Chemistry of Brain Function Basics

They elicit some actions such as muscle movement. Hence, disruption of the brain functions can lead to such a result as emotional/mood change or paralysis, etc. 

The brain consists of cells called neurons there are several hundreds of billions of such cells in our brain. A neuron makes connections to a number (several thousands) of other neurons. The signal travels within a neuron as an electric signal the electric impulse is created by ionic movement through ion channels aaoss the cell membrane such as sodium and potassium channel. When the signal comes to a junction called synapse , it has to be carried by a chemical compound across the narrow gap (which is 5-20 nm wide) between the neurons. Such a chemical compound is called neurotransmitter . A neurotransmitter molecule binds to the receptor site on the surface of a post-synaptic neuron. The receptor is an ion channel, and the binding of a neurotransmitter opens the channel, hence resulting in the creation of a new electric signal on the postsynaptic cell. 

Several different types of neurotransmitter compounds are known. One is acetylcholine, and its mechanism of action seems to be best understood and will be discussed shortly. The second group called catecholamines contains rather familiar compounds such as adrenalin (epinephrine), noradrenalin (norepinephrine), and dopamine (Fig. 17.1). The third group consists of several amino acids such as regular ones glutamic acid and aspartic acid, and unusual ones such as y-aminobutyric acid (GABA) and A-methyl-D-aspartate (NMDA). Another group contains several small proteins (peptides). Examples are enkephalin, endorphin, gonadotropin, oxytocin, and vassopressin. 

The mechanisms of all the neurotransmitters function have not been well understood. One neurotransmitter, acetylcholine, has been studied intensely and will be discussed briefly here. The structure of acetylcholine is shown in Fig. 17.2, along with those of nicotine, serotonin and muscarine. Acetylcholine is released from the synapse and migrates to the next neuron surface nearby, and binds to a receptor. There are two types of acetylcholine receptor one is nicotinic , implying that it also binds nicotine, and the other muscarinic . Nicotine and muscarine (as seen in Fig. 17.2) have a common feature, i.e., a positively charged nitrogen such as acetylcholine. The receptor itself is an ion channel. When acetylcholine binds with the receptor, the ion channel opens up, and the inflow of Na and outflow of K ensues. The sudden change of the cationic concentration inside and outside of the postsynaptic neuron creates an 

It has been demonstrated also that serotonin (another neurotransmitter, alternatively called 5-HT (5-hydroxytryptamine), see Fig. 17.2) similarly binds to a receptor through the interaction between a tryptophan residue and the positive charge on serotonin. 

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