Development of the nervous system Flashcards
Which of the three germ layers does the nervous system arise from?
Ectoderm
Which structure that arises in the ectoderm forms the basis of the nervous system?
Neural plate
What happens to the neural plate once it starts to develop?
Starts to invaginate/fold > forms tube beneath ectoderm
What is the tube that forms beneath the ectoderm when the neural plate invaginates known as?
Neural groove
Where does the neural groove lie in relation to the notochord?
Neural groove is above notochord
What happens to the neural groove after it begins to form?
Deepens > edges come together and join in midline > creates a tubular structure that can break free from overlying ectoderm
What is the tubular structure formed from the folding of the neural groove called?
Neural tube
How is the neural tube formed?
Neural groove deepens > edges come together and join in midline > creates a tubular structure that can break free from overlying ectoderm
What is the first physical structure of the nervous system to form?
Neural tube
Describe the neural tube?
Simple tube Single cell thick
What does the neural tube go on to form?
Brain and spinal cord
What does the hole in the neural tube go on to form?
Ventricular system
What does the ventricular system arise from?
Hole in the neural tube
Describe the gradient that exists in the neural tube?
Rostral to caudal gradient
What is the consequence of the rostral to caudal gradient in the neural tube?
Development occurs faster at the head end and slower at the tail end Rostral end is older
Describe the order of neural tube closure?
Closure tends to start towards middle, and leave ends of neural tube open
Zippers shut up and down from that midpoint
Gove examples of birth defects that arise as a result of failure of closure of the neural tube?
Spina bifida
Anencephaly
Are the five ‘zipping’ processes in the closure of the neural tube dependent on each other?
No, largely indepedent
Briefly describe the segmentation process of the neural tube?
Rostral end of tube starts to well
3 distinct vesicles form
Further segmentation of these vesicles occurs
Name the three vesicles initially formed by the segmetation of the neural tube? Which brain structure does each vesicle correspond to?
Prosencephalon (forebrain)
Mesencephalon (midbrain)
Rhombencephalon (hindbrain)
What does the prosencephalon further divide into?
Telencephalon and diencephalon
What does the rombencephalon further didvide into?
Seven segments (r1-r7)
Whathappens to the part of the neural tube that does not become segmented?
Intact neural tube goes on to form spinal cord
What do the pons and cerebellum arise from?
Metencephalon division of rhombencephalon
What does the medulla arise from?
Myelencephalon division of rhombencephalon
What are the major derivatives of the telencephalon?
Cortex, basal ganglia, hippocampus
What are the major derivatives of the diencephalon?
Thalamus and hypothalamus
What does the caudal part of the neural tube go on to form?
Spinal cord
Describe the structure of the developing brain after neural tube segmentation has occured?
series of thin-walled bubbles
What is the neural crest?
cells tha lie between the neural groove and neural tube after the neural tube forms
What is the fate of the neural crest?
Cells migrate away to form a variety of structures:
- melanocytes
- PNS
- muscle, cartilage and bone of skul, jaw, face and pharynx
- dentine
Why are neural crest cells able to migrate so far throughout the developing embryo?
Cells are incredibly mobile
What is the longest migration that the neural crest cells undergo?
Enteric migration
Enter gut at oesophagus and migrate down to anal end
What feature of neural crest cells to cancer cells regain when they metastasise?
Ability to migrate through body tissues
What is the epithelium of the neural tube called? Describe it?
Neuroepithelium
Sinle cell thick, pseudostratified columnar
How is the cortex developed?
Neuroepithelium adds layers (6)
Dividing cells at the base move to new position at the outer
Which defects can lead to cortex malformation?
Defects in genes that affect migration
What is induction?
Developmental process in neurons that gives us the variety of neuronal types that we need for a functioning brain
Process for differentiating neurons
Describe the process of induction that occurs in the spinal cord?
Neural tube sits on top of notochord, which acts as prime organiser
Notochord sends out signals which affects closest part of neural tube
Floor plate formed > ANTERIOR/VENTRAL identified
Roof plate formed > POSTERIOR/DORSAL
Why is the floor plate so important in spinal cord development?
Cells start releasing signals > forms diffusion gradient up and across rest of spinal cord > cells immediately next to them know that they are in ventral part of spinal cord > form ventral horn motor neurons
What is the consequence of the absence of the floor plate?
No motor neurons develop
How are interneurons induced in the spinal cord?
Appear just dorsal to motor neurons due to inductive events
How do axons grow?
Grow out to meet target cell
Towed into position by growth cone
What are pioneer axons?
First axons to appear
Form a scaffold which later axons can build upon/follow
What are growth cones?
Structures which guide axon growth and tow them into position
Describe the structure of growth cones?
Dynamic structure of cytoskleleton
What guides axon navigation?
Growth steers towards target due to diffusible and membrane bound signals
Is the development of the nervous system complete at birth?
No; only a crude nervous system
What is the critical period in the development of the nervous system?
Time after birth in which refinement of the crude NS occurs
What is the effect of temporary eye closure during the critical period on the visual cortex?
Cortex changes
Open eye has greatly increased representation , deprived eye has greatly reduced representation
