Bone Markings and Skeletal Divisions

Bone Markings

• Surface features characterize each bone in the body
• Depressions are clefts located when bone meets another structure
• Allow blood vessels and nerves to travel along the bone
• Allows two bones to articulate
• Openings are holes in the bone
• Indicate where blood vessels or nerves travel through the bone
• Projections are bony extensions of various shapes and sizes
• Projection points are where muscles, tendons, and ligaments attach to the bone
• Examples of bone markings include facet, fossa, fovea, groove/sulcus, canal/meatus, fissure, foramen, condyle, crest, head, tubercle/tuberosity, epicondyle, process, spine, protuberance, trochanter, and line.

Divisions of the Skeleton

• Axial skeleton forms the long axis of the body
• Axial skeleton includes: skull, vertebral column, rib cage
• Axial skeleton bones are involved with protecting, supporting, and carrying other body parts
• Appendicular skeleton includes bones of the upper and lower limbs and girdles
• Appendicular skeleton includes hip and shoulder
• Appendicular skeleton bones are involved in locomotion

Skull

• Most complex bony structure in the body
• Composed of 22 bones, with 8 cranial bones and 14 facial bones
• Most skull bones are flat bones
• Skull bones are united together by sutures, which are interlocking joints with saw-toothed or serrated appearances
• The exception is the mandible, which is freely moving

Cranium

• Encloses the brain
• Furnishes attachment sites for the head & neck muscles
• The single bones are frontal, occipital, ethmoid, & sphenoid bone
• Paired bones are the temporal & parietal bones
• The cranium has two parts: cranial vault and the cranial base
• Cranial vault is the round portion that makes up the superior, lateral, and posterior portions of the skull
• Cranial base makes up the floor or interior portion of the skull
• Foramen magnum is where the spinal cord exits the cranium

Cranial Fossae

• Contoured depressions that make up the floor of the cranium
• Anterior cranial fossa is formed by the frontal, ethmoid, and sphenoid bones and supports the frontal lobe
• Middle cranial fossa is formed by the sphenoid and temporal bones and supports the temporal lobe and the pituitary gland
• Posterior cranial fossa is formed by the temporal and occipital bones and supports the cerebellum and part of the brainstem

Cranial Sutures

- Immovable joints that form boundaries between the cranial bones
- Four major sutures: coronal, lambdoid, sagittal, squamous
- The coronal suture extends laterally across the superior surface along the coronal plane
- The coronal suture allows for articulation between the frontal and parietal bones
- The lambdoid suture arcs across the posterior surface of the skull and looks like a lambda (I)
- The lambdoid suture allows for articulation between parietal and occipital bones
- The sagittal suture extends between coronal and lambdoid sutures along the midsaggital plane
- The sagittal suture allows for articulation between the paired parietal bones
- The squamous suture is one on each side of the skull
- The squamous suture allows for articulation between the temporal and parietal bone (lateral)

Facial Skeleton

• Bones form the framework for the face
• Single bones: mandible & vomer
• Paired bones: the nasal, lacrimal, zygomatic, palantine bones, maxilla, and inferior nasal concha
• Functions to contain or form cavities for the special sense organs (sight, smell, taste)
• Helps to turbinate air
• Provides openings for the passage of air and food
• Secures teeth
• Anchors facial muscle

Cavities of the Skull

• Cranial cavity is the largest cavity
• Cranial cavity surrounds the brain
• Orbital cavities contain eyeballs, blood vessels, muscles, nerves, and lacrimal glands that secrete tears
• Orbital cavities formed by frontal, sphenoid, ethmoid, zygomatic, palantine, maxilla, & lacrimal bones
• Nasal cavity contains passages for air and special sensory neurons for smell and it is considered the first part of the respiratory tract
• The nasal cavity is divided by the septum (formed by vomer & ethmoid bone)
• The nasal cavity is formed by sphenoid, ethmoid, palantine, nasal bones, maxilla, & inferior nasal concha
• Oral cavity contains teeth, tongue, a passage for both food and air, and most of the salivary glands
• Oral cavity formed by mandible and maxilla

Hyoid Bone

• Found in the anterior neck region
• No direct articulations with any other bones
• Position maintained by a combination of ligaments and muscles
• Two pairs of projections called lesser and greater horns
• These projections are important sites of attachment for muscles involved in swallowing and speech production

Nasal and Paranasal Sinuses

• Air filled chambers within the bones of the skull
• Located around the nasal cavity
• Four paranasal sinuses, named for which bone they are located
• Possess small openings between sinuses and the nasal cavity
• Mucus-lined and air-filled, with air moving in from the nasal cavity
• Mucus drains out to nasal cavity
• Functions help to warm & humidify air, lighten the skull, and enhance resonance of the voice

Vertebral Column

• Five divisions & four curvatures: 7 Cervical, 12 Thoracic, 5 Lumbar, 5 Sacral, 4 Coccygeal
• 7 Cervical vertebrae have a concave curvature
• 12 Thoracic vertebrae have a convex curvature
• 5 Lumbar vertebrae have a concave curvature
• 5 Sacral vertebrae are fused and have a convex curvature
• The 4 Coccygeal vertebrae are fused
• Letter designates the type of vertebrae and with a subscripted number marks its position
• The spine curves to provide flexibility, increased resilience, and to better support the weight of the body
• Functions more like a spring

Structure of the Vertebrae

• Body is the weight-bearing portion and located anteriorly
• Vertebral foramen is the space between the body & arch and make up the vertebral canal
• Vertebral arch is a composite structure and located posteriorly
• Vertebral arch is composed of two pedicles and two laminae
• Spinal process single and extends anteriorly
• Articular processes are in two pairs and extend superiorly & inferiorly
• Transverse processes are in one pair and extend laterally

Intervertebral Discs

• Reside between the vertebrae to provide cushioning
• Made of anulus fibrosis, which is the outer portion composed of collagen fibers and fibrocartilage
• Anulus fibrosis limits the expansion of the nucleus pulposus
• Nucleus pulposus is the inner portion of the intervertebral discs and helps to be elastic and compressible

Characteristics of the Vertebrae

• Cervical vertebrae are small and oval, C1 lacks has the dens on the superior surface of its body
• Thoracic vertebrae are larger and heart-shaped and contain costal facets
• Lumbar vertebrae are largest and kidney-shaped
• Cervical vertebrae have triangular vertebral foramen shape
• Thoracic vertebrae have circular vertebral foramen shape
• Lumbar vertebrae have flattened triangular vertebral foramen shape
• Cervical vertebrae contain transverse foramina
• Thoracic vertebrae are long and contain articular facets for ribs
• Lumbar vertebrae are short with no facets or foramina
• Most Cervical vertebrae are fork-shaped
• Thoracic vertebrae are long and point inferiorly
• Lumbar vertebrae are thick and point posteriorly
• Transverse processes contain facets for the rib of thoracic vertebrae
• Thoracic vertebrae are called the costal facet

Sacrum and Coccyx

• Sacrum formed by 5 fused vertebrae
• Superior articular process connects to the hip
• Sacrum possesses foramen for blood vessels & spinal nerves to pass through
• Coccyx formed by 4 fused vertebrae and occurs around age 25
• Coccyx is an attachment site for several ligaments

Sternum

• Breastbone and stabilizes the thoracic cage
• Protects the heart, vena cava, and thymus
• Made of three bones: manubrium, body, and the xiphoid process
• Manubrium articulates with the clavicle and ribs
• Body articulates with ribs
• Xiphoid process is initially composed of hyaline cartilage and ossifies by age 40
• The xiphoid process is an attachment point for the abdominal muscles

Ribs

• Attach posteriorly to the thoracic vertebrae
• Ribs 1-7 are true ribs and attach directly to the sternum
• Ribs 8-12 are false ribs
• Ribs 8-10 attach to rib 7
• Ribs 11 & 12 are floating ribs

Rib structure

• Bowed flat bone
• Shaft comprises the bulk of the rib
• Head Articulates with the thoracic vertebrae at the costal groove, divided into the superior and inferior articular facets
• Neck is the area between the head and the tubercle
• Angle is the point at which the rib curves toward the sternum
• Tubercle is Articulates with the transverse process of the vertebrae

Pectoral Girdle

• Composed of two bones; the clavicle and the scapular
• Clavicle; AKA the collar bone, located anteriorly
• Clavicle is an attachment point for many muscles
• Clavicle acts as a brace to hold the arms & scapula away from the body
• The Sternal end articulates with the manubrium of the sternum
• Acromial end articulates with the acromion of the scapula
• Scapula; AKA Shoulder blade, located posteriorly
• Scapula is attached to the axial skeleton via articulation with the clavicle and various muscles
• Dorsal surface possesses ridge called the spine, which ends at the acromion
• Lateral border where glenoid cavity serves as the site of articulation with humerus
• Three fossae for muscle attachment: ventral surface/subscapular, and dorsal surface(Supraspinous & Infraspinous)

Humerus

• Articulates with scapula to form the shoulder
• Head/ proximal end and fits into the Glenoid cavity
• Tubercules (Greater & Lesser): attachment sites for the rotator cuff
• Deltoid tuberosity: attachment for the deltoid muscle
• Distal end that articulates with ulna and radius to form the elbow
• Capitulum/lateral that Articulates with the head of the radius
• Trochlea/medial that Articulates with the trochlear notch of the ulna
• Epicondyles (Lateral and medial) that are Attachment sites for muscles, ulnar nerve travels posterior to the medial epicondyle

Forearm

• Includes the ulna and radius connected via interosseous membrane
• Ulna- medial, it is slightly longer than the radius
• The ulna creates the trochlear notch that forms the elbow joint with humerus
• The ulna has a bony end of Olacrannon
• The ulna has a Styloid process that connects to wrist