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_system/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. */Written by Rob McEntarffer, Lincoln Southeast High School/* rmcenta@lps.org <mailto:rmcenta@lps.org>, /Adapted from an idea by Jan Daniel/

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