The brain is a complex, versatile, and flexible network that controls our behaviors and mental processes.
The evolutionary psychology approach, which emphasizes the importance of adaptation, reproduction, and natural selection in explaining psychology, considers how the human nervous system has evolved to its complex present state.
Most scientists believe that behavior is determined by the interaction of the environment and the organism’s biological inheritance.
The nervous system is made up of interconnected nerve cells that transmit information throughout the body. There are four defining characteristics of the nervous system: (1) it communicates via electrochemical transmission; (2) it is characterized by its complexity, since the brain alone is composed of billions of nerve cells; (3) it can integrate information from many sources and create a coherent psychological experience; and (4) it has a great capacity to adapt to changes in the environment and the body.
The capacity of the brain to adapt is termed plasticity.
Cells that carry input to the brain are called sensory neurons; those that carry output from the brain are called motor neurons. Most of the communication in the nervous system takes place through neural networks, which are nerve cells that integrate sensory input and motor output.
The nervous system is divided into the central nervous system and the peripheral nervous system.
The central nervous system consists of the brain and the spinal cord.
The peripheral nervous system connects the brain and the spinal cord to the other parts of the body.
The peripheral nervous system is divided into the somatic nervous system, which contains sensory and motor nerves, and the autonomic nervous system, which monitors the body’s internal organs.
There are two types of nerve cells: neurons and glial cells. The neurons are in charge of communication, and the glial cells support and nourish the neurons. A neuron is made of (1) a cell body, which regulates the cell’s growth and maintenance; (2) dendrites, which collect information for the neuron; and (3) an axon, which carries information away from the cell body to other cells. Most axons are covered with a layer of fat cells called the myelin sheath, which insulates the axon and speeds up the impulse.
Neurons send information down the axon in the form of waves of electricity called the action potential.
The neuron has a cell membrane that allows certain substances to enter the cell and other substances to exit the cell. The action potential operates according to the all-or-none principle.
Each axon branches out into numerous fibers that store substances called neurotransmitters. When the electrochemical wave arrives at the end of an axon, the neurotransmitter is released onto the synapse, the tiny gap between neurons. The neurotransmitters carry the message across the synapse to the receiving dendrite or cell body of the next neuron.
Dendrites and some soma have receptor sites, which are neurotransmitter specific. The most
common analogy is that of a lock and key. The neurotransmitter is the key and the receptor site is the lock.
When the neurotransmitter latches onto a receptor site, it initiates an electrochemical wave in the receiving neuron. This is how neurons communicate! However, some neurotransmitters are inhibitory, which means that when they latch onto a receptor site, they keep the next neuron from starting an action potential. The neurotransmitters that stimulate other neurons to start the action potential are referred to as excitatory.
Chapter 2 includes a discussion of six neurotransmitters that are very important in the human nervous system: acetylcholine, GABA, norepinephrine, dopamine, serotonin, and endorphins.
Glial cells provide support and nutritive functions for neurons.
The neural communication is the foundation of our psychology. Whenever we have an experience, say stepping on a sharp stone, a number of neurons are stimulated and neural communication takes place throughout the nervous system. Some of those neurons will control your movements as you retrieve your foot and regain your balance; they will communicate again in the future when you recall the event and when a similar experience occurs.
The brain consists of the hindbrain, the midbrain, and the forebrain.
The hindbrain is the lowest portion of the brain and consists of the medulla, the cerebellum, and the pons.
The midbrain is an area where many nerve-fibers ascend and descend and relay information between the brain and the eyes and ears. An important structure of the midbrain is the reticular formation.
The highest region of the brain is the forebrain. Its major structures include the limbic system, thalamus, basal ganglia, hypothalamus, and cerebral cortex. Each performs certain specialized functions involving emotion, memory, senses, movement, stress, and pleasure.
The cerebral cortex consitutes the largest part of the brain and comprises two hemispheres (left and right) and four lobes (occipital, temporal, parietal, and frontal). The cerebral cortex consists of the sensory cortex, the motor cortex, and the association cortex. The two hemispheres are connected by the corpus callosum. No complex function can be assigned to one single hemisphere or the other. There is interplay between the two hemispheres.
A number of important body reactions produced by the autonomic nervous system result from its action on the endocrine glands. The endocrine system is a set of glands (pituitary, thyroid, parathyroid, adrenal, pancreas, and the ovaries in women and the testes in men) that regulate the activities of certain organs by releasing hormones into the bloodstream. The anterior part of the pituitary is called the master gland; it is controlled by the hypothalamus. The adrenal glands play an important role in mood, energy, and stress.
Our psychology has genetic and evolutionary foundations. The last part of Chapter 2 explores the basic concepts of genetics and heredity. The nucleus of each human cell contains 46 chromosomes (23 pairs) that contain DNA.
Genes, the units of hereditary information, are short segments of chromosomes.
Genes combine with other genes to determine our characteristics. There are dominant and recessive genes.
Polygenic inheritance is the effect that multiple genes have on behaviors and mental processes.
The study of genetics has progressed from the basic experiments of Mendel to molecular genetics and the development of genomes. The Human Genome Project strives to describe the complete set of instructions for making a human being. There are great expectations for this project to contribute to the understanding of physical disease and mental disorders. Genetic methods include selective breeding and behavior genetics.
Psychologists now face the challenge of finding theoretical frameworks that successfully integrate the biological foundations of psychology and research in genetics and neuroscience with the wealth of psychological theories that explore the influences of the environment and experiences on human psychology.
Building Blocks of Chapter 3
Clarifying some of the tricky points in Chapter 3 and
In Your Own Words
To respond to the questions and exercises presented in the “In Your Own Words” section, please write your thoughts, perspectives, and reactions on a separate piece of paper.
The Nervous System
The body’s electrochemical communication circuitry is known as the nervous system; the field that
studies this system is called neuroscience. The four characteristics of the nervous system are complexity, integration, adaptability, and electrochemical transmission. The capacity of the nervous system to adapt is
reflected in plasticity, which is the capacity of the brain to modify and change. This means with experience our brain literally changes!
When neurons communicate with one another they use chemicals, called neurotransmitters. Our nervous system is divided into two parts: the central nervous
system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord; the
PNS connects the brain and spinal cord to other parts of the body.
The peripheral nervous system consists of two major divisions: one, which contains both sensory nerves and motor nerves, is called the somatic nervous system. The other, which monitors breathing, heart rate, and digestion, is the autonomic nervous system. The autonomic nervous system is divided intothe sympathetic nervous system, which helps arouse the body, and the parasympathetic nervous system, which helps calm the body.
In Your Own Words
Please write your thoughts, perspectives, and reactions on a separate piece of paper.
9 What are some circumstances in which the sympathetic nervous system is activated? In these circumstances, what advantage does one gain from the sympathetic nervous system being activated?
There are two types of cells in the nervous system: neurons and glial cells.
Helpful Hints for Understanding Neuropsychology
Helpful Hint #1:
Neurons are the cells that process information; the glial cells provide support and nutrition in the nervous system. Think
of the glial cells as the caretakers of the neurons. There are many more glial cells in the human brain than there are neurons, so we know neurons need nutrition and support to function well.
Neurons have three parts: dendrites, cell body, and axon. The part of the neuron that receives information is the dendrite; the part that carries the information away from the cell body is the axon.
Neurons send messages by creating a brief wave of electrical charge; this charge is called an action potential. The action potential abides by the all-or-none principle. Each axon branches out into numerous fibers that store those chemicals called neurotransmitters. These are chemicals that are released onto the synapse, the tiny gap between neurons.
Acetylcholine is a neurotransmitter involved in the actions of muscles, learning, and memory. GABA is a neurotransmitter that inhibits the firing of neurons. Too little of the neurotransmitter norepinephrine is associated with depression, and too much is linked to agitated, manic states. Low levels of the neurotransmitter dopamine are associated with Parkinson’s disease. A neurotransmitter that is involved in the regulation of sleep and attention is serotonin. Finally, neurotransmitters that seem to function as
natural opiates are called endorphins.
Helpful Hint #2:
A release of endorphins is what runners experience when they say they have a “runners high.” You may have
experienced that same feeling after a workout at the gym or other physical exercise.
Structures of the Brain and Their Functions
There are three major divisions of the brain: hindbrain, midbrain, and forebrain. The hindbrain contains
the medulla, which helps control breathing. The cerebellum is believed to help control movement. The pons
is a bridge in the hindbrain involved in sleep and arousal.
The midbrain is involved in the relay of information between the brain and the hindbrain and forebrain. A
midbrain structure called the reticular formation is involved in stereotyped patterns of behavior.
The highest region of the brain is called the forebrain. A forebrain structure that plays important roles in both memory and emotion is the limbic system. One main part of the limbic system is the amygdala, which is important in the organism’s survival and emotion. Another part of the limbic system, the hippocampus, plays a role in the storage of memory. (Hint: if you saw a hippo walking across your campus, you would remember it!) A forebrain structure that serves mainly as a relay station is called the thalamus. The forebrain structure that regulates eating, drinking, and sex is called the hypothalamus. Olds and Milner’s rat research in the 1950s pointed to the existence of a pleasure center in the hypothalamus. Their research has important implications for drug addiction.
The largest part if the brain in volume is the cerebral cortex, which is divided into two halves, called hemispheres. Each is half divided into four lobes. The temporal lobe processes visual information; hearing is associated with the occipital lobe; control of the voluntary muscles, personality and intelligence is associated with the frontal lobe. The parietal lobe is involved in body sensation.
The corpus callosum is a large bundle of axons connecting the two cerebral hemispheres. Speech and grammar are localized to the left hemisphere, which mainly controls this ability in most people. Understanding aspects of language such humor and metaphors is localized in the right hemisphere, which is involved in the processing of nonverbal information. Researchers believe that complex thinking involves both sides of the brain.
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