NEUROTRANSMITTERS

Neurotransmitters are chemicals in the brain that pass signals by traveling from one neuron to another neuron or cell. Here are the basic steps in the movement of neurotransmitters:

1. Action potential reaches the synapse of the transmitting neuron.
2. Neurotransmitters present in the synaptic vesicles within the synapse of the transmitting neuron are released in the synaptic cleft.
3. Neurotransmitters from the transmitting neuron are bound to the receptors of the receiving neuron or cell.
4. A signal is generated in the receiving neuron or cell. 

There are many different types of neurotransmitters, some of the important ones are:

Acetylcholine: is the first and the most common neurotransmitter, isolated by German scientist Otto Loewi. Acetylcholine is abbreviated as ACh. It works both in the peripheral nervous system and central nervous system. In the peripheral nervous system, it activates muscles related to digestive, urinary, respiratory and cardiovascular systems. In the central nervous system, it is associated with memory and learning. Lack of acetylcholine in the brain is responsible for Alzheimer's disease.  Blocking Acetylcholine can cause Myasthenia Gravis, a disease where muscles are weakened and the body feels fatigued.

Glutamate: is the most abundant neurotransmitter in the brain. Glutamate is involved with memory and learning. It is also an excitatory neurotransmitter, meaning it's presence simulates parts of the brain. Glutamate is also toxic and an excess of it will kill parts of the brain. Excess of Glutamate in the brain is the cause for Lou Gehrig's disease.

GABA: also known as gamma Aminobutryic acid, is an inhibitory neurotransmitter. Which means that it prevents nearby neurons from getting excited. In other words, when an inhibitory neurotransmitter is received by a receptor, it blocks the action potential of that neuron, thus prevents it from firing excitatory neurotransmitter. People suffering from Anxiety disorder, Epilepsy or Huntington's disease lack in GABA.

Dopamine: is also an inhibitory neurotransmitter. Dopamine is associated with rewards mechanism in brain. Parkinson's disease is caused by a loss of dopamine producing neurons, on the other hand schizophrenia is caused by an excess of dopamine. Blocking dopamine receptors helps reduces psychotic symptoms. Dopamine also regulates the endocrine system by directing the hypothalamus to manufacture hormones and hold them in the pituitary gland.

Serotonin: is yet another inhibitory neurotransmitter. About 80% of human bodies serotonin is found in the gastrointestinal tract, where it controls the movement of the intestines. Remainder of it is found in the brain, where it is involved with sleep quality, mood and emotions. Lack of serotonin causes depression and intestinal disorders.

Norepinephrine: is both a hormone and a neurotransmitter. It is involved in memory and cognitive functions. It is released from the sympathetic nervous system and it increases our blood pressure and heart rate. Deficiencies in norepinephrine causes Alzheimer’s disease, Parkinson’s disease, and Korsakoff’s syndrome a cognitive disorder associated with chronic alcoholism.

Epinephrine: is also a hormone and a neurotransmitter. It is also known as adrenaline. It is responsible for attention, focus, cognition and arousal. Excess of epinephrine can cause ADHD, anxiety and sleep problems, where as lack of it can cause focus problems and fatigue.

Endorphin: falls in the category of peptides (short chains of amino acids that are linked together). The brain also makes peptide like neurotransmitters like endorphin. It acts like painkillers by preventing nerve cells from releasing more pain signals. It is produced by the pituitary glands and the hypothalamus during exercise and excitement. It is the neurotransmitter that lets animals hibernate.

Gaseous Neurotransmitters: neurotransmitters can also be in the form of gases. Two important ones are nitric oxide and carbon monoxide. Gases don’t work like normal neurotransmitters; they don’t have a reception site instead they just diffuse into other neurons.

Lipid Neurotransmitters: Lipids (naturally occurring organic compounds, like fats) like gasses can also function as neurotransmitters. Prostaglandins are a class of compounds made from lipids by an enzyme called cyclooxygenase. These molecules have powerful effects in inducing of fever and generation of pain, in response to inflammation. Aspirin reduces fever and lowers pain by inhibiting the cyclooxygenase enzyme. 

 

BRAIN COMPONENTS AND THEIR FUNCTIONS

The brain is the most complex and important organ of the human body. It has different components and each component has specific functions. Some of the basic components of the brain are:

Cerebral Cortex - is the outermost layer of the brain. It covers the cerebrum and is divided into the left and right hemispheres of the brain.  It wrinkles up into grooves to include more neurons. Cerebral Cortex is what we see when we look at the brain. Cerebral cortex is also called as grey matter and is responsible for the distinct human traits like higher order thinking and language and also traits like imagination and reasoning.

Cerebrum - is the largest part of the brain, covered by cerebral cortex and controls complex things like thinking, voluntary behavior, perceiving and understanding language. Cerebrum is split into two hemispheres (left and right) that are connected by a bundle of fibers called the corpus callosum. Each of the hemispheres has different parts or lobes, namely frontal lobe, parietal lobe, occipital lobe and temporal lobe.

The different lobes make up the fore brain.

Corpus Callosum - is a bundle of nerve fibers, located under the cerebrum, at the center of the brain. It connects the two cerebral hemispheres of the brain and helps them communicate. It also helps proper functioning of the eye movement, attention and spatial perception. If there was no corpus collosum the left and the right hemispheres of the brain would not be able to communicate and the brain would be divided.

Thalamus - is located above the brain stem. It acts as a relay station between different parts of the brain. All of the sensory signals (vision, touch, hearing) except those associated with smell, pass through the thalamus to the cerebral cortex and vice versa.

Hypothalamus - is located underneath the thalamus. It's main function is homeostasis, or controlling factors like blood pressure, body temperature, hunger, thirst, weight, emotions, circadian rhythms (24 hr cycle in the physiological processes of living beings). It also controls the pituitary gland by secreting hormones.

Limbic system - is situated deep within the brain and consists of these main structures; Amygdala, Hippocampus, Fornix, Thalamus, Hypothalamus, Olfactory cortex and Cingulate gyrus. Limbic system controls emotions, basic drives like thirst and hunger, pleasure/pain, smell, modd and memory.

Basal Ganglia - is a group of cell bodies, connected to the cerebral cortex, thalamus and other brain areas. It is situated at the base of the fore brain. Basal Ganglia is concerned with the coordination of movement. Dysfunction in Basal Ganglia is responsible for some well-known neurological disorders such as Parkinson's and Huntington's diseases.

Brain Stem - connects the brain to the spinal cord. It consists of three parts medulla oblongata, pons and midbrain. The medulla oblongata is the lowest portion of the brain stem and is continuous with the spinal cord. It helps in transferring messages from the different parts of brain to the spinal cord. It controls autonomous nervous activities such as breathing, swallowing, sneezing, heart rate and digestive processes. Pons are located just above the medulla and connect it to the cerebral cortex. It relays sensory information between the cerebrum and cerebellum. Midbrain is above the pons and is the smallest region of the brain stem. It acts as a relay station for the auditory and visual information.

Cerebellum - is located in the hindbrain, behind the brain stem. The cerebellum is connected to the brain stem, basal ganglia and the cerebral hemispheres. Together they control the smooth coordination of movement.

Cranial Nerves - are twelve pair of nerves seen on the bottom of the brain. Most of them originate from the brain stem.

Neurons - are the cells that makes up the brain . There are about 100 billion neurons in the human body. The neuron is made up of cell body, dendrites and axons. The neuron cell body contains the nucleus and cytoplasm. The axon extends from the neuron cell body and often gives rise to many smaller branches before ending at nerve terminals. Dendrites extend from the neuron cell body and receive messages from other neurons. The dendrites are covered with synapses formed by the ends of axons from other neurons. Synapses are the contact points where one neuron communicates with another. Ions flow from outside of one neuron to inside of other neuron through the ion channels. The difference in charge creates an action potential, which triggers neurotransmitters. 

PARKINSON'S DISEASE

People Affected and Costs

Parkinson's disease is important to understand because it effects a significant part of the US population around 50,000 people are diagnosed with Parkinson every year, with more than half a million Americans affected at any given time. Also an estimated 7 to 10 million people worldwide are living with Parkinson's disease. However Parkinson's also has a significant impact economically as well. The combined direct and indirect cost of Parkinson’s, including treatment, social security payments and lost income from inability to work, is estimated to be nearly $25 billion per year in the United States alone. Medication costs for an individual person with PD average $2,500 a year, and therapeutic surgery can cost up to $100,000 dollars per patient.

Causes and Symptoms

Parkinson's disease is a degenerative disorder of the brain. This means that a part of the brain and its function are increasingly deteriorated over time. In Parkinson's this part of the brain is called the basal ganglia and its function is to control movement. The disease is both chronic, meaning it persists over a long period of time, and progressive, meaning its symptoms grow worse over time. The basal ganglia makes the neurotransmitter dopamine which controls our body's movement. Dopamine sends messages to other parts of the brain to coordinate movement. Patients who have Parkinson's Disease have a low amount of dopamine so that means the body doesn't receive the right messages it needs to move normally. Because Parkinson's is a degenerative disorder, it occurs slowly and in stages. In the first stages of Parkinson's a barely noticeable tremor in just one hand. The patients speech may become soft or slurred. However over time these conditions worsen to a point where the person needs assistance with all daily activities. There is no cure for Parkinson's however scientist's have managed to make the diseases progression slower.

Research

There has also been research done on the topic of diagnosing Parkinson's disease, as sometimes diagnosis are not always clear. There are no standard tests to diagnose Parkinson’s. The best way testing for PD is specialized brain scanning techniques that can measure the dopamine level in the system and brain metabolism. Scientists are also exploring the idea that loss of cells in other areas of the brain and body contribute to Parkinson’s. For example, researchers have discovered that one sign of Parkinson’s disease (called Lewy bodies) are found in the mid-brain. This area of the brain deal with non-motor functions such as sense of smell and sleep regulation. The presence of Lewy bodies in these areas could explain why patients experience non-motor functions before any motor related function appear.

Treatments

There are currently three major treatments for Parkinson's. These are medication, surgery and therapy. Medication is the most commonly used method to treat Parkinson's and there are many types of medications that do different things. The main medication used to treat Parkinson's is levodopa and carbidopa. Levodopa alone causes nausea and vomiting once it reaches the brain however it is converted to dopamine once it reaches the brain. Parkinson's patients need this dopamine to suppress their symptoms. Carbidopa works by preventing levodopa from being broken down before it reaches the brain. This allows for a lower dose of levodopa, which causes less nausea and vomiting. This is the best way of curing Parkinson symptom. Another one of these medications are dopamine agonists. These are drugs that stimulate the parts of the rain influenced by dopamine. So the brain is tricked into thinking it is receiving the dopamine it needs. Therefore the symptoms of Parkinson die down. However dopamine agonists are not as effective as the combination of levodopa and carbidopa.

The surgical way of treating Parkinson is through deep brain simulation. This is when surgeon put electrodes into the areas on the brain affected by Parkinson's. Surgeons use using MRI and neurophysiological mapping to put them in the right place. Another device known as the impulse generator is put under the collarbone, providing electrical impulses to part of the brain that deals with motor functions.

ALZHEIMER'S DISEASE

Why understanding about Alzheimer's disease is important?

Alzheimer's disease is a form of dementia which is an umbrella term for a set of symptoms related to memory loss and logical thinking impairments, among other things. Alzheimer is unique because it affects 5.4 million Americans and is the 6th leading cause of death in the US. That means that it affects 1 out of 10 Americans over the age of 65. No one is exempt from the disease and there is no way to actively prevent it. Since the year 2000 the death rates of other diseases such as HIV, stroke and heart disease have decreased, but the death rate of Alzheimer's disease has grown by 66%. The last reason why understanding about Alzheimer's is important because there is no known cure. There are treatments that will slow the progression of the disease but none that will stop it.

What is Alzheimer's disease?

Alzheimer's is a disease that affects the brain in many of it's critical functions. It's difficult to diagnose because it may sometimes be confused with just “growing old” or symptoms of too much stress. However, Alzheimer's disease is a very real condition with biological impairments. Because of the way it spreads in the brain, Alzheimer's disease is categorized in separate stages. 

It originates in the hippocampus which is the area in the brain in charge of forming new memories. Alzheimer's patients have difficulty recalling events from a few hours or days ago. The disease then spreads to the part of the brain where language is processed. Thus it becomes harder to recall “the right word”. Next it spreads to the part of the brain where logical thinking takes place. So, it becomes harder to solve problems where complex thought is required. It then progresses to the part of the brain where emotions are regulated, therefore it becomes difficult to respond/control to emotional circumstances appropriately. Next is the part of the brain where senses are perceived, so patient may start to hallucinate. After that it spreads to the part of the brain where the persons most oldest memories are stored. Late stage of Alzheimer's disease is where balance and coordination of a person deteriorates causes them to be wheelchair bound. The last stage is where the persons breathing and heart regulation is affected, ultimately causing death. All these stages take place in about between 8-10 years time, sometimes more or less depending on the individual.

How Alzheimer's disease takes place?

Research has shown that Alzheimer's disease happens when two unusual substances are produced by the brain. These substances are know as Plaques and Tangles.

Cell membranes of neurons process proteins. Plaques are formed when proteins in the neurons cell membrane are processed abnormally. In a normal neuron an enzyme known as alpha-secretase cut apart a protein called APP (Amyloid Precursor Protein), a normal and in fact vital substance needed for the cell. A second enzyme known as gamma-secretase cuts another part of APP. The two released fragments from these enzymes are normal. In patients suffering from Alzheimer's disease the first cut of APP is made by an enzyme called beta-secretase instead of alpha-secretase, this combined with the second cut of APP by gamma-secretase releases a part of APP known as beta amyloids. The beta amyloids clump together and become bigger and bigger until they form structures known as plaques. Plaques are too big in size and are insoluble in cerebral fluid. Plaques attach themselves to the neuron membrane. This triggers the brain to release powerful chemicals, however these powerful chemicals backfire because they set of a series of reactions that destroy the neuron.

Tangles are formed inside the neurons in contrast to plaques which are formed outside the neurons. Tangles are made when a protein known as Tau is modified inside a neuron. Tau is a protein that keeps together an organelle inside neuron known as microtubules. Microtubules are tube like strands inside the neuron that transport important materials to all parts of the neuron. In Alzheimer's disease tau protein becomes hyperphosphorylated (Phosphorylation is the process of addition of phosphate groups), which means that an extra phosphate group cannot be added to tau. This causes the tau to separate from the microtubules causing them to fall apart. These abnormal tau bond together inside of the neuron and makes structures know as “tangles”, which disrupts the normal functioning of neurons.