Intro to Psych Chapter 3

Chapter 3 Biopsychology 

3.1 Human Genetics 

Psychological researchers study genetics in order to better understand the biological factors that contribute to certain behaviors. While all humans share certain biological mechanisms, we are each unique.

Sickle-cell anemia is a genetic condition in which red blood cells, which are normally round, take on a crescent-like shape

The changed shape of these cells affects how they function: sickle-shaped cells can clog blood vessels and block blood flow, leading to high fever, severe pain, swelling, and tissue damage.

Malaria is rare in the United States, so the sickle-cell gene benefits nobody: the gene manifests primarily in minor health problems for carriers with one copy, or a severe full-blown disease with no health benefits for carriers with two copies.

theory of evolution by natural selection In simple terms, the theory states that organisms that are better suited for their environment will survive and reproduce, while those that are poorly suited for their environment will die off.

Luwi’s mutation is highly adaptive in her African homeland; however, if she resided in the United States (where malaria is rare), her mutation could prove costly—with a high probability of the disease in her descendants and minor health problems of her own.

Genetic variation, the genetic difference between individuals, is what contributes to a species’ adaptation to its environment.

Chromosomes are long strings of genetic material known as deoxyribonucleic acid (DNA). DNA is a helix-shaped molecule made up of nucleotide base pairs. In each chromosome, sequences of DNA make up genes that control or partially control a number of visible characteristics, known as traits, such as eye color, hair color, and so on. A single gene may have multiple possible variations, or alleles. An allele is a specific version of a gene. So, a given gene may code for the trait of hair color, and the different alleles of that gene affect which hair color an individual has.

A person’s genotype is the genetic makeup of that individual. Phenotype, on the other hand, refers to the individual’s inherited physical characteristics, which are a combination of genetic and environmental influences

dominant allele either from one parent (Bb) or both parents (BB) will always result in the phenotype associated with the dominant allele. When someone has two copies of the same allele, they are said to be homozygous for that allele. When someone has a combination of alleles for a given gene, they are said to be heterozygous. For example, smooth chin is a recessive trait, which means that an individual will only display the smooth chin phenotype if they are homozygous for that recessive allele (bb).

In sickle cell anemia, heterozygous carriers (like Luwi from the example) can develop blood resistance to malaria infection while those who are homozygous (like Sena) have a potentially lethal blood disorder. Sickle-cell anemia is just one of many genetic disorders caused by the pairing of two recessive genes. For example, phenylketonuria (PKU) is a condition in which individuals lack an enzyme that normally converts harmful amino acids into harmless byproducts. If someone with this condition goes untreated, they will experience significant deficits in cognitive function, seizures, and an increased risk of various psychiatric disorders. Because PKU is a recessive trait, each parent must have at least one copy of the recessive allele in order to produce a child with the condition

Most traits are polygenic: controlled by more than one gene. Height is one example of a polygenic trait, as are skin color and weight.

A mutation is a sudden, permanent change in a gene. While many mutations can be harmful or lethal, once in a while, a mutation benefits an individual by giving that person an advantage over those who do not have the mutation. Recall that the theory of evolution asserts that individuals best adapted to their particular environments are more likely to reproduce and pass on their genes to future generations. In order for this process to occur, there must be competition—more technically, there must be variability in genes (and resultant traits) that allow for variation in adaptability to the environment.

Range of reaction asserts that our genes set the boundaries within which we can operate, and our environment interacts with the genes to determine where in that range we will fall. For example, if an individual’s genetic makeup predisposes them to high levels of intellectual potential and they are reared in a rich, stimulating environment, then they will be more likely to achieve full potential than if they were raised under conditions of significant deprivation. 

According to the concept of range of reaction, genes set definite limits on potential, and environment determines how much of that potential is achieved. Some disagree with this theory and argue that genes do not set a limit on a person’s potential with reaction norms being determined by the environment.

Another perspective on the interaction between genes and the environment is the concept of genetic environmental correlation. Stated simply, our genes influence our environment, and our environment influences the expression of our genes

the field of epigenetics looks beyond the genotype itself and studies how the same genotype can be expressed in different ways. In other words, researchers study how the same genotype can lead to very different phenotypes.

3.2 Cells of the Nervous System

The nervous system is composed of two basic cell types: glial cells (also known as glia) and neurons.

Glial cells provide scaffolding on which the nervous system is built, help neurons line up closely with each other to allow neuronal communication, provide insulation to neurons, transport nutrients and waste products, and mediate immune responses.

Neurons, on the other hand, serve as interconnected information processors that are essential for all of the tasks of the nervous system. This section briefly describes the structure and function of neurons.

A neuron’s outer surface is made up of a semipermeable membrane. This membrane allows smaller molecules and molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules.

The nucleus of the neuron is located in the soma, or cell body.

The soma has branching extensions known as dendrites. The neuron is a small information processor, and dendrites serve as input sites where signals are received from other neurons.

These signals are transmitted electrically across the soma and down a major extension from the soma known as the axon, which ends at multiple terminal buttons

The terminal buttons contain synaptic vesicles that house neurotransmitters, the chemical messengers of the nervous system.

glial cells form a fatty substance known as the myelin sheath, which coats the axon and acts as an insulator, increasing the speed at which the signal travels. The myelin sheath is not continuous and there are small gaps that occur down the length of the axon. These gaps in the myelin sheath are known as the Nodes of Ranvier. 

The myelin sheath is crucial for the normal operation of the neurons within the nervous system: the loss of the insulation it provides can be detrimental to normal function.

The synaptic cleft is a very small space between two neurons and is an important site where communication between neurons occurs. Once neurotransmitters are released into the synaptic cleft, they travel across it and bind with corresponding receptors on the dendrite of an adjacent neuron.

 Receptors, proteins on the cell surface where neurotransmitters attach, vary in shape, with different shapes “matching” different neurotransmitters.

This difference in charge across the membrane, called the membrane potential, provides energy for the signal.

Between signals, the neuron membrane’s potential is held in a state of readiness, called the resting potential. Like a rubber band stretched out and waiting to spring into action, ions line up on either side of the cell membrane, ready to rush across the membrane when the neuron goes active and the membrane opens its gates.

Reuptake involves the neurotransmitter being pumped back into the neuron that released it, in order to clear the synapse

Psychologists who take a biological perspective and focus on the physiological causes of behavior assert that psychological disorders like depression and schizophrenia are associated with imbalances in one or more neurotransmitter systems. 

In this perspective, psychotropic medications can help improve the symptoms associated with these disorders. Psychotropic medications are drugs that treat psychiatric symptoms by restoring neurotransmitter balance.

Agonists are chemicals that mimic a neurotransmitter at the receptor site. 

An antagonist, on the other hand, blocks or impedes the normal activity of a neurotransmitter at the receptor.

 Agonists and antagonists represent drugs that are prescribed to correct the specific neurotransmitter imbalances underlying a person’s condition.

3.3 Parts of the Nervous System 

The nervous system can be divided into two major subdivisions: the central nervous system (CNS) and the peripheral nervous system (PNS)

The CNS comprises the brain and spinal cord; the PNS connects the CNS to the rest of the body.

The peripheral nervous system is made up of thick bundles of axons, called nerves, carrying messages back and forth between the CNS and the muscles, organs, and senses in the periphery of the body

The PNS has two major subdivisions: the somatic nervous system and the autonomic nervous system.

The somatic nervous system is associated with activities traditionally thought of as conscious or voluntary. It is involved in the relay of sensory and motor information to and from the CNS; therefore, it consists of motor neurons and sensory neurons.

The autonomic nervous system controls our internal organs and glands and is generally considered to be outside the realm of voluntary control. It can be further subdivided into the sympathetic and parasympathetic divisions

The sympathetic nervous system is involved in preparing the body for stress-related activities; the parasympathetic nervous system is associated with returning the body to routine, day-to-day operations. 

The two systems have complementary functions, operating in tandem to maintain the body’s homeostasis. Homeostasis is a state of equilibrium, or balance, in which biological conditions (such as body temperature) are maintained at optimal levels.

The sympathetic nervous system is activated when we are faced with stressful or high-arousal situations. 

The activity of this system was adaptive for our ancestors, increasing their chances of survival.The pupils dilate, the heart rate and blood pressure increase, the bladder relaxes, and the liver releases glucose; adrenaline surges into the bloodstream. 

This constellation of physiological changes, known as the fight or flight response, allows the body access to energy reserves and heightened sensory capacity so that it might fight off a threat or run away to safety.

3.4 The Brain and Spinal Cord 

Neuroplasticity refers to how the nervous system can change and adapt. 

Neuroplasticity can occur in a variety of ways including personal experiences, developmental processes, or, as in Woodruff's case, in response to some sort of damage or injury that has occurred. 

Neuroplasticity can involve creation of new synapses, pruning of synapses that are no longer used, changes in glial cells, and even the birth of new neurons. Because of neuroplasticity, our brains are constantly changing and adapting, and while our nervous system is mostly plastic when we are very young, as Woodruff's case suggests, it is still capable of remarkable changes later in life.

The surface of the brain, known as the cerebral cortex, is very uneven, characterized by a distinctive pattern of folds or bumps, known as gyri (singular: gyrus), and grooves, known as sulci

These gyri and sulci form important landmarks that allow us to separate the brain into functional centers. 

The most prominent sulcus, known as the longitudinal fissure, is the deep groove that separates the brain into two halves or hemispheres: the left hemisphere and the right hemisphere.

lateralization—in each hemisphere, mainly regarding differences in language functions. The left hemisphere controls the right half of the body, and the right hemisphere controls the left half of the body. 

Decades of research on lateralization of function by Michael Gazzaniga and his colleagues suggest that a variety of functions ranging from cause-and-effect reasoning to self-recognition.

The two hemispheres are connected by a thick band of neural fibers known as the corpus callosum, consisting of about 200 million axons. 

The corpus callosum allows the two hemispheres to communicate with each other and allows for information being processed on one side of the brain to be shared with the other side.

The frontal lobe is located in the forward part of the brain, extending back to a fissure known as the central sulcus. 

The frontal lobe is involved in reasoning, motor control, emotion, and language. 

It contains the motor cortex, which is involved in planning and coordinating movement; the prefrontal cortex, which is responsible for higher-level cognitive functioning; and Broca’s area, which is essential for language production.

The brain’s parietal lobe is located immediately behind the frontal lobe, and is involved in processing information from the body’s senses. 

It contains the somatosensory cortex, which is essential for processing sensory information from across the body, such as touch, temperature, and pain. 

The somatosensory cortex is an area of the brain which processes touch and sensation.

A computerized tomography (CT) scan involves taking a number of x-rays of a particular section of a person’s body or brain. 

The x-rays pass through tissues of different densities at different rates, allowing a computer to construct an overall image of the area of the body being scanned.

A CT scan is often used to determine whether someone has a tumor or significant brain atrophy.

Positron emission tomography (PET) scans create pictures of the living, active brain

PET scans show little detail, are unable to pinpoint events precisely in time, and require that the brain be exposed to radiation; therefore, this technique has been replaced by the fMRI as an alternative diagnostic tool. 

However, combined with CT, PET technology is still being used in certain contexts.

In magnetic resonance imaging (MRI), a person is placed inside a machine that generates a strong magnetic field. The magnetic field causes the hydrogen atoms in the body’s cells to move. When the magnetic field is turned off, the hydrogen atoms emit electromagnetic signals as they return to their original positions.

 Functional magnetic resonance imaging (fMRI) operates on the same principles, but it shows changes in brain activity over time by tracking blood flow and oxygen levels. The fMRI provides more detailed images of the brain’s structure, as well as better accuracy in time, than is possible in PET scans

Electroencephalography (EEG) serves this purpose by providing a measure of a brain’s electrical activity. An array of electrodes is placed around a person’s head. 

The signals received by the electrodes result in a printout of the electrical activity of their brain, or brainwaves, showing both the frequency (number of waves per second) and amplitude (height)

3.5 The Endocrine System 

The endocrine system consists of a series of glands that produce chemical substances known as hormones

hormones are chemical messengers that must bind to a receptor in order to send their signal. 

However, unlike neurotransmitters, which are released in close proximity to cells with their receptors, hormones are secreted into the bloodstream and travel throughout the body, affecting any cells that contain receptors for them.

The pituitary gland descends from the hypothalamus at the base of the brain, and acts in close association with it. 

The pituitary is often referred to as the “master gland” because its messenger hormones control all the other glands in the endocrine system, although it mostly carries out instructions from the hypothalamus.

Located in the neck, the thyroid gland releases hormones that regulate growth, metabolism, and appetite.

In hyperthyroidism, the thyroid secretes too much of the hormone thyroxine, causing agitation, bulging eyes, and weight loss.