Skeletal System

McCaskill - ICS

“No bridge was ever built with girders like this! The bones in our bodies aren’t just strong and flexible,

they’re constantly building and repairing themselves.”

“As you do not know what is the way of the wind, or how the bones grow in the womb of her who is with child, so you do not know the

works of God who makes everything” (Ecclesiastes 11:5).

In biology, the skeleton or skeletal system is the biological system

providing physical support in living organisms.

Internal skeletonsAn internal skeletal system consists of rigid (or semi-rigid) structures, within the body, moved by the muscular system (attachment). If the

structures are mineralized or ossified, as they are in humans, they are referred to as bones .

Cartilage is another common component of skeletal systems, supporting and

supplementing the skeleton. The bones or other rigid structures are connected by

ligaments and connected to the muscular system via tendons.

The most obvious function of bone is to (1)support the body. It is also the site of (2)hematopoiesis, the manufacture of blood cells, that takes place in bone marrow (which is why bone marrow cancer is very often a terminal disease). It is also necessary for (3)protection of vital organs. Bone also serves as a (4)mineral storage deposit in which nutrients can be stored and retrieved. All of the cellular components of the blood are derived from hematopoetic stem cells.

All blood cells are divided into three lineages.

1. Erythroid cells are the oxygen carrying red blood cells. 2. Lymphoid cells are the

cornerstone of the immune system. The lymphoid lineage is

primarily composed of T-cells and B-cells. (white blood cells)

3. Myeloid lineage which includes granulocytes, megakaryocytes,

and macrophages (Platelets). The myeloid lineage is involved in such diverse roles as innate immunity,

adaptive immunity, and blood clotting.

Bone marrow (or medulla ossea) is the soft tissue found in the hollow interior of bones. It is the place where most new blood cells are produced

There are two types of bone marrow: red marrow (also known as myeloid tissue) and yellow marrowyellow marrow.

Red Blood Cells, platelets and most white blood cells arise in red marrow; some white blood cells develop in yellow marrow.

The color of yellow marrow is due to the much higher number of fat cells. Both types of bone marrow contain numerous blood vessels and capillaries.

An osteocyte, a star-shaped cell, is the most abundant cell found in bone. Osteocytes are networked to each other via

long processes called Canaliculi, which are used for exchange of nutrients and waste. The space that an

osteocyte occupies is called a lacuna (Latin for a pit). Their main function involves maintaining the bone tissue.

An osteoblast (from the Greek words for “bone" and "germ" or embryonic) is a mononucleate cell that is responsible for bone formation. Osteoblasts are responsible for mineralization of the osteoid matrix. Bone is a dynamic tissue that is constantly being

reshaped by osteoblasts, which build bone.

An osteoclast (from the Greek words for "bone" and

"broken") is a type of bone cell that removes bone tissue by

removing the bone's mineralized matrix.

Osteoclasts and osteoblasts are instrumental in controlling

the amount of bone tissue. Osteoblasts form bone;

osteoclasts resorb bone.

Haversian canals are a series of tubes around narrow channels.

Osteons are arranged in parallel to the long axis of the bone. The

Haversian canals surround bloods vessels and nerve cells

throughout the bone and communicate with osteocytes in

lacunae (spaces within the dense bone matrix that contain the

living bone cells) through canaliculi. This unique

arrangement is conducive to mineral salt deposits and storage

which gives bone tissue its strength.

In its most common use, a ligament is a short band of tough fibrous connective tissue composed mainly of long, stringy collagen fibers. Ligaments connect bones to other bones to form a joint.

Ligaments are slightly elastic; when under tension, they

gradually lengthen. The term double-jointed refers to people

who have more elastic ligaments, allowing their joints to stretch and contort further. The

medical term for describing such double-jointed persons is hyperlaxity.The study of

ligaments is known as desmology.

The anterior cruciate ligament (or ACL) connects from a posterio-lateral (back &

outside) part of the femur to an anterio-

medial (front & inside) part of the

tibia. These attachments allow it

to resist forces pushing the tibia

forward relative to the femur.

Other Knee ligaments for Identificationlateral collateral ligament (or LCL) posterior cruciate ligament (or PCL) medial collateral ligament (or MCL)

Tendon (or sinew) is a tough band of fibrous connective tissue that connects muscle to bone, or muscle to muscle and is designed to withstand tension. Tendons and muscles work together and can only exert a pulling force.

Tendonitis Tendonitis refers to refers to inflammation of a inflammation of a

tendon.tendon.

The Achilles tendon is a particularly large tendon

connecting the heel (calcaneus) to the

gastrocnemius (calf) muscle.

Types of jointsIn Fibrous joints bones are joined by tight and inflexible layers of dense connective tissue, consisting mainly of collagen fibers. In adults, these are not designed to allow any movement; however, in children, fibrous joints have not solidified and are movable. Examples of fibrous joints are:•Cranial sutures, joining the bones of the cranium (See slide in later section).

In cartilaginous joints bones are connected entirely by cartilage. Cartilaginous joints allow only slight movement. Examples of cartilaginous joints are the joints between the ribs and the sternum, the cartilage connecting the growth region of immature long bones and the spinal column - the cartilaginous region between adjacent vertebrae.

Synovial joints are the most common and most moveable type of joints in the body. There are 6 types of synovial joints (see next slide).

Synovial joints can be further grouped by their shape, which controls the movement they allow.

1.Ball and Socket joints, such as the shoulder and hip joints. These allow a wide range of movement. 2.Condyloid joints (or ellipsoid), such as the thumb. A condyloid joint is where two bones fit together with an odd shape (e.g. an ellipse), and one bone is concave, the other convex. 3.Saddle joints, such as at the thumb (between the metacarpal and carpal). Saddle joints, which resemble a saddle, permit the same movements as the condyloid joints. 4.Hinge joints, such as the elbow (between the humerus and the ulna). These joints act like a door hinge, allowing flexion and extension in just one plane.

5. Pivot joints, such as the elbow (between the radius and the ulna). This is where one bone rotates about another.

6. Gliding joints, such as in the carpals of the wrist. These joints allow a wide variety of movement, but not much distance.

Cancellous bone (or spongy bone) is a spongy type of bone with a very high surface area, found at the ends of long bones. The spongy bone contains red bone marrow where hematopoises, the production of blood cellular components, takes place. The cancellous is the place where most of the arteries and veins of the bone are found.

Cortical bone (compact bone) is one of two main types of bone. Cortical bone is dense and forms the surface of bones. It

is also known as compact bone.

The endosteum is a thin layer of connective tissue which lines the surface of the medullary cavity of long bones.

The periosteum is a thin layer of connective tissue that covers the outer surface of a bone in all places except at joints.

Diaphysis, shaft

The long, relatively straight main body of the bone; region of primary ossification.

epiphyses The end regions of the bone; regions of secondary ossification.

epiphyseal plate, growth plate

The thin disc of hyaline cartilage between the diaphysis and epiphyses; disappears by twenty years of age.

head The proximal articular end of the bone.

neck The region of bone between the head and the shaft.

Several terms are used to refer to

specific features of long bones:

The skeleton is not unchanging; it changes

composition over a lifespan. Early in gestation, a fetus

has no hard skeleton; bones form gradually during nine months in the womb. At birth, all bones will have

formed, but a newborn baby has more bones than an

adult. On average, an adult human has 206 bones, but

a baby is born with approximately 300 bones.

Skeletal System and Embryonic Development

A 10mm embryo from an ectopic pregnancy, still in the oviduct. This embryo is about five weeks old (or from the 7th week of pregnancy).

Endochondral ossification occurs in long bones, such as limbs; the bone is formed from cartilage. The steps in endochondral ossification are:1.Development of cartilage model 2.Growth of cartilage model 3.Development of the primary ossification center (They mostly appear during fetal development, though a few short bones begin their primary ossification after birth. They are responsible for the formation of the diaphyses of long bones, short bones and certain parts of irregular bones). 4.Development of medullary cavity 5.Development of the secondary ossification center (Secondary ossification occurs after birth, and forms the epiphyses of long bones and the extremities of irregular and flat bones). 6.Formation of articular cartilage and epiphyseal plate

3.

1.

2.

5.6.4.

The diaphysis and both epiphyses of a long bone are

separated by a growing zone of cartilage (the epiphyseal plate). When the child reaches skeletal maturity (18 to 25 years of age), all of the cartilage is replaced by bone, fusing the diaphysis and

both epiphyses together (epiphyseal closure).

Bone pathologies

One of the most common bone

illnesses is a bone fracture. Bones heal by natural processes,

but untended and unsupported can lead

to misgrown bone.Other illnesses are osteoporosis, and

bone cancer (osteosarcoma). The joints can be affected

by arthritis.

Osteoporosis is a disease of bone in which the bone mineral density (BMD) is reduced. Osteoporotic bones are more susceptible to fracture.

Arthritis (from Greek arthro-, joint + -itis, inflammation) is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability over the age of 65.

In general, male skulls tend to be larger and more robust than female skulls, which are more gracile. Male skulls typically have more prominent supraorbital ridges (brow), and more prominent temporal lines. Male skulls on average have larger mastoid processes, and larger occipital condyles than those of females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles.

All of these features vary considerably within human populations, making it difficult to identify the sex of a skull without knowledge of the population it came from. The pelvis is considered the best skeletal indicator of sex, due to the fact that the female pelvis must allow for a baby to exit.

Sexual dimorphism in human skeletons

Female → ← Male

Several terms are used to refer to features and components of bones:

Process A relatively large projection or prominent bump.

articulation The region where adjacent bones contact each other—a joint.

articular process

A projection that contacts an adjacent bone.

eminence A relatively small projection or bump.

tuberosity A projection or bump with a roughened surface.

tubercle A projection or bump with a roughened surface, generally smaller than a tuberosity.

trochanter One of two specific tuberosities located on the femur.

spine A relatively long, thin projection or bump.

suture Articulation between cranial bones.

malleolus One of two specific protuberances of bones in the ankle.

condyle A large, rounded articular process.

epicondyle A projection near to a condyle but not part of the joint.

line, ridge A long, thin projection, often with a rough surface.

crest A prominent ridge.

facet A small, smooth articular surface.

foramen An opening through a bone.

fossa A broad, shallow depressed area.

canal A long, tunnel-like foramen, usually a passage for notable nerves or blood vessels.

meatus A short canal.

sinus A cavity within a cranial bone.

The axial skeleton consists of the bones in the head and trunk of the human body. It is composed of five parts; the human skull, the ossicles of the inner ear, the hyoid bone of the throat, the chest, and the vertebral column.

The appendicular skeleton is the part of the skeleton that includes the pectoral girdle, the upper limbs, the pelvic girdle, and the lower limbs. The appendicular skeleton, consisting of 126 bones, makes body movement

possible and protects the organs of digestion, excretion, and reproduction. The word appendicular means referring to an appendage or anything

attached to a major part of the body, such as the upper and lower extremities.

In humans, the adult skull is normally made up of 29 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, semi-rigid articulations formed by bony ossification. Sutures:

Primarily visible from the side (norma lateralis)Coronal suture- between the frontal and parietal bones Lambdoidal suture - between the parietal bones and the occipital boneSquamosal suture - between the parietal and the temporal bone

Primarily visible from front (norma frontalis) or above (norma verticalis)Frontal suture - between the two frontal bones, prior to the fusion of the two into a single bone Sagittal suture - along the midline, between parietal bones

Skull

Cranial bones: Identification1. Frontal boneA. Supraorbital

Foramen2. Parietal bone (2) 3. Temporal bone (2)

A. Tympanic part of temporal

B. External acoustic (auditory)meatus and internal auditory meatus

C. Zygomatic ProcessD. Styloid processE. Mandibular cavityF. Mastoid Process

Mastoid process

The Frontal is one of the bones that make of the orbit!

4. Occipital bone A. Foramen Magnum

B. Occipital CondyleC. Superior and Inferior Nuchal lines

Inferior nuchal line

Superior nuchal line

F.M.O.M

*Sphenoid Bone

A. Lateral and Medial Pterygoid platesB. Optic CanalC. Foramen rotundumD. Foramen ovaleE. Foramen spinosum

*Ethmoid bone A. Cribriform plate

The Ethmoid is one of the bones that make of the orbit!

The Spenoid is one of the bones that make of the orbit!

Facial bones:Facial bones:

5. Zygomatic bone(2) 6. superior and inferior maxilla – the largest bone of the face

A. Infraorbital foramen9. Nasal bone (2)

The Maxilla is one of the bones that make of the orbit!

7. mandible A. mental foramenB. mandibular foramenC. Coronoid processD. Condyle process- fits into the articular fossa of the temporal bone (between the two there is articular cartilage)

*Palatine bone(2)

Facial bones:

mental foramen

Coronoid processCondyle process

*lacrimal bone(2) – the smallest bone of the face *vomer *inferior nasal conchae(2)

In the middle ears (6):*malleus(2) *incus(2) *stapes(2) In the throat (1):*hyoid bone

Smallest bones of the body!

In human anatomy, a fontanelle is one of two "soft spots" on a newborn human’s skull. The skull of a newborn consists of five main bones: two frontal bones, two parietal bones, and one occipital. These are joined by fibrous sutures, which allow movement that facilitates childbirth and brain growth.At birth, the skull features a small posterior fontanelle (occipital) where the two parietal bones adjoin the occipital bone. This fontanelle usually closes during the first several months of an infant's life.There is also a much larger, diamond-shaped anterior fontanelleanterior fontanelle (frontal) (frontal) where the two frontal and two parietal bones join. This fontanelle remains open until the child is about two years of age. Two other fontanelles are the sphenoidal fontanelle and the mastoid fontanelle

The anterior fontanelle is useful clinically. A sunken fontanelle indicates dehydration, whereas a very tense or bulging anterior fontanelle indicates raised intracranial pressure.

In the thorax (25):10. sternum is a long, flat bone

located in the center of the thorax (chest). It connects to the rib bones via cartilage, forming the rib cage with them, and thus helps to protect the lungs, heart and major blood vessels from

physical trauma. A. ManubriumB. BodyC. Xiphoid Process

28. ribs (2 x 12) protect the lungs, heart, and other internal organs. Humans (both male and female) have 24 ribs (12 sets, the first 7 are true ribs, 8-10 are attached

to the cartilage of the7th and are considered false ribs, 11th and 12th are free or floating ribs).

Manubrium

Body

Xiphoid Process

10.

7.

6.

5.

4.

3.

2.

1.

8.

9.

11.

12.

In the vertebral column (26):8. Cervical vertebrae (7) incl. atlas & axis are the smallest of the true vertebrae, and can be readily distinguished from other vertebrae by the presence of a foramen (hole) in each transverse process, through which passes the vertebral artery. 14. Lumbar vertebrae (5) are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen (hole) in the transverse process, and by the absence of facets on the sides of the body.

*Thoracic vertebrae (12) increase in size as one proceeds down the spine, the upper vertebrae being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs.

In the shoulder girdle (4):25. clavicle or collarbone (2) is classified as a long bone that makes up part of the shoulder girdle (pectoral girdle).

A.Articulation with scapulaB. Articulation with sternum (manubrium)

29. scapula or shoulder blade (2) is the bone that connects the humerus (arm bone) with the clavicle (collar bone).

A. coracoid processB. AcromionC. Glenoid Cavity (Fossa)D. Scapular spine

In the arms (6):11. humerus (2)

A. headB. greater tubercle C. lesser tubercleD. neckE. bodyF. Olecranon FossaG. Coronoid FossaH. CapitulumI. Trochlea

J. Medial EpicondyleK. Lateral Epicondyle

Posterior – Humerus (R) - Anterior

12. Ulna (2) A. olecranon process –

fits into the olecranon fossa of the humerus.

B. coronoid process – fits into the coronoid fossa of the humerus

C. semilunar notch – articulates with humerus (trochlea)D. radial notch E. bodyF. styloid Process – articulates with radius

13. Radius (2) A. Radial TuberosityB. Head– articulates with the ulnaC. BodyD. Styloid Process –

articulates with wrist (carpals)

Proximal: A=Scaphoid, B=Lunate, C=Triquetral, D=PisiformDistal: E=Trapezium, F=Trapezoid, G=Capitate, H=Hamate

In the hands (54):Wrist (carpal) bones:

Scaphoid bone (2) Lunate bone (2) Triquetrum bone (2) Pisiform bone (2) Trapezium bone (2) Trapezoid bone (2) Capitate bone (2) Hamate bone (2)

Palm or metacarpal bones: *Metacarpal bones (5 × 2) Finger bones or phalanges: *Proximal phalanges (5 × 2) *Intermediate phalanges (4 × 2) *Distal phalanges (5 × 2)

The sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the tailbone or coccyx.

The coccyx, commonly referred to as the tailbone, is the final segment of the human vertebral column, of three to five (usually four) fused vertebrae (the coccygeal vertebrae), below the sacrum. It provides an attachment for muscles, such as the gluteus maximus, and serves as something of a shock absorber when the person sits down

The pelvis is the bony structure located at the base of the spine The pelvis incorporates the socket portion of the hip joint for each leg. It forms the lower limb girdle of the skeleton. The pelvis is formed of three bones: the ilium, ischium and pubis.

The Acetabulum - Articulation with Femur

In the legs (8):18. femur (2) The femur or thigh bone is the longest, most voluminous, and strongest bone of the human body. It forms part of the hip and part of the knee.

A. Head –articulates with the acetabulum of the pelvis bone.B. 22 Greater TrochanterC.Lesser TrochanterD. BodyE. NeckF. Lateral condyleG. Medial condyle

17. Hip joint (joint, not bone) (2) 19. patella (2) The patella or kneecap is a thick, triangular bone which articulates with the femur and covers and protects the front of the knee joint.

20. Tibia (2) The tibia or shin bone, in human anatomy, is found medial (towards the middle) and anterior (towards the front) to the other such bone, the fibula. It is the second-longest bone in the human body. The tibia articulates with the femur and patella superiorly, the fibula laterally and with the ankle inferiorly.

A. Lateral condyleB. Medial condyleC. Tibial TuberosityB. BodyC.Medial Malleolus –articulates with Talus

21. Fibula (2) The fibula or calf bone is a bone placed on the lateral side of the tibia, with which it is connected above and below.

A. Lateral Malleolus – articulates with Talus

In the feet (52):Ankle (tarsal) bones: the tarsi are the cluster of bones in the foot between the tibia and fibula and the metatarsus. The bones of the tarsus do not belong to individual toes, whereas those of the metatarsus do. The joint between the tibia and fibula and the tarsus is called the ankle.

*calcaneus (heel bone) (2) *talus (2) articulates with tibia and fibula

*navicular bone (2) *medial cuneiform bone (2) *intermediate cuneiform bone (2) *lateral cuneiform bone (2) *cuboidal bone (2)

Instep bones: Metatarsal bones (5 × 2)

Toe bones: Proximal phalanges (5 × 2) Intermediate phalanges (4 × 2) Distal phalangesDistal phalanges (5 × 2)

Added Skull References

Most images on this PowerPoint presentation are from the online edition of Gray’s Anatomy and are public domain because the copyright

has expired.

        

These plates are from Gray’s Anatomy. Unless stated otherwise, it is from the online edition of the 20th U.S. edition of Gray's Anatomy of the Human Body, originally published in 1918.