Untitled Flashcards Set

Lecture 5

Life on Earth 

• Nervous systems represent a very new development. 

• Simple neural nets about 700 million years ago. 

• Advanced brains, such as the human brain, are more recent still. 

Animals Without Neurons! Independent Effectors Sea Sponges (phylum Porifera) • The body has tiny pores. Water flows through the pores into a central cavity and then back out a hole on top. This is how they extract nutrients from the environment. • How do they do this?

Independent Effectors “Myocytes” • Also called “myocytes,” independent effectors are cells that produce a motor response when directly stimulated—without the intervention of neurons • Myocytes have contractility—they can shorten and thus do work • They’re arranged around the pores on the sponges surface • When certain chemicals (e.g., nutrients) come into contact with the outer surface of the sponge, the myocytes can work to take in more water 

The First Nervous Systems Hydra’s Body and Behavior • Jellyfish, corals, sea anemones, and hydra are some of the simplest animals with a nervous system. • Phylum Cnidaria. • Hydra’s tentacles have sensorimotor neurons, which can act as nutrient detectors (e.g., to initiate feeding) How does hydra do that?

“Sensorimotor neuron” because it detects stimuli and projects directly to effector cells. Independent effectors (Ei , yellow) act alone. Receptors may occur anywhere on the cell’s surface. Responses are relatively insensitive, slow, long-lasting, and individualized. a) Input from a sensory neuron (SM) can provide input to and activate a set of “independent effectors” (E1,2)almost simultaneously. Branches (axons) from more than one sensory neuron may end up on one effector (convergence). And, one sensory neuron may innervate more than one effector (divergence). Sensory neurons afford more sensitivity, speed, amplification, and coordination. They also allow for highly localized distributions patterns within the animal’s body.

No nervous system “One-layer” nervous system “Two-layer” nervous system “Three-layer” nervous system Interneurons lie between sensory and motor neurons. In this example, the axon of a sensory neuron provides excitatory (+) input to a motor neuron and an inhibitory (-) interneuron. Because both motor neurons provide excitatory (+) input to an effector, a stimulus swill lead to contraction in Effector 1 and relaxation in Effector 2.

E.g. Stretch Reflex

“Three-layer” nervous system Basic cellular physiology is similar from hydra to humans. What changes dramatically through the course of evolution is the arrangement of the three fundamental neuron types into more and more highly organized systems or networks.

Why Did the Human Brain Evolve So Quickly? Australopithecus Homo erectus Homo sapiens * 20 Extinct Hominins Lucy First appeared about 4 million years ago. Disappeared about 2 million years ago. • Bipedalism • Basic tools • Ancestor of genus Homo First appeared about 2 million years ago. Disappeared about 140,000 years ago. • Used fire • Stone tools Humans first appeared about 250,000 years ago. Only began using complex technology like fishhooks, bows, sewing needles only about 65,000 years ago—the Great Leap Forward or “Cognitive Revolution” The Cognitive Revolution wasn’t caused by a “genetic leap” –we didn’t suddenly develop smarter brains. A series of environmental, social, and cultural pressures drove humans to fully express their cognitive abilities.

Sumer (3100 to 2000 BCE) The first known civilization …about 270,000 years after humans first appeared! Ancient Egypt Emerged roughly at the same time Indus Valley (India and Pakistan) (2600 BCE to 1900 BCE) Ancient China Early Dynasties (~2100 BCE) Roman Empire (27 BCE to AD395)

Some Evolutionary Terminology Artificial selection: The selective breeding and domestication by humans of other species, e.g., breeding dairy cattle for maximization of milk yield. Natural selection: Changes in the gene pool of a species due to differences in the ability of individuals to survive and reproduce. Genetic variation  variation in survival and reproduction  genes of survivors and reproducers get passed on Sometimes, “natural selection” covers differences in survival ability only. Sexual selection: Evolutionary change due to heritable differences in the ability to attract sexual partners, repel sexual rivals, or do anything else that promotes reproduction. 

The Social Brain Hypothesis (Robin Dunbar, 2003) The cognitive demands of living in complexly bonded social groups selected for increases in executive brain. * 26 Humans have neocortices that are disproportionately large compared to their bodies 

The Mating Mind Hypothesis (Miller, 2000) • The demands of attracting and evaluating sexual mates drove the evolution of “higher” brain abilities. • Our ancestors' cognitive abilities, such as creativity, humor, and musical talent, were not only useful for problem-solving and survival but also served as signals of genetic quality and mate attractiveness. * 27 • Early humans developed a preference for these traits in their sexual partners, which led to the evolution of more intelligent and creative individuals over time.

Mammals Share Main Brain Structures

Some More Terminology Homology is a term used to indicate genetic relatedness of bodily structures • E.g., Human arms and bird wings are homologous because they both arise from the genetic information that controls forelimb development. Analogy is a term used to indicate the functional similarity of bodily structures that do not share common genetic inheritance • E.g., The wings of birds and bees are analogous because they’re both used for flying. • “Convergent” evolution • Similar selection pressures lead to similar adaptations in distantly related organisms 

Exercise Caution Example Using the Visual Pathways Tree shrew mammal Galago primate Striedter (2005). Principles of Brain Evolution. * 31 Frontally placed eyes and bilateral retino-collicular pathways  better depth perception

Nurture Affects Gene Expression The pups of nurturant (high) mothers showed high levels of glucocorticoid receptors (GR; shown in red) in the hippocampus regardless of whether they were handled (H) or not handled (NH). However, pups of non-nurturant (low) mothers showed nearly normal levels of gene expression when handled, but reduced levels when not handled. Maternal licking and grooming stimulated epigenetic processes  Greater gene expression of GR  Greater tolerance to stress Aside: Cortisol is a stress hormone; GR in the hippocampus “measure” cortisol in the blood and turn off the body’s stress mechanism (negative feedback loop). Fewer receptors means prolonged stress response.  

Medical Application GBM and MGMT Status • Glioblastoma multiforme (GBM) is a primary brain tumor that arises from astrocytes. Median overall survival is less than 15 months. • Standard of care includes: (1) tumor resection; (2) chemoradiation with temozolomide; (3) adjuvant chemotherapy with temozolomide • The O(6)-methylguanine-DNA methyltransferase or MGMT gene encodes a DNA repair enzyme that can stop the effects of certain toxins. However, it can also reduce the effectiveness of chemotherapy drugs such as temozolamide. • MGMT methylation generally is generally associated with better outcomes.

The Results of a Recent Study in the Elderly. Patients with unmethylated MGMT had a lower survival rate than those with methylated MGMT. Methylation stops DNA from producing protein which means that the protein that fights chemo is not present.

Behavioral Genetics and Heritability • Behavioral genetics = the study of genetic and environmental influences on behavior • Heritability = the contribution of genetics to the variation of a trait observed in a population i.e., How are individual differences explained by genetic differences? • Always refers to a population, NOT to individuals • The heritability for having a heart is zero (because we all have one, no variance) • Cannot be assessed without taking the environment into account • E.g., In the USA, height is very heritable, 90% of the variation can be attributed to genetic differences. • But, if you’re a 6 foot tall American, it doesn’t mean that 5.4 feet of your height is produced by your genes and the remaining 0.6 feet is produced by the environment.

Behavioral Genetics and Heritability Thinking About the Role of Environments In a country with greater social disparities in nutrition, height would be less heritable  greater role for the environment In a country with zero social disparities in nutrition, height would be 100% heritable  no role for the environment Ridley (2003, p. 262): “Ironically, the more egalitarian a society is, the more innate factors will matter. In a world where everybody gets the same food, the heritability of height and weight will be high; in a world where some live in luxury and others starve, the heritability of height and weight will be low. If everyone gets the same education, the best jobs will go to those with the most native [genetic] talent.”

The Heritability of Personality Traits 68 • What are personality traits? • Traits are stable patterns of behavior, motivation, emotion, and cognition that are not specific to a particular social setting or culture. • Universal dimensions of individual variation • Dispositional tendencies  how people tend to respond to specific classes of stimuli • Relatively stable across the lifespan. • The “Big Five” personality traits

Two common perspectives on traits. Traits are behavioral dispositions or they are neurophysiological substrates. 

Twin Studies and The Heritability Quotient. Monozygotic (identical) twins = 100% genetically similar, fertilized from the same egg. Dizygotic (fraternal) twins = 50% genetically similar, fertilized from different eggs. Heritability Quotient: heritability = 2 (rMZ - rDZ). How heritable are the big 5? Based on self reports 40-60%. Based on multiple raters: 60-80%.

Components of Variation in Personality Traits. Shared environment Environmental influences that operate to make family members alike • Parenting style • SES • Religion • Home nutrition. Nonshared environment Environmental influences that operate to make family members unalike • Different friends • Different school experiences • Parenting differences • Random events. The non-shared environment generally accounts for more variance in personality traits than the shared environment.

Genes Shape the Environment Helps explain why the heritability of some traits increases with age • Evocative influences: People elicit responses from their environment that may reinforce pre-existing traits • A naturally outgoing and sociable child may elicit more positive social interactions from others. Teachers may encourage them to take leadership roles, and peers may seek them out for friendships, reinforcing their extraversion over time. • Passive influences: Parents and family may select and shape environments in ways that are like their own genetic endowments; children are genetically related to their parents; thus, indirectly, parents and family may create environments that reinforce the child’s pre-existing traits • A child born to highly intelligent parents is likely to inherit genes for high cognitive ability (genetic influence). Additionally, their parents may fill the house with books, engage in intellectual discussions, and value education (environmental influence), reinforcing the child’s natural intellectual curiosity. • Active influences: people search for and select environments that fit their genotype • A musically gifted teenager may seek out a music club, take up piano lessons, or choose to attend a specialized arts school. Their genetic predisposition for musical ability leads them to actively select an environment that further enhances their talent.

Lecture 6

One week after conception… The zygote arrives at the uterus At this point, three layers of cells can be distinguished—the trilaminar embryonic disc • Ectoderm: outer layer that develops into the nervous system, skin, and hair. • Mesoderm: middle layer that develops into connective tissues, muscles, blood vessels, bone, and urogenital systems. • Endoderm: develops into internal organs 

Stage 6: Myelination • Myelination starts in the spinal cord and moves rostrally • First observed in cranial and spinal nerves around 23 weeks after conception • Peak rate of myelination occurs around 3 years of age. • The last area to be myelinated is the prefrontal cortex, around 25 years of age! * Why does this matter?

Healthy Brain Aging • Educational attainment and mental activity are negatively associated with Alzheimer’s risk • Brain health is associated with • general health and physical fitness • being married • social support • religion • depression (negative association) • Multiple reserve hypothesis. Quality of life in later adulthood depends on the resources that people have to offset age-related declines. According to the Alzheimer's Association, the risk of developing Alzheimer's disease doubles approximately every five years after age 65. By age 85, the risk of developing Alzheimer's disease is about one in three.

Lecture 7

Cybernetic Control The Negative Feedback Loop 6 Negative feedback loops are composed of four elements: (a) A set point which the system tries to maintain. (b) An input function, that reads to current status of the system. (c) A comparator that detects discrepancies between set points and input values. (d) An output function that affects the environment to reduce the discrepancy

A “type” of warm-sensitive neuron: Receptors are known as TRPV1 receptors, Transient Receptor Potential Vanilloid 1. They’re found in the POA. TRPV1 receptors are sensitive to high temperatures and are also embedded in the mouth! Capsaicin, the active component in chili peppers that makes them spicy, produces the sensation of heat by activating specific receptors in the sensory neurons.