ANATOMY AND PHYSIOLOGY CHAPTER 5: THE SKELETON (SKULL) ANATOMY AND PHYSIOLOGY

Articulated skeleton – dried bones held together by wires and rods to show spatial relationships to one another Disarticulated skeleton – taken apart so anatomy of individual bones can be studied SKELETON: (bones, cartilage, tendons, ligaments); means “dried up body” or “mummy” in greek 2 regions AXIAL SKELETON: central supporting axis of body; includes skull Made up of 80 different bones Skull Bony thorax (ribs, sternum) Vertebral column APPENDICULAR SKELETON: bones of the upper limb , pectoral girdle, lower limbs, pelvic girdle

BONES OF THE ADULT SKELETAL SYSTEM

206 bones in adult skeleton 20 % of body mass Weighs 30 pounds in a 160 pound man Around 270 bones in newborn Even more bones form during childhood but number decreases with age when separate bones begin to fuse together

THE SKULL Most complex part of skeleton; formed by 2 sets of bones, the CRANIAL BONES and the FACIAL BONES; made up of 22 bones (sometimes more). Cranial bones (or cranium) functions: site for head muscle attachment enclose/protect brain, organs of hearing and equilibrium

Facial bones functions: form facial framework hold eyes in front position provides cavities for organs of taste, smell, openings for air and food passage secure teeth anchor facial muscles of expression

Bones of skull are connected by immovable joints called SUTURES (except for the mandible). They are the CORONAL, SAGITTAL, SQUAMOUS, LAMBDOIDAL – connect cranial bones; other sutures connect facial bones and are named according to specific bones that they connect.

Most skull bones are flat bones Most skull bones are flat bones. They are very strong due to curvature of skull bones.

Cavities of the skull: Cranial cavity – largest, encloses brain orbits (eye sockets)

nasal cavity buccal cavity (mouth)

middle- and inner-ear cavities paranasal sinuses

Foramen (foramina = singular) “holes” of skull allow passage for nerves and blood vessels. FORAMEN MAGNUM – “large hole” or opening where spinal cord enters brain case.

CRANIAL BONES CRANIUM encloses cranial cavity (brain case) and protects brain and sense organs. 8 cranial bones: FRONTAL BONE (1) PARIETAL BONES (2) TEMPORAL BONES (2) OCCIPITAL BONE (1) SPHENOID BONE (1) ETHMOID BONE (1)

Severe swelling of brain can lead to brainstem forced out of foramen with fatal consequences.

Brain tissue doesn’t touch skull, instead is separated by 3 membranes called MENINGES. Includes the pia mater (closest to the brain), the arachnoid and the dura mater (farthest from the brain). The meninges also support blood vessels and contain cerebrospinal fluid. Dura Mater is the thickest, toughest, outer most layer and firmly attached to cranium at a few points. These are the structures involved in meningitis, an inflammation of the meninges, which, if severe, may become encephalitis, an inflammation of the brain.

Cranium consist of 2 parts: CALVARIA - “skull cap” – forms roof and walls BASE – “floor” which is divided into 3 basins due to contour of inferior surface of brain. ANTERIOR CRANIAL FOSSA – crescent shaped accommodates frontal lobes of brain CENTRAL CRANIAL FOSSA – drops deeper, is shaped like pair of outstretched bird’s wings and hold the temporal lobes. POSTERIOR CRANIAL FOSSA – deepest and houses large posterior division of brain called CEREBELLUM

THE 8 CRANIAL BONES FRONTAL BONE Extends from forehead back to CORONAL SUTURE (which crosses crown of head from right to left and joins frontal bone to PARIETAL BONES). Forms anterior wall and 1/3 of the roof of cranial cavity; turns inward to form almost all of anterior cranial fossa and roof of the orbit.

The frontal bone is thickened and protrudes slightly at the SUPRAORBITAL MARGINS underlying the eyebrows. Each supraorbital margin is pierced by a SUPRAORBITAL FORAMEN or “supraorbital notch”, which allows supraorbital artery and nerves to pass to the forehead region. The GLABELLA is the smooth area of frontal bone just above the front of the nose. Here the frontal bone meets the nasal bones at the frontonasal suture. The frontal bone also contains FRONTAL SINUSES.

PARIETAL BONES (2) Forms most of cranial roof and part of its walls. Each bordered by 4 sutures that join it to other skull bones: SAGITTAL SUTURE (between parietal bones), CORONAL SUTURE (anterior margin), LAMBDOID SUTURE (posterior margin), and SQUAMOUS SUTURE (laterally).