chapter 2 - biological basis of behavior - pearson...

Psychology: An IntroductionCharles A. Morris & Albert A. Maisto

© 2005 Prentice Hall

The Biological Basis of Behavior

Chapter 2



Neurons: The MessengersAbout 100 billion neurons (nerve cells) in

the human brainNeurons have many of the same features

as other cellsNucleusCytoplasmCell membrane

What makes neurons unique is their shape and function



Structure of Neurons Dendrites

Carry information to the cell body from other neurons

Cell Body (Soma) Contains nucleus

Axon Carries information to the

next cell Myelin Sheath

Insulates the axon and speeds up the neural impulse



Types of Neurons Sensory neurons

Carry information from sensory systems to the brain Also referred to as afferent

Motor neurons Carry information from the brain to muscles and

glands Also referred to as efferent

Interneurons Carry information between other neurons



Glial CellsCells that insulate and support neuronsCreate the myelin sheathRemove waste productsProvide nourishmentPrevent harmful substances from entering

the brain



The Neural Impulse



The Neural Impulse Ions

Charged molecules Resting Potential

When more negative ions are inside the neuron than outside

Charge is approximately -70mV

Neuron is not transmitting information



The Neural ImpulsePolarization

When the electrical charge of a cell moves away from zero

DepolarizationWhen the electrical charge of a cell moves

toward zero



The Neural Impulse Action Potential

Sudden, massive change in charge in the neuron

Occurs when depolarization reaches the threshold of excitation

Ions flow across cell membrane



The Neural ImpulseGraded Potentials

Subthreshold depolarizationMany subthreshold depolarizations are added

together to produce an action potential (a process known as summation)



The Neural ImpulseAll-or-None Law

A neuron either fires or it does notWhen it does fire, it will always produce an

impulse of the same strengthIntensity of a stimulus is coded by the

frequency of action potentials



The Neural Impulse Absolute refractory period

Period immediately after an action potential when another action potential cannot occur

Relative refractory period Period following absolute

refractory period when a neuron will only respond to a stronger than normal impulse



The SynapseSynaptic space (synaptic cleft)

Tiny gap between neuronsTerminal button

Enlarged area at the end of an axonThe synapse

Composed of the terminal button of one neuron, the synaptic space, and the dendrites or cell body of the receiving neuron



Transmission Between Neurons Synaptic vesicles

Sacs in terminal button that release chemicals into synaptic space

Neurotransmitters Chemicals released by

synaptic vesicles Receptor sites

Location on receptor neuron for specific neurotransmitter



Some Well-Known Neurotransmitters

Acetylcholine (ACh) Released at the neuromuscular junction Plays an important role in arousal and attention Loss of ACh producing cells is linked to Alzheimer’s

Disease Dopamine

Affects neurons associated with voluntary movement Plays a role in learning, memory, and emotions Loss of dopamine-producing cells causes symptoms

of Parkinson’s Disease



Some Well-Known Neurotransmitters

SerotoninFound throughout the brainAppears to sets an “emotional tone”Low serotonin levels are implicated in

depressionEndorphins

Reduce pain by inhibiting or “turning down” neurons that transmit pain information



PsychopharmacologyMost psychoactive drugs (and toxins) work

by blocking or enhancing synaptic transmission

BotulismBlocks release of ACh at the neuromuscular

junction, causing paralysis“Botox” is botulism toxin used to prevent facial

muscles from making wrinkles



Psychopharmacology Curare

Can stun or kill prey quickly Blocks ACh receptors causing paralysis

Antipsychotic medications Block dopamine receptors Reduces schizophrenic hallucinations

Caffeine Increases the release of excitatory neurotransmitters

by blocking the inhibitory neurotransmitter adenosine



PsychopharmacologyCocaine

Prevents reabsorption of dopamineLeads to heightened arousal of entire nervous

system



Neural PlasticityThe brain can be changed, both structurally

and chemically, by experienceRat studies show that an “enriched”

environment leads to larger neurons with more connections

Has also been shown in humansRecent research has uncovered evidence of

neurogenesis, or the production of new brain cells, in human brains



Nervous System Organization Central nervous

system (CNS) Consists of the brain

and spinal cord Peripheral nervous

system Connects the CNS to

the rest of the body Somatic nervous

system Autonomic nervous

system



Central Nervous System

Central Nervous System

Brain Spinal Cord



The Brain – The Central Core Medulla

Controls breathing, heart rate, and blood pressure

Pons Maintains the sleep-

wake cycle Cerebellum

Coordinates body’s movements



The Brain – The Central Core Thalamus

Relays information from sensory receptors to the brain

Hypothalamus Influences motivated

behavior Regulates hunger, thirst,

body temperature, and sexual drive.

Directly involved in emotional behavior



The Brain – The Central CoreReticular formation

Network of neurons found throughout the brain

Serves to alert and arouse higher brain in response to incoming information



The Brain – The Limbic System Ring of structures located

between the central core and the cerebral hemispheres

Important to learning and emotional behavior Hippocampus essential in

formation of new memories Amygdala, together with

the hippocampus, is important for regulating emotions



The Cerebral Cortex Occipital lobe

Receives and processes visual information

Temporal lobe Complex visual tasks such

as face recognition Receives and processed

auditory information Involved in balance, some

emotions and motivations Some language processing



The Cerebral Cortex Parietal lobe

Receives sensory information from body

Involved in spatial abilities Frontal lobe

Coordinated information from other lobes

Controls voluntary movement, attention, setting goals, and expression of appropriate emotions



Hemispheric Specialization Corpus Callosum

Fibers that connect the two hemispheres

Allow close communication between left and right hemishphere

Each hemisphere appears to specialize in certain functions



Split-Brain ResearchMuch information about functions of each

hemisphere has come from studying split-brain patients



Tools for Studying the Nervous System



Microelectrode TechniquesVery small electrodes inserted into

individual neuronsUsed to study activity of a single neuron



Macroelectrode TechniquesUsed to get a picture of overall activity in

the brainAn example is an EEG, which uses

electrodes placed on a person’s scalp to measure brain activity



Structural ImagingComputerized Axial Tomography (CT-

scan)Uses X-rays to create a 3-dimensional image

of the brainMagnetic Resonance Imaging (MRI)

Uses a magnetic field and radio waves to produce images



Functional ImagingEEG imaging

electrical activity on the scalp from millions of neurons is used to produce a continuous picture of activity in the brain

Magentoencephalography (MEG) and Magnetic source imaging (MSI)Can localize activity more precisely than EEG



Functional ImagingPositron Emission Tomography (PET) and

Single Photon Emission Computed Tomography (SPECT)Use radioactive glucose to determine location

of greatest brain activityFunctional Magnetic Resonance Imaging

(fMRI)Shows function and structure by measuring

movement of blood molecules within the brain



The Spinal Cord



The Spinal CordComplex cable of nerves that connects

brain to rest of the bodyCarries motor impulses from the brain to

internal organs and musclesCarries sensory information from

extremities and internal organs to the brain



The Spinal CordThe spinal cord controls some protective

reflex movements without any input from the brain



The Peripheral Nervous System

Peripheral Nervous System

Somatic Nervous System Autonomic Nervous System

Sympathetic Division Parasympathetic Division



The Somatic Nervous SystemConsists of neurons that communicate

between the body and the brainAfferent neurons

Neurons that carry messages from sense organs to spinal cord

Efferent neuronsNeurons that carry messages from the spinal

cord or brain to muscles and glands



The Autonomic Nervous System Sympathetic division

Most active when you are angry, afraid, or aroused

Fight-or-flight response

Increases heart rate and breathing

Stops digestion



The Autonomic Nervous System Parasympathetic

division Calms body Produces effects

opposite to those of the sympathetic division

Reduces heart rate and breathing

Restores digestion



The Endocrine System



The Endocrine SystemHelps coordinate and integrate complex

psychological reactionsEndocrine glands secrete hormones into

the bloodstreamHormones serve to organize the nervous

system and bodyHormones also activate behavior, such as

sexual behavior



The Endocrine System Thyroid gland

Secretes hormones (primarily thyroxin) that control metabolism

Parathyroid glands Control levels of

calcium and phosphate which in turn controls levels of excitability



The Endocrine System Pineal gland

Secretes melatonin which regulates the sleep-wake cycle

Pancreas Regulates blood-sugar

levels Secretes insulin and

glucagon



The Endocrine System Pituitary gland

Referred to as the “master gland” because it regulates many other glands

Gonads Ovaries and testes

secrete estrogens and androgens

Adrenal glands Secretes hormones in

reaction to stress



Genes, Evolution, and Behavior



GeneticsHeredity - transmission of trait from one

generation to nextChromosomes

Pairs of thread like bodies that contain genesDeoxyribonucleic acid (DNA)

Organic molecule arranged in a double-helixContains the “code of life”



Behavior Genetics Study of behavior from a genetic

perspectiveAnimal behavior genetic studies include:

Strain studiesSelection studies



Human Behavior GeneticsFamily studies

Assume that close family members share more of a trait than non-relatives

Used to assess the heritability of psychological disorders or traits

Twin studiesUsed to determine how heritable a trait or

disorder may beIdentical twins would have highest heritability



Human Behavior GeneticsAdoption studies

Used to assess the influence of environmentMolecular genetics

Direct study of the genetic code



Evolutionary PsychologyNatural selection

“Survival of the fittest”Evolutionary psychology looks at the

adaptive or survival value of behaviors



Social ImplicationsStudy of biological origins of behavior

could lead to genocide and eugenics aimed at eliminating certain types of people

Could also be used to create new categories of people, such as people bred to be good soldiers or manual laborers

chapter 2 - biological basis of behavior - pearson...

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