Human Anatomy PDF Lecture Notes

Human Anatomy Lec. 2/ Dr. Mortadha Sami The Basic structures Skin The skin is a multifunctional organ, it helps in the protection of the body from microbes and harmful external influences, regulation of body temperature, maintain the moisture and sensation. It is divided into two main layers : I....

Human Anatomy Lec. 2/ Dr. Mortadha Sami The Basic structures Skin The skin is a multifunctional organ, it helps in the protection of the body from microbes and harmful external influences, regulation of body temperature, maintain the moisture and sensation. It is divided into two main layers : I. The epidermis: Is the superficial layer of stratified squamous epithelium. This layer consists of many special cells, including keratinocytes cells that make keratin a protein that provides strength to skin, hair, and nails and melanocytes cells which produce melanin (a pigment giving the color of skin). II. The dermis: Is the deep layer of the skin. It is a thick layer made up of connective tissues containing many blood vessels (which supply nutrients to the different layers of the skin), lymphatic vessels and nerves. The dermis also contains a number of specialized structures known as appendages, these include: ①hair follicles, ②sweat glands, ③sebaceous glands (produce sebum which helps lubricate skin & hair), and ④nails. 1 The Fascia Is a band or sheet of connective tissue, primarily collagen, lies beneath the skin around muscles, groups of muscles, bones, nerves, blood vessels, organs and cells. Attaches, stabilizes, encloses, and separates muscles and other internal organs, and allows the muscles to move freely alongside other structures and reduces friction. The fascia of the body can be divided into two types: I. The superficial fascia: or subcutaneous tissue is the loose connective tissue layer that lies deep to the dermis of the skin consists of: blood vessels, nerves, lymphatics, variable amount of fat. In palm and sole, the superficial fascia is quite thick and contains dense connective tissue. II. The deep fascia: is a membranous layer of connective tissue that invests the muscles and other deep structures. In the neck, it forms well-defined layers. In the thorax and abdomen, it is a thin film of areolar tissue covering the muscles. In the limbs, it forms a definite sheath around the muscles and other structures, holding them in place. 9 The Muscles There are three types of muscles in the body: 1. Skeletal muscles (striated). 2. Smooth or visceral muscles (non-striated). 3. Cardiac muscles. 1. Skeletal Muscles  Also known as voluntary muscles. These muscles are made up of bundles of muscle fibers with special property of contraction.  Each skeletal muscle has at least two attachments: 1. The origin of the muscle is usually the proximal and more fixed attachment of the muscle. 2. The insertion of the muscle is usually the distal and relatively mobile attachment of the muscle. 9  The main part of the muscle between the two attachments is called muscle belly.  Tendons are dense regularly arranged collagen fiber bundles, that attach the muscle fibers towards the insertion point of the muscle to bones or cartilage.  Aponeurosis is a type of deep fascia, in the form of a sheet of fibrous tissue continuous with external tendons to join muscles and the body parts they act upon (whether they were bones or other muscles). They are supplied with blood vessels and nerves. 9  A raphe is a fibrous structure, formed by the inter - digitation of muscle fibers of the two sides.  The nerve supply of the skeletal muscle is mixed nerve, about 60% motor nerve fibers and 40% is sensory nerve fibers. The skeletal muscles are classified according to their actions: 1. The prime movers: are the main muscles responsible for a particular movement at a joint. Example: Biceps, is a prime flexor of the elbow joint. 2. The antagonists: are the muscles that are just opposite in action to the prime movers. Examples: Triceps, is antagonist to the biceps. 3. The synergists: are the muscles which help in the action of the prime movers by stabilizing the joints or preventing unwanted movements. 4. The fixators: are those muscles which contract isometrically to stabilize the attachment of the prime movers, so that they may contract more effectively. Example: Scapular muscles fix the scapula, so that the deltoid muscle can abduct the shoulder joint. 9 2. Smooth Muscles  Smooth muscle (non-striated) consists of elongated or spindle-shaped fibers capable of slow and sustained contractions.  Smooth muscle is not under voluntary control; thus, it is called involuntary muscle.  It is found in the walls of blood vessels, associated with hair follicles in the skin, and found in the walls of various structures associated with the gastrointestinal, respiratory, genitourinary.  Smooth muscle is innervated by visceral motor nerves.  The triggers for smooth muscle contraction include hormones, neural stimulation and local factors, such as the walls of visceral organs, stretching the muscle can trigger its contraction (the stretch-relaxation response). 3. Cardiac Muscle  Cardiac muscle is a striated, involuntary muscle found only in the walls of the heart (myocardium) and in some of the large vessels close to where they join the heart.  It consists of a branching network of individual cells linked electrically and mechanically to work as a unit.  Its contractions are less powerful than those of skeletal muscle and it is resistant to fatigue. Cardiac muscle is innervated by visceral motor nerves. 9 The Joints The joints are formed, where two or more than two bones meet and get united. The joints can be classified broadly into three groups: ① The fibrous joints: are immovable or hardly movable joints. Example: the sutures of the vault of the skull. ② The cartilaginous joints: may allow a limited movement. These joints can be further divided into two types: a. The primary cartilaginous joint: is a joint, where two bones are joined together by hyaline cartilage plate. No movement is possible in these joints: Example: the union between the 1st rib and the sternum, union between epiphysis and diaphysis of growing bone. 9 b. The secondary cartilaginous joint: is a joint, where the two bones are covered by hyaline articular cartilage and united by a plate of fibro-cartilage. Example: the joints between the vertebral bodies, small movement is possible. ③ The synovial joints: permits relatively free movements. The articular surfaces are covered by hyaline articular cartilage, that can withstand pressure. The joint is surrounded by a fibrous articular capsule, that keeps the bones together, and prevents their separation during movements of the joint. The joint cavity has synovial membrane, which lines the inner surface of the fibrous capsule, and also covers all intra-articular structures. The synovial membrane produces the synovial fluid to lubricate the articular surface. 9 The Synovial Bursa Is a small fluid-filled sac lined by synovial membrane filled with synovial fluid (similar in consistency to that of a raw egg white). It provides a cushion between bones and tendons and muscles around a joint. This helps to reduce friction between the bones and allows free movement. The Ligaments Are cord-like or strap-like structures made up of dense connective tissue. The ligaments firmly connect the bones forming the joints. Most of the ligaments are composed of thick bundles of collagen fibers, and are stretchable. Such ligaments contribute to the stability of the joint. A few ligaments are composed of elastic fibers and therefore, can be stretched normally. 9