Human Anatomy PDF

# General Human Anatomy ## Introduction to Human Anatomy Human anatomy is the study of the structure of the human body. For descriptive purposes, the human body is divided into regions: head, neck, trunk, and limbs. The trunk is subdivided into the chest (thorax) and the abdomen. The abdomen is fu...

# General Human Anatomy ## Introduction to Human Anatomy Human anatomy is the study of the structure of the human body. For descriptive purposes, the human body is divided into regions: head, neck, trunk, and limbs. The trunk is subdivided into the chest (thorax) and the abdomen. The abdomen is further subdivided into the abdomen proper and the pelvis. Systemic anatomy is the study of the body's organ systems that work together to carry out complex functions. The basic systems are the skin, muscular system, skeletal system, nervous system, cardiac system, respiratory system, digestive system, etc. ## Anatomic Terminology Understanding the terms used for describing the structures in different regions of the body is essential for students. ### The anatomical position: The anatomical position is the standard reference position of the body used to describe the location of structures. In this position, - A person is standing erect and facing forward, with the eyes looking forward. - The upper limbs are by the sides, the palms of the hands are directed forward. - The lower limbs are together, the soles of the feet are on the ground, and the toes are pointing forward. ### Anatomical Planes: Four geometric planes are applied to the body in the anatomical position: 1. The median plane (midsagittal plane) is a vertical plane passing through the center of the body, dividing it into equal right and left halves. 2. A sagittal plane (paramedian plane) is any vertical plane passing through the body parallel to the median plane. It divides the body into unequal right and left portions. 3. The coronal (frontal) plane is a vertical plane situated at a right angle to the median plane. The coronal plane divides the body into anterior (front) and posterior (back) parts. 4. The horizontal (transverse) plane lies at right angles to both the median and the coronal planes. A horizontal plane divides the body into upper (superior) and lower (inferior) parts. ### Anatomic terms used in relation to position: Note that the subjects are standing in the anatomical position. These terms describe the relationship of parts of the body or compare the position of two structures relative to each other. - Median: refers to any structure lying in the median plane. - Medial: refers to a structure situated nearer to the median plane of the body than another. - Lateral: refers to a structure that lies farther away from the median plane than another. For example, the thumb is lateral to the little finger. - Anterior (ventral) surface: describe the position of structures nearer to the "front" of the body. - Posterior (dorsal) surface: describe the position of structures nearer to the "back" of the body. - Proximal: refers to a structure nearer to the attachment of a limb. - Distal: refers to a structure farther from the attachment of a limb. (e.g., in the upper limb, the shoulder is proximal to the elbow, and the hand is distal to the elbow). - Superior: refers to a structure that is nearer to the vertex of the skull. - Inferior: refers to a structure that is situated nearer the sole of the foot. - Superficial: refers to a structure closer to the surface of the body. - Deep: refers to a structure farther away from the surface of the body. (e.g., the skin is superficial to the ribs, but the heart is deep to the ribs). - The terms internal and external are used to describe locations relative to the center of a structure or space. Internal is inside the structure and external is outside the structure. - Ipsilateral: refers to structures on the same side of the body (e.g. the right thumb and right big toe are ipsilateral). - Contralateral: refers to structure on the opposite side of the body relative to another structure (e.g. the right hand is contralateral to the left hand). - The supine position of the body is lying on the back. - The prone position is laying face downward. ### Terms Related to Movement: In the musculoskeletal system, movement takes place at joints. - Flexion indicates bending or decreasing the angle between the bones or parts of the body occurring in a sagittal plane. For joints above the knee, flexion involves movement in an anterior direction. - Extension indicates straightening or increasing the angle between the bones or parts of the body. Extension usually occurs in a sagittal plane. - Lateral flexion refers to a lateral bending movement of the trunk in the coronal plane. - Dorsiflexion describes the movement of the foot with flexion at the ankle joint (lifting the top of the foot superiorly). * In describing the hand, the terms palmar and dorsal surfaces are used in place of anterior and posterior, respectively. In describing the foot, the term plantar surface refers to the sole of the foot and dorsal surface indicates the upper (top) surface. ## The Skin The skin provides: - Protection of the body from environmental effects, such as ultraviolet radiation and invading microorganisms. - Containment for the body's structures (e.g., tissues and organs). - Thermal regulation. - Sensation (e.g., pain) by way of superficial nerves and their sensory endings. - Synthesis and storage of vitamin D. The skin is the largest organ in the body. It is divided into two parts: the superficial part, the epidermis, and the deep part, the dermis. ### The epidermis Is a keratinized stratified epithelium that provides a protective outer surface. The epidermis has no blood vessels or lymphatics. The avascular epidermis is nourished by the underlying vascularized dermis. On the palms of the hands and the soles of the feet, the epidermis is extremely thick to withstand the wear and tear that occurs in these regions. In other areas of the body, such as on the anterior surface of the arm and forearm, it is thin. ### The dermis Is composed of dense connective tissue containing many blood vessels, lymphatic vessels, collagen and elastic fibers, and nerves. The collagen and elastic fibers provide skin tone and account for the strength and toughness of skin. The bundles of collagen fibers in the dermis run in all directions to produce a tough felt-like tissue, in any specific location most fibers run in the same direction determining the characteristic tension and wrinkle lines in the skin, this is called tension lines (cleavage lines or Langer lines) tend to run longitudinally in the limbs and run transversely in the neck and trunk. The dermis of the skin is connected to the underlying deep fascia or bones by the superficial fascia. * The elastic fibers of the dermis deteriorate with age and are not replaced; consequently, in older people, the skin wrinkles and sags as it loses its elasticity. ### The appendages of the skin: They are the nails, hair follicles, sebaceous glands, and sweat glands. * The nails are keratinized plates on the dorsal surfaces of the tips of the fingers and toes. The proximal edge of the plate is the root of the nail. Except for the distal edge of the plate, the nail is surrounded and overlapped by folds of skin known as nail folds. The surface of skin covered by the nail is the nail bed. * Hairs grow out of follicles, which are invaginations of the epidermis into the dermis. The deep part of the hair follicles is called hair bulbs, penetrate to the deeper part of the dermis and its concavity is occupied by vascular connective tissue called the hair papilla. A band of smooth muscle, the arrector pili, connects the undersurface of the follicle to the superficial part of the dermis. The muscle is innervated by sympathetic nerve fibers, and its contraction causes the hair to move into a more vertical position; it also compresses the sebaceous gland and causes it to extrude some of its secretion. * Sebaceous glands secrete an oily material (sebum) onto the shafts of the hairs as they pass up through the necks of the follicles. They are situated on the sloping undersurface of the follicles and lie within the dermis. Sebum is that helps preserve the flexibility of the emerging hair. * Sweat glands are long, spiral, tubular glands distributed over the surface of the body, except on the red margins of the lips, the nail beds, and the glans penis and clitoris. ## Fascia Fascia is the connective tissue that encloses the body deep to the skin. The fasciae of the body can be divided into two types, superficial and deep. ### The superficial fascia, or subcutaneous tissue, Is a mixture of loose areolar and adipose tissue that unites the dermis of the skin to the underlying deep fascia. It is thick in the scalp, the back of the neck, the palms of the hands, and the soles of the feet, where it contains numerous bundles of collagen fibers. **Contents of the superficial fascia:** 1. Fat: The thickness of the superficial fascia varies with the amount of fat in it. Its distribution and amount vary in both sexes. In the eyelids, auricle of the ear, penis and scrotum, and clitoris, it is devoid of fat. 2. Muscles e.g. platysma muscle in the neck, and dartos muscle in the scrotum. 3. Mammary gland in the pectoral region. 4. Blood vessels, lymph vessels, and nerves. ### The deep fascia Is a dense, inelastic membranous layer of connective tissue. It is attached to the deep surface of the superficial fascia, and often ensheathes muscles and divides them into functional groupings. Extensions of the deep fascia may attach to the skeleton, forming the intermuscular septa. In the thorax and abdomen, it is a very thin film of areolar tissue covering the muscles and aponeuroses. The deep fascia at the wrists and ankles is thickened to form retinacula which hold the tendons in place. ## Bone Bone is a living tissue. It is a highly specialized, hard form of connective tissue that makes up most of the skeleton. It is often stated that there are 206 bones in the skeleton. Bones of the adult skeleton provide; - Support for the body and its vital cavities. - Protection for vital structures (e.g., the heart and brain). - The mechanical basis for movement (leverage). - Storage for salts (e.g., calcium). - A continuous supply of new blood cells (produced by the marrow in the medullary cavity of many bones). The periosteum is a dense fibrous connective tissue surrounding the bones and covering the surfaces of bones, except where they articulate with other bones. The periosteum nourishes the external aspects of the bones. It is capable of laying down more bone (particularly during fracture healing) and give attachment to tendons and ligaments. ### Classification of Bones **A-Regional classification:** In the regional classification, the bones are organized into two main groups: the axial and appendicular skeletons. 1. **The axial skeleton** consists of the central supporting axis of the body including the skull, vertebral column, ribs, and sternum. The vertebral column consists of a chain of 33 vertebrae with intervertebral discs of fibrocartilage between most of them. The vertebrae are divided into five groups: 7 cervical vertebrae in the neck, 12 thoracic vertebrae in the chest, 5 lumbar vertebrae in the lower back, 5 sacral vertebrae at the base of the spine, and 4 tiny coccygeal vertebrae. 2. **The appendicular skeleton** includes the bones of the upper limb and shoulder (pectoral) girdle, and bones of the lower limb and pelvic girdle. The shoulder girdle consists of the clavicle and scapula, whereas the pelvic girdle consists of the hip bones. * The shoulder girdle and the pelvic girdle provide connection points between the appendicular and the axial skeletons for the mechanical load transfer. Each of the upper and lower limbs consist of three segments (proximal, intermediate and distal). **B-According to the structure:** Bone is found in two forms: 1. **Compact bone:** is dense mass of bone and forms the superficial layer of bone and the tubular shafts of the long bones. It provides strength. 2. **Cancellous bone (spongy or trabecular):** is a less dense branching network of bone trabecula, it occurs in the ends of long bones and fills the flat and irregular bones; the spaces between the spicules are filled with a highly vascular bone marrow. **C-According to the general shape:** Bones are classified according to their shape into 1. **Long bones** (e.g., the humerus in the arm). 2. **Short bones** are cuboidal and are found only in the tarsus (ankle) and carpus (wrist). 3. **Flat bones** e.g. the sternum, scapula, and vault of the skull. 4. **Irregular bones** e.g., the vertebrae, hip bones and the bones of the face. 5. **Sesamoid bones** (e.g., the patella or knee-cap) develop in certain tendons and are found where tendons cross the ends of long bones in the limbs. The function of a sesamoid bone is to reduce friction on the tendon; it can also alter the direction of pull of a tendon 6. **Pneumatic bones** of the skull contain air spaces (paranasal sinuses). **D-According to their development and ossification:** Bones develop in one of the following two ways: 1. **Intramembranous ossification (membranous bone formation):** This is the process of bone formation in connective tissue and mesenchymal models of bones form during the embryonic period. Most flat bones develop in this way by direct calcium deposition into a mesenchymal model. 2. **Endochondral ossification (cartilaginous bone formation):** Cartilage models of the bones form from mesenchyme during the fetal period, and bone subsequently replaces most of the cartilage. Most long and irregularly shaped bones develop by calcium deposition into a cartilaginous model of the bone. ### Bone Classification Based on Shape - **Long bones** are found in the limbs (e.g., the humerus, femur, metacarpals, metatarsals, and phalanges). They have a tubular shaft, the **diaphysis**, and usually an epiphysis at each end. During the growing phase, the **diaphysis** is separated from the epiphysis by an **epiphyseal plate**. - The part of the diaphysis that joins the epiphysis and epiphysial plate is called the **metaphysis**. The shaft has a central marrow cavity containing **bone marrow**. The outer part of the shaft is composed of **compact bone** that is covered by **periosteum**. The ends of long bones are composed of cancellous bone surrounded by a thin layer of compact bone. The articular surfaces of the ends of the bones are covered by hyaline cartilage. ## Joints Joints (articulations) are unions or junctions between two or more bones or rigid parts of the skeleton. Joints exhibit a variety of forms and functions. ### Types of Joints Joints are classified into one of the following three types: 1. **Fibrous joint (synarthrosis):** bones joined by fibrous connective tissue. - **Suture:** The articulating surfaces of the bones are tightly linked by fibrous tissue that fills the joint space. The example of this subtype is sutures of the vault of the skull. - **Syndesmosis:** It is a type of fibrous joint unites the bones with a sheet of fibrous tissue, either a ligament or a fibrous membrane. This type of joint allows for little movement. Examples of this type are the interosseous membrane in the forearm (a sheet of fibrous tissue that joins the radius and ulna) and the inferior tibiofibular joint. - **Gomphosis:** it is an articulation between the root of the tooth and the socket in the alveolar process of the jaw. 2. **Cartilaginous joint (amphiarthrosis):** Bones are joined by cartilage, or by cartilage and fibrous tissue. It includes - **Primary cartilaginous (synchondrosis) joints:** The bony ends (articular surfaces) are fused by hyaline cartilage. * Example is the epiphysial plate of the growing long bones connecting the diaphysis with the epiphysis. Primary cartilaginous joints permit growth in the length of a bone. When full growth is achieved, the epiphysial plate converts to bone and the epiphyses fuse with the diaphysis. - **Secondary cartilaginous (symphysis) joints:** The articular surfaces are lined by hyaline cartilage with an intervening fibrocartilaginous disc. Joints of this type of are strong, slightly movable united by fibrocartilage. They are located along the midline of the body. Examples of this type are the intervertebral joints between the vertebral bodies, the manubriosternal joint, and the symphysis pubis. 3. **Synovial joints (diarthroses):** This is the most common type of joints. The articular surfaces of the bones are covered by a thin layer of hyaline cartilage and are separated by a joint cavity filled with a small amount of synovial fluid and surrounded by a fibrous capsule. The cavity of the joint is lined by a synovial membrane, which extends from the margins of one articular surface to those of the other, also, the synovial membrane lines the fibrous capsule. Synovial fluid is produced by the synovial membrane, it lubricates the articular surfaces. Synovial joints generally allow for considerable movement and are classified according to their shape and the type of movement that they permit (uniaxial, biaxial, or multiaxial movement), as follows: - **Plane (gliding):** The articular surfaces are flat. It only allows simple gliding movement. Examples are the acromioclavicular joint (between the acromion of the scapula and the clavicle), and joints between the carpal bones. - **Hinge:** These are uniaxial joints permitting flexion and extension only. An example is the elbow joint. - **Pivot joints:** are uniaxial joints permit rotation around a central axis. In these joints, a rounded process of bone rotates within a sleeve or ring. Examples are the median atlanto-axial joint (in which the atlas (C1 vertebra) rotates around a finger-like process, the dens of the axis (C2 vertebra), during rotation of the head) and the superior radioulnar joint. - **Saddle:** The opposing articular surfaces are shaped like a saddle on the horse's back (i.e., they are reciprocally concave and convex). These are biaxial joints (movements occurring around two axes at right angles to each other) permitting flexion, extension, abduction, and adduction. The example is carpo-metacarpal joint at the base of the thumb. - **Condyloid joints:** Condyloid joints are biaxial permitting flexion and extension as well as abduction and adduction. The metacarpo-phalangeal joints (knuckle joints) are condyloid joints. - **Ball and socket joints:** These are multiaxial joints allow movement in multiple axes and planes: flexion and extension, abduction and adduction, medial and lateral rotation, and circumduction. Examples are the hip joint and the shoulder joint. - **Ellipsoid joint:** An elliptical convex articular surface fits into an elliptical concave articular surface. Mainly biaxial movements are allowed (flexion, extension, adduction and abduction). Example is the radiocarpal (wrist) joint. ### Joint Stability The stability of a joint depends on three main factors: - The morphology of the bony articular surfaces, - The ligaments, and - The tone of the muscles around the joint. ## Muscles Muscle cells (muscle fibers) are specialized contractile cells. They are organized into tissues that move body parts or temporarily alter the shape of internal organs. Associated connective tissue conveys nerve fibers and capillaries to the muscle cells as it binds them into bundles or fascicles. Three types of muscle are described based on distinct characteristics relating to: - whether it is normally willfully controlled (voluntary or involuntary). - whether it appears striped or unstriped when viewed under a microscope (striated or smooth). - whether it is located in the body wall and limbs (somatic) or makes up the hollow organs (viscera, e.g., the heart) of the body cavities or blood vessels (somatic or visceral). The three types of muscle are skeletal, smooth, and cardiac. ### I- Skeletal muscle It is a striated voluntary somatic muscle that makes up the gross skeletal muscles that compose the muscular system, moving or stabilizing bones and other structures. A skeletal muscle has two or more attachments. The more proximal, less mobile attachment is referred to as the origin. The more distal, more mobile attachment is the insertion. When a muscle contracts, the insertion is drawn proximally toward the origin. However, under varying circumstances, the degree of mobility of the attachments may be reversed (or interchanged). The fleshy part of the muscle is referred to as its belly. The ends of a muscle are attached to supporting elements (bones, cartilage, ligaments, or other muscles) by cords of fibrous tissue called tendons. Some tendons (e.g., those belonging to the flat, wide abdominal oblique muscles) form a thin, strong sheet termed an aponeurosis. Other tendons may form a raphe, which is an interdigitation of the tendinous ends of fibers of flat muscles. - The architecture and shape of a skeletal muscle depend on the arrangement of its fibers.