I. Genes and Evolution

Gene: a stretch of DNA that produces a specific protein, which in turn forms building blocks of our bodies or drives the processes that allow us to live

• DNA (deoxyribonucleic acid): molecule that contains genes
• Human instruction manual: genes affect physical features, such as eye color and height, and behavior

• Mutation: depending on environment, genetic makeup or organisms evolves throughout generations of offspring, producing changes in the dominant physical features and behavior of a group of organisms
• Characteristics of organisms are molded to the requirements for survival in a particular environment
• “Survival” genes will come to be widespread in a population because those with these genes are the ones that live long enough to have many offspring
• In turn, those offspring, equipped with the favorable characteristics inherited from parents, will survive to have more offspring

• How much of the differences among people are due to their genes and how much are due to the environment?  How much do genes affect behavior/mental processes compared to environmental influences?
• Genes cannot be described in isolation: they can only be characterized in relation to the environments in which they operate
• How do we effectively study whether the differences in mental processes/behavior are genetic?
• Twin studies are a good way to gain heritability estimates for mental processes/behaivor
• Compare identical twins (monozygotic: from the same egg; have identical genes) to fraternal twins (dizygotic: from different eggs; only share ~half as many genes, similar to any pair of brothers/sisters)
• If environment is same for both identical and fraternal twins, then you can estimate heritablility for mental processes & behavior
• Adoption studies: compare adopted kids with biological and adopted parents or siblings
• Very powerful when adopted child being compared has an identical twin in another household/environment.

A. Part 1: Central nervous system

• Brain: ~2.5% of body weight, uses ~20% of resources; composed of bunches of neurons, which form nerves
• Spinal cord: complex tangle of nerves that stretch from brain to tailbone
• Collects & transmits info between brain and body
• Also initiates reflexes: automatic responses to an event
• Reflexes don’t require thought; that is, they aren’t sent by brain to spinal cord
• Sensory neurons from skin are sent to spinal cord, which send out signals to motor neurons in the muscles to produce reflex

• Cerebral Cortex: “gray matter” of brain where most mental processes take place
• Divided into 4 parts (lobes)
• Occipital lobe: back of the head; concerned with visual perception
• Temporal lobe: under the temples, in front of the ears, where sideburns begin to grow down; processing of sound; storing visual memories; language comprehension
• Parietal lobe: top, center/rear of head; spatial location; attention; motor control; consciousness
• Frontal lobe: behind the forehead; planning; memory search; motor control; reasoning; emotions
• Two Cerebral Hemispheres
• Each hemisphere receives information from, and controls the muscles of, the opposite side of the body (e.g., if you write w/ your right hand, then your left hemisphere controls your hand as you write)
• Corpus callosum: thick band of nerve fibers connecting the two hemispheres
• The 2 hemispheres communicate via the corpus callosum
• Right-brained vs. left-brained?
• Right hemisphere is associated intuition and perception, while the left hemisphere is associated with analytic and verbal processing
• Cerebellum: physical coordination, movement, balance
• Thalamus
• “Switching center”: filters & organizes info from senses
• Attention: your thalamus is allowing you to fix your attention on each word that you read
• Hypothalamus: regulates basic bodily functions & biological drives: eating/drinking, body temp, blood pressure, heart rate, sexual behavior, hormone secretion
• Hippocampus: allows us to storage of new information in memory
• Amygdala: emotions, especially fear & anger

B. Part 2: Peripheral nervous system

• PNS links the CNS to the organs of the body
• Has two parts…
• Skeletal/Somatic (SNS): nerves controlling voluntary muscle movements
• Autonomic (ANS): controls glands, organs, blood vessels; ANS is divided into 2 major divisions…
• Sympathetic: arouses body to prepare for action (i.e., fight or flight/flee)
• Speeds up heart, increases breathing for oxygen, dilates pupils for light sensitivity and sharper vision, produces sweat slightly for grip, inhibits stomach activity, relaxes bladder
• Parasympathic: slows down body to reserve energy
• Tends to counteract the sympathetic response

Neuron: A cell that receives signals from other neurons or sense organs, processes these signals, and sends them to other neurons, muscles, or organs

• The basic unit of the nervous system: all brain activity originates with the neuron
• Three types: sensory (respond to sensory organ input), motor (send signals to muscles to control movement), and interneuron (the go-between b/w sensory & motor neurons)

• Cell body houses nucleus
• Cell membrane: skin of cell
• Axon: cable extending from the cell body
• Impulse from cell body travels along axon to its end, where terminal buttons release neurotransmitters (i.e., chemical messengers) to be received by other neurons.
• Axon is covered by myelin sheath, which is composed of a fatty substance that helps impulses travel the length of the axon
• Dendrite: branches extending from cell membrane that receive neurotransmitters from other neurons

• When a neuron receives impulses from other neurons, the cell membrane allows open exchange of positively & negatively charged ions…
• This shifting change in electrical charge (i.e., action potential) runs down axon to terminal buttons, terminal buttons release neurotransmitters, neurotransmitters cross synaptic cleft (space between terminal button & dendrite) to dendrite of receiving neuron
• “All-or-none” impulse: action potential process described above either happens or it doesn’t happen

• Neurotransmitters are either excitatory (making receiving neuron more likely to fire action potential) or inhibitory (less likely to make receiving neuron fire)
• Selected types of neurotransmitters…
• Acetylcholine (ACh): slows down body, memory attention
• Dopamine (DA): voluntary movement, attention & learning
• Serotonin: arousal, sleep
• Endorphins: reduce sensitivity to pain