Nervous System

Psychology

Twelfth Edition

Chapter 4

The Brain and Nervous System

The Nervous System: A Basic Blueprint

LO 4.1.A List the major structures of the central nervous system, and describe their primary functions.

LO 4.1.B List the major structures and major divisions of the peripheral nervous system, and describe their primary functions.

The Central Nervous System (1 of 3)

The function of a nervous system is to:

gather and process information

produce responses to stimuli

coordinate the workings of different cells

Scientists divide the nervous system into the:

central nervous system (CNS)

peripheral nervous system (PNS)

The Central Nervous System (2 of 3)

The CNS, which includes the brain and spinal cord:

receives, processes, interprets, and stores information

sends out messages destined for muscles, glands, and organs

The spinal cord produces some behaviors on its own without any help from the brain.

These spinal reflexes are automatic, requiring no conscious effort.

The Central Nervous System (3 of 3) Figure 4.1 The Central and Peripheral Nervous Systems

The central nervous system includes the brain and the spinal cord. The peripheral nervous system consists of 43 pairs of nerves that transmit information to and from the central nervous system. Twelve pairs of cranial nerves in the head enter the brain directly; 31 pairs of spinal nerves enter the spinal cord at the spaces between the vertebrae.

The Peripheral Nervous System (1 of 3)

The peripheral nervous system (PNS) handles the central nervous system’s input and output.

The peripheral nervous system consists of the:

somatic nervous system, which permits sensation and voluntary actions

autonomic nervous system, which regulates blood vessels, glands, and internal (visceral) organs

The autonomic system usually functions without conscious control.

The Peripheral Nervous System (2 of 3)

The autonomic nervous system is further divided into the:

sympathetic nervous system, which mobilizes the body for action

parasympathetic nervous system, which conserves energy

These two parts work together, but in opposing ways, to adjust the body to changing circumstances.

The Peripheral Nervous System (3 of 3) Figure 4.2 The Autonomic Nervous System

In general, the sympathetic division of the autonomic nervous system prepares the body to expend energy, and the parasympathetic division restores and conserves energy. Sympathetic nerve fibers exit from areas of the spinal cord shown in orange in this illustration; parasympathetic fibers exit from the base of the brain and from spinal-cord areas shown in blue.

Communication in the Nervous System

LO 4.2.A Compare the functions of neurons and glial cells in the nervous system.

LO 4.2.B Describe each of the three main parts of a neuron, and explain their functions.

LO 4.2.C Explain how stem cells contribute to the process of neurogenesis.

LO 4.2.D Outline the process by which neurons communicate with each other, and explain the basic functions of the synapse, action potential, synaptic vesicles, and neurotransmitters.

LO 4.2.E Summarize the effects of some of the main neurotransmitters in the brain, and list four hormones that influence behavior.

Types of Cells (1 of 2)

Neurons are the basic units of the nervous system.

They are held in place by glial cells, which:

nourish

insulate

protect, and

repair neurons

Types of Cells (2 of 2) Figure 4.3 Different Kinds of Neurons

Neurons vary in size and shape, depending on their location and function. More than 200 types of neurons have been identified in mammals.

The Structure of the Neuron (1 of 3)

Each neuron consists of:

dendrites

cell body

axon

Many axons are insulated by a myelin sheath that:

speeds up the conduction of neural impulses

prevents signals in adjacent cells from interfering with one another

The Structure of the Neuron (2 of 3)

In the peripheral nervous system, axons (and sometimes dendrites) are collected together in bundles called nerves.

The human body has 43 pairs of peripheral nerves.

Most of these nerves enter or leave the spinal cord.

12 pairs in the head, the cranial nerves, connect directly to the brain.

The Structure of the Neuron (3 of 3) Figure 4.4 The Structure of a Neuron

Incoming neural impulses are received by the dendrites of a neuron and are transmitted to the cell body. Outgoing signals pass along the axon to terminal branches.

Neurogenesis: The Birth of Neurons (1 of 5)

Research has disproven two old assumptions:

that neurons in the human central nervous system cannot be induced to regenerate

that no new neurons form after early infancy

Neurogenesis: The production of new neurons from immature stem cells.

Neurogenesis: The Birth of Neurons (2 of 5)

Embryonic stem cells are pluripotent, meaning that they can generate many different kinds of cells in the body.

Amazingly, ES cells can generate many types of specialist cells, from neurons to kidney cells.

Stem cells may be useful for treating damaged tissues.

Highly controversial because ES cells come from aborted fetuses and embryos.

Neurogenesis: The Birth of Neurons (3 of 5)

These stem cells in various organs continue to divide and mature throughout adulthood.

They give rise to new neurons.

These include brain areas associated with learning and memory.

Neurogenesis: The Birth of Neurons (4 of 5)

Neurogenesis can be enhanced by:

physical exercise

effortful mental activity

enriched environment

Aging and stress can inhibit the production of stem cells.

Nicotine can kill them.

Neurogenesis: The Birth of Neurons (5 of 5) Figure 4.5 Stem Cell Production

Embryonic stem cells (ES) exhibit pluripotency, the capacity to develop into many types of mature cells. ES cells appear when an embryo is just a few days old, consisting of a cluster of approximately 100 cells.

How Neurons Communicate (1 of 3)

Communication between two neurons occurs at the synapse.

When a wave of electrical voltage (action potential) reaches the end of a transmitting axon, neurotransmitter molecules are released into the synaptic cleft.

How Neurons Communicate (2 of 3)

These molecules bind to receptor sites on the receiving neuron.

When binding occurs, that neuron becomes either more or less likely to fire.

How Neurons Communicate (3 of 3) Figure 4.6 Neurotransmitter Crossing a Synapse

Neurotransmitter molecules are released into the synaptic cleft between two neurons from vesicles (chambers) in the transmitting neuron’s axon terminal. The molecules then bind to receptor sites on the receiving neuron. As a result, the electrical state of the receiving neuron changes and the neuron becomes either more likely to fire an impulse or less so, depending on the type of neurotransmitter.

Chemical Messengers in the Nervous System (1 of 6)

Neurotransmitters play a critical role in mood, memory, and psychological well-being.

Neurotransmitters exist not only in the brain but also in:

the spinal cord

peripheral nerves

certain glands

Chemical Messengers in the Nervous System (2 of 6)

Four neurotransmitters each travel a particular path through parts of the brain:

serotonin

dopamine

acetylcholine

norepinephrine

Two other common neurotransmitters are distributed through the entire brain:

GABA

glutamate

Chemical Messengers in the Nervous System (3 of 6)

Hormones are produced mainly by the endocrine glands:

pancreas

ovaries

testes

adrenal glands

They are released directly into the bloodstream.

They affect—and are affected by—the nervous system.

Chemical Messengers in the Nervous System (4 of 6)

Neuroscientists are especially interested in:

melatonin

oxytocin and vasopressin

adrenal hormones

epinephrine

norepinephrine

sex hormones

Chemical Messengers in the Nervous System (5 of 6)

The brain is awash in thousands of other chemicals.

These chemicals affect how neurons and neurotransmitters function.

Because these chemicals modulate (vary the strength of) neural functions, they are called neuromodulators.

Chemical Messengers in the Nervous System (6 of 6)

Endorphins have effects similar to those of natural opiates such as heroin.

They reduce pain and promote pleasure.

They are also thought to play a role in:

appetite

sexual activity

blood pressure

mood

learning

memory

Mapping the Brain

LO 4.3.A Describe three techniques researchers use for intervening in the brain and observing the behavior that results.

LO 4.3.B Describe five techniques researchers use for intervening in behavior and observing the effects on the brain.

Intervening in the Brain and Observing Behavior

Researchers study the brain:

by observing patients with brain damage

by using the lesion method with animals

by using recent techniques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS)

Intervening in Behavior and Observing the Brain (1 of 5)

Tools allow researchers to investigate the structure and function of the brain:

electroencephalograms (EEGs)

event-related potentials (ERP)

PET (positron emission tomography) scans

magnetic resonance imaging (MRI)

functional MRI (fMRI)

Intervening in Behavior and Observing the Brain (2 of 5)

These tools reveal which parts of the brain are active during different tasks.

However, they do not reveal discrete “centers” for particular functions.

Studies must be interpreted with great caution.

Technology cannot replace critical thinking.

Intervening in Behavior and Observing the Brain (3 of 5) Figure 4.7 An Event-Related Potential

An ERP is the brain’s response to a specific event—a wave of electrical activity detected on the scalp after a person encounters a stimulus, such as a picture or a word. The first parts of the wave show brain activity associated with encountering the stimulus; later parts show activity associated with understanding it.

Intervening in Behavior and Observing the Brain (4 of 5) Figure 4.8 Scanning the Brain

Pearson Education

(a) The PET scan shows the brain of a healthy 20-year-old. The colors indicate different levels of activity, where red reveals the highest level. (b) An MRI scan shows a child’s brain and the bottle he was drinking from while the image was obtained. (c) This fMRI image shows how a person’s visual cortex is activated while he or she views a red hibiscus flower.

Intervening in Behavior and Observing the Brain (5 of 5) Figure 4.9 Coloring the Brain

Pearson Education

By altering the colors used in brain images, such as in this PET scan, researchers can create the appearance of dramatic brain differences. These scans are actually images of the same brain.

A Tour Through the Brain (1 of 3)

LO 4.4.A List and describe three main structures in the brain stem, explain the primary functions each structure performs, and discuss the processes controlled by the cerebellum.

LO 4.4.B Describe the structure, function, and location of the thalamus.

LO 4.4.C Describe the structure, function, and location of the hypothalamus and pituitary gland.

LO 4.4.D Describe the structure, function, and location of the amygdala.

A Tour Through the Brain (2 of 3)

LO 4.4.E Describe the structure, function, and location of the hippocampus.

LO 4.4.F Describe the structure of the cerebrum, and explain the function of the corpus callosum.

LO 4.4.G Sketch the location of each of the lobes of the cerebral cortex, and explain the major functions each lobe performs, with particular reference to the prefrontal cortex.

A Tour Through the Brain (3 of 3) Figure 4.10 Major Structures of the Human Brain

This cross section depicts the brain as if it were split down the middle and shows the structures described in the text.

The Brain Stem and Cerebellum (1 of 3)

In the lower part of the brain, in the brain stem, the medulla controls automatic functions:

heartbeat

breathing

The pons is involved in:

sleeping

waking

dreaming

The Brain Stem and Cerebellum (2 of 3)

The reticular activating system (RAS):

screens incoming information

is responsible for alertness

The cerebellum:

contributes to balance and muscle coordination

plays a role in cognitive and emotional learning

If your cerebellum were damaged:

you would become clumsy, uncoordinated

have trouble using pencil, threading needle, walking

The Brain Stem and Cerebellum (3 of 3) Page 120

The Thalamus (1 of 2)

The thalamus directs sensory messages to appropriate higher centers in the brain.

Smell is the only sense that bypasses the thalamus.

Specialized cells are located in the olfactory bulb.

near areas involved in emotion

may be why particular odors rekindle memories

The Thalamus (2 of 2) Page 121

The Hypothalamus and the Pituitary Gland (1 of 2)

The hypothalamus is involved in emotion and in drives associated with survival.

It also:

controls the operations of the autonomic nervous system

sends out chemicals that tell the pituitary gland when to “talk” to other endocrine glands

The Hypothalamus and the Pituitary Gland (2 of 2) Page 121

The Amygdala (1 of 2)

The amygdala is responsible for:

evaluating sensory information

quickly determining its importance

This affects the initial decision to approach or withdraw from a person or situation.

It is also involved in:

mediating anxiety and depression

forming and retrieving emotional memories

The Amygdala (2 of 2) Page 121

The Hippocampus

The hippocampus moderates the reticular activating system.

It has been called the “gateway to memory.”

It plays a critical role in the formation of long-term memories for facts and events and other aspects of memory.

combines different components of experiences

binds them together into one “memory”

The Cerebrum

Much of the brain’s circuitry is packed into the cerebrum, which is:

divided into two hemispheres (connected by the corpus callosum)

covered by thin layers of cells known collectively as the cerebral cortex

The Cerebral Cortex (1 of 3)

The lobes of the cortex have specialized (but partially overlapping) functions:

occipital

parietal

temporal

frontal

They tend to respond differently when directly stimulated with tiny electrodes during brain surgery.

The Cerebral Cortex (2 of 3)

The association cortex appears to be responsible for higher mental processes.

The frontal lobes, particularly areas in the prefrontal cortex, are involved in:

social judgment

making and carrying out plans

decision making

The Cerebral Cortex (3 of 3) Figure 4.11 Lobes of the Cerebrum

Deep fissures divide the cortex of each cerebral hemisphere into four regions.

The Two Hemispheres of the Brain

LO 4.5.A Discuss the basic format of a split-brain experiment, and describe what the results of such experiments reveal about the functioning of the cerebral hemispheres.

LO 4.5.B Describe why the two hemispheres of the brain are allies rather than opposites.

Split Brains: A House Divided (1 of 4)

Split-brain surgery involves a severing of the corpus callosum.

Myers and Sperry

Studies of split-brain patients show that the two cerebral hemispheres have somewhat different talents.

Example: In most people, language is processed mainly in the left hemisphere.

Split Brains: A House Divided (2 of 4)

The left hemisphere is generally specialized for:

logical,

symbolic, and

sequential tasks

The right hemisphere is associated with:

visual–spatial tasks

facial recognition

the creation and appreciation of art and music

Split Brains: A House Divided (3 of 4) Figure 4.12 Visual Pathways

Each cerebral hemisphere receives information from the eyes about the opposite side of the visual field. Thus, if you stare directly at the corner of a room, everything to the left of the juncture is represented in your right hemisphere, and vice versa. This is so because half the axons in each optic nerve cross over (at the optic chiasm) to the opposite side of the brain. Normally, each hemisphere immediately shares its information with the other one, but in split-brain patients, severing the corpus callosum prevents such communication.

Split Brains: A House Divided (4 of 4) Figure 4.13 Divided View

Pearson Education

Split-brain patients were shown composite photographs (a) and were then asked to pick out the face they had seen from a series of intact photographs (b). They said they had seen the face on the right side of the composite, yet they pointed with their left hands to the face that had been on the left. Because the two cerebral hemispheres could not communicate, the verbal left hemisphere was aware of only the right half of the picture, and the relatively mute right hemisphere was aware of only the left half (c).

The Two Hemispheres: Allies or Opposites?

In most mental activities the two hemispheres cooperate as partners.

Each makes a valuable contribution.

The brain is more like an interactive federation than a house divided.

The Flexible Brain

LO 4.6.A Define neural plasticity, and summarize some of the main evidence that the brain has the ability to change in response to new experiences.

LO 4.6.B Summarize five cautions surrounding whether sex differences in anatomical brain size are linked to sex differences in behavior.

Experience and the Brain (1 of 4)

The brain’s circuits are not fixed and immutable.

They are continually changing in response to:

information

challenges

changes in the environment

This phenomenon is known as plasticity.

brain “rewires” itself to adapt

Experience and the Brain (2 of 4)

Examples of plasticity:

in people blind from an early age, brain regions usually devoted to vision are activated by sound

stroke victim regains ability to speak

head injury victim regains use of limb

Experience and the Brain (3 of 4) Figure 4.14 Getting Connected

Neurons in a newborn’s brain are widely spaced, but they immediately begin to form new connections. These drawings show the marked increase in the number of connections from birth to age 15 months.

Experience and the Brain (4 of 4) Figure 4.15 Adapting to Blindness

(Adapted from Gougoux et al., 2005.)

In some blind people, brain areas usually associated with vision may become active in tasks requiring hearing. The purple circles to the left of the dotted line represent blind individuals with low error rates in a sound-localization task; those to the right represent blind individuals with high error rates. The graph shows that error rates for blind people—but not sighted ones—were correlated with changes in cerebral blood flow (CBF), and thus neural activity, in a visual area of the brain. The more accurate blind people were, the greater the activity in this region. (Adapted from Gougoux et al., 2005.)

Are There “His” and “Hers” Brains? (1 of 3)

Brain scans and other techniques have revealed many male–female differences in brain anatomy and function.

connections between cortex and amygdala

frontal lobes

cortical folds

number of neurons

lateralization of amygdala

Controversy exists, however, about what such differences mean in real life.

Are There “His” and “Hers” Brains? (2 of 3)

Some of the brain research has focused on behavioral or cognitive differences that are small and insignificant.

Even when gender differences are statistically significant, they are often quite small in practical terms.

Some findings have been widely accepted but then have failed to replicate.

Are There “His” and “Hers” Brains? (3 of 3)

Nervous System

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