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Preface

Like the sun being central to our solar system, the brain is the major organ responsible for the physiological aspect of living and to human life as well. It controls all activities of man, no matter how trifle. It makes breathing, eating, sensation and thinking possible – it makes living possible. To a doctor, the human anatomy is the most skillfully architected structure. It was made perfect for communicating impulses and signals in such a way that events happen simultaneously and all systems needing the participation of each to be able to complete a task. With one in failure, the whole of it collapses.

Introduction

This paper aims to evaluate how the brain makes psychological functioning possible. Consider, for example, all the processes that happen when you accidentally touched a hot cooker. Upon contact with the hot cooker your pain receptors or nociceptors will send sensory impulses to the brain telling it that something is hot and painful. The brain will realize that you are in pain and the area experiencing pain and will send back motor impulses to it. The hand will now pull back, the muscles controlling the hand to move away. After this, the brain does not stop. It will now command you to find a cold object to apply to the painful area. And once accomplished, you will feel relief. But if you were having a hard time looking for a cold compress, you will feel your respirations go up and your heartbeat also to keep your body alert and moving to alleviate pain sooner.

            This is how the brain helps the body cope up with stresses. Our perception of events in the environment depends largely on our sense organs and how the brain is able to analyze and interpret these.

            It has been identified that structures in the brain are responsible for certain tasks that human beings perform on a daily basis. This paper will analyze how these structures enable certain psychological functions, like that of emotion and memory possible. A background on the nervous system especially on the structures and their functions will also be included in the discussion of this paper.

The Nervous System

            Neurons and Neurotransmitters

Neuron, a specialized cell that transmits neural impulses or messages to other neurons, glands and muscles, is the basic functional unit of the brain.[1] It is composed of a cell body, an axon and a dendrite.

            Neurotransmitters are substances released by the presynaptic neuron that has the potential to excite or inhibit the postsynaptic neuron. [2] These communicate messages from one neuron to another by crossing the synaptic cleft and binding to specific receptors in the postsynaptic cell membrane. [3] There are seven major neurotransmitters known and these are the acetylcholine, serotonin, dopamine, norepinephrine, gamma-aminobutyric acid or GABA, endorphin and glutamate.

            Acetylcholine, the major transmitter of the parasympathetic nervous system, is usually excitatory, but can also be inhibitory. [4] It is mostly found in the forebrain or the hippocampus, and is thought to be responsible in the formation of new memories. [5] Serotonin has been found to play important roles in the regulation of mood, sleep and appetite. Its action is usually restraining and it also inhibits pain pathways. [6] Dopamine usually restrains and affects behavior and fine movement. [7] It is also known that release of dopamine in certain areas of the brain produces intense pleasure. Also, studies have shown that too little dopamine is said to cause Parkinson’s disease and too much results in schizophrenia. [8]

            Norepinephrine, the major transmitter of the autonomic nervous system, is usually excitatory and affects mood and overall activity. [9] GABA is a major inhibitory transmitter and is used to treat anxiety. [10] Endorphins are excitatory; it is known to play a role in pleasurable sensation and inhibiting pain. Glutamate, an excitatory neurotransmitter, is believed to play a role in learning and memory. [11]

            Neural Structures

            The nervous system is divided into the central nervous system and the peripheral nervous system. The central nervous system is composed of the brain and the spinal cord. The cranial nerves, spinal nerves and the autonomic nervous system form the peripheral nervous system.

Figure 3. The brain and its parts.

            The brain can be divided into the cerebrum and the cerebellum. The cerebrum, which regulates our higher intellectual processes, can be divided into right and left hemispheres. These hemispheres are made up of the frontal, parietal, occipital and temporal lobes. Each will be an important landmark in identifying functional areas of the brain. [12]

            The cerebrum has areas specified for a function that is distinct for each. These are the primary motor area, the primary somatosensory area, the primary visual area and the primary auditory area. The primary motor area controls voluntary movements of the body; the primary somatosensory area recognizes heat, touch, cold pain and the sense of body movement, the primary visual area for visual recognition and the primary auditory area for hearing.

            The thalamus, responsible for relaying information and for control of sleep and wakefulness, the hypothalamus which controls endocrine activity, homeostasis, eating, drinking and sexual behavior, the pituitary gland, and the limbic system can also be found in the cerebrum. [13]

Psychological Functions

            The Human Memory

            Memory is the retention of, and ability to recall, information, personal experiences, and procedures (skills and habits). [14] Memory is very important to human beings; it defines who we are and what we know. Without it, we cannot recall even our names, how to read, write and talk in different languages, how to cook, and other things that we have learned to do all throughout our lifetime. There have been a number of researches done to find out how the brain is able to store memory, where it is stored, how the memory works, how the short-term memory is converted to long-term memory and what happens when we recall these memories.

            Short-term memory or working memory is made up of facts or data that a person needs to retrieve in a matter of seconds, minutes or an hour. For example, when we are watching the telly and we cannot decide on a program to watch so we flip through the remote and scan the channels. When we like a program, we remember the channel where we saw it and then when we have finished scanning and have found nothing better than our first choice program, we try to recall what channel it was on and put it on the telly.

            Long-term memory is composed of information that we need to recall from time to time for the rest of our lives. These are names of people that we know, certain procedures that we always do, information about ourselves like our names, birthdates, and telephone numbers. There are three types of long-term memory, the explicit memory, the implicit memory and the semantic memory. The explicit memory stores facts that an individual made an effort to learn, like those that are learned in school, chemical formulas and scientific names and these can be remembered at will. The implicit memory stores procedures to tasks that one performs on a daily basis, like driving. And semantic memory stores facts that do not require any effort to recall, like the days of the week. [15]

            Now for memory to work, it will involve three steps, first is acquisition of information, next is consolidation, and finally retrieval. We will first learn an information before it can actually be acquired. Once the information is learned and eventually acquired, the information will be stored in temporary nerve-cell pathways. This is where short-term memory is stored. [16]

            Sometimes, short-term memory will now move into long-term memory, through the process of consolidation. There are several theories as to how this happens. Many researchers believe that the process of transforming a short-term memory into a long-term memory begins when brain cells receive signals that induce reactions involving the molecule, protein kinase A. This, in turn, sets off another molecule in the cell known as cyclic AMP-response element binding protein (CREB). CREB activates genes, which are segments of the cell’s deoxyribonucleic acid (DNA). Genes hold sequences of coding molecules that provide the biological instructions for producing proteins. The development and function of the body and brain is directed by many different proteins. The genes activated by CREB lead to the production of special proteins that change the structure and activity of nerve cells. These reactions fasten information for days, weeks or longer. The core molecular switch appears to be involved in securing the memories of facts and events, known as explicit memories, as well as implicit memories. [17] While other studies show that the nerve-cell pathways are strengthened in an attempt to move short-term memory into long-term use. The memory molecule, protein kinase M zeta, is discovered to play a role in the strengthening of synaptic connections between neurons. [18]

            Recalling memory is a process that is not yet clear. There are studies though that shows that the stored memories do not stay forever in the hippocampus. Older, lifetime memories stay in the anterior cingulate cortex according to new research. Initially, memories for everyday life events appear to depend on networks in the region of the brain called the hippocampus. However, over time, these memories become increasingly dependent upon networks in the region of the brain called the cortex. [19] But others argue that the hippocampus and adjacent medial temporal lobe structures are known to support declarative memory, long-term memory for facts and events. [20]

            It is not only the hippocampus and the medial temporal lobe that is involved in memory. There are studies being conducted to elaborate on semantic memory being processed in the areas where the learned procedures take place. Like if driving, the primary motor area is also being used, not just the memory lobe.

            Neuroscientists are still struggling on memory studies. What we know is that short-term memory if not transferred to long-term will be forgotten in a matter of minutes. The process of converting short-term memory to long-term memory is still a blur as to how it takes place, the same goes for retrieval of memory.

            The Visual Pathway

            The eyes are our window to the world. Although science tells us that it is the brain that enables us to see and interpret these objects, it is with the eyes that we get to transmit the light waves bounced by the images. Without it, we would never be able to enjoy the beautiful things, people and places around us. To understand how the brain gets to interpret everything in our field of vision, which is the total area in which objects can be seen in the peripheral vision while the eye is focused on a central point,[21] we need to discuss the visual pathway, particularly the Thalamofugal Pathway.

            The Thalamofugal Pathway is mostly concerned with visual distinction of form and colour, and visual motion perception.[22] But there are three main visual pathways, and these are the Techtofugal pathway, the already mentioned Thalamofugal Pathway and the Accessory Optic System. The Techtofugal System is concerned with the processes necessary for visual orientation and spatial attention, and neurons within this neural circuit are frequently found to be sensitive to visual motion stimuli [23]; while the Accessory Optic System is a subcortical pathway necessary for the perception of self-motion and gaze stabilization.[24] These pathways are to be discussed later.

            Let us go back to how the eye perceives an image. What we think we see is an object, but what the eyes receive are light waves. When the eyes have been set on an object, the light waves would be reflected by the object and would pass our eyes first through the cornea. [25] The cornea is the outermost layer of the eyes, which is the main light focusing structure. It is a transparent dome; the transparency is due to the fact that it does not contain blood vessels. But it is extremely sensitive to pain because of the high concentration of nerve fibers. [26] After passing through the cornea, the light will pass through the pupil. The pupil, which is found at  the circular opening in the center of the colored iris, is the one regulating the amount of light that will pass through the retina. [27] Behind the iris and the pupil is the lens which is crystalline in nature. The lens is another light focusing structure, which is composed of fibers from epithelial cells. Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens, to a nodal point (N) located immediately behind the back surface of the lens. [28] An inverted image of the object is projected by the lens to the retina. At that point, the image becomes reversed and inverted. The vitreous humor is the next structure that the light waves will be passing through. This structure is composed mainly of clear gel making up eighty percent of the eye’s bulk. [29] The light will then be bounced back to the retina. The retina has rods and cones that enable the eyes to sense light. The rods senses vision in low light while color vision and detail is sensed by the cones. Impulses are now passed onto the optic nerve after being processed by the retina. [30] Then it passes through the optic chiasm and finally to the optic nerve where it will be forwarded to the lateral geniculate nucleus and will reach the primary visual cortex in the occipital lobe. [31]

            However, this is not always the case. Conditions like astigmatism, hyperopia and myopia may occur. Myopia, or nearsightedness, is the ability to see close objects more clearly than distant objects. This can be caused by the eyeball being too long or the cornea having too much curvature, which in turn will make light focusing a little harder for people who have this condition. Light is focused in front of the retina, and this blurs the image. [32] Hyperopia is the opposite of Myopia. Hyperopia or farsightedness is the ability to see distant objects more clearly than close objects. This happens when the light is focused behind the retina. [33] The last of the refractive error condition is astigmatism. Astigmatism is caused by an irregular curvature of the cornea. What the person will see will be blurry objects at any distance. [34] Fortunately, for people suffering these irregularities, there are corrective lens for each condition.

            In normal cases, the image received by the lateral geniculate cortex (LGN) is normal and no adjustments are needed. The Thalamofugal Pathway continues. The LGN is composed of six layers numbered 1 to 6. Input from the contralateral eye will be received by layers 2, 3,  and 5 while inputs from the ipsilateral eye will be received by the rest. There are two types of neurons present in the LGN. These are the parvocellular and the magnocellular neurons. The parvocellular neurons exhibit the following characteristics: small receptive fields, medium conduction velocity, sustained neuronal response to visual stimuli, high spatial resolution , slow temporal resolution, and it projects to brain regions responsible for colour and form perception. [35] On the other hand, the magnocellular neurons have larger receptive fields, higher conduction velocity, transient neuronal response to visual stimuli, lower spatial resolution, faster temporal resolution and it projects to brain regions responsible for motion perception. [36] And these neurons are found in layers 1 and 2, while layers 3 and 6 contain parvocellular neurons.

            After being processed by the LGN, the information will now go to the primary visual cortex 1 of V1, which is located in the occipital lobe of the brain. Cortical processing of visual information starts here. retinotopic organization or spatial relationships of images on the retina is what is seen in V1. [37] Next area is the V2 or the extrastriate visual cortex. V2 is mainly for processing form and color, with relatively few neurons dedicated to motion processing. [38] Also, the V2 is responsible for relaying the information to the middle temporal cortex, the dorsal region of medial superior temporal cortex, and the ventral intraparietal area. The middle temporal cortex receives information from the V2, it is mainly involved in the visual analysis of motion. [39] It passes this information to the dorsal region of medial superior temporal cortex, where visual navigation takes place. It will enable an individual to see moving objects while he himself is moving. [40] From the medial superior temporal cortex, the information is passed on to the area 7a and to the ventral intraparietal area. The ventral intraparietal area receives major input from the middle temporal cortex. Approximately two thirds of the neurons in the ventral intraparietal area respond selectively to optic flow stimuli. [41] Area 7a is located in the posterior part of the parietal cortex, and is responsive to optic flow. [42]

             The occipital lobe, the area where the primary visual visual cortex is found, is located at the posterior portion of the brain. Studies have been emerging regarding neuronal development in this area. It was researched that as infants, we did not have the capacity to see the whole world as one. Our capabilities regarding vision now are solely based on our past visual experiences. For example, in the studies conducted, it revealed that when a kitten only sees vertical lines at birth it looses its ability to see horizontal lines. The significance of this study is that  the brain structure is not genetically determined and that the interconnections between neurons in this area are not fixed at birth. [43]

            The things mentioned here are all subjected to change. At one point they may all make sense here with all the studies and researched being conducted as we speak, and maybe there will be more scientific breakthroughs in the future. And these breakthroughs might even disprove all the discoveries mentioned here. What is important is that people are trying to find out why things are the way they are and that they are not stopping at finding what is out there. Also, they do not harm or try to injure human beings while they are conducting research. If they do include humans, these are volunteers. Animals are usually the test subjects. We may not believe in some of the studies, but we should not stop looking for answers.

Glossary

Cerebellum: Part of the vertebrate hindbrain, concerned primarily with somatic motor function, the control of muscle tone and the maintenance of balance. Important model for cell migration in developing mammalian brain owing to well studied migratory pathway of the granule neuron and to the existence of the neurological mutant mouse weaver in which granule cell migration fails.

Cerebrum: The portion of the brain (frontal lobes) where thought and higher function reside.

Neuron: An excitable cell specialised for the transmission of electrical signals over long distances. Neurons receive input from sensory cells or other neurons and send output to muscles or other neurons. Neurons with sensory input are called sensory neurons, neurons with muscle outputs are called motoneurons, neurons that connect only with other neurons are called interneurons. Neurons connect with each other via synapses. Neurons can be the longest cells known, a single axon can be several metres in length. Although signals are usually sent via action potentials, some neurons are nonspiking.

Neurotransmitter: Any of a group of substances that are released on excitation from the axon terminal of a presynaptic neuron of the central or peripheral nervous system and travel across the synaptic cleft to either excite or inhibit the target cell. Among the many substances that have the properties of a neurotransmitter are acetylcholine, noradrenaline, adrenaline, dopamine, glycine, y aminobutyrate, glutamic acid, substance P, enkephalins, endorphins and serotonin.

[1] Atkinson, R. L., et al., in Hilgard’s Introduction to Psychology 33-48 (Harcourt Inc., California, 2000)

[2] Bullock, B. L. & Henze, R. L., in Focus on Pathophysiology 1175 (Lippincott Williams & Wilkins, Philadelphia, 2000)

[3] Smeltzer, S. C. & Bare, B. G., in Medical – Surgical Nursing 1821 – 1822 (Lippincott Williams & Wilkins, Philadelphia, 2004)

[4] Ibid.

[5] Atkinson, 38.

[6] Ibid., 39.

[7] Smeltzer, 1822.

[8] Atkinson, 39.

[9] Smeltzer, 1822.

[10] Atkinson, 39.

[11] Ibid.

[12] Smeltzer, 1821 – 1822.

[13] Atkinson, 42-48.

[14] Robert  Carroll, Memory, http://www. http://skepdic.com/memory.html (December 2007).

[15] Aetna, Inc., Types of Memory, http://www.intelihealth.com/IH/ihtIH/WSIHW000/31393/31397/347125.html?d=dmtContent (August 2004).

[16] Aetna, Inc., How Memory Works, http://www.intelihealth.com/IH/ihtIH/WSIHW000/31393/31397/347126.html?d=dmtContent (August 2004).

[17] Society for Neuroscience, How do Facts Stick in our Mind?, http://www.sfn.org/index.cfm?pagename=brainBackgrounders_howDoFactsStickInOurMind (2007).

[18] SUNY Downstate Medical Center. “Scientists Discover Memory Molecule.” ScienceDaily 3 September 2006. 9 January 2008 <http://www.sciencedaily.com­ /releases/2006/08/060830204206.htm>.

[19] University Of Toronto. “Scientists Uncover How Brain Retrieves And Stores Older Memories.” ScienceDaily 7 May 2004. 9 January 2008 <http://www.sciencedaily.com­ /releases/2004/05/040507081403.htm>.

[20] Yael Shrager, Peter J. Bayley, Bruno Bontempi, Ramona O. Hopkins, and Larry R. Squire, “Spatial memory and the human hippocampus.” Proceedings of the National Academy of Sciences 104: 2961-2966; published online before print as 10.1073/pnas.0611233104

[21] A.D.A.M., Inc., Visual Field, http://0-medlineplus.nlm.nih.gov.catalog.llu.edu/medlineplus/ency/article/003879.htm (1997-2008)

[22] University of Alberta, Visual Neural Pathway, http://www.psych.ualberta.ca/~iwinship/vision/visualpathways.html, (2007)

[23] Ibid.

[24] Ibid.

[25] Macula Foundation, Inc., Anatomy of the Eye, http://www.macula.org/anatomy/eyeframe.html (2006)

[26] Ted M. Montgomery, Anatomy and Physiology of the Human Eye, http://www.tedmontgomery.com/the_eye/ (1998)

[27] Ibid.

[28] Ibid.

[29] Ibid.

[30] Dr. Carl Bianco,  “How Vision Works”.  April 01, 2000  http://health.howstuffworks.com/eye.htm  (January 09, 2008)

[31] Diana Weedman Molavi, Basic Visual Pathways,  http://thalamus.wustl.edu/course/basvis.html (2007)

[32] Charlotte E. Grayson, Myopia, http://www.medicinenet.com/myopia/article.htm  (October 2004)

[33] Charlotte E. Grayson, Hyperopia, http://www.medicinenet.com/farsightedness/article.htm (October 2004)

[34] Cynthia Hanes, Astigmatism, http://www.medicinenet.com/astigmatism/article.htm  (October 2005)

[35] University of Alberta, The Thalamofugal Pathway, http://web.psych.ualberta.ca/~iwinship/vision/thalamo_path.html#lgn (2001)

[36] Ibid.

[37] Ibid.

[38] Ibid.

[39] Ibid.

[40] Ibid.

[41] Ibid.

[42] Ibid.

[43] Risto Miikkulainen & Joseph Sirosh, The Shifting View of Vision, http://www.psc.edu/science/Miikkulainen/Miikkul.html (1995)

Further Information

            Figure 1:         http://www.apsu.edu/thompsonj/Anatomy%20&%20Physiology/2010/2010%20Exam            %20Reviews/Exam%204%20Review/reflex.arc.fig.13.12.jpg

Figure 2: http://www.infovisual.info/03/img_en/041%20Neuron.jpg

Figure 3: http://www.web-books.com/elibrary/medicine/Physiology/Nervous/cerebrum_lobes.jpg

Figure 4: http://ahsmail.uwaterloo.ca/kin356/ltm/images/amygdala_hippocampus_lateral_large.jpg

Figure 5: http://instruct.uwo.ca/anatomy/530/vistopo.gif

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