MicroRNAs (miRNAs) are a family of small non-coding RNAs that control the expression levels of multiple proteins by decreasing mRNA stability and translation, and could therefore be key regulatory mechanisms and therapeutic targets in epilepsy In epilepsy, the resistance of excitatory neurons to fire during this period is decreased. This may occur due to changes in ion channels or inhibitory neurons not functioning properly. This then results in a specific area from which seizures may develop, known as a "seizure focus". Another mechanism of epilepsy may be the up-regulation of excitatory circuits or down-regulation of inhibitory circuits following an injury to the brain. These secondary epilepsies occur through processes known as epileptogenesis. Failure of the blood–brain barrier may also be a causal mechanism as it would allow substances in the blood to enter the brain. Seizures
There is evidence that epileptic seizures are usually not a random event. Seizures are often brought on by factors (also known as triggers) such as stress, excessive alcohol use, flickering light, or a lack of sleep, among others. The term seizure threshold is used to indicate the amount of stimulus necessary to bring about a seizure; this threshold is lowered in epilepsy.In epileptic seizures a group of neurons begin firing in an abnormal, excessive, and synchronized manner. This results in a wave of depolarization known as a paroxysmal depolarizing shift. Normally, after an excitatory neuron fires it becomes more resistant to firing for a period of time.
Hutchinsons sign is a clinical sign which may refer to:

Hutchinsons pupil, an unresponsive and enlarged pupil on the side of an intracranial mass
Vesicles on the tip of the nose, or vesicles on the side of the nose, precedes the development of ophthalmic herpes zoster. This occurs because the nasociliary branch of the trigeminal nerve innervates both the cornea and the lateral dorsum of the nose as well as the tip of the nose. This sign is named after Sir Jonathan Hutchinson. Melanonychia with pigmentation of the proximal nail fold. : 671  This is an important sign of subungual melanoma although is not an infallible predictor. Periungual hyperpigmentation occurs in at least one nonmelanoma skin cancer, Bowens disease of the nail unit. This is a nail fold pigmentation which then widens progressively to produce a triangular pigmented macule with associated nail dystrophy. Hyperpigmentation of the nail bed and matrix may reflect through the "transparent" nailfolds simulating Hutchinsons sign. Hutchinsons triad - pattern of presentation of congenital syphilis. See also
Green nail sign
List of cutaneous conditions


== References ==