Neurotransmission: The Backbone of Sensory Perception in Living Organisms - Essay Sample

Introduction

Declaration: I declare that this assessment is my work and that I have accurately acknowledged the work of other scholars using the APA referencing style. Therefore, this assessment has taken into consideration the University’s guidelines on good academic conduct.

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Process of Neurotransmission

Living organisms derive their ability to sense from the structure and function nervous system, which includes billions of interconnected neurons. Emotions, thoughts, feelings, sensations, movement, memory and learning, and physiological functions and dysfunctions could be traced back to the nervous system. The brain plays a major role in this process. Nerve cells, known as neurons, are highly differentiated and adapted to their roles (Greengard, 2000). Nerve cells maintain communication for an organism by responding to somatic signals. It is important to note that the transmission of responses across the nervous system does not occur through physical contact. Instead, electrical impulses transmitted across the synaptic cleft provide interaction between a signal and a response. Chemical messengers referred to as neurotransmitters are essential for this transmission of impulses (Goyal & Chaudhury, 2013). The process through which impulses are transmitted across the nervous system is called neurotransmission. Neurotransmission occurs when chemicals in forms of electric signals move across the synapse, which depends on the event, types of neurotransmitters, and the activating receptors of the postsynaptic cell.

The synapse is the point of communication between two nerve cells. Charles S. Sherrington's reflective observations pointed out that there are different types of synapses depending on their function and properties. Since reflex arc transmission is slower than transmission through a corresponding axon length, Sherrington concluded that a process at the synapse delays transmission (Sherrington, 1932). EPSP and IPSP are graded responses. Excitatory postsynaptic potentials (EPSP) is a postsynaptic potential with the capacity to increase the likelihood of postsynaptic neuron making an action potential. On the other hand, postsynaptic hyperpolarization is referred to as inhibitory postsynaptic potentials (IPSP) because they reduce the firing likelihood of a neuron action. In this case, while EPSPs are known for increasing activity, IPSPs have a calming effect, which is the opposite of the former. EPSP temporary depolarization happens when the ligand ion channel gate opens to permit sodium to go into the neuron's membrane (Sherrington, 1932). The opening of the ligand-gated ion channels allows the positive ions to move into the cells while allowing the negative ions to move out through the membrane. However, when positive ions such as potassium move out or negative ions such as chloride move into the cell, then an IPSP has occurred.

The balance between EPSPs and IPSPs increases or decreases neurons' frequency of action potentials. In this case, EPSPs compete with the IPSPs. Graded potentials like EPSPs allow positively charges ions while IPSPs allow negatively charged ions into the cell respectively for a response cycle to be completed. Temporal summation takes place when the high-frequency action potentials from stimuli occur at different periods, which implies that one pre-synaptic neuron will fire multiple times (Huang, Bao, & Sakaba, 2010). Spatial summation is the summation of potentials from distinct pre-synaptic locations. Neurotransmitters exert ionotropic effect to bind the receptor, which in turn opens the gate for a specific ion such as sodium to pass through the cell membrane. According to Lisman, Raghavachari, and Tsien, (2007), the ionotropic effects are fast and short-lived. However, neurotransmitter exerts metabotropic effects that activate a second messenger in the postsynaptic cell, which causes slower but more lasting changes (Greengard, 2000). Most synapses work by transferring a neurotransmitter from the presynaptic cell to the postsynaptic cell. Otto Loewi demonstrated this point when he electrically stimulating the heart of a frog and then transferred the fluids from the stimulated from to the heart of another frog. Loewi discovered that the transfer of the stimulated fluids caused the reactivity of the heart muscle on the other frog (Haider, 2007).

By understanding chemical reactions at a synapse, one could comprehend how the nervous system works. Each year, different scholarly outcomes reveal more details about the chain of reactions and responses associated with synapses, their structure, and the link between their respective structures and their functions (Barnes & John, 2017). The primary process is how the neuron synthesizes chemicals that subsequently act as neurotransmitters. It synthesizes the smallest neurotransmitters at axon terminals and neuropeptides in the somatic cells. The action potential then crosses the axon. At the presynaptic terminal, an action potential allows calcium ions to enter the cell. Calcium releases neurotransmitters from the terminals to the synaptic cleft, which is the space between the presynaptic and postsynaptic neurons (Wilson, 2002). The released molecules diffuse through the cleft, bind to the receptors on the dendrites of another neuron, and modify the postsynaptic neuron activity (Barnes & John, 2017). Neurotransmitter molecules then disconnect from their receptors. Neurotransmitter molecules may return to the presynaptic neuron for release or recycling. Most postsynaptic cells send feedback to control the subsequent delivery of presynaptic cell neurotransmitters.

According to Borodinsky et al. (2004), hundreds of chemicals are suspected to be playing the role of neurotransmission. The chemicals could be categorized into five main groups. Amino acids are chemicals that contain an amino group (NH2), which include Glutamine, GABA, Aspartate, and other Modified Amino Acid such as Acetylcholine. Monoamines are chemicals formed by a change in certain amino acids, which include indoleamines such as serotonin and catecholamines such as dopamine. Acetylcholine is a one-member “family” chemical like amino acid but it includes an N(CH3)3 group instead of an (NH2). Neuropeptides are chemicals occurring as chains of amino acids such as endorphins, substance P, and neuropeptide Y. The other category is purines, which is a category of chemicals such as adenosine and its derivatives. The final group of chemicals considered as neurotransmitters is gases such as nitric oxide, which is considered as one of the oddest transmitters released by some small local neurons and relates to blood flow to the brain (Dawson et al., 1998).

Additionally, scholarly assessments based on clinical evidence ascertain that there are two-way effects of drugs on synaptic transmissions. Agonists facilitate synaptic transmissions as seen in patients diagnosed with Parkinson's disease. Patients with limited dopamine take an L-dopa, which can bind to dopamine receptors. Antagonists inhibit synaptic transmissions as seen in antipsychotic medications that block the dopamine actions at the postsynaptic membrane. Various drugs such as LSD, nicotine, and opiates exert their effects on the nervous system by binding to receptors on the postsynaptic neuron (O'Rourke et al., 2012). After a neurotransmitter has activated the receptor, numerous transmission molecules re-enter the presynaptic cell through transporter molecules in the membrane. A process referred to as reuptake allows the presynaptic cell to recycle its neurotransmitter. Stimulants and several antidepressants inhibit the reuptake process (Beuming et al., 2008; Schmitt & Reith, 2010; Zhao et al., 2010). On the other hand, postsynaptic neurons send chemicals to receptors to inhibit the subsequent release of neurotransmitters.

Conclusion

In conclusion, the process of neurotransmission is complex and involves the movement of ions into and out of neurons across the synaptic cleft. This process depends on the types of transmitters as well as the activating receptors of the postsynaptic cells. Communication between neurons occurs at the synapse. When stimulation reaches the synapse, it builds a graded potential in the postsynaptic cell, which leads to the formation of two potential summations: temporal and spatial summations. During the response, neurons synthesize neurotransmitters where the smallest are synthesized at the axon while the neuropeptides in the cell body. The resulting action potential at the presynaptic terminal permit calcium ions released in the process to diffuse through the cleft and bind to their receptors. Moreover, from the above analysis, it is evident that there are different types of neurotransmitters, whose chemical compositions determine how the receptors are activated.

References

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