Research Paper On Special Senses

Introduction

The five organs of the human body associated with sense are the eyes, nose, ears, tongue and skin. These organs sense all kinds of external stimuli to the body through receptors and send the input information to the brain, and the body responds quickly as per the direction of the brain. All these sense organs have sensory receptors, and on activation the receptors send electrochemical signals to neurons attached to them. The electrochemical signals, through a network of neurons, reach the brain where the information is processed. The body’s internal communication network is called the nervous system, and the brain along with the spinal cord constitutes the central nervous system of the body. Billions of neurons, grouped as nerves, form the body’s peripheral nervous system to transmit impulses of nerves between the central nervous system and various other parts of the body. Neurons of the nervous system continue to collect information on the internal conditions of the body and the external surroundings, evaluate the gathered information, and organize activities in accordance to the situation besides the requirement of the moment (Cardoso). For example, when someone touches a hot iron box, a sensory nerve stipulated for a rise in temperature gets activated, which in turn alerts the brain by sending a warning signal. The brain translates the message fast enough so that the person swiftly takes off the fingers before the skin gets burnt. Similarly, the sensory nerves associated with the eyes and nose send signals to the brain so that the body reacts as per the order of the brain.

Path of the Message

The long journey of an impulse through the nervous system has to do more with cell biology in addition to the sciences of chemistry and physics. The human brain has got around thirty billion neurons. The neurons, on getting a message from the environment, process the information through an impulse. An impulse of the nerve is nothing but transmitting a signal from a particular stimulus through the membrane of the neuron, beginning from the point where the stimulus occurred. A nerve impulse is capable of passing from cell to cell, thus producing a chain of message transmission within a particular neuron network. The neurons constituting the nervous system have a unique structure, and look more like body cells with a body, known as soma. The soma holds the nucleus that carries the DNA and gives direction to the cell for synthesizing different types of protein. The neuron of the nervous system has got two distinct ends. At one end the soma sprouts a number of branching dendrites meant for receiving signals like a TV antenna; at the other end of the neuron, the axon of around one meter length stretches out as multiple axon ends, and each end branching out to send signals (Bushwick). The terminals of the axon are often positioned very near to the sprouting dendrites of the adjacent neuron, thus forming a coupling called a synapse. In fact, the axon terminals of a neuron do not touch the dendrites of an adjacent neuron. Each and every neuron in the body has got around one thousand synapses or links with adjacent neurons, thus enabling message sending from one neuron to the other.
The synapses that link two adjacent neurons are nothing but empty space, and there is no direct link between two adjoining neurons. Nevertheless, the message has to pass through the gap from one neuron to another so as to finally reach the brain. The synaptic gap is filled with a fluid. The signal from one neuron to the other cannot electrically pass through gap between the axon of one neuron to the dendrite of the nearby neuron. Instead, neurotransmitters or special chemicals aid in transmitting the impulse. Neurotransmitters released by the message sending neuron into the synaptic gap enable exchange of ions between the cells, thus establishing a link (Cardoso).

Chemical Events Aiding Transmission of Impulse

The axon ends have sacks, also called vesicles filled with a chemical called neurotransmitter. There are around sixty different types of neurotransmitters, and each one passes a distinct message, which is duly sensed by the receiving neuron. The receptor locks are opened only by appropriate neurotransmitters sent from the vesicles of transmitting neuron. As the neurotransmitters reach the dendrites of the receiving neuron they have two possibilities – either being excitatory or encouraging the receiving neuron to pass on the signal; or inhibitory or discouraging the receiving neuron from doing so. The dendrites of a particular neuron may receive signals from a number of other neurons. If the excitatory impulse is stronger than the inhibitory impulse, the receiving neuron is fired up to pass on the message. Even as chemicals aid sending message from one neuron to another, for transmitting the signal from the dendrite of the receiving neuron to the axon ends of its own the medium of electricity comes to play its role (Stufflebeam). When a receiving neuron is fired up to pass on a message, a pulse of electricity passes through the length of the cell as though flowing through a metal wire to pass the signal to the axon. To make the human cells conduct electric signal, the cell changes the charge of its own in relation to the cell exterior by manipulation of the charged ions both inside and outside the cell wall. While at rest, the ions are so distributed in a cell in such a way that the interior of the cell is further negatively charged than the exterior to create an electric potential across the cell wall. Potassium and sodium conduits in the cell wall regulate the passage of positive potassium and sodium ions both inside and outside the cell, thus sustaining the negative charge when the neuron is at rest (Bushwick).
Some neurotransmitters, on entering the receptor neuron, change the characteristics of the axon’s cell membrane thus making the cell membranes closer to the soma more permeable. This enables positive ions of sodium reach the cells and make the interior of the cells of the section positive. Slowly, this condition of being positively charged within the cell wall moves toward the axon ends. The electrical charge reverses on the signal reaching the axon ends. Now, positive calcium ions enter the further permeable cell wall. The presence of calcium drives the neurotransmitter in the vesicles get inside the cell membrane, where, on mixing together, it releases an appropriate neurotransmitter to the exterior. The same process is repeated by the next neuron to transmit the message further.

Conclusion

Neurotransmitters play a crucial role in transmitting the message from the sensory organs of the human body to the brain. By composition neurotransmitters are tiny, simple molecules. Each different neurotransmitter chemical works in different brain locations. Although the process of sending the impulse through the neurotransmitters seems lengthy, the action, in fact, is incredibly fast. An axon with a length of a football ground can pass the signal within a second. The sensory organs of the body have receptor neurons that sense various impulses the human body sees, hears, smells, tastes, and feels through the skin. The neurons are also responsible to translate physical forces stimulating the sensory organs into impulses. The neurons transform thermal, chemical, or mechanical reactions into electrical signals. The electrical signal in turn travels the long path way through the neurons to reach different areas of the brain for processing and interpreting the signal.

References

Bushwick, S. (2012, January 19). How exactly do neurons pass signals through your nervous system? Retrieved February 15, 2015, from http://io9.com/5877531/how-exactly-do-neurons-pass-signals-through-your-nervous-system
Cardoso, S. (n.d.). Communication Between Nerve Cells. Retrieved February 15, 2015, from http://www.cerebromente.org.br/n12/fundamentos/neurotransmissores/neurotransmitters2.html
Stufflebeam, R. (2008, January 1). Neurons, Synapses, Action Potentials, and Neuro transmission. Retrieved February 15, 2015, from http://www.mind.ilstu.edu/ curriculum/neurons_intro/neurons_intro.php