Week 4 - The biology of the developing nervous system Flashcards
At fertilisation what is the name of the cell that is formed by the fusing of the egg and sperm?
Zygote
What is a zygote?
The single cell created by the fusion of sperm and egg where genetic material from each is combined
What does diploid mean?
A cell that carries two complete paired sets of chromosomes
What term do we use to refer to two complete paired sets of chromosomes?
Diploid
What is the term for reproductive cells?
Gametes
How many sets of chromosomes do gametes have?
One
What is the name given to a cell which only carries one set of unpaired chromosomes?
Haploid
What does haploid mean?
A cell that only has one set of unpaired chromosomes
When the genetic material of a cell is replicated and the cell has divided, what is the name for the two n ew cells that are formed?
Daughter cells
What are daughter cells?
The two new cells which are created as a result of the process of cell division
What is the term for any cell other than reproductive cells?
Somatic cells
What are somatic cells?
All cells other than gametes?
What are the two main phases of the cell cycle?
- Interphase
- Mitotic phase
What is the name for the sequence of events which occurs leading and up to somatic cell division?
Cell cycle
What happens during the interphase part of the cell cycle?
The cell prepares to divide
What happens during the mitotic phase of the cell cycle?
Division occurs
What are the three subphases of interphase called?
- G1
- S
- G2
What happens during the G1 stage of the cell cycle?
The cell becomes highly active and prepares for division by replicating many of its organelles and synthesising proteins
What is the name for the stage of the cell cycle where the cell replicates its DNA so that there are two complete copies available?
The S phase
What happens during the G2 stage of the cell cycle?
Division occurs
What is the name for the final stage of the interphase part of the cell cycle?
G2
What part of the cell cycle occurs after the G2 stage?
The mitotic phase
What are the names of the two processes of the mitotic phase of the cell cycle?
- Mitosis
- Cytokinesis
What is mitosis?
The part of the cell cycle where the nucleus divides
What is cytokinesis?
The part of the cell cycle where the cytoplasm divides
What are the four stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
What is the order of the four stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
At the end of the mitotic stage of cell division, the cell has divided and two new cells are formed. What is the name for those new cells?
Daughter cells
After dividing, what two things may the cell do?
It may either re-enter G1 and divide again, or pause
What is the G0 stage of cell division also known as?
The quiescent phase
What happens to the cell during the quiescent phase of the cell cycle?
Nothing, it has paused dividing
Is there a limit to how long a cell may remain in the G0 or quiescent phase of the cell cycle?
No
DNA is replicated in which phase of the cell cycle?
S phase
During the mitotic phase of cell division, what two things occur?
- Mitosis
- Cytokinesis
What happens during the prophase part of mitosis?
Chromatin fibres shorten and condense in order to form chromosomes
What are chromatids?
Two identical copies of a chromosome, joined at the centromere, that are involved in cell division
What is the name for the specialised region on a chromosome which serves as the attachment point for spindle fibres during cell division?
A centromere
What is the name for the protein complex which surrounds the centromere?
The kinetochore
What happens during the prophase stage of mitosis?
The copied DNA condenses into chromosomes, which are made up of two identical sister chromatids
What are sister chromatids?
Two identical copies of a chromosome, joined at the centromere, which are produced during DNA replication and separated during cell division
What is the name for the two identical copies of a chromosome which are produced during DNA replication?
Sister chromatids
During which phase of mitosis does the nuclear envelope begin to break down?
Prophase
What happens to the chromosomes during the metaphase stage?
They line up along the centre of the cell
Why do chromosomes line up along the centre of the cell during the metaphase stage of mitosis?
To ensure that when they split, each daughter cell receives an equal and complete set of genetic information
In the anaphase stage of mitosis, what occurs?
The sister chromatids are pulled apart, towards opposite ends of the cell
How are the sister chromatids pulled apart during the anaphase stage of mitosis?
By spindle fibres that attach to the centromere of each chromatid
What is the name for the stage of mitosis where the nuclear envelope reforms
Telophase
What is a nuclear envelope?
A double membrane that encloses the cell’s nucleus, regulating material flow in and out of the nucleus
What do we call it when a cell physically divides into two separate daughter cells?
Cytokinesis
When a cell divides and two identical copies of the cell are produced, what do we call this?
Symmetrical division
What does the term cytokinesis refer to?
The cell membrane pinching in around the middle of the cell and the cell splitting in to two daughter cells
Which is the most important type of cell division?
Asymmetrical
What is the zygote called when it reaches the 16-cell stage of development at around day 4?
A morula
What is a morula?
The ball of cells that reaches the uterus at around day 3-4 post-fertilisation
What is the name for the ball of cells at the stage that it implants into the wall of the uterus?
A blastocyst
What is a blastocyst?
The ball of cells which implants into the uterine wall
What is it that makes the blastocyst different from a morula?
It has two different types of cells within it
What is the name of the outer layer of the blastocyst?
The zona pellucida
What type of cells make up the outer layer of the blastocyst?
Trophoblast cells
What do trophoblast cells go on to become after the blastocyst implants into the uterus?
The placenta
What is gastrulation?
The formation of three distinct tissue source layers via cell diversification
Which type of cell division is necessary for cell diversification?
Asymmetrical
What do ectoderm cells go on to become?
- Skin
- Hair
- The lining of structures such as the nose and mouth
- The nervous system
What do mesoderm cells go on to become?
- Muscles
- Skeleton
- Blood
What do endoderm cells go on to become?
The lining of the digestive tract, respiratory tract and bladder
What type of cells do each of the three layers formed during gastrulation go on to form?
- Ectoderm cells
- Mesoderm cells
- Endoderm cells
Around roughly how many days post-fertilisation does the nervous system start to develop?
18 days
The development of the nervous system begins shortly after which other process has occurred?
Gastrulation and the generation of the ectoderm layer
The developing nervous system arises from a layer of ectoderm known as the what?
The neural plate
What is the first step of the developing nervous system?
The formation of the neural groove
What is the structure which lies underneath the lower surface of the neural tube?
The notochord
What structure plays a key role in aiding diversifying and migrating cells finding their way around the body?
The notochord
How does the notochord help diversifying and migrating cells find their way around the body?
By signalling the midline
What is the position of the notochord?
Underneath the neural tube
The backbone of the developing embryo is formed from which structure?
The notochord
What does the notochord provide?
Signalling molecules that cause cells to diversify into motor neurons
Where in the neural tube do motor neurons form?
In the ventral region, via development of an area called the floor plate
What orientation does ventral refer to?
Bottom or lower
In humans, where in the body is the ventral part of the spinal cord?
Towards the front of the body
What is the Sonic hedgehog gene?
The gene that encodes one signal used by the notochord to help cells orient themselves during development
What are neural tube defects (NTDs)?
Congenital conditions that occur when the neural tube does not close which leaves the neural tissue exposed to the amniotic fluid
What is the name for the congenital conditions that occur when the neural tube does not close, leaving neural tissue exposed to amniotic fluid?
Neural tube defects
If the neural tube fails to close properly and neural tissue is exposed to amniotic fluid, what happens to the neural tissue?
It eventually dies
Around how many babies per year are estimated to be born with neural-tube defects?
Around 300,000
What are two conditions that can be caused by failure of the neural tube to close properly?
- Anencephaly
- Spina bifida
What is anencephaly?
A severe congenital condition in which a large part of the skull is absent, along with the cerebral hemispheres of the brain
What is spina bifida?
A congenital condition in which part of the spinal cord and its meninges are exposed through a gap in the backbone, caused by the neural tube failing to close properly
How many types of spina bifida are there?
Three types
What are the three types of spina bifida?
- Spina bifida occulta
- Meningocele spina bifida
- Myelmeningocele
Which is the most serious type of spina bifida?
Myelomeningocele
What type of physical defect occurs due to myelomeningocele spina bifida?
A sac of fluid protrudes from the baby’s spine, and part of the spinal cord is present in the sac in a damaged state
What can be a risk factor for spina bifida?
Low levels of the micronutrient folic acid in the diet of the mother
By roughly how much can taking folic acid supplements reduce the risk of spina bifida?
About 70%
Although spina bifida is not considered a mental health condition, some sensory and cognitive symptoms may occur. What are they?
- Numbness in areas of the skin
- Poor hand-eye coordination
- Concentration problems
- Short-term memory problems
What is a genotype?
The genetic constitution of an individual organism
What is the term for variation in the risk of a health condition as a result of an environmental factor?
A gene-environment interaction
What does heritability refer to?
Population variation, rather than individual risk
What does heritability determine?
The extent to which the variation of a particiular characteristic (in a population) can be determined purely by genes
What does a heritability value of 1 mean?
That all of the variation in a population is determined by genes
What does a heritability value of 0 mean?
That none of the variation in a pop ulation is determined by genes
What mostly determines a condition which has a heritability value of 0.85?
Genes, because the value is close to 1 (or 100%)
Which parts of the developing nervous system are most likely to be damaged by maternal alcohol consumption?
The brain and spinal cord cells
In Western countries, around how many pregnancies are thought to be affected by FASD (fetal alcohol spectrum disorders)?
1 in 500
Of all the possible substances of abuse that may be consumed by a pregnant woman, what substance can have the. most serious and wide-ranging consequences on a developing baby?
Alcohol
What are some of the characteristic facial features that FASD may cause?
- Flattened nose bridge
- Lack of ridge that should be characteristic of the upper lip
What condition/s can FASD be misdiagnosed as in early childhood?
- Autism spectrum disorder
- ADHD
What are some of the cognitive and behavioural problems which children with FASD may have?
- Language deficits
- Attention problems
- Social problems such as difficulty making friends
- Problems with sensory integration
- Poor reasoning
What are neuromeres?
The segments in the developing nervous system
What is segmentation?
The process by which distinct sections or segments within the neural tube develop
What are the names of the three neuromeres which initially form during segmentation?
- Prosencephalon
- Mesencephalon
- Rombencephalon
The forebrain is formed from which neuromere?
Prosencephalon
The midbrain is formed from which neuromere?
Mesencephalon
The hindbrain is formed from which neuromere?
Rombencephalon
How many segments are formed at the second stage of segmentation?
Five
What are the names of the five secondary segments?
- Telencephalon
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencephalon
Of the first three segments which are formed, which goes on to form the midbrain?
Mesencephalon
The hindbrain is formed from which of the initial three segments?
Rhombencephalon
The forebrain is formed from which of the three initial segments?
Prosencephalon
Which of the initial segments then forms the telencephalon?
Prosencephalon
What are the three segments formed during segmentation known as?
Neuromeres
What is cell fate?
The final identity or type of cell at the end of its cell lineage
What is cell lineage?
The history of a differentiated cell traced back to the original cell from which it developed
What does the term totipotent mean?
It describes a cell that is capable of becoming any type of cell within an organism, including placental cells
At what stage during development does cell division change from symmetrical to asymmetrical?
Around day 5 post-fertilisation
What are pluripotent cells?
Cells which are able to become almost any cell in an organism aside from placental cells
If a cell can become any kind of cell in an organism other than a placental cell, what is it known as?
Pluripotent
If a cell can become any kind of cell in an organism including a placental cell, what is that cell known as?
Totipotent
What else are pluripotent cells in a developing embryo known as?
Embryonic stem cells
What are embryonic stem cells?
Pluripotent cells found in the developing embryo
What are the inner cells in a blastocyst known as?
Either embryonic stem cells or pluripotent cells
What are progenitor cells?
Cells that become a specific type/s of cell
Which have a more restricted fate, progenitor cells or multipotent cells?
Progenitor cells
What are bipotential progenitor cells?
Cells that can become one of two types of cell
In the nervous system, what type of cells are produced by bipotential progenitor cells?
- Neurons
- Glial cells
What is a neuroblast?
An embryonic cell that will become a neuron
What is neurogenesis?
The process by which new neurons are created
What is the neurotransmitter used by the neurons that die in Parkinson’s disease?
Dopamine
For how many specific purposes are human embryos allowed to be created ex vivo and stored for research purposes?
Four
What are the four purposes for which a human embryo is allowed to be created ex vivo and stored for research?
- Improving understanding of embryonic development processes
- Improving detection and understanding of human disease
- Developing treatments for human disease
- Promoting advances in understanding of miscarriage, techniques of contraception, and treatment of infertility
What are radial glial cells?
A type of glial cell in the developing nervous system that provides a structural scaffold for migrating neurons to move along
Which condition may be connected with differences in the precise patterning of cortical layers?
Autism spectrum disorders
What are the names given to the ridges and grooves that create the wrinkled appearance in the cortex?
- Gyri are the ridges
- Sulci are the grooves
How many layers can the adult cerebral cortex have?
Six
What are the main differences in human cortical regions than in animals?
Humans have a larger number of cortical areas and a denser interconnected cortical network
What is the outer subventricular zone (oSVZ)?
A developmental region of the ventricular zone in the developing nervous system that is unique to primatesq
Which part of the developing ventricular zone is unique to primates?
The outer subventricular zone (oSVZ)
What is radial migration?
Migration which occurs in a perpendicular direction to the ventricular surface
If cells migrate in a perpendicular direction to the ventricular surface, what type of migration is that known as ?
Radial migration
Cells in radial migration move in a perpendicular direction. What other direction may cells migrate in?
Tangential
Can a cell move in more than one type of direction?
Yes
What is the outer edge of the developing neural tube known as?
Pial surface
What is the pial surface?
The outer edge of the developing neural tube
What is the name fot the process that occurs when the nucleus of a migrating cell moves into the leading arm?
Nuclekinesis
What is nucleokinesis?
The process by which a cell’s nucleus is actively moved within the cell
When does nuclekinesis often occur?
During cell migration or neuronal development
What is the term for the use of chemical cues as a guide during cell migration?
Chemotactic guidance
What is chemotactic guidance?
The directed movement of cells in response to chemical gradients
What is the name for the arm which neurons extend during neuronal migration?
Leading process
What is the chemical known as semaphorin 3A used for?
It is used by neurons to determine how far away from the pial surface they are?
What are neuronal processes?
Thin, elongated extension of neurons that transmit signals to other neurons or cells
Dendrites do what?
Receive signals
Axons do what?
Transmit signals
What is a growth cone?
An area at the end of a leading process of a neuron that moves through the surrounding tissue during development
What does the term neurites refer to?
Both axons and dendrites
What are filopodia?
Small projections from growth cones of migrating cells that sense the surrounding environment
What are the small projections around the growth cone that detect chemical signals?
Filopodia
What is synaptogenisis?
The formation of new synaptic connections
What is the term for the formation of new synaptic connections?
Synaptogenisis
The ribosome in a cell does what?
Make proteins
Proteins are made by which component of a cell?
The ribosome
How does the ribosome get the instructions it needs to begin making the proteins that will be involved in neuronal communication?
Through mRNA, which transcodes the coded instructions from DNA and carries that to the ribosome
What is the key molecule for signalling synaptogenisis?
Brain-derived neurotrophic factor (BDNF)
What is brain-derived neurotrophic factor (BDNF)?
A key molecule for signalling synaptogenisis and neurogenisis
If the activity of BDNF (brain-derived neurotrophic factor) is reduced, what is the outcome?
The activity of neurogenisis and synaptogenisis decreases
