Chapter 3: The Biological Bases of Behavior

The nervous system is the body’s communication network

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.

Communication in the Nervous System

The basic components of the nervous system are living cells called neurons and glia.

Hardware– Glia – structural support and insulation– Neurons – cells that receive, integrate, and

transmit information – Soma – cell body– Dendrites – which are feeler-like structures

specialized to receive information– Axon – a long, thin fiber that transmits signals

away from the soma to other neurons, or to muscles or glands

Neural Communication:Insulation and Information Transfer

• Myelin sheath – an insulating material that speeds up transmission (MS)

• Terminal Button – end of axon; secretes neurotransmitters

• Neurotransmitters – chemical messengers• Synapse – point at which neurons

interconnect• The chemicals flow across the synapse and

stimulate the next cell.

Figure 3.1 Structure of the neuron

The Neural Impulse:Electrochemical Beginnings

• Hodgkin & Huxley (1952) - 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.– Fluids inside and outside neuron – Electrically charged particles (ions)– Neuron at rest – negative charge on inside

compared to outside– -70 millivolts – resting potential

The Neural Impulse: The Action Potential

• Stimulation causes cell membrane to open briefly

• Positively charged sodium ions flow in• The Action Potential: Shift in electrical

charge travels along neuron• All – or – none law: Either an action

potential occurs, or it doesn’t. Once an action potential is initiated, it goes full force

Figure 3.2 The neural impulse

The Synapse: Chemicals as Signal Couriers

• Synaptic cleft: 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

• Presynaptic neuron: the neuron that is sending the message across the gap

– Synaptic vesicles: storage sacs for the neurotransmitter

– Neurotransmitters• Postsynaptic neuron

– 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

Figure 3.3 The synapse

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 makes the

neuron more likely to fire…decreases the negativity of the inside of the neuron with respect to the outside

• Negative voltage shift – inhibitory PSP increases the negativity of the inside of the neuron with respect to the outside, making it less likely to fire.

Figure 3.4 Overview of synaptic transmission

Signals: From Postsynaptic Potentialsto Neural Networks

• One neuron, signals from thousands of other neurons• Requires integration of signals

– PSPs: Each neuron must integrate the many signals arriving at the same time before it “decides” to fire

– EPSPs: pos. volt charge • enough can cause the cell’s voltage to reach

the threshold at which the action potential will begin

– IPSPs: neg. volt shift that decrease action pot.– EPSPs and IPSPs may balance out, as well, and

the neuron would remain at rest• the state of the neuron is a weighted balance

Signals: From Postsynaptic Potentialsto Neural Networks

• Neural networks– 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: Interconnected neurons that fire together or sequentially

Signals: From Postsynaptic Potentialsto Neural Networks

• Synaptic connections– Synaptic pruning: the elimination of old or

unused synapses • plays a larger role than the creation of

new synapses in the sculpting of neural networks

• the number of synapses in the human visual cortex begins to decline after the age of 1 year.

Figure 3.5 Synaptic pruning

Neurotransmitters

• Specific neurotransmitters work at specific synapses– Lock and key mechanism

• Agonist – mimics neurotransmitter action• Antagonist – opposes action of a

neurotransmitter• 15 – 20 neurotransmitters known at present• Interactions between neurotransmitter circuits

– most aspects of behavior are probably regulated by many

Types of Neurotransmitters

• Acetylcholine: only NT b/w motor neurons and voluntary muscles (every move you make depends on ACh)– Nicotine is an agonist

• Monoamines– Dopamine voluntary movements and pleasure

emotions (Parkinson’s, Schiz.)– Norepinephrine: modulates mood and arousal

(cocaine and amphet.)– Serotonin: reg. Of sleep and wakefulness,eating

and aggression (depression/ OCD)

Types of Neurotransmitters

• Gaba: strictly inhibitory PSPs– Regulation of anxiety and plays a key role

in seizures and modulation of sleep• Endorphins: resemble opiate drugs and

effects, contribute to pain relief and some perhaps pleasurable emotions

Table 3.1 Common Neurotransmitters and Some of their Functions

Organization of the Nervous System

• Central nervous system (CNS)– The central nervous system consists of the

brain and spinal cord • Afferent = nerve fibers toward the CNS• Efferent = nerve fibers away from the CNS

Figure 3.7 The central and peripheral nervous systems

Organization of the Nervous System

• Peripheral nervous system: the peripheral nervous system consists of nerves that lie outside the brain and spinal cord.– Somatic nervous system: voluntary portion– Autonomic nervous system (ANS)

• governs involuntary, visceral functions• Sympathetic:

mobilizes the body’s resources for emergencies and creates the fight-or-flight response

• Parasympathetic: activates processes that conserve bodily resources…slowing heart rate, reducing blood pressure, etc

Figure 3.6 Organization of the human nervous system

Figure 3.8 The autonomic nervous system (ANS)

Studying the Brain: Research Methods

• Electroencephalography (EEG): monitoring electrical activity of the brain

• Damage studies/lesioning: observing consequences of damage to certain areas

• Electrical stimulation (ESB): stimulating a portion of the brain and observing effects

Studying the Brain: Research Methods

• Transcranial magnetic stimulation (TMS): enhance or suppress activity in a particular region of the brain

• 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

Brain Regions and Functions

• Hindbrain – vital functions – – Medulla: attaches to the spinal cord;

controls: circulation, breathing, muscle tone, and regulating reflexes

– Pons: means “bridge”, connects brainstem and cerebellum; sleep and arousal

– Cerebellum: means “little brain” coordination of movement and equilibrium

Brain Regions and Functions

• Midbrain: lies between the hindbrain and the forebrain

– integrates sensory functions (sight,smell,etc.)– dopaminergic projections: performance in

voluntary movements– reticular activating system: bundle of nerve fibers

running through the brain stem; sleep and arousal as well as breathing and pain perception (hind and midbrain)

– Parkinson’s disease is due to degeneration of the substantia nigra, a structure in the midbrain

Brain Regions and Functions

• Forebrain – emotion, complex thought – Thalamus: the way station for all incoming

sensory information before it is passed on to appropriate higher brain regions

– Hypothalamus: regulator of basic biological needs such as hunger, thirst, sex drive, and temperature regulation

– limbic system: emotion, motivation, memory, and other aspects of behavior

Brain Regions and Functions

• Forebrain (cont.)– Cerebrum: largest and most complex

portion of the human brain, responsible for complex mental activities such as learning, remembering, thinking, and consciousness

– cerebral cortex: convoluted outer layer of the cerebrum

The Cerebrum:Two Hemispheres, Four Lobes

• Cerebral Hemispheres – two specialized halves connected by the – corpus collosum: thick band of fibers

(axons) that transmits information between the hemispheres

– Left hemisphere – verbal processing: language, speech, reading, writing

– Right hemisphere – nonverbal processing: spatial, musical, visual recognition

The Cerebrum:Two Hemispheres, Four Lobes

• Four Lobes:– Occipital – vision– Parietal – somatosensory (senses)– Temporal - auditory– Frontal – movement, executive control

systems

Figure 3.16 Structures and areas in the human brain

Right Brain/Left Brain

• Broca’s Area: left frontal lobe; plays an important role in the production of speech

• Wernicke’s Area: left temporal lobe; comprehension of speech

Split-Brain Research

• Severing of the corpus callosum (the part that shares information b/w the 2 hemispheres)

Hemispheric Specialization

• Right Hemisphere: better at visual-spatial tasks, music, perception of emotions, neg. emotions exhibited

• Left Hemisphere: better at verbal stimuli (lang., speech, reading, and writing), positive emotions exhibited

Figure 3.18 The cerebral hemispheres and the corpus callosum

Figure 3.19 The cerebral cortex in humans

Figure 3.20 The primary motor cortex

Figure 3.21 Language processing in the brain

The Endocrine System:Glands and Hormones

• Hormones – chemical messengers in the bloodstream– Pulsatile release by endocrine glands– Negative feedback system: The levels of many

hormones increase to a certain level, then signals are sent to the hypothalamus or other endocrine glands to stop secretion of that hormone

• Endocrine glands– Pituitary – “master gland,” growth hormone– Thyroid – metabolic rate– Adrenal – salt and carbohydrate metabolism– Pancreas – sugar metabolism– Gonads – sex hormones

Genes and Behavior:The Field of Behavioral Genetics

• Behavioral genetics = the study of the influence of genetic factors on behavioral traits

• 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• Dominant: sometimes a member of a pair has a

louder voice, always expressing itself and masking the other, different, member of the pair

• Recessive: gene is one that is masked when the paired genes are different

Genes and Behavior:The Field of Behavioral Genetics

• Homozygous: a person has two genes in a specific pair that are the same

• Heterozygous: a person has two genes in a specific pair that are different

• Genotype/Phenotype: Genotype refers to a person’s genetic makeup (lifelong), while phenotype refers to the ways in which a person’s genotype is manifested in observable characteristics (variable)

• Polygenic Inheritance: most human traits are not so simple with regard to genetic transmission…they are polygenic, or influenced by more than one pair of genes.

Figure 3.25 Genetic material

Research Methods in Behavioral Genetics

• Family studies – Family studies simply assess hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait

• Twin studies – compare resemblance of identical (monozygotic) and fraternal (dizygotic) twins on a trait (monozygotic are more correlated in terms of intelligence and personality, but nor perfectly alike- environment plays a part)

Research Methods in Behavioral Genetics

• Adoption studies – examine resemblance between adopted children and their biological and adoptive parents– They have found very similar correlations

between both adoptive (.20) and natural parents (.22)

Section Summary

• “Genes confer dispositions, not destinies.”

Figure 3.27 Genetic relatedness

Figure 3.28 Family studies of risk for schizophrenic disorders

Figure 3.30 Twin studies of intelligence and personality

Modern Approaches to theNature vs. Nurture Debate

• Molecular Genetics = the study of the biochemical bases of genetic inheritance– Genetic mapping – locating specific genes

and their chemical sequence of specific genes on specific chromosomes

– The Human Genome Project: produced a working draft of all 3 billion letters of DNA in the human genome (a genetic atlas)

Modern Approaches to theNature vs. Nurture Debate

• Behavioral Genetics– The interactionist model

• Genetic research has yielded no easy answers about nature vs. nurture

• Instead, it has led to the interactionist model- people with certain genes are more likely to exhibit certain behaviors when environmental influences are present

– Richard Rose (1995) – “Genes confer dispositions (we inherit dispositions), not destinies.”

Evolutionary Psychology:Behavior in Terms of Adaptive Significance

• The field of evolutionary psychology is a major new field in psychology focusing on analyzing human behavior in terms of adaptive significance

Evolutionary Psychology:Behavior in Terms of Adaptive Significance

• Based on Darwin’s ideas of: – Natural selection

• Successful transmission of genetic evolution depends on providing either a reproductive advantage (firefly’s light) or a survival advantage (turtle shell)

• Change is very gradual

Evolutionary Psychology:Behavior in Terms of Adaptive Significance

• Inclusive fitness– Used to explain self-sacrifice– An organism may succeed in helping

natural selection by sacrificing itself to save others that share the same genes

Evolutionary Psychology:Behavior in Terms of Adaptive Significance

• Adaptations (inherited characteristics) – behavioral as well as physical; more difficult to study behaviors b/c they are infrequent and relatively quick in length of display– Fight-or-flight response: helpful in primitive

times, but now it is related to a number of stress-related diseases

– Taste preferences: humans show a taste preference for fatty foods…this was adaptive in a hunter/gatherer society, when dietary fat was scarce

Evolutionary Psychology:Behavior in Terms of Adaptive Significance

• Adaptations (cont.)– Parental investment and mating (Trivers- 1972)

• When parental investment is high for females and low for males, polygyny results –each male seeks to mate with multiple females and each female seeks only one male.

• Polyandry: 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.

• Shut-Up you!