Biological Psychology I: Genetics, Nervous System Cells, and Neurotransmission

Gene Editing

Psychological Enhancements and Epigenetics

Gene editing refers to the deliberate modification of genetic material to alter traits, including psychological characteristics. Epigenetics studies how environmental factors can influence gene expression without changing the DNA sequence itself.

• DNA, Genes, and Chromosomes: DNA is the molecule that carries genetic information. Genes are segments of DNA that code for proteins, and chromosomes are structures that organize and contain genes within the cell nucleus.

• Genotype: The unique set of genes that comprises an individual's genetic code.

• Phenotype: The observable physical traits and behavioral characteristics produced from the genotype.

• Example: Intelligence is a phenotype influenced by both genetic and environmental factors.

Twin Studies

Behavioural Genetics: Genes and Environment Influence on Behaviour

Twin studies are a key method in behavioral genetics, used to disentangle the effects of genes and environment on psychological traits.

• Monozygotic Twins: Identical twins, originating from a single egg (ovum) that splits and is fertilized by one sperm.

• Dizygotic Twins: Fraternal twins, originating from two separate eggs fertilized by two sperm.

• Heritability: The degree to which genetic differences contribute to individual differences in behavior or traits within a population.

Trait	Heritability (3-year-olds)	Heritability (12-year-olds)
Depression & Anxiety	0.76	0.48

Additional info: Heritability values range from 0 to 1, with higher values indicating greater genetic influence.

Adoption Studies

Nature vs. Nurture: Biological and Adoptive Parents

Adoption studies compare traits in adopted children to those of their biological and adoptive parents to assess the influence of genetics (nature) and environment (nurture).

• Intelligence: Studies suggest that both biological and adoptive parents can influence intelligence, highlighting the role of both genetic and environmental factors.

• Longitudinal Studies: Research that follows the same individuals over time to observe changes and development (e.g., Seven Up Series).

Darwin and Natural Selection

Evolutionary Theory and Psychological Traits

Charles Darwin's theory of natural selection explains how favorable traits become more common in a population over generations, influencing both physical and psychological characteristics.

• Key Concepts:

  • Fossils of extinct species provide evidence for evolution.

  • Differences among individuals of the same species are the basis for natural selection.

  • Natural selection favors traits that enhance survival and reproduction.

  • Evolution is defined as a change in the frequency of genes occurring in a population over time.

• Human Brain Evolution:

  • Homo sapiens vs. ancestors: Homo sapiens have a larger frontal lobe and more convolutions in the brain, associated with advanced cognitive abilities.

Cells of the Nervous System and Neurotransmitters

Neurons

Neurons are the primary cells of the nervous system responsible for transmitting information through electrical and chemical signals.

• Structure: Neurons consist of dendrites (receive signals), a cell body (soma), and an axon (transmits signals).

• Function: Neurons communicate via action potentials and synaptic transmission.

Glia

Glial cells support and protect neurons, playing essential roles in nervous system function.

• Types of Glia:

  • Astrocytes: Maintain the blood-brain barrier and provide nutrients to neurons.

  • Microglia: Act as immune cells within the brain.

  • Myelin-producing cells: Oligodendrocytes (CNS) and Schwann cells (PNS) form myelin sheaths that insulate axons and speed up signal transmission.

Neuronal Communication

Regions and Steps of Signal Transmission

Neuronal communication involves the transmission of signals through distinct regions and processes.

1. Input (chemical): Dendrites receive chemical signals from other neurons.

2. Integration (electrical): The cell body integrates incoming signals to determine if an action potential will be generated.

3. Conduction (electrical): The action potential travels down the axon.

4. Output (chemical): Neurotransmitters are released at the synapse to communicate with the next cell.

Resting and Action Potentials

Electrical Properties of Neurons

Neurons maintain a resting membrane potential and generate action potentials to transmit information.

• Resting Membrane Potential: The difference in electrical charge across the neuron's membrane at rest, typically around $-70\text{mV}$.

• Ion Distribution:

  • Intracellular: High concentration of potassium ions (K+), negative charge.

  • Extracellular: High concentration of sodium ions (Na+), positive charge.

• Action Potential: A rapid change in membrane potential that occurs when the threshold (about $-55\text{mV}$) is reached.

Key Phases of Action Potential:

1. Depolarization: Na+ channels open, Na+ enters the cell, membrane potential becomes positive.

2. Repolarization: K+ channels open, K+ leaves the cell, membrane potential returns to negative.

3. Hyperpolarization: Membrane potential temporarily becomes more negative than resting potential.

Equation for Resting Membrane Potential:

$V_{m} = E_{K} = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$

Additional info: The Nernst equation above describes the equilibrium potential for potassium ions, a major contributor to the resting membrane potential.

Synapses and Neurotransmitters

Chemical Communication Between Neurons

Synapses are specialized junctions where neurons communicate with each other using neurotransmitters.

• Presynaptic Neuron: Releases neurotransmitters into the synaptic cleft.

• Postsynaptic Neuron: Receives neurotransmitters, leading to changes in its membrane potential.

• Neurotransmitters: Chemical messengers such as dopamine, serotonin, and acetylcholine that influence mood, cognition, and behavior.

Additional info: Neurotransmitter release is triggered by the arrival of an action potential at the axon terminal, causing vesicles to fuse with the membrane and release their contents.