Neurotransmitters

There are many organs that are a part of the endocrine system. Many are controlled in part by the actions of the pituitary gland and hypothalamus. Many bodily functions are regulated by the endocrine system and its hormones.

The pituitary gland is sometimes considered to be the master gland because it has so many hormones that ultimately regulate other endocrine glands. The pituitary gland is itself under the control of the hypothalamus in the brain.

The thyroid gland is located in the front of the neck. It is important in appetite, metabolism, and growth. There are diseases of an overactive thyroid that results in increased metabolism as well as diseases of an underactive thyroid gland, which greatly slows metabolism. Medications and surgery can help to balance these thyroid disorders. Some psychological disorders are directly linked to problems with an overactive or underactive thyroid gland.

The other major glands in the endocrine system include the adrenal glands, which makes stress hormones, including those responsible for the fight or flight response, the pancreas, which regulates blood sugar levels, the pineal gland, which makes melatonin as part of the Circadian rhythm of the body, and the gonads, which make the sex hormones responsible for sexual maturation and sexual behaviors.

NEUROTRANSMITTERS

There are dozens of neurotransmitters in the nervous system. As mentioned, they act across synapses in order to send a signal to another neuron, a muscle cell, or some type of endocrine gland. Neurotransmitters tend to be small molecules, often made from amino acid precursors, after which they are synthesized into their final form. They are stored in presynaptic vesicles close to the axon terminal so they can be released into the synaptic cleft.

When they are released into the synapse, they cross the small space and attach to specific receptors, initiating an action potential in the postsynaptic cell. Neurotransmitters can be excitatory and will turn on the target cell s action or inhibitory, which means it will block the target cell s action. If excitation exceeds inhibition, the neuron will be activated and will fire an action potential.

There are different types of neurotransmitters. These include those based on amino acids, those that are gaseous, monoamines, peptides, catecholamines, purines, and trace amines. One major excitatory neurotransmitter is glutamate, the most prevalent neurotransmitter. Another highly prevalent neurotransmitter is GABA, which stands for gamma-aminobutyric acid. This is largely inhibitory. Most psychoactive drugs will act specifically on neurotransmitter systems and many drugs of abuse act on the dopamine system, such as amphetamines and cocaine. Opioid drugs act on opioid receptors of the brain.

The following is a partial list of important neurotransmitters:

• Glutamate—this is the major excitatory neurotransmitter that can lead to seizures or strokes if it is overactive in the body.

• GABA—this is the major inhibitory neurotransmitter and is mimicked by many sedative and hypnotic drugs.

• Acetylcholine—this is the major neurotransmitter that acts at the neuromuscular junction in order to activate musculature activity.

• Dopamine—this is important in motivation, the experience of pleasure, emotional arousal, and motor function. High levels have been implicated in schizophrenia.

• Serotonin—this is a major intestinal neurotransmitter and affects things like mood, behavior, sleep, appetite, learning memory, and body temperature. Low levels have been implicated in depression.

There are several diseases that are believed to be related to imbalances of certain neurotransmitters in the brain. Some examples of these include the following:

1. Dopamine—low levels are seen in Parkinson’s disease, while high levels are seen is schizophrenia and ADHD (attention deficit hyperactive disorder). Addiction is strongly related to the dopamine system. Opioid drugs and methamphetamine will increase dopamine levels, leading to a pleasurable feeling.

2. Serotonin—low levels may or may not be associated with depression but selective serotonin reuptake inhibitors (SSRIs) will increase serotonin and will help improve depressive symptoms.