1. Chapter 3: The Biological Bases of Behavior

2. Communication in the Nervous System
Glia – structural support and insulation
Neurons – communication
Soma – cell body
Dendrites – receive
Axon – transmit away
Myelin sheath – speeds up transmission
Terminal Button – end of axon; secretes neurotransmitters
Neurotransmitters – chemical messengers
Behavior depends on rapid information travel and processing. The nervous system is the body’s communication network, handling information just as the circulatory system handles blood.
The basic components of the nervous system are living cells called neurons and glia.
Glia are cells that provide structure and insulation for neurons. They are like neural “glue.”
Neurons are cells that receive, integrate, and transmit information, permitting communication in the nervous system.
A “typical” neuron consists of a soma, or cell body; dendrites, which are feeler-like structures specialized to receive information; and an axon, which is a long, thin fiber that transmits signals away from the soma to other neurons, or to muscles or glands. The basic flow of information is as follows: the dendrite receives a signal, the signal passes through the soma and down the axon to the dendrites of another neuron.
For efficient neural transmission to take place, many axons are covered with an insulating material called myelin. Myelin sheaths speed up transmission of signals that move along axons. Multiple sclerosis is a myelin degeneration disease, causing loss of muscle control, etc. due to loss of transmission efficiency in the nervous system when the myelin sheaths deteriorate.
At the end of an axon, the terminal buttons are small knobs that secrete chemical messengers called neurotransmitters. When the signal gets to the end of the axon, it causes these chemical messengers to be released into the synapse…the junction of two neurons. The chemicals flow across the synapse and stimulate the next cell.

3. Figure 3.1 Structure of the neuron
Structure of the neuron. Neurons are the communication links of the nervous system. This diagram highlights
the key parts of a neuron, including specialized receptor areas (dendrites), the cell body (soma), the axon fiber
along which impulses are transmitted, and the terminal buttons, which release chemical messengers that
carry signals to other neurons. Neurons vary considerably in size and shape and are usually densely interconnected.
Figure 3.1 Structure of the neuron

4. Hodgkin & Huxley (1952) - giant squid Fluids inside and outside neuron
The Neuron at Rest
Hodgkin & Huxley (1952) - giant squid
Fluids inside and outside neuron
Electrically charged particles (ions)
Neuron at rest – negative charge on inside compared to outside
-70 millivolts – resting potential
Alan Hodgkin and Andrew Huxley in the 1950’s discovered the mechanics of neural transmission by studying giant squid, which have axons that are about 100 times larger than human axons.
Found that fluids inside and outside the neuron contain electrically charged particles, or ions.
Also found that when a neuron is “at rest” the inside has more negative ions than the outside. The stable negative charge of a neuron when it is inactive is its resting potential.

5. Stimulation causes cell membrane to open briefly
The Action Potential
Stimulation causes cell membrane to open briefly
Positively charged sodium ions flow in
Shift in electrical charge travels along neuron
The Action Potential
All – or – none law
When a neuron is stimulated, channels in the cell membrane open briefly, allowing the positive ions outside the cell to flow into the electronegative inside. This shift in the electrical charge travels along the axon and is referred to as an action potential.
Either an action potential occurs, or it doesn’t. Once an action potential is initiated, it goes full force.

6. Figure 3.2 The neural impulse
The neural impulse. The electrochemical properties of the neuron allow it to transmit signals.
The electric charge of a neuron can be measured with a pair of electrodes connected
to an oscilloscope, as Hodgkin and Huxley showed with a squid axon. Because of its exceptionally
thick axons, the squid has frequently been used by scientists studying the neural impulse.
(a) At rest, the neuron’s voltage hovers around 70 millivolts. (b) When the axon is stimulated,
there is a brief jump in a neuron’s voltage, resulting in a spike on the oscilloscope recording
of the neuron’s electrical activity. This change in voltage, called an action potential, travels
along the axon like a spark traveling along a trail of gunpowder.
Figure 3.2 The neural impulse

7. The Synapse Synaptic cleft Presynaptic neuron Synaptic vesicles
Neurotransmitters
Postsynaptic neuron
Receptor sites
Neurons don’t actually touch at a synapse, instead they are separated by a microscopic gap between the terminal button of one neuron and the cell membrane of another neuron - the synaptic cleft.
Electrical signals can’t jump this gap. Instead, the neuron that is sending the message across the gap (the presynaptic neuron) releases neurotransmitters into the synaptic cleft. This occurs when the action potential gets to the terminal button and causes the synaptic vesicles (storage sacs for the neurotransmitter) to fuse with the membrane at the end of the axon and spill its contents into the synaptic cleft.
The neurotransmitters diffuse across the space where they find open receptor sites on the postsynaptic neuron. These sites recognize and respond to some neurotransmitters, but not to others.

8. Figure 3.3
The synapse. When a neural impulse reaches an axon’s terminal buttons, it triggers the release of
chemical messengers called neurotransmitters. The neurotransmitter molecules diffuse across the synaptic
cleft and bind to receptor sites on the postsynaptic neuron. A specific neurotransmitter can bind only
to receptor sites that its molecular structure will fit into, much like a key must fit a lock.
Figure 3.3 The synapse

9. When a Neurotransmitter Binds: The Postsynaptic Potential
Voltage change at receptor site – postsynaptic potential (PSP)
Not all-or-none
Changes the probability of the postsynaptic neuron firing
Positive voltage shift – excitatory PSP
Negative voltage shift – inhibitory PSP
When a neurotransmitter from the presynaptic neuron crosses the synapse, it finds an appropriate receptor site on the postsynaptic neuron, and binds, and a voltage change occurs. This voltage change in the postsynaptic neuron is not an all-or-none, the neuron will fire or it won’t, kind of thing. Instead, it changes the probability or potential that the postsynaptic neuron will fire. This is, therefore, called a postsynaptic potential.
The postsynaptic potential can be excitatory or inhibitory. An excitatory potential makes the neuron more likely to fire. It decreases the negativity of the inside of the neuron with respect to the outside.
An inhibitory postsynaptic potential increases the negativity of the inside of the neuron with respect to the outside, making it less likely to fire.

10. Figure 3.4 Overview of synaptic transmission
Overview of synaptic transmission. The main elements in synaptic transmission are summarized here, superimposed on a
blowup of the synapse seen in Figure 3.3. The five key processes involved in communication at synapses are (1) synthesis and storage,
(2) release, (3) binding, (4) inactivation or removal, and (5) reuptake of neurotransmitters. As you’ll see in this chapter and the remainder
of the book, the effects of many phenomena— such as pain, drug use, and some diseases— can be explained in terms of how they alter one or
more of these processes (usually at synapses releasing a specific neurotransmitter).
Figure 3.4 Overview of synaptic transmission

11. One neuron, signals from thousands of other neurons Neural networks
Integrating Signals
One neuron, signals from thousands of other neurons
Neural networks
Patterns of neural activity
Interconnected neurons that fire together or sequentially
Synaptic connections
Elimination and creation
Synaptic pruning
One neuron may receive signals from thousands of other neurons, across thousands of different synapses.
Thought occurs through the firing of millions of neurons in unison. Our perceptions, thoughts, and actions depend on patterns of neural activity in interconnected neurons that fire together or sequentially – neural networks.
The links in these networks are constantly changing, with synaptic pruning or the elimination of old or unused synapses playing a larger role than the creation of new synapses in the sculpting of neural networks. For example, the number of synapses in the human visual cortex begins to decline after the age of one year.

12. Neurotransmitters and Behavior
Specific neurotransmitters work at specific synapses
Lock and key mechanism
Agonist – mimics neurotransmitter action
Antagonist – opposes action of a neurotransmitter
More than 40 neurotransmitters known at present
Interactions between neurotransmitter circuits
NTs deliver their messages by binding to a receptor site…in a lock and key type manner. Not just any receptor site will do. There must be a perfect fit between the shape of the NT and the shape of the receptor site.
Some drugs mimic neurotransmitters, fitting into receptor sites so perfectly that the site is fooled and a PSP is set up. These chemicals are called agonists.
Other chemicals oppose the action of a NT…they bind to the receptor site but don’t really fit well enough to “fool” the site. They just block it.
Right now, we know of more than 40 substances that qualify as NTs. Nine are commonly researched.
While research has outlined many interesting connections between neurotransmitters and behavior, most aspects of behavior are probably regulated by many neurotransmitters interacting.

13. Table 3.1 Common Neurotransmitters and Some of their Functions

14. Organization of the Nervous System
Central nervous system (CNS)
Afferent = toward the CNS
Efferent = away from the CNS
Peripheral nervous system
Somatic nervous system
Autonomic nervous system (ANS)
Sympathetic
Parasympathetic
The nervous system has two main divisions, central and peripheral.
The central nervous system consists of the brain and spinal cord, while the peripheral nervous system consists of nerves that lie outside the brain and spinal cord.
In the peripheral nervous system, afferent nerve fibers send information toward the CNS, while efferent nerve fibers send information away from the CNS.
There are two divisions of the peripheral nervous system, the somatic, or voluntary portion, and the autonomic, or involuntary portion.
The autonomic portion of the peripheral nervous system governs involuntary, visceral functions, such as heart and breathing rate, blood pressure, etc.
When a person is autonomically aroused, these speed up. This speeding up is controlled by the sympathetic division of the autonomic nervous system. The sympathetic nervous system mobilizes the body’s resources for emergencies and creates the fight-or-flight response.
The parasympathetic division, in contrast, activates processes that conserve bodily resources: slowing heart rate, reducing blood pressure, etc.

15. Figure 3.5 Organization of the human nervous system
Organization of the human nervous system. This overview of the human nervous system shows the relationships of its various
parts and systems. The brain is traditionally divided into three regions: the hindbrain, the midbrain, and the forebrain. The reticular
formation runs through both the midbrain and the hindbrain on its way up and down the brainstem. These and other parts of
the brain are discussed in detail later in the chapter. The peripheral nervous system is made up of the somatic nervous system,
which controls voluntary muscles and sensory receptors, and the autonomic nervous system, which controls the involuntary activities
of smooth muscles, blood vessels, and glands.
Figure 3.5 Organization of the human nervous system

16. Figure 3.6 The central and peripheral nervous systems
The central and peripheral nervous systems. The central nervous system consists of the brain and the spinal cord. The peripheral
nervous system consists of the remaining nerves that fan out throughout the body. The peripheral nervous system is divided into
the somatic nervous system, which is shown in blue, and the autonomic nervous system, which is shown in green.
Figure 3.6 The central and peripheral nervous systems

17. Figure 3.7 The autonomic nervous system (ANS)
The autonomic nervous system (ANS). The ANS is composed of the nerves that connect to the heart, blood vessels, smooth muscles,
and glands. The ANS is divided into the sympathetic division, which mobilizes bodily resources in times of need, and the parasympathetic
division, which conserves bodily resources. Some of the key functions controlled by each division of the ANS are summarized in the diagram.
Figure 3.7 The autonomic nervous system (ANS)

18. Studying the Brain: Research Methods
Damage studies/lesioning
Electrical stimulation (ESB)
Brain imaging –
computerized tomography
positron emission tomography
magnetic resonance imaging
Transcranial magnetic stimulation (TMS)
Damage studies/lesioning – observing consequences of damage to certain areas
Electrical stimulation (ESB) – stimulating a portion of the brain and observing effects
Brain imaging:
computerized tomography – computer enhanced X-ray
positron emission tomography – radioactively tagged chemicals serve as markers of blood flow or metabolic activity in the brain that are monitored by X-ray
magnetic resonance imaging – uses magnetic fields, radio waves, and computer enhancement to image brain structure
Transcranial magnetic stimulation – enhance or suppress activity in a particular region of the brain

19. Brain Regions and Functions
Hindbrain – vital functions – medulla, pons, and cerebellum
Midbrain – sensory functions – dopaminergic projections, reticular activating system
Forebrain – emotion, complex thought – thalamus, hypothalamus, limbic system, cerebrum, cerebral cortex
The hindbrain is located at the lower end of the brain, where the spinal cord joins the brainstem. The medulla is in charge of circulation, breathing, muscle tone, and regulating reflexes. The pons is important in sleep and arousal. The cerebellum is critical in the coordination of movement and equilibrium.
The midbrain lies between the hindbrain and the forebrain. It is involved in sensory functions such as locating where things are in space. It also contains structures which are important for voluntary movement (Parkinson’s disease is due to degeneration of the substantia nigra, a structure in the midbrain).
The reticular activating system is found in both the hind and midbrain, and is important in sleep and arousal as well as breathing and pain perception.
The forebrain is the largest and most complex region of the brain. It includes the thalamus – the way station for all incoming sensory information before it is passed on to appropriate higher brain regions; the hypothalamus – which is the regulator of basic biological needs such as hunger, thirst, sex drive, and temperature regulation; the limbic system – which is a loosely connected network of structures involved in emotion, motivation, memory, and other aspects of behavior; and finally, the cerebrum, which is the largest and most complex portion of the human brain. The convoluted outer layer of the cerebrum is the cerebral cortex. The cerebrum is responsible for complex mental activities such as learning, remembering, thinking, and consciousness.

20. Right Brain/Left Brain: Cerebral Specialization
Cerebral Hemispheres – two specialized halves connected by the corpus collosum
Left hemisphere – verbal processing: language, speech, reading, writing
Right hemisphere – nonverbal processing: spatial, musical, visual recognition
The cerebrum is divided into two specialized hemispheres that are connected by the corpus collosum. The corpus collosum is a thick band of fibers (axons) that transmits information between the hemispheres.
Researchers using split brain methodology (severing of the corpus collosum) have learned that each hemisphere is specialized for different functions, with the left usually dominant for language and the right for spatial skills.

21. The Cerebrum: The Seat of Complex Thought
Four Lobes:
Occipital – vision
Parietal - somatosensory
Temporal - auditory
Frontal – movement, executive control systems
Each hemisphere has four lobes: occipital – where the primary visual cortex is located, parietal – where the primary somatosensory cortex is located, temporal – where the primary auditory cortex is located, and frontal – where the primary motor cortex and executive control system is located.

22. Figure 3.12 Structures and areas in the human brain
Structures and areas in the human brain. (Top left) This photo of a human brain shows many of the structures discussed in this
chapter. (Top right) The brain is divided into three major areas: the hindbrain, midbrain, and forebrain. These subdivisions actually
make more sense for the brains of other animals than of humans. In humans, the forebrain has become so large it makes the other
two divisions look trivial. However, the hindbrain and midbrain aren’t trivial; they control such vital functions as breathing, waking,
and maintaining balance. (Bottom) This cross section of the brain highlights key structures and some of their principal functions. As you
read about the functions of a brain structure, such as the corpus callosum, you may find it helpful to visualize it.
Photo: Wadsworth collection.
Figure Structures and areas in the human brain

23. Figure 3.14 The cerebral hemispheres and the corpus callosum
In this drawing the cerebral hemispheres have been “pulled
apart” to reveal the corpus callosum. This band of fibers is
the communication bridge between the right and left halves
of the human brain.
Figure The cerebral hemispheres and the corpus callosum

24. Figure 3.15 The cerebral cortex in humans
The cerebral cortex in humans. The cerebral cortex consists of right and left halves, called cerebral hemispheres. This diagram provides a view of
the right hemisphere. Each cerebral hemisphere is divided into four lobes (which are highlighted in the bottom inset): the occipital lobe, the parietal
lobe, the temporal lobe, and the frontal lobe. Each lobe has areas that handle particular functions, such as visual processing. The functions of the
prefrontal cortex are something of a mystery, but they appear to include relational reasoning, attention, and planning.
Figure The cerebral cortex in humans

25. Figure 3.16 Language processing in the brain
Language processing in the brain. This view of the
left hemisphere highlights the location of two centers for
language processing in the brain: Broca’s area, which is
involved in speech production, and Wernicke’s area,
which is involved in language comprehension.
Figure Language processing in the brain

26. The Endocrine System: Another Way to Communicate
Hormones – chemical messengers in the bloodstream
Endocrine glands
Pituitary – “master gland,” growth hormone
Thyroid – metabolic rate
Adrenal – salt and carbohydrate metabolism
Pancreas – sugar metabolism
Gonads – sex hormones
Hormones are chemical messengers in the bloodstream.
The endocrine glands include: the pituitary – the master gland that secretes substances influencing the operation of all the other glands, as well as growth hormone; the thyroid gland – which controls metabolic rate; the adrenal glands – which control salt and carbohydrate metabolism; the pancreas – which secretes insulin to control sugar metabolism; and the gonads – which secrete sex hormones involved in the development of secondary sex characteristics and reproduction.

27. Basic Principles of Genetics
Chromosomes – strands of DNA carrying genetic information
Human cells contain 46 chromosomes in pairs (sex-cells – 23 single)
Each chromosome – thousands of genes, also in pairs
Polygenic traits
Questions about how much of behavior is biologically based and how much is environmentally based are very old ones in psychology. Since the 1970’s, however, research methodologies have been developed in the field of behavioral genetics that shed new light on the age-old nature vs. nurture question.
Chromosomes are strands of Deoxyribonucleic Acid (DNA) carrying genetic information. Each human cell contains 23 pairs, or 46 total, chromosomes, with the exception of sex cells which have 23 single chromosomes. They are not yet paired.
Most human traits are polygenic, or influenced by more than one pair of genes.

28. Research Methods in Behavioral Genetics
Family studies – does it run in the family?
Twin studies – compare resemblance of identical (monozygotic) and fraternal (dizygotic) twins on a trait
Adoption studies – examine resemblance between adopted children and their biological and adoptive parents
Family studies simply assess hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait, to determine whether it runs in the family Many things run in families, however, that are not genetic, like dessert recipes or speaking a certain language.
Twin studies can yield better evidence about the possible influence of heredity, because identical twins have the exact same genotype. They share 100% of the same genes. Fraternal twins only share 50% genetic relatedness, the same as any two siblings born to a set of parents at different times. Twins of both types, however, are raised in more similar environments (same age, configuration of relatives, etc.). If identical twins are more similar on a given trait than fraternal, the assumption is that it is probably genetic.
Adoption studies assess genetic influence by comparing adopted children with both their biological and adoptive parents. If they are more like their biological parents (who they have never met) on a trait, it is probably genetic.

29. Figure 3.19 Genetic relatedness
Genetic relatedness. Research on the genetic bases of behavior takes advantage of the different degrees of genetic relatedness
between various types of relatives. If heredity influences a trait, relatives who share more genes should be more similar with regard
to that trait than are more distant relatives, who share fewer genes. Comparisons involving various degrees of
biological relationships will come up frequently in later chapters.
Figure Genetic relatedness

30. Figure 3.20 Twin studies of intelligence and personality
Twin studies of intelligence and personality. Identical twins tend to be more similar than fraternal twins (as reflected in higher
correlations) with regard to intelligence and specific personality traits, such as extraversion. These findings suggest that intelligence
and personality are influenced by heredity. (Intelligence data from McGue et al., 1993; extraversion data based on Loehlin, 1992)
Figure Twin studies of intelligence and personality

31. The Evolutionary Bases of Behavior
Based on Darwin’s ideas of natural selection
Reproductive success key
Adaptations – behavioral as well as physical
Fight-or-flight response
Taste preferences
Parental investment and mating
The field of evolutionary psychology is a major new field in psychology focusing on analyzing human behavior in terms of adaptive significance.
Based on the work of Charles Darwin and the ideas of natural selection and reproductive fitness, that variations in reproductive success are what really fuels evolutionary change.
Evolutionary theorists study adaptations, or inherited characteristics, that increase in a population because they help solve a problem of survival or reproduction during the time they emerge, e.g., giraffes and long necks.
May extend even when no longer needed, for example the fight-or-flight response may have been very helpful in primitive times, but now it is related to a number of stress-related diseases. Similarly, humans show a taste preference for fatty foods…this was adaptive in a hunter/gatherer society, when dietary fat was scarce (before potato chips, etc.) resulting in obesity, heart disease, etc. While this may lead to decreased longevity, the effect on reproductive success is more difficult to gauge.
Parental investment refers to time, energy, survival risk, and forgone opportunities that each sex has to invest in order to produce and nurture offspring. Trivers (1972) suggests that a species courting and mating patterns are based in parental investment. When parental investment is high for females and low for males, polygyny results – a mating system whereby each male seeks to mate with multiple females and each female seeks only one male. Polyandry occurs when each female seeks to mate with multiple males and each male with only one female – this emerges when parental investment is high for males and low for females. Monogamy emerges when male and female parental investment is roughly equal.