Universal Genetic Code: The system by which genetic information is interpreted in all living organisms. All living organisms use the same genetic code to translate genetic information in DNA and RNA into proteins.
Genes and Codons
Codon: A sequence of three nucleotide bases in a DNA or RNA strand; each codon specifies an amino acid. Genes provide instructions for making specific proteins, with gene expression leading to functional proteins in cells.
Example: DNA makes a copy in RNA, which is then translated into proteins at ribosomes.
Genotype vs. Phenotype
Genotype: The genetic makeup (alleles) of an organism, consisting of two complete copies of the human genome in each cell.
Phenotype: The observable characteristics or traits of an organism that result from the interaction between the genotype and the environment.
Example: BPA in pregnant mice affecting the coat color of offspring illustrates how environment can influence phenotype based on genotype.
Functions of Genes
Genes primarily code for proteins but can also have other functions, like coding for transport RNA (tRNA) and ribosomal RNA (rRNA).
Revised Definition: A gene is a nucleic acid sequence transcribed into an RNA strand with biological function.
Heritability is influenced by genetic variability affecting behaviors, where environment stability or change can lower or increase heritability estimates.
Synaptic Signal Transmission
Electrical vs. Chemical Synapses:
Electrical Synapses: Utilize gap junctions, allowing ions/molecules to pass bidirectionally.
Chemical Synapses: Use neurotransmitter vesicles that bind to post-synaptic receptors, facilitating signal modulation.
Neurons and Ions
Neurons: Functional units of the nervous system, transmitting signals through electrical impulses via ions.
Resting Membrane Potential: Approximately -65 mV, maintained by Na+/K+ pump and ion permeability.
Action Potential Phases
Depolarization: Triggered when the cell membrane reaches a threshold, causing Na+ channels to open, leading to rapid membrane potential change.
Repolarization: K+ channels open, bringing the potential back to resting state.
Hyperpolarization: Membrane potential drops below resting level, making it difficult to trigger another action potential.
Myelin Role
Myelin insulates axons, facilitating rapid signal transmission and reducing energy consumption. Damage to myelin (e.g., in multiple sclerosis) leads to neurological impairments.
Synaptic Integration
Involves summation of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) to determine if an action potential will occur in the post-synaptic neuron.
Lateral Inhibition
Mechanism that creates contrast in sensory perception by inhibiting nearby neurons, enhancing edge detection in visual images.
Olfactory System
Olfactory Epithelium: Contains receptor cells for smell, supporting cells for structure, and basal cells for regeneration.
Olfactory Processing: Involves binding of odor molecules to receptors, leading to action potentials sent through olfactory pathways to the brain.
Auditory System
Sound processing involves the outer ear collecting sound waves, middle ear amplifying vibrations, and inner ear converting them to neural signals.
Somatosensory System
The structure and function of tactile receptors illustrate how sensory systems encode stimuli, mapping body parts to specific cortical areas (homunculus).
Memory and Learning
Memory Phases: Encoding, storage, retrieval, each involving synaptic plasticity, leading to long-term changes in neuron structure.
Motivation and Emotion
Hypothalamus: Regulates motivated behavior and homeostasis, influencing hunger, thirst, and sexual behavior due to its connections with the endocrine system.
Sleep and Circadian Rhythms
Sleep stages and associated brain wave patterns can be monitored with EEG, involving cyclical transitions between REM and non-REM stages.