About one-third of the dry weight of bone is composed of collagen fibers and glycosaminoglycans, which enable a bone to bend slightly under stress. Pain in the viscera is often mistakenly thought to come from the skin or other superficial sites-for example, the pain of a heart attack is felt "radiating" along the left shoulder and medial side of the arm (fig. Additionally, registers should have a mechanism to share this information with usual care providers, ideally through integrating with clinical record systems. Impact of regionalisation of a national rheumatic heart disease registry: the Ugandan experience. A presynaptic nerve fiber cannot cause other neurons in its to fire, but it can make them more sensitive to stimulation from other presynaptic fibers. In the United States, it accounts for about 30 million doctor visits per year and about half of all antibiotic prescriptions for children; it affects about 11% of the entire world population each year. Task Shifting: Rational Redistribution of Tasks Amongst Health Workforce Teams: Global Recommendations and Guidelines. Normalized end-systolic volume and preload reserve predict ventricular dysfunction following surgery for aortic regurgitation independent of body size. The sacroiliac joint is formed where the surface of the sacrum articulates with that of the ilium. The protein is a uniport if it transports only one solute, a symport if it carries two types of solutes at once in the same direction, and an antiport if it carries two or more solutes in opposite directions. Thyroid hormone is secreted or inhibited in response to fluctuations in metabolic rate. Iron Metabolism Iron is a critical part of the hemoglobin molecule and therefore one of the key nutritional requirements for erythropoiesis. Testosterone stimulates development of the male reproductive system in the fetus and adolescent, the development of the masculine physique in adolescence, and the sex drive. During normal embryonic development, neural crest cells migrate to the large intestine and establish the enteric nervous system. It is sometimes used to dilate the pupils for eye examinations and to dry the mucous membranes of the respiratory tract before inhalation anesthesia. The same for elevation, depression, protraction, retraction, and lateral and medial excursion of the mandible 14. The most common form of dwarfism results from a failure of cartilage growth in the long bones (see Deeper Insight 7. Note the relationship of the articular facets of the rib with the costal facets of the two vertebrae. It prevents the body from absorbing excess water when you are swimming or bathing, but even more importantly, it prevents the body from losing excess water. The more hydroxyapatite that forms, the more it attracts additional minerals from the tissue fluid, until the matrix is thoroughly calcified. The epithelial root sheath is an extension of the epidermis; it consists of stratified squamous epithelium and lies immediately adjacent to the hair root. This development of a more specialized form and function is called differentiation. Therefore, when the two bellies of the digastric contract, they elevate the hyoid; but if the hyoid is fixed from below, the digastric aids in wide opening of the mouth. This effect, called ion trapping (pH partitioning), can be controlled to help clear poisons from the body. This is called a split-skin graft because part of the dermis is left behind to proliferate and replace the epidermis that was removed-the same way a second-degree burn heals. Hydrogen has two other isotopes, however: deuterium (2H) with one proton and one neutron, and tritium (3H) with one proton and two neutrons (fig. The Mental and Buccal Regions Adjacent to the oral orifice are the mental region (chin) and buccal region (cheek). In situs perversus, a single organ occupies an atypical position-for example, a kidney located low in the pelvic cavity instead of high in the abdominal cavity.
Which nerves carry taste signals, what routes they take to the brain, and what brain centers receive gustatory input 6. Since it consists of the plasma membranes of glial cells, its composition is like that of plasma membranes in general. All molecules are in constant motion, and reactions occur when mutually reactive molecules collide with sufficient force and the right orientation. Furthermore, the action of a given muscle depends on what other muscles are doing. Trans fats came to be abundantly used not only by home cooks but also in snack foods, baked goods, frosting, coffee creamer, margarine, and fast foods such as french fries and take-out fried chicken. Bones support the body; cartilage supports the ears, nose, larynx, and trachea; fibrous tissues form the framework of organs such as the spleen. Corrected with concave lenses, which cause light rays to diverge slightly before entering the eye, shifting the focal point posteriorly so that it falls on the retina of the elongated eyeball. Among other functions, this mechanism is crucial to penile erection (see Deeper Insight 27. A stalk penetrates the dura to connect the pituitary gland to the base of the brain. Pregnancy outcomes and cardiac complications in women with mechanical, bioprosthetic and homograft valves. The cell came to be regarded, and still is, as the simplest structural and functional unit of life. Infective endocarditis in Ethiopian children: a hospital based review of cases in Addis Ababa. Short chains of three or more monosaccharides are called oligosaccharides, and long chains (up to thousands of monosaccharides long) are called polysaccharides. The second phase of the murmur is in late diastole, as a result of atrial contraction, occurring immediately before the S1 sound creating a late diastolic, crescendo murmur. It is not difficult to see how this happens-the only thing hard to imagine is that it can happen as often as 20,000 times per second! List three or more functions of the skeletal system other than supporting the body and protecting some of the internal organs. This is why some cells acquire two or more nuclei or multiple identical sets of chromosomes. Endocrine components of the ovaries and testes, and their hormones and functions 10. If a dominant allele is silenced and has no effect on some people who carry it, it is said to show incomplete penetrance in that population-that is, the genotype does not "penetrate to" and affect everyone who has it. The patella (kneecap) is a sesamoid bone at the junction of the femoral and crural regions. For example, the vagina of a young girl is lined with a simple cuboidal epithelium. The last action potential at the end of a nerve fiber is just as strong as the first one in the trigger zone, no matter how far away-even in a pain fiber that extends from your toes to your brainstem. They are common in fast sports such as tennis and football, and sometimes cause ankle sprains. Growth factors and their receptors are a central issue in understanding the uncontrolled growth of cancer (see Deeper Insight 4. During exercise, they receive an abundant flow while capillaries elsewhere-for example, in the skin and intestines- shut down to compensate. Molecules are represented by molecular formulae that identify their elements and show how many atoms of each are present. The menisci absorb the shock of the body weight jostling up and down on the knee and prevent the femur from rocking from side to side on the tibia. Gaps a: Biophoto Associates/Science Source between the keratinocytes are an artifact created by cell shrinkage during fixation, but are typically seen in microscope slides of skin. The structure and function of intervertebral discs; which vertebrae have discs between them and which ones do not 9. The most superficial muscles are shown on the left and the next deeper layer on the right.
The superior processes face medially (like the palms of your hands about to clap), and the inferior processes face laterally, toward the superior processes of the next vertebra. This is the only cranial nerve that arises from the posterior side of the brainstem. It is bordered laterally by the tendons of the abductor pollicis longus and extensor pollicis brevis, and medially by the tendon of the extensor pollicis longus. Mesenteric Blood Supply the mesentery is a translucent sheet that suspends the intestines and other abdominal viscera from the posterior body wall (see figs. Excitatory synapses; how acetylcholine and norepinephrine excite a postsynaptic neuron 6. Thus, the right brain receives signals from the left side of the body and vice versa. Finer connective tissue septa may further subdivide each lobe into microscopic lobules. Muscle plays a highly important role in absorbing blood glucose and buffering glycemia, so as muscle mass diminishes, a person becomes less and less able to regulate glycemia. The following are not acceptable: sulfonamides, trimethoprim, tetracyclines, and fluoroquinolones. The absolute refractory period lasts from the start of the action potential until the membrane returns to the resting potential- that is, for as long as the Na+ channels are open and subsequently inactivated. Cerebrospinal fluid is secreted partly by a mass of blood capillaries called the in each ventricle. If you pluck the wire at one end, a wave of vibration travels down its length and back. Calcium imbalances therefore affect not only heart rate, as we have already seen, but also contraction strength. Horizontal cells and amacrine57 cells form horizontal connections between rods, cones, and bipolar cells and intervene in the pathways from receptor cells to ganglion cells. Osmosis, examples of its physiological and clinical relevance, factors that determine its speed and direction, and the role of aquaporins 5. In some places, after wrapping around the intestines or other viscera, the mesentery continues toward the anterior body wall as the anterior mesentery. Why protein function depends so strongly on the shape (conformation) of the molecule; how and why functionality is affected by denaturation; and the most common causes of protein denaturation 15. Pulled hamstrings-strained hamstring muscles or a partial tear in their tendons, often with a hematoma (blood clot) in the fascia lata. This enhances the strength of bone on the same principle as plywood, made of thin layers of wood with the grain running in different directions from one layer to the next. Lignans are metabolized to form mammalian lignans known as pinoresinol, lariciresinol, enterodiol secoisolariciresinol, matairesinol, hydroxymatairesinol, syringaresinol and sesamin and enterolactone by intestinal bacteria. In order to contract, a muscle cell must also be extensible-able to stretch again between contractions. By innervating the lateral rectus muscle, this nerve makes the eye turn away from the facial midline, as its name implies ("to turn away"). That inspired her to set up a little laboratory in her bedroom, where she studied nervous system development in chick embryos. Questions remain as to whether implanted stem cells may lodge in the wrong place in the body or grow into tumors instead of healthy functional tissue. If a heart wall weakened by disease should rupture, or if it suffers a penetrating injury such as a knife or gunshot wound, blood spurts from the heart into the pericardial cavity, filling the cavity more and more with each heartbeat. Abnormally wide sutures may indicate hydrocephalus, the accumulation of excessive amounts of cerebrospinal fluid, which causes the cranium to swell. A descending motor pathway typically involves two neurons called the upper and lower motor neurons. Braininjured peo ple are sometimes unable to recall things they once knew (retrograde amnesia) or unable to store new information (anterograde amnesia). Light rays striking the very center of the cornea pass straight through, but because of the curvature of the cornea, rays striking off center are bent toward the center (fig. Outcome after aortic valve replacement for low-flow/low-gradient aortic stenosis without contractile reserve on dobutamine stress echocardiography. Posterior to the body of each vertebra is a triangular space called the vertebral foramen. Nerve cells exhibit neurofibrillary tangles-dense masses of broken and twisted cytoskeleton (fig.
It projects into the vertebral foramen of the atlas, where it is nestled in a facet and held in place by a transverse ligament (fig. In heavy sweating, fluid loss from the bloodstream can be so great as to cause circulatory shock. Slow pain originates in small unmyelinated type C nerve fibers, which conduct at only 0. Papaver somniferum (Fruit capsule) Heroin Morphine Alkaloid Narcotic analgesic Heroin is converted into morphine by deacetylation. Would you expect this reflex arc to show more synaptic delay, or less, than the ones in figure 13. The envelope is perforated with nuclear pores formed by a ring of proteins called the nuclear pore complex. The sciatic nerve passes through the greater sciatic notch of the hip bone, extends for the length of the thigh, and ends at the popliteal fossa (back of the knee). Distinctions between a uniport, symport, and antiport; the meanings of cotransport and countertransport; and examples of where each is relevant in human physiology 11. If ischemia (poor blood flow) persists for more than 2 to 4 hours, nerves begin to die, and after 6 hours, so does muscle tissue. Stellate cells have spheroidal neurosomas with short axons and dendrites projecting in all directions. Salvestrol on administration with other dietary supplements can provide promising positive outcomes for patients undergoing oncotherapy. In strict anatomical terminology, the words arm and leg both refer to regions with only one bone. The number of electrons equals the number of protons, so their charges cancel each other and an atom is electrically neutral. Food and Drug Administration, are treatments using bone marrow and umbililcal cord blood for certain leukemias and other bloodand immune-related diseases (see Deeper Insight 18. Usually their cells are not in direct contact with each other, but are separated by expanses of matrix. These are especially abundant in the skin and mucous membranes and occur in nearly all organs, although not in the brain or liver. Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 cases of death, 1990e2013: a systemic analysis for the Global Burden of Disease Study 2013. The most medial column is the spinalis, divided into spinalis thoracis, spinalis cervicis, and spinalis capitis. The scope of cytology Basic tenets of the cell theory the nine common cell shapes the size range of most human cells; some extremes outside this range; and some factors that limit cells from growing indefinitely large 5. Comparisons of the histology of spongy bone with that of compact bone; where spongy bone is found; and why bones are not composed solely of compact bone 6. Such a circuit is also important in withdrawal reflexes, in which a brief pain produces a longer-lasting output to the limb muscles and causes you to draw back your hand or foot from danger. Excessive pressure on one side or the other muffles the sense of hearing and may cause pain, as one commonly experiences in airline flight. Pilocarpine, for example, relieves glaucoma (excessive pressure in the eyeball) by dilating a vessel that drains fluid from the eye. They occur as the lens fibers darken with age, fluid-filled clefts appear between them, and the clefts accumulate debris from degenerating fibers. About 650,000 Americans die annually of thromboembolism (traveling blood clots) in the cerebral, coronary, and pulmonary arteries. Soon, chondrocyte enlargement and death and vascular invasion occur in the epiphysis of the model as well, creating a secondary ossification center. The images 49 50 Refraction Image formation depends on refraction, the bending of light rays. Afterload Afterload is the sum of all forces a ventricle must overcome before it can eject blood. In glycoproteins, as described earlier, the carbohydrate moiety is a prosthetic group. These transport blood to the air sacs (alveoli) of the lungs, where carbon dioxide is unloaded and oxygen is picked up.
When you stand up, these ligaments become twisted and pull the head of the femur tightly into the acetabulum. Flexion and extension occur at nearly all diarthroses, but hyperextension is limited to only a few. Signs of trochlear nerve damage include double vision and a weak ability to look downward. A chromosome territory is permeated with channels that allow regulatory chemicals to have access to the genes. The role of sympathetic and vasomotor tone in controlling vessel diameter is explained in section 15. The medial sternal end has a rounded, hammerlike head, and the lateral acromial end is markedly flattened. Throughout the autonomic nervous system, the neurotransmitter released by the preganglionic fiber binds to receptors on the postganglionic neuron. A student moving out of a dormitory crouches, in correct fashion, to lift a heavy box of books. This idea of spontaneous generation-that living things arise from nonliving matter-was rooted in the scientific thought of the times. Jose Luis Calvo/Shutterstock taken from the lumbar cistern by a procedure called a spinal tap or lumbar puncture (see Deeper Insight 13. In patients that are hemodynamically stable, an echocardiogram within 48 h of admission is recommended if cardiac structure/function is unknown or may have changed since the last study. For example, if you hold out your hands with the palms up, flexion of the wrist tips your palms toward you. In most places, this is the thickest stratum, but on the palms and soles it is usually exceeded by the stratum corneum. In hyperkalemia,30 a potassium excess, K+ diffuses into the cardiomyocytes and keeps the membrane voltage elevated, inhibiting cardiomyocyte repolarization. A muscle spindle is a bundle of usually seven or eight small, modified muscle fibers enclosed in an elongated fibrous capsule about 5 to 10 mm long (fig. Many of these nuclei belong to the reticular formation, which extends from the medulla to the hypothalamus. Acting as a hormone, it travels in the blood to the small intestine and regulates its absorption of dietary iron. In association with this decline, register-based control programs had largely ceased throughout the United States and were even closing in parts of New Zealand. The synovial membrane folds around them, however, so that they are excluded from the fluid-filled synovial cavity. The joint capsule encloses only the lateral and posterior aspects of the knee joint, not the anterior. Studies on fish and other experimental animals have shown that social and sensory deprivation causes these spines to decline in number, while a richly stimulatory environment causes them to proliferate-an intriguing clue to the importance of a stimulating environment to infant and child development. This high temperature raises the metabolic rate, which makes the body produce heat faster than it can get rid of it. The relative roles of transthoracic compared with transesophageal echocardiography in children with suspected infective endocarditis. If it were not for this elastic recoil, resting muscles would be too slack or flabby. They are large ovoid receptors, up to 1 or 2 mm long, found in the periosteum of bones; in joint capsules; in the pancreas and some other viscera; and deep in the dermis, especially on the hands, feet, breasts, and genitals. At rest, the air pressures within the syringe barrel and in the atmosphere surrounding it are equal. Types of Secretions Glands are classified not only by their structure but also by the nature of their secretions. Childhood acquired heart disease in Nigeria: an echocardiographic study from three centres. The neuron must assemble molecules and organelles in its "tennis ball" soma and deliver them through its "mile-long garden hose" to the end of the axon. In humans, two such systems are especially prominent-the nervous and endocrine systems, which communicate with neurotransmitters and hormones, respectively.
They initiate the formation of a clot-dissolving enzyme that dissolves blood clots that have outlasted their usefulness. An intercalated disc is a complex steplike structure with three distinctive features not found in skeletal muscle: 1. Open reduction involves the surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments (fig. The gracile fasciculus carries sensory signals from the lower trunk and lower limbs, and the cuneate fasciculus from the chest and upper limbs. It receives drainage from posterior intercostal veins 4 through 8 and sometimes the left bronchial veins. We will start with the relatively familiar and large-scale aspects of this system-a survey of the endocrine glands, their hormones, and the principal effects of those hormones. Anatomy of the thyroid gland; its hormones and functions; and the cells that produce each hormone 4. Conclusively, they reported superior gastrointestinal stability, enhanced membrane permeability with appropriate biotransformation of prodrug in intestinal cell (Sun et al. When the award was announced, Banting was furious about having to share it with Macleod. A deficiency of vitamin B12 also causes anemia, but B12 is so abundant in meat that a deficiency is rare except in strict vegetarians. In early long-term space missions, astronauts developed osteoporosis because in a microgravity environment, their bones were subjected to too little of the stress that normally stimulates bone deposition. You can feel their effect by carefully moving a single hair with a pin or by lightly running your finger over the hairs of your forearm without touching the skin. The anterior body wall is removed, and the ribs, intercostal muscles, and pleura are removed from the anatomical left. Thus, a hollow organ such as the bladder can be greatly stretched yet not become flabby when it is empty. Receptor defects lie at the heart of several endocrine diseases (see Deeper Insight 17. At least seven more bursae are found on the lateral and medial sides of the knee joint. Pain pathways from receptors in the head to the cerebral cortex, including the cranial nerves that carry pain signals 10. In this and subsequent tables, each photograph is accompanied by a labeled drawing of the same specimen. A shift in the balance of regulatory T and T helper 17 cells in rheumatic heart disease. Profiling cytochrome P450 expression in ovarian cancer: Identification of prognostic markers. Complex skeletal muscles insert in the dermis and pull on the skin to create subtle and varied facial expressions. The threads of screws and bolts are designed with the relative strength of the supinator in mind, so the greatest power can be applied when driving them with a screwdriver in the right hand. Differences in the fibers provide a basis for classifying cartilage into three types: hyaline cartilage, elastic cartilage, and fibrocartilage (shown in table 5. The central panel represents the blood reservoir of calcium and shows its normal (safe) range. Knowledge and awareness assessment tools exist for a number of other diseases in low-resource settings, including hypertension and diabetes. Sleep is associated with restorative anabolic processes in the immune, nervous, endocrine, and other systems. Since estrogen supports bone mass, the risk of osteoporosis rises sharply after menopause, when the ovaries cease to produce it.
Peptide hormones such as growth hormone and oxytocin, and catecholamines such as epinephrine and dopamine, are stored in secretory vesicles of the endocrine cell until needed and released by exocytosis when the cell receives a stimulus to do so. Thick skin covers the palms, soles, and corresponding surfaces of the fingers and toes. We now see physiology as largely a group of mechanisms for maintaining homeostasis, and the loss of homeostatic control as the cause of illness and death. Phases G1, S, and G2 are collectively called interphase-the time between M phases. The fibrous pericardium is anchored by ligaments to the diaphragm below and the sternum anterior to it, and more loosely anchored by fibrous connective tissue to mediastinal tissue posterior to the heart. In most nerves, the fibers are gathered in bundles called fascicles, each wrapped in a sheath called the perineurium. Thus, in the figure, you can see the development of muscle tension (myocardial contraction) following closely behind the depolarization and plateau. Additional stretch therefore produces a significant increase in contraction force on the next beat. Central noncoaptation or eccentric regurgitation between retracted or rolled cusps are both common findings. The sarcomeres move independently of the sarcolemma, creating tears in the membrane. The gallbladder discharges the bile into the small intestine, where bacteria convert bilirubin to urobilinogen, responsible for the brown color of the feces. The gluteus maximus can generate 1,200 kg of tension, and all the muscles collectively can produce a total tension of 22,000 kg (nearly 25 tons). Death typically ensues from pneumonia or other complications of confinement and immobility. It is the principal visual center of the brain, where we first become aware of visual stimuli and process them to identify what we see. Postganglionic fibers emerging from the sympathetic chain form the cardiac nerves. After prolonged stimulation, the adrenal cortex may stop producing glucocorticoids, making it all the more difficult to maintain glucose homeostasis. Thus, many chemicals have a two-way traffic between the blood and connective tissue, leaving the capillaries at one point and entering at another. The computer displays a color image that shows which tissues were using the most glucose at the moment. When Watson and Crick came to share a laboratory at Cambridge University in 1951, both had barely begun their careers. The location and extent of the vomer; contributions of the vomer and ethmoid bone to the nasal septum 21. The term plexus in some of the tables refers to weblike networks of spinal nerves adjacent to the vertebral column. The plate persists through childhood and adolescence and serves as a growth zone for bone elongation. When the body detects an antigen of foreign origin, it activates an immune response. A ridge, the superior nuchal line, can be traced horizontally from this protuberance toward the mastoid process (see fig. Such experiments demonstrated the existence of one-way valves in veins of the arms. Why the autonomic effect on a target cell depends on both the neurotransmitter released and the type of receptor on the target cell 2. Further progress had to await improvements in microscope technology and histological staining methods. It is relatively concentrated in freckles and moles, on the dorsal surfaces of the hands and feet as compared with the palms and soles, on the nipple and surrounding area (areola) of the breast, around the anus, on the scrotum and penis, and on the lateral surfaces of the female genital folds (labia majora).
Perilymph, like other liquids, cannot be compressed, so it flows away from the stapes footplate. Thyroid hormone also promotes alertness and quicker reflexes; growth hormone secretion; growth of the bones, skin, hair, nails, and teeth; and development of the fetal nervous system. Structure of the mandible, including the body, ramus, and angle; its two main processes and the notch between them; its foramina, symphysis, protuberance, and spines 22. The direction in which a reversible reaction goes is determined by the relative abundance of substances on each side of the equation. Abnormalities in this interval can thus indicate defects that affect conduction time. He had become a public hero, and the Canadian Parliament awarded him an endowment generous enough to ensure a life of comfort. These muscles are tightly bound by fasciae that compress them and aid in the return of blood from the legs. For example, 90% of warfarin-related deaths are due to intracerebral hemorrhage and most of those who survive are left with permanent disability. What muscle is the prime mover in sucking through a soda straw or spitting out a mouthful of liquid The three large muscles on the posterior side of the thigh are commonly known as the muscles. How Schleiden and Schwann revolutionized and unified the understanding of biological structure, ultimately including human anatomy and physiology 1. Over a longer time, a hypoxic tissue can increase its own perfusion by angiogenesis8-the growth of new blood vessels. Note the shift from net filtration at the arterial end (left) to net reabsorption at the venous end (right). Many of these studies have also reported rare recurrences occurring despite high adherence to secondary prophylaxis. This coverage will, however, provide some intriguing insights and lay a foundation for further study in other courses. For example, the amnion is a transparent sac that forms around the developing fetus. Supination is usually achieved by the supinator of the upper forearm, with the biceps brachii aiding when additional speed or power is required (fig. It may be a consequence of blood loss, dehydration, anemia, or other factors and is normal in people approaching death. Hence design and synthesis of hexanoate ester prodrugs of rohitukine with improved drug-like properties such as chemical stability, enzymatic hydrolysis in plasma (esterase), optimum aqueous solubility and lipophilicity to achieve intestinal absorption support prodrug design strategy (Dhareshwar et al. Connec tions between the cerebellum and brainstem are very complex, but overlooking some exceptions, we can draw a few generalizations. Filtration, where it occurs in the body, and why it depends on hydrostatic pressure 3. Triglycerides that are liquid at room temperature are also called oils, but the difference between a fat and an oil is fairly arbitrary. When we lay the 46 chromosomes out in order by size and other physical features, we get a chart called a karyotype12 (fig. External to the neurilemma is a basal lamina and then a thin sleeve of fibrous connective tissue called the endoneurium. Our olfactory sense is very subject to "top-down" influences of emotional and cognitive states, so the same odorant and concentration may smell different to us under different circumstances. No one passenger moves from the door to the rear, but the crowding and transfer of energy from person to person forces even those at the rear to move a little, like the sodium ions at the next node. When the circular smooth muscle contracts, it may propel contents such as food through the organ. Each papillary muscle has two or three basal attachments to the trabeculae carneae of the heart wall. Stretch reflexes often feed back not to a single muscle but to a set of synergists and antagonists. Because each Na+ carries a positive charge, this flow constitutes an electrical current through the membrane. What physical properties of sound waves correspond to the sensations of loudness and pitch Explain how vibration of the tympanic membrane ultimately produces fluctuations of membrane voltage in a cochlear hair cell.