Introduction To Anatomy PDF

INTRODUCTIO N TO ANATOMY   BY   Dr EDU OTONG MUSCLE Consists predominantly of contractile cells, produces the movements of various parts of the body by contraction, and occurs in three types: A. Skeletal Muscle Is voluntary and striated; make...

INTRODUCTIO N TO ANATOMY   BY   Dr EDU OTONG MUSCLE Consists predominantly of contractile cells, produces the movements of various parts of the body by contraction, and occurs in three types: A. Skeletal Muscle Is voluntary and striated; makes up approximately 40% of the total body mass; and functions to:  produce movement of the body,  generate body heat, and  maintain body posture.  Has two attachments, an origin (which is usually the more fixed and proximal attachment); an insertion (which is the more movable and distal attachment).  Is enclosed by epimysium, a thin layer of connective tissue.  Smaller bundles of muscle fibers are surrounded by perimysium.  Each muscle fiber is enclosed by endomysium.  B. Cardiac Muscle Is involuntary and striated and forms the myocardium, the middle layer of the heart. Is innervated by the autonomic nervous system but contracts spontaneously without any nerve supply. Includes specialized myocardial fibers that form the cardiac conducting system.  C. Smooth Muscle Is involuntary and nonstriated and generally arranged in two layers; circular and longitudinal, in the walls of many visceral organs. Is innervated by the autonomic nervous system, regulating the size of the lumen of a tubular structure. Undergoes rhythmic contractions called peristaltic waves in the walls of the gastrointestinal (GI) tract, uterine tubes, ureters, and other organs Clinical correlation Lou Gehrig’s disease (amyotrophic lateral sclerosis) is a fatal neurologic disease that attacks the neurons responsible for controlling voluntary muscles. The muscles gradually weaken and atrophy; the brain is unable to control voluntary movement of the arms, legs, and body; and patients lose the ability to breath, swallow, and speak. The earliest symptoms may include cramping, twitching, and muscle weakness. STRUCTURES ASSOCIATED WITH MUSCLES A. Tendons Are fibrous bands of dense connective tissue that connect muscles to bones or cartilage. Are supplied by sensory fibers extending from muscle nerves. B. Ligaments Are fibrous bands that connect bones to bones or cartilage or are folds of peritoneum serving to support visceral structures. C. Raphe Is the line of union of symmetrical structures by a fibrous or tendinous band such as the pterygomandibular, pharyngeal, and scrotal raphes.  D. Aponeuroses Are flat fibrous sheets or expanded broad tendons that attach to muscles and serve as the means of origin or insertion of a flat muscle. E. Retinaculum Is a fibrous band that holds a structure in place in the region of joints. F. Bursae Are fluid-filled flattened sacs of synovial membrane that facilitate movement by minimizing friction. G. Synovial Tendon Sheaths Are synovial fluid-filled tubular sacs around muscle tendons that facilitate movement by reducing friction.  H. Fascia Is a fibrous sheet that envelops the body under the skin and invests the muscles and may limit the spread of pus and extravasated fluids such as urine and blood. 1. Superficial Fascia Is a loose connective tissue between the dermis and the deep (investing) fascia and has a fatty superficial layer (fat, cutaneous vessels, nerves, lymphatics, and glands) and a membranous deep layer. 2. Deep Fascia Is a sheet of fibrous tissue that invests the muscles and helps support them by serving as an elastic sheath or stocking. Provides origins or insertions for muscles, forms fibrous sheaths or retinacula for tendons, and forms potential pathways for infection or extravasation of fluids. VASCULAR SYSTEM Functions to transport vital materials such as oxygen, nutrients, and waste products, including carbon dioxide, hormones, defense elements, and cells involved in wound healing. Consists of the heart and vessels (arteries, capillaries, veins) that transport blood through all parts of the body. Includes the lymphatic vessels, a set of channels that begin in the tissue spaces and return excess tissue fluid to the bloodstream.  A. Circulatory Loops 1. Pulmonary Circulation Transports blood from the right ventricle through the pulmonary arteries to the lungs for the exchange of oxygen and carbon dioxide and returns it to the left atrium of the heart through the pulmonary veins. 2. Systemic Circulation Transports blood from the left ventricle through the aorta to all parts of the body and returns it to the right atrium through the superior and inferior venae cavae and the cardiac veins. Heart Is a hollow, muscular, four-chambered organ that pumps blood to two separate circulatory loops, the pulmonary circulation and the systemic circulation. Is regulated in its pumping rate and strength by the autonomic nervous system, which controls a pacemaker (i.e., sinoatrial node).  Blood Vessels Carry blood to the lungs, where carbon dioxide is exchanged for oxygen. Carry blood to the intestines, where nutritive materials in fluid form are absorbed, and to the endocrine glands, where hormones pass through the vessel walls and are distributed to target cells. Transport the waste products of tissue fluid to the kidneys, intestines, lungs, and skin, where they are excreted. Are of four types: arteries, veins, capillaries, and sinusoids.  Arteries Carry blood from the heart to the capillary beds and have thicker walls than do veins. Consist of three main types:  elastic arteries,  muscular arteries, and  arterioles. Veins Return blood to the heart from the capillary beds and consist of; the pulmonary veins, which return oxygenated blood to the heart from the lungs; the systemic veins, which return deoxygenated blood to the heart from the rest of the body. Contain valves that prevent the reflux of blood and have venae comitantes that closely accompany muscular arteries in the limbs.  Capillaries Are composed of endothelium and its basement membrane and connect the arterioles to the venules. Are the sites for the exchange of carbon dioxide, oxygen, nutrients, and waste products between the tissues and the blood. Are absent in the cornea, epidermis, and hyaline cartilage and may be absent in some areas where the arterioles and venules have direct connections (arteriovenous anastomoses or shunts), which may occur in the skin of the nose, lips, fingers, and ears, where they conserve body heat.  Sinusoids Are wider and more irregular than capillaries and substitute for capillaries in some organs, such as the liver, spleen, red bone marrow, adenohypophysis, suprarenal cortex, and parathyroid glands. Often contain phagocytic cells on their walls and form a part of the reticuloendothelial system, which is concerned chiefly with phagocytosis and antibody formation.  Portal System Is a system of vessels in which blood collected from one capillary network passes through a large vessel(s) and then a second capillary network before it returns to the systemic circulation. Consists of the hepatic portal system in which blood from the intestinal capillary bed passes through the hepatic portal vein and then hepatic capillaries (sinusoids) to the hepatic veins and the hypophyseal portal system in which blood from the hypothalamic capillaries passes through the hypophyseal portal veins and then the pituitary capillary sinusoids to the hypophyseal veins. LYMPHATIC SYSTEM  Provides an important immune mechanism for the body. Is involved in the metastasis of cancer cells and provides a route for transporting fat and large protein molecules absorbed from the intestine to the thoracic duct. A. Lymphatic Vessels Serve as one-way drainage toward the heart and return lymph to the bloodstream through the thoracic duct (the largest lymphatic vessel) or the right lymphatic duct. Are not usually visible in dissections but are the major route by which cancer metastasizes.  Function to absorb large protein molecules and transport them to the bloodstream because the molecules cannot pass through the walls of the blood capillaries back into the blood. Carry lymphocytes from lymphatic tissues to the bloodstream. Have valves, which are constricted at the sites of valves, showing a beaded appearance. Are absent in the brain, spinal cord, eyeballs, bone marrow, splenic pulp, hyaline cartilage, nails, and hair.  Lymphatic Capillaries Begin blindly in most tissues, collect tissue fluid, and join to form large collecting vessels that pass to regional lymph nodes. Absorb lymph from tissue spaces and transport it back to the venous system. Are called lacteals in the villi of the small intestine, where they absorb emulsified fat. Lymph Nodes Are organized collections of lymphatic tissue permeated by lymph channels. Produce lymphocytes and plasma cells and filter the lymph. Trap bacteria drained from an infected area and contain reticuloendothelial cells and phagocytic cells (macrophages) that ingest these bacteria. Are hard and often palpable when there is a metastasis and are  Lymph Is a clear, watery fluid that is collected from the intercellular spaces. Contains no cells until lymphocytes are added in its passage through the lymph nodes. Its constituents are similar to those of blood plasma (e.g., proteins, fats, lymphocytes). Often contains fat droplets (called chyle) when it comes from intestinal organs. Is filtered by passing through several lymph nodes before entering the venous system. NERVOUS SYSTEM Is divided anatomically into:  the central nervous system (CNS), consisting of  the brain and  spinal cord,  the peripheral nervous system (PNS), consisting of  12 pairs of cranial nerves and  31 pairs of spinal nerves, and their associated ganglia.  peripheral nervous system (PNS) divided functionally into  the somatic nervous system, which controls primarily voluntary activities, and  the visceral (autonomic) nervous system, which controls primarily involuntary activities. Is composed of  neurons and  neuroglia (nonneuronal cells such as astrocytes, oligodendrocytes, and microglia) It controls and integrates the body activity. NEURONS Are the structural and functional units of the nervous system (neuron doctrine). Are specialized for the reception, integration, transformation, and transmission of information. Components of Neurons 1. Cell bodies are located in the gray matter of the CNS, and their collections are called ganglia in the PNS and nuclei in the CNS. 2. Dendrites (dendron means “tree”) are usually short and highly branched and carry impulses toward the cell body. 3. Axons are usually single and long, have fewer branches (collaterals), and carry impulses away from the cell body. Classification of Neurons 1. Unipolar (Pseudounipolar) Neurons Have one process, which divides into a central branch that functions as an axon and a peripheral branch that serves as a dendrite. 2. Bipolar Neurons Have two processes (one dendrite and one axon); are sensory; and are found in the olfactory epithelium, the retina, and the inner ear. 3. Multipolar Neurons Have several dendrites and one axon and are most common in the CNS (e.g., motor cells in anterior and lateral horns of the Other Components of the Nervous System Cells That Support Neurons Include Schwann cells and satellite cells in the PNS. Are called neuroglia in the CNS and are composed mainly of three types:  astrocytes;  oligodendrocytes, which play a role in myelin formation and transport of material to neurons; and  microglia, which phagocytose waste products of nerve tissue.  Myelin Is the fat-like substance forming a sheath around certain nerve fibers. Is formed by  Schwann cells in the PNS and  oligodendrocytes in the CNS.  Synapses Are the sites of functional contact of a neuron with another neuron, an effector (muscle, gland) cell, or a sensory receptor cell. Are classified by the site of contact as axodendritic, axoaxonic, or axosomatic. Subserve the transmission of nerve impulses, commonly from the axon terminals (presynaptic elements) to the plasma membranes (postsynaptic elements) of the receiving cell. CENTRAL NERVOUS SYSTEM Brain Is enclosed within the cranium, or the brain case. Spinal cord Is cylindrical, occupies approximately the upper two- thirds of the vertebral canal, and is enveloped by the meninges. Meninges Consist of three layers of connective tissue membranes (pia, arachnoid, and dura mater) that surround and protect the brain and the spinal cord. PERIPHERAL NERVOUS SYSTEM A. Cranial Nerves Consist of 12 pairs and are connected to the brain B. Spinal Nerves Consist of 31 pairs:  8 cervical,  12 thoracic,  5 lumbar,  5 sacral, and  1 coccygeal. AUTONOMIC NERVOUS SYSTEM Is divided into  Sympathetic (thoracolumbar outflow),  Parasympathetic (craniosacral outflow), and  Enteric divisions. A. Sympathetic Nerve Fibers Have preganglionic nerve cell bodies that are located in the lateral horn of the thoracic and upper lumbar levels (L2 or L1–L3) of the spinal cord. Function primarily in emergencies or catabolism (energy consumption), preparing individuals for fight or flight, and thus increase the heart rate, inhibit GI motility and secretion, dilate pupils and bronchial lumen. They liberate norepinephrine (except sweat glands) and are classified as adrenergic. B. Parasympathetic Nerve Fibers Comprise the preganglionic fi bers that arise from the brain stem (cranial nerves III, VII, IX, and X) and sacral part of the spinal cord (second, third, and fourth sacral segments). Function primarily in homeostasis or anabolism (energy conservation), tending to promote quiet and orderly processes of the body. They liberate acetylcholine and are classifyed as cholinergic C. Enteric Division Consists of enteric ganglia (parasympathetic postganglionic neuron cell bodies) and plexus of the GI tract, including the myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses. Plays an important role in the control of GI motility and secretion.