By A. Stan. Tennessee Technological University.
The special features of action potentials in Inmanycases cabergoline 0.25 mg line,potassiumconductance cheap 0.5 mg cabergoline otc,gKis cardiac and smooth muscle fibers are de- still increased after the original resting poten- scribed on pages 192 discount 0.25 mg cabergoline free shipping, 70 and 59A buy 0.5mg cabergoline mastercard. Action potential (1) and ion conductivity (2) (nerve and skeletal muscle) 1 2 + “Overshoot” + (20–30mV) 0 0 – Action – potential gNa Action potential gK Threshold After-hyper- polarization Resting Pre- GK depolari- sation Resting GNa 0 Time Time ca. Closed, [mV] activatable + Depolarization 0 – –90mV [mV] Resting potential Na+ + 0 2. Closed, inactivated + 0 – Reversal of potential and start of repolarization In 47 Despopoulos, Color Atlas of Physiology © 2003 Thieme All rights reserved. Propagation of Action Potentials in Action potentials normally run forward (or- thodromic) because each segment of nerve Nerve Fiber fiber becomes refractory when an action Electrical current flows through a cable when potentialpasses(! The metal wire inside the impulses are conducted backwards (anti- the cable is well insulated and has very low- dromic)due,forexample,toelectricalstimula- level resistance, reducing current loss to a tion of nerve fibers from an external source minimum. C) conduct much faster (up to 80 m/s = 180 Propagation of action potentials: The start mph in humans). In the internode regions, a ofanactionpotentialisaccompaniedbyabrief myelin sheath (! The fibers from the surroundings; thus, longitudi- cell membrane that previously was inside nal currents strong enough to generate action negative now becomes positive ( +20 to potentials can travel further down the axon +30mV), thus creating a longitudinal poten- (ca. This results in more rapid tial difference with respect to the adjacent, conduction because the action potentials are still unstimulated nerve segments (internal generated only at the unmyelinated nodes of –70 to –90mV;! This is followed by a Ranvier, where there is a high density of Na+ passive electrotonic withdrawal of charge from channels. This results in rapid, jump-like pas- the adjacent segment of the nerve fiber, caus- sage of the action potential from node to node ing its depolarization. Thesaltatorylengthis another action potential is created in the adja- limited since the longitudinal current (1 to cent segment and the action potential in the 2nA) grows weaker with increasing distance previous segment dissipates (! Before it drops below the threshold Because the membrane acts as a capacitor, level,thesignalmustthereforeberefreshedby the withdrawal of charge represents a capaci- a new action potential, with a time loss of tating (depolarizing) flow of charge that be- 0. Because of the rela- fiber limits the spread of depolarization, as de- tively high Ri of nerve fiber, the outward loops scribed above, the axon diameter (2r) also af- of current cross the membrane relatively close fectstheconductionvelocity,θ(! R ispro-i to the site of excitation, and the longitudinal portional to the cross-sectional area of the current decreases as it proceeds towards the nerve fiber (πr ),2 i. Atthesametime,depolarizationin- therefore require fewer new APs per unit of creasesthedrivingforce(=Em–EK;! K+ fluxing out of the cell therefore fiberdiameterareaccompaniedbyan increase accelerates repolarization. Hence, distal action in both fiber circumference (2πr) and mem- potentials are restricted to distances from branecapacity,K(K! Althoughθdecreases, which the capacitative current suffices to the beneficial effect of the smaller Ri predomi- depolarizethemembranequicklyandstrongly nates because of the quadratic relationship. Otherwise, the Na+ channels will be deactivated before the threshold potential is 48 reached (! Continuous (1a, 1b) and saltatory propagation (2) of action potentials AP AP Myelin sheath Na+ Na+ Action potential (AP) Na+ Depolarization Na+ Action potential Rest 1a Refractory + Na+ Na AP Depo- Depolarization larization 1b 2 B. Pulse propagation (action currents) in myelinated and unmyelinated nerve fibers AP AP 1nA 1nA AP 1 2 ms 2 0. Classification of nerve fibers (in humans) Fiber type Function according to fiber type Diameter Conduction (Lloyd and Hunt types I–IV) (µm) rate (m/s) Aα Skeletal muscle efferent, afferents in muscle 11–16 60 – 80 spindles (Ib) and tendon organs (Ib) Aβ Mechanoafferents of skin (II) 6 –11 30 – 60 Aγ Muscle spindle efferents Aδ Skin afferents (temperature 1– 6 2 – 30 and „fast“ pain) (III) B Sympathetic preganglionic; 3 3 –15 visceral afferents C Skin afferents (“slow” pain); 0. They can facilitate or inhibit nerve cell from an external source, current the neuronal transmission of information or flows from the positive stimulating electrode processthemwithotherneuronalinput. Atthe (anode) into the neuron, and exits at the nega- chemical synapse, the arrival of an action tive electrode (cathode). Depending on distance from each other, then stimulating the the type of transmitter and receptor involved, nerve (containing multiple neurons) and rec- the effect on the postsynaptic membrane may ording the time it takes the summated action either be excitatory or inhibitory, as is de- potential to travel the known distance. In the case of the motor body to high-voltage electricity, especially end-plate (! Some of the electrical outlet) and low contact resistance vesicles are already docked on the membrane (barefeet,bathtubaccidents),primarilyaffects (active zone), ready to exocytose their con- the conduction of impulses in the heart and tents.
Additionally buy cabergoline 0.25mg on-line, anatomic exposure is necessarily limited to what is clinically war- ranted purchase cabergoline 0.25 mg on-line, and usually this is minimized to improve recovery time 0.5 mg cabergoline otc, hampering visual- ization in many situations discount 0.5 mg cabergoline overnight delivery. In this regard, virtual reality simulators may help residents advance sooner by demonstrating more complete dissections and underlying anatomy. Technical expertise is a combination of practice, supervision providing guidance, and the repetitive use of the hands as needed for motor learning. The technical side is currently handled by direct observation and apprenticeship, with progressive responsibility based on certain steps or levels. One training tool is cadaveric dissection that provides residents the potential to improve anatomic understanding, visuospatial perception, and motor skills. Cadav- eric dissections are interactive, three-dimensional, and relatively transferable to the operating room setting. However, dissection also has important limitations including significant costs (preparation, facilities, instructors, and equipment), limited avail- ability of specimens, and the substantial differences between living and cadaveric tissues. Finally cadaveric dissection involves a substantial time commitment and is not amenable to repeated rehearsal of a specific procedure. Animal dissection provides opportunities to improve visuospatial and motor skills, but the technique has both practical and ethical limitations and the anatomic differences are usually significant. Thus, current training involves a large amount of direct intraoperative assisting to allow direct visualization of human anatomy and exposure and small (but key) cadaveric and small animal dissection experience to augment the clinical experience gained over many years. Technical competence is achieved through “gradual delegation of earned responsibility for investigative and operative care to penultimate levels. Learn to relate and work effectively with colleagues in medicine and surgery and other health care professionals and ensure the development © 2005 by CRC Press LLC of a keen sense of responsibility and compassion toward patients and their families 5. Understand the impacts of neurosurgery on society including medical ethics, health care economics, law, prevention of disease, and promotion of health 6. Develop an understanding of clinical and basic research techniques includ- ing biostatistics and epidemiology Residents must assume graduated responsibility throughout the course of their residencies in terms of background knowledge, pre- and postoperative management, operative experience and independence in decision making. However, supervision is critical to a training program, and feedback from more experienced individuals is essential to education along with a constant and sincere effort to learn on the part of the resident. Patient care is the core background to neurosurgical education and thus intimate knowledge of patients forms the basis for informed decision making and increased participation by residents in patient care decisions and management. The objectives for technical competence build upon progressive training experience in neurosurgical procedures, usually in an apprenticeship mode under direct supervision. The current fixed length residency program is relatively short, compared to the large number of judgment skills, procedures, and care issues that must be adequately taught. For that reason, some flexibility in training length may be important to accommodate and overcome such differences. These limitations are compounded by insufficient exposure to and understanding of less common cases because residents commonly handle more common situations. The skills routinely taught in most residency programs are primarily aimed at a high quality clinical practice situations. They are not necessarily directed toward academic investigations in the fields of basic neuroscience, translational neuro- science, or clinical neuroscience. For many years, the minimum requirement for the adequate pursuit of quality basic neuroscience has been at least 3 to 5 years of experience beyond residency, at the graduate student (i. Unless a clinician investigator is competitive in obtaining funding, it is unlikely that research of sufficiently high quality will continue to make valuable contributions to neurosurgery and the wider field of neuroscience. Developing and maintaining adequate clinical credentials and sufficient research experience to be truly compet- itive are difficult challenges at both the resident trainee and faculty levels. These © 2005 by CRC Press LLC abilities are under-emphasized. The difficulties are compounded by the additional requirements for teaching and mentoring, as well as family commitments and obli- gations (Figure 16. Ethically, family commitments cannot be handled by a sub- stitute person and have a much higher priority than any of the other demands. This initial degree provides some training in clinical investigation and trial design and can provide a base upon which to build further training.
During that time discount cabergoline 0.5 mg online, a famous columnist for the New York Times generic cabergoline 0.5 mg with mastercard, James Reston 0.25 mg cabergoline free shipping, had to undergo surgery and elected to use acupuncture instead of pain medication 0.5mg cabergoline mastercard, Benefits and he wrote some convincing stories on its effectiveness. The World Health Organization (WHO) recom- Today acupuncture is being practiced in all 50 states mends acupuncture as an effective treatment for over by more than 9,000 practitioners, with about 4,000 MDs forty medical problems, including allergies, respiratory including it in their practices. Acupuncture has shown no- conditions, gastrointestinal disorders, gynecological table success in treating many conditions, and more than problems, nervous conditions, and disorders of the eyes, 15 million Americans have used it as a therapy. In 2002, a center in Maine has been resistant to researching it, as it is based on con- received a unique grant to study acupuncture treatment cepts very different from the Western scientific model. Japanese acupuncture uses extremely thin on relaxation response helped those abusing drugs and needles and does not incorporate herbal medicine in its alcohol better deal with the anxiety and life circum- practice. Auricular acupuncture uses acupuncture points stances thought to lead them to substance abuse. In France, where acupuncture is Acupuncture is an effective and low-cost treatment very popular and more accepted by the medical estab- for headaches and chronic pain, associated with prob- lishment, neurologist Paul Nogier developed a system of lems like back injuries and arthritis. It has also been used 16 GALE ENCYCLOPEDIA OF ALTERNATIVE MEDICINE 2 BL ST LI GV CV SI KI LU HE PE TW BL GB SP LV Traditional Chinese medicine teachings state that channels of energy flow throughout the body, and that disease is caused by too much or to little flow of energy along these channels. In the illustration, points are shown on the bladder (BL), conception vessel (CV), gall bladder (GB), governing vessel (GV), heart (HE), kidney (KI) large intestine (LI), liver (LV), lung (LU), pericardium (PE), small intestine (SI), spleen (SP), stomach (ST), and triple warmer (TW) meridians. Acupuncture is generally ble and is found in the environment in the air, water, food most effective when used as prevention or before a and sunlight. In the body, it is the invisible vital force that health condition becomes acute, but it has been used to creates and animates life. In 2002, amounts of chi, and we also get acquired chi from the the National Institutes of health announced that pain food we eat and the air we breathe. Chi travels through the ited in treating conditions or traumas that require surgery body along channels called meridians. In the Chinese system, there are twelve main organs: the lung, large intestine, stom- Description ach, spleen, heart, small intestine, urinary bladder, kid- ney, liver, gallbladder, pericardium, and the “triple Basic ideas of Chinese medicine warmer,” which represents the entire torso region. Each Chinese medicine views the body as a small part of the organ has chi energy associated with it, and each organ universe, and subject to universal laws and principles of har- interacts with particular emotions on the mental level. Chinese medicine does not draw a sharp there are twelve organs, there are twelve types of chi line, as Western medicine does, between mind and body. Chinese are every bit as influential on disease as purely physical doctors connect symptoms to organs. Each organ has a different profile of symp- different symbols and ideas to discuss the body and health. Another basis of Chinese theo- of measurable physical processes made up of chemical reac- ry is that the world and body are made up of five main tions, the Chinese use ideas like yin and yang, chi, the organ elements: wood, fire, earth, metal, and water. These ele- system, and the five elements to describe health and the ments are all interconnected, and each element either body. To understand the ideas behind acupuncture, it is generates or controls another element. The Chinese the universe and the body can be described by two sepa- system uses elements and organs to describe and treat rate but complementary principles, that of yin and yang. For instance, the kidney is associated with For example, in temperature, yin is cold and yang is hot. In light, yin is dark and ney is weak, then there might be a corresponding fire yang is bright; in direction yin is inward and downward problem in the heart, so treatment might be made by and yang is outward and up, and so on. Nothing is ever acupuncture or herbs to cool the heart system and/or in- completely yin or yang, but a combination of the two. These two principles are always interacting, opposing, and influencing each other. The goal of Chinese medi- The Chinese have developed an intricate system of cine is not to eliminate either yin or yang, but to allow how organs and elements are related to physical and men- the two to balance each other and exist harmoniously to- tal symptoms, and the above example is a very simple one. For instance, if a person suffers from symptoms Although this system sounds suspect to Western scientists, of high blood pressure, the Chinese system would say some interesting parallels have been observed. For in- that the heart organ might have too much yang, and stance, Western medicine has observed that with severe would recommend methods either to reduce the yang or heart problems, kidney failure often follows, but it still to increase the yin of the heart, depending on the other does not know exactly why. Another fundamental concept of Chinese medi- organ system or chi meridians, and the goal of any reme- cine is that of chi (pronounced chee, also spelled qi).