week 5 development of nervous system and genetics Flashcards
Understand the terms ‘DNA’, ‘gene’, ‘chromosome’, ‘RNA’, ‘amino acid’ and ‘protein’
DNA-deoxyribonucleic acid. Double strands of which form genes.
Gene-unit of genetic material. previously thought to be contained a by a discrete loci, but now it seems that combinations of loci, even on different chromosomes, might be responsible for multiple genes together influencing the expression of a genetic characteristic. A gene codes for a protein.
Chromososme: unit of genetic material. Each chromososme is paired. in the human there are 46 chromosomes, 23 pairs. Pairs look similiar (or ought to) in shape to each other, except for the sex chromosomes of X and Y (or XX in female) which are paired together.
RNA-is ribonucleic acid, which is single stranded. Dna strands separate and act as the template for messenger RNA.
Amino acid-an organic compound which includes amino and comboxylic acid groups. Many types, the alpha type of amino acids is what is coded for by the genetic code. In the genetic code, each triplet of bases, determines one amino acid. Amino acids then together form proteins.
Protein-nitrogenous organic compounds made up of long chains of amino acids.
Understand the process whereby DNA leads to the production of proteins.
- A gene is on.
- Rna polymerase separates out the double strands of DNA.
- A strand of messenger RNA is made alongside the DNA. (transcription)
4.mRNA strand is then processed, with pieces added or removed - completed mRNA moves out of nucleus and into cytoplasm.
6.Ribosomes bind to mRNA - Transfer RNA brings in corresponding amino acids, one amino acid per triple base of mRNA.
- Last amino acid added, chain separates from mRNA and chain folds and is a protein.
Understand (in simple terms) how genes can affect behaviour.
Genes cause proteins to be made. Such proteins might influence appearance, cognition, physical prowess etc and these characteristics, along with environmental interactions, can influence behaviour.
Understand the concept of Epigenetics and how histones are involved.
Epigenetics-studies how the expression of genes change. ie under environmental influence, genes might change from “off” to “on” or vice versa. This is NOT the same as a permanent mutational change, although the change can sometimes be passed to offspring.
Whilst our genes are the same from one cell to the next, which ones are most active etc differs for different cells (different body parts require different proteins). Learning can also change neural synapses and also gene activity. Drug addictions and sole isolation can also alter gene expression.
Histones are proteins which actually have the dna strands wound around /amongst them. Sometimes various chemical groups might attach to the histones, which then alters the histone “grip” on the DNA which may then alter it’s shape and hence which genes are on or off. An acetyl group added to histones usually results in loosened dna and facilitation of gene expression. In the beginning (“promoter”) section of a gene, adding methyl usually turns off a gene and removing it turns it on. eg Severe traumatic experiences early in childhood decreases methylation of many brain genes, which increases later risk of depression and or ptsd.
Understand the terms ‘Sex-linked gene’, ‘autosomal gene’, ‘sex-limited gene’, ‘dominant gene’ and ‘recessive gene’.
Sex-linked genes-those located on the X or Y chromosome.
Autosomal gene; those located on any chromosome EXCEPT the X or Y.
Sex-limited gene;gene present in both sexes but has greater activity in one sex. eg testosterone greater activity in males.
Dominant gene=characteristic of that gene is strongly displayed in both homozygote or heterozygote.
Recessive gene-characteristic of gene shown only on homozygote.
Understand the terms ‘homozygous’ and ‘heterozygous’.
Homozygous= have same gene on both chromosomes (in one individual), for a particular characteristic/loci
Heterozygous= have different genes on both chromosomes pertaining to a particular characteristic/loci, within the same individual.
Be able to determine likely outcomes for off-spring given information about genes carried by the parents.
7
After completing your study of the text you should be able to understand (in simple terms) the major changes in gross structure that occur during the embryonic development of the human brain.
Homeobox genes control the expression of other genes and anatomical development. Deficits in homeobox genes in insects might cause a leg eg to grow where an antenna should be. In humans, many deficits of such genes have been linked to mental retardation and or physical deformity.
CNS starts to form at 2 weeks. dorsal surface thickens into neural tube.
Hindbrain, midbrain and forebrain form and spinal cord and ventricles.
At 7.5 weeks first muscle movements occur.
Early infancy primary sensory cortex areas mature before other cortical areas.
Many cortical changes during first few years of life.
Name and Understand the five distinct stages in the development of neurons.
- Proliferation-production of new cells. Stem cells arise from the ventricles of the brain and divide. Might remain there as stem cells able to divide later, or might migrate to other parts of the cns and differentiate.
- Migration-stems cells migrate and become neurons or glia. Most neurons have forme by 28 weeks of gestation and premature birth prior to this inhibits neural development. Migration is guided by immunoglobulins and chemokines.
3.Differentiation-cells differentiate and dendrires/axons/syapses form. - Synaptogenesis-formation of synapses. This process begins long before birth but the process actually continues throughout life. (so technically could argue is the last stage of neural develpment)
- Myelination-glia produces insulating myelin around many axons. Firstly occurs in spinal cord, then in hindbrain, midbrain and lastly forebrain. This process also continues for decades due to learning new motor skills.
Understand the chemical and physiological factors that determine the survival of a neuron.
Axons find their targets through a process of following specific chemical gradients. (the preferences/gradients differ for different neurons).
In this process, many synapses are formed with many cells, but in time, the “best”/”correct” synapses are reinforced and others eliminated. This process is called Neural Darwinism.
The sympathetic nervous system initially has more neurons than required. Muscle/neuron synapses form and the muscle releases Nerve Growth Factor. Axons which do not receive NGF die via apoptosis. (apoptosis involves parcelling off of the cell’s components and re-cycling them).
Within the CNS many neurons normally die off also, as a normal part of maturation. It is speculated that within the brain, neuron survival requires Brain-derived Neurotrophic Factor and synapses with other neurons.
Understand the processes that appear to be involved in neuronal differentiation.
Neuronal differentiation seems to be determined by timeframe of development and also location anatomically of the neuron. Transplanting neurons early enough cause them to develop into neurons specific to the new location, whereas fractionally later, they are a blend of old and new location characteristics.
Understand how Sperry’s research on frogs supports the chemoaffinity hypothesis of synaptogenesis.
Sperry surgically cut the optic nerve and rotated an eyeball in a newt. Newt’s have the ability to regenerate axons. The axons connected correctly back to their original locations. It was shown that there were different chemical gradients in the dorsal cf the ventral technum, and so thought the axons must be following the chemical gradients.(p121)
Outline evidence that adult brains can develop new neurons, highlighting the significance of stem cells / primitive neurons in this process.
By measuring radioactive carbon isotopes, it has been determined that in humans, most brain cells were present at birth. Some new neurons (maybe 2%)do form in the hippocampus and basal ganglia. These new neurons tend not to be those with very long axons though.
Consider the implication of synaptic elimination in brain development (sometimes less is more when it comes to brain ability).
Improves efficiency and leaves space for required synapses.
Be familiar with how some factors (such as alcohol) can adversely affect brain development.
Many in utero factors can impact neuronal development. Typically offspring of mother’s who had alcohol during pregnancy, have thinner frontal cortices (even as adults). Iodine deficiency or fever during gestation also impedes neuronal proliferation in the foetus.
