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.