Neuropsychology- Lectures 9-12 Flashcards
What is Evolution?
“Biological evolution is concerned with inherited changes in populations of organisms over time leading to differences among them.”
Or, change over time.
Darwin’s Theory of Evolution
Two central concepts:
Adaptation – the ability to adapt to changing environments.
Natural selection – process by which some species’ variations are passed on and others are not.
The Four Principals of Darwin’s Theory.
Plant and animal species are dynamic over time (change is inevitable)
Evolution is gradual and continuous (environment > species modification)
But, sudden dramatic changes to the environment can challenge species’ ability to adapt
Natural selection occurs with and without environmental change
Universal common ancestry
Survival of the fittest
Survival and Reproduction Process.
Fittest Means:
Fittest’ can refer to different traits and behaviours in different species.
Variation and competition influence reproductive success.
Variation
Variability in traits (e.g., colouration).
Genetic variation – mutations in DNA.
Competition
Overproduction of offspring – not all will survive/reach maturity.
The environment cannot support unlimited population growth.
Struggle for survival:
Competition between and within species for resources, predation, climate.
Selection – traits are passed on.
Universal Common Ancestry
“I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed”
(Darwin, 1859, p. 484)
Evidence for universal common ancestry:
Brown et al. (2001):
Focused on 45 species of archaea, bacteria and eukaryotes
Identified 23 proteins conserved in all 45 species
Constructed a universal tree that provided a link between the three domains of life
Inferred from the tree = one species providing the genetic code for all later forms of life
Mendel and his pea plant experiments.
Dominant and recessive genes.
What is a gene?
DNA = molecule with a double helix Gene = section of DNA (~200 – 2 million base pair) Codon = 3 x nucleobase (unit of DNA code)
Gene Expression: From Genes to Proteins
Transcription: segment of DNA is copied into messenger ribonucleic acid (mRNA)
Translation: a process of protein synthesis
Transfer RNA (tRNA): carries an amino acid to the ribosome
Mendel Experiments
Gene for flower colour: 2 alternative versions.
An alternative version of a gene: Allele (inherit from each parent).
Gene for flower colour has a specific location on the chromosome.
If the alleles at a locus differ: Dominant allele will be expressed.
Mendel and his Laws of Heredity
The Law of Segregation:
Each inherited trait is defined by a gene pair.
Offspring inherit one genetic allele from each parent when sex cells unite in fertilization.
The Law of Independent Assortment:
Genes for different traits are sorted separately from one another.
Inheritance of one trait is not dependent on the inheritance of another.
The Law of Dominance:
If the alleles at a locus differ, the dominant allele will be expressed.
Evolution: Modern Synthesis (Huxley, 1942)
Darwin + Mendel = The Genetical Theory of Natural Selection (Fisher, 1918, cited in Moran & Smith, 1966; 1930)
Variation and competition → survival and reproduction
Genetic mutations = essential for natural selection
Genetic mutation:
Majority due to error in DNA replication.
Epigenetics: Study of Heritable Phenotypic Change
Epigenome:
Chemical compounds that can regulate the activity of genes (turn off / on)
Not part of the DNA sequence – attached or added to DNA.
Culture and Evolution: Role of Social Learning
Culture
Adaptation to the environment:
E.g., hunting strategies in killer whales (ecotype)
Gene variants linked with different strategies (Foote et al., 2016)
Can help survival and, therefore, the ability to reproduce
Behaviours learnt → over time → selection for these behaviours
Structure of Grey Matter
Cortical layers are regionally specific. Primary sensory cortex, association cortex and primary motor cortex.
Oligodendrocytes
Send projections that wrap axons with myelin to speed up signal conduction.
Microglia
Immune cells of the brain. Monitor cells for damage and clearance of cell debris.
Astrocytes
Monitor neural activity along axons at synapses and will signal to blood vessels to dilate blood vessels to increase blood flow to provide energy to the neurons.
How does the brain work?
Electrical activity allows for communication between neurons.
The brain is composed of 86 billion neuron.
What is an action potential?
A movement of electrical activity down the Axon.
- Membrane becomes depolarised
- Action potential and repolarisation
- Refractory period
Action potential: All or nothing response
Excitatory postsynaptic potential (EPSP)
EPSP ↑ likelihood of an AP
Positively charged ions flow into cell
Additive effect = depolarisation
Inhibitory postsynaptic potential (IPSP) IPSP ↓ likelihood of an AP Negatively charged ions flow into cell Or, positively charged ions flow out of cell Additive effect = hyperpolarisation
Glutamate and GABA
Cortical excitability:
Balance between excitation and inhibition
Glutamate (glutamic acid)
Major excitatory NT
Gamma-aminobutyric acid (GABA)
Major inhibitory NT (brain and spinal cord)
Linked with seizures:
↑ glutamate or
↓GABA or GABA receptor dysfunction
= neural hyperexcitability > seizures
But, synchronicity of neuronal populations also needed
Acetylcholine
Acetylcholine synthesis:
Acetylcholine (ACh) is made from choline and coenzyme acetyl (CoA)
Synaptic cleft – ACh is broken down by the enzyme acetylcholinesterase
Choline is transported back into the axon terminal and used to make more ACh
Cholinergic pathways in the brain:
Linked with arousal, attention, memory
↑ sensory perception on waking
Damage = memory deficits, AD
Dopamine
Dopamine synthesis:
L-Tyrosine (amino-acid) converted into L-DOPA converted to dopamine
Synaptic cleft – enzyme degradation monoamine oxidase (MAO), catechol-O-methyl transferase (COMT) > homovanillic acid (HVA)
Dopamine is transported back into the axon terminal via dopamine transporters (DAT)
Dopaminergic pathways in the brain:
Linked with reward motivated behaviour
↑Involved in motor control
Role in addiction, PD and ADHD
