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BESC1490 Introduction to PsychologyTopic 2. Biological bases of mental life andbehaviour1. Explain the structure of neurons. How do neuronscommunicate with each other?2. How does the Endocrine system communicate?3. Describe the structure and function of the Central NervousSystem.4. What do split-bra...

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BESC1490 Introduction to Psychology Topic 2. Biological bases of mental life and behaviour 1. Explain the structure of neurons. How do neurons communicate with each other? 2. How does the Endocrine system communicate? 3. Describe the structure and function of the Central Nervous System. 4. What do split-brain studies indicate about the organization (lateralization) of the brain 5. Describe the relative roles of genetics and the environment in psychological functioning.

1. Explain the structure of neurons. How do neurons communicate with each other? A neuron (known as a nerve cell) is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the brain and spinal cord of the central nervous system (CNS), and of the peripheral nervous system (PNS). Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs that then send signals to the spinal cord and brain, motor neurons that receive signals from the brain and spinal cord to cause muscle contractions and affect glandular outputs, and interneurons

which connect neurons to other neurons within the same region of the brain, or spinal cord in neural networks. A typical neuron consists of a cell body (soma), dendrites, and an axon. 2. Dendrites are thin structures that arise from the cell body, often extending for hundreds of micrometres and branching multiple times, giving rise to a complex "dendritic tree". This is where the majority of input to the neuron occurs. 3. An axon (also called a nerve fiber when myelinated) is a special cellular extension (process) that arises from the cell body and travels for a distance, as far as one metre in humans. The axon carries nerve signals away from the soma. The axon terminal contains synapses, specialized structures where neurotransmitter chemicals are released to communicate with target neurons 1. The soma (or "cell body") is the main part of the neuron, is the bulbous end of a neuron and contains the cell nucleus. There are many different specialized types of neurons, and their sizes vary. The cell body of a neuron frequently gives rise to multiple dendrites, but never to more than one axon, although the axon may branch hundreds of times before it terminates

Synaptic signals from other neurons are received by the soma and dendrites; signals to other neurons are transmitted by the axon. A typical synapse, then, is a contact between the axon of one neuron and a dendrite or soma of another. Synaptic signals may be excitatory or inhibitory. If the net excitation received by a neuron over a short period of time is large enough, the neuron generates a brief pulse called an action potential, which originates at the soma and propagates rapidly along the axon, activating synapses onto other neurons as it goes. The key to neural function is the synaptic signaling process, which is partly electrical and partly chemical. Neurons communicate by chemical and electrical synapses. in a process known as neurotransmission, also called synaptic transmission. The fundamental process that triggers the release of neurotransmitters is the action potential, a propagating electrical signal that is generated by each neuron. This is also known as a wave of depolarization. Neurons are highly specialized for the processing and transmission of cellular signals. .

2. How does the Endocrine system communicate? The endocrine system is the collection of glands of an organism that secrete hormones directly into the circulatory system to be carried towards distant target organs. The phenomenon of biochemical processes' serving to regulate distant tissues by means of secretions directly into the circulatory system is called endocrine signaling. The major endocrine glands include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, and adrenal glands. The endocrine system is an information signal system like the nervous system, yet its effects and mechanism are classifiably different. The endocrine system's effects are slow to initiate, and prolonged in their response, lasting from a few hours up to weeks. The nervous system sends information very quickly, and responses are generally short lived. In humans, the hypothalamus [part of the brain - central nervous system] is the neural control centre for all endocrine systems. Special features of endocrine glands are, in general, their ductless nature, This is in contrast, exocrine glands, such as salivary glands, sweat glands, and glands within the gastrointestinal tract that have ducts. A number of glands that signal each other in sequence are usually referred to as an axis, for example, the hypothalamic-pituitary-adrenal axis. The hypothalamic–pituitary–adrenal axis (HPA axis) is a complex set of direct influences and feedback interactions among three endocrine glands. These endocrine organs and their interactions control reactions to stress and regulate many body processes, including digestion, the immune system, mood and emotions, sexuality, and energy storage and expenditure. [see topic on Health, stress and coping]

The HPA axis is involved in the neurobiology of the following disorders: insomnia, all forms of stress including posttraumatic stress and burnout; and, borderline personality disorder. Antidepressants, which are routinely prescribed for many of these illnesses, serve to regulate HPA axis function. Note, there are five different types of antidepressants and reflect differences in chemical structure, mechanisms of action and biochemical pathways. Experimental studies have investigated many different types of stress and their effects on the HPA axis in many different circumstances. Stressors can be of many different types—a distinction is often made between "social stress" and "physical stress", but both types activate the HPA axis, though via different pathways.

3. Describe the structure and function of the Central Nervous System.

Central Nervous System

Schematic diagram showing the central nervous system in pink, peripheral in orange

The central nervous system (CNS) is the part of the nervous system consisting of the brain and spinal cord. The central nervous system is so named because it integrates information it receives from, and coordinates and influences the activity of all parts of the bodies and it contains the majority of the nervous system. The central nervous system consists of the two major structures: the brain and spinal cord. The brain is encased in the skull, and protected by the cranium. The spinal cord is continuous with the brain and lies caudally to the brain, and is protected by the vertebra. The spinal cord reaches from the base of the skull and terminates at the end of the vertebra. The brain (cerebrum as well as midbrain and hindbrain) consists of a cortex, composed of neuron-bodies constituting both white and gray matter. The brain makes up the largest portion of the central nervous system, and is often the main structure referred to when speaking of the nervous system. The brain is the major functional unit of the central nervous system and is the major processing unit of the nervous system. Cerebrum - The cerebrum of cerebral hemispheres make up the largest visual portion of the human brain. The hemispheres together control a large portion of the functions of the human brain such as emotion, memory, perception and motor functions. Apart from this the cerebral hemispheres control the cognitive capabilities of the brain. Connecting each of the hemispheres is the corpus callosum (see split brain research). One of the most important parts of the cerebral hemispheres is the cortex, made up of gray matter covering the surface of the brain.

Functionally, the cerebral cortex is involved in planning and carrying out of everyday tasks. Spinal cord From and to the spinal cord are projections of the peripheral nervous system in the form of spinal nerves (sometimes segmental nerves). The nerves connect the spinal cord to skin, joints, muscles etc. and allow for the transmission of afferent sensory signals [sensory information to the brain] as well as efferent motor signals [brain instructions to muscles]. This allows for voluntary and involuntary motions of muscles, as well as the perception of senses.

4. What do split-brain studies indicate about the organization (lateralization) of the brain The human brain is divided into two hemispheres–left and right. Scientists continue to explore how some cognitive functions tend to be dominated by one side or the other; that is, how they are lateralized. The lateralization of brain function refers to how some neural functions or cognitive processes tend to be more dominant in one hemisphere than the other. The human brain is separated into two distinct hemispheres, connected by the corpus callosum. Although the two hemispheres appear to be almost identical, different composition of neuronal networks allows for specialized function that is different in each hemisphere. When speaking of dominance it is important to recognize that each hemisphere continues to function semi-independently but their interactions become dominated by one side. That is, each hemisphere always provides its input to the decision making process. The role of hemispheric rivalry has become a major talking point for those studying the generation of consciousness within the brain. Some believe the brain’s state of conflict is integrally linked to intelligence and genuine free will. [see chapter on Consciousness]. Lateralization of brain structures is based on general trends expressed in healthy patients; however, there are numerous excerptions; hence, each human’s brain develops differently leading to unique lateralization in individuals. The shift of information and neuron functionality between hemispheres should not be surprising, however, as it has been observed in individuals who have lost a sense. In these individuals, neurons, even those that are specialized, are semi-repurposed to compensate for the loss. For example: those who become blind after years of vision are able to repurpose specialized sections of their brain [visual cortex] to aid in the efficiency of their other senses [the increased ability to localize sound is represented by sounds eliciting electrical responses in the visual cortex. [called brain plasticity – see later in this section]. Research milestones in brain lateralization/specialization

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In 1861, the French physician Pierre Paul Broca, studied a male patient nicknamed "Tan", who suffered a speech deficit (aphasia). At Tan’s autopsy, Broca determined he had a syphilitic lesion in the frontal lobe area of his left cerebral hemisphere an important speech production region and now named area (Broca's area) German physician Karl Wernicke studied language deficits and found that damage to the temporal lobe in the left hemisphere (Wernicke's area) caused language comprehension deficits rather than speech production deficits.

• In the 1940s, neurosurgeon Wilder Penfield and his neurologist colleague Herbert Jasper developed a technique of brain mapping to help reduce side effects caused by surgery to treat epilepsy. They stimulated motor and somatosensory cortices of the brain with small electrical currents to activate discrete brain regions. They found that stimulation of one hemisphere's motor cortex produces muscle contraction on the opposite side of the body. Furthermore, the functional map of the motor and sensory cortices is fairly consistent from person to person; Penfield and Jasper's famous pictures of the motor and sensory homunculi were the result. [see opposite]

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In the 1960s, research by Michael Gazzaniga and Roger Wolcott Sperry on split-brain patients led to an even greater understanding of functional laterality [see below] Current imaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) are important in continuing this work on hemispheric specializations because of their high spatial resolution and ability to image subcortical brain structures. Split-brain patients Split-brain patients are patients who have undergone corpus callosotomy (usually as a treatment for severe epilepsy), which involves a severing of the corpus callosum. The corpus callosum connects the two hemispheres of the brain and allows them to communicate. When these connections are cut, the two halves of the brain have a reduced capacity to communicate with each other.

This led to many interesting behavioural phenomena including a finding that language was primarily localized in the left hemisphere. The right hemisphere was capable of rudimentary language processing, but had no lexical or grammatical abilities. One of the experiments carried out by Gazzaniga involved a split-brain patient sitting in front of a computer screen while having words and images presented on either side of the screen and the visual stimuli would go to either the right or left visual field, and thus the left or right brain, respectively. It was observed that if a patient was presented with an image to his left visual field (right brain), he would report not seeing anything. If he was able to feel around for certain objects, he could accurately pick out the correct object, despite not having the ability to verbalize what he saw. This led to confirmation that the left brain is localized for language while the right brain does not have this capability, and when the corpus callosum is cut and the two hemispheres cannot communicate for the speech to be produced.

Misinformation and facts about split brain findings 

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It is commonly held that the left brain is "logical" while the right is "creative", and that this exerts considerable influence on the personality of people, depending on which side is the dominant one for them. Such notions are not supported by research in psychology or neurosciences. Significant differences between male and female hemispheric rivalry and dominance have been established. Male brains have significantly better global and rivalry efficiency between the hemispheres [resulting in better spatial localization], whereas female brains possess considerably better local efficiency [leading to better locating objects] Handedness has been implicated in determining which hemisphere is naturally dominant. Right handed people have a dominant left hemisphere. Left-handed and ambidextrous individuals have been shown to have more efficient hemispheric interactions. Language functions such as grammar, vocabulary and literal meaning [ability to understand speech] are typically lateralized to the left hemisphere, especially in right handed individuals. While language production [ability to speak] is left-lateralized in up to 90% of right-handed subjects, it is more bilateral, or even right lateralized in approximately 50% of left-handers.

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There is no lateralization in many functions – for instance, the processing of visual and auditory stimuli, spatial manipulation, facial perception, and artistic ability are represented bilaterally. Brain Plasticity If a specific region of the brain, or even an entire hemisphere, is injured or destroyed, its functions can sometimes be assumed by a neighboring region in the same hemisphere or the corresponding region in the other hemisphere, depending upon the area damaged and the patient's age. When injury interferes with pathways from one area to another, alternative (indirect) connections may develop to communicate information with detached areas, despite the inefficiencies. One important example of this the return of motor and sensory functions in people who had a cerebrovascular accident [stroke] where the functions of specific brain areas are permanently damaged but neighbouring areas can be trained to take over these functions Advantages of brain lateralization The widespread lateralization in humans indicates an evolutionary advantage associated with the specialization of each hemisphere. This involves the ability to complete tasks to a higher degree of complexity and quality [e.g., human language] and to complete parallel tasks [e.g., walking and talking]

5. Describe the relative roles of genetics and the environment in psychological functioning. The phrase nature and nurture relates to the relative importance of an individual's innate qualities ("nature" in the sense of nativism or innatism) as compared to an individual's personal experiences ("nurture" in the sense of empiricism or behaviorism) in causing individual differences, especially in behavioral traits. [see topic 1, previous topic] It is important to note that the term heritability refers only to the degree of genetic variation between people on a trait. It does not refer to the degree to which a trait of a particular individual is due to environmental or genetic factors. The traits of an individual are always a complex interweaving of both. For an individual, even strongly genetically influenced traits, such as eye color, assume the inputs of a typical environment during development (e.g., certain ranges of temperatures, oxygen levels, etc.). One way to determine the contribution of genes and environment to a trait is to study twins. In one kind of study, identical twins reared apart are compared to randomly selected pairs of people. The twins share identical genes, but different family environments. In another kind of twin study,

identical twins reared together (who share family environment and genes) are compared to fraternal twins reared together (who also share family environment but only share half their genes). Another condition that permits the disassociation of genes and environment is adoption. In one kind of adoption study, biological siblings reared together (who share the same family environment and half their genes) are compared to adoptive siblings (who share their family environment but none of their genes). Twin and adoption studies have their methodological limits. For example, both are limited to the range of environments and genes which they sample. Almost all of these studies are conducted in Western, first-world countries, and therefore cannot be extrapolated globally to include poorer, non-western populations. Additionally, both types of studies depend on particular assumptions, such as the equal environments assumption in the case of twin studies, and the lack of pre-adoptive effects in the case of adoption studies. Heritability of intelligence Twin and family studies show a strong relationship between genetic relatedness and the similarity of intelligences score [see table]. However, evidence from behavioral genetic research suggests that family environmental factors may have an effect upon childhood IQ, accounting for up to a quarter of the variance. Thus the early childhood environment is playing a role in what is believed to be fully genetic (intelligence). This is certainly true which shows that severely deprived, neglectful, or abusive environments have highly

negative effects on many aspects of children's intellect development. However, by adulthood, adoptive siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6. Twin studies reinforce this pattern: monozygotic (identical) twins raised separately are highly similar in IQ (0.74), more so than dizygotic (fraternal) twins raised together (0.6) and much more than adoptive siblings (~0.0). Recent adoption studies also found that

supportive parents can have a positive effect on the development of their children.

Personality traits Personality is a frequently cited example of a heritable trait that has been studied in twins and adoptees using behavioral genetic study des...