Anatomy Exam 2 (Lecture Materia)

Bone Tissue

Organic Components: Cells fibers and ground substance.

Inorganic Components: Mineral salts that invade bony matrix.

Extracellular Matrix of Bone

Unique composition of matrix gives bone exceptional properties.

• 35% organic components: contribute to flexibility and tensile strength

• 65% inorganic components: provide hardness and resist compression.

Cells

Three types of cells in bone that produce or maintain bone.

• Osteoprogenitor cells: stem cells that differentiate into osteoblasts.

• Osteoblasts: actively produce and secrete bone matrix (bone matrix is osteoid).

• Osteocytes: keep bone matrix healthy.

• Osteoclasts: Large multinucleate cell, found within the bone tissue, responsible for resorption of bone, are derived from a line of white blood cells/immune system, secrete hydrochloric acid and lysosomal enzymes.

Long Bones

Longer than wide; a shaft plus ends. Ex: humerus

Short Bones

Roughly cube shaped. Ex: talus

Sesamoid Bone

A special type of short bone that forms within a tendon.

Flat Bone

Thin and flattened, usually curved. Ex: sternum

Irregular Bones

Various shapes, do not fit into other categories. Ex: vertebra

Compact Bone

Dense outer layer of bone

Spongy/Cancellous Bone

Internal network of bone. Trabecular: little “beams” of bone. Open spaces between trabecular are filled with marrow.

Structure of a Typical Long Bone

• Diaphysis: “shaft” of a bone

• Epiphyses: ends of a bone

• Blood Vessels: well vascularized

• Medullary Cavity: hollow cavity filled with yellow marrow

• Membranes: periosteum, perforating collagen fiber bundles (Sharpey’s fibers) and endosteum.

Structure of Short, Irregular, and Flat Bones

• Contain bonen marrow but no marrow cavity, marrow fills space in spongy bone.

• Diploë: Internal spongy bone of flat bones, covered by a thin layer of compact bone.

Anatomy of a Bone

• Reflects stresses

• Compression and tension greatest at external surfaces.

• Bending a bone creates compression on one side and tension on the other, with both forces greatest at the external surface. (Point of no stress in the middle, much less material is needed internally than superficially).

• Internal spongy bone has trabecular that align along stress lines to resist stress with minimum weight.

Bone Markings

Superficial surfaces of bones reflect stresses on them, in response to tension, pull, and pressure from surrounding tissues or to accommodate vessels and nerves. Three categories:

• Projections for muscle attachment

• Surfaces that form joints

• Depressions and openings to allow blood vessels, soft tissue, and nerves to pass safely through or along the rest of the bone.

Structure of Compact Bone

Contains passageways for blood vessels, lymph vessels, and nerves. Contains Osteons, Spongy bone.

Osteons

In compact bone, long cylindrical structures, function in support, structurally resemble rings of a tree in cross section. Contain: Lamellae, central canal, perforating canals, canaliculi.

Spongy Bone Structure

Less complex than compact bone, Trabecular contain layers of lamella and osteocytes - too small to contain osteons, osteocytes are nourished by nutrients diffusing from capillaries in the endosteum (membrane) that covers the trabeculae. Trabeculae is filled with bone marrow.

Function of Lamellae

Collagen fibers and mineral crystals in adjacent lamellae run in opposite directions. Alternating pattern allows bone to withstand torsion (twisting) stresses. It also inhibits crack propagation, as forces are dispersed at lamellar boundaries. Rings around central canal.

Bone Development

Ossification (osteogenesis) is bone tissue formation. Membranous bones formed directly from mesenchyme = Intramembranous ossification. Other bones develop initially from replacing hyaline cartilage = Endochondral ossification.

Intramembranous Ossification Process

1. Ossification centers development in the fibrous connective tissue membrane. Mesenchymal cells cluster and differentiate into osteoblasts, forming ossification center. Osteoblasts begin secreting bone matrix (osteocytes).

2. Osteoid is secreted and calcifies. The osteoid hardens as calcium and mineral salts are deposited. Osteoblasts trapped inside the hardening matrix become mature bone cells (osteocytes).

3. Immature spongy bone and periosteum form. Accumulating osteoid is laid down between embryonic blood vessels, forming a honeycomb of immature spongy bone. Vascularized mesenchyme condenses on the external face of the bone and becomes the periosteum.

4. Compact bone replaces immature spongy bone, just deep to the periosteum. Red marrow develops. Trabecular just deep to the periosteum are remodeled and replaced with compact bone. The immature spongy bone in the center is remolded into mature spongy bone that is eventually filled with red marrow.

Endochondral Ossification

All bones except some bones of the skull and clavicles, bones are modeled in hyaline cartilage (gradually replaced with bone tissue), Begins forming late in the second month of embryonic development, continues forming until early adulthood.

Endochondral Ossification

1. Bone collar forms around the diaphysis of the hyaline cartilage model.

2. Cartilage calcifies in the center of the diaphysis and then develops cavities.

3. The periosteal bed invades the internal cavities and spongy bone froms.

4. The diaphysis elongates and a medullar cavity forms. Secondary ossification centers appear in the epiphyses.

5. The epiphyses ossify. When ossification is complete, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

Anatomy of the Epiphyseal Plate

In epiphyseal plates of growing bones cartilage is organized for quick, efficient growth. Cartilage cells form tall stacks, chondroblasts at the top of the stacks divide quickly. Pushes the epiphysis away from the diaphysis, lengthens entire long bone, five zones are resting zone, proliferation zone, hypertrophic zone, calcification zone, ossification zone.

Epiphyseal Growing Areas

Older chondrocytes signal surrounding matrix to calcify. Older chondrocytes then die and disintegrate. Leaves long trabecular (spicules) of calcified cartilage on diaphysis side. Trabecular are partly eroded by osteoclasts. Osteoblasts then cover trabecular with bone tissue. Trabecular finally eaten away from their tips by osteoclasts.

Postnatal Growth of Endochondral Bones

During childhood and adolescence: bones lengthen entirely by growth of epiphyseal plates, cartilage is replaced with bone connective tissue as quickly as it grows. Epiphyseal plate maintains constant thickness. Whole bone lengthens.

As adolescence draws to an end: Chondroblasts divide less often, Epiphyseal plates become thinner, cartilage stops growing, replaced by bone tissue. Long bones stop lengthening when diaphysis and epiphysis fuse.

Growing bones widen as they lengthen. Osteoblasts add bone tissue to the external surface of the diaphysis. Osteoclasts remove bone from the internal surface of the diaphysis.

Appositional Growth

Growth of a bone by addition of bone tissue to its surface.

Hormonal Regulation of Bone Growth

• Growth Hormone is produced by the pituitary gland and stimulates the epiphyseal plate.

• Thyroid Hormone ensues that the skeleton retains proper proportions.

• Sex Hormones (estrogen and testosterone) promote bone growth, later induces closure of epiphyseal plates.

Bone Remodeling

Bone is a dynamic living tissue. 500mg of calcium may enter or leave the adult skeleton each day. Bone matrix and osteocytes are continually removed and replaced. Spongy bone is replaced every 4-5 years. Compact bone is replaced every 20-30 years. Bone deposit and removal is not uniform. Bone deposition (create new bone tissue) is accomplished by osteoblasts. Bone reabsorption (breakdown old or damaged bone tissue) is accomplished by osteoclasts.

Why Remodel Bone?

Calcium regulation, remodeling maintains blood calcium levels. Parathyroid hormone stimulates osteoclasts to resorb bone when blood calcium is low. It is also a response to mechanical stress, bone adapts to the loads it experiences. Osteons and trabeculae are replaced and realigned to resist new stresses.

Osteoclast

A bone degrading, giant cell with mani nuclei. Crawls along bone surfaces. Breaks down bone tissue by secreting concentrated HCl, secrete destructive enzymes from Lysosomes. They are derived from hematopoietic stem cells.

Repair of Bone Fractures

Simple and compound fractures, treatment by reduction wither open reduction or closed reduction.

Stages of Healing a bone Fracture

1. Hematoma forms

2. Fibrocartilaginous (soft) callus forms

3. Bony callus of spongy bone forms

4. Bone remodeling occurs

Comminuted Fracture

Bone fragments into three or more pieces

Compression Fracture

Bone is crushed

Spiral Fracture

Ragged break occurs when excessive twisting forces are applied to a bone.

Epiphyseal Fracture

Epiphysis separates from the diaphysis along the epiphyseal plate.

Depressed Fracture

Broken bone portion is pressed inward.

Greenstick Fracture

Bone breaks incompletely, much in the way a green twig breaks. Only one side of the shaft breaks; the other side bends.

Osteoporosis

Characterized by low bone mass. Bone reabsorption outpaces bone deposition. Occurs most often in women after menopause. Additional risk factors: insufficient exercise, diet poor in calcium/protein, low vitamin D. Treatments include calcium/vitamin D supplements, drugs that suppress osteoclasts, and drugs that stimulate osteoblasts.

The Skeleton

Composed of bones, cartilage, joints/articulations, and ligaments. There are 206 names bones that are grouped into axial skeleton and appendicular skeleton.

Axial Skeleton

80 bones that make up the skull, vertebral column, and thoracic cage.

Appendicular Skeleton

126 bones that make up the upper and lower limbs.

The Skull

Bodys most complex bony structure, contains cranial and facial bones.

Bones of the Cranium

Enclose and protect the brain, provide attachment sites for some muscles of the head and neck.

Facial Bones

Form framework of the face. Form cavities for sense organs of sight, taste, and smell. Provide opening for passage of air and food. Hold teeth in place. Anchor muscles to the face.

Sutures of the Skull

Most skull bones are flat bones, firmly united by interlocking, immovable joints called sutures. These suture lines have an irregular, saw-toothed appearance. As you get older these sutures harden into bone overtime and fuse together.

Skull Geography

Facial bones form anterior aspect. Cranium is divided into cranial vault (also called the calvaria or skull cap) and the base. Internal bony ridges divide the skull into anterior, middle and posterior cranial fossae. Brain sits within the cranial fossae (occupies the cranial cavity)

Smaller Cavities of the Skull

• Middle and inner ear cavities: in lateral aspect of cranial base.

• Nasal cavity: lies in and posterior to the nose.

• Orbits: house the eyeballs.

• Paranasal sinuses: occur in several bones around the nasal cavity.

Skull Openings

Skull contains approximately 85 named openings like foramina, canals, and fissures. They provide openings for important structures like the spinal cord, blood vessels to the brain, and twelve pairs of cranial nerves.

Cranial Bones

Formed from eight large bones. Paired bones are Temporal and Parietal bones. Unpaired bones are Frontal, Occipital, Sphenoid, and Ethmoid bones.

Parietal Bones

Form the superior and lateral parts of the skull.

Sutures of Cranium

• Coronal: runs in the coronal plane, Located where parietal bones meet the frontal bone.

• Squamous: occurs where each parietal bone meets a temporal bone inferiorly.

• Sagittal: occurs where right and left parietal bones meet superiorly.

• Lambdoid: occurs where the parietal bones meet the occipital bone posteriorly.

Sutural Bones

Small bones that occur within sutures, especially in the lambdoid suture. Irregular in shape, size, and location. Not all people have sutural bones. These develop between the major cranial bones during the fetal period and persist throughout life.

Frontal Bone

Forms the forehead and roofs of orbits. Superior to the orbits, it protrudes slightly to form superciliary arches (above eyes). Internally contributes to anterior cranial fossa.

Supraorbital Margin

Superior margin or orbits, curved upper edge of the eye socket.

Supraorbital Foramen

Passage of supraorbital nerve and artery, small hole or notch sitting on the Supraorbital Margin.

Glabella

Smooth part of frontal bone between superciliary arches. Frontal sinuses within frontal bone begin forming here.

Occipital Bone

Forms the posterior portion of the cranium and cranial base. Connects with the temporal bones and parietal bones. Internally forms the posterior cranial fossa. Foramen magnum is located at its base.

Features, Structures, and Functions of the Occipital Bone

• Occipital condyles: head nodding

• Hypoglossal foramen: for cranial nerve XII to exit the skull

• External occipital protuberance: secures the ligament nuchae

• Superior and Inferior nuchal lines: anchor muscles of the neck and back

Temporal Bones

Lie inferior to parietal bones. Form the inferolateral portion of the skull. Term temporal comes from the Latin word time (this is the area most people go grey first). Specific parts include squamous, tympanic, and petrous. Contributes to the middle and posterior cranial fossae.

Mastoid Process

Bony projection located at the base of the temporal bone, directly behind the earlobe. Site for neck muscle attachment, contains air sinuses.

Petrous Part of the Temporal Bone

Projects medially and contributes to the cranial base. Houses cavities of middle and internal ear.

Squamous part of the Temporal Bone

Forms the zygomatic arch (cheek bone). The mandibular fossa on its interior surface forms the temporomandibular joint (hinging and sliding of the mandible).

Tympanic part of the Temporal Bone

Surrounds the external acoustic meatus (external ear canal).

Foramina (openings) of the Temporal Bone

• Jugular foramen: formed by the union of the petrous part of the temporal bone and the occipital bone. Is the passage for internal jugular vein and cranial nerves IX, X, and XI.

• Carotid canal: Internal carotid artery passes through.

• Foramen lacerum: Closed by cartilage in living person.

• Stylomastoid foramen: Passageway for a branch of cranial nerve VII.

• Internal acoustic meatus: Transmits cranial nerves VII and VIII.

Sphenoid Bone

Spans the width of the cranial floor. Resembles a bat with its wings spread. Consists of a body and three pairs of processes. Contains 5 important openings. Is the “keystone” of the cranium.

Important Landmarks of the Sphenoid Bone

• Body: Sella turcica - the seat of this saddle, called the hypophyseal fossa, holds the pituitary gland. Sphenoidal sinuses.

• Greater wings

• Lesser wings

• Pterygoid processes: attachment sites for the pterygoid muscles that help close the jaw in chewing.

Important Openings of the Sphenoid Bone

• Optic canal: cranial nerve II passes through

• Superior orbital fissure: cranial nerves III, IV, VI pass through.

• Foramen rotundum: maxillary branch of cranial V passes through.

• Foramen ovale: Mandibular branch of cranial nerve V passes through.

• Foramen spinosum: Middle meningeal artery passes through.

Ethmoid Bone

Lies between the nasal and sphenoid bones. Forms most of the medial bony region between the nasal cavity and orbits

Cribriform Plate

Superior surface of the ethmoid bone. Contains cribriform foramina through which filaments of cranial nerve I pass.

Crista Galli

Attachment for falx cerebri, a fibrous membrane that helps secure the brain. In the midline of the ethmoid bone.

Perpendicular Plate

Forms the superior part of nasal septum.

Ethmoidal Labyrinth

Contains air cells

Superior and Middle Nasal Conchae

Extend medially from laterial masses

Facial Bones

Unpaired bones are the mandible and vomer. Paired bones are maxillae, zygomatic, nasal, lacrimal, palatine, inferior nasal conchae bones.

Mandible

The lower jawbone is the largest and strongest facial bone. Only moveable bone of the skull. Composed of horizontal body and two upright rami. Major landmarks include mandibular fossa, mandibular foramen, alveolar process, mental foramen, condylar process, and ramus.

Maxillary Bones

Connect with all other facial bones except the mandible. Contains maxillary sinuses (largest paranasal sinuses). Forms part of the inferior orbital fissure. Are the “keystone” bones of the face.

Zygomatic Bones

Form lateral wall of orbits

Nasal Bones

Form bridge of nose

Lacrimal Bones

Located in the medial orbital walls

Palatine Bones

Complete the posterior part of the hard palate

Vomer Bone

Forms the inferior part of the nasal septum

Inferior Nasal Conchae Bones

Thin, curved bones that project medially from the lateral walls of the nasal cavity.

Nasal Cavity

• Roof: Ethmoid’s cribriform plates

• Floor: Palatine processes of maxillae and horizontal plates of palatine bones

Special Parts of the Skull

• Nasal Cavity

• Paranasal Sinuses

• Orbits

• Hyoid Bone

Paranasal Sinuses

• Air-filled sinuses are located within frontal, ethmoid, sphenoid, and maxillary bones. Lined with mucous membrane, they are extensions of the nasal cavity that help to warm, moisten, and filter inhaled air. Lighten the skull.

Hyoid Bone

Lies inferior to the mandible. The only bone with no direct articulation with any other bone. Acts as a moveable base for the tongue.

Vertebral Column

Formed form 26 bones in the adult. Transmits the weight of the trunk to the lower limbs. Surrounds and protects the spinal cord. Serves as attachment sites for muscles of the neck and back.

Major Regions of the Vertebral Column

• Seven cervical vertebrae of the neck region

• Twelve thoracic vertebrae

• Five lumbar vertebrae

• Sacrum of five fused bones (inferior to lumbar vertebrae)

• Coccyx is inferior to the sacrum

Curvatures of the Spine

Curvature increases resilience of spine

• Cervical and lumbar concave (curves inward) posteriorly

• Thoracic and sacral convex (curve outward) posteriorly

Primary Curvatures of the Spine

Thoracic and sacral curvatures are present at birth. Convex form.

Secondary Curvatures of the Spine

Cervical and lumbar curvatures develop when baby beings to walk. Concave form.

Ligaments of the Spine

Major supporting ligaments are anterior longitudinal ligament and posterior longitudinal ligament.

Anterior Longitudinal Ligament

Attaches to bony vertebrae and intervertebral discs, prevents hyperextension.

Posterior Longitudinal Ligament

Narrow and relatively weak. Attaches to intervertebral discs.

Ligament Flavum

Posterior, Connects the laminae of adjacent vertebrae and stretches during forward bending and record upon straightening.

Intervertebral Discs

Cushion like pads between vertebrae. Composed of Nucleus pulpous, and annuls fibrosis. Shock absorbers.

Nucleus Pulposus of Intervertebral Discs

Gelatin inner sphere, absorbs compressive stresses.

Anulus Fibrosus of Intervertebral Discs

Outer ring formed of ligament, inner ring formed of fibrocartilage, contains nucleus pulposus. Rings surrounding nucleus proposus to keep it contained.

Structure of Vertebrae

• Body

• Vertebral arch

• Vertebral foramen

• Spinous process

• Transverse process

• Superior and inferior articular processes

• Intervertebral foramina