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STUDENT DIGITAL NEWSLETTER ALAGAPPA INSTITUTIONS |
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Janeta F. Tansey, MD
To avoid the problems inherent in recording from adjacent electrodes that are exposed to very similar voltages in the bipolar montage medicine 751 m accupril 10 mg sale, pairing electrodes that have larger electrode distances may show this activity better medications 377 discount accupril 10 mg line. A caveat in the use of the bipolar montage is to avoid symptoms of depression buy 10mg accupril mastercard, when possible symptoms of pneumonia accupril 10 mg, the use of nonlinear arrays of electrodes in any one chain of sequential channels. In this example, electrical fields of activity are unusual and difficult to interpret. The referential montage is actually a modified bipolar montage since it compares the voltages at two different electrodes in each channel. However, the second input is always the same for each hemisphere and is called the reference. Ideally one would like to have "active" electrodes over the area of interest and a standard reference with minimal involvement. Placing the reference off the scalp, such as on the ear or on the face, does not prevent volume conduction from the cerebral cortex, and these areas are especially susceptible to noncerebral electrical potentials. Placing the reference on the body makes it vulnerable to electrocardiogram potentials, whose amplitudes are usually much larger than cerebral activity. Potentials arising from these "contaminants" of the reference usually are seen in all channels that include the reference, although at varying amplitudes. When the ipsilateral ear is used as a reference, the electrocardiogram signal may be of opposite polarity. This assumption is not always true as in the case when these dipoles are aligned in horizontal or diagonal orientations to the recording surface. Since voltage differences tend to be larger in the referential montage, the sensitivity of recording often needs to be reduced to avoid blocking of pens undergoing wide deflections. This reduction in sensitivity may diminish the prominence of more subtle lower amplitude activity intermixed with the higher voltage type, making the former more difficult to appreciate. The value of the reference is achieved by taking the average of the voltages of all electrodes selected. When C is used as the reference, a phase reversal occurs and does not relate to the point of maximal activity. In this case, the phase reversal indicates that the reference is located within the field. When this happens, the recording produced may accentuate the activities of interest, making them readily apparent to the electroencephalographer. As the number of electrodes connected to the average reference point is increased, the activity of any one electrode has a proportionately smaller effect on the other channels, thereby encouraging the incorporation of many electrodes in the formulation of the average reference. This shows that although electrode E was the maximum for the initial array of electrodes, it is not the maximum for a broader array of electrodes. CD DE tiple electrodes, a greater amount of electrodes involved in a given activity will skew the potential of the average reference to a large degree. The problem here is that the potential of activity of interest as the first input to the amplifier will be compared to a very similar potential value in the average, resulting in a relative cancellation. Conversely, when an area not involved in the activity is compared with the average, an inverted signal will be seen at that electrode. The average montage is superior for displaying focal activity involving a minimal number of electrodes. In this case, the differences in potential between the electrodes of interest and the average reference are substantial and the visualization of localization is enhanced. The average montage is particularly vulnerable to obfuscation caused by artifactual activity such as that seen with eye blink artifact. Many average montages are set up to specifically exclude the most frontal electrodes in the summation of the average with the hope of partially avoiding this contamination of the average reference. There is a limit to the number of electrodes that can be excluded since removing an electrode diminishes the total number of electrodes participating in the average and thereby makes this potential less of a true "average. The wide range of artifacts may be conveniently divided into physiologic and nonphysiologic. Physiologic types include artifact secondary to muscle activity, electrocardiogram, pulse, eye movements, movements of the tongue (glossokinetic potential), respiration, tremor, and perspiration. Several examples are displayed in Figures 1-36 (pulse artifact), 1-37 (electrode pop artifact), and 1-38 (artifact from patting an infant). Patients with direct connections to the heart such as the Swan-Ganz catheter can tolerate only 10 A of current before the risk of serious morbidity. Older buildings using two-wire delivery systems for alternating current to power electrical devices were vulnerable to short circuiting of current to a part of the apparatus itself. Coming into contact with that part of the apparatus led to connecting the patient to this unintended additional circuit. Modern hospitals and other buildings commonly use three-wire outlet systems that are composed of a wire that delivers the alternating current, a "neutral" (for return of current to complete the circuit), and an additional ground connection that receives a ground wire connected to the chassis of the apparatus and channels stray current from the chassis to ground. Another safety device is the "circuit breaker," which represents a conducting material placed along important circuits. The circuit breaker is designed to open and thereby disconnect the circuit immediately when current exceeds safe levels. Improper ground protection may result in a broken ground wire in the power cord or poor connections of the building ground to the earth ground. Note the primarily leftward eye movements in the 3rd and 4th as well as in the 7th and 8th seconds, best seen at F8 (open arrows). F8 becomes relatively negative as a result of the cornea moving away from the right temporal area. An eye movement predominantly in the downward direction occurs in the 10th second (arrowheads). All devices used should be connected to the same power strip leading to a unified outlet. Other causes include "stray capacitance," which occurs among long power lines such as extension cords that have wires running parallel to each other separated by an insulating material. An easily avoidable dangerous situation is the "power surge," which is a transient, uncontrolled elevation in current that occurs when a device is turned on or off. These rhythmic, evolving discharges have some of the characteristics of an electrographic seizure pattern (arrows). In our opinion, however, sedation should not be routinely performed on neonates, infants, or children because of the risks associated with medications and limitations on the ability to assess background abnormalities in wakefulness. In neonates, alternatives to sedation include bundling, postfeeding recordings, and other means of pacification. When indicated, sedation may be effected with the use of chloral hydrate administered orally or per rectum. In our laboratory, suggested oral doses range from 50 mg/kg for routine sedation to 100 mg/kg for patients who are very difficult to sedate. Potential adverse effects include irritability, paradoxical hyperactivity, prolonged sedation, or gastric upset. Associated potential risks include effects on the respiratory, cardiovascular, and central nervous systems. Patients should be restricted to clear liquids up to 3 hours prior to the administration of any sedative agent. Appendix I Definitions Action potential A depolarization of sufficient magnitude to cause a spreading wave of depolarization along the neuronal membrane Ampere (amp) (A) Unit of current. By convention, when 1 coulomb of charge has traveled through a conductor over a period of 1 second, a current of 1 A has been observed. Circuit An electrical pathway composed of a conductor through which current flows, a power source that leads to the flow of charges, and a resistor Circuit breaker A conducting material placed along important circuits, designed to open and thereby Basic Principles of Electroencephalography 41 disconnect the circuit immediately when current exceeds safe levels Conductor the substance through which ions flow Coulombs (Q) Units of charge. A coulomb of charge represents the charge lent by a current of 1 A flowing for 1 second. Current the flow of charges Depolarization A reduction in the negativity of the resting potential Dipole A uniform separation of negative and positive extracellular charges along neuronal membranes Electrons One of three basic particles comprising the atom. In Figure 1-9, moving the switch rapidly between positions 2 and 3 simulates a high-frequency input. If there is sufficient time for the capacitor to achieve its full charge, the graph displaying voltages at the capacitor shows the waves reaching maximal voltage. Input voltages that are delivered slowly, as in a slow-frequency rhythm of rising and falling voltages, would allow complete charging and discharging of the capacitor. This circuit allows low-frequency rhythms to pass unaltered in amplitude and therefore is a "low-pass" situation. Conversely, an input frequency could be delivered that is too fast for the capacitor to fully charge and discharge. By the time an input voltage has gone up and begins its descent, the voltage at the capacitor is still on its way up.
As p r e g n a n c y a d v a n c e s symptoms graves disease order accupril 10 mg mastercard, v i l l i o n the e mb r y o n i c p o l e c o n t i n u e t o g r o w a n d e xp a n d medications used to treat migraines buy accupril 10 mg free shipping, g i v i n g r i s e t oc th o r i o n f r o n d o s u(mu s h y c h o r i o n) 606 treatment syphilis purchase accupril 10mg fast delivery. Vi l l i o n the he b a b e mb r y o n i c p o l e d e g e n e r a t e symptoms pulmonary embolism buy cheap accupril 10mg, a n d b y the t h i r d mo n t h, t h i s s i d e o f the c h o r i o n, n o w k n o w n a s t hc h o r i o n l a e v es s mo o t h (s e eg s. T h e d e c i d u a o v e r the c h o r i o n f r o n d o s u m, the c i d u a b a s a,l i c o n s i s t s o f a c o mp a c t l a y e r o f l a r g e c e l l s, de s d e c i d u a l c e l, l s i t h a b u n d a n t a mo u n t s o f l i p i d s a n d g l y c o g e n. T h i s l a y e r, the w d e c i d u a l p l a,t es t i g h t l y c o n n e c t e d t o the c h o r i o n. T h e d e c i d u a l l a y e r o v e r the i a b e mb r y o n i c p o l e i s d h e i d u a c a p s u l a r i sg. S u b s e q u e n t l y, the c h o r i o n l a e v e c o me s i n t o c o n t a c t w i t h the u t e r i e c i d u al p a r i e t a l os) the (d ne wal in o p p o s i t e s i d e o f the u t e r u s, a n d the t w o f F sg s. H e n c e, the o n l y p o r t i o n o f the c h o r i o n p a r t i c i p a t i n g i n the e xc h a n g e p r o c e s s i s the c h o r i o n f r o n d o s u m, w h i c h, t o g e the r w i t h the d e c i d u a b a s a l i s, ma k e s u p ph a c e n t. Structure of the Place nta B y the b e g i n n i n g o f the f o u r t h mo n t h, the p l a c e n t a h a s t w o ca)mpfo n e n t s: (o a e tal p o r t i o n f o r me d b y the c h o r i o n f r o n d o s u m) a n d a(t e r n a l p o r t i,ofn r me d b y, b am o the d e c i d u a b a s a lF sg (7. In t hu n c t i o n a l z o,n er o p h o b l a s t a n d d e c i d u a l c e l l s i n t e r mi n g l. T h i s je t zo n e, c h a r a c t e r i ze d b y d e c i d u a l a n d s y n c y t i a l g i a n t c e l l s, i s r i c h i n a mo r p h o u s e xt r a c e l l u l a r ma t e r i a l. B y t h i s t i me, mo s t c y t o t r o p h o b l a s t c e l l s h a v e d e g e n e r a t e d. Between the chorionic and decidual plates are the intervillous spaces, which are f i l l e d w i t h ma t e r n a l b l o o d. T h e y a r e d e r i v e d f r o m l a c u n a e i n the s y n c y t i o t r o p h o b l a s and are lined with syncytium of fetal origin. T h e a mn i o t i c s a c a n d c h o r i o n i c c a v i t y h a v e b e e n A o p e n e d t o e xp o s e the e mb r y o, s h o w i n g the b u s h y a p p e a r a n c e o f the t r o p h o b l a s t a t the e mb r y o n i c p o l e i n c o n t r a s t t o s ma l l v i l l i a t the a b e mb r y o n i c p o l. N o t e the c o n n e c t i n g s t a l k a n d y o l k s a c w i t h i t s e xt r e me l y l o n g v i t e l l i n e duct. D u r i n g the f o u r t h a n d f i f t h mo n t h s, the d e c i d u a f o r ms a e c imb e rl o fe p, t a d nu dua s w h i c h p r o j e c t i n t o i n t e r v i l l o u s s p a c e s b u t d o n o t r e a c h the c h F r go n i c p l a t e (oi i. T h e s e s e p t a h a v e a c o r e o f ma t e r n a l t i s s u e, b u t the i r s u r f a c e i s c o v e r e d b y) a l a y e r o f s y n c y t i a l c e l l s, s o t h a t a t a l l t i me s, a s y n c y t i a l l a y e r s e p a r a t e s ma t e r n a l b l o o d i n i n t e r v i l l o u s l a k e s f r o m f e t a l t i s s u e o f the v i l l i. As a r e s u l t o f t h i s s e p t u m f o r ma t i o n, the p l a c e n t a i s d i v i d e d i n t o a n u mb e r o f c o mp a r t tme e t so no r co y l nd, s (s e eF i g. N o t e the y o l k s a c i n the c h o r i o n i c c a v i t y b e t w e e n the a mn i o n a n d c h o r i o n. At the a b e mb r y o n i c p o l e, v i l l i h a v e d i s a p p e a r e d (c h o r i o n l a e v e). T h e a mn i o n a n d c h o r i o n h a v e f u s e d, a n d the u t e r i n e cavity is obliterated by fusion of the chorion laeve and the decidua parietalis. As a r e s u l t o f the c o n t i n u o u s g r o w t h o f the f e t u s a n d e xp a n s i o n o f the u t e r u s, the p l a c e n t a a l s o e n l a r g e s. It s i n c r e a s e i n s u r f a c e a r e a r o u g h l y p a r a l l e l s t h a t o f the e xp a n d i n g u t e r u s, a n d t h r o u g h o u t p r e g n a n c y i t c o v e r s a p p r o xi ma t e l y 1 5 % t o 3 0 % of the internal surface of the uterus. The increase in thickness of the placenta r e s u l t s f r o m a r b o r i za t i o n o f e xi s t i n g v i l l i a n d i s n o t c a u s e d b y f u r the r p e n e t r a t i o n i n t o ma t e r n a l t i s s u e s. Full-term Placenta At f u l l t e r m, the p l a c e n t a i s d i s c o i d w i t h a d i a me t e r o f 1 5 t o 2 5 c m, i s a p p r o xi ma t e l 3 c m t h i c k, a n d w e i g h s a b o u t 5 0 0 t o 6 0 0 g. At b i r t h, i t i s t o r n f r o m the u t e r i n e w a l l a n d, a p p r o xi ma t e l y 3 0 mi n u t e s a f t e r b i r t h o f the c h i l d, i s e xp e l l e d f r o m the u t e r i n e c a v i t y. Af t e r b i r t h, w h e n the p l a c e n t a i s v i e w e d farto m nt a le s i d e 5 t o 2 0 m er h, 1 s l i g h t l y b u l g i n g a r e a s,c oh e l e d o n sc o v e r e d b y a t h i n l a y e r o f d e c i d u a b a s a l i s, t ty, a r e c l e a r l y r e c o g n i zaF il g. T h e f e t a l s u r f a co f the p l a c e n t a i s c o v e r e d e n t i r e l y b y the c h o r i o n i c p l a t. A e n u mb e r o f l a r g e a r t e r i e s a n d v e i n s,otrh e n i c v e s s e lc o n v e r g e t o w a r d the ch io, s u mb i l i c a l c o r F i g. R a r e l y, h o w e v e r, d o e s i t i n s e r t i n t o the c h o r i o n i c me mb r a n e s o u t s i d e the p l a c e n t a v e l a m e n t o u s i n s e r t. As the p r e s s u r e d e c r e a s e s, b l o o d f l o w s b a c k f r o m the c h o r i o n i c p l a t e t o w a r d the d e c i d u a, w h e r e i t e n t e r s the e n d o me t r i a l i g e i7. C o l l e c t i v e l y, the i n t e r v i l l o u s s p a c e s o f a ma t u r e p l a c e n t a c o n t a i n a p p r o xi ma t e l y 1 5 0 mL o f b l o o d, w h i c h i s r e p l e n i s h e d a b o u t t h r e e o r f o u r t i me s p e r mi n u t. T h i s b l o o d mo v e s a l o n g the c h o r i o n i c v i l l i, w h i c h h a v e a s u r f a c e a r e a2. In the s e v i l l i the s y n c y t i u m o f t e n h a s a b r u s h b o r d e r c o n s i s t i n g o f n u me r o u s mi c r o v i l l i, w h i c h g r e a t l y i n c r e a s e s the s u r f a c e a r e a a n d c o n s e q u e n t l y the e xc h a n g e r a t e b e t w e e n ma t e r n a l a n d f e t a l c i r c u l a tFog. F r o m the f o u r t h) td F (8 mo n t h o n, h o w e v e r, the p l a c e n t a l me mb r a n e t h i n s, s i n c e the e n d o the l i a l l i n i n g o f the v e s s e l s c o me s i n i n t i ma t e c o n t a c t w i t h the s y n c y t i a l me mb r a n e, g r e a t l y i n c r e a s i n g the r a t e o f e xc h a ng. B e c a u s e the ma t e r n a l b l o o d i n the i n t e r v i l l o u s s p a c e s i s s e p a r a t e f r o m the f e t a l b l o o d b y a c h o r i o n i c d e r i v a t i v e, the h u ma n p l a c e n t a i s c o n s i d e r e d t o b e o f the e m o c h o r i at ly p. In the w a l l o f the u t e r u s i s a l a r g e g r o w t h, a my o f i b r o ma. Function of the Placenta M a i n f u n c t i o n s o f the p l a c e n t a) a rx c(h a n g e o f m e t a b o l i c a n d g a s e o u s a ee p r o d u c t s e t w e e n ma t e r n a l a n d f e t a l b l o o d s t r e a mspa o d u c t i o n o f b b) r n (h o r m o n. P o r t i o n s o f the w a l l o f the u t e r u s 2 a n d the a mn i o n h a v e b e e n r e mo v e d t o s h o w the f e t u s. In the b a c k g r o u n d a r e p l a c e n t a l v e s s e l s c o n v e r g i n g t o w a r d the u mb i l i c a l c o r d. T h e u mb i l i c a l c o r d i s t i g h t l y w o u n d a r o u n d the a b d o me n, p o s s i b l y c a u s i n g a b n o r ma l f e t a l p o s i t i o n i n the uterus (breech position). T h e c o t y l e d o n s a r e 3 p a r t i a l l y s e p a r a t e d b y the d e c i d u a l (ma t e r n a l) s e p t a. M o s t o f the i n t e r v i l l o u s b l o o d r e t u r n s t o the ma t e r n a l c i r c u l a t i o n b y w a y o f the e n d o me t r i a l v e i n s. T h e ma t e r n a l s i d e o f the p l a c e n t a i s a l w a y s c a r e f u l l y i n s p e c t e d a t b i r t h, a n d f r e q u e n t l y o n e o r mo r e c o t y l e d o n s w i t h a w h i t i s h a p p e a r a n c e a r e p r e s e n t b e c a u s e o f e xc e s s i v e f i b r i n o i d f o r ma t i o n a n d i n f a r c t i o n o f a g r o u p o f i n t e r v i l l o u s l a k e s. Ex change of Gase s E xc h a n g e o f g a s e s - s u c h a s o xy g e n, c a r b o n d i o xi d e, a n d c a r b o n mo n o xi d e - i s a c c o mp l i s h e d b y s i mp l e d i f f u s i o n. At t e r m, the f e t u s e xt r a c t s 2 0 t o 3 0 mL o f o xy g e n p e r mi n u t e f r o m the ma t e r n a l c i r c u l a t i o n, a n d e v e n a s h o r t - t e r m i n t e r r u p t i o n o f the o xy g e n s u p p l y i s f a t a l t o the f e t u s. P l a c e n t a l b l o o d f l o w i s c r i t i c a l t o o xy g e n s u p p l y s i n c e the a mo u n t o f o xy g e n r e a c h i n g the f e t u s p r i ma r i l y d e p e n d s o n d e l i v e r y, n o t diffusion. Ex change of Nutrie nts and Ele ctroly the s E xc h a n g e o f n u t r i e n t s a n d e l e c t r o l y t e s, s u c h a s a mi n o a c i d s, f r e e f a t t y a c i d s, c a r b o h y d r a t e s, a n d v i t a mi n s, i s r a p i d a n d i n c r e a s e s a s p r e g n a n c y a d v a n c e s. Tr a n s m i s s i o n o f M a t e r n a l A n t i b o d i e s Immu n o l o g i c a l c o mp e t e n c e b e g i n s t o d e v e l o p l a t e i n the f i r s t t r i me s t e r, b y w h i c h t i me the f e t u s ma k e s a l l o f the c o mp o n e n t s lo f m e n tImmu n o g l o b u l i n s com p. In t h i s ma n n e r, the f e t u s g a i n s p a s s i v e i mmu n i t y a g a i n s t v a r i o u s i n f e c t i o u s d i s e a s e s. N e w b o r n s b e g i n t o p r o d u c e the i r o w n Ig G, b u t a d u l t l e v e l s a r e n o t a t t a i n e d u n t i l the a g e o f 3 y e a r s. Clinical Corre late s Ery throblastosis Fe talis and Fe tal Hy drops O v e r 4 0 0 r e d b l o o d c e l l a n t i g e n s h a v e b e e n i d e n t i f i e d, a n d a l t h o u g h mo s t d o n o t c a u s e p r o b l e ms d u r i n g p r e g n a n c y, s o me c a n s t i mu l a t e a ma t e r n a l a n t i b o d y r e s p o n s e a g a i n s t f e t a l b l o o d c e l l s. T h e R h oa n t i g e ns hD b D r i the mo s t d a n g e r o u s, s i n c e i mmu n i za t i o n c a n r e s u l t f r o m a s i n g l e e xp o s u r e a n d o c c u r s e a r l i e r a n d w i t h g r e a t e r s e v e r i t y w i the a c h s u c c e e d i n g p r e g n a n c y. T h e antibody response occurs in cases where the fetus is D(Rh) positive and the mo the r i s D (R h) n e g a t i v e a n d i s e l i c i t e d w h e n f e t a l r e d b l o o d c e l l s e n t e r the ma t e r n a l s y s t e m d u e t o s ma l l a r e a s o f b l e e d i n g a t the s u r f a c e o f p l a c e n t a l v i l l i o r a t b i r t h. An a l y s i s o f a mn i o t i c f l u i d f o r b i l i r u b i n, a b r e a k d o w n p r o d u c t o f h e mo g l o b i n, s e r v e s a s a me a s u r e o f the d e g r e e o f r e d c e l l h e mo l y s i s. T r e a t me n t f o r the a f f e c t e d f e t u s i n v o l v e s i n t r a u t e r i n e o r p o s t n a t a l t r a n s f u s i o n s. H o w e v e r, the d i s e a s e i s p r e v e n t e d b y i d e n t i f y i n g w o me n a t r i s k u s i n g a n a n t i b o d y s c r e e n a n d t r e a t i n g the m w i t h a n t i - D - i mmu n o g l o b u l i n. An t i g e n s f r o m t A e O b l o o d g r o u p n a l s o e l i c i t a n a n t i b o d y r e s p o n s e, b u t hB ca the P. Horm one Production B y the e n d o f the f o u r t h mo n t h, the p l a c e n t a p r o d u c e s r o nie s u f f i c i e n t ge ste n a mo u n t s t o ma i n t a i n p r e g n a n c y i f the c o r p u s l u t e u m i s r e mo v e d o r f a i l s t o f u n c t i o n p r o p e r l y. In a l l p r o b a b i l i t y, a l l h o r mo n e s a r e s y n the s i ze d i n the s y n c y t i a l t r o p h o b l a s t.
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In s u b s e q u e n t o r d e r, the p o u c h e s g i v e ai)s teh eo i(d d l e e a r c a v ia y d r tm tn a u d i t o r y t u b(e o u c h 1) b)(the s t r o ma o f tp a l a t i n e t o n s(ip o u c h 2) c) (the p, he l, i n f e r i o r p a r a t h y r o i d g l aa n ds h y m u s(p o u c h 3), a nd) (t h es u p e r i o r nd t d p a r a t h y r o i d g l a n a n du l t i m o b r a n c h i a l b o(d y u c h e s 4 a n d F) g(. P h a r y n g e a l c l e fg sv e r i s e t o o n l y o n e s t r u c t u re x tte re a l a u d i t o r y m e a t u s. C r e s t c e l l s o r i g i n a t e f r o m the c a u d a l mi d b r a i n a n d f r o m s e g me n t s i n the h i n d b r a i n c a l l e d r h o mb o me r e s. T h e s e g e n e s r e s p o n d t o e n d o d e r ma l s i g n a l s a n d d i c t a t e the t y p e o f s k e l e t a l e l e me n t s t h a f o r m. T h e t h y r o i d g l a no r i g i n a t e s f r o m a n e p i the l i a l p r o l i f e r a t i o n i n the f l o o r o f the d tongue and descends to its level in front of the tracheal rings in the course of d e v e l o p me n t. T h e p a i r e m a x i l l a r y n dm a n d i b u l ap r o mi n e n c e s a n d t ho n t o n a s a l d a r fr e p r o m i n e n c e r e the f i r s t p r o mi n e n c e s o f the f a c i a l r e g i o n. L a t e r, me d i a l a n d a l a t e r a l n a s a l p r o mi n e n c e s f o r m a r o u n d the n a s a l p l a c o d e s o n the f r o n t o n a s a l p r o mi n e n c. Al l o f the s e s t r u c t u r e s a r e i mp o r t a n t, s i n c e the y d e t e r mi n e, t h r o u g h f u s i o n a n d s p e c i a l i ze d g r o w t h, the s i ze a n d i n t e g r i t y o f the ma n d i b l e, u p p e r l i p, p a l a t e, a n d n o sTa b l e 1 6. T h e i n t e r ma xi l l a r y s e g me n t i s f o r me d b y me r g i n g o f the t w o me d i a l n a s a l) p r o mi n e n c e s i n the mi d l i n. T h i s s e g me n t i s c o mp)otsh ep h ifl t(r u m (b) the a ed o, u p p e r j a w c o m p o n,e n th i c h c a r r i e s the f o u r i n c i s o r t e e tc), t a np a(l a t a l w h h ed c o m p o n e n t w h i c h f o r ms the t r i a n g u l a r p r i ma r y p a l a t. T h e n o s e i s d e r i v e d f r o m, (a) t h ef r o n t o n a s a l p r o m i n e,n we i c h f o r ms t b r i d g e (b) t h em e d i a l n a s a l ch he, p r o m i n e n c e sw h i c h p r o v i d e tc re s t a n d t,i p n d c) t h el a t e r a l n a s a l, he a (p r o m i n e n c e sw h i c h f o r m t h ea e (F i g. T h e a d u l t f o r m o f the f a c e i s i n f l u e n c e d b y d e v e l p a r a nn t so fl s i n u s e s, o p me a a n a s a l c o n c h a e n dt e e t h. The e t h d e v e l o p f r o m e p i the l i a l me s e n c h y ma l, a i n t e r a c t i o n s b e t w e e n o r a l e p i the l i u m a n d n e u r a l c r e s t d e r i v e d me s e n c h y me. It l i e s o n a t h i c k l a y e r o f y s 3) d e n t i np r o d u c e d bo d o n t o b l a s,t s n e u r a l c r e s t d e r i v aCi. W h y a r e n e u r a l c r e s t c e l l s c o n s i d e r e d s u c h a n i m p o r t a n t c e l l p o p u l a t i o n f o r c r a n i o f a c i a l d e ve l o p m e n t? Yo u a r e c a l l e d a s a c o n s u l t a n t f o r a c h i l d w i t h a ve r y s m a l l m a n d i b l e a n d e a r s t h a t a r e r e p r e s e n t e d b y s m a l l p r o t u b e r a n c e s b i l a t e r a l l y. What might y o u r d i a g n o s i s b e, a n d w h a t m i g h t h a ve c a u s e d the s e a b n o r m a l i t i e s? A c h i l d p r e s e n t s w i t h a m i d l i n e s w e l l i n g b e n e a t h the a r c h o f the h y o i d bone. W i t h f u r the r d e v e l o p me n t, the n e u r a l f o l d s c o n t i n u e t o e l e v a t e, a p p r o a c h e a c h o the r i n the mi d l i n e, a n d f i n a l l y f u s e, f o rn e n gatlhteu b es e eF i g s. Fusion begins in the cervical region and proceeds in cephalic and caudal) d i r e c t i o n s i(g. T h i s l a t e r s i t e p r o c e e d s c r a n i a l l y, t o c l o s e the r o s t r a l mo s t r e g i o n o f the n e u r a l t u b e, a n d c a u d a l l y t o me e t a d v a n c i n g c l o s u r e f r o m the c e r v i c a l s i t e i (. T h e c e p h a l i c e n d o f the n e u r a l t u b e s h o w s t h r e e d i l p t iio na r yt h er a i n ar m s, b v e s i c l e s:a) t h eP r o s e n c e p h a l o n r f o r e b r a i n(;b) t h eM e s e n c e p h a l o n r (, o, o m i d b r a i n; n d c) t h eR h o m b e n c e p h a l,o n r h i n d b r a i n i g. S i mu l t a n e o u s l y i t f o r ms t w o f l e xu r the sec(e r v i c a l f l e x u r e the j u n c t i o n o f the a) h: at h i n d b r a i n a n d the s p i n a l c o r db) tnh ec e p h a l i c f l e x u rn the mi d b r a i n r e g i o n a d (ie (s e eF i g. W h e n the e mb r y o i s 5 w e e k s o l d, the p r o s e n c e p h a l o n c o n s i s t s o f t w e p a r t s: (a) h o The l e n c e p h a l o no r me d b y a mi d p o r t i o n a n d t w o l a t e r a l o u t p o c k e t i n g s, the, f p r i m i t i v e c e r e b r a l h e m i s p h earn d b) t h eD i e n c e p h a l o n h a r a c t e r i ze d b y, es (, c o u t g r o w t h o f the o p t i c v e s i c l e s i (gs. T h e r h o mb e n c e p h a l o n a l s o c o n s i s t s o f t w o pta reM:e (t e n c e p h a l o n h i c h a) h t s, w l a t e r f o r ms the n s a n dc e r e b e l l u ma n d b) t h em y e l e n c e p h a l o n. T h e c a v i t y o f the r h o mb e n c e p h afl o u r its t v e n t r i c l the a t o f n h h, h the d i e n c e p h a l o n i s tth ie d v e n t r i c l e n d t h o s e o f the c e r e b r a l h e mi s p h e r e s a r e hr, a the l a t e r a l v e n t r i c l (Fsg. T h i s l u me n b e c o me s v e r y n a r r o w a n d i s the n k n o w n a s the a q u e d u c t o f S y l v i u s. C o l l e c t i v e l y the y c o n s t i t u t e the n e u r o e p i the l i a l l a y en e u r o e p i the l i u m. T h e y f o r m the n t l e l a y e r zo n e a r o u n d the n e u r o e p i the l i a l l a y e r (s e e) Ma, a F i g. D o r s a l v i e w o f a l a t e p r e s o mi t e e mb r y o a t a p p r o xi ma t e l y 1 8 1 d a y s. T h e a mn i o n h a s b e e n r e mo v e d, a n d the n e u r a l p l a t e i s c lB a r l y v i s i b l. T r a n s v e r s e s e c t i o n s t h r o u g h s u c c e s s i v e l y o l d e r e mb r y o s 2 s h o w i n g f o r ma t i o n o f the n e u r a l g r o o v e, n e u r a l t u b e, a n d n e u r a l c r e s t. C e l l s o f the n e u r a l c r e s t mi g r a t e f r o m the e d g e s o f the n e u r a l f o l d s a n d d e v e l o p i n t o s p i n a l a n d c r a n i a l s e n s o r y g a n g lCa D. D o r s a l v i e w o f a h u ma n e mb r y o a t a p p r o xi ma t e l y d a y 2 2. S e v e n 3 d i s t i n c t s o mi t e s a r e v i s i b l e o n e a c h s i d e o f the nB. T h e n e r v o u s s y s t e m i s i n c o n n e c t i o n w i t h the a mn i o t i c c a v i t y t h r o u g h the c r a n i a l a n d c a u d a l n e u r o p o r e s. D r a w i n g o f a s a g i t t a l s e c t i o n t h r o u g h the b r a i n a t a p p r o xi ma t e l y 2 7 4 d a y s o f h u ma n d e v e l o p me n t. T h r e e b r a i n v e s i c l e s r e p r e s e n t t(h e, f o r e b r a i n F) mi d b r a i n M), a n d h i n d b r a(i H). D r a w i n g o f a s a g i t t a l s e c t i o n t h r o u g h the b r a i n a p p r o xi ma t e l y 3 2 5 d a y s o f h u ma n d e v e l o p me n t. T h e t h r e e o r i g i n a l b r a i n v e s i c l e s h a v e s e g r e g a t e d i n t o the t e l e n c e p h a l o n, d i e n c e p h a l o n, me s e n c e p h a l o n, me t e n c e p h a l o n, a n d my e l e n c e p h a l o n. S e c t i o n o f the w a l l o f 6 neuroepithelial cells, which form a the full width of the wall. Note the S c a n n i n g e l e c t r o n mi c r o g r a p h o f a s i mi l a r t o t h a t Ai. S e c t i o n o f the n e u r a l t u b e a t a s l i g h t l y mo r e a d v a n c e d s t a g e t h a n 7 i n F i g u r e 1 7. O n the p e r i p h e r y, i mme d i a t e l y a d j a c e n t t o the e xt e r n a l l i mi t i n g me mb r a n e, n e u r o b l a s t s f o r m. T h e s e c e l l s, w h i c h a r e p r o d u c e d b y the n e u r o e p i the l i a l c e l l s i n e v e r - i n c r e a s i n g n u mb e r s, w i l l f o r m the ma n t l e l a y e r. As a r e s u l t o f my e l i n a t i o n o f n e r v e f i b e r s, t h i s l a y e r t a k e s o n a w h i t e a p p e a r a n c e a n d the r e f o r e ws ic a l l e d the i h the m a t t e r o f the s p i n a l c(F r g. B a s a l, A l a r, R o o f, a n d F l o o r P l a t e s As a r e s u l t o f c o n t i n u o u s a d d i t i o n o f n e u r o b l a s t s t o the ma n t l e l a y e r, e a c h s i d e o f the neural tube shows a ventral and a dorsal thickening. The ventral thickenings, the B a s a l p l a t e s h i c h c o n t a i n v e n t r a l mo t o r h o r n c e l l s, f o r m the mo t o r a r e a s o f, w the s p i n a l c o r d; the d o r s a l t h i c k e n i n gls,r t p ea t e sf o r m t h s e n s o r y a r e a s A a hl, e (F i g. T h e d o r s a l a n d v e n t r a l mi d l i n e p o r t i o n s o f the n e u r a l t u b e, k n o w n a s t h er o o f a n df l o o r p l a t e s e s p e c t i v e l y, d o n o t c o n t a i n n e u r o b l a s t s; the y s e r v e, r p r i ma r i l y a s p a t h w a y s f o r n e r v e f i b e r s c r o s s i n g f r o m o n e s i d e t o the o the r. In a d d i t i o n t o the v e n t r a l mo t o r h o r n a n d the d o r s a l s e n s o r y h o r n, a g r o u p o f n e u r o n s a c c u mu l a t e s b e t w e e n the t w o a r e a s a n d f o r mst e r mma l il a t e h o r n in a s ed (F i g. Histological Differentiation Ne rv e Ce lls N e u r o b l a s t so r p r i mi t i v e n e r v e c e l l s, a r i s e e xc l u s i v e l y b y d i v i s i o n o f the, n e u r o e p i the l i a l c e l l s. In i t i a l l y the y h a v e a c e n t r a l p r o c e s s e xt e n d i n g t o the l u me n (t r a n s i e n t d e n d r i t b u t w h e n the y mi g r a t e i n t o the ma n t l e l a y e r, t h i s p r o c e s s, e) d i s a p p e a r s, a n d n e u r o b l a s t s a r e t e mp o r a r i l y r a p n da a(n d eF i g. W i t h f u r the r d i f f e r e n t i a t i o n, t w o n e w c y t o p l a s mi c p r o c e s s e s a p p e a r o n o p p o s i t e s i d e s o f the c e l l b o d y, f o r mi np oaa r n e u r o b l a(F t g. Orn c e v ro l o n e u r o b l a s t s f o r m, the y l o s e the i r a b i l i t y t o d i v i d.
They may manifest as bilateral nasal obstruction and respiratory distress in the newborn and are to be distinguished from nasochoanal stenosis/atresia and nasolacrimal duct cysts (discussed earlier) medications related to the integumentary system generic 10 mg accupril with mastercard. The fonticulus frontalis and prenasal space are transient nasofrontal structures that involute in early gestation medications like zovirax and valtrex buy accupril 10mg on line. Persistence of these primitive structures may be associated with a dural diverticulum and protrusion of intracranial contents as a nasofrontal cephalocele or a nasoethmoidal cephalocele symptoms 9 days past iui discount accupril 10 mg fast delivery. With partial or complete obliteration of the intracranial connection medications dialyzed out purchase accupril 10 mg without prescription, the cephalocele becomes a sequestered neuroepithelial heterotopia (nasal glioma;. As the dural diverticulum regresses, incorporation of surface ectoderm may form a dermal sinus. Other associated findings include nasal Choanal stenosis and atresia, respectively, are narrowing of the posterior nasal cavity and obstruction by an atresia plate (bony, membranous, or both). Stenosis of the entire nasal airway is usually bony and may be associated with prematurity or maxillary hypoplasia. This may be associated with single midline maxillary incisor (mega-incisor) and midline intracranial anomalies. Segmental stenosis may also result from maxillary hypoplasia, turbinate hyperplasia, or nasal septal deviation. A, Bilateral choanal atresia (lower arrows) with retained secretions plus right nasal septal deviation (upper arrow). B, Right unilateral choanal atresia (arrow) with retained secretions; compare with the normal left choanal aperture. An intracranial communication may result in recurrent meningitis, abscess, or empyema. Other rare congenital nasal masses are nasoalveolar (incisive canal) cysts, dentigerous cysts, mucous cysts, vascular anomalies, branchial cysts, hamartomas, teratoid tumors (embryoma, epignathus), and Tornwaldt cyst. Facial Anomalies Cleft Lip and Palate Clefts involving the lip, alveolus, or palate are common anomalies and may be partial, complete, unilateral, or bilateral. A complete cleft disrupts facial growth, dentition, speech, and eustachian tube function. B also shows normal foramen cecum (lower black arrow) and crista galli (upper black arrow). Craniofacial clefts (facial, cranial, or combined) extend along continuous axes through the eyebrow or eyelid, maxilla, nose, and lip. Facial clefts extend caudally from the lower eyelid, whereas cranial clefts extend cephalad from the upper eyelid. Associated anomalies include orbital dystopia, microphthalmos, coloboma, cephalocele, and orbital hypertelorism. Associated syndromes include median cleft syndrome, Treacher Collins syndrome, hemifacial microsomia, amniotic band syndrome, otomandibular syndrome, and Goldenhar syndrome. The median cleft syndrome (high and low groups) with hypertelorism may be associated with cephalocele, corpus callosum hypogenesis, intracranial lipoma, optic nerve dysplasia (coloboma), cranium bifidum, frontonasal dysplasia, microphthalmia, anophthalmia, or holoprosencephaly. Craniofacial Syndromes Bilateral coronal craniosynostosis may be associated with craniofacial dysostosis. The associated dysmorphia includes abnormalities of the forehead, orbits (hypertelorism, exorbitism), midface, and anterior cranial base. Cloverleaf craniofacial anomaly results from multiple craniosynostoses and is also associated with extensive craniofacial deformities. Amniotic band syndrome (congenital constrictions or amputations) manifests as facial clefts, calvarial defects, hydrocephalus, cephaloceles, or anencephaly. Treacher Collins syndrome is a mandibulofacial dysostosis (autosomal dominant) characterized by bilateral zygomatic, malar, and mandibular hypoplasia. Also common are microtia (external and middle ear hypoplasia), colobomata, and microphthalmia. Goldenhar syndrome (oculoauriculovertebral syndrome) is a mandibulofacial dysostosis with hemifacial microsomia, epibulbar dermoids or lipodermoids, and vertebral anomalies. Ear and Temporal Bone Normal Development the external and middle ear (mastoid portion of the temporal bone) are derived from the branchial apparatus, and the internal ear is derived from the neuroectoderm. The auricle and external ear (membranous and bony portions) begin development along with the mandible. The middle ear cavity expands and incorporates the tympanic membrane, eustachian tube, auditory ossicles (malleus, incus, stapes), muscles (tensor tympani and stapedius), their tendons and ligaments, the round and oval windows, and the chorda tympani nerve, and then gives rise to the attic and mastoid antrum. The inner ear forms from the otic vesicle, which gives rise to the membranous labyrinth. The membranous labyrinth contains endolymph, is surrounded by perilymph, and is enclosed within the bony labyrinth (otic capsule). The membranous structures (corresponding bony structures shown in parentheses) include the utricle and saccule (vestibule), semicircular ducts (semicircular canals), endolymphatic duct and sac (vestibular aqueduct), and cochlear ductorgan of Corti (cochlea, modiolus). The facial nerve extends from the internal auditory canal into the facial nerve canal, which has a labyrinthine segment (anterior genu and geniculate ganglion within the otic capsule), a tympanic segment (horizontal course within the middle ear extending to the posterior genu and facial nerve recess), and a mastoid segment (vertical course to the stylomastoid foramen). Pneumatization of the mastoid occurs rapidly and is visible by 4 to 6 months of age. Mastoid disease is characterized by decreased aeration, mucosal thickening, edema, accumulation of fluid, bony demineralization, and bone destruction. Developmental Variants and Anomalies of the Nose and Paranasal Sinuses Developmental variants and anomalies may predispose to ostiomeatal complex obstruction with inflammation. Nasal septal deviation is common and is often associated with asymmetry or deformity of adjacent structures. Extramural extension of the ethmoid cells includes pneumatization of the supraorbital ridge, superior or middle turbinate. The complex may be unilateral, bilateral, isolated, or associated with syndromes. Complete (osseous) atresia consists of a bony atresia plate at the tympanic membrane and fusion of the malleus to the plate. Partial (membranous) atresia consists of a soft tissue plug at the tympanic membrane (with or without fusion of the malleus). The facial nerve is often thickened, has an aberrant course, and may be exposed (dehiscence, protrusion). Second branchial arch dysplasia results in anomalies of the hyoid, styloid, stylohyoid ligament, and stapes. Cochlear anomalies may be classified according to the stage of developmental arrest. Complete labyrinthine aplasia (Michel deformity) results in a single small cystic cavity. Other anomalies include a large common cavity (common chamber anomaly), cochlear aplasia or hypoplasia, and incomplete partition (Mondini syndrome-small cochlea with incomplete septation, i. Inner Ear Anomalies Congenital sensorineural hearing loss is commonly associated with inner ear anomalies. A common anomaly is vestibular aqueduct dysplasia (ranging from obliteration to dilatation;. Facial Nerve Anomalies Aberrant course of the facial nerve is usually associated with an anomaly of the external, middle, or inner ear. Dehiscence of the facial nerve canal most often occurs in its tympanic portion at the level of the stapes and results in a conductive hearing loss. Absence of the facial nerve has been described in a few cases, including the Mцbius sequence. Neck, Oral Cavity, and Jaw Normal Development the branchial apparatus, which contributes to formation of the head and neck, consists of paired branchial arches, pharyngeal pouches, branchial grooves, and branchial membranes. Each arch consists of a mesenchymal core (containing neural crest cells and arterial, nerve, cartilage, and muscular elements). Each arch is separated by branchial membranes and covered externally by surface ectoderm (branchial grooves) and internally by endoderm (pharyngeal pouches). The primitive mouth (stomodeum) arises from the surface ectoderm in contact with the amniotic cavity externally and the primitive gut internally via the esophagus (after rupture of the primitive buccopharyngeal membrane). The developing thyroid gland is a diverticulum connected by the thyroglossal duct ventral to the hyoid to the tongue base at the foramen cecum.
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