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Biomedical subjects

G W Sypert

Publications and source records attributed to G W Sypert.

At least 55 records · Page 3Linked to original sources
PubMed1981

Basis of segmental motor control: motoneuron size or motor unit type?

The principles of organization of motor control at the segmental level are developed and discussed in this review. Consideration is given to the concepts of the motor unit, and the motoneuron pool. Recent studies from our laboratories that have significance for hypotheses regarding segmental motor control are presented. These studies indicate that the critical factor controlling motor unit recruitment in heterogenous muscles is motor unit type. This results in motor unit recruitment in the order of increasing contraction strength and fatigability: slow twitch, fatigue-resistant first; fast twitch, fatigue-resistant second; fast twitch with intermediate fatigue resistance third; and fast twitch, fatigable units last. A recruitment model that incorporates this hypothesis is presented in which there is an orderly recruitment of motor units by type. This recruitment model, based on data from cat medial gastrocnemius motor units, closely approximates a theoretical optimal recruitment strategy and is consistent with actual medial gastrocnemius muscle forces generated during free movements in intact animals.

Animals↗
PubMed1980

Acute FeCl3-induced epileptogenic foci in cats: electrophysiological analyses.

Fifteen cats were rendered acutely epileptic via transpial iontophoresis of ferric ions. Extracellular electrical activity of individual cortical neurons was temporally correlated with ECoG epileptic spikes. Each unit's activity was characterized as excited, inhibited, or unaffected. The spatial coordinates of each neuron were logged, thereby generating a 3-dimensional activity map. Discharge patterns were further classified as bursting or non-bursting. A significantly increased population of inhibited cells was detected at radial distances greater than 3 mm from the iontophoretic site. This increase was at the expense of "unaffected-bursting" cells. Pathological discharge patterns, including units which fired in long-first-interval bursts, were common in the focus. A system was designed to electronically calculate single-unit firing probability before, during and after surface epileptiform spikes. An 8-12 Hz oscillation in firing probability level, time-locked to the epileptic spike, was observed in most excited-bursting units. Many of these findings in the ferric-induced epileptic focus accurately model the electrophysiological characteristics previously reported for human epileptic foci examined at neurosurgery.

Animals↗
PubMed1980

Dendritic alterations in rat isocortex within an iron-induced chronic epileptic focus.

Ferrous chloride was injected into the rat isocortex in 5-microliters volumes as an aqueous solution with a concentration of 100 mM. Bursts of epileptiform discharges were sustained throughout the 6 weeks of observation. Nissl and Golgi-Cox stains showed gliosis and neuronal loss within the injection site. Neurons adjacent to the cavitory lesion showed deformity of dendrites, dendritic nodularity, loss of spines, and string-of-beads deformity. These changes are identical to those found in human epileptogenic foci.

Animals↗
PubMed1980

Cervical carotid dissecting aneurysms.

Thirteen cases of cervical carotid dissecting aneurysm have been seen at the University of Florida during the past 3 years. In our experience, two groups of patients with this disease can be distinguished clearly by either clinical or angiographic criteria. One group of cervical carotid dissecting aneurysms is characterized by spontaneous onset, unilaterality, and the absence of pseudoaneurysm formation. These lesions have a strong tendency to resolve with appropriate medical therapy. The other group is characterized by an association with obvious predisposing factors, such as fibromuscular dysplasia, angiography, or trauma. These lesions are often associated with pseudoaneurysms and rarely resolve spontaneously. These two groups of lesions probably represent a spectrum of the same basic disease process. The natural history of patients who survive a cervical carotid dissection is usually one of stability or improvement. A trial of medical therapy (to prevent embolic symptoms) and repeat arteriography are indicated before the consideration of surgical therapy.

Adult↗
PubMed1979

Properties of single central Ia afferent fibres projecting to motoneurones.

1. Electrical potentials in the cat lumbosacral spinal cord evoked by the action of single medial gastrocnemius Ia afferent fibres were recorded using low impedance, bevelled micropipette electrodes and the spike triggered averaging technique. 2. Axonal potentials from the Ia fibres recorded extracellularly appeared as brief triphasic predominantly negative potentials. 3. Terminal potentials recorded in regions of Ia afferent termination appeared as brief diphasic positive-negative waves, often with additional wavelets. 4. Focal synaptic potentials, recorded extracellularly in regions of the medial gastrocnemius Ia afferent termination, appeared as slow (about 10 msec duration) negative potentials following terminal potentials. 5. Excitatory post-synaptic potentials, recorded intracellularly in Ia target cells of the medial gastrocnemius, appeared as slow (about 10 msec duration) positive potentials following terminal potentials. 6. Analysis of the temporal progression of these potentials through the spinal cord allowed calculations of the Ia conduction velocity in the dorsal funiculus stem axon (50-60 m/sec), in major collateral branches (8-19 m/sec) and in terminal branches (0.2-1.0 m/sec). 7. The number of major collateral branches (nine or fewer) and their spacing along the spinal cord (1071 micron mean value) were determined by analysing the extent of the triceps surae motoneurone column. 8. The structural and functional properties of medial gastrocnemius Ia afferent fibres are discussed in relation to recent single fibre anatomical data and the present single fibre electrophysiological data.

Action Potentials↗
PubMed1979

Properties of single fibre excitatory post-synaptic potentials in triceps surae motoneurones.

1. E.p.s.p.s and terminal potentials (t.p.s) produced by the action of single medial gastrocnemius Ia afferent fibres were examined with intracellular microelectrodes in cat triceps surae motoneurones. 2. Simple terminal potentials (t.p.s) appeared as positive-negative diphasic waves with a single positive peak. Shape indices of excitatory post-synaptic potentials (e.p.s.p.s) recorded in conjunction with simple t.p.s indicate that these e.p.s.p.s were generated at an electrotonically confined compartment on the motoneurone somadendritic membrane. 3. Compound t.p.s. were similar ones, except that they had two or more positive peaks. Shape indices of e.p.s.p.s recorded in conjunction with compound t.p.s indicate that these e.p.s.p.s were generated at two or more electrotonically separate compartments. 4. E.p.s.p. latency and post-synaptic electrotonic delay were determined for a group of single fibre e.p.s.p.s with simple t.p.s. The shortest recorded latency was 0.26 msec. By subtracting estimated electrotonic delay, the shortest synaptic delay obtained for a medial gastrocnemius Ia single fibre e.p.s.p. was 0.17 msec. 5. The finding of a significant synaptic delay supports the hypothesis that the Ia-motoneurone synapse is a chemically mediated synapse.

Action Potentials↗
PubMed1979

Traumatic false aneurysm and carotid-cavernous fistula: a complication of sphenoidotomy.

Severe head injury with resultant basilar skull fracture is the most common etiology for traumatic false aneurysm of the cavernous carotid artery and for traumatic carotid-cavernous fistula. We present a case of false aneurysm and fistula that occurred as a complication of sphenoidotomy, fortunately a rare etiology of these two serious problems. Because of the current resurgence of trans-sphenoidal surgery, it is of utmost importance that all neurosurgeons possess an accurate and detailed knowledge of the anatomy of the carotid artery and its intracavernous route.

Adult↗
PubMed1979

Angiographically cryptic cerebrovascular malformations.

Three cases of angiographically cryptic cerebrovascular malformations are presented and a review of the cases in the English literature is tabulated. The typical patient is a 30- to 40-year-old woman with a history of seizures and headache. There is no antecedent history suggesting hemorrhage. On nonenhanced computerized tomographic scans, these lesions are denser than normal brain. They enhance with contrast administration. The angiogram demonstrates an avascular mass. The history, physical findings, and radiographic studies suggest brain tumor. An accurate diagnosis requires operation and pathological examination of the lesion.

Cerebral Angiography↗
PubMed1978

Chronic focal epileptiform discharges induced by injection of iron into rat and cat cortex.

A single injection of 5 or 10 microliters of ferrous or ferric chloride into rat or cat sensorimotor cortex resulted in chronic recurrent focal paroxysmal electroencephalographic discharges as well as behavioral convulsions and electrical seizures. Recurrent focal epileptiform discharge caused by cortical injection of iron salts suggests that the development of human posttraumatic epilepsy may depend, in part, on the neurochemical alterations induced by the principal metallic ions found in whole blood.

Animals↗
PubMed1978

Identification of speech lateralization by intracarotid injection of methohexital.

Speech lateralization was assessed in 25 patients with epilepsy by direct carotid injection of carotid catheterization from a femoral approach. Hemispheric anesthesia was induced by intracarotid injection of the rapidly acting barbiturate methohexital. This technique allowed same-day study of both hemispheres, permitted repeated injection of either carotid artery without accumulation of methohexital sufficient to cause systemic effects, and added little to the total time required for three-vessel cerebral angiography. Unilateral seizures were induced by methohexital injection in 4 patients. No other complication secondary to the methohexital study was observed.

Adolescent↗
PubMed1978

Recurrent seizures induced by cortical iron injection: a model of posttraumatic epilepsy.

A single injection of 5 or 10 microliters of ferrous or ferric chloride into rat or cat sensorimotor cortex resulted in chronic recurrent focal paroxysmal electroencephalographic discharges as well as behavioral convulsions and electrical seizures. Iron-filled macrophages, ferruginated neurons, and astroglical cells surrounded the focus of seizure discharge. Recurrent focal epileptiform discharges caused by cortical injection of iron salts suggests that the development of human posttraumatic epilepsy may depend, in part, on neurochemical alterations induced by the principal metallic ions found in whole blood.

Animals↗