Biology 2404 A&P Basics

The bones that make up the skeleton can be one of five distinct shapes: square, long, round, flat, and irregular. Bones also have distinct markings that help identify them.

Examples of these markings are:

Head rounded articular process at the proximal end of a bone

Condyle rounded articular process at the distal end of a bone

Epicondyle a small raised area above a condyle for joint capsule attachment

Foramen a short passageway through bone for vessels and nerves

Meatus a long canal like passageway

Fossa a depression in bone

Sinus a cavity in bone lined by a mucous membrane

Tuberosity a large rounded projection for muscle attachment

Tubercle a small rounded projection

Fissure a slit like opening through bone

Associated structures that are seen with bone are cartilage, tendons, and ligaments.

Cartilage is the basis for most bone formation and remains at the ends of many bones to help form joints. Tendons are epimysial connective tissue extensions of muscle that attach to bones. Ligaments are periosteal connective tissue extensions of bone that help join bone to bone.

Articulated Skeleton

Bone markings

Drawing of Supportive Connective Tissues

Classification of Cartilage

Cartilage cells or chondrocytes produce collagen fibers and proteoglycans such as chondroitin sulfate to form the cartilage matrix that create the three types of cartilage.

Hyaline cartilage is the most abundant type of cartilage. It forms most of early fetal skeleton and will remain over articular surfaces of joints, in the respiratory system airways, and at the ends of ribs. Elastic cartilage contains elastic fibers within the collagen and is found in the ears and epiglottis of the larynx. Fibrous cartilage has thick layers of collagen and is found in areas of great weight bearing pressure such as the intervertebral discs and the menisci of the knee.

Hyaline Cartilage Histology

Elastic Cartilage Histology

Fibrous Cartilage Histology

Intervertebral Disc Model : Lumbar

Classification of Bones

Bone shapes determine bone classification. For most bone shapes, there is a spongy arrangement internally and a compact bony arrangement externally. This arrangement is seen in short (square), round, flat, and irregular bones.

For long bones, the matrix arrangement is modified. Long bones do have spongy centers, but most of the center is hallowed out to create a space or marrow cavity. This cavity along the length or shaft of bone is called the yellow marrow cavity because it is filled with fat or adipose tissue.

The ends of long bones or the epiphyseal regions look just like the other bones with spongy filling the center and compact bone on the outside.

Bone Shapes

Formation of Bone

Bone formation is based on a connective tissue plate or model. Ossification is the process where one tissue is turned into bone. Precursor bone cells are deposited in the connective tissue matrix and begin secreting bone. This process is called intramembranous ossification. If cartilage cells are deposited on the connective tissue matrix and then later changed to bone, the process is called endochondral ossification.

Both occur in the fetus in order to develop the skeleton. Ossification steps will also occur in bone fracture repair.

The bone cells responsible for ossification are called osteoblasts. Remember that bone is a connective tissue and the cells secrete their fiber and ground substance fluid to form a matrix. The fiber for bone is collagen and the ground substance contains hydroxyapetate salts such as Calcium Carbonate and Calcium Phosphate in addition to other substances.

As osteoblasts lay down their foundation, the matrix can take one of two arrangements: compact or spongy. External forces such as gravity work on the fetus during development to help determine the matrix arrangement as well as shape and projections of individual bones.

All bones will have both an outer compact arrangement and an internal spongy arrangement.

Compact bone is regularly arranged into functional units called osteons that makes it dense. Spongy bone has a lattice like arrangement called trabecular or cancellous. Blood supply is important to bone, since it is a living tissue and replaces itself yearly. Blood vessels will follow the structure of the bone, such as the Haversian canals seen in compact bone.

Red marrow containing blood precursor cells can be found in areas of some spongy bone.

Once the osteoblasts secrete its matrix, the bone cell is trapped. These cells then mature and are called osteocytes whose function is to maintain, repair, and replace the bony matrix.

As ossification occurs, there is still left over connective tissue and cartilage. The left over connective tissue is found both inside and outside the forming bone. It will become the endosteum and periosteum of bone. These connective tissue layers will house bone cells such as the osteoblasts and a modified white blood cell called the osteoclasts. The periosteum will also form the ligaments for bone. Osteoblasts and osteoclasts in these regions are under hormonal control by thyroid hormone, growth hormone, Parathormone, Calcitonin, and the reproductive hormones. Osteoblasts build bone while osteoclasts tear down and destroy bone. It is a dynamic process that is usually balanced, especially when dealing with calcium levels in the body.

The cartilage that is left at the ends of the bone helps in joint formation to provide a smooth surface, especially in moveable, Synovial joints.

Chemical analysis of bone reveals approximately 33% organic compounds, mainly collagen and approximately 67% inorganic compounds, mainly salts. The minerals found in the inorganic matrix of bone are as follows: 99% Calcium, 88% Phosphate, 80% Carbonate, 50% Magnesium, 35% Sodium, and 4% Potassium.

Histology of Bone

Intramembranous Ossification

Endochondral ossification

Fetal bones

Sectioned bones

Bone Histology model

Bone Growth

Bone growth can occur in two planes: length and width. Lengthening of bone occurs during the original ossification processes at growth plates or metaphyseal regions in bones that use endochondral ossification processes and at fontanels for bones that use intramembranous ossification processes. Both growth plates and fontanels have the original tissue model that is still being replaced. At growth plates for short, round, long, and irregular bones, cartilage is being replaced by bony tissue. At fontanel regions for flat bones, connective tissue is being replaced by bony tissue. Growth plates and fontanels will close based on hormonal signals, thus ending longitudinal growth.

Width or appositional bone growth can happen at any time in life. Factors that influence this type of growth are gravitational forces, stress burdens, injury, and weight changes.

Bone is deposited or removed at the periosteal and endosteal layers based on the new needs of the body in order to overcome the changing requirements for support and movement.

Growth Plates

Fontonelles

Bone Plate to repair broken Bone

Factors that affect bone

Although we will discuss these hormones again in the endocrine system, it is good to be aware of the hormones that affect osteoblasts and osteoclasts. These hormones are:

Growth Hormone signals osteoblasts at metaphyseal growth plates

Signals Chondrocytes at growth plates

Thyroid Hormone works with Growth hormone

Signals energy production and protein synthesis

Reproductive Hormones signal the closing of the growth plates

Helps retain calcium in bone to maintain strength

Calcitonin signals osteoblasts to build bone

use calcium from blood, lowers blood Ca++ level

Parathormone signals osteoclasts to tear down bone

release calcium from bone, raises blood Ca++ level

Heredity factors (genes) will control the potential for a person’s height although nutritional factors (environment) are also important during development.

Vitamin D is needed for calcium absorption

Vitamin A and C help in matrix formation

Weight bearing exercises are also important to keep bone healthy and maintain calcium.

The Skeleton

Axial Skeleton

Skull: Cranial and Facial Bones

Anterior, Lateral, Exploded Anterior, Exploded Lateral, Ventral, Interior, Sagittal, Medial

Paranasal Sinuses: Medial View, Transverse View

Fetal Skull

Vertebral Column:

Vertebral regions= Cervical, thoracic, lumbar, sacral, coccygeal

Vertebral Numbers

Intervertebral Disc

Thoracic cage:

Sternum, Ribs, Thoracic vertebra, Hyoid bone

Appendicular Skeleton

Girdles:

Pectoral Girdle: Scapula, clavicle

Pelvic Girdle: Os coxa

Arm:

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Leg:

Femur

Tibia

Fibula

Tarsals

Metatarsals

Phalanges

Skeletal System Web Site click on the skeletal system for review and a quiz

Paranasal Sinuses

A sinus is a mucus membrane lined air space in bone. In the skull, sinuses help lighten the skull and help in the tonal quality of the voice.

There are five skull bones that contain sinuses around the nasal cavity and together are called the paranasal sinuses. The paranasal sinuses are named for the bones involved which are the frontal, maxillary, sphenoid, ethmoid. The other bone that contains a sinus is the mastoid process of the temporal bone. The mastoid process can be felt behind the ear.

Joints

Joints are defined as a bone or components of a bone meet. They provide support for the skeleton and can provide movement for the body.

Joints can be classified based on anatomical structure and physiological movement.

Anatomical classifications are: Fibrous, Cartilaginous, and Synovial.

Because the structure dictates the function, this also determines the joint classifications.

Fibrous joints have fibrous connective tissue between the bones. They hold the bones together and do not usually allow movement. These joints are also known as synarthroses.

Cartilaginous joints have cartilage tissue between the bones. They can allow for limited movement if necessary. These joints are also known as amphiarthroses.

Synovial joints have a unique structure that allows a space between the bone. They have a joint capsule, joint fluid, and other supporting structures such as ligaments that allow for free movement. Synovial joints are also known as diarthroses.

Examples of each joint type are as follows:

Fibrous Synarthrotic Joints

Syndesmosis interosseous membrane between radius/ulna & tibia/fibula

Synostosis sutures between bones of the skull

Gomphosis periodontal ligament between skull and teeth

Cartilaginous Amphiarthrotic Joints

Symphysis at intervertebral discs and between pubic bones of pelvis

Synchondrosis metaphyseal or growth plate region, a temporary joint

Synovial Joints all freely moveable joints that have movement in a body plane and within a certain range.

Synovial Joint Structure:

* articular hyaline cartilage

* joint cavity or space

* articular capsule

* Synovial membrane that lines the capsule

* Synovial fluid produced by the membrane

* additional structures for Synovial joints (some may or may not be present)

- ligaments: reinforce, strengthen and help direct bone movement

- fat pads : cushion

- fibrocartilage discs (menisci) : increase stability

- bursa : flat Synovial sacs that help to decrease friction

- tendon sheath: elongated bursa sacs wrapped around tendons to decrease friction

Synovial Joint stability depends on

1) Shape of articular surfaces (how well the bones fit together)

2) Ligaments

3) Muscle tone via tendons of origin and insertion

4) Joint capsule thickness

Synovial Joint drawing

Synovial Joint Structures

Synovial Joint models

Synovial Joint Radiograph: the Knee

Movement by Synovial Joints

Movement achieved by Synovial joints is based on muscle shortening for an isotonic contraction that produces motion. Muscles are anchored by their tendons of origin in order to pull (never push) their tendons of insertions which are attached to bones across a moveable joint. Movement is created when a more moveable bone is pulled toward a less moveable or stationary bone. Movement can be summarized as the plane of motion + the range of motion.

Planes of motion are along the axis formed by the three major body planes which are transverse, frontal, and sagittal.

Range of motion [ROM] can be nonaxial, uniaxial (one plane), biaxial (two planes), and tri or multiaxial (all three planes).

With the planes and range of motion, three general types of movement can be identified: gliding, angular, and rotational.

Gliding :: one flat surface slips over another

Angular :: changing the angles that form a circle

Flex, extend, abduction, adduction, circumduction

Rotation :: turning of a bone along its long axis

Pivot, rotate

Other specialized movements can be seen at certain joints ::

Supination / pronation radius/ulna

Inversion / eversion foot

Protraction / retraction mandible

Elevation / depression mandible

Opposition thumb

The major joints identified in the body are the shoulder, elbow, hip, and knee.

Each has alternate surgical names and can be identified either by bone fit or physiological movement. Joints are usually named for bones involved from proximal to distal.

Shoulder Glenohumeral Joint Ball and socket Multiaxial

Elbow Cubital Joint Hinge uniaxial

Hip Coxal Joint Ball and socket multiaxial

Knee Stifle Joint hinge biaxial

Due to bone fit and other stabilizing factors, each joint has unique movement as well as problems.

Medical Terminology

Ad- to, toward amphi- both

Ab- away, from ankyl/o- bent, crooked

Arthro- joint articul/o- joint

Brachi- arm cost/o- rib

Circum- around fract- break

Crani/o- skull gnath- jaw

Genicula- knee like structure man- hand

Ili/o- ilium nas/o- nose

Myel/o- marrow os, or/o- mouth

Os, osteo bone orth/o- straighten

Pterygo- wing rach/i- spine

Sacr/o- sacrum synov/i- synovial

Spin/o- spine, vertebral column lumb/o- lumbar

Scapul/o- scapula phalang/o- phalanges

Mandibul/o- mandible rad/i- radius

Brachy- short hyo- u-shaped

Styl/o- stake, pole ante- before

Crur- shin, leg circum- around

Exercises/Activities

Identify Bones of axial and appendicular skeleton

Example One, Example Two, Example Three, Example Four, Example Five

Compare and contrast the human and cat articulated skeleton using 6 similarities and 6 differences.

Chicken Bone Experiment

Ox (beef) tail: Purchase an ox tail from the grocery store.
Describe the vertebra and intervertebral disc parts seen and give their function. Use gloves to handle specimen!

Palpation points: Identify these palpation points. Pick 6 of them and explain how they are used clinically.

ROM : give the range of motion for all major types of joints

fibrous

cartilagenous

synovial : shoulder, elbow, foot, vertebral column

ID bones and stabilizing factors for a major joint

ID bone shape

Specimens : Femur section ID

Bone histo Identify

Ingredients in a Joint health label : Go to the store (GNC, Whole Foods, Pharmacy section of various stores) and read the label for a Joint Health product. Write down two ingredients that you do not recognize and research their use in this product.

Skeletal review and quizzes : click on appropriate system to begin

Concept Map: Make a concept map of the skeletal system (histo and gross) anatomy using the bone tissue and bones involved. Include joint types and movements as well. This concept map is part of your LAR lab report (if selected) included as a document insert or as an additinal PDF scan of the map.

Case Study

Applications

Sprains

DJD

Dislocations

Aging changes

Arthritis: Osteoarthritis, Rheumatoid

Bursitis / Tendonitis

Cartilage tears

Sports injury

Bone fractures

Deformities of the Spine: Lordosis, Kyphosis, Scoliosis