Handle the material gently, but firmly.

Transcription

1 Care and Handling of Material In this lab you may work with actual bone and/or with plastic or plaster models of bone. In both cases the material is not indestructible, and it is expensive and difficult to obtain. It is essential the material be handled with care. To avoid mishaps, please do the following: Handle the material gently, but firmly. Do not pick up skulls by inserting fingers into the eye orbits or the foramen magnum, or by the zygomatic arches. Pick them up with both hands supporting the skull. Do not set down material on a slanted surface such as a desktop from which it might slide. If an accident does occur, inform the instructor immediately. 6

2 A Brief Introduction to Muscles: Muscle Anatomy and Actions and Their Affect on Bones Bones are shaped and remodeled during the lifetime of the individual as they respond to functional demands and to muscle activity and attachments. Muscles are made up of cells called muscle fibers. Muscle fibers are joined to bones by tendons, a tough flexible connective tissue. One end of a muscle is attached to a bone that does not move. This end is called the origin. The other end is attached to a bone that moves when the muscle contracts. This end is called the insertion. Generally, when the muscle contracts, the insertion is pulled toward the origin. For example, the biceps muscle functions to bend the elbow and rotate the forearm. It has two anchor points on the scapula. One origin attaches above the glenoid fossa and the other originates from the coracoid. The biceps insertion is attached to the radius. When the biceps muscle contracts it pulls the forearm up (see illustration). Muscles can only pull, however; they cannot push. To function properly they must operate in pairs, called flexors and extensors. The flexor bends a joint and brings a limb closer to the body. The extensor reverses the action. For example, the biceps is a flexor that bends the elbow and pulls the forearm and hand toward the shoulder. The triceps is an extensor with its origin on the humerus and scapula, and its insertion on the olecranon process of the ulna. When the triceps contracts it straightens the elbow and pulls the forearm and hand away from the shoulder. The insertion may cover a smaller point on a bone than the origin, since the insertion tendon must move through a greater range of motion than the origin tendon. As noted in France, "If the tendon fibers covered a large area, some fibers at the extreme edge of the insertion would stretch farther during muscle contraction and could be strained or torn" (2007:61). The origin has a limited range of movement, and may be spread over a greater 7

3 area of bone. Since more force is applied to a smaller area, the point of insertion will be denser and rougher, showing more response to muscle attachment and activity than will the origin. As you study the skeleton, be aware that some bone features, such as the radial tuberosity, arise in response to such muscle activity. Vocabulary Extensor: One of a complementary pair of muscles. The extensor contracts to straighten a joint and move a limb away from the body. The complementary flexor does the opposite. Flexor: One of a complementary pair of muscles. The flexor contracts to bend a joint and bring a limb closer to the body. The complementary extensor does the opposite. Insertion: The end of the muscle that is attached to the bone that moves in response to the muscle contraction. The muscle contracts from the insertion toward the origin. Origin: The end of the muscle that is attached to the bone that does not move in response to the muscle contraction. The muscle contracts from the insertion toward the origin. Tendons: Muscles move bones by pulling tendons. One end of a tendon arises from the end of a muscle. The other is woven into the substance of a bone. 8

4 Human Osteology Formation and Study of the Human Skeleton Introduction When most of us see bone it is in a post-mortem state, perhaps in a classroom skeleton or in the pork chop we eat for dinner. In our mind's eye we see bone as a material that is inert: rigid, hard, and unchanging. As a matter of fact, bone is a living, dynamic material, made up of several kinds of tissues supplied by blood, which forms and reforms continually during the course of an individual's life. Bone is defined by Steinbock (1976:3) as a specialized connective tissue composed of "living cells embedded in an extra-cellular matrix of collagenous fibrils made rigid by calcium salts." This association of flexible and rigid elements gives bone a remarkable combination of strength, rigidity, and resistance to impact and stress. It allows bone to function as a source of internal support for the soft tissues, as an attachment for muscles, as protection for organs, as storage for and a source of blood calcium, and as an enclosure for the blood cell-producing marrow. In the course of the life of an individual from conception to death the skeleton may be altered from the normal range of development by aspects of the individual's internal and external environment. Bone Formation and Remodeling The process of bone formation, growth, and remodeling is very complex, and in certain details not well understood (Levine and Miller 1991:871-4). In this class it is necessary to have some basic knowledge of the processes involved in order to understand the cumulative impact of those processes on the bones we study. Throughout the lifetime of the individual, bone formation and remodeling takes place through the continual interaction of three types of bone cells: 1) osteoblasts, which form bone tissue 2) osteocytes, which maintain bone tissue 3) osteoclasts, which destroy bone tissue The actions of these cells are affected by various internal and external environmental factors such as genetic abnormalities, nutrition, growth and sex hormones, mechanical stress, metabolic disease, trauma, infection, and cultural alterations. And as the cells are affected, the bones they produce develop characteristic differences that can be identified by physical anthropologists. Differences in the bones at different ages allow estimation of age from the skeleton. Differences in the bones of males and females allow determination of sex from the skeleton. Height can even be estimated from certain fragmentary bones. 9

5 Other events that take place during the lifetime of the individual, such as childbirth, malnutrition, disease, injury, or particular types of repetitive physical activity, all leave characteristic marks on the bones that may be read by the trained anthropologist. The Growth of Bones At birth the human skeleton is composed mostly of a dense, fibrous connective tissue called cartilage. During growth, which may continue through roughly age 25, the majority of that cartilage is replaced by bone. In adults, the cartilage that remains provides support for body parts that don't carry much weight, such as the nose, ears, larynx, and trachea. It also is found in various joints where it absorbs shocks and provides lubrication for bone surfaces as they slide past one another. During embryonic development most of the skeleton is present as a kind of "scale model" made of cartilage. As embryonic and fetal growth occurs, new cartilage is added as older cartilage is degraded and replaced by bone. This process of replacement of cartilage by mineralized bone is called ossification, and the areas at which it occurs are called primary centers of ossification, or diaphyses (singular = diaphysis). After birth, most growth in bone length takes place at secondary centers of ossification or epiphyses (singular = epiphysis). Diaphyses are separated from epiphyses by thin layers of cartilage called growth plates. These are the points at which actual bone growth occurs. Bone length increases as new cartilage is produced and the older cartilage is ossified (calcium is added). (Growth in width occurs as new cells are added around the outside of the bone. At the same time, removal of bone is taking place on the internal surfaces of the bone.) When no new cartilage is produced, the old cartilage is completely converted to bone, and the epiphyses fuse to the diaphyses, growth stops. The fact that fusion typically occurs in a characteristic order and at an average age allows anthropologists to estimate age at death from skeletal material. Epiphysis (cap) Diaphysis (shaft) Growth plate As noted above, however, the activities of the bone producing and destroying cells do not stop at the end of growth, but continue to act in response to stimuli throughout the lifetime of the individual. For example, maintenance of normal healthy bone requires day-to-day exercise; in the absence of such exercise (as in an astronaut weightless in space, for instance) osteoclasts begin to dissolve bone minerals, weakening the skeleton. Pregnancy in 10

6 a woman whose diet does not contain sufficient minerals for fetal development can also result in demineralization of the mother's skeleton. Calcium can also be redeposited, however, as a number of senior citizens participating in exercise programs have discovered. Bone remodeling also allows bones to heal if broken, to strengthen in response to repetitive exercise, to remodel in response to childbirth, to degenerate in response to aging or disease... and so on and so forth. Events that take place from conception to death can leave characteristic marks on the skeleton that the trained anthropologist can read like an open book, allowing the bones to speak to the lifetime of that individual. Bibliography Campbell, Neil A., Lawrence G. Mitchell and Jane B, Reece 1994 Biology: Concepts and Connections. Redwood City, California: Benjamin/Cummings Publishing Company, Inc. French, Diane L Lab Manual and Workbook for Physical Anthropology, Sixth Edition. Thompson Wadsworth. Levine and Miller 1991 Biology: Discovering Life. Lexington, Massachusetts: D. C. Health and Company. Steinbock, R. Ted 1976 Paleopathological Diagnosis and Interpretation: Bone Diseases in Ancient Human Populations. Springfield, IL: Charles C. Thomas 11

7 STANDARD ANATOMICAL POSITION AND ORIENTATION OF THE BODY l Standard Anatomical Position refers to the body when it is positioned with the feet facing forward and the hands at the side with the palms forward. In this position, no long bones are crossed. When the back of the hands face forward, the radius crosses over the ulna. l Always orient the bone you are studying as it is positioned in you body. When you are determining the side from which a bone came, the bone always will be from the same side as it is in your body. Median Sagittal Plane (Midline of body) Cranial Superior Proximal Posterior (Dorsal) Anterior (Ventral) Distal Medial Lateral Inferior Caudal Anterior Cranial Posterior Caudal 12

8 Human Osteology Anatomical Terms l Learning and using these terms will make it much easier to learn the features of the bones and to orient bones in the body. Directional Vocabulary Anterior Caudal Cranial Distal Dorsal External Inferior Internal Lateral Medial Posterior Proximal Superior Ventral Toward the front of the body Toward the tail or coccyx Toward the head On a limb, away from the body (Hint: a distance from the body) Toward the back Outside of Below; lower surface Inside of Away from the midline; to the side Toward the midline; to the middle Toward the rear of the body On a limb, toward the body (Hint: in the proximity of the body) Above, top surface Toward the abdomen Human Osteology: Directional Vocabulary Exercise 1 l It is easier to understand and remember these terms if they are organized in oppositional pairs rather than alphabetically. Instructions: Define each pair of descriptive words. 1. Anterior/Posterior 2. Dorsal/Ventral 3. Distal/Proximal 4. Caudal/Cranial 5. Inferior/Superior 6. Lateral/Medial 13

9 Human Osteology: Standard Anatomical Position & Directional Terms Exercise 2 Station A. Human. Instructions: Examine the human skeleton. Identify the median sagittal plane (midline of the body). Using information from previous pages, label the illustration with the following directional term(s): ª Cranial/Caudal; ª Proximal/Distal; ª Medial/Lateral. ª Anterior/Posterior; ª Dorsal/Ventral; Station B. Ape. Instructions: Examine the ape skeleton. Using information from previous pages, label the illustration with the following directional term(s): ª Cranial/Caudal; ª Anterior/Posterior; ª Dorsal/Ventral; ª Proximal/Distal. 14

10 Human Osteology: Directional Vocabulary and Bones Exercise 3 Instructions: At each station examine the bone(s); then refer to the appropriate lab manual pages (those related to the bone(s) at the station) to fill in the blanks using the directional vocabulary terms from the previous pages. Station C. Clavicle. l The the sternum, while the end of the clavicle is rounded for articulation with end is flattened for articulation with the scapula. The conoid tubercle is located and on the clavicle. Station D. Scapula. l The body of the scapula is concave on the scapular spine is on the surface. The surface. The glenoid fossa is and is the point of articulation with the head of the humerus. Station E. Rib. l Most of the ribs are flat, but the first rib is flat and is very much shorter than the rest. Station F. Humerus. l The rounded head at the end of the humerus articulates with the glenoid fossa of the scapula. The olecranon fossa is located at the distal end on the Station G. Femur. l The acetabulum. Station H. Radius/Ulna. l The radius is the the surface of the humerus. end of the femur articulates with the os coxa at the bone of the forearm, while the ulna is bone of the forearm. Station I. Tibia/Fibula. l The tibia is the the bone of the lower leg, while the fibula is bone of the lower leg. 15

11 Human Osteology Anatomical Terms l Learning and using these terms will make it much easier to learn the features of the bones and to orient bones in the body. Vocabulary used to describe features of the bones Condyle (condyles) Epicondyle Conoid Rounded projection at the point of articulation with another bone Projection on a bone above a condyle serving for the attachment of muscles and ligaments Cone shaped Crest (crests) A projecting ridge Diaphysis (diaphyses) Epiphysis (epiphyses) Foramen (foramina) The shaft of a bone A process of bone initially attached to another piece of bone by cartilage, and usually later consolidated with it by bone A hole or opening Fossa (fossae) A depression or pit Meatus (meatuses) A canal Process (processes) A projection or prominence of bone Torus (tori) An elevation or prominence Tubercle (tubercles) Tuberosity (tuberosities) A small, knob-like projection (a small tuberosity) A large, rough projection or eminence on bone 16

12 Human Osteology: Features of the Bones Exercise 4 Instructions: At each station, first define the term, and then looking at the picture and the bone, name the feature on that bone with that term included in its name. Station J. Meatus (meatuses) l On the lateral view of the skull Station K. Foramen (foramina) l On the mandible l On the inferior (basal) view of the skull Station L. Condyle (condyles) l On the inferior (basal) view of the skull Station M. Process (processes) l On the sternum l On the dorsal view of the scapula l On the proximal end of the ulna Station N. Fossa (fossae) l On the lateral view of the scapula l On the posterior view of the distal humerus Station O. Tuberosity (tuberosities) l On the ischium of the os coxa l On the anterior view of the proximal tibia Station P. Tubercle (tubercles) l On the inferior (caudal) view of the clavicle Station Q. Crest (crests) l On the os coxa 17