Nerve impulses always flow in one direction – from the branched extensions called dendrites, down the neuron to the presynaptic terminals. The join between the presynaptic terminals of one neuron and the dendrites of another is called the synapse. The two neurons do not actually touch each other but are separated by a space called the synaptic cleft. When a nerve impulse arrives at a presynaptic terminal it causes neurotransmitters to be released into the synaptic cleft. The neurotransmitters then bind with special “postsynaptic receptors” in the dendrites of the receiving neuron. When a postsynaptic receptor receives a neurotransmitter it can either cause a nerve impulse to travel down the neuron or it can inhibit a nerve impulse depending on the neurotransmitter released.
Neurotransmitters which propagate nerve impulses in the receiving neuron are called excitatory neurotransmitters. Those which inhibit nerve impulses are called inhibitory neurotransmitters.
Neurotransmitters are sythesized in the cell body (the soma) and migrate down the axon to the presynaptic terminals. Here they are stored in little packets called vesicles which fuse with the synaptic membrane. When a depolarizing current (the action potential) is received, these vesicles release their contents into the synaptic cleft.Many different substances effect the transmission of nerve impulses across the synapse and many of these are falsely called neurotransmitters. To be a neurotransmitter a substance must:
Neurotransmitters activate receptors by “sticking” to them and thus preventing other neurotransmitters from activating them. Inactivation of the transmitter happens in one of three ways:
Substances that effect neurotransmission but are not neurotransmitters can be broadly divided into two categories – agonists and antagonists. Agonists make transmission of nerve impulses more likely. They do this in a number of ways including preventing reuptake (cocaine works this way), actually triggering the receptor themselves (nicotine works this way) and by making the receptor more responsive (a lot of anti-anxiety drugs work like this). Antagonists do the opposite – they interfere with nerve transmission across the synapse sometimes by blocking receptor sites (many spider and snake venoms work this way) and sometimes by preventing release of the neurotransmitter from the presynaptic terminal (many anti-psychotic drugs operate like this).
What Are Neurotransmitters and How They Affect Your Life?
Just like hormones govern many chemical functions in the body, the brain’s chemical functions are governed by messengers called neurotransmitters.
A neurotransmitter is a chemical messenger used by neurons (nerve cells) to communicate in one direction with other neurons. These neurotransmitters are either excitatory or inhibitory. Each cell receives its instructions through nerve processes called dendrites and it passes on instructions to the next cell through its axon. The gap between the axon of one cell and the dendrite of the next is called a synapse.
Special molecules in the dendrite are called receptors. They are shaped to receive only one type of neurotransmitter, which fits it like a key in a lock. The result is that if an excitatory neurotransmitter reaches the specific receptor, the cell tends to fire. If an inhibitory neurotransmitter reaches the receptor, the cell does not fire.If neurotransmitters of either type are in short supply, or if they are blocked from reaching their proper receptors, (as a result of either genetics and/or chemical use) cell function tends to be abnormal. The lack of neurotransmitter function then results in maladaptive behavior.
The human brain is very capable of automatically manufacturing the quantity of chemicals it needs IF it is given the raw materials (nutrients from foods) to do so. However, normal diet does not supply enough of the raw materials the brain needs to manufacture the needed level of neurotransmitters. Additionally, stress, worry, chemical use, poor nutrition, pollution and other factors of modern life are known to deplete neurotransmitter levels.
In order to ingest the required amount of food to provide the necessary amount of amino acids needed to maintain normal neurotransmitter levels we would have to eat each day:
Not only is this impractical it is impossible, so therefore another source of nutritional support is necessary so we do not gain hundreds of pounds.
Neurotransmitters are small molecules whose function is to transmit nerve signals (impulses) from one nerve cell (neuron) to another. Neurotransmitters are chemical messengers which neurons use to tell other neurons that they have received an impulse. There are many different neurotransmitters – some trigger the receiving neuron to send an impulse and some stop it from doing so.
See this simplified diagram of a neuron: