Biospychology mid-term exam

Running head: MIDTERM ESSAY EXAMINATION

MIDTERM ESSAY EXAMINATION 2

Biopsychology: Midterm Essay Examination

Question 1

The nature-nurture debate is far from being settled considering the divergent research opinions. The role of biology (nature) and environment (nurture) in development of behavior or personality has motivated extensive research on the issue. The role of genetics in a person’s behavior is difficult to evaluate considering the nature of heredity. Each human cell contains 23 pairs of chromosomes, which means that there are 46 chromosomes with roughly 20,000 genes. Interaction of genes from each member contributes to a specific trait (Pinel, 2013). Heredity is intricate and difficult to evaluate because the human egg and sperm, which are the products of cell division contain 23 unpaired chromosomes. This implies that half of an individual’s genes come from the father and the other half from the mother. Therefore, every person has a unique genetic profile except for identical twins.

The Human Genome Project, which entailed marking genes in the human DNA made it possible to identify genes that contribute to certain diseases such as Huntington’s disease, cystic fibrosis and some forms of cancers (Pinel, 2013). Although the heritability of some diseases and physical traits have genetic foundations, the genetic foundation of behavior is difficult to determine. Even research studies on the behavior of family members cannot establish conclusive relationships between genes and behavior. This is because it is difficult to isolate behavioral traits that have not been affected by environmental factors. Twin studies have attempted to link genetics and behavior because identical twins tend to share similar behaviors compared to fraternal twins (Pinel, 2013). However, these studies are not conclusive because the environments may be similar and identical twins reared together may develop noticeably unlike behaviors. The implication for the biopsychologits is that both environmental and genetics factors play a role in the development of personality (behaviors). This means that there is no controversy at all despite some scientists disagreeing on the contributions of nature and nurture.

Question 2

Neurotransmission is the process through which neurons communicate at the synapses to realize the overall function of the CNS (Central Nervous System). In order to realize long distant communication, neurons possess unique abilities of transmitting electrical signal through axons. Neurons derive input from adjacent neurons through neurotransmitters. The movement of the signal in the neuron is facilitated by the voltage-gated ions channels that cause a short reversal of resting membrane potential l to generate an action potential (Freberg, 2010). The generation of an action potential involves five steps. First, stimuli from adjacent neurons or from sensory cells cause the depolarization of the target cell to the threshold potential. Secondly, if the threshold of excitation is achieved, the sodium ion channels open leading to the depolarization of the membrane. Third, when the peak action potential is achieved, potassium ion channels open and potassium ions move out of the cell and the sodium ion channels close. The continued exit of potassium ions from the cell leads to the hyperpolarization of the membrane. In this ate, the membrane is in a refractory state and cannot fire (Freberg, 2010). Lastly, the potassium ions channels close and the voltage-gated ions channels re-establish the resting potential.

The action potential travels along the axon due to the depolarization and repolarization of the axon membrane. The myelin sheath in the axon contains natural gap known as nodes of Ranvier. These nodes do not contain myelin and hold the voltage-gated ion channels. The flow on ions through the voltage gated channels generates the action potential, which travels along the axon by jumping from one node to the next (salutatory conduction). The presence of the nodes of Ranvier ensures that the action potential is propagated very fast. To avoid the continuous stimulation of the ion channels, the neurotransmitters are deactivated in three ways: degradation, reuptake or autoreceptors. Enzymes found in the synaptic cleft may degrade the neurotransmitter into a neutral substance. Secondly, the neurotransmitters reenter the presynaptic cell via channels located in the membrane. Autoreceptors function like thermostats and are located at presynaptic membrane. When sufficient amount of neurotransmitters has been released, further release is stopped when the action potential arrives. This may be achieved by diminishing the number of calcium ion channels that open as the subsequent action potential arrives.

Question 3

The initial stage of the visual system starts from the eye to the retina. Light energy enters the eye via the cornea after encoding the image of an object in photons. The amount of light entering the eye is adjusted by a process of accommodation under the control of the ciliary muscles. These muscles adjust the iris, which in turn regulate the dilation of the pupil. This is then followed by the transduction of the image at eh retina through inversion and projection. The retina has two sections: the central and peripheral vision. The central vision is found in the middle of the fovea and it is associated with enhanced visual acuity. The optic gap generates a blind spot in vision towards the periphery of the retina, but this gap is filled to prevent our consciousness of it. The retina has five rows of cells that process visual information. The bipolar and ganglion cells are the most significant. At the back of the retina are rods and cones. These cells contain photopigments that react with light photons. The rods adapt the eye to light and darkness through the breakdown of rhodopisn when excess light enters the eye. The electrical signals travel to the brain through two different pathways to the (LGN) Lateral Geniculate Cortex in the thalamus and the superior collicus (Freberg, 2010). After minimal processing in the LGN, the visual information is transmitted to the primary visual cortex in the occipital lobes, which generates visual perception. The remaining visual information is transmitted to the three clusters of the subcortical nuclei. These clusters are responsible for visual attention and integrative functions, mediation of light responsiveness, and photic entertainment of an organism.

The trichromatic and opponent theories attempt to explain color vision. According to the trichromatic theory, color vision is founded on the activities of three different receptors each possessing unique peak sensitivity. Therefore, the balance of activity in short, medium, and long wavelengths cones determine color perception. Opponent-process theory posits that cone photoreceptors are intimately connected to forms three contrasting color pairs: black/white, blue/yellow, and red/green (Freberg, 2010). The activation of any member of a pair inhibits activity in the other, which explains why no two colors of a paper can be seen in one location.

References

Freberg, L. (2010). Discovering biological psychology. Belmont, Calif: Wadsworth, Cengage Learning.

Pinel, J.P. (2013). Biopsychology. New York: Pearson Education.