Building the Nervous System L2 Flashcards
What is the name for the earliest multicellular organisms?
Metazoans
What is the name of a single celled organism?
Protazoa. Although they’re single celled, they can be surprisingly differentiated and show complex behaviors in the complete absence of a nervous system.
What is ethology?
The scientific analysis of animal behavior
What 3 fundamental classes of behavior are displayed by protazoa and metazoans for survival?
Ingestive, digestive and reproductive behaviors. (ingestive refers to the internal regulation of water and nutrients.)
Name 4 mechanisms for ingestive behavior displayed by the protazoan Paramecia.
Gullet/Oral groove used to take in food
A system of vacuoles that shuttle food around and digest it within cells.
Anal pore/Cytophyge used for waste expulsion.
Cilia/flagella to move towards sources of food or away from an environmental threat.
What is a taxis?
The movement of an organism in response to a stimulus
What organelle is responsible for energy production in Protazoans?
Chloroplasts.
What is the simplest multicellular organism?
Sponge
How long did it take for a sponge to evolve from a protazoa?
1 billion years
Name two considerable advantages of the sponge over unicellular organisms.
Larger size provides a greater resistance to environmental stress.
Having different cell types allows a division of labor in that different cell types can have different jobs, increasing the efficiency of specific tasks, such as nutrition and defense.
Describe the passage of water into and out of a sea sponge.
Environmental water flows into the sponge through pores into the inner cavity called the spongocoel. The water then travels out through the osculum.
What is responsible for the circulation of water though the pores of the sponge?
The circulation of water through the pores to the spongocoel and back out through the osculum is determined by the beating of flagellated cells which line the inside of the spongocoel.
What regulates the feeding behaviour (and ultimately water flow) in sponges?
Myocytes.
What is the most important property of a myocyte in sponges and why?
Contractility. As they’re able to shorten, they’re able to ‘do work’. They’re arranged concentrically (similar to that of a dart board) around channels in the sponge body wall allowing them to cat as Sphincters so that when they contract, they are able to control the rate of nutrient saturated water flowing through the animal.
Why are myocytes described as independent effectors?
As they’re cells that produce a motor response when directly stimulated, without the interference of a neurone.
Why is the response in myocytes slower than that of neurones?
As myocytes are independent effectors, they’re not under the interference of a neurone. As a result, myocytes are less sensitive which means they require a large stimulus to initiate a response. These responses are typically much slower but last much longer, compared to that of neurones.
Give two reasons why HYDRA (cnidaria) provide are a favorite example of how the nervous system originally evolved.
They have a simple body plan (A mouth at one end and a foot at the other.
They have intriguing patterns of feeding and locomotion behaviors, in that they bring food into their mouths using their tentacles which they also use to move around the environment.
What does the prototypical sensory neurone derive from in HYDRA?
The ectodermal layer
Where does gangliation occur in flatworms?
The Cephalic region (anterior/rostral end - head)
How many neurones does c.elegans have?
302
How many glia does c.elegans have?
56
What is the function of a glial cell?
A glial cell is a NON- neuronal cell, responsible for maintaining homeostasis, forming myelin and providing structural protection for neurones in the peripheral and central NS.
What is the name for the initial ganglia in the worm what are it’s advantages?
Super-pharyngeal. It is located around the mouth, allowing the worm to process what they’re eating, providing a more efficient way of food digestion, capturing and releasing, allowing better survival.
What is delamination?
The process of cells pinching off from the outside surface of the embryo and migrating towards the center. This is an important featire in developing a complex NS. These cells are still ectodermal cells (not mesenchymal).
What cell type does delamination form?
neuroblasts
What is the function of neuroblasts?
Neuroblasts form ganglion mother cells which ultimately form neurones and glia.
What becomes the hypothalamus in Drosophila and where is it located?
Protocerebrum located close to the optic lobes.
Which germ layer does the NS in humans develop from?
Ectoderm
What are the two classes of processes of motor neurons in HYDRA?
An axon that conducts electrical impulses to non-neuronal effector cells.
a tangential process that conducts electrical activity between motor neurons.
What is a reciprocal synapse?
A synapse between two dendrites.
What are amacrine processes?
Neural processes which normally conduct in either direction and have reciprocal synapses with other processes.
What are the three functionally distinct types of processes suggested by Cajal in HYDRA?
Axonal, dendritic and amacrine.
What is centralization?
The condensation of neural tissue. Involves the aggregation of axons and neuronal cell bodies.
What is a ganglion?
A collection of neuronal cell bodies.
What is cephalization?
The concentration of special sensory and motor systems in the rostral (head) end of the body.
Define a comminsural nerves.
Nerves which cross the midline of the organism allowing information to be passed from one side of the body to the other.
Define axodendritic.
A synapse between an axon and a dendrite
Define neurophil.
Tissue comprised of a mixture of axons, dendrites and synapses.
What is a BMP?
Bone Morphogenetic Protein. This is a group of proteins responsible for generating dorsoventral patterning in vertebrates.
What is the role of sog in the dorsoventral patterning in drosophila?
Sog dictates the ventral side of the drosophila body plan. Sog is an antagonist to Dpp. Neural cells develop in the region where dpp is inhibited by sog.
What BMPs are responsible for generating the dorsoventral pattern in drosophila?
Dpp/sog. Sog is an antagonist to Dpp
What BMPs are responsible for generating the dorsoventral pattern in vertebrates?
BMP4/Chordin. Chordin is an antagonist to BMP4
Why is Telloid required for Dpp activation?
When Dpp is initially synthesized, it is in an inactive form, thus requires to undergo enzymatic proteolysis to be activated. Telloid contains metalloidprotease and therefore is a candidate for Dpp proteolysis. Thus activating Dpp.
What vertebrate BMP is homologous to Tolloid?
BMP1
What vertebrate BMP is homologous to Dpp?
BMP4
What vertebrate BMP is homologous to Sog?
Chordin
What vertebrate BMP is homologous to Skrew?
BMP7
Where does the nerve cord lie in invertebrates?
ventrally.
Where does the nerve cord lie in vertebrates?
dorsally
What is a coelenterate?
An organism characterized by a single internal capsule responsible for digestion, excretion and other functions.
What subdivisions of the Drosophila embryo arise as a result of Sog antagonising Dpp?
Aminoserosa and dorsal ectoderm.
Although homologues, why do Sog and Chordin act as a paradox?
Sog is expressed ventrally in drosophila.
Chorodin is expressed dorsally in xenopus.
Sog can promote dorsal development in Xenopus and Chordin can promote ventral development in drosophila.
What hypothetical pathway occurs in the absence of BMPs? Neural by default.
Neuralizing transcription factors (Xlpou2 and Sox2) are produced in the absence of BMPs. These activate the gene for Neurogenin.
Neurogenin then acts as a transcription factor to activate NeuroD.
NeuroD then acts as a transcription factor to cause the differentiation of cells into neurons.
Name two neuralizing transcription factors produced in the absence of BMPs
Xlpou2 and Sox2
Suggest 2 key differences between the NS of an invertebrate and a vertebrate.
Vertebrates NS lies dorsally whilst invertebrates NS lies ventrally.
In invertebrates, individual neuroblasts delaminate, then form neurones which form clusters called ganglia.
Whereas in vertebrates a sheet of cells on the dorsal side of the embryo are induced to form the neural plate. Through the process of neurulation, this then becomes the neural tube, ultimately becoming the NS.
What is neural induction and who was it proposed by?
Proposed by Spemann and Mangold.
Neural induction is the process by which a specialised group of cells (the organizer - hensens node) produce signals which cause the induction of neural development in the ectoderm.
Which germ layer contains the inducer node? (organizer region)
Mesoderm
Name 3 transcription factors expressed in the inducer node (organizer node)
Goosecoid, Xnot, Xlim
Under the influence of transcription factors goosecoid, xnot and xlim, the inducer node secretes antagonists of the BMP signal. Name 4 of these antagonists.
Chordin, Noggin, Frizbee, Follistatin,
What do BMP antagonists block?
The formation of ligand-receptor complexes
What is the name of the specialised border that develops ar the neural ectoderm boundary?
Neural plate border
What is the neural plate border crucial for?
Neural crest formation (peripheral NS development)
Roof plate formation and dorsal neural tube patterning/differentiation
Transferring a region of the dorsal lip (dorsal mesoderm) from an early blastula, in the stage of gastrulation, to another blastula in the ventral region causes the formation of a secondary body axis, why?
The dorsal lip (dorsal mesoderm) originally differentiates into notochord and prechordial mesoderm. It does this through curling (involuting) and convergent extension as it lies underneath the top (ectodermal layer) of the embryo. The process of convergent extension alters the shape of the embryo, thus creating the anterior-posterior and dorso-ventral axis.
What is convergent extension?
The process by which the tissue (collection of cells) of an embryo is restructured to converge (narrow) along one axis and extend (elongate) along a perpendicular axis.
What is the role of Shh?
Sonic Hedgehog Homologue is a protein secreted by the cells of the notochord. It establishes the ventral region of the dorso-ventral axis of the developing embryo
How, experimentally, has it been shown that BMP antagonists give neural expression? (2 types of experiments)
- Express BMP antagonists ectopically
- Injection of dominant negative effector (BMP receptors) of signalling pathway into organiser region
