Acting on the Motor System

Cannabis has been used by humans for thousands of years for both psychoactive and non psychoactive purposes. It has long been known and remains in popular use for recreational purposes. Through the study of cannabis, we have discovered new chemical systems in the brain and body, and are just beginning to appreciate their functions. To be certain, cannabis is not an innocuous substance. Its chemical constituents potently act on the nervous system and other physiological systems. Several neurochemical systems in the brain are affected, with consequences in systems governing cognitive, motor, and emotional function. 

Certain organic forms of mercury can elicit specific damage in the main cell body of peripheral neurons. Similar responses are associated with certain natural products called vincristine and vinblastine, both of which have been used as antileukemic medicines. The deadly botulinum toxins, mentioned earlier in this chapter, block transmission of nerve impulses at the synapses of motor neurons. This blockage results in muscular paralysis which, if sufficiently severe, can lead to death, usually because respiration is impaired. The once widely used pesticide, DDT, is an organic chemical that also acts on the nervous system at this site, although it can also mount an attack on areas of the CNS. 

Colonic transit time is only slightly affected by food, but is redueed under stress. Studies have shown that drugs, which act on the parasympathetie or sympathetie nervous system, affeet the propulsive motor aetivity, thereby influeneing the eolonie transit time [12]. Although not significantly affected by most diseases [13], the transit time is shorter in patients who complain of diarrhea and longer in patients with eonsti-pation. 

Because these drugs relax muscles, they can cause prolonged muscle weakness and motor coordination problems. Some of these drugs also act on the central nervous system and cause side effects such as confusion, dizziness, sedation, nausea, and dry mouth. Most muscle relaxants are prescribed... 

Sydnocarb acts on the central nervous system and has been patented in many countries as a psychostimulant, an antidepressant and as a stimulant to motor activities (80RCR28). Sydnocarb has been tested extensively in the U.S.S.R. (80MI42102-7). 

BDNF brain derived neurotrophic factor is a member of the nerve growth factor family of trophic factors. In the brain, BDNF has a trophic action on retinal, cholinergic, and dopaminergic neurons, and in the peripheral nervous system it acts on both motor and sensory neurons. (From Kendrew, The Encyclopedia of Molecular Biology, 1994). 

The biogenic amine octopamine (OA) is widely recognized as an important neuroregulator in many invertebrates. It has been proposed as a neurotransmitter in the firefly light organ, and as a neuromodulator of muscle action and a neurohormone in the locust (J, 2). Octopamine also appears to act on central nervous system (CNS) sites affecting coordinated motor actions (3,4), and has been shown to modulate CNS thresholds for feeding in blowflies (5), and olfaction in honeybees (6). 

When ethanol is ingested, it acts on the central nervous system. Ingesting moderate amounts of ethanol affects one s judgment and lowers one s inhibitions. Higher concentrations interfere with motor coordination and cause slurred speech and amnesia. Still higher concentrations cause nausea and loss of consciousness. Ingesting very large amounts of ethanol interferes with spontaneous respiration and can be fatal. 

The skeletomotor system provides the structure and drives to move the body and Kmbs relative to the surroundings and to maintain the posture in space. The motor systems act on the environment by transforming neural information and metabolic energy into movement. Changes in external events or in the internal environment, signaled by the sensory systems, set up commands that are transmitted to the skeletal muscles by nerve impulses. The muscles convert the neural information into a command that transforms chemical into mechanical energy by generating a contractile force. 

Pharmacologically, the action of the various bacterial toxins is specific for each individual toxin. In the case of botulinus and tetanus toxins, action seems to be restricted to brain or nerve tissue. Bishop and Bronfenbrenner (11) state that botulinus toxin has a curare-like action and that the toxin is specific for the myoneural jimctions. Death in animals is due to respiratory paralysis. By means of artificial respiration, these authors and more recently Legroux and Levaditi (79) have been able to prolong the life of intoxicated animals for a considerable length of time. The pharmacological action of tetanus toxin is still a controversial question. Two main hypotheses have been summarized by Topley and Wilson (135) as follows (I) That the toxin is absorbed by the motor nerve endings and carried up the axis cylinders to the anterior horn cells of the central nervous system, which are then stimulated to produce muscular contractions and 2) that the toxin acts locally on the motor nerve endings and centrally on the anterior horn cells, which it reaches via the lymphatic vessels and the blood stream. ... 

The effect of BoTx and the pre-junctional release of ACh has been considered above. In addition, there are a number of neurotoxins acting on sensory and motor nerves. Examples include saxitoxin and blue water algal toxin. These toxins act by blocking the sodium channels in the nerves which lead to a failure of nerve conduction. In the motor system, this will in turn lead to a failure of NM transmission and paralysis. Paralysis of the respiratory muscles again leads to death from type 2 respiratory failure. 

Several parameters come into the relation between density and equivalence ratio. Generally, the variations act in the following sense a too-dense motor fuel results in too lean a mixture causing a potential unstable operation a motor fuel that is too light causes a rich mixture that generates greater pollution from unburned material. These problems are usually minimized by the widespread use of closed loop fuel-air ratio control systems installed on new vehicles with catalytic converters. 

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