Chapter 3

Biology and Behavior

Biology and Behavior

Huntingon’s disease( 亨丁頓舞蹈症 )is a deadly genetic disorder that affects the brain

After psychologist Lenore Wexler’s mother died of Huntington’s, she changed her research from the clinical to the biological area and eventually discovered the genetic marker for the disease

基底核

丘腦

小腦

3.1 How Does the Nervous System Operate?

Distinguish between the functions of distinct types of neurons.

Describe the structure of the neuron. Describe the electrical and chemical

changes that occur when neurons communicate.

Identify the major neurotransmitters and their primary functions.

How Does the Nervous System Operate?

The nervous system is responsible for everything we think, feel, and do

Basic components: Neurons(神經元 ): receive, integrate, and

transmit information in the nervous system; form neural networks

Central nervous system (CNS；中樞神經系統 ): brain and spinal cord

Peripheral nervous system (PNS ；周邊神經系統 ): all other nerve cells in the body

Neurons Are Specialized for Communication

Nerve cells are powered by electrical impulses; communicate with other nerve cells through chemical signals

Three basic phases: Reception （接收） : Chemical signals are

received from neighboring neurons Integration （整合） : Incoming signals are

assessed Transmission （傳遞） : Signals are

passed on to other receiving neurons

Types of Neurons

Sensory (afferent) neurons （感覺 / 輸入神經元） : detect information from the physical world and pass that information along to the brain Somatosensory nerves provide information

from the skin and muscles Motor neurons （運動 / 輸出神經元） :

direct muscles to contract or relax Interneurons: communicate within local

or short-distance circuits

Neuron Structure

Dendrite （樹突） : detects chemical signals from neighboring neurons

Cell body (soma ；細胞體 ): collects and integrates information

Axon （軸突） : transmitselectrical impulses

Terminal buttons （終端） : bulbous end of an axon

Neuron Structure

Synapse （突觸 / 胞突結合） : supports chemical communication between neurons Synaptic cleft （突觸間隙） : narrow gap

between terminal button (presynaptic membrane) and dendrite (postsynaptic membrane) of neighboring neuron

Myelin sheath （髓鞘） : encases and insulates axons Composed of glial cells Nodes of Ranvier: Spaces between glial

cells

突觸間隙

2013 年諾貝爾醫學獎

囊泡

How Neurons Work

Membrane potential the difference in electrical charge between the

inside and the outside of a neuron the resting potential is about –70 mV

(millivolts) the potential inside the neuron is 70 mV less

than outside it, and the neuron is polarised （極化） .

Ions positively or negatively charged particles at the resting potential a higher proportion of

negative ions are inside the neuron compared to outside it.

Resting Membrane Potential ( 休止電位 )

The Resting Membrane Potential is Negatively Charged

Resting membrane potential: The ratio of negative to positive ions is greater inside the neuron than outside Polarized （已極化） : when a neuron

has more negative ions inside it than outside

Polarization （極化） : creates the electrical energy necessary to power the firing of the neuron

Action Potentials （行動電位）

Action potential (neural firing): the electrical signal that passes along the axon and causes the release of chemicals that transmit signals to other neurons

Changes in Electrical Potential Lead to Action

Neurons receive chemical signals from nearby neurons Excitatory （興奮） signals depolarize

the cell membrane (i.e., reduce polarization), increasing the likelihood that the neuron will fire

Inhibitory （抑制） signals hyperpolarize the cell (i.e., increase polarization), decreasing the likelihood that the neuron will fire

Changes in Electrical Potential Lead to Action

When a neuron fires, the inside of the neuron becomes slightly more positively charged than the outside

After firing, the inside of the neuron returns to its slightly negative resting state

“action potential” is synonymous with “neural impulse （神經衝動）”

All-Or-None Principle

Neuronal firing is determined by the number and frequency of signals it receives

An action potential occurs when the sum of excitatory and inhibitory signals leads to a change in voltage that exceeds the neuron’s firing threshold.

All-or-none principle: A neuron will either fire or not

Neurons fire with the same potency each time;

they do not fire in a way that can be described as weak or strong

Neurotransmitters Bind to Receptors across the Synapse

Action potentials cause presynaptic neurons to release chemicals called neurotransmitters （神經物質） from terminal buttons

Chemicals travel across the synaptic cleft and, like a key fitting a lock, are received by receptors （受體） on the postsynaptic neurons’ dendrites

The binding of a neurotransmitter with a receptor produces an excitatory or inhibitory signal

Neurotransmitters Bind With Specific Receptors

Neurotransmitters stimulate specific receptors and block new signals until terminated.

The effects (excitatory/inhibitory) of a neurotransmitter are a function of the receptors that the neurotransmitters bind to.

Neurotransmitters Bind With Specific Receptors

Neurotransmitters stimulate specific receptors and block new signals until terminated

The effects (excitatory/inhibitory) of a neurotransmitter are a function of the receptors that the neurotransmitters bind to

Neurotransmitters Bind With Specific Receptors

Events that terminate the neurotransmitter’s influence in the synaptic cleft are: Reuptake （回收） : Neurotransmitter is

reabsorbed into the presynaptic terminal buttons

Enzyme deactivation （去活化） : Enzyme destroys the neurotransmitter

Autoreceptors （自體受體） : signal the presynaptic neuron to stop releasing the neurotransmitter

Neurotransmitters Influence Mental Activity and Behavior

Much of what we know about neurotransmitters has been learned through the study of the effects of drugs and toxins on emotion, thought, and behavior

Neurotransmitters Influence Mental Activity and Behavior

Drugs and toxins can alter neurotransmitter action: Agonists （促效劑） : enhance the

actions of neurotransmitters Antagonists （拮抗劑） : inhibit the

actions of neurotransmitters Researchers often inject agonists or

antagonists into animals’ brains to assess how neurotransmitters affect behavior

不回收神經傳導物質，讓物質持續在受體上作用

模擬成某種神經傳導物質，作用在受體上

Types of Neurotransmitters

There are many kinds of neurotransmitters

Nine of them are particularly important in understanding how we think, feel, and behave

3.2 What Are the Basic Brain Structures and Their Functions?

Identify the basic structures of the brain and their primary functions.

What Are the Basic Brain Structures and Their Functions?

The adult human brain is best viewed as a three-pound （ 1.36 公斤） collection of interacting neural circuits

Gall & Spurzheim proposed their theory of phrenology （顱相學） , based on the idea that the brain operates through functional localization

What Are the Basic Brain Structures and Their Functions?

Karl Lashley built his research on the general idea of equipotentiality

Broca (1861) provided the first strong evidence that brain regions perform specialized functions (Broca’s area)

Modern imaging techniques have greatly advanced our understanding of the human brain

The Brain Stem Houses the Basic Programs of Survival

The spinal cord: coordination of reflexes; carries sensory information to the brain and motor signals away from the brain

Composed of two types of tissue: gray matter and white matter

Brain stem: medulla oblongata, pons, midbrain, reticular formation

The Cerebellum Is Essential for Movement

Cerebellum (little brain): extremely important for proper motor function, learning, and motor memory

Damage to its different parts produces different effects: Damage to lobes on either side

causes a loss of limb coordination Damage to the nodes at the very

bottom causes balance problems

The Cerebellum Is Essential for Movement

Cerebellum is activated when a person experiences a painful stimulus or observes a loved one receiving that stimulus, which means the cerebellum may be involved in the experience of empathy

Subcortical Structures Control Emotions and Appetitive Behaviors

The forebrain( 前腦 ) consists of the two cerebral hemispheres, right and left

The most noticeable feature of the forebrain is the convoluted surface of the cerebral cortex ( 大腦皮質 )

Subcortical Structures Control Emotions and Appetitive Behaviors

Subcortical （次皮質） structures that lie below the cerebral cortex include: Hypothalamus, thalamus, hippocampus, amygdala, and basal ganglia

Some of these structures belong to the limbic system （邊緣系統） , which controls appetitive behaviors and emotion

Hypothalamus

The hypothalamus is the brain’s master regulatory structure

Affects the functions of many internal organs, regulating body temperature, body rhythms, blood pressure, and blood glucose levels

Also involved in many motivated behaviors, including thirst, hunger, aggression, and lust

Thalamus

The thalamus is the gateway to the cortex

Excepting smell, it receives all incoming sensory information, organizes it, and relays it to the cortex

During sleep, the thalamus partially shuts the gate on incoming sensations while the brain rests

Hippocampus and Amygdala

The hippocampus (Greek, “sea horse”) plays an important role in the storage of new memories

The amygdala(Latin, “almond”) serves a vital role in our learning to associate things in the world with negative and positive emotional responses

The Basal Ganglia

Basal ganglia: crucial for planning and producing movement

Damage to the basal ganglia can produce tremors and rigidity, uncontrollable jerky movements, and can impair the learning of movements and habits

Contains the nucleus accumbens, which is important for experiencing reward and motivating behavior

The Cerebral Cortex Underlies Complex Mental Activity

Cerebral cortex (Latin, “bark”): the outer layer of the cerebral hemispheres

It is the site of all thoughts, detailed perceptions, and complex behaviors

Each cerebral hemisphere has four “lobes”: Occipital( 枕葉 ), parietal ( 頂葉 ), temporal( 顳葉 ), frontal( 額葉 )

Corpus callosum ( 胼胝體 ) : a bridge of axons connecting the hemispheres and permitting information to flow between them

運動矮人圖(motor

homunculus)

The Prefrontal Cortex in Close-Up

Phineas Gage: His accident led to major personality changes

The Prefrontal Cortex in Close-Up

Lobotomy( 額葉切除術 ): deliberate damaging of the prefrontal cortex; used in the late 1940s early 1950s

Left patients lethargic and emotionally flat, and much easier to manage in mental hospitals, but it also left them disconnected from their social surroundings

3.3 How Does the Brain Communicate with the Body?

Differentiate between the divisions of the nervous system.

Identify the primary structures of the endocrine system.

Explain how the nervous system and the endocrine system communicate to control thought, feeling, and behavior.

3.4 What Is the Genetic Basis of Psychological Science?

Explain how genes are transmitted from parent to offspring

Discuss the goals and methods of behavioral genetics

Explain how both environmental factors and experience influence genetic expression

What Is the Genetic Basis of Psychological Science?

The term genetics is typically used to describe how characteristics are passed along to offspring and to the processes involved in turning genes “on” and “off”

Genetic predispositions are important in determining the environments we select for ourselves

Biology and environment mutually influence each other

All of Human Development Has a Genetic Basis

The genome is the master blueprint for making an entire organism “The genome provides the option, and the

environment determines which option is taken” (Marcus, 2004)

Chromosomes: made of deoxyribonucleic acid (DNA), consisting of two intertwined strands of molecules in a double helix shape

Genes: segments of DNA strands Human Genome Project: mapped the

entire structure of human DNA

Heredity Involves Passing Along Genes through Reproduction

Mendel (ca. 1866): cross-pollinated different colored pea plants to see which color flowers the plants would produce

Discovered clues to the mechanisms responsible for heredity

Dominant gene:expressed whenever it is present in either parent

Recessive gene:expressed only when it is matched with a similar gene from the other parent

Genotype and Phenotype

Genotype: an organism’s genetic makeup; never changes

Phenotype: an organism’s observable physical characteristics; always changing

Genetics (nature) and environment (nurture) both influence phenotype

Polygenic Effects

Polygenic trait: a trait that is influenced by many genes

The range of skin tones among Americans shows that human skin color is not inherited the same way as flower color was in Mendel’s research

Skin tone is not the end product of a single dominant/recessive gene pairing (genotype) but rather shows the effects of multiple genes

Genetic Variation Is Created by Sexual Reproduction

From any two parents, 8 million different combinations of the 23 chromosomes are possible

The human zygote grows through cell division; errors sometimes occur during cell division and lead to mutations

Mutations produce an ability or behavior that may be advantageous/disadvantageous to the organism

Genes Affect Behavior

A person’s abilities and psychological traits are influenced by the interaction of genes and environment

Behavioral genetics: the study of how genes and environment interact to influence psychological activity

People are born like “undeveloped photographs”: The image has been captured, but the way it eventually appears depends on the development process

Behavioral Genetics Methods

Behavioral geneticists use two methods to assess the degree to which traits are inherited: Twin studies: compare similarities between

monozygotic (identical) and dizygotic (fraternal) twins to determine the genetic basis of specific traitsGreater similarity of monozygotic twins (raised together or apart) is likely due to genetic influence

Adoption studies: compare biological relatives and adoptive relatives

Understanding Heritability Heritability: a statistical estimate of the

genetic portion of the observed variation in some specific trait

Heritability refers to populations, not to individuals Example: In a certain population, height

has a heritability of .60, which means 60 percent of height variation among individuals in that population is genetic. It does not mean that any one individual gets 60 percent of his or her height from genetics and 40 percent from environment

Estimates of heritability are concerned only with the extent that people differ in terms of their genetic makeup within the group

Social and Environmental Contexts Influence Genetic Expression

Caspi et al. (2002) followed more than 1,000 New Zealanders from birth until adulthood

Every few years information was collected about the participants

When the participants were 26 years old, investigators examined which factors predicted who had become a violent criminal

Mistreatment at home + low MAO gene accounted for nearly 50 percent of criminality

Study is a good example of how genes and social context interact to affect behavior (phenotype)

Genetic Expression Can Be Modified

Gene manipulation techniques can enhance or reduce the expression of a particular gene; genes from one animal species can be inserted into the embryo of another

Changing a single gene can dramatically change behavior Example: A gene from the highly social prairie

vole was inserted into the developing embryos of normally antisocial mice. The resulting transgenic mice exhibited social behavior more typical of prairie voles (Insel& Young, 2001)

Changing one gene’s expression leads to the expression of other genes, which ultimately influences behavior

3.5 How Does the Brain Change?

Explain how environmental factors and experience influence brain organization.

Describe sex differences in brain structure and function.

How Does the Brain Change?

Despite the great precision and the specificity of its connections, the brain is extremely malleable

Plasticity （可塑性） : a property of the brain that allows it to change as a result of experience, drugs, or injury

The Interplay of Genes and Environment Wires the Brain

Nature and nurture constantly interact to affect DNA’s activity and the products of that activity

Brain plasticity reflects the interactive nature of our biological and environmental influences

Cell Identity Becomes Fixed Over Time

As an embryo develops, each cell becomes more and more committed to its identity

Tissue transplanted early enough completely transforms into whatever type is appropriate for its new location; transplanting cells too late may disfigure the organism

Many people are excited about the possibility of transplanting fetal cells because they are undeveloped enough to become any type of tissue

Experience Fine-Tunes Neural Connections

Experience is important for normal brain development and maybe even more so for superior development.

Experience Fine-Tunes Neural Connections

Example: One group of rats was raised in a “normal”

lab environment (featureless boxes with bedding at the bottom, plus dishes for food and water); another group was raised in an enriched environment

The “enriched” group developed bigger, heavier brains than the first group (Rosenzweig, Bennett, & Diamond, 1972)

Culture Affects the Brain

Our cultural experiences contribute to different patterns of brain activity

Example: One group of participants in Japan and

another group in the United States were shown pictures of both neutral and fearful facial expressions portrayed by Japanese and American faces.

Activity in the amygdala was greatest when participants viewed fearful expressions within their own cultural group (Chiao et al., 2008)

The Brain Rewires Itself throughout Life

Although brain plasticity decreases with age, the brain can grow new connections among neurons and even grow new neurons into very old age

The rewiring and growth within the brain represents the biological basis of learning

Change in the Strength of Connections Underlies Learning

Changes in the brain due to experience are mainly in the strength of existing connections Hebb’s “fire together, wire together” catchphrase:

When two neurons fire simultaneously, the synaptic connection between them strengthens

Entirely new connections can grow between neurons.

Neurogenesis （神經生成） : New neurons are produced in some brain regions (e.g., the hippocampus)

Neurogenesis may underlie neural plasticity

Changes in the Brain

Wiring in the brain is affected by amount of use (e.g., recall the London taxi drivers)

Phantom limb （幻肢） : the intense sensation that an amputated body part still exists

Phenomenon suggests that the brain has not reorganized in response to the injury and that the missing limb’s cortical representation remains intact

An amputee who has lost a hand may, when his or her eyes are closed, perceive a touch on the cheek as if it were on the missing hand (Ramachandran & Hirstein, 1998)

The Puzzles of Synesthesia

Synesthesia: For synesthetes, sensory experiences are crossed One man reported the he hates driving because

the sight of road signs tastes to him like a mixture of pistachio ice cream and ear wax (McNeil, 2006)

The brain area involved in seeing colors is physically close to the brain area involved in understanding numbers, thus people with color/number synesthesia, may have some connections or cross-wiring between brain areas (Ramachandran& Hubbard, 2001)

Females’ and Males’ Brains Are Similar and Different

Females and males differ in their life experiences and hormonal makeup, which leads to differences between their brains Males tend to have larger brains Females and males may solve some complex

problems differently, with females using language-related brain regions and males using spatial-related brain regions (Haier et al., 2005)

Brain areas important in processing language are more likely to be found in both halves of females’ brains than in males’ brains

The Brain Can Recover from Injury

Following an injury in the cortex, the surrounding gray matter assumes the function of the damaged area

Radical hemispherectomy: After the surgical removal of an entire cerebral hemisphere, the remaining hemisphere eventually takes on most of the lost hemisphere’s functions

One of the most exciting (and controversial) areas of neurological research is the transplantation of human fetal tissue (stem cells) into the brain to repair damage

Instead of using fetal stem cells, new methods are emerging that allow researchers to create stem cells by reprogramming adult cells