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Biomedical subjects

J T Murphy

Publications and source records attributed to J T Murphy.

At least 91 records · Page 5Linked to original sources
PubMed1978

Genesis of the round window rupture syndrome; some experimental observations.

Clinical and experimental evidence has revealed that rupture of the round window membrane, by itself, is not a major cause of sensorineural hearing loss. Eighteen guinea pigs underwent removal of the round window. The status of cochlear function was determined by recording the cochlear microphonic. An average loss of only about 6 db was observed after surgery. It is felt that there must commonly be more cochlear damage concurrent with window rupture to explain the significant and often relatively immediate hearing losses seen in clinical practice. The site(s) of this primary trauma has not yet been discovered, but it would seen reasonable in the light of recent reports that the perilymphatic vessels, the vas spirale, the stria vascularis and/or the intergrity of the cochlear duct might be involved in the genesis of this hearing loss. We propose that the term "round window rupture syndrome" be used as a more accurate description of this entity. The round window damage provides evidence of more devastating trauma within the cochlea. Thus, the clinician, being alerted, should not stop his therapeutic efforts with surgical closure of the RW. Better prognosis for the patient, as well as leading into new avenues for the investigation of cochlear function, would be the result.

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PubMed1978

An intracortical microstimulation study of output organization in precentral cortex of awake primates.

We investigated the output organization of the forelimb control area in primate precentral cortex by using low-current (less than 30 microamperemeter) intracortical microstimulation (ICMS). Movement about a joint was selected as the index of response. Penetrations perpendicular to the cortical surface and deep into the rostral bank of the central sulcus were made in two awake unanesthetized monkeys (Macaca arctoides). Cortical areas were designated by the joint about which movements occurred. 1. ICMS loci which produced movements about finger joints were found to tightly cluster in a central zone, and were surrounded by loci controlling movement about the wrist. This wrist zone was in turn approximately encircled by an elbow zone, which itself was enclosed by a shoulder zone. 2. Appreciable overlap between these zones controlling movements about contiguous joints was observed. 3. The observations indicate a nested-ring organization of the forelimb output zones of precentral cortex, such that a cortical zone controlling movement of a more distal joint is partly encircled by the zone controlling a more proximal joint.

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PubMed1977

Simple probe for localized cryogenic blockade in the brain.

The construction of a simple probe utilizing an air-space thermal insulation and circulating coolant for localized cooling of brain tissue is described. Results of isotherm studies in the cerebellum and electrophysiological observations in the motor cortex are presented indicating the effectiveness of localized cooling by the probe.

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PubMed1977

Urological problems in aged patients.

The major urological problems encountered in geriatric patients are bladder neck obstruction, due to hyperplasia or carcinoma of the prostate in men, and urinary infection and chronic urethro-trigonitis (the urethral syndrome) in women. Senile incontinence is common to both sexes.

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PubMed1976

Integrative versus delay line characteristics of cerebellar cortex.

In order to determine which of two general models ("tapped delay line" or "integrator") provides a more accurate desciption of mammalian Purkinje cell (P-cell) activation by natural stimulation, the spatial and temporal characteristics of a population of neurons in cerebellar cortex responsive to small controlled stretches of forelimb muscles were examined in awake, locally anesthetized cats. Stretch of a single wrist muscle excited P-cells over a distance of about 1 mm in the long axis of a folium, a span which is at most half the length of parallel fibers. Both granule cells and molecular layer interneurons were excited over a wider zone than P-cells. Furthermore, P-cells across a response zone all fired on the average at the same time, as determined by computing peristimulus cross-interval histograms from pairs of simultaneously recorded neurons. Consistent delays could only be demonstrated in the minimal response latencies as measured from peristimulus time histograms. These delays, however, were longer than could be ascribed to parallel fiber conduction velocity. No evidence, therefore, was found in cat cerebellum to support the "tapped delay line" model, which postulates the successive activation of P-cells as an excitatory volley travels along a parallel fiber beam. Instead, an integrative mode of operation seems to predominate: a relatively wide substratum of activated granule cells simultaneously activates a narrower focus of P-cells centrally situated with respect to the granule cell population. The role of inhibitory interneurons in promoting the "integrator" model is discussed.

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PubMed1975

Physiological basis of cerebellar dysmetria.

A primary control system for the arm position is formulated. The hypothesis that the cerebellum is a part of the system controller is checked by studying the nerve cells responses in the cerebellum, and motor cortex, to natural activation of muscular receptors. The results show that the cerebellum receives feedback information related to the speed of these receptors. The discussion concentrates on how the interruption of this feedback may result in excessive oscillations to instability. These observations are the base for evaluating how the cerebral lesions produce dismeasurements.

Animals↗
PubMed1975

Effect of succinylcholine on responses of neurons in the motor cortex to natural activation of muscle spindle primary endings.

In locally anesthetized cats, the effects of intravenous administration of succinylcholine (SCh) in sub-paralytic dosages on the responses of single neurons in motor cortex to small dynamic muscle stretches were studied. A large transient enhancement of these cortical responses with a time course corresponding to the peripheral action of SCh on muscle spindles was observed. This finding is discussed in terms of the hypothesis that muscle spindle primary endings may activate projections to motor cortex.

Animals↗
PubMed1975

Afferent-efferent linkages in motor cortex for single forelimb muscles.

1. In locally anesthetized cats, extracellular recordings were made from single neurons in the lateral cruciate gyrus of cerebral cortex. These neurons responded to natural activation of stretch receptors in single, contralateral, forelimb wrist muscles, typically with phasic excitation. Low-velocity stretches, which activate primary endings of muscle spindles, excited one set of neurons at a mean latency of 11 ms; high-velocity stretches, which principally activate Golgi tendon organs and/or secondary spindle endings, excited a second set at 18 ms. The cortical neurons showing threshold responses to low-velocity stretches were found exclusively within restricted columns, 0.5-2.0 mm in diameter, which were spatially separate for each muscle. Neurons exhibiting threshold responses to high-velocity stretches were present in high density within the same columns and were also distributed, although more sparsely, outside the columns. 2. These afferent columns were located in cytoarchitectonic area 4gamma, and were shown by intracortical microstimulation to coincide with the efferent columns for contraction of the same muscle from which in input rose. Discrete afferent columns were also found for single muscles in the peridimple region of sensory cortex (area 3a), spatially separate from the columns in motor cortex. The excitation of the columns in motor cortex by these inputs from muscle was independent of that in sensory cortex. 3. The role of the cerebellum in controlling these feedback systems to motor cortex was investigated by selective cooling of interpositus and dentate nucleus, respectively. Cooling of interpositus markedly reduced transmission in the high-threshold system; cooling of dentate had a similar effect on the low-threshold system. 4. The latency, threshold, and cooling data indicated that the low-threshold system to motor cortex utilizes extracerebellar pathways including medial lemniscus and is facilitated by dentate nucleus. The high-threshold system involves a transcerebellar pathway including interpositus nucleus. Both systems transmit velocity-related information, with each showing different and complementary sensitivity and dynamic range. 5. The results are discussed with reference to the cortical load-compensation mechanism postulated by Phillips (37-38).

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