By A. Bandaro. Arizona State University.
Its fibers originate from the (E9) buy indinavir 400mg with amex symptoms torn meniscus, and into an inferior branch indinavir 400mg fast delivery treatment nurse, which sup- large, multipolar neurons of the nucleus of plies the inferior rector muscle (E10), the me- the abducens nerve (C3), which lies in the dial rector muscle (E11), and the inferior ob- pons in the floor of the rhomboid fossa lique muscle (E12). The fibers exit at the basal mar- The somatomotor fibers originate from gin of the pons above the pyramid. After largemultipolarneuronsofthenucleusofthe taking a long intradural course, the nerve oculomotor nerve (AC13) (p. The neurons for Trochlear Nerve (B, C, E) the inferior rector muscle (D14) lie dor- The fourth cranial nerve (BC4) is an exclu- solaterally, those for the superior rector sively somatomotor nerve and innervates muscle (D15) dorsomedially; below them the superior oblique muscle (E5) of the extra- lie the neurons for the inferior oblique ocular muscles. Its fibers originate from the muscle (D16), those for the medial rector large, multipolar neurons of the nucleus of muscle (D17) ventrally, and those for the le- the trochlear nerve (BC6) (p. In the middle third between the ascend dorsally in an arch, cross above the two paired main nuclei there usually lies an aqueduct, and leave the midbrain at the unpaired cell group, Perlia’s nucleus, which lower margin of the inferior colliculi. The is thought to be associated with ocular con- nerve is the only cranial nerve leaving the vergence (p. Itdescendsin The preganglionic visceromotor (parasym- the subarachnoid space (p. They run continues through the lateral wall of the from the oculomotor nucleus to the ciliary cavernous sinus. The third cranial nerve (AC7) contains so- matomotor and visceromotor (parasympa- (For extra-ocular muscles, see p. It innervates the remain- ing outer eye muscles (E) and, with its visceromotor portion, the intra-ocular muscles. The fibers exit from the floor of the interpeduncular fossa at the medial margin of the cerebral peduncle in the oculomotor Kahle, Color Atlas of Human Anatomy, Vol. Third, Fourth, and Sixth Cranial Nerves 139 7 19 19 13 13 4 6 7 8 A 1 3 4 6 B C A–C Nuclear regions and exits of abducens nerve, trochlear nerve, and oculomotor nerve 15 19 14 9 14 5 15 16 17 16 11 19 2 14 18 12 10 15 17 18 D Somatotopic arrangement of neurons in E Extra-ocular muscles the oculomotor nucleus (according to Warwick) 21 20 F Intra-ocular muscles Kahle, Color Atlas of Human Anatomy, Vol. They originate in the gracile nu- Some of the pyramidal tract fibers termi- cleus (B5) and the cuneate nucleus (B6), nate in the motor nuclei of cranial nerves cross as arcuate fibers (decussation of lem- (corticonuclear fibers): nisci) (B7), and form the medial lemniscus in the narrower sense (p. Bilaterally in the oculomotor nucleus (III), cuneate fibers initially lie dorsally to the in the motor nucleus of the trigeminal gracile fibers, while they lie medially to nerve (V), in the caudal part of the facial them in the pons and midbrain. They termi- nucleus (VII) (forehead muscles), and in nate in the thalamus. Spinothalamic tract (lateral and ante- cleus: in the abducens nucleus (VI), in the rior) (B8). The fibers (protopathic sensibility, rostral part of the facial nucleus (VII) (fa- pain, temperature, coarse tactile sensation) cial muscles with the exception of the have already crossed to the contralateral forehead muscles), and in the hypoglos- side at various levels of the spinal cord and sal nucleus (XII) form slightly spread, loose bundles (spinal! Uncrossed in the ipsilateral trochlear nu- lemniscus) in the medulla oblongata. Clinical Note: In central facial paralysis, paral- ysis of facial muscles is caused by injury to the 3. The fibers run corticobulbar fibers, yet the mobility of the bi- together with those of the lateral laterally innervated forehead muscles is retained. They form the lateral tip of the lemniscus in the midbrain and ter- Aberrant fibers (Déjérine) (A1). At various minatein thesuperior colliculi (pupillary re- levels of the midbrain and the pons, fine flex on sensation of pain). Anterior tegmental fasciculus (Spitzer) clear fibers and unite to form the mesen- (B10). The fibers (protopathic and epicritic cephalic aberrant tract and the pontine aber- sensibilities of the face) cross in small rant tract. Both descend in the medial lem- bundles from the spinal nucleus of the niscus (A2) and terminate in the con- trigeminal nerve (principle nucleus) to the tralateral abducens nucleus (VI) and hypo- contralateral side (trigeminal lemniscus) glossal nucleus (XII), in the two ambiguous and join the medial lemniscus at the level of nuclei (X), and in the spinal accessory nu- the pons. These origi- Medial Lemniscus (B) nate from the rostral part of the solitary nu- cleus (B12), probably cross to the con- This fiber system includes the most impor- tralateral side, and occupy the medial mar- tant ascending pathways of the exteroceptive gin of the lemniscus. It is subdivided into the spinal lemnis- cus and the trigeminal lemniscus. The spinal lemniscus contains the sensory pathways Kahle, Color Atlas of Human Anatomy, Vol. Pyramidal Tract System, Medial Lemniscus 141 III III 2 IV IV V V VI 1 VII VII 11 10 9 X X XII 8 3 11 XI XI 12 A Pyramidal system: corticospinal tract and corticonuclear fibers 10 8 3 7 6 5 B Ascending pathways of the medial lemniscus 4 Kahle, Color Atlas of Human Anatomy, Vol. It reaches from the rostral midbrain into the spinal cord and interconnects numerous nuclei of the brain stem.
The Brain: Gross Views indinavir 400 mg for sale medications prednisone, Vasculature purchase 400mg indinavir otc treatment spinal stenosis, and MRI 27 Fornix Choroid plexus, third ventricle Optic tract Posterior choroidal arteries Thalamogeniculate artery Lateral geniculate body Dorsal thalamus Posterior cerebral artery Mammillary body Medial geniculate body Quadrigeminal artery Superior colliculus Posterior communicating artery Crus cerebri Internal carotid artery Brachium of inferior colliculus Oculomotor nerve Inferior colliculus Superior cerebellar artery Trochlear nerve Trigeminal nerve Motor root Sensory root Superior cerebellar peduncle Anterior medullary velum Basilar artery Middle cerebellar peduncle Anterior inferior cerebellar artery Vestibulocochlear nerve Labyrinthine artery Facial nerve Abducens nerve Posterior inferior cerebellar artery Glossopharyngeal nerve Choroid plexus, Vagus nerve fourth ventricle Hypoglossal nerve Restiform body Accessory nerve Cuneate tubercle Gracile tubercle Posterior inferior cerebellar artery Posterior spinal artery Anterior spinal artery Vertebral artery 2-24 Lateral view of the brainstem and thalamus showing the rela- tively, are shown as dashed lines. Compare with Figure 2-22 on the fac- tionship of structures and cranial nerves to arteries. Compare to Figure 28 External Morphology of the Central Nervous System Anterior paracentral gyrus (APGy) Central sulcus (CSul) Paracentral sulcus (ParCSul) Posterior paracentral gyrus (PPGy) Precentral sulcus (PrCSul) Marginal sulcus (MarSul) Precuneus (PrCun) Cingulate gyrus (CinGy) Superior frontal gyrus (SFGy) Parieto-occipital sulcus (POSul) Cingulate sulcus (CinSul) Cuneus (Cun) Calcarine sulcus (CalSul) Lingual gyrus (LinGy) Sulcus of corpus callosum (SulCC) Isthmus of cingulate gyrus Paraterminal gyri Occipitotemporal gyri Parolfactory gyri (ParolfGy) Parahippocampal gyrus Temporal pole Uncus Rhinal sulcus APGy PrCSul CSul PPGy ParCSul MarSul SulCC CinGy PrCun CinSul POSul ParolfGy Cun CalSul LinGy SFGy MarSul Corpus callosum POSul CalSul Colloid cyst Internal cerebral vein 2-26 Midsagittal view of the right cerebral hemisphere and dien- A colloid cyst (colloid tumor) is a congenital growth usually dis- cephalon, with brainstem removed, showing the main gyri and sulci covered in adult life once the ﬂow of CSF through the interventricular and two MRI (both T1-weighted images) showing these structures foramina is compromised (obstructive hydrocephalus). The lower MRI is from a patient with a may have headache, unsteady gait, weakness of the lower extremities, small colloid cyst in the interventricular foramen. When compared to visual or somatosensory disorders, and/or personality changes or con- the upper MRI, note the enlarged lateral ventricle with resultant thin- fusion. The Brain: Gross Views, Vasculature, and MRI 29 Internal frontal branches Paracentral branches Callosomarginal branch of ACA Internal parietal branches Parietooccipital Pericallosal branch branches of PCA of ACA Frontopolar branches of ACA Orbital branches of ACA Anterior cerebral artery (ACA) Calcarine branch of PCA Posterior temporal branches of PCA Posterior cerebral artery (PCA) Anterior temporal branches of PCA 2-27 Midsagittal view of the cerebral hemisphere and dien- to serve medial regions of the frontal and parietal lobes, and the same cephalon showing the locations and branching patterns of anterior and relationship is maintained for the occipital and temporal lobes by posterior cerebral arteries. The positions of gyri and sulci can be ex- branches of the posterior cerebral artery. Inferior sagittal sinus Posterior vein of corpus callosum Superior sagittal sinus Internal occipital veins TV Veins of the caudate nucleus Straight sinus Septal veins Sinus confluens Transverse sinus Superior Anterior cerebral vein cerebellar vein Occipital Basal vein sinus Great Internal cerebral vein cerebral vein 2-28 Midsagittal view of the cerebral hemisphere and dien- (facing page). See cephalon that shows the locations and relationships of sinuses Figures 8-2 (p. The MRI (T1- weighted image) shows many brain structures from the same perspec- tive. The Brain: Gross Views, Vasculature, and MRI 31 Body of fornix (For) Dorsal thalamus (DorTh) Septum pellucidum (Sep) Massa intermedia Choroid plexus of third ventricle Interventricular foramen Stria medullaris thalami Column of fornix Habenula Anterior commissure (AC) Suprapineal recess Lamina terminalis Posterior commissure Pineal (P) Supraoptic recess Superior colliculus (SC) Optic chiasm (OpCh) Quadrigeminal HythHyth cistern (QCis) Inferior colliculus (IC) Optic nerve Cerebral aqueduct (CA) Anterior medullary velum (AMV) Fourth ventricle (ForVen) Infundibulum (In) Infundibular recess Mammillary body (MB) Hypothalamic sulcus Posterior inferior Oculomotor nerve cerebellar artery Interpeduncular fossa (IpedFos) Medulla Basilar pons (BP) For DorTh Sep Internal cerebral vein P AC Tentorium cerebelli Hypothalamus QCis OpCh SC In IC Pituitary gland AMV MB ForVen IpedFos BP CA 2-30 A midsagittal view of the right cerebral hemisphere and di- image) shows these brain structures from the same perspective. Hyth encephalon with the brainstem in situ focusing on the details primarily hypothalamus. The MRI (T1-weighted 32 External Morphology of the Central Nervous System A D Midbrain Anterior quadrangular Anterior lobule lobe (AntLb) Posterior quadrangular lobule Posterior Primary superior fissure fissure E Superior semilunar Hemisphere lobule Bpon Vermis (Ver) AntLb SCP B Fourth ventricle Basilar pons (Bpon) Medulla (Med) Flocculus (Fl) Tonsil (Ton) F Biventer lobule Gracile Med lobule Ton Inferior semilunar PostLb lobule Hemisphere Vermis (Ver) Ver C Colliculi: Anterior Superior Cerebellar peduncles: lobe (AntLb) Inferior Superior (SCP) G Middle (MCP) Inferior Primary fissure AntLb Horizontal MCP fissure Fl Flocculus (Fl) Posterior Tonsil (Ton) lobe (PostLb) Nodulus Med PostLb 2-31 Rostral (A, superior surface), caudal (B, inferior surface), with cerebellar structures seen in axial MRIs at comparable levels (D, and an inferior view (C, inferior aspect) of the cerebellum. Structures seen on the inferior surface of the cerebellum, such as in C shows the aspect of the cerebellum that is continuous into the the tonsil (F), correlate closely with an axial MRI at a comparable level. The view in C correlates with su- In G, note the appearance of the margin of the cerebellum, the general perior surface of the brainstem (and middle superior cerebellar pe- appearance and position of the lobes, and the obvious nature of the duncles) as shown in Figure 2-34 on page 34. Note that the superior view of the cerebellum (A) correlates closely The Brain: Gross Views, Vasculature, and MRI 33 A B II,III V II,III IV I V Midbrain (Mid) Primary fissure (PriFis) PriFis Basilar pons (Bpon) VI Mid VII VII Fourth Bpon ventricle (ForVen) ForVen Medulla Med VIII (Med) VIII X X IX IX Posterolateral fissure (PostLatFis) II,III IV V C PriFis Mid VI Bpon VII ForVen Med X IX VIII 2-32 A median sagittal view of the cerebellum (A) showing its re- Lobules I-V are the vermis parts of the anterior lobe; lobules VI-IX lationships to the midbrain, pons, and medulla. This view of the cere- are the vermis parts of the posterior lobe; and lobule X (the nodulus) bellum also illustrates the two main ﬁssures and the vermis portions of is the vermis part of the ﬂocculonodular lobe. Designation of these lobules follows the method devel- larities between the gross specimen (A) and a median sagittal view of oped by Larsell. Peduncles Middle cerebellar Superior cerebellar Inferior colliculus Trochlear nerve Flocculus Crus cerebri Trigeminal nerve: Sensory root Motor root Basilar pons 2-33 Lateral and slightly rostral view of the cerebellum and brain- relative positions of, and distinction between, motor and sensory roots stem with the middle and superior cerebellar peduncles exposed. See page 40, Figure 2-41D for an MRI show- the relationship of the trochlear nerve to the inferior colliculus and the ing the trochlear nerve. Figure 3-10 on page 61 also dashed line on the left represents the position of the sulcus limitans and shows a comparable view of the brainstem and the posterior portions the area of the inferior cerebellar peduncle is shown on the right. The Brain: Gross Views, Vasculature, and MRI 35 Vessels Structures Choroid plexus, third ventricle Pineal Habenula Medial thalamus Brachium of superior colliculus Thalamogeniculate arteries Superior Lateral thalamus colliculus Pulvinar nucleus Internal capsule Choroid plexus, lateral ventricle Medial and lateral Lateral geniculate body posterior choroidal arteries Medial geniculate body Quadrigeminal artery Brachium of inferior colliculus Superior cerebellar artery: Crus cerebri Medial branch Trochlear nerve (IV) Lateral branch Inferior colliculus Superior cerebellar peduncle Anterior medullary velum Facial colliculus Vestibular area Inferior cerebellar peduncle Middle cerebellar peduncle Choroid plexus, fourth ventricle Hypoglossal trigone Anterior inferior cerebellar artery Glossopharyngeal nerve (IX) Vagal nerve (X) Posterior inferior Accessory nerve (XI) cerebellar artery Restiform body Vagal trigone Trigeminal tubercle (tuberculum cinereum) Cuneate tubercle Posterior spinal artery Gracile tubercle Gracile fasciculus Cuneate fasciculus 2-35 Dorsal view of the brainstem and caudal diencephalon show- tion to serving the medulla, branches of the posterior inferior cerebel- ing the relationship of structures and some of the cranial nerves to ar- lar artery also supply the choroid plexus of the fourth ventricle. The vessels shown in this view have originated ventrally and tuberculum cinereum is also called the trigeminal tubercle. Medial eminence Superior cerebellar peduncle of fourth ventricle Facial colliculus Middle cerebellar peduncle Superior fovea Vestibular area Striae medullares Lateral recess Foramen of Luschka Hypoglossal trigone Sulcus limitans Vagal trigone Restiform body Cuneate tubercle Inferior fovea Gracile tubercle Tela choroidea (cut edge) 2-37 The ﬂoor of the fourth ventricle (rhomboid fossa) and imme- diately adjacent structures. The Brain: Gross Views, Vasculature, and MRI 37 Fornix Choroid plexus, third ventricle Optic tract Posterior choroidal arteries Thalamogeniculate artery Lateral geniculate body Dorsal thalamus Posterior cerebral artery Mammillary body Medial geniculate body Quadrigeminal artery Superior colliculus Posterior communicating artery Crus cerebri Internal carotid artery Brachium of inferior colliculus Inferior colliculus Oculomotor nerve Superior cerebellar artery Trochlear nerve Trigeminal nerve Motor root Sensory root Superior cerebellar peduncle Anterior medullary velum Basilar artery Middle cerebellar peduncle Anterior inferior cerebellar artery Vestibulocochlear nerve Facial nerve Labyrinthine artery Abducens nerve Posterior inferior cerebellar artery Glossopharyngeal nerve Choroid plexus, Vagus nerve fourth ventricle Hypoglossal nerve Restiform body Accessory nerve Cuneate tubercle Gracile tubercle Posterior inferior cerebellar artery Posterior spinal artery Anterior spinal artery Vertebral artery 2-38 Lateral view of the brainstem and thalamus, which shows the shown as dashed lines. Arteries that distribute to dorsal structures orig- relationship of structures and cranial nerves to arteries. Compare with Figure 2-36 on the fac- mate positions of the labyrinthine and posterior spinal arteries, when ing page. Rupture of aneurysms at this location is one of the are shown in axial (B, T1-weighted; D, T2-weighted) and in oblique more common causes of spontaneous subarachnoid hemorrhage.
The 1990s saw little growth in claims rates and steady but generally manageable increases in average settlement amounts (28) 400 mg indinavir with visa symptoms joint pain. Approxi- mately 70% of claims closed with no payment order 400mg indinavir free shipping symptoms to pregnancy, and defendants won the majority of cases that went to trial (29). Many insurers experienced favorable “loss ratios,” the ratio of payments and administrative costs to premiums collected. Insurers had set premiums high, apprehensive that the troubles of the 1980s would continue, but, in fact, claims rates and payouts held relatively stable. In this favorable market, new entrants appeared, aggressively sought business from all newcomers, and set off fierce competition on premiums (30). As a result, premium growth was generally slow or nonexistent during this period. A distinct “insurance cycle” is thus apparent over the past quarter-century, in which trends in claiming, reinsurance costs, interest rates, and other factors cause premiums and insurer loss ratios to rise and fall over time (30,31). EMPIRICAL RESEARCH ON THE FUNCTIONING OF THE MALPRACTICE SYSTEM Until the 1970s, little was known about the epidemiology of medical malpractice or how well the system carried out its theoretical functions. In 1973, an influential government inquiry into medical malpractice (32) led to the first efforts to evaluate the system’s efficacy from an epidemiologic perspective. The Medical Insurance Feasibility Study (MIFS) undertook review of nearly 21,000 medical records from 23 California hospitals (33). Comparison of the negligent injuries to the frequency of malpractice claims in California showed a wide gulf: the former outstripped the latter by a factor of 10 (24). This key finding provided an explanation for episodic increases in claims rates: the existence of a huge reservoir of injuries meant that plaintiff attorneys could initiate fewer or more claims at any given time, depending on their business decisions and the permissiveness of the legal environment. Prompted by the malpractice crisis of the mid-1980s, a research team at Harvard University embarked on a review of medical records from more than 30,000 hospital discharges and 3500 malpractice claims in New York (34). The reviewers found rates of adverse events and negligent adverse events (3. Extrapolations from these rates produced alarming estimates of the burden of medical injury, including projections that negligent care caused approx 20,000 disabling injuries and 7000 deaths in New York hospitals in 1984. However, it was the matching of specific claims to specific injuries in New York that threw the troubling relationship between malprac- tice claims and injuries into sharp relief. Only 2% of negligent injuries resulted in claims, and only 17% of claims appeared to involve a negligent injury (36). Paul Weiler has analogized this relationship to a traffic cop who regularly gives out more tickets to drivers who go through green lights than to those who run red lights (2). A third study conducted in Utah and Colorado in the late 1990s found injury rates similar to those from New York (37) and virtually identical disconnec- tions between injury and litigation (38), suggesting that the core prob- lems were neither regionally nor temporally idiosyncratic. Diagnoses of the system’s capacity to compensate a valid claim once it has been filed are not as bleak. A number of studies have concluded that the tort system does a reasonably good job of directing compensation to plaintiffs with meritorious claims (39–43). However, several other studies have shown fairly indiscriminate compensation of claims (44,45), including a 10-year follow-up of the Harvard data from New York that found that the key predictor of payment was the plaintiff’s degree of disability, not negligence (45). Regardless, the overall picture that emerges from these studies is disheartening. Using a wide lens—one that takes in all patients who Chapter 16 / Health Policy Review 233 experience negligent injury, not just those who manage to join the hunt for compensation as plaintiffs—the findings from California, New York, and Utah/Colorado are a searing indictment of the malpractice system’s performance. The data reveal a profoundly inaccurate mecha- nism for distributing compensation. It is also a tremendously ineffi- cient one: approx 60 cents of every dollar expended on the system is absorbed by administrative costs (predominantly on legal fees), an amount is twice the overhead rate for an average workers’ compen- sation scheme (2). There has been less empirical scrutiny of the malpractice system’s performance as a deterrent of substandard care than there has been of its record as a compensation mechanism. Legal deterrence is a noto- riously difficult phenomenon to measure (47).
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