El tracto cortico espinal: perspectiva histórica / The corticospinal tract: historical perspective

RESUMEN: La neuroanatomía y la neurofisiología han permitido en gran parte entender de forma más integrada las estructuras que conforman el sistema nervioso y los mecanismos asociados con la transmisión de los potenciales de acción, relacionados con la vía corticoespinal en la ejecución de movimientos voluntarios. Se realizó una revisión histórica sobre la vía corticoespinal, desde el punto de vista neuroanatómico y neurofisiológico mediante una revisión de literatura en distintas bases de datos y libros de texto dedicados a estas vías nerviosas. La información obtenida se ordenó cronológicamente, seleccionando los datos más relevantes que desde el punto de vista neuroanatómico y neurofisiológico han permitido comprender su mecanismo funcional. Actualmente se tiene un conocimiento muy depurado de los distintos elementos que componen la vía corticoespinal, lo que permitirá su aplicación en el campo de la salud y resolver múltiples problemas de la función motora.

SUMMARY: Neuroanatomy and Neurophysiology have, in large part, permitted a more thorough understanding of those structures that conform the nervous system and mechanisms associated with the transmission of action potentials associated with the corticospinal tract. This assertion is made based upon a literature review of various databases and textbooks dedicated to said nerve tracts. The information obtained was ordered chronologically, and data was selected that, from the neuroanatomical and neurophysiological viewpoints, were most relevant and have permitted the comprehension of its functional mechanism. The thorough understanding of those elements that compose the corticospinal tract will permit its application in the health field and resolve multiple motor function problems.

[Comparative study of central motor conduction time by using magnetic stimulation and F-wave study in normal subjects]

Central motor conduction time [CMCT] includes time for excitation of the corticospinal pathways and transmission along those tracts. Data obtained by cortical magnetic stimulation are helpful in some clinical situations such as multiple sclerosis, cervical spondylosis, motor neuron disease, and etc. However, using different methods for peripheral motor conduction time [PMCT] demonsrates two different results. In this study, we used two methods to compare CMCT from F-wave latency and spinal root magnetic stimulation. Also, this study was performed to determine normal values, effects of sex, age and upper limb length. Magnetic stimulation of the cortex and cervical spinal roots was performed on 39 healthy subjects. Responces were recorded from the abductor pollicis brevis [APB] muscle. F-wave study was performed in the median nerve. Subtraction of total motor conduction time [TMCT: cortical response] and PMCT by F-wave and cervical root stimulation, shows CMCT. The results showed 19.7 ms for TMCT, 7.3 ms for CMCT of root stimulation and 4.8 for Fwave based CMCT. CMCT to the APB correlates with upper limb length but no with age or sex. The CMCT calculated by subtracting F- wave latencies measured to APB after transcranial stimulation was shorter than the one obtained after magnetic root stimulation

Transcranial magnetic stimulation: role in the evaluation of disability in multiple sclerosis.

BACKGROUND: In patients with multiple sclerosis (MS), transcranial magnetic stimulation (TMS) has shown significant prolongation of central motor conduction time (CMCT). Abnormal CMCT may reflect sub-clinical involvement of motor pathways and correlate with clinical motor disability. OBJECTIVE: To determine the diagnostic yield of TMS in MS and the possible correlation of TMS abnormalities with clinical disability. MATERIALS AND METHODS: Thirty patients with clinically definite MS presenting in acute relapse or with progressive disease course and 30 healthy controls were evaluated. TMS parameters evaluated included threshold intensity, motor evoked potentials (MEP) amplitudes and latencies and CMCT. Reassessment studies were done after three months. STATISTICAL ANALYSIS: Student t-test, Mann-Whitney U test and Spearman's rank correlation test were used to assess the relationships. RESULTS: Patients with MS had significantly higher threshold intensities, prolonged CMCT and reduced MEP amplitudes as compared to controls. Abnormalities in at least one parameter were observed in 86.7% of patients. When inter-side asymmetries in MEP latency and/or in CMCT were considered, the diagnostic yield increased to 96.7%. The diagnostic yield was 74.7% for visual evoked potentials, 13.3% for brainstem auditory evoked response and 10% for cerebrospinal fluid oligoclonal band. One MS patient without pyramidal or cerebellar dysfunction had prolonged CMCT. CMCT abnormalities correlated significantly with the degree of pyramidal signs, limb ataxia, intention tremor, dysdiadokokinesia and overall cerebellar score. In patients who had clinical improvement, follow-up studies showed improvement in CMCT parameters. CONCLUSION: TMS is a highly sensitive technique to evaluate cortico-spinal conduction abnormalities in MS that may have no clinical correlate and in monitoring the course of the disease. The effects of cerebellar dysfunction on TMS results need further evaluation.

The Babinski sign--a critical review.

In 1896, Josph Babinski, a French neurologist, first described the best known neurologic eponym--"the Babinski sign". This sign is characterised by dorsiflexion of the big toe, by recruitment of the extensor hallucis longus muscle, on stimulating the sole of the foot. He himself emphasised from the outset the intimate relationship between this sign and the shortening movement in other leg muscles, which forms the flexion synergy of the lower limb. The Babinski sign is not a new reflex, rather it is released as a result of breakdown of the harmonious integration of the flexion and extension component of the normal defence reflex mechanism, due to pyramidal tract dysfunction. A pathological Babinski sign should be clearly distinguished from upgoing toes that may not always be a part of the flexion synergy. This article reviews the Babinski sign in detail, focusing on the historical perspectives, role of pyramidal tract dysfunction, art of elicitation and interpretation. The significance of assessing this phenomenon in the entire leg and the clinical clues that will help to dispel the myths regarding the Babinski sign has been emphasized.

Duality in physiological time: Euclidean and fractal

The aim of the present study was to differentiate two modalities of intrinsic time scales: i- the geometric or Euclidean modality, which is based on the constant speed of mass transport or of wave transmission in cylindrical structures (arteries, veins, nerves), whose allometric exponent (TE = aMb) is b = 0.33, where M is body mass (kg) and a the mass coefficient; ii- the fractal time scale (TF), which is characteristic of organs with self-similar branching structures and with volume-specific flows, whose allometric exponent is b = 0.25. The proposed dichotomy could be confirmed by means of the statistical analysis of empirical allometric exponents (b). Our findings demonstrate the need to separate the chronology of bulk transport at long distances (inter-organic) which follows an Euclidean geometry (cylinders), from the fractal time scale, which operates at short distances (intra-organic) and is represented by a self-similar branching system which determines both the morphometric and physiometric characteristics within each organ

A organizaçäo cerebral do controle motor no homem: o feixe peduncular / Cerebral organization of motor control in the man: the peduncular tract

Após análise histórica do desenvolvimento do conceito de "piramidal", é proposta a designaçäo de "feixe peduncular" para englobar as fibras corticonucleares e corticoespinhais, como o principal eferente motor cortical. É feita validaçäo desse conceito pelos efeitos motores observados na hemiplegia motora pura e síndrome de encarceramento, com ou sem discinesias pós-hemiplégicas