The g-proteins of A1 receptors continue to inhibit adenylate cyclase, some voltage gated Ca2+ channels, and activate some K+ channels, and phospholipase C and D. A1 receptors are primarily located in the hippocampus, cerebral and cerebellar cortex, and particular thalamic nuclei. Adenosine acts on A1 receptors to decrease opening of N-type Ca2+ channels in some hippocampal neurons, and therefore decrease the rate of firing since Ca2+ is necessary for neurotransmitter release. Caffeines antagonistic action on the A1 receptor thus decreases the action of adenosine, allowing increased Ca2+ entry through N-type channels and higher rates of neurotransmitter release. Other actions of caffeine
Though antagonism of adenosine receptors is the primary mechanism of caffeine, Introduction of the methylxanthine into the body also increases the rate of release and recycling of some monoamine neurotransmitters such as noradrenaline and dopamine. Caffeine also has an excitatory effect on mesocortical cholinergic neurons by acting as an antagonist on adenosine receptors that normally inhibit the neuron. Genetics and variability of caffeine consumption
While many factors contribute to individual differences in a persons response to caffeine, such as environmental and demographic factors (i.e. age, drug use, circadian factors, etc. ), genetics play an important role in individual variability. This inconsistency in responses to caffeine can take place either at the metabolic or at the drug-receptor level. The effects of genetic factors can occur either directly by changing acute or chronic reactions to the drug or indirectly by altering other psychological or physiological processes.Some of these processes include wakefulness, stimulation, and mood and cognition enhancement.
Prognosis
Laryngomalacia becomes symptomatic after the first few months of life (2–3 months), and the stridor may get louder over the first year, as the child moves air more vigorously. Most of the cases resolve spontaneously and fewer than 15% of the cases will need surgical intervention. Parents need to be supported and educated about the condition. Epidemiology
Although this is a congenital lesion, airway sounds typically begin at age 4–6 weeks. Until that age, inspiratory flow rates may not be high enough to generate the sounds. Symptoms typically peak at age 6–8 months and remit by age 2 years. Late-onset laryngomalacia may be a distinct entity, which can present after age of 2 years. References


== External links ==