CHAPTER 7 â€œThe Axial Skeletonâ€ Course objectives: Define and...
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CHAPTER 7The Axial Skeleton
Define and identify the bones of the axial skeleton
Axial Skelton 80 total bonesconsists of the bones that form the long axis of the body including the:Skull (total 28 with ear bones)Vertebral column [(total 26) C7;T12; L5; S1; Co1]Bony thorax [ribs and sternum (total 25)]Hyoid bone (1)
Skull Bones the skull has two major divisions: Cranium and Facial bonesCranium the 8 bones that enclose the brain. -1 occipital, 1 frontal, 2 parietal, 2 temporal, 1 sphenoid and 1 ethmoid.
These typical flat bones of the cranium are connected by a special kind of joint called a suture (Synarthroses).
CraniumMade up of 2 major divisions:Calvarium (skull cap)BaseBase contains three large depressions (fossa):Anterior cranial fossa where the frontal lobes sitMiddle cranial fossa where the temporal lobes sitPosterior cranial fossa where the cerebellum sits
Sutures/Sutural BonesSutures (synarthrotic) are immovable fibrous joints; except for the jaw. -all bones in the skull are united by sutures.-Coronal-Sagittal-Squamous-LamboidSutural bones- small bones that occur within the sutures, especially the lamboid suture. They are not present in all people.
There are 14 bones that can be thought of as creating the face. As part of this function they provide:- protection for many sense organs, -provide anchors for many muscles -create the openings for air and food to pass.Facial Bones2-maxilla; 2-palatine; 2-nasal; 2- zygomatic; 2-lacrimal; 2-inf nasal concha; 1- vomer; and 1-mandible
Sphenoid boneLooks like a Bat in flight. Greater and lesser wings; optic foramen; sella turcica, superior orbital fissure.
Ethmoid boneAnterior to sphenoid boneforms anterior base of skull and nasal cavity.Cribriform plate.Crista galiPerpendicularplate
Foramen/ OrbitsForamen: Special openings in bones where nerves, blood vessels enter into the bone cavity.- Ex.: Foramen magnum, Supraorbital Infraorbital, Mental, Jugular, Olfactory, Mandibular
Orbits: Cone shaped bony cavities that hold the eyes, fat, occular muscles and tear glands.
Meatus/ SinusesMeatus: a canal or opening into bone- Ex.: external auditory, internal acoustic
Sinus: cavities within bones filled with air.-Ex.: frontal, ethmoid, sphenoid and maxillary sinuses
The Fetal SkullSutures are called fontanels in fetus.Fontanels-Frontal (anterior)-Occipital (posterior)-Sphenoidal (anterior lateral)-Mastoid (posterior lateral)
Vertebral column composed of 26 irregular bones.
These bones provide a solid support structure, but are also remarkably flexible.
Regions of the Vertebral ColumnCervical neck region 7 vertebrae Thoracic thorax region 12 vertebrae Lumbar lower back 5 vertebrae Sacral low, low back 1 vertebrae (5 fused) COccygeal tail bone 1 vertebrae (4 fused)
Spinal CurvatureThoracic and sacral are concave (i.e. backward) Primary curves since they developed first.
Cervical and lumbar curves are convex (i.e. forward) and secondary curves.
Vertebrae Individual vertebrae are found in the cervical, thoracic and lumbar regions of the vertebral column.
There are significant differences between the vertebrae in each of these regions that you should know.
Cervical vertebrae C1- C7 Body is oval; spinous process is short (except C-7) and sometimes split; Large vertebral foramen Transverse foramen for vertebral artery to brainstem.C1 is Atlas articulates (atlanto-occipital joint) with occipital bone of skull -allows yes motion of headC2 is Axis characterized by peg-like process called dens or odontoid process which interlocks with atlas (atlanto-axial joint)-allows sideward rotation or no motion of head.
Thoracic vertebrae T1- T12 Body is roughly heart shapedDemifacets for rib articulation Vertebral foramen are circularSpinous process long and points inferiorly
These vertebra look like a giraffes head!
Lumbar Vertebrae L1-L5 Pedicles and laminae are short and thickerSpinous processes are short, flat and hatchet shaped Vertebral foramen is triangular Inferior and superior processes lock the adlacent vertebrae together for strength and stability.
These vertebra look like a Mooses head!
Sacral Vertebrae S1-S5Sacral vertebrae consists of 5 fused vertebrae fully fused by 30 years of age Women sacrum is shorter, wider and more curved Joins the spine to the pelvic girdle via sacroiliac joint.Sacral canal is continuation of vertebral canal.
Sacrum and Coccyx
Coccyx Vertebrae Co1-Co4Coccyx is Greek for cuckooConsists of 4 fused vertebrae Fuse between 20 and 30 years Tailbone is vestige of tail- Men it points anteriorly- Women it points inferiorly
Additional structures of the vertebral column Intervertebral discs Present between all vertebrae C2- L5/S1;Composed of fibro cartilage Two regions of disc:- nucleus pulposis central core of disc- annulus fibrosis - outer covering of fibro cartilageFunction: -discs permit various movements -provide shock absorbing functions for vertebral column
Vertebra and vertebral disc
Slipped Intervertebral discs
Vertebral Ligaments(1). Anterior and posterior longitudinal ligaments hold vertebral column together along with trunk skeletal muscles-prevent hyper-extension and hyper-flexion of the vertebral column. (2). Shorter ligaments connect adjoining vertebrae together. -There are 3 of these ligaments the ligamentum flavum, the supraspinous ligaments and the interspinous ligaments.
Bony ThoraxConsists of ribs attached to the vertebral column and sternum True ribs R1-R7 attach directly to sternumFalse ribs R8-R10 attach indirectlyTwo floating ribs R11 & R12The Sternum consisting of:- manubrium- body- Xiphoid process
Ribs1. true ribs the first (superior) seven pairs of ribs R1-R7 are directly connected to the sternum via costal cartilage. - are called vertebrosternal ribs.2. false ribs the remaining five pairs of ribs. There are two types of false ribs.vertebrochondral ribs -- rib pairs #8, #9, and #10 are connected by a single band of costal cartilage to the inferior portion of the sternum. Unlike the first seven pairs of ribs they do not have their own individual attachments.floating or vertebral ribs rib pairs #11 and #12 are connected only to the vertebral column, they have no anterior connection to the skeleton.
Sternum breast plateAnterior central portion of thoraxOnly bony attachment of axial skeleton to appendicular skeleton via clavicle.Consists of Manubrium, Body and Xiphoid processKey landmarks: calvicular notches, jugular notch suprasternal notch, sternal angle.
Hyoid boneLies inferior to the mandibleIs not attached to skeleton by bony meansHelps movement of base of tongue