The destruction of myelin sheath is very common in diseases such as multiple sclerosis. It is believed to be an autoimmune disease in which the body destroys the myelin sheath. Other diseases that may result from demyelination are myasthenia gravis and Tay-Sachs disease. Dementia is a symptom of neurodegenerative diseases such as Alzheimer's disease, which is categorized by the presence of neurofibrillary tangles and beta-amyloid plaques in the brain. Meningitis is the inflammation of the meninges. This disease can be caused by several infectious agents such as viruses and/or bacteria. Muscular dystrophy is a genetic disorder in which the dystrophin gene is mutated, disrupting the physical structure of muscles, causing skeletal muscular weakness and death of the muscle cells. 

GABA is an inhibitory neuron in the brain. When GABA levels are low, the result may be overstimulation of neurons in the brain, which can lead to epileptic seizures or development of clinical anxiety. Dopamine is a neurotransmitter that plays a role in the pleasure-reward system and is linked to schizophrenia and Parkinson's disease. Serotonin is  involved in regulating sensory perception, and onset of sleep and control of mood and emotions. Clinically, serotonin has been implicated in depression and impulsive behavior. Acetylcholine is the neurotransmitter used at the neuromuscular junction. Substance P is a non-opiod neuroactive peptide that is found in the pain pathway in the spinal cord. 

Schizophrenia is thought to be caused by excessive dopamine release or an abnormal sensitivity to dopamine. Therapeutic drugs for schizophrenia either reduce the secretion of dopamine or bind to dopamine receptors so dopamine is unable to bind. GABA is an inhibitory neuron in the brain. When GABA levels are low, the result may be overstimulation of neurons in the brain, which can lead to epileptic seizures or development of clinical anxiety. Serotonin is involved in regulating sensory perception, and onset of sleep and control of mood and emotions. Clinically, serotonin has been implicated in depression and impulsive behavior. Acetylcholine is the neurotransmitter used at the neuromuscular junction. Substance P is a non-opiod neuroactive peptide that is found in the pain pathway in the spinal cord. 

Parkinson's disease is a disorder of the basal ganglia, which plays a dominant role in movement. Those with Parkinson's will develop a tremor at rest, an increase in rigidity, and slowness in carrying out movements. The neurotransmitter dopamine plays an important role in the development of the disease and the degeneration of dopaminergic fibers occurs in Parkinson's disease. Huntington's Disease is characterized by hyperactivity (rather than a decrease, which is found in Parkinson's disease. GABAergic neurons may be affected during the early stages of the disease, causing over activity. Alzheimer's disease is a neurodegenerative disease that involves memory loss. Meningitis is an infection that causes inflammation of the meninges of the brain. Grave's disease is an autoimmune condition that is characterized by an overproduction of thyroid hormones. 

Acetylcholine is the neurotransmitter used at the neuromuscular junction. The antibodies produced against acetylcholine receptors at the neuromuscular junction prevent synaptic transmission, causing the muscle weakness and fatigue characterized by Myasthenia Gravis. Epinephrine(also known as adrenaline) is a monoamine that plays an important role in the sympathetic nervous system. GABA is the main inhibitory neurotransmitter in the brain. Dopamine is neurotransmitter that plays an important role in the body's pleasure and reward system. It is characterized as a catecholamine. Serotonin is a monoamine neurotransmitter that acts throughout the body and plays a role in depression and happiness. 

Insomnia is a sleep disorder, in which people have trouble falling or staying asleep. It can be an acute or chronic disorder. Insomnia can cause other problems such as anxiety, inattention, or depression. It can be treated by lifestyle changes, medication, or therapy.

Narcolepsy is a disorder that leads to extreme daytime sleepiness and/or muscle weakness. It causes people to fall asleep suddenly, even in the middle of tasks. There is no cure, but it can be managed by medicine, lifestyle changes, or therapy.

Sleep apnea is a disorder in which you stop breathing at night while asleep. Often, those suffering from the disorder are not aware they wake up at night to breathe. It creates a poor quality of sleep, which leads to daytime sleepiness.

Hydrocephalus occurs when there is a disruption in the circulation of cerebral spinal fluid or CSF. This can cause swelling of the head and may be treated by shunting some of the excess CSF out of the cranial cavity. Temporomandibular joint (TMJ) disorder affects the jaw and is caused by a misalignment of joints. Hemorrhagic fever is caused by an infectious agent, like the Ebola virus. Uncontrollable cell growth is also known as cancer. 

Epilepsy is also known as a seizure disorder and is a disorder of the nervous system. A seizure is a short term change in normal brain activity. There are two types of seizures: generalized, which affects both sides of the brain, and focal, which affects one area of the brain. Ebola is caused by a virus that causes hemorrhagic fever. Cerebral edema is classified by swelling of the brain, which can cause irreversible damage and death in severe cases. Elephantiasis is a symptom classified by excessive swelling of a certain part of the body.