Changes in the neuron prompting an action potential
Neural cells contain negatively charged proteins on the inside of the cell with a high concentration of positively charged ions on the outside of the cell. As a result, this leads to an electrical potential between the proteins inside of the cell and the cations outside of the cell membrane. Even at rest state, the cell contains an unequal charge distribution. At this stage, the cell therefore has to maintain a normal charge distribution which is referred to as resting membrane potential (RMP) and is at an average of 70 millivolts (Cowan, & Harter et al, 2001).
In a normal state, the difference in charged ions inside and outside the membrane and also the availability of a concentration gradient could make the positively charged sodium ions attempt to cross the membrane and enter the cell. To control this, all channels that could allow these ions to cross the membrane are closed making the membrane almost completely impermeable. This comes as a result of the concentration of positively charged potassium ions which is 30 times more on the inside of the cell than on the outside. This results in a force trying to push the potassium from the inside of the cell that is twice as strong as the gradient force trying to push the sodium ions into the cell. Due to the fact that cell membrane is more permeable to potassium ions than sodium ones, more potassium ions leave the cell than the sodium that enters and it is this difference that causes normal average of 70mv. This neutral cell RMP is also maintained by the help of the membrane structure and a process called the Sodium-potassium pump. This process works by pushing potassium ions into the cell while pushing sodium ions outside at a controlled pace. The ATPase enzyme is vital because it is responsible for the movement of potassium and sodium against the concentration and electrical gradient (Cowan, & Harter et al, 2001).
Action potential is triggered by a sufficient and well-timed stimulus. At this point the process of potassium pump stops allowing potassium and sodium to flow according to the concentration force. This occurs because the channels are opened. In the first phase called the depolarization phase, the normal RMP turns to 100mv. During this stage, the neuron experiences a refractory period. Ions continue to flow according to their respective gradients until the cell assumes a state that is more negative than usual. This is repolarisation. It is this state that allows the cell to respond to stimuli. The flow of ions continues until it reaches a state when the channels are closed. Sodium channels close faster than the potassium channels but potassium ions continue to flow leading to the third phase that is hyperpolarisation. The normal RMP is then restored when the sodium pump begins to control the movements of the ion (Cowan, & Harter et al, 2001).
The process of signal transmission from one neuron to another
The process of depolarization makes the adjacent area of the membrane also experience the same. The action potential is then transmitted to the next cell through a process called salutatory conduction. Myelinated fibers which contain a myelin sheath also experience the salutatory conduction. This occurs at special places called the nodes of Ranvier due to the sheath caused by myelin. The action potential is transmitted from one node to another until it comes to the part of the neuron called the presynaptic potion. This is the part that is next to the synapse in the pathway of a neuron. Certain ions and chemicals called the neurotransmitters are triggered by the arrival of the action potential and travel between the synapse and acting as stimulus causes another action potential in the adjacent neural on the neural pathway (Thibodeau, & Patton, 2002).
This information transmission usually takes place on the dendrites which are the information receptors. Neural membranes at the dendrites contain ion channels that correspond with the neurotransmitters from the other neuron. Some dendrites contain spines which are nobes that increase the surface on which synaptic activities can take place. The nodes have the capability to change their shapes in response to the synaptic activity’s magnitude. This activity determines the learning and memory processes of a human being. Any retardation in the maturity of these dendrites leads to mental retardation (Thibodeau, & Patton, 2002).
Major characteristics
Acetylcholine is an inhibitory neuron for heart muscles but plays a great role in the stimulation of muscle and skeletal cells.
Dopamine plays an important role in motor control, psychosis and reward. It is active in the development of diseases like Parkinson’s disease, depression and schizophrenia; it regulates movements and is important in the regulation of emotional responses.
Serotonin is found in the blood platelets, in the digestive tracts aligning, and in the brain. It is responsible for muscle contractions and plays a great role in an individual’s mood, emotions, attention and sleep.
Norepinephrine is a biogenic amine created from amino acid tyrosine. It is located in the cerebrum, spinal cord and cerebellum. It also works in the autonomic nervous system but in the opposite direction of acetylcholine.
Epinephrine plays a great role in stress transmission and is also related to blood pressure and heart rate. It is also known as adrenaline.
GABA, known in full as gamma-aminobutyric acid is found in the central nervous system and acts as an inhibitory transmitter. It plays a role in the Huntington’s disease.
Glutamate is based in the brain and due to its receptors that increase the flow of ions into the cell, the neurotransmitter is referred to as an excitatory neurotransmitter. In addition, it is involved in the facilitation of neural development, formation of memory and learning.
Melatonin is produced by the pineal gland in human beings. It is involved in the formation of hormonal signals during night-time darkness (Steen, 1998).
Effects of drugs on neurotransmitters and their psychological effects
Drugs’ effects on the human body can be directly linked to the actions of neurotransmitters. They change the normal functioning of the neurotransmitters by either making them extra active or dormant and as a result changing the overall psychological position of an individual. Cocaine’s effect is directed on the frontal cortex of the brain on dopamine-containing neurons. The general effect is the creation of a feeling of power and confidence. An excessive consumption of these elements can lead to a “crash” which results in an exhaustion, physically and emotionally and extend to depression (Thibodeau, & Patton, 2002).
Heroin and morphine act like natural peptide substances of endorphins. Killing pain, creation of pleasure and creation of a sleepy sensation are the functions played by natural endorphins. A long use of heroin and morphine can result in the brain stopping to produce natural endorphins as the endorphin receptors are used to heroin and morphine. In this case, addiction is likely to occur as the body will have stopped producing the endorphins naturally. This calls for the inception of artificial drugs which act as the natural endorphins. These drugs include nalorphine, naloxone and naltrexone. These act as the remedy for the people who are addicted to heroin and morphine (Thibodeau, & Patton, 2002).
Alcohol, which is one of the most widely used drugs, interacts directly with GABA receptors. Due to its role in muscles, great consumption of this alcohol results in poor muscle control and a delayed reaction due to alcohol’s effect on thinking (Thibodeau, & Patton, 2002).
References
Cowan, W.M., D.H. Harter, and E.R. Kandel. “The Emergence of Modern Neuroscience: Some Implications for Neurology and Psychiatry.” Annual Review of Neuroscience, 2001, 23:343–39.
Steen, F.F. (1998). University of California, Los Angeles. “Neurotransmitters.” Neuroscience Notes. 2009. Web.
Thibodeau, Gary A., and Kevin T. Patton (2002). Anatomy & Physiology, 5th ed. St. Louis: Mosby.