Development of the Nervous System Flashcards
In what three ways can the peripheral nervous system be classified?
1) How it connects to the CNS eg cranial nerves and spinal nerves
2) The direction of propagation eg afferent or efferent
3) The motor neurons target effectors eg somatic or autonomic (autonomic is divided into parasympathetic and sympathetic)
Describe the fish brain
Tubes that carry nerves to a central point
Fish ere cephalised
Mechanical and unconscious
Describe the reptilian brain
Nerves are sorted into specialised modules eg light sensitive neurons for vision
This means they show anatomical modularisation
They have a bulge on the rostral area of the spinal cord
Mechanical and unconscious
Describe the mammalian brain
Has a hypothalamus to allow reaction to a diverse stimuli
Developed thalamus which allows senses to be intergrated to form a response
The limbic system generates emotions but animals are unable to perceive these emotions
The amygdala and hippocampus can form crude memories
What is the calvurium?
The top of the skull
The enlargement of the human brain has caused what changes in the skull?
It gives the skull a high flattened forehead and its dome shape
What is grey matter?
The outer layer of the brain where no myelin is present and only contains neuronal cell bodies
Forms the cortex
What is white matter?
Contains neuronal processes and myelin
What are the ridges in the brain know as?
Gyri (sulci are the creases in the brain)
What are the frontal lobes associated with?
Personality
Temporal lobes contain what and are associated with what?
They contain the hippocampus and are associated with memory
What is the parietal lobe?
The largest lobe, associated with mathematical functions
The occipital lobe carries out what?
Visual processing
What is the cerebelllum responsible for?
Balance and movement (also higher functions such as reading)
What are the Brodmann's areas for: The visual cortex The motor cortex Broca's area Werwicke's area
14
4
44
22
What does broca’s area control?
The lips, tongue, larynx and breathing while talking
What does wernicke’s area control?
Grammar and language
How can musicians brains differ from the rest of the population?
The cortex hook controls the hands
In 90% of the population this hook has an omega shape
In the other 10% the hook is bigger and looks more like a lower case omega
What is the ability to form new synpatic connections known as?
Plasticity
On avarage how many synapses does a single neuron form?
1000 to 10,000
How many connections are there in the brain?
10^14
List three properties of a single cellular organism
Receptive
Responsive
Spontaneous
What must have been made by cells for multicellular organisms to develop?
Cell adhesion molecules so that cells stay together after mitosis
What are sponges?
They live at the bottom of the sea
They are essentially a tube with an opening
Water flows through their body walls and flows back out via the osculum
The flow in water is regulated by mycocytes
What are myocytes in sponges?
These are specialised cells which respond to stretch and mechanical pressure
What were the first neurons likely to have been like?
Sensimotory cells - these span from an exterior sensory cell to an effector cell
What are hydra (cnidaria)?
More evolved than sponges
They have an outer body largely of skin and a gut
In between the skin and the gut there are specialised nerves
What type of cell did neurons evolve from?
Skin cells (ectoderm)
What are flatworms?
Non-segmented worms
They have clusters of neurons which show; gangliation, cephalisation, bilateral symetry, fasisulation (nerves forming bundles) and commisures (tracks of axons that link two sides of an organism)
What are annelids?
Segmented worms
The brain is likely to have developed at the same time as the what and why?
The mouth because the brain allows the organism to sense and capture its food
Describe the C.Elegans nervous system
They have a mapped nervous system
Invariant cell lineage
302 neurons, 56 glia
They have ventral, dorsal and lateral nerve cords
The C.Elegans nerve lineage is from what cell?
The 1AB cell which also shares lineage with the hypodermis (skin)
How does the nervous system develop in the drosophila?
The neurogenic region is next to the ectoderm
There is the migration of the neurogenic region as gastrulation occurs
Individual neuroblasts delaminate, migrate inwards and then they coalesce
What type of cells form neurons and glia?
Ganglion mother cells (formed from neuroblasts)
In vertebrates where is the nervous system?
Dorsal
What is the hypothalamus in close proximity to?
The mouth
Do neural cells delaminate in the Xenopus?
No - the neural cells stay as a layer called the neuroepithelium which is a flat single layered plate often called the neural plate
Which animals have neural plates?
Chicks, Xenopus, humans and other vertebrates
What is cell differentiation?
The process by which cells become different from each other and acquire specialised properties
This occurs by changes in gene expression, which dictate the repetiore of the protein synthesised
Can be governed by intrinsic and extrinsic factors
What is the inhibited to form a neurogenic region?
BMP
What is BMP inhibited by?
Chordin
What are the homologues of BMP and chordin in insects?
dpp = BMP sog = chordin
What is the urbilateria theory?
That the dorsal versus ventral nervous system developed as invertebrates underwent a body twist
What is the molecular pathway for epidermal differentation?
BMP present High Smad1, Low smad 7 expressed Msx1, GATA1 and vent epidermalising transcription factors expressed LEF1 Epidermal differentiation
What is the molecular pathway for neural differentiation?
BMP inhibted Low Smad 1, High Smad7 XIpou2, Sox D, neuralising trasncription factors expressed Neurogenin Neuro D Neural differentation
How can we see where proteins are expressed?
Antisense probes/ antibodies detect transcription factors
In situ hybridisation and immunohistochemistry
What is neurulation?
How the neural plate rolls up in vertabrate development
It occurs rapidly and wraps up starting posteriorly
If the neural tube does not roll up correctly posteriorly, what is this called?
Spina bifida
What layer is the ‘organiser’ induced?
The mesoderm
What is the role of the organiser?
It expresses transcription factors and secretes ligands including chordin
Where is the neural plate induced?
Where BMP is inhibites
What is neural induction?
The process through which the neural plate forms when BMP antagonists prevent the BMP ligand from stimulating its receptor
Cells in the organiser later develop into what?
Anterior and axial mesoderm
These involute, intercalate and undergo convergent extension
What is invagination?
Where a sheet of cells bend inwards
What is ingression?
Where individual cells leave an epithelial sheet and become freely migrating mesenchymal cells
What is Epiboly?
Where a sheet of cells spread by thinning
What is convergent extension?
Rows of cells intercalate, but the intercalation is highly directional
What is the experimental proof for neural induction by the organiser?
The organ cells from an amphibian (donor) are cut and placed in a host amphibian and is cultured
A second embryo on the host forms
The same experiment can be done in chicks
How were BMP antagonists discovered?
The mRNA was extracted from the organiser cells, and reverse transcriptase was used to make cDNA
What must experiments show to proove that a molecule is a neural inducer
The molecule must be expressed in the organiser
The molecule must be secreted and act on adjacent cells
Overexpression in an ectopic state would lead to the induction of a secondary axis
Inhibition of the activity should prevent axis formation
What parts of the brain are responsible for higher order, thought and memory?
The cortex
What are the two parts of the forebrain in develepment?
The telencephalon
The Diencephalon
What is the midbrain called in development?
The mesencephalon
What is the hindbrain called in development?
The metencephalon
What is Henson’s node?
Also known as the organiser
Self differentiates into axial mesoderm
The prechordal mesoderm is anterior and the notochord is posterior
BMP antagonists induce neural plate of which character?
Anterior
Where are BMP antagonists made?
In the early node then later in the prechordal mesoderm
What is the role of the late node?
It provides signals that promote proliferation and the growth or neural cells and their posteriorisation
What is the activation-transformation model?
It describes how neural inducing molecules from the early node/organiser induce and then maintain the anterior tissue
It then describes how later other signals from the later node/organiser promote growth and posteriorisation
These signals act antagonistically
How is the AP axis established?
BMP antagonists and Wnt antagonists are maintained anteriorly
FGF, Wnt and retinoic acid are expressed posteriorly
What are the two diffusion gradient models?
The Allan Turing Reaction diffusion model
The Lewis Wolpert French Flag model
In drosophila larvae, how is segmentation controlled?
By the homeotic (Hox) genes
What does homeobox DNA encode?
DNA binding protein domain of 60 amino acids called the homeodomain
A knockout of Hoxa1 and Hoxb2 in a mouse causes what?
The failure of rhombomeres 4 and 5 to develop normally so there is no abducens nerve
What is the neural plate border cells essential for?
Neural crest formation
Roof plate formation
What is the role of the neural crest?
It forms the peripheral nervous system
How is the neural crest formed (4 steps)?
1) The neural border (between the ectoderm and the neural plate) expresses transcription factors msx, thought to be induced at intermediate BMP signal levels
2) Other signals (Wnts, FGFs) act with msx to turn on transctription factors (Pax3, Zic1, Pax7) which characterise the neural plate border cell
3) Wnt acts with the neural plate border transcription factors to upregulate c-Myc, Id and Snail - these characterise the neural crest cells and give stem cell like behaviours
4) Id is upregulated in response to c-myc and sox-9 which control cell proliferation and survival. Neural crest cell transcription factors also promote epithelial mesenchymal cell transition and neural crest cells delaminate from the border region
What do neural crest cells give rise to?
Smooth muscle cells, osteoblasts, adipocytes, chondrocytes, melanocytes, schwann cells and neurons
What does the enteric nervous system control?
The gut
The different cell types generated by the neural crest cells depend on what three things?
1) The position of origin of the neural crest cell
2) The time and generation of the neural crest cell
3) The migratory pathway and signals they encounter en-route or at the target
What are roof plate cells important for?
The final step of neuralation and is important in dorsal neural tube patterning
What do roof plate cells upregulate?
BMPs and Wnts
What do the BMPs and Wnts upregulated by the roof plate cells induce?
Pax 6, Pax 7 and Pax 3
These cause neural progenitors to acquire dorsal identities
Recent work suggests what about the BMPs made by the roof plate cells and how they cause neural progenitors to acquire their dorsal identities?
The roof plate cells express different types of BMPs, each of which induces a specific dorsal cell type rather than there being a morphogen gradient
Where is the floor plate located?
At the ventral midline
Grafting the floor plate to an ectopic position induces what?
Ventral neuron development
What is the secreted factor made by the notochord and floor plate?
Hedgehog
Shh
Why does the gene hedgehog have its name?
Fruit flies with a mutation in hedgehog look spiky as there is no segment polarity
Where is the Shh protein located?
It appears in a gradient through the ventral neural tube from ventral to dorsal
Where is Shh made?
The notochord and the floor plate
Describe the hedgehog molecular pathway when it is not stimulated
When hedgehog is not present Ptc inhibits smoothened
Therefore Gli is not activated and so the hedgehog target genes are not transcribed
Describe the hedgehog molecular pathway when it is stimulated
When hedegehog is present Ptc no longer inhibits smoothened
Therefore Gli is in its activator form and the hedgehog target proteins are transcribed
What multiple morphology can be seen in the Shh -/- mouse?
No ventralisation of the neural tube Holoprosencephaly - failure of the forebrain Cyclopia Abnormal limbs/digits Lack of a pituitary
What is notch required for?
It is used to prevent a cell from becoming a neuron so a cell expressing notch will not become a neuron
It regulates lateral inhibition
It is a receptor
What is lateral inhibition?
A special kind of induction used to make initially similar cells different to one another
It involves the transmission of an inhibitory signal between a cluster of cells to prevent cells that receive the signal from adopting a similar fate
How does delta-notch signalling cause neurons to develop?
Both cells express the same amount of delta and notch initially
Cells for a stochastic reason or as a response begin to express more delta
This means in the adjacent cell notch is upregulated so these cells can not become neuronal
Cells with hyperactive delta will become neuronal
Describe the interkinetic migration seen in the nuclei of the cells that make up the neuroepithelium
Cells in the G1 and S phase have their nucleus away from the lumen
At the M phase and cytokinesis the nuclei is close to th lumen
How do radial glial cells divide?
Asymetrically - they divide into one daughter cell like the mother and the 2nd will differentiate into a neuron
