Chapter 3: Biological Bases

of Behavior

Heredity and Behavior

Evolution and Natural Selection

• Charles Darwin- The Origin of Species• Natural Selection- theory that

favorable adaptations to features of the environment allow some members of a species to reproduce more successfully than others• What does this mean?

Evolution and Natural Selection

Over time organisms producing more favorable traits for survival will become more numerous than othersAKA: Survival of the fittest

Evolution and Natural Selection

• Short-term effects:

Evolution and Natural Selection

• Long-term effects:

Genotype vs. PhenotypeGenotype

• Inherited genetic structure from parents• Determines

development and behavior

Phenotype• Determines

observable appearance• Resulting from

interaction between genotype and environment

Process of Natural SelectionEnvironmental Pressure

Competition

Selection of Fittest

Reproductive Success

Frequency of Genotype

Language• Most important milestone for

human species

Language• Vital for:• Instruction• Sharing experiences• Social Bonds• Transmitting wisdom

Language• Basis for cultural evolution• Allows for rapid

adjustments to environmental changes• Culture is possible because

of the potential of human genotype changes

Variation in Human Genotype

• Heredity- the inheritance of physical and psychological traits from ancestors; transmission of traits from parents to offspring• Genetics- the study of heredity

Basic Genetics• DNA is found in the nucleus of

each human cell• DNA- the physical basis for

genetic information• DNA is organized into genes• Genes- biological units of herdity

Genes• Contain the instruction

for phenotypic traits: (some examples)- body build- physical strength- intelligence• Found on

chromosomes

Sex Chromosomes• Contain coding for male or female

characteristics• Mother contributes “X” chromosome• Father contributes “X” or “Y”

chromosome• XX= female• XY= male

Genes• 50% of genes in

common with siblings• Set of genes is unique• Difference in genes

and environment determine traits

Goal• Important goal of psychology is

to understand the balance between your genetics and your environment

Genes and Behavior• Human behavior genetics- unites

genetics and psychology to explore the relationship between inheritance and behavior

Happiness• Researchers propose that happiness

has a strong genetic component, less than an environmental component• Is happiness set

at birth?

Genes• Conclusion:

Genes you receive from your parents have broader effects than determining hair and eye colorSociobiologists use evolutionary explanations to analyze social behavior and social systems

Sad Brain Happy Brain • Read “Sad Brain, Happy Brain”

and answer all questions on handout

Biology and Behavior

People to Know• Rene Descartes- French Philosopher

- human action is mechanical reflex to environmental stimulation

People to Know• Sir Charles Sherrington-

- discovered reflexes are direct connections between sensory and motor nerve fibers- nervous system involves increasing and decreasing neural activity

People to Know• Santiago Ramon y Cajal-

- detected gaps between adjacent neurons and theorized how info flowed from one to another

People to Know• Donald Hebb-

- believed the brain was integrated series of structures (cell assemblies) performing specific functions

Neuroscience• Neuroscience- study of the brain

and the links between brain activity and behavior

Phineas Gage• Pre-accident: level-

headed, calm• Post-accident:

hostile, impulsive, extremely emotional, obscene language

Phineas Gage• Loss of tissue revealed the

relationship between frontal lobes and control of emotional behavior

Paul Broca• Studied brain’s role in language• Discovered area of brain connected

to language- now known as “Broca’s area”- translates thoughts into speech or signs

Lesions• Researchers began method of

destroying or injuring brain tissue on purpose to study results• Damages are “lesions”• Experimental work on non-

humans only

Lobes of the Brain

Broca’s Area

People to Know• Walter Hess- pioneered use of

electrical currents in the brain- determined what part of the brain performs specific functions

Recording Brain Activity• EEG- traces electrical activity of the brain• PET Scan- image produced by recording

radioactivity emitted by cells during different activities• MRI- scan of brain using radio waves and

magnetic fields• fMRI- combines PET and MRI

The Nervous System

Organization of Nervous System

Brain Structures and Functions

Brain• Brain- most important component of your

CNS• Brain Stem- regulates the body’s basic life

processes• Medulla- center for breathing, blood

pressure and heart rate• Pons- connects spinal cord with brain

Brain• Reticular Formation- arouses cerebral

cortex to incoming sensory signals- responsible for consciousness and awakening from sleep- massive damage coma• Thalamus- channels incoming sensory into

to appropriate area of cerebral cortex

Brain• Cerebellum- attached at base of

skull- responsible for body movement, posture, and equilibrium

Brain

Limbic System• Hippocampus- involved in the ability

to acquire memories- injury can effect recall of memory• Amygdala- role in emotional control

and formation of emotional memories

Limbic System• Hypothalamus- regulates/maintains

homeostasis, involved in motivated behavior• Equilibrium- consistency of the

body’s internal conditions

Cerebrum• Cerebrum- regulates brain’s higher

cognitive and emotional functions; 2/3s of brain• Cerebral Cortex- outer surface• Corpus Callosum- nerve fibers

connecting 2 hemispheres of cerebrum

Cerebrum• Frontal Lobe- responsible for motor

control and cognitive activities- planning, decision making, goal setting• Parietal Lobe- responsible for

sensations, touch, pain, and temp; contains somatosensory complex

Cerebrum• Occipital Lobe- contains primary

visual cortex• Temporal Lobe- contains primary

hearing

Cerebrum• Motor Cortex- controls the actions of

the body’s voluntary muscles• Somatosensory Cortex- processes

information about temp, touch, body position, and pain; devoted to parts of body that provide sensory input (lips, tongue, thumb, index finger)

Cerebrum• Auditory Cortex- receives

information from both ears processes auditory info• Visual Cortex- devoted to visual

input and transmits detailed visual info

Cerebrum• Association Cortex- portion of the

brain where high level brain process occur, such as planning and decision making occur

Cerebrum

Hemispheric Lateralization• Info from the right visual field goes

to the left hemisphere- Vice versa• In most people this info is shared

quickly between the two hemispheres via the corpus callosum

Hemispheric Lateralization• Speech is controlled by the left

hemisphere in most individuals• Speech is the most highly lateralized

function of the brain• This doesn’t mean the left hemisphere is

better!• Right hemi controls more manual tasks

Hemispheric Lateralization• Conclusion:- The right hemisphere controls

the left side of your body- The left hemisphere controls the

right side of your body

Who’s Better at What?• Look over the handout “Who’s Better

at What?”• Respond to the following questions:

- Do you agree/disagree with the info on the handout?- Are you a “left brain” or “right brain” person?

Hemispheric Lateralization1. Women have greater density of

neurons in a portion of the temporal cortex involved in language

2. Different brain areas develop more strongly for men and women

3. Hemi’s of women’s brain shares more functions than men’s

Neurons• Neuron- cell that receives, processes

and transmits into to other cells

NeuronsPARTS:1.Dendrites- receive incoming signals2.Soma- cell body; contains nucleus; passes info to the axon3.Axon- conducts info away from soma to the terminal buttons

Neurons4. Myelin Sheath- covers axon to increase speed of info

- MS cells attack and deteriorate myelin sheath

5. Terminal Buttons- bulb-like structures through which neurons stimulate nearby glands, muscles, or other neurons; release neurotrans.

Types of Neurons1. Sensory (Afferent) Neurons- carry messages

from sense receptor cells towards the CNS (sensitive to light and sound)

2. Motor (Efferent) Neurons- carry messages away from CNS towards muscles and glands

3. Interneurons (in brain)- relay messages from sensory neurons to other interneurons, or to motor neurons

Glial Cells• Hold neurons in place• Housekeeping- clean-up damaged or

dead neurons• Absorb excess neurotransmitters• Insulation- form the myelin sheath• Prevent toxic substances in blood

from reaching brain cells

Action Potentials• Neurons receive excitatory (“fire”) or

inhibitory (“don’t fire”) inputs• Neural communication is produced by the

flow of elec. charged particles – ions• Inactive/Resting State- more potassium

ions inside, more sodium ions outside the neuron• Membrane of the cell has a pump to keep

this in balance

Action Potentials

• Fluid inside the membrane has a slight negative charge (polarized)• This polarization = resting potential• When nerve cells get excitatory or

inhibitory inputs the balance of ions will change

Action Potential• Inhibitory inputs cause ion channels to

work harder to keep the inside of cell negatively charged won’t fire• Excitatory inputs allow ion pump to

allow sodium in which allows the cell to fire (sodium ions have a positive charge)

Action Potentials• Action Potential begins when the

inside of the cell is depolarized and sodium rushes into the cell makes the ion positively charged• A domino effect propels the action

potential down the axon successive depolarization

Action Potentials• Neuron returns to a resting state:

when neuron becomes positive, channels that allowed sodium in close, channels that stopped potassium open

Cell returns to negative charge and ready for next stimulation

All or None!• “All or None”- action potential is

not affected by increases in intensity of stimulation once threshold level is reached and is firing• If threshold is not reached no

firing

Refractory Period• Action potential has passed:1.Absolute refractory period- no stimulation

can generate another action potential2.Relative refractory period- neurons will only

fire in response to a stronger stimulus • This ensures that action potential will only

travel in one direction can’t move backward b/c “earlier” parts of axon are in refractory state

Synaptic Transmission1. Action potential reaches terminal

buttons2. Synaptic vesicles rupture and

neurotransmitters are released3. Neurotransmitters disperse across

synaptic cleft4. Neurotransmitters attach to receptor

molecules

Synaptic Transmission• Neurotransmitters attach to the postsynaptic

membrane only if 2 conditions are met:- the only neurotransmitter attached to that receptor molecule- shape of neurotransmitter must match the shape of the receptor molecule

5. Once job is complete detaches and decomposes or is reabsorbed