Development of the Nervous System Flashcards
3 distinct layers in the early development?
Ectoderm
Mesoderm
Endoderm
What forms the neural plate?
Proliferation of the ectoderm
What happens to the neural plate as it proliferates?
As the neural plate thickens, it folds on the sides, fusing dorsally - the space in the middle is called the NEURAL CANAL
What forms the neural crest?
A little strip at EITHER end of the dorsal tip of the neural fold forms the neural crest
Neural tube vs. neural crest?
Neural tube - all CNS cells (wall of tube made up of neuroepithelium cells)
Neural crest = all PNS cells
Cells that form the neural tube?
Neuroepithelium
What 3 cells can the neuroepithelium differentiate into?
Neuroblasts (all neurone w. cell bodies in the CNS inc. upper motor neurones)
Glioblasts (become neuroglia - astrocytes + oligodendrocytes)
Ependymal cells (line ventricles and central canal)
What 4 cells can the neural crest cells differentiate into?
Sensory neurones of dorsal root ganglia & cranial ganglia
Postganglionic autonomic neurones
Shwann cells
Non-neuronal derivatives e.g. melanocytes
Differentiation of neuroepithelium?
3 layers - inner membrane layer w. mitosis occuring, neuronal soma layer (white matter) and axonal layer (grey matter)
ALSO have an ependymal layer
Layers of the neural tube?
Innermost - ependymal layer (germinal layer)
Middle - grey matter (mantle layer)
Outer - white matter (marginal layer)
What control differentiation?
Signalling molecules - secreted by tissues which interacts with receptors on neuroblasts
These control migration & axonal growth via. excitatory and inhibitory action - this depends on [gradient] and timing
What are 2 significant features of the developing spinal cord?
- NEURAL CANAL is much SMALLER than the thickness of the wall
- GREY MATTER is split into 2 distinct types:
o Alar plate (dorsal)- receives sensory info
o Basal plate (ventral) - has interneurones and motoneurones to send info out of ventral roots
- receives sensory info
What does the fully developed spinal cord consist of?
ONENOTE!!
Neural canal
o becomes CENTRAL CANAL - now carries CSF
Alar plate
o develops into the DORSAL horns
Basal plate
o develops into the VENTRAL horns
Whole spinal cord becomes surrounded by a thick layer of WHITE MATTER
Where is the Notochord found?
Found just below the BASAL plate (ventral side)
What is the function of the Notochord?
Produces several signalling molecules
o establishes a [gradient] (highest near the notochord)
The cells within the neural tube closest to the notochord are therefore induced to become MOTOR NEURONES (in basal plate)
Where is the ectoderm found?
Dorsal to the neural tube
Function of the ectoderm?
Also produces signalling molecules
o establish a [gradient]
BUT
o tend to INHIBIT cell differentiation into MOTOR neurones
How is the brainstem developed?
Brainstem is a tubular structure
o BUT the 4th ventricle is in the middle so messes the organisation (developed first!)
The
o ROOF PLATE - proliferates rapidly
- this pushes the ALAR PLATES aside, so are NO longer dorsal to the roof plate
o DORSAL part - expands laterally
What does the development of the brainstem mean for the CNs?
CNs within the brainstem that have MOTOR FUNCTION
o tend to lie more MEDIALLY (as where basal plates end up)
Motor = medial Sensory = lateral Autonomic = in-between
What does the brain develop from?
Only the ANTERIOR portion of the NEURAL TUBE develops into the brain
Development of the brain at 4 weeks?
3 PRIMARY VESICLES form:
o Prosencephalon = future FOREBRAIN
o Mesencephalon = future MIDBRAIN
o Rhombencephalon = future HINDBRAIN
What happens in the week following the 4th week for brain development?
The most SUPERIOR VESICLE divides into 2 and The THIRD (inferior) VESICLE also divides into 2
i.e. this produces 5 SECONDARY VESICLES
Development of the brain at 5 weeks?
Forebrain
o Telencephalon - will become cerebral hemisphere
o Diencephalon - less expansion occurs here (eventually becomes thalamus, hypothalamus, epithalamus & subthalamus)
Midbrain
Hindbrain
o Pons
o Medulla
Development of the brain at 8 weeks?
As development continues, neural tube proliferates more & more
Space within the NEURAL TUBE (central canal) becomes smaller relative to wall
o becomes the VENTRICULAR SYSTEM
Development of the CEREBELLUM also beings
o out-pouching from the back of the pons
Folding of the brain during development?
The VESICLES are NOT in a straight line
o there are 3 FLEXURES
Name of FLEXURES based on position
o Cephalic flexure
o Pontine flexure
o Cervical flexure
Flexures during development of the brain?
Becomes more & more exaggerated upon development
ONENOTE!!
Grey matter and white matter in the brain?
Brain has
o a CORE of WHITE MATTER
o GREY MATTER is on the outside
Grey matter - nuclei that have migrated from the inner membrane of the neural tube
Where do neuroblasts proliferate?
Inner membrane
Explain the proliferation of neuroblasts in the development of the cortex
Some neuroblasts will stay in the MIDDLE
o forms the BASAL GANGLIA
Some neurones migrate towards the OUTER membrane:
o migration occurs by neuroblasts attaching themselves to radial glial cells
o the RADIAL GLIAL CELLS have their soma attached to the INNER membrane and have a SINGLE LONG PROCESS to the OUTER membrane
o the neurones hence CLIMB TOWARDS the OUTER membrane
How do the layers of the cortex develop?
The proliferations & migrations of the neuroblasts occur in WAVES
o this forms the layers of the cortex
o until you reach the 6th layer!
Each layer in unique
How do neural developmental disorders arise?
Genetic or environmental abnormalities!
Occurs early in gestation OR pregnancy
What environmental abnormalities can give rise to developmental disorders?
Schizophrenia - malfunction of neural development
Spina bifida - deficiency of folic acid
How to replace lost neurone?
Regulate stem cell differentiation
How to induce CNS regeneration?
Guidance mechanism for axons
