CNS - Embryology Flashcards
What does the nervous system consist of?
Central and peripheral nervous system
What does the central nervous system consist of?
- Brain
2. Spinal cord
What does the peripheral nervous system contain?
- Cranial and spinal nerve
- Ganglia
- Plexuses
- Sensory receptors
What happens in the first week of human embryology?
From ovulation to implantation
What happens following fertilisation?
The nervous system begins to form in 3rd week of development: ovulation
What happens during fertilisation?
- Fallopian tubes
- Sperm and egg = zygote
- 1st cell of a new Individual
- Results from fusion of DNA sperm and egg
Morula
96h after fertilization
32 cells raspberry
Late blastocyst
5 day after fertilisation
64 cells surrounding a fluid-filled cavity
What is implantation?
Fastening of the blastocyst in uterine wall, 7d after fertilisation
Role of Trophoblast
Forming outer layer of blastocyst
Which provide nutrient to embryo and develop into large parts of placenta
When does Gastrulation happen?
Second week of development
What is Gastrulation?
Single layered Blastula reorganises into 3 layered Gastrula
What is outer layer of Gastrulation?
Syncytiotrophoblasts
Secrets B-hcg
What happens during Gastrulation?
3 distinct germ layers are formed:
- Ectoderm
- Endoderm
- Mesoderm
What are examples of Ectoderm?
Outer layer
- Skin
- Hair
- Sweat glands
- Epithelium
- Brain and nervous system
What are examples of Mesoderm?
Middle layer
- Body muscles
- Cartilage
- Bone
- Reproductive system organs and kidneys
What are examples of Endoderm?
Inner layer
- Digestive and respiratory system
- Liver
- Pancreas
- Gall bladder
- Thyroid and parathyroid glands
What is Neurulation?
The process of folding neural plate and closure of neural tube
What does notochord induce?
Ectoderm in dorsal midline to thicken and form neural plate
What happens at the edges of neural plate?
The neural fold bend towards each other
Meet dorsally and form neural tube and overlying epidermis
What happens during 3rd and 4th week gestation?
- Development of early neural tube is initiated by indentation along midline of neural plate forming the neural groove
- Deepening of the groove creates the flanking neural fold
- Pinched off from overlying ectoderm
What are neural crest cells?
A special group of cells break off from the neural fold during formation of neural tube
Where does neural crest cells emerge from?
Between neural tube and epidermis
What does progenitor cells of neural tube undergo?
Multiple division to form CNS
What are examples of neural crest cells differentiation?
- Sensory neurons
- Autonomic ganglion cells
- Chromaffin cells
- Schwann cells
- Melanocytes
- Connective tissue
What are examples of sensory neurons of neural crest cells differentiation?
- CN V, VII, IX, X
2. Sensory Ganglia (dorsal root) of spinal nerve
What are examples of autonomic ganglion cells of neural crest cells differentiation?
- Postganglionic neuron of para and pre-vertebral Ganglia sympathetic nervous system
- Postganglionic neuron of parasympathetic nervous system (visceral organ)
What is an example of chromaffin cells?
Adrenal Medulla
What is an example of Schwann cells?
Myelin in peripheral nerves
What is an example of melanocytes?
Pigment containing cells of the epidermis
What is an example of connective tissue
Many of the skeletal and connective tissue components of head
What is an example of mesoderm?
- Smooth muscle cells
- Osteoblasts/osteoclasts
- Adipocytes
- Chondrocytes
What are examples of ectoderm?
- Melanocytes
- Schwann cells
- Neurons
Where does neural tube closure proceed ?
Both rostrally and caudally
If neural tube closure is incomplete caudally
A child is born with spina bifida
If closure is incomplete rostrally
The brain will not develop
When is the CNS completely enclosed within embryo ?
Embryonic day 28
What happens during 5th week of development?
Swellings appear at cranial end of neural tube
3 primitive vesicles appear first
Subsequently develop into 5 secondary vesicles
What does the primitive vesicles give rise to?
Structures of brain and cerebellum as well as the ventricular system
What does the 3 primitive vesicles give rise to?
- Forebrain
- Midbrain
- Hindbrain
What does the prosencephalon divide into?
3 parts
Two-part Telencephalon and Diencephalon
Where does the paired telencephalic vesicles bulge out from?
Laterally from midline diencephalon
What are examples of Telencephalon?
- Cerebrum
- Cerebral hemisphere (cortex, white matter, basal nucleus)
Location: lateral ventricles
What are examples of Diencephalon?
- Thalamus
- Hypothalamus
- Epithalamus
- Retina
Location: 3rd ventricle
What are examples of mesencephalon?
Midbrain
- Brainstem
- Cerebral aqueduct
Lumen: cerebral aqueduct
What is the hindbrain named?
Rhombencephalon
What does the Rhombencephalon divide into?
- More rostrally metencephalon
2. More caudal myelencephalon
What does the lumen of hindbrain become?
4th ventricle
What are the divisions of hindbrain?
- Metencephalon
2. Myelencephalon
What are examples of metencephalon?
- Brainstem: pons, cerebellum
What are examples of myelencephalon?
- Brainstem: Medulla oblongata
2. Spinal cord: central canal
What are the cranial nerve of forebrain?
- Telencephalon - olfactory (I)
2. Diencephalon - optic (II)
What are the cranial nerves of mesencephalon?
CN III + IV
What are the cranial nerves for metencephalon and myelencephalon?
- Metencephalon - Trigeminal (V)
2. Myelencephalon - CN VI -XI
What develops to form the spinal cord?
The caudal end
What forms the brain and cerebellum?
The cranial end of neural tube
What becomes the dorsal horn (sensory)?
Cells on the dorsal side from alar plate
What becomes the central horn (motor)?
Cells on the central end from basal plate
What are the 3 zones that the CNS is composed of?
- Ventricular zone
- Intermediate zone
- Marginal zone
What is the ventricular zone?
Site where mitosis occurs
What is the intermediate zone?
Cellular area that contains post mitotic neuron and forms CNS gray matter
What is the marginal zone?
Axonal region that becomes CNS white matter
What does the dorsal spinal cord primarily contain?
Neurons relation to sensory function while motor neurons reside in the central spinal cord
Where are dorsal root Ganglia derived from?
Neural crest cells and are part of peripheral nervous system
What are the stem cell that proliferate in ventricular zone of neural tube?
- Neurons
2. Glial cells
What is the growth phase in neural tube (G1)?
The newly divided cells begin by extending a narrow cyclinder of cytoplasm to the outer surface of neural tube at the pia mater
The nucleus and cytoplasm surrounding it then move through this cyclinder toward the outer surface
What is the DNA synthesis phase in neural tube?
The nucleus approaches the outer surface and starts to replicate its DNA
What is the mitosis preparation phase (G2) in neural tube?
Nucleus migrate back toward central canal of neural tube while cell continues to develop
What does the central nervous system progenitor cell have?
Processes attached to both inner and outer surfaces of neural tube
When are neurons generated?
Before glial cells
What are the human embryo spinal cord?
Mantle layer (Intermediaye layer): grey matter
Marginal layer: white matter
Alar plate: sensory
Basal plate: motor
What does sulcus limitan separate?
Alar plate from basal plate
Where does motor nuclei developing from basal plate lie?
Centrally near midline
Where does sensory nuclei arising from alar plate lie?
More laterally and dorsally
What does Ancephaly result from?
Failure of neural tube to close at cephalic end, leading to partial absence of brain and skull
What does Spina bifida result from?
Incomplete closure of neural tube at caudal end (most commonly in lumbar region)
What are the 3 main types of Spina bifida?
- Spina bifida occutta (malformation of the spine)
- Meningocele (protective membrane around spinal cord push out through spine)
- Myelomeningocele (defect of backbone and spinal cord)
What are factors that increase the risk of Spina bifida?
- Low folic acid intake during pregnancy
- Family history of Spina bifida
- Medication (e.g. valproate and carbamazepine)
- Genetic conditions - occur alongside Patau’s syndrome, Edward’s syndrome or Down syndrome
What is Spina Bifida occulta?
- Mildest form
- Incomplete closure of vertebrae, without protrusion of spinal cord
- Discovery is often incidental
What is meningocele?
Meningeal cyst
- Least common form
- Meninges protrude between vertebrae posteriorly, but spinal cord is undamaged
What is myelomeningocele?
- Most severe form
- Portion of spinal cord remains infused and protrude posteriorly through opening between vertebrae’s in a sac formed by meninges
- Associates with severe disability
What are the many disabilities with myelomeningocele?
- Paralysis
- Difficulty with bowel and bladder control
- Chiari II malformation
- Hydrocephalus (excessive fluid in brain)
- Developmental delay
What is used to treat hydrocephalus?
Ventriculoperitoneal (VP) shunt
What is considered to be a treatment option for some cases of myelomeningocele?
Fetal surgery
What happens during the 5th week of embryonic development?
The neural tube begins to bend and fold
What happens as the forebrain expand rapidly?
The skull restricts further anterior growth and thus forebrain grows posteriorly
What does the expanding cerebral hemisphere eventually cover?
Diencephalon and much of the brainstem
What forms the characteristic grooves and ridges?
The smooth surface of cerebral cortex gradually fold inward
Where does the neural tube bend?
- Midbrain
- Pontine
- Cervical flexure and continue
What does space constraint in skull cause?
Majority of growing brain to be displaced posteriorly over brainstem
What does synaptic pruning allow?
Unused synapses to be eliminated
