Chemical transmission of nerve impulse

The concept of a neurotransmitter originated in the 1920s with the acetylcholine molecule. Henry Dale and Otto Loewi originated the concept of chemical transmission of nerve impulses. These scientists shared the 1936 Nobel Prize in Physiology or Medicine for this work. Acetylcholine was also the first neurotransmitter for which the structure was determined. Otto Loewi accomplished that task, also in 1936. 

Figure 5.7 Diagram of the neuralmuscular system showing its parts and chemical transmission of nerve impulse...

Ulf Svante von Euler (1905-1983) was born in Stockholm, Sweden, to a distinguished academic family. His father, Hans von Euler-Chelpin, received the 1929 Nobel Prize in chemistry his godfather, Svante Arrhenius, received the 1903 Nobel Prize in chemistry and his mother had a Ph.D. in botany. Von Euler received an M.D. from the Karolinska Institute in 1930, and then remained there his entire career (1930-1971). He received the 1970 Nobel Prize in medicine for his work on the chemical transmission of nerve impulses. 

In 1936 he shared the Nobel Prize for physiology or medicine with his friend German pharmacologist otto LOEWI for their discoveries in the chemical transmission of nerve impulses. 

His neurological researches during the period 1921-26 provided the first proof that chemicals were involved in the transmission of impulses from one nerve cell to another and from neuron to the responsive organ. It was for his discovery of the chemical transmission of nerve impulses that he received the Nobel Prize in physiology or medicine in 1936, jointly with Sir Henry Dale. Loewi spent his years investigating the physiology and pharmacology of metabolism, the kidneys, the heart, and the nervous system. He became an American citizen in 1946 and died on December 25, 1961. 

Henry Hallett Dale, Otto Loewi Chemical transmission of nerve impulses... 

Epinephrine or adrenaline (X) is one of the well-known drugs in medicine. Only recently it was discovered to contain 10-18% norepinephrine or arterenol (IX) when prepared from beef adrenal glands (47). Both epinephrine and norepinephrine exist in levorotatory form and are hormones of the body. When sympathetic nerves are electrically stimulated, epinephrine and norepinephrine are liberated producing the characteristic responses of the visceral organs (48). This accounts for the chemical transmission of nerve impulses, and the two bases serve as mediators. Both epinephrine and norepinephrine are present in the venom of certain toads (49-52). 

Dale HH. The chemical transmission of nerve impulses. Science. 1934 80(2081) 450. 

N euro transmitters are chemical substances called neurohormones. These are released at Hie nerve ending that facilitate the transmission of nerve impulses. The two neurohormones (neurotransmitters) of the sympathetic nervous system are epinephrine and norepinephrine Epinephrine is secreted by the adrenal medulla Norepinephrine is secreted mainly at nerve ending of sympathetic (also called adrenergic) nerve fibers (Pig. 22-2). 

Neurohumoral transmitters are chemicals that facilitate the transmission of nerve impulses across nerve synapses and neuroeffector junctions. Acetylcholine is a neurohumoral transmitter that is present in the peripheral autonomic nervous system, in the somatic motor nervous system, and in some portions of the central nervous system. 

The cations Mg and Ca are major components of bones. Calcium occurs as hydroxyapatite, a complicated substance whose chemical formula is Cas (P04)3 (OH). The structural form of magnesium in bones is not fully understood. In addition to being essential ingredients of bone, these two cations also play key roles in various biochemical reactions, including photosynthesis, the transmission of nerve impulses, and the formation of blood clots. 

Reactions that involve the transfer of electrons are immensely beneficial in a vast range of chemical processes, from the operation of a battery to the transmission of nerve impulses. However, in the form of corrosion, electron-transfer reactions also can be highly destructive. The rasting of iron objects is a prominent example of corrosion. 

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. 

Nerve agents Highly toxic and potentially lethal chemical agents that affect the human nervous system by inhibiting the enzyme that aids the transmission of nerve impulses. Causes blurred vision, weeping, nausea, vomiting, urinary incontinence, respiratory distress, and reduced mental capability by attacking the nervous system. 

However, any compound, even if it is chemically inert, if present at high enough concentrations in biological membranes can change those membranes properties and disrupt their functions. Consequently, membrane-associated processes like photosynthesis, energy transduction, transport in or out of the cell, enzyme activities, transmission of nerve impulses, and so on may deteriorate (see van Wezel and Opperhuizen, 1995 and literature cited therein). Since these effects seem to be primarily dependent on the space that contaminating molecules occupy in the... 

As with the mental effects of nicotine, the physiological effects are brought about by its actions on the nervous system, both peripheral and central. Nicotine changes the transmission of nerve impulses by binding to acetylcholine receptors, and induces the release of several chemical messengers, which in turn affect several body systems. 

Cocaine acts as a local anaesthetic, that is at the site of application, probably by interfering with transmission of nerve impulses by changing the permeability of the nerve to sodium ions. While the drug is no longer used for this purpose, many of the newer local anaesthetics are based on the chemical structure of cocaine. 

Another arrow poison, common in South America, was curare, which was extracted from a plant (Chondrodendron). A constituent of this extract, tubocurarine, blocks transmission of nerve impulses to muscles, leading to complete paralysis and death from cessation of breathing. The chemical has been used as a drug for the purpose of relaxing the muscles of a patient. One of the arrow poisons used in Africa was extracted from a species of the plant Strophanthus and contained strophanthidin and oubain (pronounced waabain ). These have similar effects as digitalis on the heart and, in sufficient quantities, can be lethal. The poisoned patient would suffer from erratic rhythms of the heart, a slowing of the heart, and possibly uncontrolled movements of the heart muscle (ventricular fibrillation). 

Transmission of nerve Impulses at chemical synapses depends on the exoc3rt osIs of neurotransmitter-filled synaptic vesicles and the regeneration of empty vesicles by endocytosis. 

I he transmission of nerve impulses at the neuromuscular junction involves many steps, one of which is the activity of a critical enzyme, called acetylcholinesterase, which catalyzes the hydrolysis of the chemical messenger, acetylcholine, that initiated the nerve impulse. The need for this enzyme activity becomes clear when we consider the events that begin with a message from the nerve cell and end in the appropriate response by the muscle cell. Acetylcholine is a chemical messenger that transmits a message from the nerve cell to the muscle cell. Such a molecule is known as a neurotransmitter. Acetylcholine is stored in membrane-bound bags, called synaptic vesicles, in the nerve cell ending. 

We know that for many chemicals (vitamins, trace minerals, hormones, amino acids, electrolytes, etc.) there are optimal levels in the body which are required for normal function. Too little is injurious to health, as is too much. Any diabetic is only too aware of the delicate balance of insulin required to maintain health. Too little sodium in the body interferes with the transmission of nerve impulses hypertensive patients know the consequence of too much sodium. Many other examples are well described in the medical literature. 

Chemicals that affect the nervous system and cause inflammation of the nerves. The result is tenderness of the nerves, pain, interference with transmission of nerve impulses, and even paralysis. 

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