Human Anatomy: Axial Skeleton (PDF)

Human Anatomy Theory Lec. 2 “The Axial Skeleton” By Dr. Layla M. Salih 1 The Skeleton Consists of: Bones, cartilage, joints, and ligaments Joints—also called articulations 206 named bones grouped into two divisions Axial skeleton (80 bo...

Human Anatomy Theory Lec. 2 “The Axial Skeleton” By Dr. Layla M. Salih 1 The Skeleton Consists of: Bones, cartilage, joints, and ligaments Joints—also called articulations 206 named bones grouped into two divisions Axial skeleton (80 bones) Skull, vertebral column, and thoracic cage Appendicular skeleton (126 bones) Upper and lower limbs 2 The Skull Is the body’s most complex bony structure Is formed by cranial and facial bones Bones of the cranium Enclose and protect the brain Provide attachment sites for some muscles of the head and neck Cranium is divided into cranial vault and the base Facial bones form anterior aspect 3 The Skull Facial bones Form framework of the face Form cavities for sense organs of sight, taste, and smell Provide openings for passage of air and food Hold the teeth in place Anchor muscles of the face 4 Cranial Bones Formed from eight large bones Single bones include Sphenoid bone: Frontal bone: Forms base and sides of cranium, and floors -Forms forehead, roof of both nasal cavity, and and sides of orbits orbits Special features (a) Sella turcica = houses pituitary gland -Contains medially located sinuses above each eye (b) Contains 2 sinuses Occipital bone: Ethmoid bone: -Forms back and base of cranium Forms part of roof of nasal cavity, part of cranial Special features floor and orbital walls, and superior and middle (1) Foramen magnum = opening at bottom nasal conchae (2) Occipital condyles = rounded processes Special features on either side of foramen magnum that (a) Cribriform plate = opening through which articulate with atlas (=C1) olfactory nerve endings project into nasal cavity (b) Contains sinuses 5 Cranial Bones Paired bones Parietal = form sides and roof of cranium Temporal= forms side walls and part of floor of cranium Special features (a) External auditory meatus (b) Mastoid process for neck muscle attachment (c) Zygomatic process of temporal bone 6 Sutural Bones Small bones that occur within sutures Irregular in shape, size, and location Not all people have sutural bones 7 Facial Bones (14 bones) Unpaired bones Mandible (lower jaw) and vomer Paired bones Maxilla-upper jaw Zygomatic bones-cheek bones Nasal bones-bridge of nose Lacrimal bones-inner wall of eye orbit Palatine bones-roof of mouth Inferior nasal conchae-nasal cavity 8 Bones of the Face Zygomatic bones-lateral wall of orbits Nasal bones-bridge of nose Lacrimal bones-Located in the medial orbital walls Palatine bones-Complete the posterior part of the hard palate Vomer-Forms the inferior part of the nasal septum Inferior nasal conchae-Thin, curved bones that project medially form the lateral walls of the nasal cavity 9  10 Inferior view of the skull (mandible removed) Maxillary Bones Articulate with all other facial bones except the mandible Contain maxillary sinuses Forms part of the inferior orbital fissure Are the “keystone” bones of the face 11 Mandible The lower jawbone is the largest and strongest facial bone Is the only movable bone of the skull Composed of two main parts Horizontal body Two upright rami 12 Fetal Skull Infant face is very small compared to skull when born The skull has a few regions that are not fully formed yet, called fontanels, or soft-spots Allow skull to be compressed during birth and for brain growth; would not be possible if the bones were fully formed and fused (~22 to 24 months) 13 The Hyoid Bone Lies inferior to the mandible The only bone with no direct articulation with any other bone Acts as a movable base for the tongue 14 The Vertebral Column a.k.a. spine Extends from the skull, which it supports, to the pelvis, where is sends the weight of the body to the lower limbs Formed of 26 irregular bones connected and held in place by ligaments, resulting in a flexible and strong S-shaped structure Surrounds and protects the spinal cord; running through a central canal of each bone is the spinal cord Serves as attachment sites for muscles of the neck and back 15 Vertebral Column Organized into: Cervical vertebrae-neck, C1-C7 Thoracic vertebrae-thorax, T1-T12 Lumbar vertebrae-lower back, L1-L5 Sacrum-5 bones, fused by birth Coccyx-tailbone, 4 bones, fused by birth 16 Regions and Normal Curvatures Curvatures of the spine increase resilience of spine Thoracic and sacral curvatures Primary curvatures; present at birth Convex posteriority Cervical and lumbar curvatures Secondary curvatures develop when baby begins to walk Concave posteriorly 17 Abnormal Spinal Curvatures Scoliosis = abnormal lateral Lordosis [="sway curvature of vertebral column kyphosis [="hunch back"] exaggerated back" ] thoracic curvature accentuated lumbar curvature 18 Intervertebral Discs Cushion-like pads between vertebra Composed of Nucleus pulposus Gelatinous inner sphere Absorbs compressive stresses Anulus fibrosus Outer rings formed of ligament Inner rings formed of fibrocartilage Contains the nucleus pulposus 19 General Structure of Vertebrae All vertebrae have similar structures and features Body Vertebral arch Vertebral foramen-hole Spinous process-for muscle attachment Transverse process-for muscle attachment Superior and inferior articular processes Intervertebral foramina-hole formed when vertebrae are articulated 20 Cervical Vertebra Smallest vertebrae in vertebral column Short, stumpy transverse process C2–C6 have bifid spinous process C7 has large spinous process ending in tubercle Can be felt (palpated) through skin All 7 cervical vertebrae have transverse foramen – allows passage of vertebral arteries and vertebral veins 21  First Two Cervical Vertebrae Specialized to support and stabilize cranium Atlas, C1 Axis, C2 No vertebral body or spinous Prominent dens, superior projection process on body Large, round vertebral foramen Dens bound to atlas by transverse ligament Articulates with occipital condyles – permits nodding "yes“ permits rotation as in shaking head "no" 22  Thoracic Vertebra Twelve thoracic vertebrae Each one slightly larger as they move inferiorly Heart-shaped body Long, slender spinous process projects posteriorly and inferiorly Costal facets on vertebral body for rib articulation T1–T10 also have costal facets on transverse processes 23  Lumbar Vertebrae Largest vertebrae (transmits most weight) 5 (L1-L5) Thicker body than thoracic vertebra No costal facets Stumpy spinous process 24 Vertebral Sections-Features 25 26  Sacrum and Coccyx Sacrum Formed by the fusion of 5 vertebrae Begin fusing from fetal period; completed by age 25–30 Articulates superiorly with L5, inferiorly with the coccyx Coccyx Tailbone; formed by the fusion of 3-5 vertebrae 27  Thoracic Cage (bony thorax) Provides bony support to walls of thoracic cavity Protects heart, lungs, and thymus Composed of thoracic vertebrae, ribs, sternum Attachment point for muscles involved in: 1. Breathing 2. Maintaining position of vertebral column 3. Movements of pectoral girdle and upper limbs 28  Thoracic Cage Sternum Flat bone, fusion of the manubrium, body and xiphoid process Attached to the first seven pairs of ribs Ribs Twelve pairs, all of which articulate with the vertebral column posteriorly and then curve down and anteriorly True ribs, the first seven pairs attach to the sternum by individual costal cartilages False ribs, the next five pairs, attached either indirectly (8-10) or not at all (11- 12 a.k.a. floating ribs) Spaces between ribs are called intercostal spaces, and are filled with the intercostal muscles, which aid in breathing 29 30