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Bidang ini sejajar dengan bidang median. Bidang horizontal: bidang yang terletak melintang melalui tubuh bidang X-Y. Bidang ini membagi tubuh menjadi bagian atas superior dan bawah inferior. Bidang koronal: bidang vertikal yang melalui tubuh, letaknya tegak lurus terhadap bidang median atau sagital.

Contoh: Mulut terletak superior terhadap dagu. Contoh: Pusar terletak inferior terhadap payudara. Contoh: Lambung terletak anterior terhadap limpa. Contoh: Jatung terletak posterior terhadap tulang rusuk. Contoh: Otot kaki terletak superfisial dari tulangnya. Profunda: lebih jauh dari permukaan. Contoh: Tulang hasta dan pengumpil terletak lebih profunda dari otot lengan bawah.

Contoh: Jari manis terletak medial terhadap jari jempol. Contoh: Telinga terletak lateral terhadap mata.

Contoh: Siku terletak proksimal terhadap telapak tangan. Contoh: Pergelangan tangan terletak distal terhadap siku. Istilah gerakan anatomi[ sunting sunting sumber ] Adanya persendian memungkinkan gerakan yang bermacam-macam. Berbagai gerak dengan persendian dikontrol oleh kontraksi otot. Pronasi dan Supinasi Lengan yang melakukan gerakan fleksi dan pronasi. Otot biceps brachii tidak berkontraksi penuh.

Lengan yang melakukan gerakan fleksi dan supinasi. Otot biceps brachii berkontraksi penuh. If a DNA error is not repaired, it becomes a mutation. A mutation is any sequence of nucleotides in a DNA molecule that does not exactly match the original DNA molecule from which it was copied. Mutations include an incorrect nucleotide substitution , a missing nucleotide deletion , or an addition nucleotide not present in the original DNA molecule inser- tion.

When an insertion mutation occurs, it causes all subsequent nucleotides to be displaced one position, producing a frameshift mutation. Radiation or chemicals that cause mutations are called mutagens. Car- cinogens are mutagens that activate uncontrolled cell growth cancer.

Protein synthesis The DNA in chromosomes contains genetic instructions that regulate development, growth, and the metabolic activities of cells. The DNA instructions determine whether a cell will be that of a pea plant, a human, or some other organism, as well as establish specific characteristics of the cell in that organism.

For example, the DNA in a cell may establish that it is a human cell. If during development, it becomes a cell in the iris of any eye, the DNA will direct other information appropriate for its loca- tion in the organism, such as the production of brown, blue, or other pig- mentation.

DNA controls the cell in this manner because it contains codes for polypeptides. Many polypeptides are enzymes that regulate chemical reactions and influence the resulting characteristics of the cell. Thus, from the molecular viewpoint, traits are the end products of metabolic processes regulated by enzymes. A gene is defined as the DNA segment that codes for a particular enzyme or other polypeptide one-gene-one-polypeptide hypothesis.

The process that describes how enzymes and other proteins are made from DNA is called protein synthesis. There are three steps in protein synthesis—transcription, RNA processing, and translation. In translation, the processed RNA molecules are used to assem- ble amino acids into a polypeptide. There are three kinds of RNA molecules produced during transcription, as follows.

A triplet group of three adjacent nucleotides on the mRNA, called a codon, codes for one specific amino acid. For example, the codon composed of the three nucleotides cytosine-guanine-adenine CGA codes for the amino acid arginine. Interactions among various parts of the tRNA molecule result in base-pairings between nucleotides, folding the tRNA in such a way that it forms a three- dimensional molecule.

In two dimensions, a tRNA resembles the three leaflets of a clover leaf. One end of the tRNA attaches to an amino acid. Another portion of the tRNA, specified by a triplet com- bination of nucleotides, is the anticodon. Within the nucleolus, various proteins imported from the cytosol are assembled with rRNA to form large and small ribosome subunits.

Ribosomes have three binding sites—one for the mRNA, one for the tRNA that carries a growing polypeptide chain, and one for a second tRNA that delivers the next amino acid that will be inserted into the growing polypeptide chain.

Here are the details of transcription, RNA processing, and protein syn- thesis also see Figures and See 1 in Figure See 2 in Figure See 3 in Figure Figure Transcription and RNA processing. In the first modification, noncoding inter- vening sequences called introns are removed, leaving only exons, sequences that express a code for a polypeptide.

A second modifica- tion adds two special sequences—a 5-inch cap to one end of the mRNA and a poly-A tail to the other end. See 4A, 4B, and 4C in Figure In the cytoplasm, amino acids attach to one end of the tRNAs. See 6 in Figure Step 7 in Figure shows an incoming tRNA approaching a yet to be vacated position. Then, the first tRNA is released. The ribosome moves over one codon position, thereby putting the second tRNA in the first position and vacating the sec- ond position.

Step 8 in Figure shows this process after several tRNAs have delivered amino acids. Now, the two amino acids being held by the tRNA in the first position are transferred to the amino acid of the newly arrived tRNA, forming a polypeptide chain of three amino acids. Again, the tRNA in the first position is released, the ribosome moves over one codon position, and the second tRNA position is vacant. As each new tRNA arrives, the polypeptide chain is elongated by one new amino acid, growing in sequence and length as dictated by the codons on the mRNA.

See 9 in Figure Once the polypeptide is released, interactions among the amino acids give it its special three-dimensional shape. Subsequent processing by the endo- plasmic reticulum or a Golgi body may make final modifications before the protein functions as a structural element or an enzyme.

Gap junctions allow the transmission of electrical impulses and exchange of material between neighboring cells.

In mitosis, which of the following steps is not a characteristic of telophase? Chromosomes disperse into chromatin. Microtubules shorten and pull chromosomes to opposite poles. A cleavage furrow is visible.

The cytoplasm is divided into two cells. Critical Thinking Questions 1. Why is genetic recombination so crucial for a species? What two amino acids would result? Microtubules 2. These cells are arranged and organized into four basic tissues that, in turn, are assembled to form organs. When looking at tissue at a microscopic level, the ability to detect the presence and location of the four basic tissues allows identification of the organ at which you are looking.

A basic knowledge of the general characteristics and cellular composition of these tissues is essential in histology, which is the study of tissues at the microscopic level. Tissues are groups of similar cells performing a common function. There are four categories of tissues: There is little inter- cellular material. Nutrient and waste exchange occurs through neighboring connective tissues by diffusion. The basal surface rests on con- nective tissue.

A thin, extracellular layer called the basement mem- brane forms between the epithelial and connective tissue. There are two kinds of epithelial tissues: Epithelium that covers or lines Epithelial tissues that cover or line surfaces are classified by cell shape and by the number of cell layers. The following terms are used to describe these features: Cell shape: These cells produce secretions sweat, for example or absorb substances digested food, for example.

These thick cells serve to protect underlying tissues or may function to absorb substances.

Some have microvilli, minute surface extensions, to increase surface area for absorbing substances, while others may have cilia that help move substances over their surface such as mucus through the respiratory tract. Tissues 43 Number of cell layers: Names of epithelial tissues include a description of both their shape and their number of cell layers.

The presence of cilia may also be identified in their names. For example, simple squamous describes epithelium consist- ing of a single layer of flat cells. Pseudostratified columnar ciliated epithe- lium describes a single layer of tall, ciliated cells of more than one size. Stratified epithilieum is named after the shape of the outermost cell layer.

Thus, stratified squamous epithelium has outermost layers of squamous cells, even though some inner layers consist of cuboidal or columnar cells. These and other epithelial tissues are illustrated in Figure Glandular epithelium Glandular epithelium forms two kinds of glands: For example, the thyroid gland secretes the hormone thyroxin into the bloodstream, where it is distributed throughout the body, stim- ulating an increase in the metabolic rate of body cells.

Examples of secretions include sweat, saliva, milk, stomach acid, and digestive enzymes. Exocrine glands are classified according to their structure see Figure A multicellular gland consists of a group of secretory cells and a duct through which the secretions pass as they exit the gland.

Figure Exocrine glands can be classified as either simple or com- pound and according to tubular or alveolar structure. Some general characteristics of connective tissues follow. Most connective tissues have a nerve supply as does epithelial tissue.

There is a wide range of vascularity among connective tissues, although most are well vascularized unlike epithelial tissues, which are all avascular. Connective tissue consists of scattered cells immersed in an intercellular material called the matrix. The matrix consists of fibers and ground substance. The kinds and amounts of fiber and ground substance determine the character of the matrix, which in turn defines the kind of connective tissue. Fundamental cell types, characteristics of each kind of con- nective tissue, are responsible for producing the matrix.

Immature forms of these cells whose names end in blast secrete the fibers and ground substance of the matrix. Cells that have matured, or differ- entiated whose names often end in cyte , function mostly to main- tain the matrix. Fibroblasts are common in both loose and dense connective tissues. Adipocytes, or flat cells, occur in loose connective tissue. Reticular cells resemble fibroblasts, but have long, cellular pro- cesses extensions. They occur in loose connective tissue.

Chondroblasts and chondrocytes occur in cartilage. Osteoblasts and osteocytes occur in bone. Hemocytoblasts occur in the bone marrow and produce ery- throcytes red blood cells , leukocytes white blood cells , and thrombocytes blood platelets. In addition to the fundamental cell types, various leukocytes migrate from the bone marrow to connective tissues and pro- vide various body defense activities.

Macrophages engulf foreign and dead cells. Mast cells secrete histamine, which stimulates immune responses. Plasma cells produce antibodies. Matrix fibers are protein that provide support for the con- nective tissue. There are three types: Collagen fibers, made of the protein collagen, are both tough and flexible.

Elastic fibers, made of the protein elastin, are strong and stretchable. Ground substance may be fluid, gel, or solid, and, except for blood, is secreted by the cells of the connective tissue. Cell adhesion proteins hold the connective tissue together. Proteoglycans provide the firmness of the ground substance.

Hyaluronic sulfate and chondroitin sulfate are two examples. There are five general categories of mature connective tissue: Loose connective tissue has abundant cells among few or loosely arranged fibers and a sparse to abundant gelatinous ground substance. Dense connective tissue has few cells among a dense network of fibers with little ground substance. Cartilage has cells distributed among fibers in a firm jellylike ground substance.

Cartilage is tough, but flexible, avascular, and without nerves. Bone has cells distributed among abundant fibers in a solid ground substance containing minerals, mostly calcium phos- phate.

Bone is organized in units, called osteons Haversian sys- tem. Each osteon consists of a central canal Haversian canal , which contains blood vessels and nerves, surrounded by con- centric rings lamellae of hard matrix and collagen fibers.

Between the lamellae are cavities lacunae that contain bone cells osteocytes. Canals canaliculi radiate from the central canal and allow nutrient and waste exchange with the osteocytes. Blood is composed of various blood cells and cell fragments platelets distributed in a fluid matrix called blood plasma.

All mature connective tissues originate from embry- onic connective tissue. There are two kinds of embryonic connective tissues: Mesenchyme is the origin of all mature connective tissues.

Mucous connective tissue is a temporary tissue formed during embryonic development. An epithelial membrane is a combination of epithelial and connective tissues working together to perform a specific function. As such, it acts as an organ. There are four principle types of epithelial membranes: The serous mem- branes that line the heart, lungs, and abdominal cavities and organs are called the pericardium, pleura, and peritoneum, respectively.

These include the nasal cavity and the digestive, respiratory, and urogenital tracts. Nervous Tissue Nervous tissue consists of two kinds of nerve cells: Each cell consists of the following parts see Figure The cell body contains the nucleus and other cellular organelles. The dendrites are typically short, slender extensions of the cell body that receive stimuli. The axon is typically a long, slender extension of the cell body that sends stimuli.

Figure A neuron is a basic structural unit of the nervous system con- taining a cell body, dendrites, and an axon. The many nuclei in each cell multinucleated cells are located near the outside along the plasma membrane. Skeletal muscle is attached to bones and causes movements of the body. Because it is under your conscious control, it is also called voluntary muscle.

However, cardiac muscle cells have single, centrally located nucleus, and the muscle fibers branch often. Where two cardiac muscle cells meet, they form an intercalated disc containing gap junctions, which bridge the two cells.

The cells are elongated with tapered ends and do not appear striated. Smooth muscle lines the walls of blood vessels and certain organs such as the digestive and urogenital tracts, where it serves to advance the movement of substances. Smooth muscle is called invol- untary muscle because it is not under direct conscious control.

Figure Three kinds of muscle tissue exist: Which of the following statements is true concerning skeletal muscle? Blood is a type of connective tissue. What type of epithelium, connective tissue, and muscle would you expect to see in the duodenum? Identify three locations in the body where the mechanical protection of stratified squamous epithelium is needed and found.

Microvilli 2. Besides providing a layer of protection from pathogens, physical abrasions, and radiation from the sun, the skin serves many functions as well as playing a vital role in homeosta- sis. This includes maintaining a constant body temperature via the acts of sweating or shivering and by making you aware of external stimuli through information perceived within the touch receptors located within the integu- mentary system.

It only takes one visit to a burn unit to see the value of skin and the many complications that arise when this organ is compro- mised. In this chapter, you see the diverse actions of the integumentary system, as well as the composition of the skin that allows it to perform these many functions.

The Skin and Its Functions The skin, or integument, is considered an organ because it consists of two tissues: In addition, accessory organs, such as glands, hair, and nails, are present, and together with the skin make up the integumentary system. A section of skin with various accessory organs is shown in Figure The skin consists of two layers, the epidermis and the underlying dermis.

Although technically not part of the skin, the hypodermis subcutaneous layer, or superficial fascia lies beneath the dermis. The Integumentary System 55 Figure A section of skin with various accessory organs. Four cell types are present: Mature keratinocytes at the skin surface are dead and filled almost entirely with keratin.

Melanin from the melanocytes is transferred to the keratinocytes. They form Merkel discs, which, in association with nerve endings, serve a sensory function.

Five layers make up the epidermis: The outermost layers are constantly shed. This layer is usually apparent only in thick skin palms of hands and soles of feet. These cells contain keratohyaline granules, which contribute to the formation of keratin in the upper layers of the epidermis. These cells are moderately active in mitosis. The Dermis The second layer of the skin, the dermis, consists of various connective tis- sues.

The Integumentary System 57 a gelatinous matrix containing collagen, elastic, and reticular fibers. The structure provides strength, extensibility the ability to be stretched , and elasticity the ability to return to its original form.

The dermis consists of two layers: In the hands and feet, the dermal papillae generate epidermal ridges sweat from the epidermal ridges leaves fingerprints. The Hypodermis The hypodermis subcutaneous layer, or superficial fascia lies between the dermis and underlying tissues and organs.

It consists of mostly adipose tis- sue and is the storage site of most body fat. It serves to fasten the skin to the underlying surface, provides thermal insulation, and absorbs shocks from impacts to the skin.

Accessory Organs of the Skin The following accessory organs skin derivatives are embedded in the skin: Hair is composed of the fol- lowing structures: The hair shaft is the portion of the hair that is visible on the sur- face of the skin. The hair root is the portion of the hair that penetrates the skin epidermis and dermis. The hair follicle is the sheath that surrounds the hair in the skin.

The bulb is the base of the hair follicle. The matrix is the bottom of the hair follicle located within the bulb. Here, cells are actively dividing, producing new hair cells. As these cells differentiate, they produce keratin and absorb melanin from nearby melanocytes. The keratin they leave behind contributes to the growth of the hair. The color of the hair is determined by the pigments absorbed from the melanocytes. The arrector pili is a smooth muscle that is attached to the hair follicle.

The semilunar lighter region of the nail, the lunula, is the area of new nail growth. Below the lunula, the nail matrix is actively producing nail cells, which contribute to the growth of the nail. Sweat consists of water with various salts and other substances. There are four kinds of sudorifer- ous glands: Eccrine glands occur under most skin surfaces and secrete a watery solution through pores openings at the skin surface , which serve to cool the skin as it evaporates.

Apocrine glands occur under skin surfaces of the armpits and pubic regions and, beginning with puberty, secrete a solution in response to stress or sexual excitement.

The solution, more vis- cous than that secreted by eccrine glands, is secreted into hair follicles.


Ceruminous glands secrete cerumen earwax into the external ear canal. Wax helps to impede the entrance of foreign bodies. Mammary glands produce milk that is secreted through the nip- ples of the breasts. Sebum inhibits bac- terial growth and helps prevent drying of hair and skin. An accumulation of sebum in the duct of a sebaceous gland produces whiteheads, blackheads if the sebum oxidizes , and acne if the sebum becomes infected by bacteria.

Skin is very important in the metabolism of what important nutrient? The dermis is the storage site of most body fat and plays an important role in thermal regulation. Which type of epithelium is present within skin? Though it does perform these functions, bone is actually a very dynamic organ that is constantly remodeling and changing shape to adapt to the daily forces placed upon it.

Moreover, bone stores crucial nutrients, minerals, and lipids and produces blood cells that nour- ish the body and play a vital role in protecting the body against infection. All these functions make approximately bones of the human body an organ that is essential to your daily existence. Functions of Bones The skeletal system consists of bones, cartilage, and the membranes that line the bones. Each bone is an organ that includes connective tissue bone, blood, cartilage, adipose tissue, and fibrous connective tissue , nervous tis- sue, and muscle and epithelial tissues within the blood vessels.

Bones provide a framework for the attachment of muscles and other tissues. Bones such as the skull and rib cage protect internal organs from injury. Bones enable body movements by acting as levers and points of attachment for muscles. Bones serve as a reservoir for calcium and phosphorus, essential minerals for various cellular activities throughout the body. The production of blood cells, or hematopoiesis, occurs in the red marrow found within the cavities of certain bones.

Lipids fats stored in adipose cells of the yellow marrow serve as an energy reservoir. Types of Bones Bones come in several different types.

Long bones are longer than they are wide. The length of the bone, or shaft, widens at the extremities ends. Short bones are cubelike, about as long as they are wide. Flat bones, such as ribs or skull bones, are thin or flattened. Irregular bones, such as verte- brae, facial bones, and hip bones, have specific shapes unlike the other types of bones. The following two bone types are usually classified separately: Bone Structure There are two kinds of bone tissue see Figure Compact bone con- sists of cylindrical units called osteons Haversian systems.

Each osteon contains concentric lamellae layers of hard, calcified matrix with osteocytes bone cells lodged in lacunae spaces between the lamellae. Smaller canals, or canaliculi, radiate outward from a central canal Haversian canal , which contains blood vessels and nerve fibers.

Osteocytes within an osteon are connected to each other and to the central canal by fine cellular extensions. Figure Main features of a long bone. Trabeculae are similar to osteons in that both have osteocytes in lacunae that lie between cal- cified lamellae.

As in osteons, canaliculi present in trabeculae provide connections between osteocytes. However, since each trabecula is only a few cell layers think, each osteocyte is able to exchange nutrients with nearby blood vessels.

Thus, no central canal is necessary. Bones and Skeletal Tissues 63 Here are the main features of a long bone refer to Figure It is composed of compact bone tissue. It includes the epiphyseal line, a remnant of cartilage from growing bones. The adipose tissue inside the cavity stores lipids and forms the yellow marrow.

It contains osteoblasts bone-forming cells , osteoclasts bone-destroying cells , nerve fibers, and blood and lymphatic vessels.

Ligaments and ten- dons attach to the periosteum. Here are the main features of short, flat, and irregular bones: Bone Development The skeleton arises from fibrous membranes and hyaline cartilage during the first month of embryonic development. These tissues are replaced with bone by two different bone-building, or ossification, processes.

The process, occurring only in cer- tain flat bones, is summarized in two basic steps: The second ossification process, called endochondral ossification, occurs when hyaline cartilage is replaced by bone tissue. The process, occurring in most bones of the body, follows these steps: The osteoblasts produce spongy bone tissue.

The medullary cavity expands as it follows the spread of the primary ossification center to the ends of the bone. As in the shaft, a periosteal bud develops.

However, the spongy bone tissue that subsequently develops is not replaced by a medullary cavity. Bone Growth Bones elongate as chondrocytes in the cartilage of the epiphyseal plate divide.

These cell divisions produce new cartilage within the epiphyseal plate bordering the epiphyses. Bones and Skeletal Tissues 65 bordering the diaphysis, older cartilage is broken down by invading osteo- clasts and is eventually replaced by the expanding medullary cavity. Bone Homeostasis Remodeling is the process of creating new bone and removing old bone.

It occurs constantly in growing children as well as in adults in the follow- ing situations: Similarly, remodeling occurs when excess calcium is returned to the bone reservoir.

Surface Features of Bones The surfaces of bones bear projections, depressions, ridges, and various other features. A process projection on one bone may fit with a depres- sion on a second bone to form a joint. Another process allows for the attachment of a muscle or ligament. Grooves and openings provide pas- sageways for blood vessels or nerves. A list of the various processes and other surface features appears in Table Some bones are completely embedded in tendons.

Which of the following bone or bones represent s a flat bone? The skeleton arises from fibrous membranes and elas- tic cartilage during the early stages of embryonic development. T sesamoid bones 3. Though memorizing the names and locations of all bones is quite a tedious process, this knowledge can be very valuable.

This is especially true if you are planning a future in science, want to under- stand the language your physician is using, hope to do well in an anatomy course, or peruse scientific literature. Organization of the Skeleton The bones of the body are categorized into two groups, the axial skele- ton and the appendicular skeleton. The bones of the axial skeleton revolve around the vertical axis of the skeleton, while the bones of the appendic- ular skeleton make up the limbs that have been appended to the axial skele- ton.

A list of the bones in the axial and appendicular skeletons is given in Tables and , respectively. Major bones of both skeletons are shown in Figure Cranium and Facial Bones The skull consists of 8 cranial bones and 14 facial bones. The bones are listed in Table , but note that only six types of cranial bones and eight types of facial bones are listed because some of the bones as indicated in the table exist as pairs.

The bones of the skull provide protection for the brain and the organs of vision, taste, hearing, equilibrium, and smell. The bones also provide attachment for muscles that move the head and control facial expressions and chewing.

Figures and illustrate specific characteristics of these bones, while some general features of the skull follow: The spaces provide pliability for the skull when it passes through the birth canal and for brain growth during infancy. Bone growth eventually fills the spaces by age two. Their number and location vary. The cranial floor base denotes the bottom of the cranium.

These fossae, called the anterior, middle, and posterior cranial fossae, pro- vide spaces that accommodate the shape of the brain. Air enter- ing the cavity is warmed and cleansed by mucus lining the cavity. The cavities secrete mucus that drains into the nasal cavity. The cavities also act as resonance chambers that enhance vocal and singing quality. Figure Major bones of the axial and appendicular skeletons. The Skeletal System 73 Hyoid Bone Located in the neck, the hyoid bone is isolated from all other bones refer to Figure It is connected by ligaments to the styloid processes of the temporal bones.

Muscles from the tongue, neck, pharynx, and larynx that attach to the hyoid bone contribute to the movements involved in swal- lowing and speech. Vertebral Column The vertebral column spine consists of 26 vertebrae bones Table It provides support for the head and trunk of the body, protection for the spinal cord, and connecting points for the ribs and muscles.

A typical vertebra has the following characteristics see Figure The open- ing in the ring is the vertebral foramen, the passageway for the spinal cord. The vertebral canal is the continuous passageway formed by the vertebral foramina of successive vertebrae.

A spinous process projects posteriorly from the vertebral arch. Muscle and ligaments attach here. Two transverse processes project from the vertebral arch, one from each side, at each of the junctures of the pedicles and lam- inae. Muscles and ligaments attach here. Each transverse process of cervical vertebrae contains a transverse foramen through which blood vessels pass to the brain. Two superior articular processes project from the superior sur- face of the vertebral arch, one from each of the pediclelamina junctions.

These processes articulate form joints with the pre- ceding vertebrae. Two inferior articular processes project from the inferior surface of the vertebral arch, one from each of the pediclelamina junc- tions. These processes articulate form joints with the follow- ing vertebra. Adjacent notches of suc- cessive vertebrae form a passage for nerves that leave the spinal cord and emerge outside the vertebral column. Each disc consists of an outer ring of fibrocartilage annulus fibrosus surrounding a semi- fluid cushion nucleus pulposus that provides elasticity and com- pressibility.

The vertebral column is divided into four regions, each region contribut- ing to the alternating concave and convex curves of the spine see Figure As the vertebrae progress down the column, their bodies get more massive, enabling them to bear more weight.

The sacrum is a triangular bone below the last lumbar vertebra see Fig- ure It is formed by the fusion of five vertebrae S1-S5. The coccyx, formed by four fused vertebrae, is a small triangle-shaped bone that attaches to the bottom of the sacrum see Figure The sternum breastbone consists of three fused bones: The Skeletal System 77 ribs, all of which attach to their posterior ends to vertebrae. At their ante- rior ends, they differ as to how they attach, as follows: Rather, they connect with costal cartilage to the rib directly above them.

Figure The thoracic cage. Part of the tubercle also presents a place of attachment for ligaments. Pectoral Girdle Each of the two pectoral shoulder girdles consists of two bones: The clavicle articulates with the sternum and the scapula. In turn, the scapula articulates with the humerus of the arm. Figure illustrates details of these bones. Figure The pectoral girdle.

The 30 bones of each upper limb are illustrated in Figure Pelvic Girdle The pelvic hip girdle transfers the weight of the upper body to the legs. It consists of a pair of coxal bones os coxae, hip bones , each of which contains three fused bones: Together with the sacrum and coccyx, the pelvic girdle forms a bowl-shaped region, the pelvis, that protects internal reproductive organs, the urinary bladder, and the lower part of the digestive tract.

Features of these bones are given in Figure Figure The pelvic girdle. The bones of the lower limbs are considerably larger and stronger than comparable bones of the upper limbs because the lower limbs must support the entire weight of the body while walking, running, or jumping.

Figure illustrates features of the 30 bones of each lower limb. Figure The 30 bones of each lower limb. The sphenoid and occipital bones form most of the base of the cranium. The Skeletal System 81 3. Which of the following bone or bones help s compose the face? The coccyx never varies in the number of vertebrae that compose it.

Though joints allow the skeleton to be dynamic, they also play an impor- tant role in stability and protection. In fact, the mobility of a joint is often inversely proportional to its stability. For example, the sutures of the bones of the cranium are basically immovable in relationship to one another, but due to their stable nature, they serve to protect the brain throughout daily life and during incidents of trauma.

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On the other hand, the ball-and-socket of the shoulder enables a wide variety of complex movements. This increase in the amount of mobility leads to instability, which is why the shoulder is more susceptible to injury.

The goal of this chapter is to familiarize you with the wide variety of joints that occur in the human body and to help you understand how these joints are classified. Classifying Joints A joint articulation occurs wherever bones meet. Joints are classified both structurally and functionally, as shown in Table There are three structural classes. No joint cavity is present. Fibrous joints may be immovable or slightly movable.

Cartilaginous joints may be immovable or slightly movable. Synovial joints are freely movable and char- acterize most joints of the body. Figure lists other features of a synovial joint, including Articular cartilage hyaline cartilage , which covers the end of each bone. A synovial membrane, which surrounds the synovial cavity. Its areolar connective tissue secretes a lubricating synovial fluid into the synovial cavity. A fibrous capsule outside the synovial membrane, which sur- rounds the joint.

It often contains bundles of dense, irregular, connective tissue called ligaments. The ligaments provide strength and flexibility to the joint. The articulate capsule is composed of the synovial membrane and fibrous capsule.

Accessory ligaments lie outside the articular capsule extracap- sular ligaments or inside the synovial cavity intracapsular ligaments. Functional classification Functional classification is based on the degree to which the joint permits movement. Structurally, it may be a fibrous or cartilaginous joint.

Structurally, it may be fibrous or cartilaginous joint. Structurally, it is always a synovial joint. Figure A synovial joint. Name the two types of joints where no joint cavity is present. A diarthrosis joint allows little or no movement. Which of the following is an example of an amphiarthrotic joint? Discuss why each component of a synovial joint is critical to the func- tion of the joint.

To understand how muscle accomplishes these various activities, you need to know the physiology behind a muscle contraction. ATP is obtained via cellular respiration, which is accomplished by several different metabolic pathways discussed within this chapter. Types of Muscles There are three types of muscles: Skeletal muscle is also called striated muscle because of its banding pattern when viewed under a microscope or voluntary mus- cle because muscle contraction can be consciously controlled.

Cardiac muscle is involuntary—it generates its own stimuli to initiate muscle contraction. For example, it lines the walls of blood vessels and of the digestive tract where it serves to advance the movement of substances.

Smooth muscle contraction is relatively slow and involuntary. Connective Tissue Associated with Muscle Tissue A skeletal muscle consists of numerous muscle cells called muscle fibers.

Three layers of connective tissues surround these fibers to form a muscle.

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These and other connective tissues associated with muscles follow: It extends beyond the muscle tissue to connect the muscle to a bone or to other muscles. The superficial fascia merges with the deep fascia where the surfaces of the skin meet. Structure of Skeletal Muscle A muscle fiber cell has special terminology and distinguishing characteristics: The nuclei lie along the periphery of the cell, forming swellings visible through the sarcolemma.

Myofibrils consist of two types of filaments, shown in Figure Thin filaments consist of two strands of the globular protein actin arranged in a double helix. Along the length of the helix are troponin and tropomyosin molecules that cover special bind- ing sites on the actin.

Thick filaments consist of groups of the filamentous protein myosin. Each myosin filament forms a protruding head at one end. An array of myosin filaments possesses protruding heads at numerous positions at both ends.

Figure Two types of filaments. The overlapping filaments produce a repeating pattern that gives skeletal muscle its striated appearance. Each repeating unit of the pat- tern, called a sarcomere, is separated by a border, or Z disc Z line , to which the actin filaments are attached.

The myosin filaments, with their protruding heads, float between the actin, unattached to the Z disc. Muscle Contraction Muscle contraction is described by the sliding-filaments model: Ca binds to the troponin molecule causing tropomyosin to expose positions on the actin filament for the attachment of myosin heads.

When attachment sites on the actin are exposed, the myosin heads bind to actin to form cross bridges. The attachment of cross bridges between myosin and actin causes the release of ADP and Pi.

This, in turn, causes a change in shape of the myosin head, which generates a sliding movement of the actin toward the center of the sacromere. This pulls the two Z discs together, effec- tively contracting the muscle fiber to produce a power stroke.

When a new ATP molecule attaches to the myosin head, the cross bridge between the actin and myosin breaks, returning the myosin head to its unattached position. Without the addition of a new ATP molecule, the cross bridges remain attached to the actin filaments.

This is why corpses become stiff with rigor mortis new ATP molecules are unavailable. Stimulation of muscle contraction Neurons, or nerve cells, are stimulated when the polarity across their plasma membrane changes. The polarity change, called an action poten- tial, travels along the neuron until it reaches the end of the neuron.

Muscle Tissue 91 called a synapse or synaptic cleft separates the neuron from a muscle cell or another neuron. If a neuron stimulates a muscle, then the neuron is a motor neuron, and its specialized synapse is called a neuromuscular junc- tion. Muscle contraction is stimulated through the following steps: When an action potential of a neuron reaches the neuromuscular junction, the neu- ron secretes the neurotransmitter acetylcholine Ach , which diffuses across the synaptic cleft.

Receptors on the motor end plate, a highly folded region of the sarcolemma, initiate an action potential. The action potential travels along the sarcolemma throughout the transverse sys- tem of tubules.

The Ca released by the sarcoplasmic reticulum binds to troponin molecules on the actin helix, prompting tropomyosin molecules to expose binding sites for myosin cross- bridge formation. If ATP is available, muscle contraction begins. Phases of a muscle contraction A muscle contraction in response to a single nerve action potential is called a twitch contraction. A myogram, a graph of muscle strength tension with time, shows several phases, shown in Figure For skeletal muscle fibers, this period typically ends during the early part of the contraction period.

Depending upon the frequency of stimuli, several effects are observed. A staircase effect treppe is produced if each successive stimu- lus occurs after the relaxation period of the previous stimulus.

Each successive muscle contraction is greater than the previous one, up to some maximum value. Muscle Tissue 93 Wave temporal summation occurs if consecutive stimuli are applied during the relaxation period of each preceding muscle contraction. In this case, each subsequent contraction builds upon the previous contraction before its relaxation period ends.

Incomplete unfused tetanus occurs when the frequency of stimuli increases. Successive muscle contractions begin to blend, almost appearing as a single large contraction. Complete fused tetanus occurs when the frequency of stimuli increases still further. In this case, individual muscle contractions completely fuse to produce one large muscle contraction. Muscle contractions intensify when more motor neurons stimulate more muscle fibers.

This effect, called recruitment or multiple motor unit summation, is also responsible for fine motor coordination because by continually varying the stimulation of spe- cific muscle fibers, smooth body movements are maintained.

Because a muscle is attached to bones, muscle contraction is restricted to lengths that are between 60 percent and percent of the length that produces optimal strength. This range of muscle lengths limits myosin cross bridges and actin only to positions where they overlap and thus can generate contractions.

Muscle contraction implies that movement occurs between myosin cross bridges and actin. However, this move- ment does not necessarily result in shortening of the muscle. As a result, two kinds of muscle contractions are defined. Isotonic contractions occur when muscles change length during a contraction. Picking up a book is an example. Isometric contractions occur when muscles do not change length during a contraction. When holding a book in midair, muscle fibers produce a force, but no motion is generated.

Muscle fibers are classified into two groups. Slow fibers contract slowly, have a high endurance, and are red from their rich blood supply. However, they do not produce much strength. These fibers are used for long distance running.

Fast fibers contract rapidly, fatigue rapidly, and are white because the blood supply is limited. They generate considerable strength. These fibers are used for short distance running. In any relaxed skeletal muscle, a small number of con- tractions continuously occur. Observed as firmness in a muscle, these contractions maintain body posture and increase muscle readiness.

Muscle fibers stop contraction when inadequate amounts of ATP are available. Lack of oxygen and glycogen and the accumulation of lactic acid a byproduct of ATP production in the absence of oxygen , together with the lack of ATP, all contribute to muscle fatigue. Muscle metabolism In order for muscles to contract, ATP must be available in the muscle fiber.

ATP is available from the following sources: ATP available within the muscle fiber can maintain muscle contraction for several seconds. Creatine phosphate, a high-energy molecule stored in muscle cells, transfers its high-energy phosphate group to ADP to form ATP. The creatine phosphate in muscle cells is able to generate enough ATP to maintain muscle contraction for about 15 seconds.

Glucose within the cell is stored in the carbohydrate glycogen. Through the metabolic process of glycogenolysis, glycogen is broken down to release glucose. ATP is then generated from glucose by cellular respiration. When energy requirements are high, glucose from glycogen stored in the liver and fatty acids from fat stored in adipose cells and the liver are released into the bloodstream. Glucose and fatty acids are then absorbed from the bloodstream by muscle cells.

ATP is then gener- ated from these energy-rich molecules by cellular respiration. Cellular respiration is the process by which ATP is obtained from energy- rich molecules. Several major metabolic pathways are involved, some of which require the presence of oxygen.

Because no oxygen is used during the vari- ous metabolic steps of this pathway, glycolysis is called an anaerobic process.

No ATP is generated and, as its name indicates, no oxy- gen is required. The importance of this process is that it regenerates certain coenzymes necessary for glycolysis to continue. Thus, in the absence of oxygen, anaerobic respiration is indirectly responsible for the production of two ATPs during glycolysis. Advantages of anaerobic respiration: Anaerobic respiration is rel- atively rapid, and it does not require oxygen.

Disadvantages of anaerobic respiration: Anaerobic respiration generates only two ATPs, and lactic acid is produced. Most lac- tic acid diffuses out of the cell and into the bloodstream and is subsequently absorbed by the liver.

Some of the lactic acid remains in the muscle fibers, where it contributes to muscle fatigue. Because both the liver and muscle fibers must convert the lactic acid back to pyruvic acid when oxygen becomes avail- able, anaerobic respiration is said to produce oxygen debt. A total of 36 ATP molecules is produced including the two from gly- colysis. However, oxygen is required for this pathway. Advantages of aerobic respiration: Aerobic respiration generates a large amount of ATP.

Disadvantages of aerobic respiration: Aerobic respiration is rel- atively slow and requires oxygen. When the ATP generated from creatine phosphate is depleted, the imme- diate requirements of contracting muscle fibers force anaerobic respiration to begin. Anaerobic respiration can supply ATP for about 30 seconds.

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If muscle contraction continues, aerobic respiration, the slower ATP-pro- ducing pathway, begins and produces large amounts of ATP as long as oxy- gen is available. Eventually, oxygen is depleted, and aerobic respiration stops.

However, ATP production by anaerobic respiration may still sup- port some further muscle contraction. Ultimately, the accumulation of lac- tic acid from anaerobic respiration and the depletion of resources ATP, oxygen, and glycogen lead to muscle fatigue, and muscle contraction stops. These discs contain desmosomes and gap junctions. In addition, cardiac muscle is autorhythmic, generat- ing its own action potential, which spreads rapidly throughout muscle tis- sue by electrical synapses across the gap junctions.

Structure of Smooth Muscle Due to its irregular arrangement of actin and myosin filaments, smooth muscle does not have the striated appearance of skeletal muscle. In addi- tion, the sarcolemma does not form a system of transverse tubules.

As a result, contraction is controlled and relatively slow; properties appropriate for smooth muscle function. In addition to the thick myosin and thin actin filaments, smooth muscles also possess noncontracting intermediate filaments. The intermediate fibers attach to dense bodies that are scattered through the sarcoplasm and attached to the sarcolemma.

During contraction, the movement of myosin and actin is transferred to intermediate fibers, which pull on the dense bodies, which, in turn, pull the muscle cell together. In this way, the dense bodies function similarly to the Z discs in striated muscles. Fast-twitch fibers contract rapidly, fatigue rapidly, and are highly vascularized.

Which of the following is true of glycolysis? Muscle Tissue 97 4. In muscle contractions, the length of the muscle is always shortened. F isometric contractions 5. With an understanding of where a muscle originates and inserts, you can calculate the movements that will occur at a joint when these two points are brought together following an isotonic muscu- lar contraction. The orientation, placement, and coordination of these muscles allow the human body to produce a wide range of voluntary movements.

The muscular system consists of skeletal muscles and their associated con- nective tissues. It does not include cardiac muscle or smooth muscle, which are associated with the systems in which they are found, such as the car- diovascular, digestive, urinary, or other organ systems. Skeletal Muscle Actions A skeletal muscle may attach a bone to another bone often across a joint or a bone to another structure, such as skin. When the muscle contracts, one of the structures usually remains stationary, while the other moves.

The following terms refer to this characteristic of muscle contraction. Several muscles usually influence a particular body movement:This includes maintaining a constant body temperature via the acts of sweating or shivering and by making you aware of external stimuli through information perceived within the touch receptors located within the integu- mentary system.

A cell that begins mitosis in the diploid state—that is, with two copies of every chromosome—will end mitosis with two copies of every chromo- some. A selectively per- meable membrane allows only specific substances to pass. However, oxygen is required for this pathway. The process, occurring in most bones of the body, follows these steps: In fact, the mobility of a joint is often inversely proportional to its stability.

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