Rajesh R. Gandhi, M.D.

• Critical Care/Trauma Fellow
• University of Pennsylvania
• Philadelphia, PA

Rather than describing all the afferent and efferent fiber tracks of the projection system at this point chronic gastritis risk factors cheap sevelamer 800 mg amex, the details of individual afferent and efferent projection fiber tracks will be highlighted in subsequent chapters gastritis esophagitis buy sevelamer 800 mg without a prescription. Simply realize that those future pathways that you will learn about are part of the projection fiber system gastritis diet �� order 800 mg sevelamer. The representative colored lines denote the relative position of the corpus callosum radiations gastritis diet ����� discount sevelamer online master card, forceps major gastritis or appendicitis best purchase sevelamer, and the forceps minor. Within the cerebrum, though, corticopetal and corticofugal fibers congregate into two massive interconnected white matter structures: the internal capsule and the corona radiata (Carpenter, 1991; Gilroy & MacPherson, 2016; Haines, 2013; Mtui et al, 2015; Schuenek et al. The best way to visualize this structure is to look at a horizontal section of the cerebrum through the internal capsule. The point where each anterior limb joins its corresponding posterior limb on the same side is called the genu (Latin for "bending" as in the word "genuflect"). The perspective shown in this illustration is an axial section as seen from overhead. Rostral and caudal directions correspond to the top and bottom of the illustration, respectively. The connections between the mediodorsal thalamus and the prefrontal cortex are thought to provide a corticofugal pathway that influences cognitive function; disruption of the pathway has been implicated in psychological disorders such as schizophrenia. Connectivity between the anterior nuclei of the thalamus and the cingulate are thought to be involved in states of alertness, in responsiveness to threats, and in learning and memory. Corticofugal axons of the posterior limb include descending efferent connections to the lower motoneurons of the neck, arms, trunk, and legs, and the cranial nerve systems (Carpenter, 1991; Gilroy & MacPherson, 2016; Haines, 2013; Mtui et al, 2015; Schuenek et al. These pathways are called the corticospinal and corticobulbar pathways, respectively. Regardless of its specific location, corticobulbar fibers projecting to cranial nerve nuclei hold particular significance to us as communication disorder specialists. These are the descending projections that mediate vocalization, articulation, resonance, facial expression, and swallowing motor function. The superior thalamic radiation is of particular importance to the production of sensorimotor behaviors like speech, because these axons mediate somatosensation (tactile and proprioceptive) from the thalamus to the primary sensory cortex in the parietal lobe (Guenther, 2016). Other fibers within the superior thalamic radiation project to parietal association areas and to premotor and primary motor cortical regions. Together, these thalamic inputs are critical for updating action plans of behavior and for providing timely feedback to the sensory consequences of voluntary movement. The importance of sensation in generating and guiding movement is discussed in later chapters on somatosensation and motor control principles. The posterior thalamic radiation, also known as the optic radiation, originates from the lateral geniculate nucleus of the thalamus and establishes the corticopetal connection between this site and the primary visual cortex (Prasad & Galetta, 2011). The inferior thalamic radiation, also called the auditory radiation, contains axons originating from the medial geniculate nucleus of the thalamus and extending to the temporal lobe cortex (Bartlett, 2013). This pathway contains the auditory axons that target the primary auditory regions of the superior temporal gyrus. Lesions to the posterior limb will result in deficits that include: (a) loss of motor control to the limbs and trunk, (b) loss of tactile and proprioceptive detection/discrimination abilities, (c) visual and auditory disturbances, and (d) motor deficits in speech and swallowing. In this illustration, all other white matter pathways have been removed to allow you to visualize the projection fibers in isolation. Lateral perspective of the brainstem, crus cerebri, internal capsule, and corona radiata. The internal capsule is positioned in front of the thalamus and behind the optic tract. The corona radiata is seen as it would exist if all the cerebral tissues were removed, leaving only these projection fibers. Note the fan-like appearance and broad distribution of projections axons from the frontal pole (far left point) to the occipital pole (far right point). Meninges consist of high percentages of fibroblasts, the source of collagen, reticular and elastic fibers found in most varieties of connective tissues throughout the body. The term dura mater is loosely translated from Latin to mean the "tough" or "thick "mother" of the brain. In fact, the dura mater is often characterized as having the unyielding property and texture of leather or raw animal hide. In this representative block of tissue, the three meningeal layers are seen beneath the skull. The dura mater consists of a superficial periosteal layer and a deep meningeal layer. Note how the sagittal sinus in the midline is comprised of a channel created between these two dural sublayers. The meningeal layer of the dura continues between the cerebral hemispheres to form the falx cerebri. The dura mater structurally consists of two layers: (a) an external periosteal layer that adheres to the deep surface of the skull and spinal canal, and (b) an internal meningeal layer that attaches to the arachnoid layer directly underneath (Schuenek et al. The function of the periosteal layer of the dura mater is to ensure that the dural lining remains firmly affixed to the rigid superstructure of the skeleton. Along the deep fissures and natural points of division of the brain and cerebellum, the meningeal layers detach from the periosteal layer and fold or invaginate inward, forming fairly rigid and thick dural folds. Within the calvarium are three principal dural folds: the falx (Latin for "sickle" shaped) cerebri, the falx cerebelli, and the tentorium (Latin for "tent-like") cerebelli (Carpenter, 1991). This compartmentalization provides a strong and semistiff protective and support framework for the soft tissues of the cerebral and cerebellar hemispheres. First up, the falx cerebri (red shading) is the fold separating the left and right hemispheres. Staying in the midline, but this time looking down to the region of the cerebellum, you can see the much smaller falx cerebelli (blue shading). This dural fold extends from the occipital midline and is found situated in the space between the cerebellar hemispheres. Lastly, between the falx cerebri and cerebelli is the tentorium cerebelli (green shading). The tentorium is found in the horizontal plane between the ventral surfaces of the occipital lobes and the cerebellar hemispheres. The tentorium is not perfectly flat, but rather is elevated in the midline, giving the fold the appearance of a shallow old-fashioned A-frame tent. In this frontal view of the posterior cranial vault, the meningeal layer of the dura is seen separating from the periosteal layer at several locations to create dural folds and sinus spaces. The dural folds create a honeycomb of compartments that support and protect the soft tissues of the brain. The upper two chambers house the cerebral hemispheres, while the lower chambers contain the cerebellar tissues. The sinuses that are formed become components of the venous system and are used to drain deoxygenated blood from the brain back to the cardiopulmonary system. In this illustration, the lateral and posterior wall of the skull along with all brain tissues have been removed, leaving visible the three principal dural folds: the falx cerebri, falx cerebelli, and tentorium cerebelli. The falx cerebri (red) compartmentalizes the cerebral hemispheres, while the falx cerebelli (blue) compartmentalizes the cerebellar hemispheres. The horizontally oriented tentorium cerebelli (green) separates the cerebellum from the cerebrum. Because the skull and dura are unyielding, the addition of mass in the form of a tumor or pooled blood from trauma or stroke dramatically increases intracranial pressure. Put simply, brain tissue is one of those things that does not react well to being squeezed and put under extreme pressure. More often than not, under conditions of increased intracranial pressure, the cerebral cortex experiences the greatest compressional forces; and, as you already know, damage to the cortex negatively impacts all forms of cognitive and sensorimotor behavior. A common condition that typifies this situation is the subdural hematoma, often heard on medical television shows. As the name suggests, the subdural hematoma is a pooling of blood directly beneath the dura that, if left unchecked, will cause massive compressional damage to the underlying brain tissue. Immediate medical action is required to evacuate the pooling blood and provide pressure release. At times, compressive forces and intracranial pressure become so great that they can actually cause a displacement of entire brain regions from their normal positions within the calvarium. These con- cHaPter 5 Neuroanatomy: the diencephalon, cerebrum, cerebral cortex, and the infrastructure of the cNs 225 ditions, collectively known as herniation syndromes, result in the gelatinous brain tissue being forced under or around one of the dural folds or through a foramen of the skull. My old German neuroanatomy teacher likened this situation to squeezing toothpaste out of a tube with a very narrow opening or pushing jello through a pasta strainer. The arachnoid layer consists of two subcomponents: the barrier layer and the subarachnoid space. The barrier layer adheres to the deep surfaces of the dura and is comprised of cells whose membranes are joined in a configuration known as tight junctions. This property of the barrier layer prevents the leakage of fluids (blood and cerebrospinal fluid) from below and makes this layer resilient to strain. The second subcomponent, the subarachnoid region, is an open space populated by arrays of collagen fibers, arteries, veins, and in some locations cranial nerve roots. The collagen fibers are randomly arranged between the barrier layer and the pia mater, giving the space a lattice or weblike appearance, hence the anatomical name of the region. The subarachnoid is the chief passageway for arteries and veins entering and exiting brain tissue, making this area particularly susceptible to hemorrhaging coincident with head trauma (Carpenter, 1991). Second, fill a sink with water and completely submerge the empty and open second container. With the container submerged in the sink, place the second egg inside of it and seal the container underwater tightly with the lid. Now, take the first container with only the raw egg inside and give it a good vigorous shake. Pick up the second fluid-filled container with the egg suspended within and give this one a good vigorous shaking. Flattened bands of reticular and elastic fibers from the upper layer of the pia mater surrounding the spinal cord form what are called denticulate ligaments. The denticulate ligaments are not true ligaments in the skeletal sense, but instead operate to suspend the spinal cord from the dura layer. They extend outward and laterally from the spinal cord toward the dura, looking like fine tether lines or spokes on a wheel. The ventricular system can be divided into four major segments: the left and right lateral ventricles, the 3rd ventricle, and the 4th ventricle (Carpenter, 1991; Gilroy & MacPherson, 2016; Haines, 2013; Mtui et al, 2015; Schuenek et al. The lateral ventricles make up a large paired chamber with one chamber found on each side of midline. A lateral ventricle in a human brain is large enough to easily fit one or two of your fingers inside, depending on which segment of the ventricle you are examining. Each lateral ventricle consists of an anterior, posterior, and inferior horn, which are all attached onto a central body. Each segment of the lateral ventricles can be found in different cerebral lobes, with the anterior horn found in the frontal lobe, the body in the parietal, the posterior horn in the occipital region, and finally the inferior horn located in the temporal lobe. When taken together as a pair, the left and right lateral ventricles are separated anteriorly by a thin membrane called the septum pellucidum. Each lateral ventricle is connected to the 3rd ventricle in the midline via a short canal called the interventricular foramina (known also as the Foramen of Monro). The 3rd ventricle is effectively a sliver of space that exists between the left and right thalamus and hypothalamic nuclei. Frontal and lateral perspective of the cerebrum with the fluid-filled ventricular system visible in ghost view. The ventricular system divided into four major interconnected chambers: the left and right lateral ventricles, the 3rd ventricle, and the 4th ventricle. The diamond-shaped 4th ventricle is positioned between the brainstem and the cerebellum. The 4th ventricle is a roughly diamond-shaped chamber that comprises the space between the dorsal brainstem and the cerebellum. The 4th ventricle is a prominent landmark that divides the pons and medulla from the cerebellum. Rostrally, the 4th ventricle connects to the cerebral aqueduct, and caudally, the ventricle narrows to become the central canal that runs down the entire length of the spinal cord. In fact, many motor speech and language disorders, such as aphasia and apraxia of speech, can be traced back directly to an infarct or injury to a segment of the vascular system. The brain constitutes approximately 2% of the mass of the body, but consumes roughly 20% of the total oxygen intake and glucose available in the blood stream (Mason, 2011). To put this in perspective, the 1,440 liters of blood used by the brain in a day is enough to easily fill six to seven typical bathtubs. Of course, this volume of blood is necessary to maintain the high metabolic demand of neural tissue for oxygen and glucose to maintain normal function. A typical adult will lose consciousness in as little as 10 seconds when deprived of oxygen. The person will start showing signs of neuronal decay and death after 1 minute, and after 3 to 5 minutes have elapsed without adequate levels of oxygen, the person will have irreversible brain damage. The neurovascular system can be subdivided broadly into the arterial and venous systems. Arterial blood is rich in oxygen and glucose, and originates directly from the heart. Venous blood, or deoxygenated blood, travels from the brain back to the cardiopulmonary system for conversion back into arterial blood. Looking only at the arterial system for now, this portion of the neurovascular system can be further divided into the anterior circulatory and posterior circulatory systems (Carpenter, 1991; Gilroy & MacPherson, 2016; Haines, 2013; Mtui et al, 2015; Schuenek et al.

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One question that comes to mind when looking at the various cortical locations from which the corticospinal and corticobulbar tracts emerge is gastritis vitamin c order cheapest sevelamer, if these pathways are supposed to be involved in executing voluntary movement gastritis ultrasound discount sevelamer 400 mg free shipping, why do only 30% of descending fibers come from M1 given that this area is necessary for the execution of actions In a similar vein gastritis tips buy sevelamer canada, why are the vast majority of fibers coming from S1 and from premotor areas gastritis jello 800 mg sevelamer buy free shipping, regions that are involved in tactile and proprioceptive sensation and the planning of an action gastritis diet ��������� cheap sevelamer 400 mg otc, respectively In the case of sensory gating, corticospinal and corticobulbar tracts are known to synapse upon the thalamus, brainstem sensory nuclei, and dorsal gray areas of the spinal cord. The thalamus is a prime example of a sensory element that is known to receive heavy projections from both M1 and S1 via what are known as corticothalamic fibers. These cortical projections operate to modulate and regulate the flow of sensory inputs coming from the periphery depending on a variety of task conditions and the attention being paid to the sensory input (Sommer, 2003). The importance of sensory gating in the thalamus is to directly influence what sensory information gets transmitted to perceptual and motor control centers of the brain and how these inputs will be used during functional behaviors (see the discussion of sensory gain control and gating within the thalamus in Chapter 5) (Sherman & Guillery, 2002). Both the modulation of pain (see discussion on the gate theory of pain in Chapter 6) and tactile sensations (see the filtering and gatekeeping example in Chapter 5) are good examples of the extent to which descending efferent inputs can actively regulate the quality and quantity of sensory information made available to higher neural processing elements (Basbaum & Jessell, 2013; Mendell, 2014). Anatomic illustration of the corticospinal tract (red pathway) and the corticobulbar tract (blue pathway). As you can see by this illustration, any notion that the motor cortical areas (M1 and premotor cortex) are in direct and solitary "control" for expression of an action can be dismissed. For the sake of clarity and because there are some subtle differences to make note of, the pathway descriptions for each tract are explained separately in the following sections. Near the transition of the medulla into the spinal cord, the axons of the corticospinal tract begin to decussate (cross the midline). Of the total number of corticospinal axons, anatomical course of the corticospinal and corticobulbar Pathways Luckily for us, the corticospinal and corticobulbar tracts share many common anatomical elements as they descend through the neuraxis (Carpenter, 1991; Kiernan, 2005; Mtui, Gruener, & Dockery, 2016; Schuenek et al. Schematic overview of the corticospinal tract (anterior and lateral segments) is shown in a frontal section of the entire neuraxis. What this means, essentially, is that corticospinal tract neurons that project to the lower lumbar areas of the spinal cord for example can extend to more than 1 meter in length, depending on the height of the person. The remaining 2% of fibers permanently stay ipsilateral in their projection and influence upon their respective targets. All in all, roughly 98% of all corticospinal axons 446 Neuroscience Fundamentals for communication sciences and disorders sectioN 3 decussate at one point or another to drive the contralateral musculature of the body (Kiernan, 2005; Haines, 2013; Mtui et al. The capacity to independently control the left and right musculature affords us a great advantage when needing to perform skilled and fine force control tasks with our hands. Contralateral innervation patterns allow for the development of a richer repertoire of complex manual behaviors. This innervation pattern also imparts on us the ability to generate more gross voluntary behaviors that require left­ right alternating patterns of action such as walking, running, and driving a car with a manual transmission and stick shift (a lost art these days). Schematic overview of the corticobulbar tract (bilateral and contralateral components) is shown in a frontal section of the entire neuraxis. Contralateral innervation to the trigeminal motor nucleus, the lower half of the facial motor nucleus, and the hypoglossal nucleus are depicted by the blue lines. Such a pattern likely contributes to the anatomical foundation for our refined motor skill capacity in muscle systems innervated by the cranial nerves. A major difference of the corticobulbar compared to the corticospinal tract is that the former innervates the majority of cranial nerve motor nuclei bilaterally, rather than contralaterally (Carpenter, 1991; Haines, 2013; Schuenek et al. Bilateral innervation means that one side of the brain provides signals to both the ipsi- and contralateral motor nuclei simultaneously. Effectively, each motor nucleus (or reticular area closely surrounding a motor nucleus) gets a redundant set of commands for an action - one from the ipsilateral cortex and the other from the contralateral cortex. Why would a bilateral innervation pattern need to arise in evolution for cranial nerve motor nuclei Why not maintain the contralateral innervation pattern found in the corticospinal tract system This is an interesting question to ponder, with the answer related to the types of behavior cranial nerve motor nuclei subserve. To perform well and accurately, all of these behaviors require synchronization of muscle activity on both sides of the midline. Bilateral innervation provides the anatomic means to perform this synchronization, but it also does something else. It would be advantageous (evolutionarily speaking) to your survival to be able to maintain the capacity to chew, bite, swallow, protect the airway, vocalize, and control motion of the eyes. In other words, in spite of signal loss from one side of the brain, bilateral innervation allows you to retain the ability to perform critical survival behaviors such as eating (chewing and swallowing), detecting predators (motion of the eyes), protecting yourself (biting), communication (sound source production), and breathing safely (airway protection). By my estimation, these are all excellent reasons to want to possess a bilateral innervation pattern for cranial nerve motor nuclei. In the corticobulbar system, the bilateral innervation pattern typically observed is broken at three specific locations. There are, in fact, two very good reasons why these specific cell populations receive more contralateral innervation - speech and the manipulation of food in the mouth. Both behaviors require the ability to independently activate the left and right musculature to accomplish all of the nuanced actions underlying each particular skill. For bolus manipulation, independent left­right tongue control allows for shifting of food from one side to another and for shaping the bolus to swallow. Independent control of both sides of the jaw also contributes to bolus manipulation, allowing the individual to vary chewing forces as necessary based on the consistency and size of the bolus in the mouth. In the context of speech, though, varying and carefully shaping the anterior opening of the vocal tract in different and nuanced ways modulates the acoustics of the spectra emanating from the oral cavity. Differentially contracting lower face muscle groups leads to contouring changes to the facial skin and the walls of the oral cavity. For example, varying degrees and patterns of lip rounding lead to a lowering of all vowel formant frequencies. Independent left­ right control of the lower face also contributes to producing different forms of facial gesturing. This is not a trivial question and, in fact, is one that leads us toward understanding the nature of a common disorder known as facial palsy (Jenny, & Saper, 1987). To begin understanding what we just described, you need to keep in mind two behavioral consequences related to bilateral versus contralateral innervation in general. First, any neural area that is bilaterally innervated will continue to function if one of its two inputs are lost. Such would be the case because you still have one good signal driving the neurons in that area. Second, any neural area that is contralaterally innervated will lose its ability to operate normally when its sole input is removed; with no redundancy present, no operation is possible. Damage to the left facial nerve distal to the nucleus, though, results in a loss of input to both the lower and upper face ipsilaterally. It should be appreciated that in older medical terminology and in descriptions still used by seasoned physicians and clinicians, the corticospinal and corticobulbar tracts are collectively referred to as the pyramidal tract. The "pyramidal" label is used not because of the name of the cortical cell of origin for these pathways (which would make intuitive sense), but rather because a large proportion of these descending axons happen to pass through the pyramids on the ventral medulla. The reason for the updated nomenclature for these descending efferent pathways is because use of the term "pyramidal tract" leads to some confusion when discussing innervation of the brainstem by motor cortical areas. Technically, the only fibers that pass through the pyramids of the ventral medulla are those that descend toward the spinal cord (corticospinal tract), not those that stop in the brainstem (corticobulbar tract). As such, saying that a descending axon is part of the "pyramidal tract" is not specific enough to accurately capture the differences in the destination targets for a given axon. Use of the updated terminology clearly distinguishes between spinal and brainstem termination locations for any given descending efferent axon from the cortex. In all cases, the grayed-out lines indicate reduced or eliminated signal transmission. The tracts projecting from these brainstem regions are the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts. These 450 Neuroscience Fundamentals for communication sciences and disorders sectioN 3 tracts mediate a number of fundamental and unconsciously executed movement behaviors that involve the axial muscles of the torso, neck, and proximal limbs (muscles of the shoulders and hips). These regulatory behaviors include posture, balance, gait, and visual orientation responses. Collectively, these tracks are known as the extrapyramidal system pathways, to distinguish them from the pyramidal projections (corticospinal and corticobulbar tracts) that are strongly active during volitional motor behaviors (Carpenter, 1991; Kiernan, 2005; Mtui et al. As mentioned earlier, the extrapyramidal system has minimal effect on speech production outside of perhaps to maintain postural control of the upper torso to facilitate speech breathing activities under certain conditions. For example, stage actors and opera singers routinely need to think about posture and torso position when performing their roles, especially when staging effects are complex. Once in the spinal cord, the rubrospinal tract become localized within the lateral fasciculus just ventral to the lateral corticospinal tract. The rubrospinal tract shares many similarities with the corticospinal tract (Kennedy, 1990; Massion, 1988). Second, the red nucleus (origin of the rubrospinal tract) receives motor input from the same frontal lobe motor cortical zones that are the sources of the corticospinal tract. The rubrospinal system appears more influential in nonhuman primates, operating as a functionally parallel system to the corticospinal tract in these animals. In the human, rubrospinal activity is far less important with the majority of its action having been transferred and taken over instead by the more directly connected corticospinal tract (Kennedy, 1990; Massion, 1988). Rubrospinal tract originates in the red nucleus of the mesencephalon, decussates, and projects to the spinal cord via the rubrospinal tract. Brainstem in shown in dorsal perspective and spinal cord is shown in a horizontal section. Both pathways transmit descending balance and vestibular-related signals to axial muscle systems of the head and neck, and extensor muscles of the limbs (Shinoda, Sugiuchi, Izawa, & Hata, 2006). The medial vestibulospinal tract originates, as the name implies, from the medial vestibular nucleus. The tract descends bilaterally through the brainstem in a centrally located white matter tract known as the medial longitudinal fasciculus (Kiernan, 2005; Mtui et al. Activation of the pathway leads to rotation and lifting of the head, as well as to reflexive responses of neck muscles to sudden and unexpected changes in position and orientation. A classic example of a medial vestibulospinal reflex is that which is initiated when you happen to fall forward. In this scenario, rapid acceleration of the head forward and downward triggers a backward flexing of the head as well as extension of the upper arms to try and catch or brace yourself from the ground that is rapidly getting closer to your face. Both actions operate to protect the head and the upper torso from potential injury. The tract originating from the pons is known as the pontine reticulospinal tract, while the tract from the reticular formation of the medulla is called the medullary reticulospinal tract (Horn, 2006). Recall from Chapter 4 that the reticular formation of the brainstem is formed by a generally diffuse and complex network of neurons that are active in a host of vegetative functions such as cardiovascular and respiratory operations, reflexive eye movements, sleep and alertness, and regulation of the torso and limbs. It is this last activity of the reticular formation that is influenced by reticulospinal pathways. Such activity is crucial to maintaining an upright posture against gravitational forces. The medullary reticulospinal tract has the opposite effect; it inhibits proximal voluntary movements and decreases muscle tone. The lateral vestibulospinal tract originates from the lateral vestibular nuclei and projects ipsilaterally to the spinal cord. Activation of this second pathway leads to rotation and lifting of the head, and reflexive neck actions. Brainstem in shown in dorsal perspective, and spinal cord is shown in a horizontal section. The pontine reticulospinal tract originates in the pontine reticular formation and descends to the spinal cord ipsilaterally. The medullary segment originates from the medullary reticular formation, decussates, and then innervates the proximal muscles of the limbs. The medullary reticulospinal tract inhibits proximal muscles and will decrease muscle tone. Tectospinal tract originates from the superior colliculus, decussates, and descends to the spinal cord. Brainstem in shown from a dorsal perspective, and spinal cord is shown as a horizontal section. The multimodal integration of visual, auditory, and/ or somatosensory information in the superior colliculus is thought to highlight and bring to the forefront of your attention the sensory inputs that would be missed entirely if encountered by themselves (Stein, 1998; Stein & Meredith, 1993). The superior colliculus coordinates multiple cranial cHaPter 11 motor control systems of the cNs 453 nerve systems innervating the extraocular muscles and those of the neck and upper torso to rapidly move the head and our gaze to unexpected events entering our periphery. Tectospinal activity is thus an important protective pathway that helps orient our visual gaze to potentially threatening inputs. These descending tracts afford us the ability to perform voluntary movements and to execute all forms of fractioned (fine-force) and skilled behaviors. Evidence for this is derived from studies showing that low-level electrical stimulation of M1 neurons produce discrete contractions of the contralateral muscles for body areas connected to the corticospinal tract and bilaterally for cranial nerve motor systems mediated by the corticobulbar tract (noting our earlier exceptions of the lower face, tongue, and jaw) (Dum & Strick, 2002; 2005). The primary motor cortex and the premotor cortex are the two principal direct motor systems found within the frontal lobe and, together, are chiefly recognized as participating in the voluntary performance of skilled actions. This visual analogy grossly characterizes the pattern and ordering of neurons in M1. The motor homunculus indicates that the number of neurons needed to control muscles for a given body region are different and related to the skill and behavior performed by that body part. The homunculus also reveals that the proportion of neurons devoted to controlling the muscles for a given body region are different and correlated to the skill-producing capacity of the region. As we have seen many times before in the sensory systems, the pattern of devoting greater cortical resources to the management of skilled behaviors is a central rule of cortical organization regardless of the species.

She is 132 cm tall gastritis lipase 800 mg sevelamer purchase with visa, weighs 44 kg gastritis diet ketogenic buy sevelamer online now, has swelling around the neck gastritis symptoms right side purchase online sevelamer, increased carrying angle at the elbow and poorly developed secondary sexual characteristics gastritis diet 17 sevelamer 400 mg buy online. On performing a pelvic ultrasound gastritis symptoms pain in back sevelamer 800 mg otc, the physician observes her ovaries are small and elongated. A tall man with gynecomastia and testicular atrophy has a testicular biopsy that shows sparse, completely hyalinized seminiferous tubules with a complete absence of germ cells and only rare Sertoli cells. Chromosomal abnormality in Mongolism is (a) Trisomy 21 (Karnataka 2005) (b) Trisomy 22 (c) Trisomy 17 (d) Trisomy 5 53. The number of chromosomes in Klinefelter syndrome is: (a) 47 (b) 46 (c) 45 (d) 44 60. Chromosomes are visualized through light microscope with resolution of: (a) 5 Kb (b) 50 mb (c) 5 (d) 500 Kb 60. Which of the following techniques can be used to detect exact localisation of a genetic locus Males are more commonly affected than females in which of the following genetic disorders Inheritance pattern of the disease in the family is: (a) Autosomal recessive type (b) Autosomal dominant type (c) X-linked dominant type (d) X-linked recessive type 66. Kinky hair disease is a disorder where an affected child has peculiar white stubby hair, does not grow, brain degeneration is seen and dies by age of two years. A is hesitant about having children because her two sisters had sons who had died from kinky hair disease. An albino girl gets married to a normal boy, what are the chances of their having an affected child and what are the chances of their children being carriers These techniques are used in forensic medicine to compare specimens from the suspect with those of the forensic specimen. Which one of the following individuals would be most at risk for developing also hemophilia A True statement about inheritance of an X linked recessive trait is: (a) 50% of boys of carrier mother are affected (b) 50% of girls of diseased father are carrier (c) Father transmits disease to the son (d) Mother transmits the disease to the daughter 87. Male to male transmission is not seen in: (a) Autosomal dominant diseases (b) Autosomal recessive disease (c) X-linked dominant disease (d) Genomic imprinting 87. Microarray is best characterised by: (a) Study of multiple genes (b) Study of disease (c) Study of organisms (d) Study of blood group 87. A 22-year-old woman, Sheena presents with progressive bilateral loss of central vision. You obtain a detailed family history from this patient and produce the associated pedigree (dark circles or squares indicate affected individuals). Genetics (a) (b) (c) (d) (e) Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant Mitochondrial 87. He notes the following characteristics in the four placentas: Patient A: fused dichorionic diamnionic Patient B: dichorionic diamnionic Patient C: circumvallate placenta Patient D: monochorionic diamnionic. About 10 - 20% of newborn with a1 ­ antitrypsin deficiency develop neonatal hepatitis and cholestasis. A broad generalization is that the physiologic metabolic enzyme deficiencies are all autosomal recessive whereas Structural defects are autosomal dominant. Gardener syndrome Q Intestinal polyps + epidermal cysts + fibromatosis + osteomas (of the mandible, long bones and skull). It is an autosomal recessiveQ genetic disorder that affects most critically the lungs, and also the pancreas, liver, and intestine. In children, its value is inversely related with body mass index and insulin values. It reduces energy intake and its reduced levels in the patients of Prader Willi syndrome may contribute to hyperphagia and obesity. Since the progenitor cells of the gametes carry the mutation, there is a definite possibility that more than one child of such a parent would be affected. All code for thin filament­associated proteins, suggesting disturbed assembly or interplay of these structures as a pivotal mechanism. There is mutation in the Gs a subunit; individuals express the disease only when the mutation is inherited from the mother). Structural proteins that contribute to multimeric structures are vulnerable to dominant negative effects. It occurs in children and typically presents with an abdominal mass as well as with hypertension, hematuria, nausea and intestinal obstruction. Since it is derived from mesonephric mesoderm, it can include mesodermal derivatives such as bone, cartilage, and muscle. Multifactorial inheritance is similar to polygenic inheritance in that multiple alleles at different loci affect the outcome; the difference is that multifactorial inheritance includes environmental effects on the genes. Huntington disease is transmitted as an autosomal dominant trait with 100% penetrance, meaning that if a child inherits the abnormal gene, that child will inevitably develop Huntington disease. An earlier age of onset is associated with a larger number of trinucleotide repeats. Thus, patients who receive an abnormal gene from their fathers tend to develop the disease earlier in life. Anticipation is common in disorders associated with trinucleotide repeats as in Fragile X syndrome, myotonic dystrophy and Friedreich ataxia. The likelihood that the properties of a gene will be expressed is called penetrance. Dissecting aortic aneurysm (Ref: Robbins 8th/145, 9/e 145) the patient has Marfan syndrome, an autosomal dominant disorder caused by a defect in the gene on chromosome 15 encoding fibrillin, a 350 kD glycoprotein. Fibrillin is a major component of elastin associated microfibrils, which are common in large blood vessels and the suspensory ligaments of the lens. Abnormal fibrillin predisposes for cystic medial necrosis of the aorta, which may be complicated by aortic dissection. Other features of the syndrome are subluxated lens of the eye, mitral valve prolapse, and a shortened life span (often due to aortic rupture). The genomic imprinting is best illustrated by the following disorders: Prader-Willi syndrome and Angelman syndrome. It is also seen in other conditions like molar pregnancy and Beckwith-Wiedemann syndrome. There are three key mechanisms by which unstable repeats cause diseases: · Loss of function of the affected gene occurs in fragile X syndrome. Similarly, insertion would lead to increase (and not loss) in the genetic material. It can be of the following types: ­ In balanced reciprocal translocation, there are single breaks in each of two chromosomes, with exchange of material. There is no loss of genetic material and so, the affected individual is likely to be phenotypically normal. This loss is compatible with a normal phenotype because it carries only highly redundant genes. Genetics Therefore, deletion, insertion and Robertsonian translocation would lead to change in genetic material. Its greatest utilization in constitutional analysis is in the detection of microdeletionsQ. In cancer cytogenetics, it is used extensively in the analysis of structural rearrangementsQ. However, interphase analysis can be used to make a rapid diagnosis in instances when metaphase chromosome preparations are not yet available. Interphase analysis also increases the number of cells available for examination, allows for investigation of nuclear organization, and provides results when cells do not progress to metaphase. There is a Strong relation with maternal age It may also be seen with Robertsonian translocation and mosaicism. Most commonly used stain is Giemsa stain, so called G-banding the chromosomes are arranged in order of decreasing length Any alteration in number or structure of chromosomes can be easily detected by karyotyping 43. The features pointing towards this diagnosis are: · Male phenotype · Hypogonadism [rudimentary testes] · Decreased secondary sexual characteristics [sparse pubic and facial hairs] · Disproportionately long arms and legs. So, the number of copies after 3 cycles would be 23 = 8 times the original copies. Mitral valve prolapse (Ref: Robbins 8th/169) the patient in question is suffering from Fragile X Syndrome which is a familial form of mental retardation with features like lax skin and joints, flat feet, large ears, long narrow face with prominent jaw and nasal bridge and macro-orchidism. Mitral valve prolapse and aortic root dilatation are the serious complications of this disorder. While trisomies and non-mosaic monosomies typically result from meiotic non-disjunction, mosaicism arises secondary to mitotic errors after fertilization has taken place. Uniparental disomy occurs in Prader-Willi syndrome (maternal uniparental disomy) and Angelman syndrome (paternal uniparental disomy). In balanced form, a reciprocal (Robertsonian) translocation is clinically silent because there is no excess or shortage of genetic material. An unbalanced trisomy 21 (in which one chromosome 14 contains the long arms of both chromosomes 14 and 21) is responsible for Down syndrome. Mosaicism (Ref: Robbins 8th/161) Mosaicism is the term used when cells with more than one type of genetic constitution are present in the same organism. The situation in the question uncommonly occurs when nondisjunction of chromosome 21 occurs during mitosis (rather than meiosis) in one of the early cell divisions. The degree to which the individual expresses the characteristics of the syndrome depends on the number of cells involved and their distribution. Balanced translocation (choice A) does not produce features of any syndrome, because critical genetic material is not lost, although progeny may be affected when the translocated chromosome is added to a complement of otherwise normal chromosomes. Chiasma (choice B) refers to the "X"-shape of chromosomes undergoing exchange of genetic material in crossover. Spermiogenesis (choice D) refers to the development of sperm precursors into mature sperm. Osteogenesis imperfecta usually results from autosomal dominant mutations in the genes that encode the1 and 2 chains of collagen. Most commonly used stain is Giemsa stainQ, so called G-bandingQ the chromosomes are arranged in order of decreasing lengthQ. Any alteration in number or structure of chromosomes can be easily detected by karyotyping 60. It usually results from complete or partial monosomy of X chromosome and associated with hypogonadism in phenotypic females. The probe hybridizes to its homologous genomic sequence and thus labels a specific chromosomal region that can be visualized under a fluorescent microscope. Limitation of this technique: the number of chromosomes that can be detected simultaneously by chromosome painting is limited due to the availability of fluorescent dyes that emit different wavelengths of visible light. Currently used for detection of cancer, mutations in mental retardation and the detection of microdeletions. Instead of dividing longitudinally to separate the two sister chromatids, the centromere undergoes a transverse split that separated the two arms from one another. Testicular germ cell carcinoma has the presence of gain of 12p through isochromosome formation or amplification. The mutant recessive gene on the X chromosome expresses itself in a male child because it is not suppressed by a normal allele whereas in the female, the presence of a normal allele on other X-chromosome prevents the expression of the disease so, females only act as carriers. Because carrier mothers are not manifesting the disease, yet their sons do, the disorder can only be recessive. So, even if one mutant allele is present on X-chromosome, it will manifest (whether recessive or dominant). The prevailing paradigm in developmental biology is that once cells are differentiated, their phenotypes are stable. However, tissue stem cells, which are thought to be lineage-committed multipotent cells, possess the capacity to differentiate into cell types outside their lineage restrictions (called trans-differentiation or stem cell plasticity). There is presence of pleomorphic inclusion of lipids in lysosomes enclosed in concentric or parallel lamellae. Because such a child is a heterozygous at the Rb locus, it implies that heterozygosity for the Rb gene does not affect cell behavior. Each region is further subdivided into bands and sub bands and these are ordered numerically as well. A sequence of three of these bases forms the triplet code used in transmitting the genetic information needed for protein synthesis. The small variation in gene sequence (called as a haplotype) is thought to account for the individual differences in physical traits, behaviors, and disease susceptibility. It will be manifested in female having both the mutant alleles (Xh Xh) whereas XhX will be carrier. XhY will be affected male · In the given pedigree, I-1 and I-2, both are unaffected, therefore male should be normal (xy) and female should be carrier (XhX) · Now, if we see the inheritance, it will be · · · · · Therefore, half of the daughters are carrier and half are normal whereas half of males are normal whereas other half are affected. The affected male (XhY), transmits the mutant genes to females only and not to males. Patient D Read explanation below Patient D is the mother of identical (monozygotic) twins. The chorion forms before the amnion, so the possible combinations are · Monoamnionic and monochorionic; · Diamnionic and monochorionic; and · Diamnionic and dichorionic (either fused or separated). Very early separation produces completely separate membranes with duplication of both chorion and amnion; somewhat later separation produces one chorion and two amnions; and very late separation produces one chorion and one amnion. A dichorionic, diamnionic placenta develops if splitting occurs early after fertilization, before the chorion forms. Thus, we are unable to determine whether Patient A (choice A) or Patient B (choice B) had identical twins from the examination of the placentas. The hybridization (and consequently, the fluorescent signal emitted) will be strongest at the oligonucleotide that is complementary to wild-type sequence if no mutations are present, while the presence of a mutation will cause hybridization to occur at the complementary mutant oligonucleotide. Autosomal recessive diseases occur when both copies of a gene are mutated; enzyme proteins are frequently involved.

Collectively gastritis glutamine order sevelamer pills in toronto, these areas are known as the extrastriate cortex chronic superficial gastritis diet 800 mg sevelamer order with visa, which is really a catchall term to describe any area outside of V1 that participates in visual processing gastritis diet 50 sevelamer 400 mg on line. Discussing each of these areas is clearly beyond the scope of this chapter gastritis fundus sevelamer 400 mg order on line, but we can summarize them by describing two largescale visual processing streams (Ungerleider & Haxby gastritis burping order sevelamer 800 mg,1994). The first pathway is known as the dorsal stream and originates all the way back in the M-type retinal ganglion cells, projecting dorsally from V1 toward posterior parietal association areas. The dorsal stream is dedicated to processing inputs related to direction of motion, visually guided movement, and the positional relationship between segments of a visual scene (Goodale, 2011; Goodale, Westwood, & Milner, 2004). At its highest levels of operation, the dorsal stream extracts perceptions related to direction and velocity of motion. The second pathway, known as the ventral stream, begins with the P-type retinal ganglion cells and projects in parallel ventrally toward the temporal association areas. Ventral stream neurons are active during object recognition, identification, and high-resolution object form analysis (Afraz, Yamins, & DiCarlo, 2014). At its highest levels, the ventral stream can demonstrate extreme specificity, responding preferentially to specific combinations of features that define a category of objects, such as faces or other semantically related objects (Ungerleider & Haxby, 1994). The dorsal and ventral streams of the visual cortex reveal that cortical processing occurs in both a serial and parallel manner. Serial processing of information is represented within a pathway as the successive connection of different visual cortical areas along a hierarchy. Such a pathway is organized in a functional manner to extract increasingly complex visual details from raw visual inputs originating within V1. Although serial processing is often hierarchical or bottomup in nature, with lower areas projecting to higher and more complex processing zones, top-down processing is also observed within a serial pathway. By top-down processing, we mean that higher processing areas project their information back down to lower areas in a more diffuse manner to provide some regulatory control over the processing occurring within these lower areas. The back-and-forth sharing of information along reciprocal connections is quite important, because it allows for different areas within a pathway to stay "in touch" with one another and ensure that the timing of information between processing areas remains consistent. Without reciprocal processing, you would have difficulty reconciling such an experience into a unified and, more importantly, a recognizable perception of the object. In the visual system, parallel processing allows for a shared set of stimulus features to be operated upon simultaneously along two or more different routes. The parallel processing in the visual system occurs between the dorsal and ventral streams. In fact, a particular submodality of visual information is processed in both pathways, but for different purposes. For example, orientation-related inputs are processed in both the dorsal and ventral streams, because orientation is an aspect of both motion and object recognition. Remember that nothing is ever completely exclusive to or isolated from anything else in the cerebral cortex. There is a great deal of crosstalk between the visual dorsal and visual ventral pathways, and it is through this crosstalk that all the submodalities of vision are thought to become combined for a unified perception of a visual scene (Milner, 2017; van Polanen & Davare, 2015). Keep in mind that the dorsal versus ventral stream designation is only a heuristic that currently allows us to frame an enormous number of experimental findings into a reasonable and understandable form. Surrounding V1 are the extrastriate cortical areas depicted by different colors: V2 (red), V3 (light green), V3a (dark green), V4 (gold), and V5 (dark pink). V2 through V5 are considered the extrastriate cortical areas and are tasked with processing higher-order features of visual inputs from the retina, as noted in the corresponding colored boxes. In the bottom medial perspective of the cerebrum, the organization of the primary and extrastriate cortical areas are shown. Thalamus V2 V1 V4 tems, the more we realize how extensively these pathways are interlinked to develop higher-order visual perception. It is hypothesized that the dorsal stream serves three important behavioral roles: (a) motion perception, (b) direction of eye position in the visual field, and (c) environmental navigation. From the primary visual cortex, orientation columns output to a secondary visual cortex abbreviated V2. Within V2, the cortex is subdivided into three anatomical zones referred to as the thick stripe, thin stripe, and interstripe zones. Orientation column outputs project to the thick stripe and interstripe zones of V2. Within these zones, features related to orientation, such as depth and direction of movement, are extracted. From there, depth and movement direction outputs are handed off to posterior parietal association areas where further extraction of motion-related signals takes place. The dorsal and ventral pathways are shown from their origination point in the retina through their termination in the parietal and temporal association areas. The dorsal pathway originates from M-type retinal ganglion cells, projecting through orientation and ocular dominance columns in V1 to thick stripes in V2. Extrastriate regions of the occipital lobe eventually channel signals in this pathway to parietal association areas. The dorsal stream processes inputs related to direction of motion, velocity, visually guided movement, and the positional relationship between segments of a visual scene. The ventral stream begins at with P-type retinal ganglion cells and projects through orientation columns and blobs to the thin and interstripe regions of V2. Ventral stream neurons are active during object recognition, identification, and high-resolution object form analysis. In cases of stroke bilaterally to the parietal cortex, patients present with normal visual acuity, but may have a severe deficit of visually detecting movement. Imagine the perceptual disconnect of not being able to detect the motion of an object. Living in such a state would be synonymous with living in a world of photographic still shots or within a stop-motion or claymation film. At one moment you would see the person at some distance from you, and in the next moment the person would appear right next to you! Neurons within various subregions of the ventral stream receive retinotopic inputs from V1. The ventral stream not cHaPter 8 the Visual system 369 only encodes object structure, but also appears to process advanced forms of color perception. Within V2, orientation column outputs project to the interstripe zone, whereas color blob outputs project to the thin stripe zone of V2. Within this zone, features related to orientation, form, and color are further extracted. From this point, color and form outputs become increasingly refined and are handed off to temporal association areas, including the ventral occipital lobe and extending into the middle and inferior gyri of the temporal lobe where further processing for objection recognition takes place (Afraz et al. Evidence for ventral stream organization, like that of the dorsal stream, is derived from clinical data (Barton, 2010, 2011; Goodale et al. Achromatopsia is a rare condition caused by cortical damage to the juncture of the posterior temporal lobe and the occipital lobe, whereby the perception of color vision is lost even though retinal input into the visual system remains healthy (Rizzo, Smith, Pokorny, & Damasio, 1993). Individuals with this syndrome often describe living in a world where everything takes on a shade of gray. In addition, individuals with this syndrome have deficits in identifying object form. Another fascinating syndrome that further highlights the complexity and detail of form processing by the ventral stream is a condition known as prosopagnosia (Barton, 2011). Under normal conditions, the fusiform area is highly selective for complex objects that resemble faces. For example, in primates the specificity of this zone is so discrete that certain profile views of faces are differentially encoded. Individuals with this syndrome possess normal vision in every other manner, except for the ability to identify and recognize a face. Further interest: multistable visual perception awareness Draw a simple wireframe cube - the type that you create when doodling during a boring lecture. Can you make yourself perceive the front face of the wireframe cube pointing upward and then downward If you were able to make these switches in perception, you just experienced multistable perception awareness. It appears that multistable visual perception requires activation of different collections of visual processing zones. As indicated in the text, there are many extrastriate areas and locations along the dorsal and ventral visual processing streams that specifically contribute to the perception of different visual features. For example, motion is related to parietal association area activation along the dorsal stream, while the perception of object characteristics appears to need temporal association area activity within the ventral stream. Within a given association area are subsets of cortical regions that process visual inputs with certain combinations of features. For example, perceiving a face activates the fusiform area of the ventral temporal lobe, while perception of an inanimate object that might look like a face (such as the front of a car) activates regions outside of the fusiform area. Work by Wolf Singer (1993) has suggested that perception for a given collection of visual features may result from the synchronization of neural activity in many different, yet related, populations of cells across widespread areas of the cortex. In other words, the timing of firing responses in distributed, yet related populations of neurons during real-time experience may be important for developing unified perceptual responses to a given set of features (Singer, 1993). Switching from one set of synchronized neuronal activations to another may account for our multistable perceptual abilities. Synchronization of cortical activity and its putative role in information processing and learning. Visual Field and Pathway Deficits By understanding the organization of the visual pathway, its pattern of projections, and how inputs are transduced across the retina, it is relatively easy to localize, differentiate, and describe the consequences of a variety of visual disturbances. In other words, retinotopy becomes our friend and allows us to identify the site of lesion from the behavioral deficits observed in a patient. Large visual field losses are 370 Neuroscience Fundamentals for communication sciences and disorders sectioN 2 referred to as anopsias, whereas smaller more discrete deficits are called scotomas (Kiernan, 2005; Mason, 2011; Snowden et al. Also note that all visual field losses are labeled for the visual hemifield that is absent. Finally, to interpret the behavioral visual deficits of central visual path lesions correctly, you must always remember that the visual field (your visual environment) projects in a reversed and inverted manner onto the retina. Briefly, the key summarizes the mapping relationship between binocular, monocular, and retinal fields using our familiar spotted purple butterfly as our visual image reference. Remember, to appreciate what you are actually seeing and perceiving, you will need to take the monocular visual fields (a. In this illustration, left-sided visual fields (binocular or monocular) are always green-shaded, and right-sided fields are always red-shaded. Demyelinating diseases such as multiple sclerosis, focal ischemia to the blood supply of the optic nerve, viral or bacterial neuritis, or acute trauma (to differing degrees) are all candidate conditions that will account for this pattern of blindness. The right central visual pathway is shown with six (a through f) sites of injury, each demarcated by heavy black lines. If you were looking at the butterfly against a background image with an optic chiasm lesion, then any visual inputs to the left and right of the wings would be absent. This type of deficit is often referred to as bitemporal hemianopsia or heteronomous hemianopsia. Optic chiasm damage is typically the result of mechanical pressure placed on the chiasm by pituitary tumors or gliomas on the ventral surface of the mesencephalon. Binoc Visual Hemi Binocular Image Right Optic Nerve Lesion Right Optic Chiasm Lesion (c) (d) T-U N-U N-U T-U Monocular Visual Fields T-L T-U N-L N-U N-L N-U T-L T-U Right Optic Tract Lesion Right Lower Optic Rad. Lesion Monocular Retinal Surfaces T-L N-L N-L T-L (e) (f) Left Eye Right Eye Right Upper Optic Rad. On the left-hand side is a key that summarizes the mapping relationship between binocular, monocular, and retinal fields using the spotted purple butterfly as a reference. For each injury location shown in a, the monocular visual fields and retinal fields for the left and right eye are shown with blacked out areas demonstrating the visual and retinal field consequences to a specific injury (a through f) along the central visual pathway. For a right optic tract lesion, the injury pattern results in the absence of the entire left binocular visual hemifield, but preservation of the entire right binocular hemifield. As such, a right optic tract lesion creates left homonymous hemianopsia and vice versa. Note that this pattern of visual field deficit can also be caused by damage to the internal capsule through stroke, because optic tract fibers pass through the internal capsule before becoming optic radiations. Beyond the optic tract, visual field deficits can get very complex because damage is often not complete. In this example, such an injury eliminates inputs to the cortex from the left lower nasal retina and from the right lower temporal retina, which in turn eliminates the vision from the upper quadrant of the left binocular visual field. In this case, the entire butterfly is visible except for the wing with the blue spot. In this example, the injury eliminates inputs to the cortex from the left upper nasal retina and the right upper temporal retina, which in turn eliminates the vision from the lower quadrant of the left binocular visual field. The entire butterfly is visible to the patient except for the wing with the yellow spot on it. Cortical lesions are by far the most complex in terms of their visual deficits and interpretation. There is no single form of deficit because the outcome depends on what part and how much of the visual cortex are lost. In this example, notice that the pattern is very similar to that of an optic tract lesion, except for one thing. The center area of the visual field - what would correspond to vision mediated by the fovea - is preserved, while the rest of the hemifield in blinded. It is thought that this visual information may be part of the input needed to help the hypothalamus set our internal body clocks or circadian rhythms (Haines, 2013). The suprachiasmatic nucleus is the chief target for visual inputs and uses these signals to verify daily light­dark cycles and trigger rhythmic release of a variety of hormones.

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