Books on the topic 'Compound Motor Action Potential'

The chapter begins with a description of the normal findings in healthy sensory and motor nerves. The distribution of nerve fibres by diameter in the sensory nerve and its effect on the recorded action potential is outlined. The method by which velocity and compound muscle action potential are derived from motor stimulation follows. H-reflex studies and F-wave identification are described. A section on the strategies used for nerve conduction study in children and the nerves chosen for examination leads on to a description of the difficulties of deriving normative data in children. Next follows a detailed description of the findings in both sensory and motor nerves in demyelination where a distinction between patchy and homogenous demyelination is possible. An analysis of the nerve findings in axonal degeneration is then presented. The chapter finishes with a discussion of the variability in nerve testing.

This chapter on primary muscle diseases explains how analysis of compound muscle action potential (CMAP) amplitude, abnormal spontaneous activity on needle electromyography (EMG), and motor unit action potentials (MUAP) characteristics may be used to give an indication of pathophysiological processes, and goes on to describe the combination and distribution of abnormalities that may be expected in the more commonly encountered myopathies. The conditions considered in detail are inflammatory myopathy (including myositis), critical illness myopathy, disorders with myotonia, inherited myopathy (including muscular dystrophy), and endocrine, metabolic and toxic disorders. Each of these has a characteristic combination of CMAP, spontaneous EMG, and MUAP findings, but the systematic approach to clinical neurophysiology as a way of understanding muscle pathophysiology can be used to investigate the myriad of rare myopathies that may be encountered in clinical practice.

In this chapter, the inability of electromyography (EMG) to be able to further progress the diagnosis of myopathy on its own—requiring muscle biopsy and other modalities such as genetics to complete this process—is emphasized. The role of EMG particularly in the era of genetics is discussed. Findings in neurogenic abnormality are next described and the important hereditary conditions such as spinal muscular atrophy (SMA), distal SMA, Brown–Vialetto–Van Laere syndrome, segmental anterior horn cell disease, conditions with progressive bulbar palsy, SMARD1, and pontocerebellar hypoplasia with spinal muscle are discussed in detail. The differential diagnosis of 5q SMA type 1 is specifically outlined. Acquired forms of anterior horn disease, including Hirayama disease, poliomyelitis and enteropathic motor neuropathy, Hopkins syndrome, tumours, and vascular lesions are covered. There is discussion of the use of physiological tests to monitor progress in SMA, with tests including compound muscle action potential amplitude and motor unit number estimation. Finally, the important correlation between muscle biopsy and EMG is highlighted.

The motor unit represent the final output of the motor system. Each consists of a motoneuron, its axon, neuromuscular junctions, and muscle fibres innervated by that axon. The discharge of a motor unit can be followed by recording its electromyographic signature, the motor unit action potential. Motoneurons are not passive responders to the excitatory and inhibitory influences on them from descending and segmental sources. Their properties can change, e.g. due to descending monoaminergic pathways, which can alter their responses to other inputs (changing ‘reflex gain’). Contraction strength depends on the number of active motor units, their discharge rate, and whether the innervated muscle fibres are slow-twitch producing low force, but resistant to fatigue, fast-twitch producing more force, but susceptible to fatigue, or intermediate fast-twitch fatigue-resistant. These properties are imposed by the parent motoneurons, and the innervated muscle fibres have different histochemical profiles (oxidative, glycolytic, or oxidative-glycolytic, respectively).

Use of DBS extends beyond what are typically referred to as “movement disorders,” for which issues of motor control are paramount; currently approved for treatment of refractory obsessive-compulsive disorder (OCD) disorder, DBS is expected to gain approval as a treatment for epilepsy as well. Indeed, no neurological or psychiatric disorder ought to be excluded a priori from consideration as a potential indication for DBS. Post-operative management of DBS for these other disorders will benefit from a better understanding of the mechanisms of action. An understanding of the ways in which the brain responds to DBS (see Chapter 6—Nervous System Responses to DBS) related to motor control may therefore serve as an important metaphor for understanding the use of DBS for other conditions.

This chapter focuses on four of the best known and most well characterized EDCs: the polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), diethylstilbestrol (DES), and bisphenol A (BPA) as prototypical EDCs. For each compound, historical information regarding use, sources of contamination, descriptions of toxic effects, nature of endocrine disruptive mechanisms, and detailed summaries of critical research findings are highlighted. Each of these chemicals are seminal illustrative examples of EDCs that came to be recognized, defined, and considered seriously by the general public and the regulatory community. Continuing work with these well-studied chemicals continues to reveal new mechanisms of EDC action and identifying new potential health outcomes and effects, and have become important “positive control chemicals” for toxicity and chemical testing strategies and identification of emerging EDCs.

Immune-mediated polyneuropathies are important to recognize since the majority of them are treatable. Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) is the prototype of the acquired chronic demyelinating polyneuropathies. It should be distinguished from other acquired demyelinating polyneuropathy such as those associated with monoclonal gammopathy, myeloproliferative disorder, and myelin-associated glycoprotein. This case presents a patient with a chronic demyelinating polyneuropathy associated with monoclonal gammopathy of unknown significance. The discussion includes the clinical and electrodiagnostic criteria for CIDP and distinguishing features from axonal polyneuropathies, other acquired demyelinating polyneuropathies, and inherited demyelinating polyneuropathies such as Charcot-Marie-Tooth disease type I. The case also highlights the diagnostic criteria for conduction block and temporal dispersion based on analysis of compound muscle action potential amplitude, area, and duration.

Myasthenia can be caused by acquired or autoimmune conditions and other conditions resulting from genetic abnormalities of the proteins in the neuromuscular junction. The clinical clues to diagnosis in the paediatric population are highlighted in this chapter. Among these are sudden death, episodic apnoea, stridor, association with myopathy, and limb-girdle weakness presentation. Acquired disorders of the neuromuscular junction occur, such as infantile botulism, tick paralysis, and persistence of neuromuscular blocking agents. Some patterns of abnormality are seen in the neurophysiological findings, the most notable of which is a repetitive compound muscle action potential at low rates of stimulation. Decrement only seen after long-duration, high-frequency repetitive nerve stimulation is described in choline acetyltransferase (CHAT) abnormalities. DOK7 myasthenia may demonstrate patchy abnormalities of jitter and this is described along with the profound increment of the high-frequency repetitive nerve stimulation in Lambert–Eaton syndrome.

Nerve conduction studies and needle EMG represent the two essential parts of the clinical EMG study. In almost all patients, both studies need to be completed before a final conclusion is made. This chapter outlines the basic concepts of nerve conduction studies including stimulations, recordings, variables and sources of errors. This is followed by detailed discussions of basic pathophysiological changes that accompany peripheral nerve disorders. The chapter then covers the normal needle EMG findings including normal insertional activity, motor unit action potential morphology and recruitment. This is followed by details on abnormal spontaneous activity findings and changes in motor unit action potential morphology and recruitment seen on needle EMG with peripheral nerve and muscle disorders.

Ulnar nerve lesions are the second most common mononeuropathies encountered in clinical practice. The majority of ulnar neuropathies are across the elbow, more specifically due to entrapment or compression of the ulnar nerve at the cubital tunnel or ulnar groove. This case highlights the clinical and electrodiagnostic findings of ulnar neuropathies across the elbow and discusses the challenges in making an accurate diagnosis. Focal slowing of conduction velocities and/or conduction block are the main findings that pinpoint the site of the lesion, while the needle electromyography is poor in accurate localization, mostly due to the limited number of ulnar innervated muscles in the forearm. Important additional testing that often is recommended to aid in the accurate diagnosis of ulnar nerve lesions across the elbow includes the dorsal ulnar sensory nerve action potential, ulnar motor conduction study recording the first dorsal interosseous, and inching studies across the elbow.

Local anaesthetic agents cause a pharmacologically induced reversible neuropathy characterized by axonal conduction blockade. They act by blocking the sodium ionophore and exhibit membrane stabilizing activity by inhibiting initiation and propagation of action potentials. They are weak bases consisting of three components: a lipophilic aromatic ring, a link, and a hydrophilic amine. The chemical link classifies them as esters or amides. Local anaesthetics diffuse through the axolemma as unionized free-base and block the ionophore in the quaternary ammonium ionized form. The speed of onset of block is therefore dependent on the pKa of the agent and the ambient tissue pH. Esters undergo hydrolysis by plasma esterases and amides are metabolized by hepatic microsomal mixed-function oxidases. Local anaesthetics are bound in the blood to α‎1-acid glycoproteins. Pharmacological potency is dependent on the lipid solubility of the drug as is the potential for systemic toxicity. The blood concentrations required to cause cardiovascular system (CVS) collapse and early central nervous system (CNS) toxicity are used to quantify the CVS:CNS toxicity ratio. Local anaesthetics also have the potential to induce direct neuronal damage. Intravenous lipid emulsion is used for the treatment of systemic toxicity but the scientific evidence is inconsistent. With regard to the pipecoloxylidine local anaesthetics, early evidence indicated that the S- was less toxic than the R-enantiomer. However, clinical research using minimum local analgesic concentration designs suggests that reduced systemic toxicity and motor block sparing is mainly explained by potency rather than enantiomerism.

Disorders affecting the lower cranial nerves – V (trigeminal), VII (facial), IX (glossopharyngeal), X (vagus), XI (accessory) and XII (hypoglossal) – are discussed in the first part of this chapter. The clinical neuroanatomy of each nerve is described in detail, as are disorders – often in the form of lesions – for each nerve.Trigeminal nerve function may be affected by supranuclear, nuclear, or peripheral lesions. Because of the wide anatomical distribution of the components of the trigeminal nerve, complete interruption of both the motor and sensory parts is rarely observed in practice. However, partial involvement of the trigeminal nerve, particularly the sensory component, is relatively common, the main symptoms being numbness and pain. Reactivation of herpes zoster in the trigeminal nerve (shingles) can cause pain and a rash. Trigeminal neuralgia and sensory neuropathy are also discussed.Other disorders of the lower cranial nerves include Bell’s palsy, hemifacial spasm and glossopharyngeal neuralgia. Cavernous sinus, Tolosa–Hunt syndrome, jugular foramen syndrome and polyneuritis cranialis are caused by the involvement of more than one lower cranial nerve.Difficulty in swallowing, or dysphagia, is a common neurological problem and the most important consequences include aspiration and malnutrition (Wiles 1991). The process of swallowing is a complex neuromuscular activity, which allows the safe transport of material from the mouth to the stomach for digestion, without compromising the airway. It involves the synergistic action of at least 32 pairs of muscles and depends on the integrity of sensory and motor pathways of several cranial nerves; V, VII, IX, X, and XII. In neurological practice dysphagia is most often seen in association with other, obvious, neurological problems. Apart from in oculopharyngeal muscular dystrophy, it is relatively rare as a sole presenting symptom although occasionally this is seen in motor neurone disease, myasthenia gravis, and inclusion body myositis. Conversely, in general medical practice, there are many mechanical or structural disorders which may have dysphagia as the presenting feature. In some of the disorders, notably motor neurone disease, both upper and lower motor neurone dysfunction may contribute to the dysphagia. Once dysphagia has been identified as a real or potential problem, the patient should undergo expert evaluation by a clinician and a speech therapist, prior to any attempt at feeding. Videofluoroscopy may be required. If there is any doubt it is best to achieve adequate nutrition through the use of a fine-bore nasogastric tube and to periodically reassess swallowing. Anticholinergic drugs may be helpful to reduce problems with excess saliva and drooling that occur in patients with neurological dysphagia, and a portable suction apparatus may be helpful. Difficulty in clearing secretions from the throat may be helped by the administration of a mucolytic agent such as carbocisteine or provision of a cough assist device.

Imagination is a core driver of human development as well as social transformation. Long ignored in psychology, imagination enjoys renewed interest in developmental and sociocultural approaches to mind and culture. In this Handbook, the enquiry is broadened, and imagination is explored by a number of eminent scholars and practitioners within and at the frontiers of cultural psychology. Organized in four main sections, the Handbook of Imagination and Culture first examines the history and extension of the concept of imagination, its proximity to creativity, and the methodology used to approach it. The second section examines imagination as a dynamic, lifelong developmental process: its emergence in childhood and expression in adulthood and into old age. The third section explores imagination as a pervasive phenomenon in domains such as music, theatre, work, and education. The fourth sections shows that imagination can function as a motor for social change in community work, in the use of new technologies, in society’s relation to the past, and in political change. As a whole, the book invites us to go beyond the frontiers of our knowledge: it opens perspectives for future research and cultivates the potential for individual and collective action toward an imagined future.