Ch. 4 Flashcards
Chapter 4 of The Mind's Machine
Ectoderm
The outer cellular layer of the developing embryo, giving rise to the skin and the nervous system
At a week, what does the human embryo show?
three distinct cell layers which are the beginnings of all the tissues of the body.
Neural Tube
An embryonic structure with subdivisions that correspond to the future brain and spinal cord. Cells in the neural crest will migrate to form the peripheral nervous system
At the anterior part of the neural tube in an embryo, what three subdivisions become apparent?
corresponding to the future forebrain (cortical regions, thalamus, and hypothalamus), midbrain, and hindbrain (cerebellum, pons, and medulla)
Forebrain
The front division of the neural tube and brain, which in a mature vertebrate contains the cerebral hemispheres, the thalamus, and the hypothalamus
When does a developing human move from being called an embryo to a fetus?
It is called an embryo during the first 10 weeks after fertilization and a fetus thereafter
Embryo
earliest stage in a developing animal
fetus
A developing individual after the embryo stage
What are the six distinct stages of development for the nervous system?
- neurogenesis- the mitotic division of nonneuronal cells to produce neurons
- Cell migration- the massive movement of nerve cells or their precursors to establish distinct nerve cell populations (nuclei in the CNS, layers of the cerebral cortex, and so on)
- Cell differentiation- the refining of cells into distinctive types of neurons or glial cells
- Synaptogenesis- the establishment of synaptic connections as axons and dendrites grow
- Neuronal cell death- the selective death of many nerve cells that begins well before birth
- Synapse rearrangement- the loss of some synapses and the development of others, to refine synaptic connections, which extends throughout our lifespan
Neurogenesis
The mitotic division of nonneuronal cells to produce neurons
Mitosis
The process of division of somatic cells that involves duplication of DNA
Where does mitosis occur for neurons?
The Ventricular Zone– inside the neural tube
Cell Migration
The movement of cells from site of origin to final location
Once cells reach their destination after mitosis in the ventricular zone, what happens?
alter their gene expression
Gene Expression
The process by which a cell makes an mRNA transcript of a particular gene; the turning on or off of specific genes
Cell Differentiation
The development stage in which cells acquire distinctive characteristics, such as those of neurons, as a result of expressing particular genes
After the cells take on the characteristics of neurons, what happens?
they begin making synaptic connections with one another
Synaptogenesis
The establishment of synaptic connections as axons and dendrites grow
Cell-Cell Interactions
The general process during development in which one cell affects the differentiation of other, usually neighboring, cells
Stem Cells
A cell that is undifferentiated and therefore can take on the fate of any cell that a donor organism can produce
The postnatal increase of human brain weight is due to what?
growth in the size of neurons, branching of dendrites, elaboration of synapses, increase in myelin, and addition of glial cells
Adult Neurogenesis
The creation of new neurons in the brain of an adult
Cell Death
Also called apoptosis. The developmental process during which “surplus” cells die
Neurotrophic Factors
A target-derived chemical that acts as if it “feeds” certain neurons to help them survive.
Synapse Rearrangement
The loss of some synapses and the development of others
Fragile X Syndrome
A condition that is a frequent cause of inherited intellectual disability and is produced by a fragile site on the X chromosomes that seems prone to breaking because the DNA there is unstable. Results in too many synapses
Intellectual Disability
A disability characterized by significant limitations in intellectual functioning and adaptive behavior
Amblyopia
Reduced visual acuity of one eye that is not caused by optical or retinal impairments
Binocular Deprivation
Depriving both eyes of form vision, as by sealing the eyelids
In order to achieve normal vision in adulthood, what has to happen in childhood?
realignment of the eyes (if the child was born with misalignment in the eyes)
What happens to the structure in the visual cortical neurons as a result of binocular deprivation?
loss of dendritic spines and a reduction in synapses. After several weeks during development, the animal will be blind
Sensitive Period
Also called critical period. The period during development in which an organism can be permanently altered by a particular experience or treatment
Monocular Deprivation
Depriving one eye of light during the developmental sensitive period
What are the effects of monocular deprivation during developmental sensitive period?
produces profound structural and functional changes in the thalamus and visual cortex and permanently impairs vision in the deprived eye
Ocular Dominance Histogram
A graph that portrays the strength of response of a brain neuron to stimuli presented to either the left eye or the right eye
Hebbian Synapses
A synapse that is strengthened when it successfully drives the postsynaptic cell. These cells grow stronger at the expense of ineffective synapses. Other definition: synapses that grow stronger or weaker depending on their effectiveness in driving their target cell
How do genes influence the form, arrangements, and connections of the developing brain?
Genes direct the production of every protein the cell can make. An individual who has inherited an altered gene will make an altered protein, which will affect every cell that uses that protein.
Genotype
All the genetic information that one specific individual has inherited
Phenotype
The sum of an individual’s anatomical, physiological, and behavioral characteristics
How are genotypes and phenotypes different?
Your genotype was determined at the moment of fertilization and remains the same throughout your life. However, the phenotype changes constantly, as you grow up and grow old. Phenotype is determined by the interaction of genotype and extrinsic factors, including experience
Phenylketonuria (PKU)
An inherited disorder in which the absence of an enzyme leads to a toxic buildup of phenylalanine metabolites (amino acid present in many foods), causing intellectual disability
How can PKU be prevented?
reducing phenylalanine in the diet
Why is interaction of genes and the environment important in PKU?
the dysfunctional gene causes intellectual disability only in the presence of dietary phenylalanine. Reducing phenylalanine consumption reduces or prevents this effect of the gene
Clones
Asexually produced organisms that are genetically identical
What is found in the behavior and temperament of clones?
Genetically identical clones show as much variation in behavior and temperament as do normal siblings
Epigenetics
The study of factors that affect gene expression without making any changes in the nucleotide sequence of the genes themselves
What does it mean when a cell has expressed a gene?
When the cell uses a particular gene to make a particular protein
What results in the variation of brain development?
The same protein is produced in gene expression, but the amount of protein can vary considerably, which leads to variation in brain development
Methylation
A chemical modification of DNA that does not affect the nucleotide sequence of a gene but makes that gene less likely to be expressed
How can mothering affect gene expression in rodents?
Rodent pups provided with inattentive mothers, or subjected to interruptions in maternal care, secrete more glucocorticoids in response to stress as adults. poor maternal care produces this heightened stress hormone response by inducing methylation of the glucocorticoid receptor gene in the brain, making the pups hyperresponsive to stress for the rest of their lives
Starting at age 40, what happens to the brain?
Human brain volume steadily declines
Memory impairment correlates with what during aging?
hippocampal shrinkage
Alzheimer’s Disease
A form of dementia that may appear in middle age but is more frequent among the aged
Dementia
Drastic failure of cognitive ability, including memory failure and disorientation
What reduces the risk of alzheimer’s disease?
remaining physically and mentally active
What happens in the brain that correlates with alzheimer’s?
-cortical atrophy (shrinkage) in the frontal, temporal, and parietal areas
-reduction of metabolism in posterior parietal cortex and some portions of the temporal lobe
-amyloid plaques appear in the cortex, hippocampus, and associated limbic system sites. Plaques are formed by the buildup of substance called beta-amyloid
-Neurofibrillary tangles
-lose of neurons in the basal forebrain, which make the transmitter acetylcholine (ACh)
Amyloid Plaques
A small area of the brain that has abnormal cellular and chemical patterns
Beta-amyloid
A protein that accumulates in amyloid plaques in Alzheimer’s disease
Neurofibrillary Tangles
An abnormal whorl of neurofilaments that from a tangled array inside the cell
