17. CNS Development Flashcards

Question

What is spinal dysraphism?

Answer 1

* These are defects that occur when the neural tube does not close properly rostrally, and can include the bone, nerves, spinal cord and fluid coverings * Spina bifida comes in 3 forms: * Myelomeningocele - defect includes spinal cord contents in a sac outside of the body * Babies typically have weakness below the sac * Meningocele - defect only contains spinal fluid/no nerves in a sac outside of the body, only the meninges * Spine normally otherwise develops normally, so can often be solved using surgery * Spina bifida occulta - common bony deficit (5-10% of population), 1 or more vertebrae do not form properly but the gap formed is very small, so there are frequently no effects * People often do not realise they have the issue, and is often associated with lumbrosacral abnormalities, e.g. tuft of hair, dimple, sinus or 'port wine stain' * [EXTRA] DO NOT confuse with Mongolian blue spots (common in Asian populations), there are bluish/grey skin markings that appear at/shortly after birth, are transient and are not associated with illnesses

Answer 2

* Only ~50% of pregnancies in the UK are planned, therefore it was suggested that the fortification of flour with folic acid would be necessary to aid foetal development * The UK has now fortified flour since 2018 * There was no evidence that the fortification of flour resulting in an ingestion of \>1mg of folic acid per day would result in neural defects/toxicity in the nervous system. * Folic acid is not the answer for everything, it only covers around 50% - inositol must also be considered, and even then things can still go wrong, as a single molecule cannot cure everything within such a complex process.

Answer 3

* **Notochord** - this is a signalling centre outside of the CNS, and is of mesodermal origin, using **Shh** as a signalling molecule * Notochord induces the **floor plate**, which induces further differentiation along the neural tube * Patterning also allows the establishment of motor neuron pools (somatic motor and visceral)

Answer 4

Floor plate (FP), which lies **ventrally**, using Shh

Answer 5

* Induces further differentiation throughout the neural tube * This is not limited to the spinal cord but also extends to the brainstem and base of the telencephalic vesicle

Answer 6

* Thickening on the **dorsal** side of the neural tube * Expresses **BMP4** to effect development of neurons * Specifically induces the formation of commissural interneurons (decussating interneurons) * Dorsal side contains sensory (somatic and visceral) nerve fibres

Answer 7

Yes, roughly

Answer 8

* Cells released from the dorsal lip when the neural tube is closing * Neural tube cells undergo epithelial-to-mesenchymal transition (EMT), delaminate and migrate to the periphery * These cells are essentially a sea of stem cells that can then migrate and differentiate to form a wide range of cells in the periphery * The PNS is derived from neural crest cells

Answer 9

Hirschsprung's disease, congenital megacolon * This is the congenital absence of Meissner’s and Auerbach’s autonomic plexuses in the bowel wall due to a failure in migration by the neural crest cells, resulting in a failure to colonise the abdomen and form the enteric nervous system * This is usually limited to the colon, most commonly anal and only very rarely involving the entire GI tract * Peristalsis is absent or abnormal, with spasms and obstructions within the bowel – dilation of more proximal, normally innervated segment * Correct diagnosis is needed ASAP, including biopsy, or else it can result in toxic enterocolitis * Treatment is a colostomy: resection of the aganglionic bowel (this region is determined via biopsy) and then the two ends are reconnected, to form a somewhat functioning and complete GI tract

Answer 10

* Regional differences in the rostro-caudal axis * Hindbrain segments contain cranial nerve nuclei and are patterned using rhombomeres * Different cranial nerves are associated with different rhombomeres * Different regions specified in part by the activation of Hox genes and segmental Hox gene patterning (Hox signals come from within the CNS, there are partially overlapping patterns along the structure)

Answer 11

* Altering gene expression patterns in the rhombomeres * For example, mutation or KO in Gbx2 causes a failure to develop the trigeminal nerve

Answer 12

* Hox gene patterning is highly conserved, even between organisms (e.g. humans and Drosophila) * Experimental example: antennapedia, mutation in homeotic Hox gene * Homeotic gene = gene which, if mutated, causes the conversion of one body part into another * In this case causes antennas to be substituted for legs

Answer 13

Depends on the dimensions and signals from the rhombomeres, and the location of the nulcei

Answer 14

The process by which new neurons are produced in the brain (essential for development, also continues in some regions throughout life e.g. olfactory bulb)

Answer 15

* **Neuroepithelium** generates neurons at a very high rate * Progenitor cells (therefore partially restricted) are found within the **neuroectoderm**

Answer 16

Next to the ventricular zones/CSF-filled ventricles

Answer 17

* Cells then migrate out towards the pial surface/towards the skull * The first post-mitotic cells are found at this surface, which is known as the primordial plexiform zone or 'pre-plate' * This patterning method is the same within all mammals, with projenitors in the ventricular zone/subventricular zone and mature post-mitotic cells lying close to the pial membrane/pre-plate region * This migration route starts short but eventually grows longer

Answer 18

* This method of patterning is the same within all mammals, with progenitors in the VZ (ventricular zone) and SVZ (subVZ), with mature post-mitotic cells being observed close to the pial membrane/in the pre-plate region – the route starts short and then increases in length * This is initially split into two regions (marginal zone and the sub-plate), then the cortical plate develops from an inner- to outermost fashion between the two, largely transient cell layers. * [EXTRA] To discover where the divisions occur, a very simple immunological stain for phospho-histone H3 (anti-phospho histone H3 binds at the epitope), which is only exposed in dividing cells.

Answer 19

* Radial (glia) progenitor cells, with extended, long projections * There are also other progenitors, including intermediate, short neural and outer radial glial progenitors * These classifications depend on the shape and connections

Answer 20

* Different progenitors can produce different numbers of neurons and in different combinations * Some of the radial progenitors can generate neurons directly (direct neurogenesis) * Some produce intermediate progenitors, which then cycle and produce more neurons – in species with very large brains, there are more intermediate neurons as this helps to generate more neurons and therefore a bigger brain.

Answer 21

* This is the process by which nuclei from radial glia progenitors migrate through the cytoplasm as they divide * The nuclei descend to the subventricular zone to meet the centrosomes

Answer 22

* If abnormal spindle-like microcephaly-associated protein is present, APSM microcephaly occurs as the progenitor cells cannot divide – the head circumference will be two standard deviations below average (definition of microcephaly) * This is a breakdown of mitotic machinery, resulting in a devastating output from the germ layers and a far, far smaller brain * If there is an alteration in the expression of transcription factors within the telencephalic vesicle, for example those involved with the SVZ, again the result is a smaller brain – if there is a Tbr2 mutation, for example, a smaller brain with fewer neurons is produced due to the reduced number of progenitor cells * In humans, Tbr2 knockout is known to cause silencing of T-box transcription factor EOMES, leading to microcephaly with polymicrogyria (smaller gyri and sulci) and agenesis of the corpus callosum (which usually communicates between the two hemispheres) * ZIKA virus is an example of an environmental influence that affects neurogenesis – the virus has a devastating effect on pregnant mothers, especially if the mother became infected during the first trimester, causing cases of microcephaly (study showed strong temporal clusters relating the condition to the ZIKA virus) * About 80% of the population had no symptoms and the other 20% only had mild symptoms (e.g. swelling, mild oedema, facial rash) * In about 1% of infections during the first trimester, the baby would be born with a microcephaly condition, including microcephaly, corpus callosum agenesis, lissencephaly, ventriculomegaly, arthrogryposis (curving of joints) * ZIKA virus kills off some of the progenitor cells, also effecting the retina and joints, making this virus result in a complex congenital syndrome * Microcephaly cannot be ‘grown out of’, so the children born with the condition just have to be managed * The risk of adverse effects from ZIKA were relatively low (1%), but the effect was seen to such a huge extent due to the extremely high proportion of cases within the population

Answer 23

* ZIKA virus is an example of an environmental influence that affects neurogenesis – the virus has a devastating effect on pregnant mothers, especially if the mother became infected during the first trimester, causing cases of microcephaly (study showed strong temporal clusters relating the condition to the ZIKA virus) * About 80% of the population had no symptoms and the other 20% only had mild symptoms (e.g. swelling, mild oedema, facial rash) * In about 1% of infections during the first trimester, the baby would be born with a microcephaly condition, including microcephaly, corpus callosum agenesis, lissencephaly, ventriculomegaly, arthrogryposis (curving of joints) * ZIKA virus killed off some of the progenitor cells, also effecting the retina and joints, making this virus result in a complex congenital syndrome * Microcephaly cannot be ‘grown out of’, so the children born with the condition just have to be managed * The risk of adverse effects from ZIKA were relatively low (1%), but the effect was seen to such a huge extent due to the extremely high proportion of cases within the population

Answer 24

* Direct neurogenesis is asymmetric mitosis, the radial glia progenitors (subtype I) give rise to one neuron with each round of division * Produces comparatively fewer neurons * Indirect neurogenesis is where radial glia progenitors (subtype II) give rise to intermediate progenitors upon mitosis, and it is these secondary cells that divide within the sub-ventricular zone and give rise to neurons * Intermediate progenitor cells do not have the same long, radial projections * This process gives rise to comparatively more neurons

Answer 25

No, there is a lot of apoptosis

Answer 26

* Caspase-9 KO mice caused a lack of cell death among progenitor cells, resulting in a protruding brain that cannot be contained within the skull

Answer 27

* Transient cells, which die off after the cortical plate develops * Subplate allows for connections between different regions in the developing brain, but these cells die off in large numbers * Preferential death is shown in the subplate as opposed to cortical regions, for example * The white matter below the cortical plate initially contains cells, but these die off with only some interstitial cells remaining

Answer 28

* The sub-plate is a very important platform in which connections are made within the developing brain, but then these cells will die off in very large numbers * This has been shown through the use of birth-dating studies – to show that a cell was born at a particular time, a thymidine analogue is injected and then incorporated into the genetic information of new-born cells which can then be followed * Hypoxia can cause ischaemia within these cells even before they begin to function, preventing connections from being made between different developmental regions

Answer 29

Most neurons are generated at a site distant from their final destination, so then have to migrate to their proper location. This is a very vulnerable process.

Answer 30

The last S phase of neurogenesis

Answer 31

* Cells are destined for a particular region upon leaving the germinal zone * If there is an abnormality in migration, the cells simply do not make it and function is lost * When cells have to migrate, they must first extend a leading process (growth cone) * These cells are thought to follow radially orientated radial glia progenitor cells (using their projections as a guide) * Once the cells reach their proper destination, they then dissociate and begin to differentiate

Answer 32

* These migrate and development in a different method to other cells of the cortex * These are generated away from the cerebral cortex and migrate in a tangential manner, to then end up residing within the cortex * They have to make it into the cerebral cortex via several channels

Answer 33

* This is likely because an enourmous number and variety of both neuronal and supportive cell types must be generated, therefore neurogenesis must be spatially and temporally seperated * This allows different combinations of transcription factors to be available to different progenitor cells, creating huge variety * For example, in direct neurogenesis within the VZ, there is different transcriptional control to indirect neurogenesis occurring in the SVZ * Waves of transcription factor expression in different combinations results in the development of different cells * Different layers within the brain form vastly different interconnections, with various circuits forming very different computational functions depending on the circuitry present

Answer 34

* During development (prior to birth/in utero), with very little neurogenesis occurring in later life * In adulthood, there are only limited sites at which neurogenesis occurs: * Sub-ventricular/subepyndymal zone * In the angle of the lateral ventricle, produce neurons that then migrate out to the olfactory bulb (site of continued cell replacement) * Dentate gyrus * Part of the hippocampus, involved in learning and memory - [EXTRA] Cab driver experiment, hippocampus increased in size compared to age-matched controls, also larger hippocampus relative to time spent on the job

Answer 35

There is no mitosis of mature neurons, with very limited sites of adult neurogenesis (SVZ, dentate gyrus) * There is no mitosis of mature neurons * There is no or very limited neurogenesis in the cerebral cortex * There are limited sites of adult neurogenesis after birth, but it is debated for how long this process continues (SVZ, dentate gyrus) * In injured brain, there may be potential for action of dormant progenitors, which is thought to be able to restore some function

Answer 36

* There is debate as to whether there are other sites of neurogenesis, and it has been suggested that humans have little adult neurogenesis and are slightly different to other mammals * In experimental animals, thymidine analogues can be injected into neuronal cells and then incorporation of these labelled cells can be measured to see whether there is any neurogenesis taking place * This will not reflect human actions, however * Researchers believe that positive results may be due to injection of analogues into satellite and glial cells as opposed to neurons, leading to debate * In the biotope, there has been a recent drastic increase in the number of ¹⁴C isotopes due to surface testing of nuclear weapons – after 1963, the limited nuclear test ban treaty was signed, stopping the surface testing of nuclear weapons and decreasing the concentration of ¹⁴C levels in the atmosphere * These isotopes will have been incorporated into neurons and glia, so could use someone born around 1963/1964 and test the ¹⁴C content of their brain to see whether levels indicate that they were born at this time – human carbon dating! * If the result and the DOB don’t match up, this could indicate neurogenesis – however, it was indicated that the neurons were the same age as the individuals, but the glial cells were approx. 10 years younger * Debate concerning dentate gyrus and SVZ is still going on, as it has only been confirmed in animal models * Some papers suggest that there is very limited neurogenesis occurring from a few years after birth

Answer 37

* Yes, their fate is predetermined * This means that restriction of migration can have a massive effect on function * Neuronal migration defects are relatively common, as fates of neurons are likely to be determined in the last S phase before final division

Answer 38

* Glutamatergic neurons migrate radially (VZ to CP – cortical plate cells mature inside first, then outside) * In GABA-ergic cells there is a tangential migration to travel from the ganglionic eminence to the cortex.

Answer 39

High levels of intellectual defects seen in children after the atomic bombs were dropped in Japan at the end of WW2

Answer 40

Intact molecular machinery, including: * Filamin * Actin * Small GTPases * Microtubules (essential for establishing a perinuclear cage that then drags the nucleus after the leading edge extension) Neurons extend a leading edge and then drag the nucleus behind themselves - this process needs to be repeated several times in order for the neuron to reach its target destination.

Answer 41

* If there is no leading-edge extension, then cells do not really leave the site of generation and instead form disorganised clusters of cells * This can lead to heterotopias, which means ‘altered location’ * The cells next to the ventricular zone were never able to leave the site of neurogenesis and fail to develop properly or reach the cortex, resulting in altered neuronal activity * For example, filamin mutations can lead to X-linked periventricular heterotopias – failures in the role of actin microfilaments or small GTPases can also lead to this sort of malformation * Can also be observed as smaller, periventricular nodules with potential ectopic activation * Lissencephaly (smooth brain, issues with the folding of the brain) is another type of migration defect * There will be an only partially developed cortex due to a failure of the more superficial layers to migrate through those that are already established – this results in a failure of the brain to fold properly * There are different degrees of lissencephaly with varying degrees of smoothness from a condition where there are no gyri (agyria), where only certain regions of the brain have no folding (e.g. posterior agyria) or just different degrees of smoothness * E.g. Type 2 lissencephaly is where cells breach the pial surface as they do not stop in their migration, forming heterotopias at the surface of the brain - this gives the brain a cobblestone-like appearance

Answer 42

* This results in the formation of a super-plate * This causes the cortical plate to develop in an inverse manner (outside to inside) * This is caused by a defect in the Reelin pathway, causing a cerebellum and cerebral-cortical defect * The name is derived from the characteristic movements seen in this condition

Answer 43

* Through finding the determinants of the lissencephaly spectrum

Answer 44

* Tallinen, 2016: made 3D-printed brain models of early brains from scans, then using it to produce a master moulds and replicated a brain using specific gels that would expand after absorbing specific solutions * This was achieved in two stages: there was a core and then a separate outer layer with different properties * This was then put into solution and observed the way in which their ‘brain’ was expanding * It was shown that as the brain expanded, folds occurred, due to differential growth between the core and the outer layer * The jelly brain showed extremely similar structural changes to an actual brain as it expands during development – the pattern of folds etc was very similar * The major sulci and gyri are the same between individuals – genetic or epigenetic alterations are what will cause major changes in the folding of the brain

Answer 45

* The brains which have more layers of progenitor cells (esp. OSVZ/outer subventricular zone cells) are suggested to receive more sulci and gyri * This is not a complete association, however, as these cells are found in less folded mammals and in individuals suffering from lissencephaly * You must look at a huge variety of species to understand this concept

Answer 46

* Foetal alcohol syndrome results in a devastating neurological pathology * It is a lifetime disability – children do not just ‘grow out of it’, but early diagnosis and intensive (and appropriate) can make an enormous difference in the prognosis for that child * Prevention, however, is still the most important factor * In the US and Europe, 1 in 100 babies being born has some degree of FAS, and up to 30% of pregnant women are taking alcohol during pregnancy

Answer 47

Rubix cubes - there are only a limited number of transcription factors, but their order and arrangement (both temporally and spatially) can result in the huge amount of cell variety seen within the cortex

Answer 48

Yes, both during embryogenesis and in adulthood

Answer 49

* Some transcription factors have a cross-suppressing effect on each other, allowing the gene expression to be regional and keeping proper development * It is important to regulate expression in order to retain the correct proportion of cells * For example, COUP-TFI KO mice have specific impairment in corticospinal tract-mediated fine motor skills due to imbalances in molecular messaging during development – this means that the mice are unable to retrieve a piece of food from between a small gap where a wild type mouse would be able to with ease (KO can see and smell the food pellet, but is unable to produce the correct motor control to retrieve it)

Answer 50

* ‘Cerebral organoids’ – induced pluripotent stem (iPS) cells as models * The organoids have very similar early development processes as to those seen in the early developing brain of humans – they are able to model some human brain disorders and the earliest stages of brain development * The timing of the molecular waves is preserved and is very similar to that seen in human brains, working on the same time period

Answer 51

* Some die in the germinal zone * Some cells are destined to die, for example subplate/subcortical neurons that are the earliest generated cells in the brain and lie adjacent to white matter

Answer 52

* Earliest generated cells * Lie adjacent to the white matter * These cells are frequently destined to die * They are very susceptible to hypoxic ischaemic brain damage, whilst also retaining an important role in the development of the cortex * Transient/only present during development before dying off * [EXTRA] This pattern has been observed using birth dating * These cells act as a dynamic, transient scaffold essential for brain development * Removal of subplate cells means that the connectivity of the brain cannot be established and therefore cortical circuits cannot be modified

Answer 53

* They can have different levels of severity * Removal of the sub-plate cells means that the connectivity of the brain cannot be established, and the cortical circuits are not able to be modified * When the insult occurs has a large effect on the severity of the condition and development of the baby – earlier tends to be more devastating

Answer 54

* Inflammation hypoxia can have an impact on the physiology of the oxygenation of the brain, and it can also disrupt the BBB function which will in turn lead to secondary effects * It can change the developing axons, the grey matter, then cascading down to all sorts of complex reduced brain functions

Answer 55

* If there are lots of projections extending from one region of the brain to another, they have to interconnect in a topographic way/organised manner * Some rely upon molecular cues to reach their final destination, whereas a small proportion are able to find their way using neuronal activity * The axons and cells extend long neurites that are able to navigate within the environment through the use of growth cones * Connections are usually established when the distance between cells is minimal * The growth cone exists on the tip of the advancing neuron, using filopodia to explore the immediate environment (look like flickering fingers) * There is actin polymerisation occurring within these filopodia (can be visualised using GFP) * There is local attraction and repulsion, the insertion of new cytoskeleton and autonomous action * Growth cones respond to various positive and negative cues (e.g. contact, distance, diffusible chemicals)

Answer 56

* Using molecular cues - growth cones are either attracted or repelled by these * These cues can be local (substrate-bound) or long-range (diffusible) * A given molecule can be both attractive and repulsive, depending on the interaction

Answer 57

* Netrin is a diffusible molecular guidance cue, which is expressed by the notochord (after initial expression of Shh) * If a dorsal neural tube explant is put next to a floor plate, then the explants will grow towards the floor plate * Netrin is also able to repel some neuronal populations (it does not attract all neurons) – for example, in the brainstem, netrin is repulsive to the developing cranial nerves, causing them to exit the brainstem in a dorsal direction (opposite side to netrin expression) * The action of netrin is able to switch from attraction to repulsion if they go through the region

Answer 58

* Initial connections can be imprecise, with incorrect target nuclei or incorrect locations within the target nuclei * Axons connect to more targets and targets are contacted by more axons that required during development (therefore refinement/pruning is necessary) * Regulation is achieved through: * Neuronal death * Axonal retraction * Synapse elimination/pruning

Answer 59

* Primary axons typically extend way beyond their target, causing their target to instead by innervated by de novo collateral branches that form interstitially along the primary axon * Excess or inappropriate collaterals, alongside the considerable length of the primary axon that overshoots the distal target are eliminated by a process that appears to rely primarily on degeneration

Answer 60

* Best studied example is of cortico-optical connectivity development * Layer 5 neurons (largest of the brain) send out projections all the way into the spinal cord * All cortical areas send projections into the spinal cord, even the visual cortex (although these are eventually lost) * The same is not true for the motor areas, their projections are maintained throughout development

Answer 61

* 'Cells that fire together, wire together' * Donald Hebb, 1904-1985, suggested that neuronal connections that are co-activated have a stronger coactivity * Connections are made within the nervous system from a very young age – neuronal activity is possible from the very beginning of development and even has some action in deciding which connections are retained * The brain is essentially put together by itself * This can lead to situations where being efficient at a task can lead to loss of circuits, as travel of impulses within the brain will affect the structure * This causes better use of what is available, but also reduces the ability to adapt due to a lack of connections

Answer 62

Age 11 where there is the highest number of neurons, after this point there is a general decline due to cell death

Answer 63

The ability to change synapses - once neuronal cells are generated, they can interconnect in many different ways and are able to change their synapses/are plastic throughout their lifetime

Answer 64

* Initially there is no peripheral input, only spontaneous activity within the brain * Innate process * At a later stage in development, neuronal activity is driven by sensory input as they are exposed to the outside world * This has a major effect on organisation and circuit development within the brain * Determines response to the environment

Answer 65

* If the eye is removed in embryonic stages (as has been done in monkeys), the shape of the brain is changes and the development of the primary visual cortex is limited * Rakic, 1988, indicated that borders between cortical areas were not fixed using the above method * If a similar manipulation is done after birth, such changes are not seen - this removal has to occur during a **critical stage of development** to see the effect * This experiment indicates that it is a combination of both nature (genetics/embryonic development) and nurture (environmental influences) that affects the patterning of the brain

Answer 66

* Initial production of neurons is achieved through gradients of molecules within the brain * These gradients are then modified by external (i.e. sensory) influences, carving out specific regions that are optimised for specific functions

Answer 67

All visual, audition and somatic-sensory inputs mediate through the thalamus, and the thalamocortical connections mediate extrinsic signals, transmitting them to the cortex

Answer 68

* Experiments using barrel fields in mice - these are huge areas devoted to the representation of whiskers in the upper lip of mice * If a whisker is stimulated, then some of the contralateral cortical region is stimulated where rings of cells are found (rough shape of a barrel in coronal sections) * If the sensory input is changed early on by removing some of the whiskers in a new-born mouse, the cortical representation is changed * If the infraorbital nerve is cut (carried sensory information to the trigeminal nucleus), then no barrel patterns are formed * The cortex has not been touched – the alterations occur purely through alterations to methods of input * If a similar manipulation occurs later on, there will be no changes – the plasticity is only available for a limited amount of time

Answer 69

* To establish connections between neurons, a certain level of activity needs to occur and be delivered to the cerebral cortex * For example, the connections of the eyes to the cerebral cortex are initially mixed but segregate during development * This process is dependent upon a certain level of activity occurring within the visual cortex * There is a very specific pattern that develops over time, and is not found in young samples * If the connection between the eye and the thalamus is blocked in very early stages, blocking the activity as if the eye is unopened, then the patterns and distinctions between the connections of the two eyes are not seen * Early inputs into the brain are mediated by cholinergic mechanisms, before glutaminergic mechanisms begin to dominate * **Spontaneous** activity also has an important role in the development of early sensory maps

Answer 70

* If one eye is blocked, then the other will take over but this has to occur in the very early stages of development * This indicates the critical period immediately after birth upon which full eye development is dependent on * If one eye is blocked at birth, then the other eye takes over/dominates the connections within the visual cortex * If one eye is blocked after 3 weeks, then the unblocked eye will become dominant but both will still have representations within the cortex * After 6 weeks, the closing of one eye has no effect on development/representation in the visual cortex

Answer 71

* Use of different body parts in different ways will affect representation of these actions within the brain – for example, the middle three digits on a monkey’s hand were trained for 1 hour a day and there was a noticeable change in representation; after 3 months the 3b area associated with this movement was noticeably larger * This type of plasticity is even present in adults * If a human subject is trained to do a rapid sequence of finger movements for 3 weeks (10-20 mins per day), then a huge change in the region of activation was seen during an MRI scan – the change persisted for several months * It is clear that nerve connections can reorganise, even in the adult * Example: the sensory pathways for the hand and the face run separately through the cortex, but if the arm is amputated, then the pathways can join * So if asked to close your eyes after this injury, someone touching your face can feel like someone is touching your non-existent arm, due to plasticity of the connections * ‘Facial remapping’, which can be explained by the plasticity of the system * Touching of the face can be perceived as touching of the non-existent hand * E.g. after a mastectomy, the sensory innervation of the breast can re-wire to be connected to the ear, due to plasticity and the close proximity of both of these circuits

Answer 72

* The basal plate is the region of the neural tube ventral to the sulcus limitans (found in the 4th ventricle, separates the cranial nerve motor nuclei (medial) from the sensory nuclei (lateral)) * It extends from the rostral mesencephalon to the end of the spinal cord and contains primarily motor neurons * Is split into left and right basal plates by the floor plate (spinal cord is symmetrical)

Answer 73

* The alar plate is a dorsal region of the neural tube * Associated with sensory neurons, including the sensory nuclei of some cranial nerves

Answer 74

* The telencephalon is a swelling at the rostral end of the neural tube * These begin to expand into two symmetrical structures that sit alongside each other at the end of the neural tube * These will become the cerebral hemispheres

17. CNS Development Flashcards

(101 cards)