Risher - Development of Central Nervous System Flashcards
1. Understand how early embryonic development results in the formation of the neural tube and the various derivatives of the neural crest. 2. Identify the 3 and 5 vesicle stages of development and what mature CNS regions they give rise to. 3. Discuss abnormalities of CNS development.
Embryonic Germ Layers - Gives Rise to?
Ectoderm - CNS / PNS, parts of skin
Mesoderm - Blood vessels, bones, muscles
Endoderm - Inner lining of organs such as liver and pancrease
Germ layer origin of notochord?
Role?
Mesodermal
Induces neural plate development
Neurulation
Fusion of the Neural Tube (complete by day 28)
Brain Vesicle Formation and Differentiation:
Developing Structure - Mature Structure
- Telencephalon - ?
- Diencephalon
- Mesencephalon
- Metencephalon
- Myelencephalon
- Telencephalon - Cerebral Hemispheres
- Diencephalon - Thalamus
- Mesencephalon - Midbrain
- Metencephalon - Pons, Cerebellum
- Myelencephalon - edulla`
3 Vesicle Stage
Developing Structure - Mature Structure
Prosencephalon - Forebrain
Msesncephalon - Midbrain
Rhombencephalon - Hindbrain
Spinal Cord
5 Vesicle Stage
Developing Structure - Mature Structure
Telencephalon - Cerebral Hemisphere
Diencephalon - Thalamus
Optic Vessicle - Retina
Mesencephalon - Midbrain
Metencephalon - Pons
Myelencephalon - Medulla
Neural portion of the eye is derived from what?
Retina dericed from prosencephalon that gives rise to diencephalon
Spinal cord derivation?
Layers of Neural Tube?
Spinal cord derived from Posterior region of Neural Tube
In order of formation:
- Ventricular
- Mantle
- Marginal
Mantle Layer
Contains?
Becomes?
Marginal Layer
Becomes?
Contains primary neuronal cell bodies
Becomes grey matter in CNS
Axons extend into the Marginal Layer
- - -
Becomes white matter in CNS
What is neurocyte (immature neuron) migration organized around in spinal cord development?
What is the difference between Dorsal and Ventral Neurocytes?
Sulcus Limitans
Dorsal - Alar Plate (sensory)
Ventral - Basal Plate (motor)
Myelencephalon
Develops to?
Organization of Sensory / Motor
Medulla
Lateral = Sensory
Medial = Motor
Choroid Plexus
2 areas where neural tube does not fuse or close initially, main function is to produce cerebrospinal fluid (CSF)
Also act as blood/CSF barrier
Metencephalon
Develops to?
What are these derived from?
Pons & Cerebellum
Pons - Tegmentum, Basilar Pons
Cerebellum - Derived from Dorsal Alar Plate
Mesencephalon
Develops into?
Alar Plate develops?
Basal Plate develops?
What does the anterior portion contain?
Midbrain
Alar Plate - Superior (visual) Colliculus, Inferior (auditory) Colliculus
Basal Plate - CN IV, CN III
Anterior portion contains cerebral peduncle, motor tracts from cortex
Origin of Diencephalon?
What does it develop to?
What are these all derived from?
Prosencephalon
Epithalamus, Thalamus, Hypothalamus, Subthalamus
All derived from various aspect of the Alar Plate
Thalamus and Hypothalamus
Thalamus - Sensory relay center of the brain
Hypothalamus - Controls autonomic function through hormones (via pituitary gland)
Hypophysis (Pituitary Gland)
Most common cause of hypopituitarism in childrin
Remnant of Rathke’s Pouch, congenital cystic tumor
Telencephalon
Develops to?
Direction of migration?
Develops to Cerebral Cortex
Migrates from mantle into marginal layer
Neocortex vs Allocortex
What regions belong to the Allocortex?
Neo = 6 layers
Allo = 3 layers (smaller)
Allocortex regions:
- Paleocortex (Olfactory)
- Archicortex (Hippocampal)
Corpus Striatum
Emerges from?
Gives rise to?
Emerges from floor of lateral telencephalic vesicle
Gives rise to:
- Caudate nucleus
- Putamen
- Amygdaloid Nucleus
- Claustrum
- Globus Pallidus
- - -
2 & 5 Together make lentiform nucleus, which is separated from the caudate nucleus by the internal capsule
What makes the basal ganglia?
What clinical conditions are involved with this structure?
Caudate, Putamen, Globus Pallidus, Substantia Nigra
Vulnerable in movement disorders such as Huntington’s and Parkinson’s
Critical Periords for Neuronal/Synaptic Development
1st Critical Period: Rapid neuronal proliferation between 4th and 6th month (Zika Virus infects neural stem cells and reduces their numbers)
2nd Critical Period: Neuron process (axon/dendrite) growth and formation of synaptic connections from 3rd trimester to 2 y.o.
Astrocyte
Predominant cell type in the brain
Secrete instructive signals that facilitate the formation of synapses between appropriate axon/dendrite pairs
Synaptic Refinement
Elimination of weak inputs and strengthening of active ones by astrocytes and microglia from 0 - third decade of life
Myelination
Axon insulation that facilitates synaptic transmission
Begins in 4th fetal month and continues until the end of 2nd postnatal year (corticospinal tracts) compared to decade 3 in the neocortex
CNS vs PNS Myelination
CNS - Oligodendrocytes
PNS - Schwann Cells
Lissencephaly
Cephalic disorder resulting form faulty neuronal migration, children have developmental delay, seizure and shortened life expectancy
Spina Bifida
Spinal Bifida Occulta
Meningomyelocele
Myeloschisis
Neural tube defect where posterior neuropore fails to close properly
Occulta - Vertebral arch defect (least severe)
Meningomyelocele - Most common variation, typically present in Arnold-Chiari malformation
Myeloschisis - Most severe, no skin/meningeal covering
Anencephaly
Neural tube defect where anterior neuropore fails to close, not compatible with life
Encephalocele (cranium bifidum)
Ossification defect
Skull fails to close/ossify
May result in hydrocephalus, lumb paralysis, ataxia
Requires reparative surgery; shunts can be insrted to drain CSF
Dandy Walker Syndrome
Posterior fossa cyst leads to 4th ventrical dilation
Poor cerebellum development, lack of general brain development
Hydrocephalus
Excess CSF from blockage of circulation or overproduction leads to dilation of ventricles
Post Closure Defects:
Holoprosencephaly
Failure of cleavage and rotation, single ventricle
Can be caused by maternal diabetes, fetal alcohol syndrome risk factors
Encephaloclastic Defects
Porencephaly/Schizencephaly (loss of tissue)
Hydraencephaly (tissue loss replaced with fluid)
= Loss of tissue
Risk Factor: Materal Coccaine Use
Tethered Spinal Cord (Filum Terminale Syndrome)
Filum Terminale attached to wall of spinal canal
Weakness and sensory deficits in lower extremities
Transection can significantly alleviate symptoms
Cells Derived from Neural Crest during Neural Tube formation?
Melanocytes
Schwanna Cells
Adrenal Cells (Chromaffin)
Dorsal Root Ganglion Cells, Cranial Nerve Sensory Cells
Autonomic Ganglion Cells
