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Transcript of Chp 03
What is the basic structural and functional unit of our body?
A single cell, a zygote, is formed by the union of a sperm and an egg.
This single cell, as every other human cell, carries 46 chromosomes in its nucleus.
Chromosomes operate in 23 pairs.
One of each pair is derived from the mother and one from the father.
Each chromosome carries a DNA molecule.
DNA contains instructions, known as genes.
Genes carry the chemical code for how the body will grow, develop, function and maintain itself.
The full set of genetic instructions for a living thing, controlling its development from a single cell into a complex adult body is known as Genome.
Discoveries in the History on the Genetic Basis of Human Body
Heredity was a well-known fact before Darwin.
Biologists studied the earth’s fossils and noted that various species have undergone gradual changes over the course of many generations .
Darwin explained how and why those changes occurred. Two points in Darwin’s theory is very important.
Adaptation: Changes in characteristics occur over time to meet the changing demands of their environment. These changes pass on to next generations.
Just like physical traits, species’ typical patterns of behaviour reflect adaptation and passed to following generations.
Following Darwin’s ideas, other scientists continued to study the mechanisms responsible for heredity.
Mendel was working with plants. He was breeding peas with only purple flowers or white flowers and observing which colour flowers would be produced.
He noticed that there is a pattern in the colour of flower. While 75 percent had purple flowers, 25 percent had white flowers.
Mendel deduced that there are discrete units, known as genes, and they exist in two versions (white and purple). Like chromosomes, genes work in pair, and one of them is dominant and the other is recessive.
Dominant genes are expressed whenever they are present and recessive genes are expressed only when they are matched with another recessive gene.
The existence of dominant and recessive genes means that not all genes are expressed.
The genotype is the genetic make up of an organism, determined at the conception.
Phenotype is the observable physical characteristics of an organism that result from both genetic and environmental influences.
Most human traits and diseases are polygenic; they are influenced by more than one pair of genes.
How genes and environment interact to influence psychological activity
Behavioural genetics: How much and which of our characteristics are influenced by genetic make up and the environment.
Three types of studies :
If heredity influences a trait, relatives who share more traits should be more similar with regard to that trait than are more distant relatives, who share fewer genes.
Certain traits such as psychological disorders are shared by family members to some extent but these studies did not yield enough evidence about the effect of heredity on our psychological characteristics.
The Human Genome Project
Researchers compared the resemblance of identical twins (100% genetic overlap) and fraternal twins (50% genetic overlap).
Fraternal twins provide a useful comparison to identical twins because in both cases the twins usually grow up in the same home and at the same time.
Since they have similar influences from the environment, any difference between these two groups can be attributed to genetic factors.
It was found that identical twins were more similar to each other than fraternal twins on intelligence and personality traits.
However, it was also found that identical twins were not identical on those traits, either. Environment also influence these characteristics.
Researchers assessed heredity influence by examining the resemblance between adopted children and both their biological and adoptive parents.
These studies found that there are modest similarities between adopted children and biological parents and between children and adoptive parents.
Both heredity and environment play a role on certain traits.
A biological revolution occurred in 2001 when two groups of scientists announced that they mapped the basic gene sequence of human DNA, in other words the human genome.
Scientist all over the world worked for this project.
The project has produced a working draft of the sequence of all 3 billion letters of DNA in the human genome and the locations of all human genes have been identified.
The most striking findings from the project is that we have only around 30,000 genes, not many more than are found in a fly (13,000), a worm (18,000), or even a plant (26,000).
This is a big step to find out the link between specific genes and specific traits and disorders.
Nervous system is a communication network that serves as the foundation for all psychological activity. It consists of billions of nerve cells or neurons. It is comprised of two systems- central nervous system and peripheral- defined by both anatomy and function.
Central Nervous System
Peripheral Nervous System
Central nervous system is central to the body’s structure and workings. It is composed of the brain and spinal cord. Nearly all functions of the CNS are performed by the brain.
Its main job is to receive sensory signals from the body and transmit them to the brain, and to receive signals from the brain and relay them to the body to control muscles, glands and internal organs.
When necessary, it can bypass the brain, for example in reflex actions.
It is the part of nervous system that extends outside the central nervous system.
PNS connects the brain and spinal cord (CNS) to the rest of the body.
Somatic Nervous System
Autonomic Nervous System
The part of PNS that is responsible from those voluntary actions.
It transmits sensory signals to the CNS via nerves.
Specialized receptors in the skin, muscles and joints send sensory info to the spinal cord, which relays it to the brain.
Signals are sent from the CNS to muscles, joints, and skin to control movement.
The part of PNS that controls automatic, involuntary functions.
It regulates internal body functions that we are not really aware of, such as digestion, blood pressure, heart rate, or perspiration. Autonomic nervous system works in two ways:
prepares the body for action and stress
For example, in case of a fire alarm:
blood flows to muscles,
heart rate and blood pressure are increased,
your digestion stops to conserve energy,
your pupils dilate to maximize visual sensitivity,
and you start perspiring to keep cool.
restores normal function to conserve energy
Many times, the fire bell is a false alarm.
your heart returns to its normal steady beat,
your pupils constrict,
you resume digesting food,
and you quit perspiring
Neurons are the basic units of the nervous system. Neurons are cells that specialize in communication. They operate through electrical impulses and communicate with other neurons through chemical signals.
Neurons have different shapes and sizes, but they typically share some common features:
Dendrites: branchlike extensions of the neuron that receive information from other neurons.
Cell body (soma): Main part of the neuron, contains nucleus. This is where information from other neurons is collected and integrated.
Axon: Once the incoming information has been integrated in the cell body, electrical impulses are transmitted along a long narrow fiber to other neurons or to muscles or glands. Many axons are wrapped with a special substance called myelin. This myelin sheath speeds up the transmission of signals that move along the axon.
Terminal Buttons: Small knobs at the ends of axons that release chemical signals from the neuron to an area called the synapse.
Synapse: is a junction (tiny gap) where chemical signals, neurotransmitters are transmitted from one neuron to the other one.
What is the neural impulse exactly?
A complex electrochemical reaction. Both inside and outside of the neuron are fluids. There are negatively and positively charged ions in that fluid. When not active, inside of the neuron is negatively charged. This is called the resting potential. When neuron is stimulated, balance of the electrical charge changes and it creates an action potential, an electrical charge or a neural impulse that passes along the axon.
Neurons are like guns. It either fires or it does not. And their action potential, electrical charge is always the same size. Intensity is coded in two ways:
-the number of neurons firing (the more neurons are firing; the more intense is the sensation)
-the frequency of firing. (the more frequent the firing is, the more intense is the sensation)
How do neurons communicate with each other?
Neurons communicate to one another chemically.
When an electrical impulse arrives at the synapse, it triggers the release of chemicals called neurotransmitters. They cross the synaptic cleft between the neurons. They either trigger a new impulse (excitatory) in the receiving neuron or inhibit it from firing (inhibitory).
More than 60 chemicals transmit information.
Different transmitters are responsible for influencing emotion, behaviour and thoughts.
Drugs can change the way neurotransmitters work. They can enhance the actions of neurotransmitters (agonist), or they can inhibit their action (antagonist).
-Acetylcholine: control over muscles; regulation of mental processes such as learning, memory, and attention. Alzheimer’s disease is associated with diminished ACh functioning.
-Dopamine: is used by neurons that control voluntary movements. Impairment of such neurons causes Parkinson Disease. The drug L-Dopa is used to increase the supply of dopamine.
-Serotonin: is especially important for emotional states, impulse control, and dreaming. Low levels of serotonin are associated with sad and anxious moods, food cravings, and aggressive behaviour. Prozac and similar antidepressant drugs work on serotonin.
-Endorphins: its name comes from “endogenous morphine”. Internally produced chemicals that resemble morphine in effect. It minimizes the sensation of pain.
different parts do different things VS. entire brain acts in unison
Phrenology. Anatomists tried to understand personality traits and mental abilities by measuring the bumps on the human skull.
Scientists were able to examine the nerve cells.
Scientists were able to explain the electrical impulses and neurotransmitters
A machine that could record the broad patterns of electrical activity in the brain was developed.
Researchers focused on people who suffered from specific brain damages to investigate brain-behaviour relationship. Dr. Penfield worked with epilepsy patients, used electrical stimulation and made important contributions to the area.
Measuring the electrical activity in brain became one of the most important techniques used in brain research and it is developed further in recent years.
Ex: EEG, computerized tomography, MRI, and PET scans.
-provide us information about brain structure,
-help us map brain activity
Now, we know that the brain consists of highly specialized areas mostly for physical activities, but different areas coordinate for even routine mental operations.
Specialized Areas of the Brain
As we move upward, the functions of the brain structures go from regulation of basic processes to the control of more complicated and complex mental processes.
Medulla: -attached to the spinal cord,
-in charge of highly vital functions
including blood circulation,
breathing, regulating reflexes.
Pons: -connects brainstem with cerebellum.
-contains several cell bodies involved
with sleep and arousal.
Cerebellum:-critical to the coordination of
movement and physical balance.
-segment between hindbrain and forebrain.
-Dopamine-releasing neurons originate from midbrain, so it is indirectly related to the
performance of voluntary movements.
-contains other network of neurons known as reticular formation, which mainly
contributes to regulation of sleep and arousal.
Hindbrain and midbrain are evolutionarily older part of the brain. Newer, larger and more complex region of our brain is the forebrain.
-integrates and directs sensory info (except smell) to correct location in the cortex.
-the smell is the oldest and most fundamental of the senses, so it has a direct route
to the cortex.
-governs biological drives related to survival: fighting, fleeing, feeding and mating.
-controls the autonomic nervous system. It is responsible for regulating the vital
functions- body temperature, blood pressure, glucose level.
-controls the master gland of the body, pituitary gland, which by releasing hormones
into bloodstream controls all other glands.
-the structure in the brain most closely aligned to memory formation.
-plays an important role in spatial navigation.
-involved in processing emotions, and fear–learning.
-intensifies memory during times of emotional arousal, especially fear.
Cerebral Cortex (Cerebrum):
-Largest and most complex part of human brain.
-responsible for the most complex mental activities, including learning,
remembering, thinking, and consciousness.
-Cerebrum is divided into two hemispheres. These right and left hemispheres are
connected to each other by corpus callosum, bundle of fibers.
-Hemispheres control the opposite side of the body.
Each cerebral hemisphere is divided into four lobes that are dedicated to specific purposes.
-Primary visual cortex area.
-Partially devoted to the sense of touch.
-Primary somatosensory cortex.
-involved in representing the spatial relationships between ourselves and objects
-primary auditory cortex
-contains specialized visual areas for recognizing detailed objects such as faces.
-critical for memory.
-the largest lobe of the brain.
-essential for planning and movement.
-primary motor cortex.
The rest of the frontal lobe is prefrontal cortex. This area occupies almost 30 percent of the brain in humans and it is responsible from planning, reasoning, attention and working memory.
Can Brain change?
Research showed that brain is more plastic or malleable than we think.
-studies have shown that experience can reorganize the brain structure
-damage in some part of the body can lead to reorganization in the cortex
-new neurons are also produced in the adult brain, and this process is known as neurogenesis.
Case Studies and New Insights on Hemisphere Specialization
“Are hemispheres specialized?’
The answer came from brain surgery studies. One strategy in surgeries to treat epilepsy was cutting the connections between the two hemispheres. This condition is known as the split brain.
Studies showed that left hemisphere is better on verbal tasks, while the right one is better at face recognition, spatial tasks.
An alternative communication system in the body
Endocrine system, like nervous system, influences thoughts, behaviours and actions. The main distinction is their mode of communication. Endocrine system uses hormones, whereas nervous system uses electrochemical signals (neurotransmitters).
Hormones are chemical substances released into bloodstream by glands, such as pancreas and thyroid. Once released, hormones travel through the blood stream until they reach the target tissue. Because they travel the whole body, hormones can take from second to hour to have an effect on body and their effect can last long time.
Endocrine system is controlled by the nervous system through hypothalamus, which works closely with the pituitary gland (master gland).