Download the Skeletal System Notes

(Students: Bolded, italicized, and underlined sections will be on the exam)
The Skeletal System:
I. Function of the System:
The primary functions of the skeletal system are to provide shape and support for
the body, to protect the internal organs, allow for bodily movement, produce
blood cells, and storage of minerals. The average human adult skeleton has 206
bones joined to ligaments and tendons to form a protective and supportive
framework for the attached muscles and the soft tissues which underlie it. This
system allows for many other systems to operate properly while providing a safe
place for the body’s vital organs. The brain is protected by the skull and the heart
and lungs are protected by the sternum and rib cage. The skeleton plays an
important part in movement by providing a series of independently movable
levers, which the muscles can pull to move different parts of the body. Muscles are
attached to bones by tendons and bones are attached to other bones by ligaments.
It also supports and protects the internal body organs. Bone marrow is also
important for the production of red and white blood cells, and platelets. The
bones also are a storehouse of important minerals, including calcium and
phosphorus.
II. The Main Parts of the System:
Types of Bone Tissue: Bones are comprised of two main types of tissue: compact
bone and spongy bone.
A. Compact Bone Tissue: Compact, or dense bone is a hard and forms the
protective outer portion of all bones. It is made of haversian systems, a term
describing the very precise arrangements of osteocytes, matrix, and blood
vessels of bone. The arrangement involves cylinders of bone matrix with
osteocytes in concentric rings around central haversian canals (blood vessels).
The osteocytes (bone cells) are in contact with the blood vessels and with each
other through microscopic channels (canaliculi) in the matrix.
B. Spongy Bone Tissue: Spongy bone is found on the inside of most bones and is
full of tiny holes. It is named for its appearance. The cavities, in the very center
of the bone, often contain red bone marrow, which produces red blood cells
(to carry oxygen), platelets, and five types of white blood cells (to destroy
harmful bacteria).
The Structure of Bone:
Mineral Storage/Salts: The bones are also a storehouse for minerals. All
bone tissue is composed of several types of bone cells embedded in a web of
inorganic salts (a substance mostly containing the minerals calcium and
phosphorus). Phosphorus and calcium are stored in the blood, when supply is
low they are taken from the bones and used to replenish the supply. The
matrix of bone contains calcium salts (calcium carbonate -- CaCO3, and calcium
phosphate -- Ca3(PO4)2), and collagen. These salts give the bone strength and
the collagenous fibers and ground structure give the bones flexibility.
Classification of Bones: The bones of the body fall into four general categories:
long bones, short bones, flat bones, and irregular bones.
A. Long Bones: Long bones are those that are longer than they are wide and
work as levers. They are the bones of the arms, legs, hands, and feet. Bones
such as the humerus, tibia, femur, and ulna are of this type. The shaft is called
the diaphysis (hollow, but made of compact bone to form a canal within the
shaft known as the marrow canal). The ends are called epiphyses (made of
spongy bone covered with a thin layer of compact bone, as are the short, flat,
and irregular bones). The marrow canal, or medullary cavity, contains yellow
bone marrow, which is mostly adipose tissue which gradually replaces the red
bone marrow during aging.
B. Short Bones: Short bones are short, cube-shaped, and found in the wrists and
ankles.
C. Flat Bones: Flat bones have broad surfaces for protection of organs and the
attachment of muscles. They are the bones of the ribs, shoulder blades, hips,
and cranium.
D. Irregular Bones: Irregular bones are all other bones that do not fit into any
other category. They have varied shapes, sizes, and surface features that
include the skull (face) and the vertebrae.
The Main Parts:
Bones, along with cartilage and ligaments, support, protect soft tissues, and stores
minerals. The skeleton is divided into two main parts:
A. Axial Skeleton: The axial skeleton protects and supports the organs of the
neck head and trunk. Specifically, it protects the brain, spinal cord, sensory
organs, and soft tissue of chest cavity. The axial skeleton consists of the skull,
the spine, the ribs and the sternum (breastbone) and includes 80 bones. It
supports the body weight over the legs .
B. Appendicular Skeleton: The appendicular skeleton is comprised of bones that
anchor the appendages to the axial skeleton. It provides internal support and
positioning of arms and legs; supports and moves axial skeleton. The
appendicular skeleton includes two limb girdles (the shoulders and pelvis) and
their attached limb bones. This part of the skeletal system contains 126 bones,
64 in the shoulders and upper limbs and 62 in the pelvis and lower limbs.
Major Bones in the Body:
Main Bones in the Human Body:
A. Axial Skeleton (80 bones):
1. Skull (28):
a) Cranium (8):
1) Frontal bone (1) forms the forehead and the superior surface of the orbits.
2) Parietal bones (2) found on both sides of the skull, posterior to the frontal
bone.
3) Occipital bone (1) forms the posterior and inferior portions of the cranium.
4) Temporal bones (2) are below the parietal bones, contributing to the sides
and base of the cranium.
5) Sphenoid bone (1) forms part of the floor of the cranium.
6) Ethmoid bone (1) found anterior to the sphenoid bone, consisting of two
honeycombed masses of bone.
b) Facial (14):
1) Maxillary bones (2) forms the floor and medial portion of the rim of the orbit,
the walls of the nasal cavity, and the anterior roof of the mouth (hard palate).
2) Zygomatic bones (2) are found on each side of the skull, articulating with the
frontal bone and the maxilla to complete the lateral wall of the orbit. Along
the lateral margin, each gives rise to a slender bony extension that curves
laterally and posteriorly to meet a process from the temporal bone, together
forming the zygomatic arch.
3) Palatine bones (2) form the posterior surface of the hard palate. The superior
surfaces of the horizontal portion of each contributes to the floor of the nasal
cavity. The superior tip of the vertical portion of each forms a small portion of
the inferior wall of the orbit.
4) Mandible (1) forms the lower jaw.
5) Lacrimal bones (2) are located within the orbit on its medial surface and
articulate with the frontal, ethmoid, and maxillary bones.
6) Nasal bones (2) form the bridge of the nose and articulate with the superior
frontal bone and the maxillary bones.
7) Inferior nasal conchae (2) project from the lateral walls of the nasal cavity.
8) Vomer (1). The inferior margin articulates with the paired palatine bones and,
with the ethmoid bone, supports a prominent partition that forms part of the
nasal septum.
!2. Middle Ear (Auditory ossicles) (6):
! a) Malleus (2) attaches at three points to the interior surface of the tympanum
(tympanic membrane).
! b) Incus (2) attaches the malleus to the inner bone (stapes).
! c) Stapes (2) is seated within the "oval window."
!3. Hyphoid Bone:
(1) is U-shaped and hangs below the skull, suspended by ligaments from the
styloid processes of the temporal bones, and serves as a base for muscles
associated with the tongue and larynx.
!4. Vertebral Column (26):
! a) Cervical vertebrae (7) extend from the head to the thorax (C1-C7).
! b) Thoracic vertebrae (12) extend from the cervical portion to the lumbar section
(T1-T12).
! c) Lumbar vertebrae (5) continues from the thoracic vertebrae to the sacrum (L1L5).
! d) Sacrum (1) forms the posterior wall of the pelvis.
! e) Coccyx (1) is one mass of four to five small coccygeal vertebrae that have
fused into one commonly called the "tailbone."
5. Thoracic Cage (25):
! a) True ribs (14) are 7 pairs that reach the anterior body wall, and are connected to
the sternum by separate cartilaginous extensions (costal cartilage).
! b) False ribs (10) are ribs 8-12 that do not attach directly to the sternum. The last
two pairs are floating ribs because they have no connection with the sternum.
! c) Sternum (1) has three parts in the adult. The manubrium articulates with the
clavicles of the appendicular skeleton and with the cartilage of the first pair of
ribs. The body ends at the xiphoid process.
B Appendicular Skeleton (126):
1. Pectoral girdle (4);
a) Scapula (2) is commonly called the "shoulder blade" and is supported and
positioned by the skeletal muscles. It has no bony or ligamentous bonds to the
thoracic cage, but is extremely important for muscle attachment.
b) Clavicle (2) is commonly called the "collarbone" and articulates with the
manubrium of the sternum, and is the only direct connection between the
pectoral girdle and the axial skeleton.
2. Upper Limbs (60):
a) Humerus (2) extends from the scapula to the elbow.
b) Radius (2) lies along the lateral side (or thumb side) of the forearm.
c) Ulna (2) forms the medial support of the forearm.
d) Carpals (16) are 8 pairs of bones of the wrist and are composed of four
proximal bones (scaphoid, lunate, triangular or triquetral, and the pisiform
bone) and four distal bones (trapezium, trapezoid, capitate, and the hamate
bone).
e) Metacarpals (10) are 5 pairs of bones that articulate with the distal carpal bones
forming the palm of the hand.
f) Phalanges (28) From the tip to the first joint, the ‘finger bones’ are called
phalanges. There are 14 pairs of ‘finger’ bones. The four fingers contain
three phalanges while the pollex (thumb) has only two.
3. Pelvic girdle (2) articulates with the thigh bone.
a) Os coxae (2) is commonly called the "hip bone," formed from a fusion of three
bones (ilium, ischium, and pubis).
4. Lower Limbs (60):
a) Femur (2), commonly called the "thigh bone," is the longest, strongest, and
heaviest bone in the body. Distally, it articulates with the tibia at the knee
joint. The head (epiphysis) articulates with the pelvis at the acetabulum.
b) Tibia (2), commonly called the "shinbone," is the large medial bone of the leg,
attached to the patella by a ligament.
c) Fibula (2) parallels the lateral border of the tibia.
d) Patella (2) is the "knee cap."
e) Tarsals (14) include 7 pairs of bones (talus, calcaneus, navicular, cuboid, and the
1st, 2nd, and 3rd cuneiform bones). Only the talus articulates with the tibia and
fibula.
f) Metatarsals (10) support the sole of the foot and numbered I to V from medial to
lateral with the distal ends forming the ball of the foot.
g) Phalanges (28). From the tip to the first joint, the ‘toe bones’ are called
phalanges, and have the same arrangement as with the fingers and thumb,
but only with the toes and great toe (hallux).
5. Important Parts of the Bones of the Shoulder and Arm: (bone; part;
description)
a) Scapula:
1) glenoid fossa (depression that articulates with humerus);
2) spine (long, posterior process for muscle attachment);
3) acromian process (articulates with clavicle).
b) Clavicle:
1) acromial end (articulates with scapula);
2) sternal end (articulates with manubrium of sternum).
c) Humerus:
1) head (articulates with the ulna);
2) olecranon fossa (posterior, oval depression for the olecranon process of the
ulna);
3) capitulum (round process superior to radius);
4) trochlea (concave surface that articulates with ulna).
d) Radius:
1) head (articulates with the ulna).
e) Ulna:
1) olecranon process (fits into olecranon fossa of humerus);
2) semilunar notch (half-moon depression that articulates with the trochlea of
ulna).
f) Carpals:
1) Scaphoid, Triquetrum, Lunate, and Pisform (proximal row);
2) Trapezium, capitate, trapezoid, and hamate (distal row).
6. Important Parts of Bones of the Hip and Leg: (bone; part; description)
a) Pelvic (hip bones):
1) ilium (flared upper portion);
2) iliac crest (upper edge of ilium);
3) posterior superior iliac spine (posterior continuation of iliac crest);
4) ischium (lower, posterior portion);
5) pubis (anterior, medial portion);
6) pubic symphysis (joint between the two pubic bones).
b) Femur:
1) head (round process that articulates with hip bone);
2) neck (constricted portion distal to head);
3) greater trochanter (large lateral process for muscle attachment);
4) lesser trochanter (medial process for muscle attachment);
5) condyles (rounded processes that articulate with tibia).
c) Tibia:
1) condyles (articulates with femur);
2) medial malleolus (distal process - the medial "ankle bone").
d) Fibula:
1) head (articulates with tibia);
2) lateral malleolus (distal process -- the lateral "ankle bone").
e) Tarsals (7):
1) calcaneus (heel bone);
2) talus (articulates with calcaneus and tibia);
3) cuboid, navicular;
4) cuneform: 1st, 2nd, 3rd.
7. Parts of the Bones of the Skull:
a) Frontal:
1) Frontal sinus (air cavity that opens into the nasal cavity);
2) Coronal suture (joint between frontal and parietal bones).
b) Parietal:
1) sagittal suture (joint between the two parietal bones).
c) Temporal:
1) squamosal suture (joint between temporal and parietal bone);
2) external auditory meatus (the ear canal);
3) mastoid process (oval projection behind the ear canal);
4) mastoid sinus (air cavity that opens into the middle ear);
5) mandibular fossa (oval depression anterior to the ear canal; articulates with
mandible).
d) Occipital:
1) foramen magnum (large opening for the spinal cord);
2) condytes (oval projections on either side of foramen magnum that articulates
with the atlas);
3) lambdoidal suture (joint between occipital and parietal bones).
e) Sphenoid:
1) greater wing (flat, lateral portion between the frontal and temporal bones);
2) sella turcica (central depression that encloses the pituitary gland);
3) sphenoid sinus (air cavity that opens into the nasal cavity).
f) Ethmoid:
1) ethmoid sinus (air cavity that opens into nasal cavity);
2) crista galli (superior projection for attachment of meninges;
3) cribriform plate and olfactory foramina (on either side of base of crista galli;
olfactory nerves pass through foramina).
4) perpendicular plate (upper part of nasal septum);
5) conchae - four are part of ethmoid and two inferior are separate bones (shelflike projections into nasal cavities, which increase surface area of nasal
mucosa).
g) Mandible:
1) body (U-shaped portion with lower teeth);
2) condyles (oval projections that articulate with the temporal bones);
3) sockets (conical depressions that hold roots of lower teeth).
h) Maxilla:
1) maxillary sinus (air cavity that opens into nasal cavity);
2) palatine process (projection that forms anterior part of hard palate);
3) sockets (conical depressions that hold roots of upper teeth).
i) Nasal bones forms the bridge of the nose.
j) Lacrimal:
1) lacrimal canal (opening for nasolacrimal duct to take tears to nasal cavity).
k) Zygomatic bones form point of cheek and articulates with frontal, temporal and
maxillae bones.
l) Palatine bones form the posterior part of the hard palate.
m) Vomer forms the lower part of the nasal septum.
Joints and Movement:
There are two main types of joints. Movable (which move) and Immovable
(which are rigid and do not allow movement). An example of an immovable
joint can be found in your skull where the piece of bone are ‘fused’ together.
Movable joints are found at your hips, elbows, and your knees. Your skull is
made of joints that are hard and compact. These joints are called fixed joints. Ball
and socket joints are found in the hip and let you move more flexibly. Gliding
joints are found in your wrist and help you turn and move the wrist up and down.
Hinge joints are like doors and only let you bend to an extent. Hinge joints are
found in your elbows and knees. Finally, the pivot joints let you side to side, and
up and down. These joints are found the Vertebrae which protect the nerve cord.
III. Interaction with Other Systems:
The skeletal system interacts with all of the body’s systems, as it provides overall
structural support and protection to the body. Systems that interact most closely
with the skeletal system include:
• The Circulatory System: The marrow creates red and white blood cells, and
platelets.
• The Muscular System: The muscles attach to bones to allow for movement.
• IV. Some Diseases and Disorders:
• Bursitis is a disorder that causes pain in the body's joints. It most commonly affects
the shoulder and hip joints. It is caused by an inflammation of the bursa, small
fluid-filled bags that act as lubricating surfaces for muscles to move over bones.
This inflammation usually results from overactivity of an arm or leg. Antiinflammatory drugs may provide some relief of discomfort.
• Osteoporosis is a disease resulting in the loss of bone tissue. In osteoporosis, the
cancellous bone loses calcium, becomes thinner, and may disappear altogether.
Treatment may include mineral supplements and hormonal treatment.
• A sprain is an injury to a ligament or to the tissue that covers a joint. Most sprains
result from a sudden wrench that stretches or tears the tissues of the ligaments. A
sprain is usually extremely painful. The injured part often swells and turns black
and blue. Rest, and sometimes physical therapy are needed for recovery.
• A fracture is a broken bone. There are some many classifications of fractures:
Restriction of movement (affected area placed in a splint or cast), rest, mineral
supplements, and sometimes physical therapy are needed for recovery.
• Spina bifida is a spinal defect that is present at birth. In spina bifida, the spinal cord
does not form properly and the vertebrae and skin cannot form around it. Spina
bifida results from an error in the development of the embryo that occurs about a
month after a woman becomes pregnant. This error may have various causes,
including the use of alcohol or certain medications by the pregnant woman or
exposure to extreme heat. Genetic factors appear to be very important. No cure.
V. Other Facts:
Babies are born with 270 soft bones - about 64 more than an adult; and many of
these will fuse together by the age of twenty or twenty-five into the 206 hard,
permanent bones.
There are only minor differences between the skeletons of the male and the female:
the men's bones tend to be larger and heavier than corresponding women's bones
and the women's pelvic cavity is wider to accommodate childbirth.
Hormones involved in bone growth:
a) GH (growth hormone); anterior pituitary gland; increases the rate of mitosis of
chondrocytes and osteoblasts, and increases the rate of protein synthesis (collagen,
cartilage matrix, and enzymes for cartilage and bone formation).
b) Thyroxine; thyroid gland; increases the rate of protein synthesis and increases
energy production from all food types.
c) Insulin; pancreas; increases energy production from glucose.
d) Parathyroid hormone; parathyroid glands; increases the reabsorption of calcium
from bones to the blood, thereby raising blood calcium levels and increases the
absorption of calcium by the small intestine and kidneys.
e) Calcitonin; thyroid gland; decreases the reabsorption of calcium from bones
thereby lowering blood calcium levels.
f) Estrogen or Testosterone; ovaries or testes; promotes closure of epiphyses of
long bones, thereby stopping growth, and helps retain calcium in bones, thereby
maintaining a strong bone matrix.