Where does the nervous system develop from
The embryonic ectoderm
What week does the CNS appear
3rd week
Define the neural plate
thickening of ectoderm anterior to the primitive node
Define the Neural folds
Edges of the neural plate thicken and move upwards to form the neural folds
Neural fold migrate towards each other to form what?
Neural tube
Remains open at anterior and posterior ends
When does the anterior (cranial/rostral) neuropore close
Dat 25
18-20 somite stage
When does the posterior (caudal) neuropore close
Day 27
Where is neural tube closure initiated
Several points along A-P axis
When does neural tube closure begin
Day 18
When is neural tube closure completed
Day 27 (end of 4th week)
How many closure sites are there in humans
Up to 5
Failure of neural tube to close properly leads to what neural tube defects
Anencephaly
Encephalocoele
Spina bifida
How common is Anencephaly
1:1500
4 x more common in women
What causes Anencephaly
Failure of anterior neuropore to close
Skull fails to form
Brain tissue degenerates
incompatible with life
Define Craniorachischisis
Failure of neural tube closure along entire neuraxis
How common is Encephalocoele
1:4000 births
What is Encephalocoele
Herniation of cerebral tissue though a defect in the skull
Failure in closure of rostral neural tube
Where is Encephalocoele most common and where else can it be found
Occipital region
Fronto-nasal region
What is the cause of Spina Bifida
Defective closure of the caudal neural tube. Affects tissues overlying the spinal cord. Non fusion of vertebral arches
What are the types of Spina bifida
Spina bifida with meningomyelocele Spina bifida with myeloschisis Spina Bifida Occulta Spina Bifida Cystica Spina bifida with meningocele
Define Spina bifida with meningomyelocele
This is when the neural tube has failed to close and the neural tissue is exposed on the baby’s back
Define Spina bifida with myeloschisis
The nerve tissue is here fully bare and a dermal or meningeal covering is absent
Define Spina Bifida Occulta
Most minor form
Failure of embryonic halves of vertebral arch to grow normal and fuse
What are the features of Spina Bifida Occulta
No clinical symptoms
Dimple with small tuft of hair
What vertebral level does spina bifida occult occur
L5 and L6
What is Spina Bifida Cystica
Protrusion of spinal cord and/or meninges through the defect in the vertebral arches
How common is Spina Bifida Cystica
1:1000
What is Spina bifida with meningocele
Rarest form
Protrusion of meninges and CSF
What is Spina bifida with meningomyelocle associated with
Hydrocephalus
Neurological deficits- loss of sensation and muscle paralysis(loss of sensation and muscle paralysis)
What is the most severe form of spina bifida
Myeloschisis- • Spinal cord in affected area open due to failure of neural folds to fuse
When does the brain vesicles develop
Begins with closure of anterior neuropore (~day 25; 18 – 20 somite stage)
How is Spina bifida prevented
Folic acid supplements
How is Spina bifida diagnoses pre-natal
Maternal blood screening- AFP from foetal liver (16-20 weeks)
Aminocentesis (AFP in amniotic fluid)
US- anencephaly (12 weeks ) and spina bifida (16-20 weeks )
The forebrain develops from what vesicle
Prosencephalon
The Midbrain develops from what vesicle
Mesencephalon
The hindbrain develops from what vesicle
Rhombencephalon
What week does the 3 primary brain vesicles develop
4th week
What week does the 5 secondary brain vesicles develop
5th week
What is the Prosencephalon (Forebrain) made up in the 5th week
Telencephaln
Diencephalon
What is the Rhombencephalon (hindbrain) made up of in the 5th week
Metencephalon
Myelencephalon
When does the cephalic flexure develop and where is located
between midbrain (mesencephalon) and hindbrain (rhombencephalon)
When does the cervical flexure develop and where is it located
End of 4th week
Between hind brain and spinal cord
When does the Pontine flexure develop and where is it located
5th week In hindbrain (Rhombencephalon) between mesencephalon and Myelencephalon
What develops from the telencephalon (forebrain)
Cerebral hemispheres
Hippocampus
Basal ganglia
What develops from the Diencephalon (forebrain)
Thalamus
Hypothalamus
Pituitary gland
Pineal
What develops from the Mesencephalon (midbrain)
Superior and inferior colliculi
What develops from the Mesencephalon (hind brain)
Cerebellum, Pons
What develops from the Myelencephalon (hind brain)
Medulla
What forms the ventricular system
Lumen of neural tube
The lateral ventricle is formed where
Telencephalon
The 3rd ventricle is formed from
Diencephalon
The cerebral aqueduct (of sylvius) develops where
Mesencephalon
Where does the 4th ventricle is located
Mesencephalon
Myelencephalon
What connects the lateral and 3rd ventricle
Intraventricular foramina (of Monro)
When does CSF begin to be produced
5th week
Where is the CSF produced
Choroid plexus (3rd, 4th, lateral ventricles)
Where does the CSF drain into
Subarachnoid space via openings in roof of 4th ventricle and absorbed by arachnoid villi
Define Hydrocephalus
Accumulation of CSF due to frequently due to blocked aqueduct. prevents CSF from lateral and 3rd ventricles passing into the 4th ventricle and can’t drain it properly
What are the clinical features of Hydrocephalus
Enlarged brain and cranium
What are the causes of Hydrocephalus
Genetic
Prenatal viral infection
Intraventricular haemorrhage
Spina Bifida Cystica
What is the purpose of cellular differentiation in the neural tube
Need to make neuronal cells (neuron and glia) and connect cells together. begins early embryogenesis
Describe the lining of neural tube
- Initially a single layer of rapidly dividing neuroepithelial cells.
- Pseudostratified epithelium.
- Divide at ventricular surface.
What produces most cells of the CNS
Neuroepithelium
What doe Neuroepithelial cells develop into
Neuron
Astrocytes (protoplasmi, fibrous)
Oligodendrocyte
What produces Microglia
Mesenchymal cells that migrate into CNS
What forms the PNS neurone and glia
Neural crest
Name some Neural Crest derivatives
- Sensory neurons
- Autonomic neurons (sympathetic and parasympathetic ganglia)
- Schwann cells + satellite cells of ganglia
- Aortic plexuses (nerves surrounding the aorta)
- Endocrine cells (chromaffin cells of adrenal medulla; calcitonin producing cells of carotid body; parafollicular cells of thyroid).
- Enteric nervous system
- Pigment cells (melanocytes) – all pigment except RPE
- Leptomeninges of anterior brain (prosencephalon and part of mesencephalon)
- Non-neural head structures (including bone, cartilage and connective tissue).
- Teeth (dental papilla; odontoblasts)
- Iris muscle and pigment; ciliary muscles
- Corneal stroma
- Inner ear development
- Regions of the heart + walls of large arteries
- “4th germ layer”
Neural crest extend 2 processes
Peripheral process–> body
Central process–> dorsal horn of spinal cord
Motor component of spinal cord is derived from where
Neural tube
Describe the position of the spinal cord 3 months into development
Extends entire length of vertebral column
Vertebral column and dura mater grow more rapidly than what? what is the result
Spinal cord
Spinal cord at high levels )newborn L2/L3)
Adult -L1
Spinal nerves become elongated and form
Cuada equina
The Pia mater forms what structure
Terminal filum
What is the purpose of cortical folding
Saves space
brings together brain regions that would otherwise be far apart and optimises brain wiring and organisation
What is the the initial appearance of the cerebral hemisphere and what causes it to change
Initially smooth
Sulci and Gyri cause it to become a more complex pattern
At what week is the cerebral hemisphere smooth
14 weeks
At what week does the cortical folding begin
26 weeks
Define Lissencephaly
Rare brain disorder where the brain is smooth due to gyro and sulk failing to develop.
What causes Lissencephaly
Defective neuronal migration
What is the consequence of Lissencephaly
Severe mental impairment, failure to thrive, seizures and abnormal muscle tone. Die before 10 Y.O
Define Polymicrogyria
Excessive number of small gyri
mental retardation, seizes, motor deficits
What is Micorcephaly and what causes it
Reduced brain and skull size
Genetics, drugs, infection (zika)
What are the clinical signs of Microcephaly
Intellectual impairment, delayed motor functions/speech, hyperactivity, seizures, balance/co-ordination problems etc.
What is Aegenesis Corpus Callosum
complete or partial absence of the corpus callosum.
What are the clinical signs of Aegenesis Corpus Callosum
- Effects range from subtle – severe
* Cognitive and social difficulties intellectual impairment, seizures, hypotonia
What is Porencephaly
CSF filled cysts and cavities,
What is the cause and consequence of Porencephaly
Usually from stroke or infection
Delayed growth and development, seizures, hypotonia, intellectual impairment
What is Schizencephaly
Large clefts or slits in the brain
What causes Schizencephaly
Genetic
In utero stroke
Infection
Paralysis, seizures, intellectual impairment, development delay
What is Diastematomyelia
• Spinal cord split longitudinally into 2 parts
What is Diastematomyelia associated with
Vertebral abnormalities
Scoliosis, weakness of lower extremities, hairy patch over lower back, foot deformities, loss of sensation.
Name some causes of intellectual impairment
Genetic- Down's Syndrome Radiation Infectious agents(rubella, , toxoplasmosis, cytomegalovirus) Birth trauma Postnatal insults Maternal alcohol abuse