Biological Bases of Behavior

Chapter 3

Biological Explanations of Behavior

Genes DNA or genes that code for physical and

psychological characteristics Neurons

Electrical and chemical wiring of the body and brain

Nervous System Combination of genes and neurons that

handles information and communication

Mirror Neurons

http://www.pbs.org/wgbh/nova/teachers/viewing/3204_01_nsn.html

Structure of the neuron

Neurons Hardware:

Glia (means glue) – provides structural support and insulation to promote more efficient signaling

Neurons – nerve cells that constitute the basic building blocks of nervous system (100 billion in brain and spinal cord)

Soma – cell body Dendrites – receive information Axon – transmit away

Myelin sheath covers axons to increase speed of transmission

Terminal buttons – secrete neurotransmitters Synapse – junction where information is

transmitted

Electrical Activity of Neurons

Neurons do 2 things: Generate electricity Release chemicals

Both inside and outside the neuron are electrically charged atoms and molecules called ions Positively charged sodium and potassium ions

and negatively charged chloride ions flow back and forth across cell membrane

Higher concentration of negative ions on inside (-70 millivolts) means neuron is at rest (resting potential)

The Action Potential If you sufficiently stimulate an axon, the cell

membrane opens up briefly Potassium ions then enter through the cell membrane

openings the interior voltage shifts from -70 to +40 millivolts This brief shift in a neuron’s electrical charge is called an

action potential Can occur very quickly

http://faculty.washington.edu/chudler/son.html http://lessons.harveyproject.org/development/nervous_s

ystem/cell_neuro/action_potential/propagation.html All-or-none principle

Neurons either fire or they don’t The rate of firing determines strength of stimulus Thicker neurons transmit info quicker than thinner

neurons Ex. Local anesthetics attach to sodium ions to prevent

passage of sodium into the cell membrane restricting firing potential

The neural impulse

How Neurons Communicate Synaptic space

Tiny gap between axon terminal and the next neuron

Neurons do not touch one another…then how do they communicate???

Arrival of action potential at axon’s terminal button triggers release of neurotransmitters Chemical substances that carry messages

across the synapse either to excite other neurons or inhibit their firing

Neurotransmitters cross synaptic cleft and attach to receptor sites

Receptor sites and neurotransmitters fit like a lock-and-key

Overview of synaptic transmission.

How neurons are like toilets The all-or-none principle: Toilet either flushes

or not Resting potential: Water in the represents the

resting potential. The toilet is "waiting" to fire, and the water in the tank represents the overall negative charge inside the neuron waiting for depolarization

Threshold: Toilet won’t flush properly until you push past a critical point

Direction of impulse: toilet only flushes one way; the impulse only travels one direction (you hope!)

Refractory period: after you flush, toilet won't flush again for a certain period of time, even if you push the handle repeatedly

Action potential: Represented by the water flowing down the pipe.

Peripheral nervous system Somatic (voluntary) Autonomic (involuntary)

Sympathetic (increased heart rate, increase in respiration, increase in blood circulation, pupil dilates, digestion stops, etc.)

Parasympathetic (heart rate decreases, respiration decreases, digestion restarts, pupil constricts, blood circulation decreases, etc.)

Understanding the Brain Neuropsychological tests

Measure verbal and nonverbal behaviors of victims of brain damage

Lesions Specific nervous tissue is destroyed with electricity or

chemicals or surgically remove portions of the brain Electrical Recording

Electroencephalograph (EEG) Brain Imaging

Computerized axial tomography (CAT scans): X-rays Position Emission Tomography (PET scans): measures

levels of glucose in brain Magnetic Resonance Imaging (MRI): structures and

functions

CAT scan Brain of stroke victim

Lesioned(damaged)areas

PET scans

Normal brain Alzheimer’s brain

MRI and fMRI scans

Standard MRI functional MRI

Structures and functions of the brain

Brain is separated into two cerebral hemispheres connected by the corpus callosum Neural bridge that acts as a major

communication link between two hemispheres

The left and right brains

Lateralization: relatively greater localization of a function in one hemisphere or the other Left hemisphere (verbal abilities and

speech, mathematical and logical abilities, more active with positive emotions)

Right hemisphere (spatial relationships, mental imagery, musical and artistic abilities, more active with positive emotions

Four lobes Occipital

lobe (vision)

Parietal Lobe (touch)

Temporal lobe (hearing)

Frontal lobe (movement of the body)

The Endocrine System

Consists of glands that secrete chemicals into the bloodstream that help control bodily functioning Mostly controlled by hypothalamus Uses hormones (chemical substances

released into the bloodstream by endocrine glands)

Pituitary gland: master gland Gonads: sexual glands that release sex

hormones

Evolution and Behavior

Based off of Darwin’s work on natural selection Characteristics that increase likelihood of

survival and ability to reproduce will be more likely preserved in population and become more common in species over time

THUS…Natural selection acts as a filter Adaptation is product of natural selection

Changes that allow organisms to meet recurring environmental challenges so their survival and increases reproductive ability

Can be physical or behavioral Woodpeckers long, strong beak allows to puncture hole

in trees and eat insects Chameleon’s blend into their environment to avoid

predators Rats won’t eat 2 unfamiliar foods at a time

Tips on evolutionary theory

Acknowledge the role of remote and proximate causes that influence behavior

There is only adaptation to environmental demands Example

Male violence is a good adaptation in a time of war

Male violence is not such an adaptive trait in a time of peace

Genetic Influences on Behavior

Genotype Specific genetic makeup of person

Ex. Commands of a computer program Phenotype

Individual’s observable characteristics Chromosomes: double-stranded molecule

of DNA carrying genetic information Every cell has 46 chromosomes in pairs

(23 from each parent) All genes encoded in various combinations of 4

chemical bases

Genetic relatedness and familial relatedness

Dominant, Recessive, or Polygenic Effects

Some genes are dominant, while other are recessive Brown eyes dominant over blue eyes Child has blue eyes only if both contribute a

recessive gene for eye color Polygenic

A # of gene pairs combine their influences to create a single phenotypic trait

Between 2 parents there are over 70 million chromosomal combinations

Is it Heredity or Environment?

Family Studies Twin Studies

Compare trait similarities in identical and fraternal twins

Monozygotic and dizygotic

Adoption Studies People who were adopted are compared on

some characteristic with both their biological (share genetic info) and adoptive parents (share no genes)

Ex. schizophrenia

Twin studies of intelligence and personality