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At least 163 records · Page 9Linked to original sources
PubMed2000

Neural pathways and central sites involved in penile erection: neuroanatomy and clinical implications.

Penile erection occurs in response to tactile, visual, and imaginative stimuli in humans. In animals olfactory and auditory cues are particularly important. The participation of multiple sites with the brain and spinal cord, and coordination of somatic and autonomic pathways make sexual behavior in general, and erection in particular, vulnerable to neurologic injury and disease. Sites within the brain and spinal cord act in concert to process, coordinate, then distribute the neural inputs necessary for sexual behavior including erection. Activation of neurons in some of these regions either pharmacologically or by electrical stimulation has been associated with penile tumescence. This review will provide a geographic framework for understanding the neuroanatomical basis of penile erection based primarily on animal data. Following discussion of the anatomical substrates, a clinical correlation is then provided to confirm and reinforce these experimental observations.

Animals↗
PubMed1988

Evidence that the neural pathways involved in backward conditioning are different from those involved in forward conditioning.

Effects of forward and backward conditioned-unconditioned stimulus (CS-US) intervals on classical conditioning of the flexion reflex were examined in a spinal cat preparation. A less intense conditioned stimulus (CS) was employed (activation of A-alpha cutaneous fibers) compared to that of a previous study (activation of both A-alpha and A-delta cutaneous fibers). Interstimulus intervals (ISIs) ranging from +3.0 to -3.0 sec were examined in 9 experimental groups, and results contrasted to those of an explicitly unpaired control group. The ISI of -0.25 sec produced optimal backward excitatory conditioning, paralleling the previous results. However, in contrast to the previous study, no conditioning was observed in any of the forward ISI groups. These observations support the hypothesis that backward and forward conditioning may be fundamentally different phenomena, induced by CS activation of different spinal reflex pathways: backward conditioning involves spinal reflex pathways activated by A-alpha cutaneous fibers of the CS, while forward conditioning involves spinal reflex pathways activated by A-delta cutaneous fibers of the CS.

Animals↗
PubMed1983

Neural pathway constraints in the motor innervation of the chick hindlimb following dorsoventral rotations of distal limb segments.

Several studies have demonstrated that motor axons can discriminate between dorsally and ventrally derived muscles. In this paper we present evidence that (1) the pathway axons take in the limb constrain their access to either dorsally or ventrally derived muscles, and therefore (2) the axon's ability to discriminate between dorsal and ventral is expressed already at the level of pathway selection into the limb. Surgically manipulated hindlimbs were produced consisting of a normal host thigh connected to a dorsoventrally rotated calf or to rotated and duplicated donor limb segments. The limb rotations were done distal to the level at which axons select a dorsally or ventrally destined pathway through the limb, such that at the level of the rotation, axons in each nerve were confronted with the opposite-from-normal set of muscles. In this situation, the relative influence of pathway availability versus dorsal/ventral muscle recognition could be assessed. The innervation of rotated limb segments was, in all cases, opposite from normal. Motoneurons which normally innervate dorsal muscles innervated ventrally derived muscles that had been rotated into a dorsal position. Likewise, normally ventrally destined axons served dorsal muscles in the rotated segments. Thus, motor axons did not alter their distal path to reach their normal set of muscles. While these results do not rule out intrinsic dorsal/ventral differences between muscles, they do demonstrate that muscle surface recognition is not necessary to account for dorsal/ventral discrimination in the innervation of normal, supernumerary, or duplicated limbs, nor is it sufficient to account for the innervation of rotated limb segments. These results also indicate that pathway guidance cues are an important influence on innervation patterns.

Animals↗
PubMed2002

Ultrastructural evidence for two-cell and three-cell neural pathways in the tentacle epidermis of the sea anemone Aiptasia pallida.

Sensory and ganglion cells in the tentacle epidermis of the sea anemone Aiptasia pallida were traced in serial transmission electron micrographs to their synaptic contacts on other cells. Sensory cell synapses were found on spirocytes, muscle cells, and ganglion cells. Ganglion cells, in turn, synapsed on sensory cells, spirocytes, muscle cells, and other neurons and formed en passant axo-axonal synapses. Axonal synapses on nematocytes and gland cells were not traced to their cells of origin, i.e., identified sensory or ganglion cells. Direct synaptic contacts of sensory cells with spirocytes and sensory cells with muscle cells suggest a local two-cell pathway for spirocyst discharge and muscle cell contraction, whereas interjection of a ganglion cell between the sensory and effector cells creates a local three-cell pathway. The network of ganglion cells and their processes allows for a through-conduction system that is interconnected by chemical synapses. Although the sea anemone nervous system is more complex than that of Hydra, it has similar two-cell and three-cell effector pathways that may function in local responses to tentacle contact with food.

Animals↗
PubMed2006

New insights into corollary discharges mediated by identified neural pathways.

Sensory systems respond not only to stimuli from the environment but also to cues generated by an animal's own behaviour. This leads to problems of sensory processing because self-generated information can occur at the same time as external sensory information. However, in motor regions of the CNS corollary discharges are generated during behaviour. These signals are not used to generate movements directly but, instead, interact with the processing of self-generated sensory signals. Corollary discharges transiently modulate self-generated sensory responses and can prevent self-induced desensitization or help distinguish between self-generated and externally generated sensory information. Here, we review recent work that has identified corollary discharge pathways at different levels of the CNS in vertebrates and invertebrates.

Action Potentials↗
PubMedDate not supplied

Interrupting neural pathways that transduce stressful information into physiological responses.

Stressor-stimuli evoke a noradrenergic process in the frontal lobes, the amplitude of which depends on both the individual's experience with the stimulus and his or her genetic background. Novel and noxious stimuli evoke large frontocortical responses and benign ones evoke relatively larger reactions in persons with a family history of cardiovascular disease. Blockade of neural projections from the frontal cortex and amygdala to the brainstem cardiovascular centers will normalize blood-pressure elevations in experimental hypertension and prevent lethal arrhythmias in animals with a myocardial infarction. The anti-mortality effect of the cardiac drugs known as beta-blockers is exerted by inhibition of cerebral beta-receptors, not peripheral ones. A new putative neuropeptide, NLX, may have the same desirable cardiovascular effects, but without the side-effects that limit clinical usefulness. The neural regulation of the heart during stress can be detected by a new deterministic measure of low-dimensional chaos in heartbeat intervals. In both animals and humans undergoing myocardial infarction, this deterministic measure correctly predicts lethal arrhythmogenesis, minutes to hours prior to the event. Thus an approach combining both brain and heart studies (i.e., "neurocardiology") has led to an understanding of how stressor-stimuli evoke autonomic reactions. This, in turn, has led to new methods in the diagnosis and treatment of cardiovascular disorders.

Animals↗