THE SKELETAL SYSTEM
• The skeletal system may be divided into two
functional parts:
• The axial skeleton consists of the bones of the
head (cranium or skull), neck (hyoid bone and
cervical vertebrae),and trunk (ribs, sternum,
vertebrae, and sacrum)
• • The appendicular skeleton consists of the
bones of the limbs, including those forming the
pectoral (shoulder) and pelvic girdles.
Cartilage and Bones
Cartilage is a resilient, semi rigid form of connective
tissue that forms parts of the skeleton where
more flexibility is required.example, where the
costal cartilages attach the ribs to the sternum.
The articulating surfaces (bearing surfaces) of
bones participating in a synovial joint are capped
with articular cartilage that provides smooth,
low-friction, gliding surfaces for free movement
Blood vessels do not enter cartilage (i.e., it is
avascular); consequently, its cells obtain oxygen
and nutrients by diffusion.
Bone is a highly specialized, hard form of
connective tissue
Bones of the adult skeleton provide:
• support for the body and its vital cavities; it is
the chief supporting tissue of the body.
• protection for vital structures (e.g., the heart).
• the mechanical basis for movement (leverage).
• storage for salts (e.g., calcium).
• a continuous supply of new blood cells
(produced by the marrow in the medullary cavity
of many bones).
• Periosteum
A fibrous connective tissue covering surrounds
each skeletal element like a sleeve, except where
articular cartilage occurs;
• And that of cartilages is called perichondrium.
Both nourish the external aspects of the skeletal
tissue.
They are capable of
• laying down more cartilage or bone (particularly
during fracture healing) and
• provide the interface for attachment of tendons
and ligaments.
• The two types of bone are compact bone and
spongy (trabecular) bone.
• They are distinguished by the relative amount
of solid matter and by the number and size of
the spaces they contain
• Medullary cavity
• Some of the various markings and features of bones are :
• Capitulum: small, round, articular head (e.g., capitulum of the
humerus).
• Condyle: rounded, knuckle-like articular area, often occurring
in pairs (e.g., the lateral and medial femoral condyles).
• Crest: ridge of bone (e.g., the iliac crest).
• Epicondyle: eminence superior or adjacent to a condyle
(e.g., lateral epicondyle of the humerus).
• Facet: smooth fl at area, usually covered with cartilage,
where a bone articulates with another bone (e.g., superior
costal facet on the body of a vertebra for articulation with a rib).
• Foramen: passage through a bone (e.g., obturator foramen).
• Fossa: hollow or depressed area (e.g., infraspinous fossa of the
scapula).
• Groove: elongated depression or furrow (e.g., radial groove of the
humerus).
• Head (L. caput): large, round articular end (e.g., head of the
humerus).
• Line: linear elevation (e.g., soleal line of the tibia).
• Malleolus: rounded process (e.g., lateral malleolus of the fibula).
• Notch: indentation at the edge of a bone (e.g., greater sciatic notch).
• Spine: thorn-like process (e.g., the spine of the scapula).
• Spinous process: projecting spine-like part (e.g., spinous
process of a vertebra).
• Trochanter: large blunt elevation (e.g., greater tro
chanter of the femur).
• Trochlea: spool-like articular process or process that
acts as a pulley (e.g., trochlea of the humerus).
• Tubercle: small raised eminence (e.g., greater tubercle
of the humerus
• Tuberosity: large rounded elevation (e.g., ischial
tuberosity)
 Protuberance- projection of bone e.g. external occipital
protuberance
CLASSIFICATION OF BONES
Bones are classified according to their shape.
• Long bones are tubular (e.g., the humerus in the arm).
• Short bones are cuboidal and are found only in the tarsus
(ankle) and carpus (wrist).
• Flat bones usually serve protective functions (e.g., the
flatbones of the cranium protect the brain).
• Irregular bones have various shapes other than long, short,
or flat (e.g., bones of the face).
• Sesamoid bones (e.g., the patella or knee cap) develop in
certain tendons and are found where tendons cross the ends
of long bones in the limbs
BONE DEVELOPMENT
• Most bones take many years to grow and mature.
The humerus (arm bone), for example, begins to
ossify at the end of the embryonic period (8
weeks); however, ossification is not complete
until age 20.
• All bones derive from mesenchyme (embryonic
connective tissue) by two different processes:
intramembranous ossifi cation (directly from
mesenchyme) and endochondral ossifi cation
(from cartilage derived from mesenchyme).
VASCULATURE AND INNERVATION OF BONES
• Most apparent are the nutrient arteries arise as
branches of adjacent arteries outside the
periosteum and pass obliquely through the
compact bone of the shaft of a long bone via
nutrient foramina.
• The nutrient artery divides in the medullary
cavity into longitudinal branches that proceed
toward each end, supplying the bone marrow,
spongy bone, and deeper portions of the
compact bone
osteoporosis
• During the aging process, the organic and
inorganic components of bone both decrease,
often resulting in osteoporosis, a reduction in
the quantity of bone, or atrophy of skeletal
tissue .Hence, the bones become brittle, lose
the elasticity, and fracture easily.
NERVES
• Nerves accompany blood vessels supplying
bones. The periosteum is richly supplied with
sensory nerves (periosteal nerves.
• The periosteum is especially sensitive to tearing
or tension, which explains the acute pain from
bone fractures.
• Within bones, vasomotor nerves cause
constriction or dilation of blood vessels,
regulating blood flow through the bone marrow.
JOINTS
• CLASSIFICATION OF JOINTS
• Three classes of joints are described, based on the manner
or type of material by which the articulating bones are
united.
• 1. SYNOVIAL JOINTS are united by a joint (articular) capsule
(composed of an outer fibrous layer lined by a serous
synovial membrane) spanning and enclosing an articular
cavity
• The joint cavity of a synovial joint contains a small amount
of lubricating synovial fluid, secreted by the synovial
membrane.
• internal surfaces are covered by synovial membrane.
• FIBROUS JOINTS: The sutures of the cranium are
examples of fibrous joints
• These bones are close together, either interlocking
along a wavy line or overlapping. A syndesmosis type
of fibrous joint unites the bones with a sheet of fibrous
tissue, either a ligament or a fibrous membrane.
• This type of joint is partially movable
E.g.
• 1. The interosseous membrane in the forearm is a
sheet of fibrous tissue that joins the radius and ulna in
a syndesmosis
• 2. A dento-alveolar syndesmosis (gomphosis or
socket) articulation between the root of the tooth and
the alveolar process of the jaw.
• 3. Cartilaginous joints are united by hyaline
cartilage or fibrocartilage.
• Primary cartilaginous joints permit growth in
the length of a bone. When full growth is
achieved, the epiphysial plate converts to
bone and the epiphyses fuse with the
diaphysis.(temporary unions)
• Secondary cartilaginous joints, or symphyses,
are strong, slightly movable joints united by
fibrocartilage. The fibrocartilaginous
intervertebral disc
• SYNOVIAL JOINTS, the most common type of
joint, provide free movement between the
bones they join; they are joints of locomotion,
typical of nearly all limb joints
The six major types of synovial joints are
classified according to the shape of the
articulating surfaces and/or the type of
movement they permit
• 1. Plane joints permit gliding or sliding movements in
the plane of the articular surfaces. The opposed
surfaces of the bones are flat or almost flat, with
movement limited by their tight joint capsules. Plane
joints are numerous and are nearly always small. Eg
acromioclavicular joint between the acromion of the
scapula and the clavicle.
• 2. Hinge joints permit flexion and extension only,
movements that occur in one plane (sagittal) uniaxial
joints. The joint capsule of these joints is thin and lax
anteriorly and posteriorly where movement occurs;
however, the bones are joined by strong, laterally
placed collateral ligaments. eg elbow joint
3. Saddle joints permit abduction and adduction as
well as flexion and extension, biaxial joints that allow
movement in two planes, sagittal and frontal. The
performance of these movements in a circular
sequence (circumduction) is also possible. The
Carpometacarpal joint at the base of the 1st digit
(thumb) is a saddle joint
4. Condyloid joints permit flexion and extension as well
as abduction and adduction; thus condyloid joints
are also biaxial. However, movement in one plane
(sagittal) is usuallygreater (freer) than in the other.
The metacarpophalangeal joints (knuckle joints) are
condyloid joints
• 5. Ball and socket joints allow movement in multiple axes
and planes: fl exion and extension, abduction and adduction,
medial and lateral rotation, and circumduction; thus ball
and socket joints are multiaxial joints. The hip joint is a ball
and socket joint in which the spherical head of the femur
rotates within the socket formed by the acetabulum of the
hip bone.
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6. Pivot joints permit rotation around a central axis; thus
they are uniaxial. In these joints, a rounded process of
bone rotates within a sleeve or ring. The median atlantoaxial
joint is a pivot joint in which the atlas (C1 vertebra)
rotates around a fi nger-like process, the dens of the axis
(C2 vertebra), during rotation of the head.
JOINT VASCULATURE AND INNERVATION
• Joints receive blood from articular arteries that
arise from the vessels around the joint.
• The arteries often anastomose (communicate) to
form networks (peri-articular arterial
anastomoses) to ensure a blood supply to and
across the joint
• Articular veins are communicating veins that
accompany arteries (L.venae comitantes) and, like
the arteries, are located in the joint capsule,
mostly in the synovial membrane.
anastomosis
• Joints have a rich nerve supply provided by
articular nerves with sensory nerve endings in
the joint capsule. In the distal parts of the
limbs (hands and feet), the articular nerves
are branches of the cutaneous nerves
supplying the overlying skin.
The Hilton law states that the nerves supplying
a joint also supply the muscles moving the
joint and the skin covering their distal
attachments.
Degenerative Joint Disease
• Synovial joints are well designed to withstand
wear, but heavy use over several years can cause
degenerative changes.
• Degenerative joint disease or osteoarthritis is
often
• accompanied by stiffness, discomfort, and pain.
Osteoarthritis
• is common in older people and usually affects
joints that
• support the weight of their bodies (e.g., the hips
and knees).
Arthroscopy
• The cavity of a synovial joint can be examined
by inserting a cannula and an arthroscope (a
small telescope) into it.
orthopedic surgeons use this to examine joints
for abnormalities, such as torn menisci (partial
articular discs of the knee joint).
Avascular necrosis
• Loss of arterial supply to an epiphysis or other
parts of a bone results in the death of bone
tissue— avascular necrosis (G. nekrosis,
deadness). After every fracture, small areas of
adjacent bone undergo necrosis.
• In some fractures, avascular necrosis of a large
fragment of bone may occur