By E. Raid. United States Coast Guard Academy.
The map from parallel 80 mg top avana amex, not to the rate of firing of single neu- cortex to muscles also depends on arm position rons cheap top avana 80mg. For ex- the burst frequency codes movement velocity ample purchase top avana 80mg without a prescription, when the elbow started in flexion top avana 80 mg sale, stim- and the burst duration codes the duration of ulation at one site caused it to extend to its fi- the movement 80 mg top avana free shipping. The force exerted elbow flexed to place the hand at the same po- by muscles is a summed average of the ouput sition. Spontaneous movements of the hand to of single cells that fire at variable rates and the the mouth followed the same pattern of mo- synchronization of assemblies of M1 neurons tion and EMG activity as stimulation-evoked during specific phases of a motor task. Thus, within the larger arm and gle cell activity in the motor cortex is most in- hand representation, stimulation-evoked pos- tense for reaching at a particular magnitude tures were organized across the cortex as a map and direction of force. All the evoked postures suggested typ- sembly of cells becomes active, the discharge ical behaviors such as feeding, a defensive pattern of a neuron within that population may movement, reaching, flinching, and others. As the active population Evoked postures were also found for the leg, evolves to include cells that had not previously in which stimulation elicited movements that participated or to exclude some of the cells that converged the foot from different starting had been active, the assembly becomes a positions to a single final location within its unique representation of different information ordinary workspace, much like what has about movement. The M1 Functional imaging studies reveal a small ac- computes the location of a target, the hand tra- tivation in ipsilateral motor cortex during sim- jectory, joint kinematics, and torques to reach ple finger tapping. A study by Cramer and col- and hold an object—the patterns of muscle ac- leagues found a site of ipsilateral activation tivation needed to grasp the item—and relates when the right finger taps to be shifted ap- a particular movement to other movements of proximately 1 cm anterior, ventral, and lateral the limb and body. These parameters may be to the site in M1 activated by tapping the left manipulated by therapists during retraining finger. The degree to which dis- to the uncrossed corticospinal projection, to an charges from M1 represent the extrinsic at- aspect of motor control related to bimanual ac- tributes of movements versus joint and muscle- tions, or to sensory feedback. The M1 in mon- 12 Neuroscientific Foundations for Rehabilitation keys contains a subregion located between the from steady walking, during either the stance neuronal representations for the digits and face or swing phase of gait as needed. These neu- in which approximately 8% of cells are active rons may be especially important for flexor during ipsilateral and bilateral forelimb move- control of the leg. Transcranial brains and far more unreliable in functional im- magnetic stimulation studies in man show aging studies. This phase Since motoneurons in M1 participate in, or requires ankle dorsiflexion at heel strike (see represent particular movements and contribute Chapter 6). For functional neuroimaging stud- to unrelated movements, cells may functionally ies of the leg, the large M1 contribution to dor- shift to take over some aspects of an impaired siflexion of the ankle makes ankle movements movement in the event a cortical or subcortical a good way to activate M1 (see Color Fig. As described later terest in this movement within M1 also sug- in this chapter and in Chapters 2 and 3, these gests that a cognitive, voluntary cueing strategy motor and neighboring sensory neurons adapt during locomotor retraining is necessary to best their synaptic relationships in remarkably flex- get foot clearance during the swing phase of ible ways during behavioral training. Future ex- gait and to practice heel strike in the initial perimental studies of the details of these com- phase of stance. The alternative strategy to flex putations, of the neural correlates for features the leg enough to clear the foot, when cortical of upper extremity function, and of the rela- influences have been lost, is to evoke a flexor tionships between neuronal assemblies in dis- reflex withdrawal response. Spinal segmental sensory inputs, de- a flat surface under constant sensory condi- scribed later in this chapter, may be more crit- tions. The cells increase their discharges when ical to the temporal features of leg movements a task requires more accurate foot placement, during walking. Changing the trajectory of the modulated by sensory feedback for their anti- limbs to step over obstacles also increases cor- gravity function. The cells fire es- Potential overlapping representations between pecially during a visually induced perturbation paraspinal and proximal leg muscle represen- Plasticity in Sensorimotor and Cognitive Networks 13 tations may serve as a mechanism for plastic- tribution to the corticospinal tract and have ity with gait retraining. Each of the six cortical Primary motor cortex also contains the giant motor areas that interact with M1 has a sepa- pyramidal cells of Betz. These unusual cells re- rate and independent set of inputs from adja- side exclusively in cortical layer 5. They ac- cent and remote regions, as well as parallel, count for no more than approximately 50,000 separate outputs to the brain stem and spinal of the several million pyramidal neurons in cord. Approximately 75% sup- ative contributions to the corticospinal tract ply the leg and 18% project to motor pools for and their functional roles. These motor areas the arm,53 but Betz cells constitute only 4% of also interact with cortex that does not have di- the neurons of the leg representation that are rect spinal motoneuron connections. Consis- totopically arranged prefrontal to premotor, tent with this tendency, pyramidal tract lesions corticostriatal, corticotectal, and thalamocorti- tend to allow an increase in extension over flex- cal connections. Functional imaging has revealed a somato- Ankle dorsiflexion and plantar flexion acti- topic distribution of activation during upper ex- vate the contralateral M1, S1, and SMA in hu- tremity tasks in SMA, dorsal lateral premotor, man subjects, although the degree of activity and cingulate motor cortices. With an isometric contraction functional, rather than an anatomical repre- of the tibialis anterior or gastocnemius mus- sentation. When walking on uneven sur- finding that one limb can manage a previously faces and when confronted by obstacles, BA6 learned task from another limb may have im- and 7, S1, SMA, and the cerebellum partici- plications for compensatory and retraining pate even more for visuomotor control, bal- strategies after a focal brain injury.
Young athletes may use the drug for body growth and progress toward epiphyseal closure order top avana 80 mg on line, record- building and to enhance athletic performance buy top avana 80mg otc. In addi- • For clients with diabetes insipidus 80 mg top avana free shipping, assist them to develop tion order top avana 80mg with visa, the highest levels of physiologic hormone are se- a daily routine to monitor their response to drug therapy creted during adolescence top avana 80 mg for sale. The combination of high (eg, weigh themselves, monitor ﬂuid intake and urine out- pharmacologic and high physiologic amounts increases put for approximately equal amounts, or check urine spe- risks of health problems from excessive hormone. Middle-aged and older adults may use growth • Interview and observe for compliance with instructions hormone to combat the effects of aging, such as de- for taking the drug(s). Although it is not illegal for physicians to prescribe growth hormone for these populations, such use is unproven in safety and ef- PRINCIPLES OF THERAPY fectiveness. Endocrinologists emphasize that optimal adult levels of growth hormone are unknown and 1. Hypothalamic hormones are rarely used in most clini- using the drug to slow aging is unproven and poten- cal practice settings. The drugs should be prescribed by tially dangerous because the long-term effects are un- physicians who are knowledgeable about endocrinol- known. Most drug therapy with pituitary hormones is given to tension, and increased risk of serious cardiovascular replace or supplement naturally occurring hormones disease (eg, heart failure). There is also concern about in situations involving inadequate function of the pitu- a possible link between growth hormone, which stim- ulates tumor growth, and cancer. Growth hormone stimulates the release of insulin-like growth factor-1 Nursing Notes: Apply Your Knowledge (IGF-1, also called somatomedin), a substance which circulates in the blood and stimulates cell division. Most tumor cells have receptors that recognize IGF-1, After surgery for a brain tumor, you note that Mr. Willis has bind it, and allow it to enter the cell, where it could trig- excessive, dilute urine output (8000 mL/24 h). This concern may be diagnoses deﬁcient antidiuretic hormone production and pre- greater for middle-aged and older adults, because ma- scribes lypressin (Diapid), a synthetic vasopressin. What assess- lignancies are more common in these groups than in ment data will indicate that this medication is effective? Observe for therapeutic effects Therapeutic effects vary widely, depending on the particular pitu- itary hormone given and the reason for use. With gonadorelin and related drugs, observe for ovulation Therapeutic effects depend on the reason for use. Note that differ- or decreased symptoms of endometriosis and absence of men- ent formulations are used to stimulate ovulation and treat endo- struation. With corticotropin, therapeutic effects stem largely from Corticotropin is usually not recommended for the numerous non- increased secretion of adrenal cortex hormones, especially the endocrine inﬂammatory disorders that respond to glucocorticoids. With chorionic gonadotropin and menotropins given in cases of female infertility, ovulation and conception are thera- peutic effects. With chorionic gonadotropin given in cryptorchidism, the therapeutic effect is descent of the testicles from the abdomen to the scrotum. With growth hormone, observe for increased skeletal growth Indicated by appropriate increases in height and weight. With antidiuretics (desmopressin, lypressin, and vaso- These effects indicate control of diabetes insipidus. With oxytocin given to induce labor, observe for the begin- ning or the intensifying of uterine contractions. With oxytocin given to control postpartum bleeding, ob- serve for a ﬁrm uterine fundus and decreased vaginal bleeding. With octreotide given for diarrhea, observe for decreased Octreotide is often used to control diarrhea associated with a number and ﬂuidity of stools. With gonadorelin, observe for headache, nausea, light- Systemic reactions occur infrequently. With protirelin, observe for hypotension, nausea, headache, Although adverse effects occur in about 50% of patients, they are lightheadedness, anxiety, drowsiness. With corticotropin, observe for sodium and ﬂuid retention, These adverse reactions are in general the same as those produced edema, hypokalemia, hyperglycemia, osteoporosis, increased by adrenal cortex hormones. Severity of adverse reactions tends to susceptibility to infection, myopathy, behavioral changes.
Drugs that decrease effects of caffeine: (1) Carbamazepine cheap 80mg top avana visa, phenytoin order 80 mg top avana amex, rifampin These drugs induce drug-metabolizing enzymes cheap 80mg top avana fast delivery, thereby decreas- ing blood levels and increasing clearance of caffeine generic top avana 80mg with mastercard. CHAPTER 16 CENTRAL NERVOUS SYSTEM STIMULANTS 259 Drug facts and comparisons cheap 80 mg top avana visa. What is the rationale for treating narcolepsy and ADHD tics: Drug and disease management, 7th ed. Efﬁcacy of a mixed am- phetamine salts compound in adults with attention-deﬁcit/hyperactivity disorder. Clinically significant pharmacokinetic interactions between dietary caffeine and medications. Differentiate subtypes and functions of sympa- the autonomic nervous system are stimulated. Identify physiologic effects of the parasympa- drugs affecting the autonomic nervous system. Differentiate subtypes and functions of parasympathetic nervous system receptors. Autonomic nerve im- pulses are carried through preganglionic ﬁbers, ganglia, and The nervous system is composed of two main divisions, the postganglionic ﬁbers. Preganglionic impulses travel from the central nervous system (CNS) and the peripheral nervous CNS along the preganglionic nerves to ganglia. The central nervous system includes the composed of the terminal end of the preganglionic nerve and brain and spinal cord. The peripheral nervous system in- clusters of postganglionic cell bodies. A neurotransmitter is cludes all the neurons and ganglia found outside the CNS. The postganglionic input from the periphery to the CNS and modify motor out- impulses travel from ganglia to effector tissues of the heart, put through the action of reﬂex arcs. The efferent neurons blood vessels, glands, other visceral organs, and smooth carry motor signals from the CNS to the peripheral areas of muscle (Fig. The efferent portion of the peripheral nervous sys- The main neurotransmitters of the ANS are acetylcholine tem is further subdivided into the somatic and autonomic ner- and norepinephrine (see Chap. The somatic nervous system innervates sized from acetylcoenzyme A and choline and released at skeletal muscles and controls voluntary movement. The ANS, preganglionic fibers of both the SNS and PNS and at post- without conscious thought or effort, controls involuntary activ- ganglionic fibers of the PNS. Acetylcholine is also released ities in the visceral organs of the body such as the heart, smooth from postganglionic sympathetic neurons that innervate the muscle, and secretory glands. These functions can be broadly sweat glands and from motor neurons of the somatic ner- described as activities designed to maintain a constant inter- vous system that innervate the skeletal muscles. The nerve nal environment (homeostasis), to respond to stress or emer- fibers that secrete acetylcholine are called cholinergic gencies, and to repair body tissues. Norepinephrine is synthesized from the amino acid centers in the CNS, including the hypothalamus, brain stem, tyrosine by a series of enzymatic conversions that also pro- and spinal cord. The autonomic nervous system is subdivided duce dopamine and epinephrine (ie, tyrosine → dopamine into the sympathetic nervous system (SNS) and the parasym- → norepinephrine → epinephrine). Norepi- sues in the sympathetic and parasympathetic nervous systems nephrine is released at most postganglionic fibers of the 261 262 SECTION 3 DRUGS AFFECTING THE AUTONOMIC NERVOUS SYSTEM The Human Nervous System Central Nervous System (CNS) Peripheral Nervous System (brain and spinal cord) (neurons and ganglia outside the brain and spinal cord) Afferent (sensory) Efferent (motor) Neurons Neurons Somatic Nervous System Autonomic Nervous System (ANS) (voluntary) (involuntary) Sympathetic Nervous System (SNS) Parasympathetic Nervous System (PNS) (adrenergic) (cholinergic) Figure 17–1 Divisions of the human nervous system. Muscarinic receptors Parasympathetic Acetylcholine Heart ganglion Blood vessels Acetylcholine Nicotinic receptors Glands Parasympathetic Visceral organs Postsynaptic nervous system Presynaptic neuron Smooth muscle (PNS) neuron Acetylcholine Muscarinic receptors Presynaptic Sympathetic ganglion neuron Sweat glands Dopamine Dopamine receptors Postsynaptic neuron Renal vascular Sympathetic nervous smooth muscle system with sympatho- Nicotinic receptors adrenal branch Alpha, Beta receptors Norepinephrine Heart Acetylcholine Blood vessels Glands Visceral organs Smooth muscle Epinephrine and Adrenal medulla norepinephrine (nicotinic receptors) Somatic nervous system Nicotinic receptors Skeletal muscle Acetylcholine Figure 17–2 Organization of the autonomic and somatic nervous systems. This Acetylcholine and norepinephrine act on receptors in body is a deviation from the normal postganglionic neuro- organs and tissues to cause parasympathetic or sympathetic transmitter, which is norepinephrine. Stimulation of both systems causes exci- These responses are protective mechanisms designed to tatory effects in some organs but inhibitory effects in others. The However, most organs are predominantly controlled by one intensity and duration of responses depend on the amounts of system. The two divisions of the ANS are usually antagonistic norepinephrine and epinephrine present.
Sometimes there may be as many as seven to eight paragraphs order top avana 80mg amex, each dealing with a particular aspect discount 80mg top avana mastercard. However cheap 80mg top avana overnight delivery, while IMRAD is a useful structure for authors to follow safe top avana 80 mg, it is not reader-friendly buy top avana 80mg mastercard. The main message is at the end (if at all) which is not a logical place to put it. However, the last two or three genera- tions of scientists have become used to it, and therefore if you want to communicate with them then you must conform to that structure. Under no circumstances, however, should you use this structure for anything other than original scientific papers, and perhaps some papers for other professionals who are somehow expecting that you write this way. The trouble is that they end up writing to please themselves, not the reader (see false feedback loop). Instructions to Authors Most academic journals publish a wide range of specific rules on what contributions they seek and how they wish to have them presented (see style guide). Most of them go into considerable detail, with instructions on the size of paper, how to lay out the first page, copy- right and reprints, and the number and style of references. Such differences, although subtle, can give useful information to those planning where they should target their paper. This should not be a problem if you make sure that you do not write a paper without first deciding where you wish it to be published (see brief setting); indeed the instructions should make things clearer and easier. One warning, however: when it comes to working out the precise market requirements of a journal, the Instructions to Authors are only one part of the picture. There are many aspects of a paper, such as the way in which the title is written, or the favoured style, that can be discovered only by careful analysis of the papers published in your target journal (see evidence-based writing). Interviewing The ability to carry out a good interview gives writers a valuable tool. It enables them to gather information quickly from those who have expertise in a given area, and in a language that, because it is informal and spoken, is more likely to pass the pub test and be accessible to the target readers. The quality of an interview, however, depends on how well you have chosen the person to be interviewed. Watch for biases and hidden agendas – and if possible balance one expert with another. Once you have found your interviewee, the following step-by-step plan should be helpful: • Be absolutely clear before you start what you want to achieve. There are, broadly speaking, three reasons for an interview: (1) to get facts and information; (2) to add opinion or description to facts that you already have, and (3) to provide information for a profile of the interviewee. Use a technique such as branching to work out the information you need, and use this to construct a checklist of questions. Group these questions into three or four broad areas and either memorize this summary or write it down on a piece of paper. Check your equipment: most writers have etched on their memories the disas- trous times when they discovered that their tape recorder had broken, or had to borrow a pen or some pieces of paper from the interviewee. Interviews are not the time to make a fashion statement: the more acceptable you appear to the interviewee, the more likely you will be to get good quality informa- tion. This is the time to set any ground rules (see off the record; non-attributable information). These should be negotiated before you start rather than when the questions start getting difficult. Keep the interviewee on track, 65 THE A–Z OF MEDICAL WRITING though sometimes desperate measures may be needed, such as knocking over a glass of water. Using a tape recorder will free you to concentrate on the business in hand – though keep some written notes as well, just in case there is a systems failure. Interviewees will often ask to see a copy of what you have written before it is published. The danger with this is that they will try to get rid of their bright, clear quotes and try to put back their posh overcoat (see putting on the posh overcoat). On the other hand, passing your copy to them will probably pick up one or two errors of fact. Use your discretion: a sensible compromise is to read what you have written over the phone. In that way they can pick up errors but will have no time to fiddle with the style. Wherever possible go through the information as soon as the interview is over. When you come to write, you should be in a position to take out of it, from memory, what you need.