Chapter 7: Skeletal System
I. Bone Structure
four classes of bone according to shape are long, short, flat, and irregular.
of long bones are forearm and thigh bones.
bones are shaped like cubes.
of short bones are wrist bones and ankle bones.
bones are platelike structures.
of flat bones are some skull bones, ribs, and scapulae.
bones have a variety of shapes.
of irregular bones are vertebrae and some facial bones.
bones are also called sesamoid bones.
bones are small and nodular and embedded in tendons.
example of a sesamoid bone is the patella.
of a Long Bone
1. An expanded
end of a long bone is an epiphysis.
2. An epiphysis
articulates with another bone.
cartilage is located on an epiphysis.
shaft of a long bone is called a diaphysis.
is a tough, vascular, fibrous membrane covering the diaphysis of a bone.
functions to form and repair bone tissue.
provide sites for attachments of tendons or ligaments.
wall of the diaphysis is composed of compact bone.
bone has a continuous matrix with no gaps.
epiphyses are largely composed of spongy bone bone.
bone consists of bony plates called trabeculae.
12. A bone
usually has both compact bone and spongy bone.
13. A canal
called the medullary cavity runs through the diaphysis.
lines the medullary cavity and spaces of spongy bone.
contains bone-forming cells.
tissue that fills the spaces of bone is called marrow.
two forms of marrow are red and yellow.
a. Bone cells are
are tiny, chambers that contain osteocytes.
form concentric canals around central canals.
transport nutrients and wastes to and from nearby cells.
processes of osteocytes pass through canaliculi.
intercellular matrix of bone is composed of collagen and inorganic salts.
a. An osteon is
a cylinder-shaped unit of compact bone.
b. The substance
of compact bone is formed from many osteons cemented together.
c. Each central
canal contains blood vessels and nerves.
canals connect osteons.
canals contain larger blood vessels and nerves.
bone is also composed of osteocytes
and intercellular material.
compact bone, the bone cells do not aggregate around central canals.
the cells lie within trabeculae.
get nutrients from substances diffusing into canaliculi that lead to the surface of trabeculae.
II. Bone Development
1. Parts of the skeleton
begin to form during the first few weeks of prenatal development.
structures continue to grow until adulthood.
form by replacing existing connective tissues.
bones originate within sheetlike layers of connective tissue.
bones originate within cartilage.
of intramembranous bones are flat bones of the skull.
is bone development.
their development, membranelike layers of primitive connective tissue appear at the sites of their future bones.
of blood vessels supply the connective tissue layers.
are bone-forming cells.
deposit bony matrix around themselves.
bone can become compact bone as spaces fill with bone matrix.
8. As development
continues, osteoblasts may become surrounded by matrix.
surrounding the processes of osteoblasts gives rise to canaliculi.
isolated, osteoblasts become osteocytes.
comes from cells of the primitive connective tissue that persist outside of the developing bone.
bone is formed by osteoblasts on the inside of periosteum.
ossification is the process of replacing connective tissue to form an intramembranous bone.
of the bones of the skeleton are endochondral bones.
bones develop as masses of hyaline cartilage.
the cartilage decomposes.
4. As the
cartilage decomposes, a periosteum forms from
tissue that encircles the developing structure.
vessels and undifferentiated connective tissue cells invade the disintegrating tissue.
of the cells differentiate into osteoblasts.
form spongy bone in the spaces previously housed by cartilage.
ossification is the process of forming an endochondral bone by the replacement of hyaline cartilage.
primary ossification center is an area in the diaphysis of a long bone in which the bony tissues begin to replace hyaline
ossification centers appear in epiphyses.
epiphyseal plate is a band of cartilage between the primary and secondary ossification centers.
at the Epiphyseal Plate
1. In a
long bone, the diaphysis is separated from the epiphysis by an epiphyseal plate.
cartilaginous cells occur in four layers.
first layer is composed of resting cells that do not actively participate in growth.
first layer anchors the epiphyseal plate to the bony tissue of the epiphysis.
second layer contains rows of many young cells undergoing mitosis.
6. As new
cells appear, the cartilaginous plate thickens.
third layer is formed by older cells that are left behind as new cells appear.
cells of the third layer enlarge and thicken the epiphyseal plate.
fourth layer is composed of dead cells and calcified intercellular substance.
break down calcified matrix of bone.
originate from monocytes.
secrete acids that dissolve the inorganic component of the calcified matrix, and their lysosomal enzymes digest the organic
phagocytize components of the bony matrix.
osteoclasts remove the matrix, osteoblasts invade the region and deposit bone tissue in place of calcified matrix.
15. A long
bone continues to lengthen while the cartilaginous cells of the epiphyseal plates are active.
of the bone is no longer possible when once the ossification centers of the diaphysis and epiphysis meet and the epiphyseal
medullary cavity forms when osteoclasts erode bone tissue in the diaphysis.
bone in the central regions of the epiphyses and diaphysis remains spongy.
cartilage on the ends persists as articular cartilage.
of Bone Tissue
1. Throughout life,
osteoclasts resorb bone tissue and osteoblasts replace bone.
3% to 5% of bone calcium is exchanged each year.
Affecting Bone Development, Growth, and Repair
that affect bone development, growth and repair include nutrition, exposure to sunlight, hormonal secretions, and physical
D is necessary for calcium absorption.
of vitamin D can lead to the diseases rickets and osteomalacia.
A is necessary for osteoblast and osteoclast activity during normal development.
C is required for collagen synthesis.
hormone stimulates division of cartilage cells in epiphyseal plates.
7. In children,
the absence of growth hormone leads to pituitary dwarfism.
8. An excess
of growth hormone before the epiphyseal plates ossify leads to pituitary gigantism.
9. In adults,
an excess of growth hormone leads to acromegaly.
hormone can halt bone growth by causing premature ossification of the epiphyseal plates.
of thyroid hormone may stunt growth.
hormone stimulates an increase in the number and activity of osteoclasts.
are male sex hormones.
promote formation of bone tissue.
hormones also stimulate ossification of the epiphyseal plates.
typically reach their maximum heights earlier than males because the effects of estrogen on the epiphyseal plates are stronger
stress stimulates bone growth.
III. Bone Function
give shape to structures such as the head, face, thorax, and limbs.
bones of lower limbs, pelvis, and vertebral column support the bodys weight.
bones of the skull protect the eyes, ears, and brain.
bones of the thorax protect the heart and lungs.
of the pelvic girdle protect lower abdominal and internal reproductive organs.
1. Bones and muscles
interact as levers.
four basic components of a lever system are rigid bar, fulcrum, object that is moved against resistance, and a force.
3. In scissors,
the handle and blades form a rigid bar.
pivot of scissors is the screw.
resistance of scissors is the material to be cut.
force of scissors is supplied by the person on the handles.
7. In a
first-class lever system, the parts are arranged resistance, fulcrum, force.
scissors, other examples of first class lever systems are seesaws and hemostats.
9. In a
second-class lever system, the parts are arranged fulcrum, resistance, force.
example of a second-class lever system is a wheelbarrow.
a third class lever system, the parts are arranged resistance, force, and fulcrum.
example of a third-class lever system is a pair of tweezers.
the action of bending the upper limb at the elbow, the rigid bar is the forearm bones, the pivot is the elbow joint, the resistance
is the hand, and the force is applied by muscles on the anterior side of the arm.
the arm at the elbow is an example of a third-class lever system.
the upper limb straightens at the elbow, the rigid bar is forearm bones, the pivot is the elbow, the resistance is the hand,
and the force is applied by the triceps muscle located on the posterior surface of the arm.
the arm at the elbow is a first class lever system because the parts of
the lever are arranged resistance, pivot, force.
example of a second-class lever system in the body is a movement produced at the temporomandibular joint (opening of the mouth)
is blood cell formation.
cell formation begins in the yolk sac.
in development, blood cells are made in the liver, the spleen, and red bone marrow.
is a soft, netlike mass of connective tissue within the medullary cavities of bond bones, in the irregular spaces of spongy
bone, and in the larger central canals of compact bone tissue.
marrow functions in the formation of red blood cells, white blood cells, and platelets.
marrow occupies the cavities of most bones in an infant.
increasing age, yellow marrow replaces red marrow.
marrow stores fat.
9. In an
adult, red marrow is primarily found in the spongy bone of the skull, ribs, sternum, clavicles, vertebrae, and pelvis.
matrix of bone tissue contains collagen and inorganic mineral salts.
salts account for about 70% by weight.
are tiny crystals of calcium phosphate.
body requires calcium for many metabolic processes including blood clot formation, nerve impulse conduction, and muscle cell
blood calcium is low, parathyroid hormone stimulates osteoclasts to break down bone tissue to release calcium salts.
high blood calcium levels inhibit osteoclast activity.
stimulates osteoblasts to form bones.
tissue contains lesser amounts of magnesium, sodium, potassium and carbonate ions.
number of bones in a human skeleton is around 206.
bones of the skull are tightly joined by sutures.
of the Skeleton
major portions of the skeleton are axial and appendicular.
axial skeleton contains skull bones, middle ear bones, the hyoid bone, vertebral column bones, and thoracic cage bones.
skull is composed of 8 cranial bones and 14 facial bones.
hyoid bone supports the muscles of the tongue.
hyoid bone is located in the neck between the lower jaw and the larynx.
vertebral column consists of vertebrae, a sacrum, and coccyx.
distal end of the column is formed by the sacrum and the coccyx.
coccyx is also called the tailbone.
thoracic cage is composed of 24 ribs and the sternum.
appendicular skeleton consists of bones of the pectoral girdle, upper limbs, pelvic girdle, and lower limbs.
pectoral girdle is formed by scapulae and clavicles.
pectoral girdle connects the bones of the upper limb to the axial skeleton.
pectoral girdle aids in upper limb movements.
upper limb consists of a humerus, radius, ulna, carpals, metacarpals, and phalanges.
humerus, radius, and ulna articulate at the elbow.
wrist bones are called carpals.
bones of the palm are called metacarpals.
in the fingers are called phalanges.
pelvic girdle is formed by coxal bones.
pelvic girdle connects the bones of the lower limbs to the axial skeleton.
pelvic girdle, sacrum, and coccyx form the pelvis.
lower limb consists of a femur, tibia, fibula, patella, tarsals, metatarsals, and phalanges.
femur and tibia articulate with each other at the knee.
kneecap is called the patella.
anklebones are tarsals.
bones of the instep of the foot are called metatarsals.
of the toes are called phalanges.
1. A human skull usually
consists of 28 bones.
moveable bone in the skull is the mandible.
cranial and skull bones together form the orbit of the eye.
cranium encloses and protects the brain.
surface of the cranium provides attachments for muscles that make chewing and movements of the head possible.
are air-filled cavities in cranial bones.
reduce the weight of the skull and increase the intensity of the voice by serving as resonant sound chambers.
eight bones of the cranium are 1 frontal bone, 2 parietal bones, 1 occipital bone, 2 temporal bones, 1 sphenoid bone and 1
frontal bone forms the anterior portion of the skull above the eyes, the roof of the nasal cavity and the roofs of the orbits.
supraorbital foramen is on the upper margin of each orbit and allows blood vessels and nerves to pass to tissues of the head.
sinuses of the frontal bone are called frontal sinuses.
two halves of the frontal bone fuse together by the fifth of sixth year of life.
parietal bone is located on each side of the skull behind the frontal bone.
the parietal bones form the sides and roof of the cranium.
sagittal suture fuses the parietal bones.
coronal suture fuses the parietal bones to coronal bones.
occipital bone joins the parietal bones along the lambdoidal suture.
occipital bone forms the back of the skull and the base of the cranium.
foramen magnum is a large opening in the occipital bone through which the brain and spinal cord join.
condyles are located on each side of the foramen magnum.
condyles articulate with the first cervical vertebra.
19. A temporal
bone on each side of the skull joins the parietal bone along a squamosal suture.
temporal bones form parts of the sides and the base of the cranium.
opening leading inward to parts of the ear is called the external auditory meatus.
fossae articulate with condyles of the mandibles.
mastoid process is a site of attachment for certain muscles of the neck.
24. The styloid process is a site of attachment for
muscles of the tongue and pharynx.
carotid canal is near the mastoid process and transmits the internal carotid artery.
jugular foramen is opening between the temporal and occipital bones and accommodates the internal jugular vein.
zygomatic process projects anteriorly from the temporal bone and joins the zygomatic bone.
sphenoid bone helps form the anterior portion of the cranium.
sella turcica is an indention in the middle of the sphenoid bone and holds the pituitary gland.
sinuses of the sphenoid bone are called sphenoidal sinuses.
ethmoid bone is located in front of the sphenoid bone.
consists of two masses joined by cribiform plates.
cribiform plates form the roof of the nasal cavity.
associated with smell pass through olfactory foramina.
of the ethmoid bone also form section of the cranial floor, orbital walls, and nasal cavity walls.
36. A perpendicular
plate projects downward from the cribiform plates to form most of the nasal septum.
plates called superior and middle nasal conchae project inward from the lateral portions of the ethmoid bone.
lateral portions of the ethmoid bone contain many small air spaces called ethmoidal sinuses.
crista galli is triangular process that projects upward and is located between cribiform plates.
crista galli is attached to membranes that enclose the brain.
C. Facial Skeleton
facial skeleton consists of 13 immovable bones and a movable lower jaw bone.
facial bones provide sites of attachment for muscles that move the jaw and control facial expression.
maxillary bones form the upper jaw.
of the maxillary bones also comprise the anterior roof of the mouth, the floors of the orbits, and sides and floor of the
maxillary bones also contain sockets for the upper teeth.
the maxillae, lateral to the nasal cavity are maxillary sinuses.
maxillary sinuses extend from the floor of the orbits to the roots of the upper teeth.
development, portions of the maxillary bones called palatine processes grow together and form the anterior section of the
alveolar arch is a horseshoe shaped collection of alveolar processes.
occupy cavities in this arch.
palatine bones are L shaped.
palatine bones are located behind the maxillae.
horizontal portions of the palatine bones form the posterior section of the hard palate and the floor of the nasal cavity.
perpendicular portions of the palatine bones help form the lateral walls of the nasal cavity.
bones are responsible for the prominences of the cheeks below and to the sides of the eyes.
zygomatic bone has a temporal process that extends posteriorly to join the temporal bone.
zygomatic arch is formed by the zygomatic process of the temporal bone and the temporal process of the zygomatic bone.
bones are located in the medial wall of each orbit.
nasal bones form the bridge of the nose.
nasal bones are attachments for the cartilaginous tissues that form the shape of the nose.
21. The vomer is located along the midline within the
the vomer joins the perpendicular plate of the ethmoid bone.
nasal septum is formed from the vomer and perpendicular plate of the ethmoid.
inferior nasal conchae are attached to the lateral walls of the nasal cavity.
the ethmoidal conchae, the inferior conchae support mucous membranes within the nasal cavity.
mandible is shaped like a horseshoe.
flat projections at the ends of a mandible are rami.
rami are divided into a mandiblar condyle and a coronoid process.
mandibular condyles articulate with the temporal bones.
coronoid processes provide attachment sites for muscles used in chewing.
alveolar border is a curved bar of bone on the superior border of the mandible and it contains the sockets of the lower teeth.
foramens are located near the center of each ramus.
vessels and nerves run through mandibular foramens.
mental foramen is an opening near the point of the jaw.
1. At birth,
the skull is incompletely developed with fibrous membranes connecting the cranial bones.
are membranous areas of an infantile skull.
permit some movement between the bones so that the developing skull is partially compressible and can slightly change shape.
fontanels close and cranial bones grows together.