
Skeletal Organization
 Axial skeleton – skull, hyoid bone,
vertebral column, thorax (sternum and
ribs)
 Appendicular skeleton – pectoral girdle,
upper and lower limbs, and pelvic girdle
Skull
 Made up of 22 bones, including 8 cranial
bones, 13 facial bones, and the mandible
Cranial bones
 Frontal bone – forehead and upper
portion of eye sockets
 Parietal bone (2) – above temporal bones
 Occipital bone – base of the skull
 Temporal bones (2) – sides and base of
cranium
 Sphenoid bone – central bone
 Ethmoid bone – upper nasal region
Facial Bones
 Maxillae (2) – upper jawbones
 Palatine bones (2) – floor of nasal cavity
 Zygomatic bones (2) – cheek bones
 Lacrimal bones (2) – medial wall of eye
socket
 Nasal bones (2) – upper part of the
bridge of the nose
 Vomer bone (1) – partition between two
nasal cavities
 Inferior nasal conchae (2) – bones inside
lateral walls of the nasal cavity
 Mandible (1)
Infantile Skull
 Completely developed but features
fontanels, or soft spots to aid passage
through the birth canal
Vertebral Column
 Composed of vertebrae (bones)
separated by intervertebral disks
(fibrocartilage)
A Typical Vertebra
 Drum shaped body (different regions
have different characteristics)
 Overhead
Cervical Vertebrae
 7 bones – smallest of the vertebrae
 comprise the neck and support the head
 1st vertebrae – atlas (appears as a bony
ring and supports the head
 2nd vertebrae – axis
Thoracic Vertebrae
 12 thoracic vertebrae articulate (join)
with the ribs
 larger and stronger than cervical
vertebrae
Lumbar Vertebrae
 5 – massive – support the weight of the
body
Sacrum
 triangular structure at the base of the
vertebral column – made up of five
vertebrae fused into one bone
Coccyx
 lowermost portion – composed of four
fused vertebrae
Thoracic Cage
 ribs, thoracic vertebrae, sternum, and
costal cartilages
 supports the pectoral girdle and upper
limbs
 functions in breathing and protects
thoracic and upper abdominal organs
Ribs
 12 pairs of ribs – attach to thoracic
vertebrae
 first 7 are true ribs that join the sternum
 remaining 5 are false ribs – the first three
join the sternum and the last three are
floating ribs (don’t attach to the sternum)
Sternum
 breastbone
 consists of an upper manubrium, middle
body, and lower xiphoid process
Pectoral Girdle
 2 scapulae and 2 clavicles
Upper Limb
 Humerous – upper arm
 Radius – thumb side
 Ulna – forearm
 Hand – composed of the wrist (made up
of 8 carpal bones bound into a carpus),
hand (five metacarpal bones), and
fingers (three phalanges in each finger
accept the thumb which lacks the middle
phalanx.
Pelvic Girdle
 Consists of two coxal bones and the
sacrum – supports the trunk of the body
on the lower limbs
 Each coxal bones is made up of three
bones: iilium (largest and most superior),
ischium (L-shaped – supports weight in
sitting), and pubis (anterior portion)
Lower Limbs
 Femur – thigh bone – longest in the body
 Patella – kneecap – located in the tendon
that passes over the knee
 Tibia – shin bone – supports the weight
of the body
 Fibula - lateral to the tibia – does not
bear body weight
 Foot – consists of the ankle (7 tarsal
bones, forming a tarsus), instep (5
metatarsal bones, provides an arch), toes
(made up of three phalanges, except for
the great toe, which lacks a middle
phalanx)
Joints
 Articulations –junctions between bones
 Classified according to the degree of
movement possible and can be
immovable, slightly movable, or freely
movable
 Can also be classified according to the
type of tissue that bind s them together
Fibrous Joints
 Held close together by dense connective
tissue – immovable (sutures of the skull)
or only slightly movable (joint between
the distal tibia and fibula)
Cartilaginous Joints
 Hyaline cartilage unite the bones
 Example – Intervertebral disks between
vertebrae – helps absorb shock and are
slightly movable
Synovial Joints
 Most joints of Skelton
 Some contain shock-absorbing pads of
fibrocartilage called menisci
 Some have fluid-filled sacs called bursae
 Based on the shapes of their parts and
the movements they permit, synovial
joints can be classified as follows:
 Ball and socket joint – shoulder, hips
 Condyloid joint – metacarpal and
phalange
 Pivot joints – one bone rotates about
another (neck)
 Gliding joints – one bone slides over
another (wrists, ankles)
 Hinge joints – back and forth motion
(knee)
 Saddle joints – bones with concave
and convex surfaces (thumb)
Action terms
 Flexion – bending or decreasing the
angle between parts (calf towards thigh)
 Extension – opposite action (leg
straightened out)
 Rotation – turning on axis (head)
 Abduction – drawing away from midline
of body (lifting arm)
 Adduction – moving towards the midline
of body (lowering arm)
 Circumduction – describing a circle
(shoulder)
 Inversion – turning sole of foot inward
 Eversion – turning sole of foot away
from body
 Supination – hands up
 Pronation – hands down