Skeletal system- a brief study
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The skeletal system consists of 206 bones that fulfill six key functions, including protection of organs, support, muscle attachment, movement, blood cell production, and mineral storage. It is divided into two main parts: the axial skeleton, which includes 80 bones such as the skull, vertebral column, and rib cage, and the appendicular skeleton, which has 126 bones comprising the limbs and pelvis. The document outlines the anatomy and classification of bones, joints, and cartilage, emphasizing their roles and structure in the human body.
Skeletal system- a brief study
- 1. The 206 bones of the skeletal system carry out six important anatomic and physiologic functions: They protect internal tissues and organs; for example, the 33 vertebrae surround and protect the spinal cord, brain, and heart. They stabilize and support the body. They provide surfaces for muscle, ligament, and tendon attachment. They move through lever action when contracted. They produce red blood cells (RBCs) in the bone marrow (a process called hematopoiesis, from the Greek haima, or blood, and poiesis, meaning making or forming). They store mineral salts; for example, approximately 99% of the body’s calcium. SKELETAL SYSTEM Anatomy of the skeleton JUST THE FACTS In this chapter, you will learn: - Terminology related to the anatomy of the skeletal system - Terminology needed for the examination of the skeletal system - The important functions of the skeletal system
- 2. Bones-r-us Theskeletonisdividedintotwoparts:theaxial(from theLatinaxis, meaningaxle or wheel) and appendicular (from the Latin appendare, meaning to add or append). The axialskeleton forms the body’sverticalaxis andcontains74bonesin theheadandtorso;italsoincludes6bonesofthemiddleear,foratotalof 80bones. (See the body’sbones.) Below is a list of key terms, along with the correct way to pronouncethem. Calcaneus Kal-kay-nee-uhs Coccyx Kok-siks Hematopoiesis Hee-muh-toe-poy-ee-sis Occipital Ok-sip-uh-tuhl Periosteum Per-ee-os-tee-uhm Xiphoid process Zeye-foyd Prah-sess
- 3. Anatomically speaking Thebody’sbones Thehumanskeleton contains 206bones; 80 form the axial skeleton and 126 form the appendicularskeleton.Theillustrationsbelow showsomeof themajorbones andbonegroups.
- 4. The appendicular skeleton contains 126 bones and includes the body’s appendages, or upper and lower extremities The axial skeleton The axial skeleton forms the long axis of the body and includes bones of the skull, vertebral column, and rib cage. The skull The skull contains 28 irregular bones in two major areas: the brain case, or cranium (from the Greek kranion, meaning upper part of the head), and the face. Eight bones form the cranium, 14 bones make up the face, and the inner ears contain 6 ossicles (from the Latin ossiculum, meaning bone), or 3 small bones in each ear. The jaw bone, or mandible (from the Latin mandibula, meaning jaw) is the only movable bone in the skull. (See Bones of the skull.) Getting it together Sutures are immobile joints that hold the skull bones together. The coronal suture unites the frontal boneand the two parietal bones. In infants, this suture isn’t closed, leaving a diamond-shaped area (called the anterior fontanel), which is covered only by a membrane. This soft spot closes between ages 10 and 18 months. At the back of the head of infants, the posterior fontanel closes by age 2 months. A real airhead Sinuses are air-filled spaces within the skull that lessen the bone weight, moisten incoming air, and act as resonating chambers for the voice. Up front The sinuses, the forehead, and the area directly behind it are part of the frontal bone. This bone also forms the orbits (eye sockets) and the front part of the cranial floor. Fontanel, also spelled fontanelle,derives from French and means little fountain. Itcanalsorefer to any membrane- covered area between twobones.
- 5. Take it from thetop The main part of the skull consists of a number of bones sutured together: • The coronal suture connects the frontal bone with the parietal bones. • Two parietal bones crown the head, forming the roof and the upper part of each side of the skull. • The squamous suture connects the parietal bones with the temporal bones. • Temporal bones form the lower part of the sides of the skull and part of its floor. They contain structures of the middle and inner ear and the mastoid sinuses. Anatomicallyspeaking Bonesoftheskull The skull is a complexbonystructure. It’sformedby twosetsof bones, the cranial bonesand thefacial bones
- 6. • The lambdoid suture connects the parietal bones to the occipital bone. • The occipital bone forms the rear portion and the base of the skull and forms a movable joint with the first cervical vertebra. • A large opening at the base of the occipital bone, called the foramen magnum (meaning large hole), allows the spinal cord to pass from the encephalon into the spine. A bat in the belfry The sphenoid bone looks like a bat with outstretched wings and legs extended to the back. Located in the cranial floor, this bone is an anchor for the frontal, parietal, occipital, and ethmoid bones. It also supports part of the eye sockets and forms the lateral walls of the skull. The sphenoid sinuses are large air-filled spaces within the sphenoid bone. Facial bones The bones of the face include: • two maxillary bones that form the upper jaw, nose, orbits, and roof of the mouth as well as the maxillary sinuses • the cheekbones, called zygomatic or malar bones, that attach to chewing muscles •two nasal bones that form the upper part of the bridge of the nose (cartilage forms the lower part) • the mandible that forms the lower jaw •two lacrymal bones that contain the lacrymal bag (part of the conduit through which tears drain in the nasal cannula) • the vomer that’s part of the nasal septum •two palatine bones that form the posterior portion of the hard palate, lateral side of the nasal cavity, and small part of the orbit. jogger As a way to remember the bones of the skull,useyourhead and think “part of man”: PARietal Occipital Frontal MAlar Nasal. Jointsbetween the vertebrae allow forward, backward, and sideways movement. Not all at once, though!
- 7. The spinal column The flexible spinal column contains 24 vertebrae (plural of vertebra), the sacrum, and the coccyx. (See Some thorny words of the spine.) Joints between the vertebrae allow forward, backward, and sideways movement. The spinal column supports the head while suspending the ribs and organs in Spine comesfromtheLatinwordspina,whichmeansthorn, and is related to spike as well. Latin writers likened the thorn to the prickly bones in animals and fish and, thus, the word alsobe- camethedesignationforthevertebralcolumn. AlsofromLatin,vertebraderivesfromaverbmeaningtoturn. Therefore,itformerlyconnotedanyjoint—notjustthoseofthe spine. A Greek word, spondylos,has thesame meaning as verte- bra.Itshowsup inwordslikespondylitis,which is an inflammationofthevertebrae. Sacrum and coccyxbringing up therear Thesacrumwasformerlyknown astheossacrum,literally the holybone, so called because it was thought to be a particularly choice bit and so was offered to the gods in sacrifice. The coc- cyx derives its name from the Greek word for the cuckoo, kokkyx.The Greek anatomist Galen thought this triangularbone resembledthe shape of the bird’sbill.
- 8. front. It also anchors the pelvic girdle and provides attachment points for many important muscles. The spinal column contains: •seven cervical (neck) vertebrae, which support the skull and rotate •twelve thoracic (chest) vertebrae, which attach to the ribs •five lumbar (lower back) vertebrae, which support the small of the back • the sacrum, a single bone that results from the fusion of five vertebrae and attaches to the pelvic girdle •the coccyx, or tailbone, which is located at the bottom tip of the spinal column and is a single bone formed from the fusion of four or five vertebrae. The spinal column is curved to increase its strength and make balance possible in an upright position. The vertebrae are cushioned by intervertebral disks composed of cartilage.
- 9. The33 vertebrae of thespinalcolumn surroundandprotectthe spinalcord.They’re divided into fivesections: cervical vertebrae, thoracic vertebrae, lumbarvertebrae, sacrum, andcoccyx. Yep. I have 33 vertebrae----and they’re all perfect specimens, if I do say so myself
- 10. Sternum Located in thecenter of thechest, thesternum is a flat, sword-shapedbonethat’s attached totheclavicles (collar- bones) andtheinnermostpart ofthefirsttwopairs ofribs. Cagedin Thesternum,ribs,andthoracicvertebraeformaprotectiveenclosurearoundthe vitalorgans.Knownasthe thoracic cage, or thorax, this flexible structure protects theheartandlungsandallowsthelungstoexpandduring respiration. Ribs Theflat,curvedbonesattachedtothethoracicportion of thespinalcolumnarecalledribs. Ribs—true or false? Thetermcostalrefers toribs. Thefirstsevenpairs of ribs are attached tothesternum by costal cartilage; they’re called true ribs.Theremainingfivepairs of ribsare called falseribs becausetheyaren’tattached directly to the sternum.All ribsare independently attached to the spinalcolumn. Appendicularskeleton Theappendicular skeletonincludestheupper andlower extremities. Theupperextremities The clavicles, or collarbones, are twoflat bones at- tachedtothesternumontheiranteriorsideandtothe scapulae(shoulderblades)laterally.Thisformsthe sternoclavicular joint. Thescapulaeareapairoflarge,triangularbonesthat arelocatedatthebackofthethorax.Thesebones,plus the clavicles, form theshoulder girdles. Armed and dangerous Thehumerus,orupperarmbone,isalongbonewitha shaftandtwobulbousends.Thetwolongbonesofthe lower armaretheulna,located on thelittlefinger side of thehumerus,andtheradius,onthethumbside. These The ulna andthe radius articulate with the humerus toform the elbow joint
- 11. bones articulate with the humerus to form the elbow joint. The wrists are composed of eight small, irregular carpal bones aligned in two rows. Ligaments bind the carpals together. Anatomically speaking Bones of the hand A view of the right hand, illustrating the positions of the carpals, metacarpals, and phalanges.
- 12. A handful of terms Thebones ofthehandare comprisedofmetacarpal bonesandphalanges.(SeeBones ofthe hand.) Thewaythesebonescometogetherenablesmove- mentofthehand • Fivesmalllongmetacarpalbonesattachtothecarpals andformthepalmofthehand. Phalanges, or fingerbones,are miniaturelong bones. Eachfingerhas threephalanges, whilethethumbhastwo. • Thethumbmetacarpalhasafreelymovablejoint,allow- inga widerange ofmovementbetweenthethumbmeta- carpalandthetrapezium,thecarpalatthebaseofthe thumb. Lowerextremities Thelowerextremitiescontainbonesofthehip,thigh,leg, ankle,and foot. Girdlewords Three pairs of bones fuseduringchildhood to form the pelvic girdle, the broadest bone in the body. This bone supportsthe trunk, protectsthe abdominalorgans within its basin,andattaches thelowerextremities to thebody. The three pairs of fusedbones include the ilium, which isthelargestanduppermostofthethree;theischium,the lowerandstrongestsetofbones;and thepubis,apairof anteriorbonesthatmeetatthesymphysispubis—acar - tilaginousjoint. Give’emaleg up Thetwofemurs,orupperlegbones,arethelongestand heaviestbonesinthebody.Theyconnectattheproximal endwith thehip,articulating with theacetabulum, or hipsocket.Thefemurs connectwiththetibiaatthedis- talend.Thekneecap, orpatella,isasmall,flatbonethat protects the kneejoint andoverlaps thedistalend of the femurandtheproximalendofthetibia. Below the knee Thetibia,sometimescalledtheshinbone,isthelargest andstrongestof thelowerlegbones. Itarticulates with thefemurattheproximalendandmeetsthefibulaand Phalanges is the plural of theGreekword pha- lange, or phalanx. The latter termwas applied toGreekandRoman noted for their closely joinedandunified ma- neuvers. It says here that the word patella, for kneecap, is a Latin word that means a small, flat dish—just what the kneecap looks like
- 13. the talus at the distal end. The fibula connects with the tibia at its proximal and distal ends. The fibula’s distal end also articulates with the talus. The articulation of the fibula, tibia, and talus bones creates the bony prominence on the outside of the ankle, called the lateral malleolus. Now, fleetly, to the foot The foot bones form a strong, stable arch with lengthwise and crosswise support. Strong ligaments and tendons of the leg muscles help the foot bones maintain their arched position: •Seven short tarsal bones structurally resemble the wrist, and they articulate with the tibia and fibula: – The talus bone (astragalus) forms part of the ankle joint. –The heel, called the calcaneus, is the largest tarsal bone. – The scaphoid bone is also called the navicular because of its boat shape. –The cuneiforms (the lateral, intermediate, and medial) are three wedge-shaped bones that form the arch of the foot. –The cuboid bone articulates in the front with the metatarsal bones. • Five metatarsal bones form the foot and articulate with the tarsal bone and the phalanges. •The fourteen phalanges (toes) are similar to fingers, with three bones in each toe except the great toe, which, like the thumb, contains only two bones. Bones are classified according to their shape: •Long bones are the main bones of the limbs, except the patella, and those of the wrists and ankles. • Short bones are the bones of the wrists and ankles. •Flat bones include the sternum, scapulae, and cranium, among others. • Irregular bones include the vertebrae and hip bones. Boning up on bone material All bones consist of two types of bone material: an outer layer of dense, smooth compact bone and an inner layer Anatomy of bones Words will never hurt me. But let’s keep sticks out of it!
- 14. of spongy, cancellous (porous) bone. Compact bone is found especially in the shaft of long bones and in the outer layers of short, flat, and irregular bones. Cancellous bone fills the central regions of the epiphysis (the end of a long bone where bone formation takes place) and the inner portions of short, flat, and irregular bones. Asosteoblastsaddnewtissuetotheoutsideofa bone,large phagocytic cellscalled osteoclasts eataway bonytissuein themedullarycavityto keep thebonefrom becomingtoothick.Ahealthyboneisconstantly broken down,resorbed,andrepairedlongafteritstopsgrowing in size. Duringadulthood,boneformation (or ossifica- tion) and bone resorption balance one another so that eachboneremainsaconstant size.Duringchildhoodand adolescence, ossificationis faster than resorptionand bonesgrowlarger. Cartilage Bones andjointsneedsupportas wellas shock absorp- tion.Cartilageis adenseconnectivetissuethathas thesecapabilities.It consistsof fibersembedded ina strong,gel-likesubstance.Unlikerigidbone,cartilagehas theflexibility offirm plastic. Cartilagesupportsandshapesvariousstructures,such astheauditorycanalandtheintervertebraldisks. It alsocushionsandabsorbs shock.Cartilagehasnoblood or nerve supply. Osteon,Greekforbone,providesa keyword-formingrootformedicaltermsrelatingtobones,oste- orosteo-.Osteoblast isa com- poundofosteo-and-blast; thelatterisanother commonmedicalrootderivedfromaGreekwordthatmeansabud ora shootof a developing organism. An osteoblast is thus a cellthat buds forth new bone tissue. The Greek word clast, on the other hand,means tobreakorfragment.Therefore,anosteoclast isa cellthat breaksdownbone. TheRomanshadanameforit Anotherverycommonrootforformingwordsisthe Latinword os,oross-,alsomeaningbone.Thisroot iscontained inwords like ossify,meaningto change ortobecome bone, and ossification,theprocessofbecomingbone.
- 15. Typesofcartilage Cartilagemaybe fibrous,hyaline, orelastic: •Fibrouscartilage formsatthemeniscus andthe inter- vertebraldisks. •Hyalinecartilage coversarticularbonesurfaces (where oneormorebones meet atajoint), connects the ribs and sternum,andappears in the trachea, bronchi,andnasalseptum. •Elastic cartilageislocatedinthe auditorycanal, ex- ternalear,andepiglottis. Bonemovement Bones are rigid structures that can’t bend without being damaged, so individual bones move at joint sites, or Articulations. Every bone in the body except the hyoid bone, which anchors the tongue, is connected to another bone by flexible connective tissue. Howdoesitmove? Classifying joints Jointscanbeclassifiedbythetypeofmovementtheyal- lowand bytheirstructure. Thethreeclasses ofjointsidentifiedby therangeof movement theyalloware: • synarthrosis—immovable • amphiarthrosis—slightly movable • diarthrosis—freely movable. What is it made of? Bystructure,ajointmaybeclassifiedasfibrous,carti- laginous,orsynovial.Infibrous joints,thearticularsur- facesofthe twobones arebound closelyby fibrouscon- nective tissueandlittle movement ispossible.Thecranial suturesareexamplesoffibrousjoints. In cartilaginous joints, cartilage connects one bone to another; thesejoints allow slight movement. An example is the symphysis pubis (the junction of the pelvicbones). Body surfaces in thesynovial joints arecovered by articularcartilageandjoined by ligaments(dense, strong,flexiblebandsoffibrousconnectivetissuethat bindbonesto otherbones)linedwithsynovialmem- brane. Freelymovable,synovial joints includemost joints of thearms andlegs.Synovialjointsalsoinclude an ar- ticularcapsule—a saclikeenvelope, whose outerlayer Our joints are jumpin’! It must be that diarthrosis