It has been argued that sound scientific support is lacking for the claim that the specified purely bedside tests have the power to diagnose true and total death of the brainstem, the necessary condition for the assumption of permanent loss of the intrinsically untestable consciousness-arousal function of those elements of the reticular formation which lie within the brainstem (there are elements also within the higher brain). Knowledge of this arousal system is based upon the findings from animal experiments as illuminated by pathological studies in humans. The current neurological consensus is that the arousal of consciousness depends upon reticular components which reside in the midbrain, diencephalon and pons. It is said that the midbrain reticular formation may be viewed as a driving centre for the higher structures, loss of which produces a state in which the cortex appears, on the basis of electroencephalographic (EEG) studies, to be awaiting the command or ability to function. The role of diencephalic (higher brain) involvement is stated to be uncertain and we are reminded that the arousal system is best regarded as a physiological rather than a precise anatomical entity. There should, perhaps, also be a caveat about possible arousal mechanisms involving the first and second cranial nerves (serving sight and smell) which are not tested when diagnosing brainstem death but which were described in cats in 1935 and 1938.
A spasm is a sudden involuntary contraction of a muscle, a group of muscles, or a hollow organ such as the bladder. A spasmodic muscle contraction may be caused by many medical conditions, including dystonia. Most commonly, it is a muscle cramp which is accompanied by a sudden burst of pain. A muscle cramp is usually harmless and ceases after a few minutes. It is typically caused by ion imbalance or muscle overload. There are other causes of involuntary muscle contractions, and some of these may cause a health problem. Description and causes
Various kinds of involuntary muscle activity may be referred to as a "spasm". A spasm may be a muscle contraction caused by abnormal nerve stimulation or by abnormal activity of the muscle itself. A spasm may lead to muscle strains or tears in tendons and ligaments if the force of the spasm exceeds the tensile strength of the underlying connective tissue. This can occur with a particularly strong spasm or with weakened connective tissue. A hypertonic muscle spasm is a condition of chronic, excessive muscle tone (i.e., tension in a resting muscle). This is the amount of contraction that remains when a muscle is not working. A true hypertonic spasm is caused by malfunctioning feedback nerves. This is much more serious and is permanent unless treated. In this case, the hypertonic muscle tone is excessive, and the muscles are unable to relax. A subtype of spasm is colic.