By L. Varek. Marymount Manhattan College.

There are actually more negatively charged and positively charged groups at physiological pH (it is a zwitterion) cheap urispas 200 mg visa, and this property may enable it to interact with transporters for these molecules than are depicted in this figure purchase 200mg urispas fast delivery. This exchange is Descending and Ascending Limbs Differ mediated by an organic anion transporter (OAT) called in Water Permeability OAT1. The cells accumulate -ketoglutarate from metabo- Tubular fluid entering the loop of Henle is isosmotic to lism and because of cell membrane Na -dependent dicar- boxylate transporters. PAH accumulates in the cells at a plasma, but fluid leaving the loop is distinctly hypoos- high concentration and then moves downhill into the tu- motic. Fluid collected from the earliest part of the distal bular urine in an electrically neutral fashion, by exchanging convoluted tubule has an osmolality of about 100 mOsm/kg H2O, compared with 285 mOsm/kg H2O in for an inorganic anion (e. The organic cations are mainly amine and ammonium plasma because more solute than water is reabsorbed by the compounds and are secreted by other transporters. The loop of Henle reabsorbs about 20% of 2 into the cell across the basolateral membrane is favored by filtered Na , 25% of filtered K , 30% of filtered Ca , 2 the inside negative membrane potential and occurs via fa- 65% of filtered Mg , and 10% of filtered water. The de- cilitated diffusion, mediated by an organic cation trans- scending limb of the loop of Henle (except for its terminal porter (OCT). The exit of organic cations across the lumi- portion) is highly water-permeable. Because solutes are reabsorbed along nal membrane is accomplished by an organic cation/H antiporter (exchanger) and is driven by the lumen-to-cell the ascending limb and water cannot follow, fluid along the ascending limb becomes more and more dilute. The transporters for organic anions and organic cations show of these solutes (mainly Na salts) in the interstitial space broad substrate specificity and accomplish the secretion of of the kidney medulla is critical in the operation of the uri- a large variety of chemically diverse compounds. In addition to being actively secreted, some organic compounds passively diffuse across the tubular epithelium. The Luminal Cell Membrane of the Organic anions can accept H and organic cations can re- Thick Ascending Limb Contains a lease H , so their charge is influenced by pH. The non- Na-K-2Cl Cotransporter ionized (uncharged) form, if it is lipid-soluble, can diffuse through the lipid bilayer of cell membranes down concen- Figure 23.

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Afferent pyramid stretches the arcuate nucleus and efferent fibers of the vagus nerve (B30) (AB13) where collaterals of the pyramidal cross the medulla oblongata purchase 200mg urispas with visa. Ventrally to tract synapse (arcuatocerebellar tract) them generic urispas 200 mg on line, the spinothalamic tract (B31) (p. B8) and the spinocerebellar tract (B32) The fibers of the hypoglossal nerve (A14) (p. Medulla Oblongata, Cross Sections 109 6 4 15 16 5 7 B A 3 20 17 8 Planes of sections 9 18 10 19 11 14 1 21 5 4 15 1 16 12 23 6 3 XII 7 13 22 8 17 18 20 2 9 11 21 A Cross section through the medulla oblongata 10 22 at the level of the hypoglossal nerve (XII) 19 1 12 23 13 14 26 5 25 24 16 2 4 3 15 7 29 8 17 30 9 28 20 10 11 X 26 25 27 31 1 32 5 4 24 12 3 7 16 33 20 29 17 8 1 9 28 11 18 13 10 2 19 31 27 32 1 22 12 23 2 B Cross section though the medulla oblongata 13 at the level of the vagus nerve (X) Kahle, Color Atlas of Human Anatomy, Vol. They are corticopon- Thesemi-schematiccrosssectionsshowthe tine fibers, which synapse in the pontine nu- cellular stain (Nissl) on the left and the clei (A22), and pontocerebellar fibers, which corresponding fiber stain (myelin) on the are postsynaptic and extend to the cerebel- right. Embedded in the middle of the longitudinally cut fiber Cross Section at the Level of the bundles is the transversely cut fiber bundle Genu of the Facial Nerve (A) of the pyramidal tract (AB24). Beneath the floor of the rhomboid fossa lies the magnocellular nucleus of the abducens Cross Section at the Level of the nerve (A1) and, ventrolaterally to it, the Trigeminal Nerve (B) nucleus of the facial nerve (A2). The visceroefferent superior salivatory nucleus The medial field of the pontine tegmentum (A3) is seen between the abducens and fa- is occupied by the nuclei of the tegmentum. The lateral field is occupied by These nuclei, of which only the inferior cen- the sensory terminal nuclei of the vestibular tral tegmental nucleus (B25) is well defined, nerve and the trigeminal nerve, namely, the belong to the reticular formation. In the medial vestibular nucleus (Schwalbe’s nu- lateral field, the trigeminal complex has cleus) (A4), the lateral vestibular nucleus reached its widest expansion; lateral is the (Deiters’ nucleus) (A5), and the spinal nu- pontine nucleus of the trigeminal nerve cleus of the trigeminal nerve (A6). We distinguish an as- fibers unite to form the strong trunk emerg- cending limb (A8) and, cranial to the il- ing at the anterior aspect of the pons. The apex is the internal genu of the facial nerve The lateral lemniscus (AB17), the trapezoid (A9). The fibers of the abducens nerve (A10) body (AB15), and the adjacent posterior nu- descend through the medial field of the teg- cleus of the trapezoid body (AB19) lie ven- mentum. The following (AB11) is seen medially and the posterior ascending and descending pathways can be longitudinal nucleus (Schütz’s bundle) recognized: the posterior longitudinal (AB12) dorsally to the abducens nucleus. They synapse in part in the adjacent nuclei of the trapezoid B body, namely, the anterior nucleus of the trapezoid body (A18) and the posterior nu- cleus of the trapezoid body (superior olive) (AB19). The spinal tract of the trigeminal nerve (A20) lies in the lateral field.

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Color blindness for the majority of fibers and the motor pathways they activate constitute the tectal these people is a misnomer discount urispas 200 mg online, however 200mg urispas mastercard, because in nearly all cases there system, which is responsible for body-eye coordination. Here the fibers synapse with neurons whose axons type—is able to distinguish traffic signals without difficulty be- cause yellow has been added to the red light, and blue has been constitute a pathway called the optic radiation. This arrangement of visual fibers, known as the geniculostriate system, is responsible for perception of the Neural Pathways for Vision, visual field. Eye Movements, and Processing The nerve fibers that cross at the optic chiasma arise from the retinas in the medial portions of both eyes. The photoreceptors Visual Information of these fibers are stimulated by light entering the eyeball from the periphery. If the optic chiasma is cut longitudinally, peripheral vision The photoreceptor neurons, rod and cone cells, are the func- will be lost, leaving only “tunnel vision. Nerve impulses from the rod and cone cells eye, and the medial field of vision lost for the other. The optic nerve consists of axons of aggregated gan- Superior Colliculi and Eye Movements glion neurons that emerge through the posterior aspect of the eyeball. At this point, all of the spinal cord help mediate the startle response to the sight,for the fibers arising from the medial (nasal) half of each retina cross example,of an unexpected intruder. Sensory Organs © The McGraw−Hill Anatomy, Sixth Edition Coordination Companies, 2001 514 Unit 5 Integration and Coordination pathetic neurons by fibers from the superior colliculi. Postganglionic Monocular field neurons in the ciliary ganglia behind the eyes, in turn, stimulate Binocular field constrictor fibers in the iris. Contraction of the ciliary body during Macular field accommodation also involves stimulation of the superior colliculi. Processing of Visual Information For visual information to have meaning, it must be associated with past experience and integrated with information from other Eyeball senses.