Loading

Search

By T. Curtis. State University of New York College of Environmental Science and Forestry.

This teleological consideration is also related to theoretical work that has addressed the connectivity patterns by which neural elements can serve the functional needs of segregation and of integration while maximizing their proficiency (or complexity) in information processing generic provigil 100 mg with visa. The fundamental difference between the motor system and the visual (or somatosensory) system is that in the former there is almost no functional benefit from segregation. In other words, for a given neural unit the probability distribution of interactions with other neural units does not present distinct peaks, as in sensory systems. Translated into movements, this means that in real life there is virtually no such thing as a single muscle/single joint movement for which it would make sense to implement a segregated representation. This does not mean that single neurons cannot elicit motor actions, but only that it is virtually impossible to hardwire functional demands into the response properties of single neurons (see however Brecht et al. A classical debate in motor control research has been whether muscles or movements are “represented” in the primary motor cortex. In a way, this is equivalent to asking whether a piano functions by playing a sonata or striking chords. In other words, this debate is conceptually related to the debate about “grandmother neurons” in the visual system. In a more contemporary view, func- tionally meaningful motor acts arise from the concerted activity of many neural units, just as a sonata arises from the effect of playing a certain complex pattern of piano keys. However, in contrast with the concert pianist, we do not know which sonata is on the program today and under which biophysical circumstances we will need to play it. These prospective uncertainties impose on the motor control system the need to retain a high flexibility that permits adaptation to variable demands by virtue of flexibly associating the available neural units into a customized pattern that will yield the required action result. If we assume that movements and their direction are coded by population activity, the functional performance of such constantly regrouped populations would benefit from single keys striking several chords and single chords being accessible via several keys, i. The probability for interactions is higher within limbs than across limbs, and facial movements will again be fairly independent of those in upper and lower extremities. This is not to say that for instance ballistic arm movements will not require coor- dinated output to trunk and leg muscles, but just that the predictability is lower than for within-limb coordination. The functional anatomical consequences of this pseudo-segregation have lured many researchers into the jargon of face, arm/hand, Copyright © 2005 CRC Press LLC and leg “areas,” as if these were strictly segregated distinct representations. The data available only suggest that embedded into one continuous motor representation a greater degree of spatial separation and a lower degree of overlap can be found for the representation of different movements across than within these body parts.

generic 100mg provigil with amex

Benzodiazepines employed in the treatment of Nearly all central nervous system depressants have anxiety should be used in the lowest effective dose for some capacity to suppress seizures by virtue of their de- the shortest duration so that they will provide maxi- pressant activity on the brain and spinal cord 200 mg provigil. For most types of anxiety, that depress epileptiform activity and are used in the none of the benzodiazepines is therapeutically superior treatment of epilepsy and seizure disorders (see to any other. A benzodiazepine with a long half-life Sedation, Amnesia, and Anesthesia should be considered if the anxiety is intense and sus- tained. A drug with a short half-life may have advan- Benzodiazepines have the capacity to produce a calm- tages when the anxiety is provoked by clearly defined ing effect and to cause anterograde amnesia, in which circumstances and is likely to be of short duration. Benzo- Insomnia diazepine-induced sedation and amnesia are deemed useful in the preparation of patients for anesthesia, All of the benzodiazepines will produce sedative– surgery, and other frightening or unpleasant medical hypnotic effects of sufficient magnitude to induce sleep, and dental procedures and diagnostic tests. However, the aim is a frequently used anesthetic benzodiazepine (see in the treatment of sleep disorders is to induce sleep Chapter 25). Extensive sleep studies have been conducted with a Benzodiazepines have the capacity to depress polysyn- variety of sedative–hypnotic drugs, and all of these aptic reflexes and have been shown to decrease decere- drugs appear to alter the normal distribution of rapid brate rigidity in cats and spasticity in patients with cere- eye movement (REM) and non-REM sleep. What is not clear is whether they can, in older sedative–hypnotic agents markedly depress REM humans, relax voluntary muscles in doses that do not sleep. In contrast, when the benzodiazepines are used in cause considerable central nervous system depression. As with treatment of anxiety, the choice often prescribed for patients who have muscle spasms and pain as a result of injury. In these circumstances, the sedative and anxiolytic properties of the drug also may Pharmacokinetic Properties promote relaxation and relieve tension associated with TABLE 30. Benzodiazepines Alcohol and Sedative–Hypnotic Withdrawal Time to Elimination Withdrawal from long-term high-dose use of alcohol or Drug peak (hr) half-life (hr)* sedative–hypnotic drugs can be life threatening if phys- Chlordiazepoxide 0. These include drowsiness, ex- Many benzodiazepines are metabolized by the cy- cessive sedation, impaired motor coordination, confusion, tochrome P450 (CYP) enzyme designated CYP3A4.

Some of the actions of complement are: ulates the cells to multiply rapidly and produce large ◗ It coats foreign cells to help phagocytes recognize and numbers (clones) of plasma cells buy provigil 200mg lowest price. BODY DEFENSES, IMMUNITY, AND VACCINES ✦ 351 Box 17-1 A Closer Look Antibodies: A Protein Army That Fights DiseaseAntibodies: A Protein Army That Fights Disease ntibodies are proteins secreted by plasma cells (activated immunoglobulins that vary in molecular size and in function AB cells) in response to specific antigens. Because the plasma contains other globulins as well, bodies, because they are the first to be produced in an immune antibodies have become known as immunoglobulins (Ig). Each time a person is invaded by disease organisms, his or her cells manufacture antibodies that provide im- Artificially Acquired Immunity munity against the infection. Because the host is ac- A person who has not been exposed to repeated small tively involved in the production of antibodies, this type doses of a particular organism has no antibodies against of immunity is called active immunity. This 352 ✦ CHAPTER SEVENTEEN protective process is known as vacci- Table 17•1 Antigen-Antibody Interactions and Their nation (vak-sin-A-shun), or immu- Effects nization, and the solution used is Interaction Effects called a vaccine (vak-SENE). Ordinar- ily, the administration of a vaccine is Prevention of attachment A pathogen coated with antibody is a preventive measure designed to pro- Antibody prevented from attaching to a cell. Clumping of antigen Antibodies can link antigens together, (The term even comes from the Latin forming a cluster that phagocytes word for cow, referring to cowpox, Foreign cell can ingest. Mandatory vaccination has Antibody been discontinued because the chance of adverse side effects from the vaccine is thought to be greater than the prob- Help with phagocytosis Phagocytes can attach more easily to ability of contracting the disease. Also pregnant women should not Activation of complement When complement attaches to anti- receive live virus vaccine because the Complement body on a cell surface, a series of virus could cross the placenta and harm Antibody reactions begins that activates com- the fetus. Types of Vaccines Vaccines can Activation of NK cells NK cells respond to antibody adhering be made with live organisms or with NK cell to a cell surface and attack the cell. Antibody If live organisms are used, they must Foreign cell be nonvirulent for humans, such as the cowpox virus used for smallpox Box 17-2 Clinical Perspectives Too Much Stress Makes The Immune System SickToo Much Stress Makes The Immune System Sick he impact of stress on the immune system is the most ◗ inhibit histamine release from damaged tissues, thereby Twide-ranging and significant of its many effects on the blocking inflammation and the arrival of phagocytic leuko- body. However, the ab- Box 12-3, Stress: Mechanisms for Coping, suggests some normally high levels of cortisol that appear during periods of strategies for reducing stress. This acellular (aP) vaccine usually tered with heat or chemicals to reduce its harmfulness, is given in a mixture with diphtheria toxoid and tetanus but it can still function as an antigen to induce immunity. Boosters In many cases, an active immunity acquired Routine inoculation against Haemophilus influenzae by artificial (or even natural) means does not last a life- type B (Hib) has nearly eliminated the life-threatening time. The number of booster injections vaccine is given in either two doses or three doses begin- recommended varies with the disease and with an indi- ning at 2 months of age.