Stimulatory impulses

A meta-analysis of 32 pubhcations of nerve-conduction studies and occupational lead exposure foimd BLL to be a weak predictor of peripheral nerve impairment (Davis and Svendsgaard 1990). Nerve-conduction testing includes analysis of latent period (time it takes for stimulatory impulse to initiate an evoked potential), conduction velocity, and amplitude. Reduced nerve-conduction velocities in lead-exposed subjects revealed that the median motor nerve was most sensitive. 

This group consists of j3-adrenergic receptor blockers, the antiarrhythmic activity of which is associated with inhibition of adrenergic innervation action of the circulatory adrenaline on the heart. Because all 8-adrenoblockers reduce stimulatory sympathetic nerve impulses of catecholamines on the heart, reduce transmembrane sodium ion transport, and reduce the speed of conduction of excitation, sinoatrial node and contractibility of the myocardium is reduced, and automatism of sinus nodes is suppressed and atrial and ventricular tachyarrhythmia is inhibited. 

In patients with cardiac arrest, for example as a result of an intoxication with local anaesthetics, quinine or other cardiodepressant drugs, the stimulatory action of adrenaline on the impulse formation and propagation in the heart can be life saving. 

The secretion of epinephrine by the adrenal medulla is controlled directly by nerve impulses and also by the other stress hormones, namely, corticosteroids. This is illustrated in Figure 16.11. Nerve impulses have a major stimulatory effect on tyrosine and dopamine hydroxylases, whereas glucocorticoids have a major effect on phenylethanolamine methyltransferase. Tyrosine hydroxylase is considered the rate-controlling enzyme in the biosynthesis... 

Also important in understanding the function of the nervous system are the one-way flow of information across synapses and stimulatory versus inhibitory impulses Most synapses in the CNS will conduct an impulse (usually via a neurotransmitter) in one direction only that is, from the axon of the presynaptic neuron to the dendrite or cell body (soma) of the postsynaptic neuron (see Figures 1.2 and 1.3). This unidirectionality is critical in preserving the integrity of the information flow in the CNS. A particular postsynaptic neuron will have anywhere from 10,000 to 200,000 terminals, or receptor sites, that interact with presynaptic neurons. These terminals are activated by neurotransmitters. Activating some terminals will cause the postsynaptic neuron to fire an impulse to its neighbor neurons. When other terminals are activated, the same postsynaptic neuron will be especially quiet and will not fire off any impulses. This concept of stimulation versus inhibition and inhibitory impulses from one neuron to another is key in our discussion of mental illness and its treatment. 

Under normal conditions (A), nerve impulses from the motor neurones (M) to the muscles are under the control of neurotransmitters (- F) released by the stimulatory (S) and inhibitory (1) nerves. These bind to specific receptor molecules (W) on the surface of the neurone which... 

Dopamine, serotonin, and endogenous enkephalins (opiates) modulate neuronal activity. If you drop dopamine on isolated neurons, transmission of neuronal impulses is inhibited. Dopamine and serotonin counteract the effect of the stimulatory monoamines, epinephrine and norepinephrine. 

Relaxes nerve impulses, functioning antagonistically to calcium which is stimulatory. 

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