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Acanthocytes are red blood cells that slow weight gain and growth due to reduced uptake of have the appearance of thorns on their outer sur- nutrients 40mg levitra extra dosage with visa erectile dysfunction self treatment. Various lipids discount levitra extra dosage 60mg erectile dysfunction jacksonville doctor, such as cholesterol and its compo- Ataxia—A deficiency of muscular coordination, nents, are important in the development and normal func- especially when voluntary movements are tioning of nerve and muscle cells. MTP is necessary for the include ataxia (poor muscle coordination), loss of deep production of chylomicrons. Clubfoot—Abnormal permanent bending of the Muscular atrophy, the weakening and loss of muscle ankle and foot. Weakened heart muscle (cardiomy- Lipoprotein—A lipid and protein chemically opathy) may occur, and several severe cases have been bound together, which aids in transfer of the lipid reported that resulted in early death. Loss of clear Low density lipoproteins (LDL)—A cholesterol vision, nystagmus (involuntary movement of the eyes), carrying substance that can remain in the blood and eventual paralysis of the muscles that control the eye stream for a long period of time. Neuromuscular—Involving both the muscles and Skeletal problems associated with ABL include var- the nerves that control them. The Ocular—A broad term that refers to structure and abnormalities of the spine and feet are thought to result function of the eye. Retinitis pigmentosa—Progressive deterioration of the retina, often leading to vision loss and blind- Severe anemia sometimes occurs in ABL, and may ness. In addition, Triglycerides—Certain combinations of fatty acids because of their abnormal shape, acanthocytes are pre- (types of lipids) and glycerol. Vitamin deficiency—Abnormally low levels of a Vitamins A, E, and K are fat soluble, meaning they vitamin in the body. Low lipid levels in the blood means that people with ABL have chronic deficiencies of vitamins A, E, and K. Much believed that people with ABL were diagnosed as having of the neuromuscular disease seen in ABL is thought to either Friedreich ataxia (a more common form of hered- be caused by deficiencies of these vitamins, especially itary ataxia) or some other neurologic disorder. However, since the propor- of the reported cases of ABL have been in the Jewish tion of cases involving consanguinity is also reported to population, but individuals from other ethnic back- be about one-third, it is difficult to determine if mental grounds have been described as well. As many as one- retardation in individuals with ABL is due to the disease third of people with ABL have had genetically related itself or to other effects of consanguinity. Higher rates of consanguinity may also be responsible for other birth defects seen infre- are often seen in rare autosomal recessive disorders. Other diseases resulting in similar intestinal National Foundation for Jewish Genetic Diseases, Inc. As of 2000, there was no direct test of National Organization for Rare Disorders (NORD). Reduced triglyceride content in the diet is suggested if intestinal Acanthocytosis see Abetalipoproteinemia symptoms require it. Large supplemental doses of vita- min E (tocopherol) have been shown to lessen or even reverse the neurological, muscular, and retinal symptoms in many cases. Definition Occupational and physical therapy can assist with any muscular and skeletal problems that arise. Physicians Acardia is a very rare, serious malformation that that specialize in orthopedics, digestive disorders, and occurs almost exclusively in monozygous twins (twins eye disease should be involved. This condition results cialty clinics for individuals with multisystem disorders from artery to artery connections in the placenta causing a physically normal fetus to circulate blood for both itself such as ABL are available in nearly all metropolitan and a severely malformed fetus whose heart regresses or areas. Prognosis Description ABL is rare, which means there have been few indi- Acardia was first described in the sixteenth century. The Early references refer to acardia as chorioangiopagus effectiveness of vitamin supplementation and diet restric- parasiticus. It is now also called twin reversed arterial tions will vary from person to person and family to fam- perfusion sequence, or TRAP sequence. Life span may be near normal with mild to moderate disability in some, but others may have more serious and Mechanism even life-threatening complications. Arriving at the cor- Acardia is the most extreme form of twin-twin trans- rect diagnosis as early as possible is important. Twin-twin transfusion syndrome is a this is often difficult in rare conditions such as ABL. This abnormal connection MTP gene may lead to the availability of accurate carrier can cause serious complications including loss of the testing and prenatal diagnosis for some families. GALE ENCYCLOPEDIA OF GENETIC DISORDERS 7 Acardius amorphus appears as a disorganized mass KEY TERMS of tissues containing skin, bone, cartilage, muscle, fat, and blood vessels.
Top panel The predicted neural response to vibrissa stimulation frequency as a function of resonance ampliﬁcation of peak motion velocity purchase levitra extra dosage 60 mg without prescription xyzal erectile dysfunction, and intrinsic velocity sensitivity thresholds order 60mg levitra extra dosage otc erectile dysfunction occurs at what age. For a given amplitude of stimulation, vibrissa resonance ampliﬁcation that does not drive a neuron near its velocity threshold may fail to be ampliﬁed (purple curve, left resonance peak), while resonance ampliﬁcation that is signiﬁcantly above the velocity threshold (shown in the bottom panel) may fail to demonstrate tuning due to an upper limit on the range of possible ﬁring rates for a given neuron (blue curve, right resonance peak). A subset of vibrissa resonance tuning curves near to but not above the intrinsic velocity threshold will, in this model, show optimal frequency tuning. Preliminary data suggest that these effects occur in a subset of trigeminal and cortical neurons, and that, within SI, FSU and multi- unit recordings are more susceptible to these impacts of velocity sensitivity. Recordings were made from two trigeminal single units simultaneously (top panels) while frequency-varying sinusoidal stimuli were applied to their primary vibrissa (bottom panels). One of the single units (left panels) showed a signiﬁcant increase in mean ﬁring rate in response to the funda- mental resonance frequency at ~150 Hz, while the other showed a selective response to the higher harmonic seen at ~520 Hz (right panels). Third, many natural surfaces have spatial frequency power spectra that fall off exponentially. Perhaps the most important observation to be made at this stage of investi- gation of the vibrissa resonance hypothesis is that higher harmonics, if they are expressed and translated into neural activity in perceptually relevant contexts, should enhance the detection of high-frequency stimuli, and may or may not impair their discrimination. Speciﬁcally, if higher harmonics provide ampliﬁca- tion of subtle high-frequency inputs, they should facilitate the detection of these signals, e. Where higher harmonics pose a potential challenge to the beneﬁts of vibrissa resonance is in the place coding model of discrimination proposed above. Fundamental resonance frequencies and higher harmonics represented in the same position of the somatotopic map could create ambiguity in the interpretation of these signals by a sensing animal. That said, the pattern of positional activation — the speciﬁc regions of the map activated by a fundamental and higher harmonics — should still have a unique spatial signature that could be used to decode the frequency applied to the vibrissa. Thus, if higher harmonics are meaningfully expressed in relevant perceptual contexts, we predict that they will facilitate the detection of high frequency stimuli, and may contribute to or undermine the discrimination or identiﬁcation of high frequency input. MODULATION OF WHISKING VELOCITY Rats may actively modulate their sensory exploration strategy to enhance or suppress the impact of vibrissa resonance. During whisking, rats typically engage in a series of bouts of whisking with signiﬁcant variation in the rate of vibrissa motion between bouts. By searching over a variety of velocities, the rat can circumvent potential problems posed by the limited range of frequencies ampliﬁed by the vibrissa resonances expressed in a given sample of vibrissae. Further, comparison of activation evoked by faster or slower whisk cycles, combined with knowledge of the position of optimal activation within the pad (e. The suggestion that velocity modulation may assist perception of spatial textures through generation of different frequency inputs is consistent with recent studies of human perception of textured surfaces using a probe: Under these conditions, variation in the velocity of sampling is observed to impact roughness judgments. MODULATION OF VIBRISSA DAMPING Active sensing may also be engaged at the level of the follicle. Given that vibrissa resonance may not facilitate the perception of contact (or could even impair pro- cessing, for example, by introducing “ringing” in the system when precise contact times are desired), an intriguing hypothesis is that a perceiving rodent could modulate the expression of vibrissa resonance by regulating damping in the follicle (e. Initial calculations suggest that damping by the follicle would be particularly rele- vant for relatively shorter vibrissae, particularly microvibrisssae, but may not signiﬁ- cantly affect the biomechanics of longer vibrissae. The follicle surrounding the base of a greek arc macrovibrissa, for example, occupies only ~0. As such, the longer posterior vibrissae may be more important for encoding airborne signals. TEMPORAL CODING AND VIBRISSA RESONANCE Vibrissa resonance is obviously not required for the vibrissa sensory system to demonstrate temporal coding of high frequency stimuli. Differential frequency ampliﬁcation in response to sinuso- idal stimuli26 or to vibrissa contact with a complex surface,42 is more robust 10–100 msec following the onset of sensory stimulation. An even higher relative number of RSUs were observed to demonstrate tuning over the epoch from 100–500 msec, although the incidence of neurons driven by any frequency was decreased for this epoch. The onset response could encode initial vibrissa contact and/or somatotopic position, while the later sus- tained/developing response could encode the frequency of vibrissa motion. The map in SI may dynamically evolve over the ﬁrst 100 msec, transitioning from a map representing space to one representing frequency. This temporal distribution of signals could help resolve an important ambiguity in the place code proposed above, speciﬁcally, that a given place in a map also has a somatotopic assignment in addition to a frequency meaning. Several other mechanisms, including the integration across multiple vibrissae in an isofrequency column, and ﬁne temporal cues, could also help resolve this potential interpretive problem.
One or more interneu- Table 9•2 Components of a Reflex Arc rons may carry impulses to and from the brain 40 mg levitra extra dosage overnight delivery what is an erectile dysfunction pump, may function within the COMPONENT FUNCTION brain levitra extra dosage 40 mg visa erectile dysfunction blood pressure, or may distribute impulses to Receptor End of a dendrite or specialized cell that responds to different regions of the spinal cord. Motor neuron, or efferent neuron— system response; usually requires interneurons a cell that carries impulses away Motor neuron Carries impulses away from the CNS toward the from the CNS. Motor impulses leave effector, a muscle, or a gland Effector A muscle or gland outside the CNS that carries out a the cord through the ventral horn of response the spinal cord gray matter. Injection of anesthetic into the epidural space in the lumbar region of the spine (an “epidural”) is 2 Sensory often used during labor and childbirth. This process of demyelination (quadriceps muscle) slows the speed of nerve impulse conduction and disrupts nervous system communication. Genetic makeup, in combination with environmental fac- tors, may trigger MS. Some research suggests that a prior viral or bacterial infection, even one that occurred many Figure 9-14 The patellar (knee-jerk) reflex. ZOOMING IN How many MS is the most common chronic CNS disease of young total neurons are involved in this spinal reflex? The disease affects women transmitter is released at the synapse shown by number 5? MS progresses at different rates depending on the contracting, is one example of a spinal reflex. If you tap individual, and it may be marked by episodes of relapse the tendon below the kneecap (the patellar tendon), the and remission. At this point, no cure has been found for muscle of the anterior thigh (quadriceps femoris) con- MS, but drugs that stop the autoimmune response and tracts, eliciting the knee-jerk reflex (Fig. Such stretch reflexes may be evoked by appropriate tap- Amyotrophic (ah-mi-o-TROF-ik) lateral sclerosis is a ping of most large muscles (such as the triceps brachii in the disorder of the nervous system in which motor neurons arm and the gastrocnemius in the calf of the leg). The progressive destruction causes muscle flexes are simple and predictable, they are used in physical atrophy and loss of motor control until finally the affected examinations to test the condition of the nervous system. Poliomyelitis (po-le-o-mi-eh-LI-tis) (“polio”) is a Medical Procedures Involving the viral disease of the nervous system that occurs most com- Spinal Cord monly in children. Polio is spread by ingestion of water contaminated with feces containing the virus. It is sometimes necessary to remove the gastrointestinal tract leads to passage of the virus into a small amount of cerebrospinal fluid (CSF) from the the blood, from which it spreads to the CNS. CSF is the fluid that circu- tends to multiply in motor neurons in the spinal cord, lates in and around the brain and spinal cord. This fluid leading to paralysis, including paralysis of the breathing is taken from the space below the spinal cord to avoid muscles. Because the spinal cord is Polio has been virtually eliminated in many countries only about 18 inches long and ends above the level of through the use of vaccines against the disease—first the the hip line, a lumbar puncture or spinal tap is usually injected Salk vaccine developed in 1954, followed by the done between the third and fourth lumbar vertebrae, at Sabin oral vaccine. A goal of the World Health Organiza- about the level of the top of the hipbone. The sample tion (WHO) is the total eradication of polio by worldwide that is removed can then be studied in the laboratory vaccination programs. Anesthetics or medications are Tumors Tumors that affect the spinal cord commonly sometimes injected into the space below the cord. They anesthetic agent temporarily blocks all sensation from are frequently tumors of the nerve sheaths, the meninges, the lower part of the body. Symptoms are caused by pressure on the thesia has an advantage for certain types of procedures or cord and the roots of the spinal nerves. These include THE NERVOUS SYSTEM: THE SPINAL CORD AND SPINAL NERVES 191 Box 9-1 Hot Topics Spinal Cord Injury: Crossing the DivideSpinal Cord Injury: Crossing the Divide pproximately 11,000 new cases of spinal cord injury occur Using neurotrophins to induce repair in damaged nerve tissue. Aeach year in the United States, the majority involving males Certain types of neuroglia produce chemicals called neu- ages 16 to 30. Successfully transplanted donor duces swelling at the site of injury and improves recovery. A ganglion cord tumors are diagnosed by magnetic resonance imag- (GANG-le-on) is any collection of nerve cell bodies lo- ing (MRI) or other imaging techniques, and treatment is cated outside the CNS. The ventral roots of the spinal nerves are a combina- Injuries Injury to the spinal cord may result from tion of motor (efferent) fibers that supply muscles and wounds, fracture or dislocation of the vertebrae, hernia- glands (effectors). The cell bodies of these neurons are lo- tion of intervertebral disks, or tumors. The most common cated in the ventral gray matter (ventral horns) of the causes of accidental injury to the cord are motor vehicle cord.
Causes of compression of the ulnar nerve include infection quality levitra extra dosage 60mg hot rod erectile dysfunction pills, ganglion scarring order 60mg levitra extra dosage overnight delivery erectile dysfunction treatment options exercise, and external pressure, such as chronic compression injury in bicyclists. Sensory impairments in the ulnar aspect of the ring and little fingers and motor impairments in the hypothenar musculature are typical symptoms of this compression neuropathy. Buckup, Clinical Tests for the Musculoskeletal System © 2004 Thieme All rights reserved. Formed by the carpal bones and the flexor retinaculum, the carpal tunnel encloses all of the finger flexor tendons and the median nerve. Causes of carpal tunnel syndrome with stenosis of the tunnel include skeletal changes, bone tumors (ganglia), injuries, and tenosynovitis. Typical signs of compression include nighttime paresthesia and bra- chialgia, morning stiffness, and sensory and motor deficits in the region supplied by the median nerve (atrophy of the thenar musculature). Electromyography and measurement of nerve conduction velocity by electroneurography are important studies in diagnosing carpal tunnel syndrome. Cubital Tunnel Syndrome The ulnar nerve courses through a bony groove posterior to the medial epicondyle. Injury, traction, inflammation, scarring, or chronic compression are the most common causes of damage to the ulnar nerve. Sensory deficits (numbness in the little finger) and motor deficits in the area supplied by the ulnar nerve are typical findings in the presence of a nerve lesion. Electromyography and sensory electroneurography can determine the location of the compression neuropathy. Tests of Motor Function in the Hand Demonstrate motor and sensory deficits in the presence of nerve le- sions. Testing the Pinch Grip Procedure: The patient is asked to pick up a small object between the thumb and the index finger. Unimpaired function of the lumbricals and interossei is essential for this maneuver. Buckup, Clinical Tests for the Musculoskeletal System © 2004 Thieme All rights reserved. Assessment: A sensory deficit on the radial aspect of the index finger, such as can occur in a radial nerve lesion, renders the key grip impos- sible. Buckup, Clinical Tests for the Musculoskeletal System © 2004 Thieme All rights reserved. Where finger flexion is restricted, the test is repeated using an object with a larger diameter. Assessment: In the presence of injuries to the median or ulnar nerve, full finger flexion is not possible and strength is limited. Testing the Chuck Grip Procedure: The precision grip maneuver is evaluated by giving the patient a small ball and having him or her hold on to it. Assessment: This maneuver tests the strength of adduction in the thumb and finger flexion and thus allows evaluation of the median and ulnar nerves to be assessed. Testing Grip Strength Procedure: The examiner pumps a blood pressure cuff to 200 mmHg (about 26. Assessment: Patients with normal hand function should attain a value of 200 mmHg (about 26. Note that the difference in strength between men and women must be taken into account, as must that between adults and children. Radial Nerve Palsy Screening Test Screening method for the assessment of radial nerve palsy. Procedure: The patient is asked to extend his or her wrist with the elbow flexed 90°. Assessment: In radial nerve palsy affecting the wrist extensors, the patient will be unable to extend the wrist. In radial nerve palsy, the patient will be unable to abduct the thumb because of the paralysis of the abductor pollicis longus. Buckup, Clinical Tests for the Musculoskeletal System © 2004 Thieme All rights reserved.
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