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Biomedical subjects

E Eldred

Publications and source records attributed to E Eldred.

At least 37 records · Page 2Linked to original sources
PubMed1980

Changes in excitability of tendon tap and Hoffmann reflexes following voluntary contractions.

The effects on the Hoffmann reflex and tendon tap responses in the human soleus and medial gastrocnemius muscles of a brief conditioning volitional contraction have been compared with the objective of distinguishing contributions from the central nervous system and the periphery. The H-wave on successive trials over a 50 sec period following contraction for the most part demonstrated a depression, especially upon the initial trial. The T-wave responses in the first few trials were greater than those in the control period. Using the assumption that responses to tendon taps had been reduced by the amounts reflected in the excitability curve for H-response, it was deducted that a marked enhancement in T-wave excitability had been present at the initial tendon tap and more moderate facilitation thereafter. This is consistent with the post-contraction discharge and increase in stretch sensitivity of spindle receptors seen after contraction of a muscle in experimental animals. It is concluded that such effects on spindles may occur in man, maybe of such force as to detectably influence dynamic movements.

Adult↗
PubMed1978

Spinal projection to the dorsolateral nucleus of the caudal basilar pons in the cat.

In the cat, a spinal projection to a restricted area of the basilar pontine grey has been revealed with use of anterograde degeneration technique (Fink-Heimer). The area was ipsilateral to the spinal lesion, restricted to the far caudal limit of the pons, and included the dorsal and the dorsolateral subdivisions of the pontine nuclei (PN). Comparisons following high cervical, midthoracic and upper lumbar spinal lesions did not reveal any somatotopic organization. Only a few spinopontine fibers had origins below segmental level L4. Lesions of various quadrants of the cord indicated that the spinopontine fibers ascended through the dorsolateral funiculus, and not through either the dorsal or the ventral funiculi. Comparison with the degeneration effects of cerebral cortical lesions showed that the spinal projection to the PN overlapped to some extent with the projection from the first sensorimotor and second somatosensory cortices. In the rat no comparable spinopontine projection was found. It is suggested that the spinopontine pathway might forward information to the cerebellum from visceral sensory receptors or perhaps from pools of spinal interneurons.

Animals↗
PubMed1975

Nicotine-induced reflex depression of alpha motoneuron activity in the absence of fusimotor-spindle feedback.

The effects of nicotine on the stretch reflex and on electrically induced monosynaptic and cutaneous polysynaptic reflex responses at a lumbosacral level were studied in lightly anesthetized (chloralose-urethane) cats in which the regional fusimotor-spindle loops had been interrupted by ventral rhizotomy. Doses of 15-40 mug/kg injected into the superior vena cava or the right atrium produced depression of the reflex responses in extensor and flexor alpha motoneurons after latent periods of 1-3 sec, while gamma activity was initially accelerated. The early phase of this alpha depression was abolished by bilateral vagotomy. Sebacylcholine (a nicotinic agent) and acetylcholine also caused depression of evoked alpha activity in the absence of spindle feedback. It is concluded that nicotine activates a viscerosomatic reflex by exciting sensory receptors in the cardiopulmonary region and that alpha motor depression results independent of the changes in gamma activity. However, alpha depression with delayed onset can still be elicited by nicotine after vagotomy and Renshaw blockade, and this effect is also duplicated by sebacylcholine and abolished by hexamethonium. In the doses used, spindle or skin afferents were not excited by nicotine. Thus, two more mechanisms are described by which nicotine can depress alpha activity. Both are reflex in nature, one implicating vagal, the other nonvagal peripheral receptors.

Acetylcholine↗
PubMed1975

Persisting changes in sensory and motor activity of a muscle following its reflex activation.

A study was made to see if contractions induced by reflex action were followed by an elevation in muscle afferent activity comparable to the post-contraction sensory discharge (PCSD) that occurs after stimulation of the ventral roots. In lightly anesthetized cats, extension reflexes of the triceps surae muscle in the otherwise denervated leg were induced by contralateral stimulation of the popliteal nerve or footpad. The reflex response was followed by an elevated afferent discharge, which disappeared after a brief stretch, as is characteristic also of the PCSD. Crossed-extension responses in fusimotor activity unaccompanied by contraction of the gross muscle were also succeeded by an elevation in sensory discharge and an increased sensitivity to a vibratory stimulus applied to the tendon. Pinna reflexes had a similar effect. In the presence of the elevated discharge, alpha-motoneurons demonstrated increased sensitivity to vibration stimuli. It is suggested that the increase in spindle sensitivity may help stabilize the muscle against minor pertubations in length, at least when background fusimotor activity is relatively quiet.

Animals↗