CHAPTER 2:
THE BIOLOGY OF MIND
CHAPTER OBJECTIVES
1. Explain why psychologists are concerned with human biology.
2. Describe the structure of a neuron, and explain how neural impulses are generated.
3. Describe how nerve cells communicate, and discuss the impact of neurotransmitters
and drugs on human behavior.
4. Identify the major divisions of the nervous system and describe their functions,
noting the three types of neurons that transmit information through the system.
5. Contrast the simplicity of the neural pathways involved in reflexes with the
complexity of neural networks.
6. Identify and describe several techniques for studying the brain.
7. Describe the functions of the brainstem, thalamus, cerebellum, and limbic system.
8. Identify the four lobes of the cerebral cortex and describe the sensory and motor
functions of the cortex.
9. Discuss the importance of the association areas, and describe how damage to several
different cortical areas can impair language functioning.
10. Discuss the capacity of the brain to reorganize following injury or illness.
11. Describe research on the split brain, and discuss what it reveals regarding normal
brain functioning.
12. Discuss the relationships among brain organization, right- and left-handedness, and
physical health.
13. Describe the nature and functions of the endocrine system and its interaction with the
nervous system.
NEURAL COMMUNICATION
 Neuron consists of a cell body and branching fibers: The dendrites receive
information from sensory receptors or other neurons, and the axons pass that
information along to other neurons. A layer of fatty cells, called the myelin sheath *,
insulates the fibers of some neurons and helps speed their impulses.
 A neural impulse fires when the neuron is stimulated by pressure, heat, light, or
chemical messages from adjacent neurons. Received signals trigger an impulse only
if the excitatory signals minus the inhibitory signals exceeds a minimum intensity
called the threshold. (
CAUTION: Increasing the stimulus above the threshold will not increase the
impulse’s intensity. The neuron’s reaction is an all-or-none response, like guns,
neurons either fire or they don’t)
 The impulse, called the action potential, is a brief electrical charge that travels
down the axon rather like a line of dominos falling.
 During the resting potential, the fluid interior of the axon carries mostly
negatively charged atoms (ions) while the fluid outside has mostly positively charged
atoms.
 Then, the first bit of the axon is depolarized, and the electrical impulse travels
down the axon as channels open, admitting atoms with a positive charge.
 When these channels close, others open and positive atoms are pumped back out,
restoring the neuron to its polarized state.
 When electrical impulses reach the axon terminal, they stimulate the release of
chemical messengers called neurotransmitters that cross the junction between
neurons called the synapse.
 After these molecules traverse the tiny synaptic gap between neurons, they
combine with receptor sites of the neighboring neurons, thus passing on their
excitatory or inhibitory messages.
 Different neurotransmitters have different effects on behavior and emotion. For
example, release of acetylcholine, the neurotransmitter found at every junction
between a motor neuron and skeletal muscle, causes the muscle to contract.
Endorphins, natural opiates released in response to pain and vigorous exercise,
explain the “runner’s high” and the indifference to pain in some injured people.
 When the brain is flooded with opiate drugs such as heroin and morphine,
however, it may stop producing its own natural opiates, and withdrawal of these
drugs may result in pain until the brain resumes production of its natural opiates.
 Researchers have used this information about neurotransmitters in the brain in
their efforts to create therapeutic drugs, such as those used to alleviate depression
and schizophrenia.
 Some drugs (agonists) mimic a natural neurotransmitter, while others
(antagonists) block its effects. Still others work by hampering the neurotransmitter’s
natural breakdown or reabsorption.
THE NERVOUS SYSTEM
 Neurons communicating with other neurons form our body’s primary system --the nervous system.

The central nervous system (CNS) --- the brain and the spinal cord.
 The peripheral nervous system (PNS) --- links the CNS with the body’s sense
receptors, muscles, and glands.
 The sensory and motor neurons carrying this information are bundled into the
electrical cables we know as nerves.
 Sensory neurons send information from the body’s tissues and sensory organs
inward to the brain and spinal cord.

Interneurons of the brain and the spinal cord process the information.

Motor neurons carry outgoing information from the CNS to the body’s tissues.
 The somatic nervous system of the PNS controls the movements of our skeletal
muscles.
 The autonomic nervous system (ANS) is a dual self-regulating system that
influences the glands and muscles of our internal organs. The sympathetic nervous
system arouses; the parasympathetic nervous system calms.
 Reflexes, our automatic responses to stimuli, illustrates the spinal cord’s work *.
e.g. fingers touching a hot stove.
 Neurons in the brain cluster into work groups called neural networks. The cell
in each layer of a neural network connect with various cells in the next layer. With
experience, networks can learn, as feedback strengthens or inhibits connections that
produce certain results. One network is interconnected with other networks, which
are distinguished by their specific functions.
BRAIN
 The oldest method of studying the brain involved observing the effects of brain
diseases and injuries. Powerful new techniques now reveal brain structures and
activities in the living brain. By surgically lesioning and electrically stimulating
specific brain areas, by recording electrical activity on the brain‘s surface (EEG), and
by displaying activity with computer-aided brain scans (CT, PET, MRI),
neuroscientists examine the connections between brain, mind, and behavior.
 The Brainstem --- the brain’s oldest and innermost region, includes the medulla,
which controls heartbeat and breathing, and the reticular formation, which controls
arousal. Atop the brainstem is the thalamus, the brain’s switchboard. It receives
information from all the senses except smell and sends it to higher brain regions that
deal with seeing, hearing, tasting, and touching. The cerebellum, attached to the rear
of the brainstem, coordinates muscle movement.
 The Limbic System --- has been linked primarily to memory, emotions, and
drives. For example, one of its neural centers, the hippocampus, helps process
memories for storage. The amygdala is involved in aggression and fear. The
hypothalamus has been linked to various bodily maintenance functions and to
pleasurable rewards. Its hormones influence the pituitary gland and thus it provides a
major link between the nervous and endocrine systems.
 The Cerebral Cortex --- a thin sheet of cells composed of billions of nerve cells
and their countless interconnections. Each of the two hemispheres of the cortex is
divided into four geographic lobes (frontal, parietal, occipital, and temporal). The
motor cortex, at the rear of the frontal lobes, controls voluntary muscle movements.
The sensory cortex, at the front of the parietal lobes, registers and processes body
sensations. The occipital lobes at the back of the head receive input from the eyes.
An auditory area of the temporal lobes receives information from the ears. The
frontal lobes are involved in executive functioning e.g., making plans and judgment,
as well as speaking and muscle movements.
 The association areas are NOT involved in primary motor and sensory functions.
Rather, they interpret, integrate, and act on information processed by the sensory
areas. They are involved in higher mental functions, such as learning, remembering,
thinking, and speaking.
 In general, human emotions, thoughts, and behaviors result from the intricate
coordination of many brain areas. Language, for example, depends on a chain of
events in several brain regions. Depending on which link in this chain is damaged, a
different form of aphasia occurs. Damage to Wernicke’s area disrupts
understanding. Damage to Broca’s area disrupts speaking. Damage to the angular
gyrus leaves the person able to speak and understand but unable to read.
 Research indicates that neural tissue can reorganize in response to injury or
damage. When one brain area is damaged, others may in time take over some of its
function. For example, if neurons are destroyed as the result of a minor stroke,
nearby neurons may partly compensate by making new connections that replace the
lost ones. New evidence reveals that adult humans can also generate new brain cells.
Our brains are most plastic when we are young children. In fact, children who have
had an entire hemisphere removed still lead normal lives (*hemispherectomy).
 A split brain is one whose corpus callosum, the wide band of axon fibers that
connects the two brain hemispheres, has been severed. Experiments on split-brain
patients have refined our knowledge of each hemisphere’s special functions.
 In the laboratory, investigators ask a split-brain patient to look at a designated
spot, then send information to either the left or right hemisphere(by flashing it to the
right or left visual field). Quizzing each hemisphere separately, the researchers have
confirmed that for most people the left hemisphere is the more verbal and the right
hemisphere excels in visual perception and the recognition of emotion. Studies of
people with intact brains have confirmed that the right and left hemispheres each
make unique contributions to the integrated functioning of the brain. CAUTION:
You cannot take findings with split-brain patients who don’t have a corpus callosum
and generalize to normal people. Hemispheres act as complementary processing
systems and integrate their activities.
 Right and left-handedness --- Approximately 95 % of right-handers process
speech primarily in the left hemisphere. Left-handers are more diverse. More than
half process speech in the left hemisphere, about ¼ in the right, and the last quarter
use both hemispheres equally. THINK : Cultural bias against left-handedness? *
 The finding that the % of left-handers declines dramatically with age led
researchers to examine the leftie’s health risks. Left-handers are more likely to have
experienced birth stress, e.g., prematurity or the need for assisted respiration. They
also endure more headaches, have more accidents (?), use more tobacco and alcohol,
and suffer more immune system problems. CAUTION: Researchers continue to
debate whether left-handers have a lower life expectancy or not. Remember our
discussion on correlational data!!!
 The endocrine system’s glands secrete hormones, chemical messengers
produced in one tissue that travel through the bloodstream and affect other tissues,
including the brain. When they act on the brain, they influence our interest in sex,
food, and aggression. Compared to the speed at which messages move through the
NS, endocrine messages move more slowly but their effects are usually longerlasting.