Development of the Nervous system Flashcards
Describe the formation of the neural tube:
- Proliferation of the ectoderm in the dorsal midline of the embryonic disc called the neural plate
- Thickens and starts to fold up at the sides
- Two folds fuse dorsally to form a tube
Describe the formation of the neural crests:
A little bunch of cells at the tip of the neural fold separate from the neural tube and lie alongside it
What is present at the end of Early development of the nervous system?
At the end of this process you have a neural tube lying in the midline dorsally in the embryo and on either side of this you have two strips of neural crest tissue
What are the Neural Tube and Neural Crest sources of?
Neural Tube = All CNS cells
Neural Crest = All PNS cells
What is the neuroepithelium?
The wall of the neural tube
What three types of cells come from the neuroepithelium?
Neuroblasts
Glioblasts
Ependymal Cells
What do Neuroblasts differentiate into?
All neurones with cell bodies in the CNS
What do Glioblasts differentiate into?
Astrocytes and Oligodendrocytes
(Neuroglia)
What are Ependymal cells?
Cells lining the ventricles and central canal
They remain close to the inner membrane of the neural tube and they spread out and form a lining around the developing ventricular system
What do Neural crest cells differentiate into?
- Sensory neurones of the dorsal root ganglia
- Postganglionic autonomic neurons
- Schwann cells
- Non-neuronal derivatives e.g. melanocytes
Where do Motor Neurones originate from?
Neuroepithelium as they are neuroblasts because they have almost all their axons in the PNS but their cell bodies are in the CNS
Describe the organisation of the Neuroepithelium tissue:
Outer membrane
Neural Tube cells (Pseudostratified)
Dividing cells at the bottom
Inner membrane
Describe the process of Neuroepithelium differentiation:
- Cells withdraw from outer membrane towards inner membrane and undergo mitosis
- One daughter cell stays attached to the inner membrane and continues dividing
- The other migrates away from the inner membrane then develops into a neuroblast
- They develop processes (one will become the axon) which are further directed away from the inner membrane
What is the structure of the Neuroepithelium after initial differentiation has occurred?
Three layers:
White Matter - Axons
Grey Matter - Cell Bodies
Ependymal Layer - Dividing cells
What is the difference between the differentiation of Neuroblasts and Glioblasts?
Glioblasts show similar pattern of differentiation but can also migrate into White matter as well
Glioblasts do not develop axons (but do develop processes)
Label the layers of the Neural Tube in Cross-section
What controls the differentiation of cells?
Signalling molecules secreted by surrounding tissue which interact with receptors on the surface of neuroblasts
•Control migration & axonal growth by attraction and repulsion depending on concentration gradient & timing
What happens to the Neural Canal as the spinal cord further develops?
It becomes even smaller relative to the thickenss of the wall
What happens to the grey matter as the spinal cord develops further?
It splits into two types:
Alar Plate - Dorsal
Basal Plate - Ventral
What happens in the Alar Plate?
The interneurones are becoming specialised to receive sensory information and this information comes from the developing dorsal root ganglia that have developed from the neural crest
What happens in the Basal Plate of the developing spinal cord?
Development of Motor Neurones - The Basal Plate has a motor function - the axons leave the spinal cord to go towards the muscles
What happens to the neural crest cells in the developing spinal cord?
They form sensory neurones in the dorsal root ganglion
Label this Mature Spinal Cord:
What becomes of the neural canal in the mature spinal cord?
It becomes the central canal carrying CSF
What do the Alar Plates develop into in the mature spinal cord?
Dorsal Horns
What do the Basal Plates develop into in the Mature spinal cord?
Ventral Horns
What causes Dorso-ventral Patterning?
the Notochord and Ectoderm
The Notochord (ventral to the developing neural tube) produces signalling molecules establishing a concentration gradient so the closest cells are induced to become Motor Neurones (in the basal plates)
The ectoderm (dorsal to the neural tube) also produces signalling molecules that tend to inhibit differentiation to motor neurones
What develops into the brain?
The anterior of the neural tube
The wall of the anterior neural tube develops to form what?
(at how many weeks of development?)
Three primary vesicles:
Prosencephalon - Future forebrain
Mesencephalon - Future midbrain
Rhombencephalon - Future hindbrain
(around four weeks)
What happens to the developing brain in the fifth week?
Prosencephalon divides in two
(into Telencephalon and diencephalon)
Rhobencephalon divides in two
(Pons and Medulla)
Label this diagram of the developing brain at 5 weeks
What happens to the Neural canal in the developing brain?
What does it become?
The space in it becomes smaller relative to the wall
It forms the ventricular system
How does the Cerebellum develop?
It pouches out from the back of the pons
Quite late in development
Label these folds of the developing brain:
Recall what the folding of the Brain looks like as development progresses:
What happens in the development of the brainstem?
- The fourth ventricle develops from the neural canal
- The roof plate rapidly proliferates so the dorsal part expands laterally
- The expanding roof plate pushes the alar plates aside
Where are the Cranial, Motor, Sensory and Autonomic nerve nuclei located in the developing brainstem?
Cranial (that have motor function) = Medial
Motor = Medial
Sensory = Lateral
Autonomic = in between
How does the cortex develop?
- Neuroblasts are proliferating near the inner membrane
- Some will stay in the middle and form the basal ganglia
- The others migrate towards the outer membrane
- This happens in waves of proliferation and migration until there are six layers of cells within the cerebral cortex
- Each layer has different cell types with different functions and connections
How do neuroblasts migrate towards the outer membrane in the development of the cortex?
Neuroblasts attach themselves to radial glial cells which have their cell bodies anchored in the inner membrane and have a single long process that goes tot eh outer membrane
They climb up this process
