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Before-sleep jerks: myoclonic spasms

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It's three at night. You wake up abruptly, practically jumping out of bed, with the sensation of falling from an eight-story building. You notice how your viscera are still reacting with a certain panic.

Your partner wakes you up at three in the morning, slightly surprised and upset. It tells you that while you were sleeping you have kicked him several times. These two small fragments reflect the existence of a phenomenon that occurs with great frequency in most of the population: the making of small sudden and involuntary movements During the dream.

These movements are called nocturnal myoclonic spasms.

What is myoclonus?

When speaking of myoclonic spasms, reference is made to a series of sudden and brief muscular contractions, totally involuntary, that cause a displacement of the body or a part of it. They are usually caused by sudden muscle contractions or muscle relaxation..

Although this type of spasm can be found in some disorders such as epilepsy, there are also so-called benign myoclonus. These as a general rule are not considered pathological, being considered normal in people without associated pathology. In fact,

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a phenomenon as common as hiccups would be a valid example of benign myoclonus spasm.

These spasms can appear both while awake and during sleep, with this article focusing on the latter.

nocturnal myoclonic spasms

Although the general definition of myoclonus reflects the type of phenomenon being talked about, those that occur during sleep have a peculiarity: just like that occurs with hypnagogic and hypnopompic hallucinations, occur in a state of altered consciousness: sleep or the transition between sleep and sleep. vigil. In this case, myclonic spasms would be a type of parasomnia, episodic phenomena or disorders that occur during sleep and are characterized by the presence of vegetative or motor symptoms.

It is a generally non-pathological phenomenon with high prevalence in the population. It is estimated that around 70% of the population has had a myoclonus spasm at some point. During the dream. Now, if the symptoms occur repeatedly and constantly, it would be advisable to go to a doctor, because if they occur persistently could indicate the presence of a disorder.

It must be taken into account that it is possible to confuse this type of alteration, which is not dangerous, with an epileptic crisis. In this aspect, one of the few ways to differentiate them is by means of an electroencephalogram, not assuming myoclonic spasms the same type of alterations that are visualized in cases of epilepsy.

Neurological causes of myoclonic spasms during sleep

The reason these spasms occur during sleep has a neuroscientific explanation.

The appearance of nocturnal myoclonus it is due to the presence of a lack of coordination, to the maintenance at the same time of the activity, of two specific brain areas. Specifically, the reticular formation or reticular activating system (RAS) and the ventrolateral preoptic nucleus.

Reticular activating system

This system located in Brain stem It is the main one in charge of keeping us alive, since it is the cerebral system that directs unconscious processes such as breathing, digestion or heart rate. Apart from these physiological processes, it also participates in maintaining alertness and focusing attention, maintaining wakefulness.

ventrolateral preoptic nucleus

The ventrolateral preoptic nucleus can be found in the hypothalamus anterior, near and in contact with the lobe occipital. This nucleus is responsible for "turning off consciousness" by inducing the state of sleep, as well as for protecting the body during sleep causing body paralysis that prevents us from moving and harming ourselves during sleep deep.

When do myoclonic spasms happen?

To understand the appearance of spasms, it must be taken into account that although during sleep it reduces its operation, the SAR does not cease its operation (since such a thing would cause the death of the affected).

Thus, this system still has some activation that can sometimes go into contradiction with the functioning during sleep of the ventrolateral preoptic nucleus that causes sleep.

This contradiction, the cause of which is still unknown, can partially provoke typical motor reactions of wakefulness during sleep. In other words, it is the origin of myoclonic spasms during sleep.

Types of nocturnal myoclonus

Myoclonic spasms during sleep are not uniform and homogeneous, but there are three basic types.

A first type is found in repetitive movements during sleep. Similar to the typical movements of epileptic seizures, these movements appear during non-paradoxical sleep, being repetitive movements of short duration. Although treatment is not usually required, very severe forms can be treated pharmacologically.

A second type of myoclonic spasm presenting during sleep is nocturnal jerks or startle myoclonus. The clearest example of this type of spasm is the typical movement that is made when waking up from a dream in which we have the sensation of falling. They usually occur in superficial sleep, that is, in the first two phases of sleep, causing the sufferer to wake up with some abruptness. They are usually massive shaking of the whole body, especially the lower extremities.

Finally, some spasms can be found at the time of transition between wakefulness and sleep. This type of myoclonus, classified as non-specific, acts on the muscles of the face and extremities.

Bibliographic references:

  • Ferber, R. & Kryger, M. (1995). Principles and Practice of Sleep Medicine in the Child. W.B. Saunders Company.
  • Besag, F.M.C. (nineteen ninety five). Myoclonus and Infantile Spasms. In: Robertson MM, Eapen V, eds. Movement and allied disorders in childhood. Chichester: John Wiley and Sons, Ltd.; p. 149-76.
  • Fejerman, N.; Medina, C. S. & Caraballo, R.N. (1997). Paroxysmal disorders and non-epileptic episodic symptoms. In: Fejerman N, Fernández-Álvarez E, eds. Pediatric Neurology. 2nd ed. Madrid: Editorial Médica Panamericana S.A.; p. 584- 99.
  • Fernandez-Alvarez, E. & Aicardi, J. (2001). Movement disorders in childhood. London: MacKeith Press.
  • Morairty, S.; Rainnie, D.; McCarley, R. & Greene, R. (2004). Disinhibition of ventrolateral preoptic area sleep-active neurons by adenosine: a new mechanism for sleep promotion. neuroscience; 123: 451-7
  • Svorad, D. (1957). Reticular activating system of brain stem and animal hypnosis. Science 125 (3239): 156-156.
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