The brain needs certain chemicals--the neurotransmitters--in order to function properly. Each nerve cell in the brain is separated by tiny gaps. The neurotransmitters carry messages across these gaps to a receptor. Each neurotransmitter has a special shape that helps it fit exactly into the corresponding receptor like a key in an ignition switch. When the neurotransmitter "key" is inserted into its matching receptor's "ignition", the cell fires and sends the message on its way. Once the message is sent, the neurotransmitter is either absorbed into the cell or burned up by enzymes surrounding the gaps.
Although there are at least 100 different kinds of neurotransmitters, medical research has identified three in particular that control our moods, and thus the very quality of our lives. They are norepinephrine, seratonin, and dopamine. When the levels of one or all of these are low, messages can't get across the gaps. Sometimes a neurotransmitter can't fit into its receptor. If this happens, the nerve cell can't get the message it's supposed to send to some part of the body.
Depression has afflicted man for hundreds of years. King David had some very depressing times in his life. He wrote in Psalm 31:9,10:
"Be merciful to me, O Lord, for I am in distress; my eyes grow weak with sorrow, my soul and my body with grief. My life is consumed by anguish and my years by groaning; my strength fails because of my affliction, and my bones grow weak."
We are very fortunate to live in a time where there is help for Clinical Depression. Less than a hundred years ago people with Depression, and other forms of mental illness, would be hidden away by family members or committed to insane assylums to live out the remainder of their lives. I thank God that is no longer the case.
According to the National Institues of Health, the Symptoms of Depression can include:
Persistent sad or "empty" mood
Loss of pleasure in ordinary activities, including sex
Decreased energy, fatigue, being "slowed down"
Sleep disturbances (insomnia, early morning wakening, or oversleeping)
Eating disturbances (loss of appetite and weight, or weight gain)
Feelings of guilt, worthlessness, helplessness
Thoughts of death or suicide, suicide attempts
Irritability
Excessive crying
Cronic aches and pains that don't respond to treatment
A thorough diagnoses is needed if four or more of the symtoms of Depression persist for more than two weeks, or are interfering with work or family life.