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The auditory os- Inspecting the tympanic membrane with an otoscope during a physical examination provides clinical information about the sicles are attached to the wall of the tympanic cavity by liga- condition of the middle ear (fig purchase 15mg slimex free shipping. Vibrations of the tympanic membrane cause the auditory its curvature cheap 15 mg slimex fast delivery, the presence of lesions, and the position of the malleus of the middle ear are features of particular importance. If ruptured, the tympanic membrane will generally regenerate, healing itself within days. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 518 Unit 5 Integration and Coordination Malleus Tympanic membrane (a) (b) FIGURE 15. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 Chapter 15 Sensory Organs 519 Semicircular canals: Semicircular ducts of the Anterior membranous labyrinth Posterior Bony labyrinth Lateral Utricle Saccule Vestibule Cochlear nerve Cochlea Membranous ampullae: Lateral Cochlear duct Anterior Posterior Connection to cochlear duct Apex of cochlea FIGURE 15. The membranous labyrinth (darker color) is contained within the bony labyrinth. The principal structures of the inner ear are the cochlea for hearing and the vestibular organs (semicircular canals, utricle, and saccule) for balance and equilibrium. When atmospheric pres- sure is reduced, as occurs when traveling to higher altitudes, the dow moves a fluid within the inner ear and stimulates the recep- tympanic membrane bulges outward in response to the greater air tors of hearing. The bulging is painful and may As the auditory ossicles transmit vibrations from the impair hearing by reducing flexibility. The auditory tube, which is col- tympanic membrane,they act as a lever system to amplify lapsed most of the time in adults, opens during swallowing or yawn- ing and allows the air pressure on the two sides of the tympanic sound waves. The combined effect increases sound amplifica- Inner Ear tion about 20 times. When contracted, the tensor tympani the bony labyrinth and the membranous labyrinth is filled with a muscle pulls the malleus inward, and the stapedius muscle pulls fluid called perilymph, which is secreted by cells lining the bony the stapes outward. Within the tubular chambers of the membranous bration of the auditory ossicles. These two fluids The mucous membranes that line the tympanic cavity, the provide a liquid-conducting medium for the vibrations involved mastoidal air cells, and the auditory tube are continuous with in hearing and the maintenance of equilibrium.
A conserved aspartate residue in TM3 (Asp-113 in the b-adrenoceptor) and a NEUROTRANSMITTER RECEPTORS 71 Figure 3 buy generic slimex 15mg on-line. The extracellular structure is stabilised by the disulphide bond joining the first and second extracellular loop buy slimex 10 mg with mastercard. The third intracellular loop is the main site of G-protein interaction while the third intracellular loop and carboxy tail are targets for phosphorylation by kinases responsible for initiating receptor desensitisation conserved phenylalanine in TM6 (Phe-290) and two serine residues in TM5 (Ser-204 and 207) are known to be crucial for agonist binding. Antagonists have been shown to have extra interaction points on TM4 and TM7 but are thought to largely share the same binding sites as the agonist and so can act by simple competition. G-protein coupling All rhodopsin-like G-protein-coupled receptors have a conserved arginine residue at the intracellular end of TM3 and this residue is thought to be crucial for G-protein activation. The third intracellular loop determines the class of G-protein activated by the receptor with the second intracellular loop and C-terminus also influencing G- protein binding in some cases. Four classes of G-protein are known: (1) Gs Ð activates adenylyl cyclase (irreversibly activated by cholera toxin) (2) Gi Ð inhibits adenylyl cyclase (inactivated by Pertussis toxin) (3) Gq Ð activates phospholipase-C (not activated by Pertussis toxin or cholera toxin) (4) G Ð inhibits voltage-dependent Ca2 and K channels (inactivated by Pertussis o toxin) Using chimaeric receptors it has been shown that swapping the third intracellular loop between receptors also swaps their G-protein selectivity. The G-protein-binding 72 NEUROTRANSMITTERS, DRUGS AND BRAIN FUNCTION Table 3. Different subtypes of G-protein-coupled receptor have evolved which couple to different G-proteins (Table 3. A similar effect has recently also been described for dopamine and somatostatin receptors (Rocheville et al. The significance of this in terms of the pharmacology of the receptors is unclear, or indeed whether dimerisation affects mechanisms such as desensitisation. Three main families have been identified: NEUROTRANSMITTER RECEPTORS 73 (1) Rhodopsin-like 7-TM receptors. Monoamine, nucleotide and lipid receptors (2) Glucagon, VIP and calcitonin family. Ligand binding outside the transmembrane domains on cell surface (3) Metabotropic glutamate receptors and chemosensor (Ca2) receptors. Ligand binding on large extracellular N-terminus Rhodopsin-like 7-TM receptors By far the most studied family of the G-protein-coupled receptors are the rhodopsin- like receptors. These are also the largest group of receptors in number as they include receptors not only for the monoamines, nucleotides, neuropeptides and peptide hormones, but they also include the odorant receptors which number several hundreds of related receptors. These receptors have short N-termini, a conserved disulphide bridge between the TM2±TM3 and TM4±TM5 extracellular domains, and variable- length C-termini.
Most taste lated by transient or maintained changes in the position of experiences involve several different sensory modalities buy slimex 10 mg without a prescription, in- the head slimex 15mg low cost. If the otolithic organs are stimulated rhythmi- cluding taste, smell, mechanoreception (for texture), and cally, as by the motion of a ship or automobile, the dis- temperature; artificially confining the taste sensation to tressing symptoms of motion sickness (vertigo, nausea, only the four modalities found on the tongue (e. This symptom loocular system, to a pattern of nystagmus (eye move- may be a result of several factors, such as cerebral is- ments) appropriate to the spurious input. Such disturbances can produce the phenomenon By observing the resulting pattern of nystagmus and re- of vertigo, which may be defined as the illusion of motion ported symptoms, the location of the defect can be de- (usually rotation) when no motion is actually occurring. Another set of maneuvers known as the canalith Vertigo is often accompanied by autonomic nervous sys- repositioning procedure of Epley can cause gravity to tem symptoms of nausea, vomiting, sweating, and pallor. This procedure is highly place in space: the vestibular system, which senses posi- effective in cases of true BPPV, with a cure rate of up to tion and rotation of the head; the visual system, which pro- 85% on the first attempt and nearly 100% on a subsequent vides spatial information about the external environment; attempt. Patients can be taught to perform the procedure and the somatosensory system, which provides informa- on themselves if the problem returns. Several forms of vertigo can arise from distur- ripheral) origin associated with vertigo. Physiological vertigo can precipitating factors are not well understood. Typical asso- result when there is discordant input from the three sys- ciated findings include fluctuating hearing loss and tinni- tems. Seasickness results from the unaccustomed repeti- tus (ringing in the ears). Episodes involve increased fluid tive motion of a ship (sensed via the vestibular system). Other motion sickness, and space sickness is associated with cases of peripheral vertigo may be caused by trauma (usu- multiple-input disturbances. Central positional vertigo ally unilateral) or by toxins or drugs (such as some antibi- can arise from lesions in cranial nerve VIII (as may be as- otics); this type is often bilateral. Its nystag- ripheral vertigo arises from disturbances in the vestibu- mus fatigues and can be reduced by visual fixation. The problem may be either unilateral tion sensitive and of finite duration, the condition usually or bilateral. Causes include trauma, physical defects in the involves a horizontal orientation.
Peristaltic waves sweep down the ureters at a muscles raises intra-abdominal pressure buy slimex 15 mg cheap, and aids in the ex- frequency of one every 10 seconds to one every 2 to 3 min- pulsion of urine from the bladder buy slimex 10 mg on-line. The ureters enter the base of the bladder obliquely, Micturition is fortunately under voluntary control in forming a valvular flap that passively prevents the reflux of healthy adults. In the young child, however, it is purely re- urine during contractions of the bladder. The ureters are in- nervated by sympathetic and parasympathetic nerve fibers. Sensory fibers mediate the intense pain that is felt when a stone distends or blocks a ureter. Descending aorta L1 Inferior vena cava The Bladder Stores Urine Until It Can Be L2 Sympathetic trunk Conveniently Emptied L3 The urinary bladder is a distensible hollow vessel contain- ing smooth muscle in its wall (Fig. The muscle is called the detrusor (from Latin for “that which pushes down”). The neck of the bladder, the involuntary internal sphincter, also contains smooth muscle. The bladder body and neck are innervated by parasympathetic pelvic nerves S2 and sympathetic hypogastric nerves. The external sphinc- Right ureter S3 ter, the compressor urethrae, is composed of skeletal mus- Hypogastric S4 cle and innervated by somatic nerve fibers that travel in the pudendal nerves. Pelvic, hypogastric, and pudendal nerves nerve Pelvic nerve contain both motor and sensory fibers. Bladder The bladder has two functions: to serve as a distensible Pudendal nerve reservoir for urine and to empty its contents at appropriate intervals. When the bladder fills, it adjusts its tone to its ca- Internal (involuntary) pacity, so that minimal increases in bladder pressure occur.