Lecture 2 - Development Of CNS Flashcards
What is gastrulation?
The process where the bilaminar disc becomes the trilaminar disc
Briefly describe the process of gastrulation:
Outer layer of the bilayer germ disc invaginates at the primitive streak to produce a three layered germ disc
What are the 3 layers of the trilaminar disc?
Ectoderm
Mesoderm
Endoderm
What are some derivatives of the ectoderm?
Skin
Neural tissue and neural crest
What are the derivatives of the mesoderm?
Heart,vessels and muscles
Notochord (made of endoderm)
What are the derivatives of the endoderm?
Digestive and respiratory tracts
What is the function of the notochord?
Induces neuraltion
Induces the neural plate of ectoderm above it to start to fold in on itself to generate the neural tube = neurulation
What is notogenesis?
Formation of the notochord
Briefly describe notogenesis (formation of the notochord):
Made from the primitive node and migrates to form a rod like structure in the mesoderm during gastrulation
What is neuralation?
Formation of the neural tube
What structure induces neuraltion?
Notochord
What happens in neuraltion?
Notochord and paraxial mesoderm send signals to the overlying ectoderm causing it to thicken forming the neural plate
Neural plate thickens and begins to fold forming neural folds
Neural folds elevate and fuse in the midline at mid cervical level;
Neural crest cells detach and migrate
What way does the neural tube zip up/fuse?
Rostrally and caudally (pinches in the middle then moves rostrally and caudally)
What condition is caused if the neural tube fails to fuse in the rostral direction?
Anencephaly
What is anencephaly?
When the brain doesn’t form at all
What condition can be caused by failure of the neural tube to fuse in the caudal direction?
Spina bifida
How many main swellings form at the rostral neural tube?
3
What are the 3 main swellings from the rostral neural tube which become major parts of the adult brain?
Prosencephalon
Mesencepohalon
Rhombencephalon
What structures form from the prosencephalon, mesencephalon and Rhombencephalon?
Prosencephalon = forebrain
Mesencephalon = midbrain
Rhomencephalon = hind brain (4th ventricle that comes from this region is shaped like a rhombus)
Which of the 3 main swellings from the rostral neural tube are further subdivided into 2 swells?
Prosencephalon and Rhombencephalon
What does the prosencephalon subdivide into?
Telencephalon
Diencephalon
What does the rhombencephalon get subdived into?
Metencephalon
Myelencephalon
What forms fromt he telencephalon?
Most of the cerebral hemisphere
What forms from the diencephalon?
Thalamus
Hypothalamus
Optic nerve/retina
What is the function of the mesencephalon?
Boundary between fore and hindbrain
What does the metencephalon form?
Pons and cerebellum
Meta analysis happens after main research and pons and cerebellum sit behind or after the cerebrum
What does the myelencephalon form?
Medulla
What are the functions of the signals that the notochord produces during neuraltion?
Are BMP-4 inhibitors so causes ectoderm cells to proliferate
Generally, what part of the brain has the motor structures and what part of the brain has the sensory structures?
Motor = anterior (motor forwards)
Sensory = posterior (think occipital lobe for sight is posterior)
What structure determines the orientation of the brain and the spinal cord so that motor structures are anterior and sensory structures are posterior?
Notochord
What does the notochord produce to determine the orientaion of the brain and spinal cord structures?
Morphogens
What affect does the notochord have on the neural tube due to the morphogens?
Produces sonic hedgehog so that the cells of the spinal cord nearest to it becomes the ventral side
What does the ectoderm produce to stimulate dorsal fate?
BMP
What does the notochord stimulate the ventral portion of the neural tube/spinal cord to produce?
Basal/floor plate which gives rise to motor neurones
What forms in the dorsal portion of the neural tube in absence of influence of the notochord?
Alar/roof plate which gives rise to the sensory neurones
What roots are sensory and what roots are motor in the nervous system?
Sensory = dorsal root
Motor = ventral root
What neurones are found in the dorsal and ventral horns of the spinal cord?
Dorsal horn = sensory neurones
Ventral horn = motor neurones
How are the dorsal columns and the motor corticospinal tract postioned in the spinal cord?
Dorsal columns posterior
Corticospinal tract anterior
What forms from the neural tube central canal?
Brains ventricular system
What reflex is the superior colliculus important in?
Visual reflex’s
What reflex is the inferior colliculi important in?
Auditory reflex
How are the sensory alar and motor basal plates arranged in the neural tube at the brainstem?
Motor basal plates more medial close to canal and alar sensory more lateral
On a basic level how does the cauda equina form?
Initially cord fills entire vertebral canal
But as you get to L1 vertebra begin to grow faster than the spinal cord this stretches the lower portion of the cord producing the cauda equina
What is hydrocephalus?
Dilation of the ventricles of the brain due to occlusion leading to build up of CSF
How can neural tube defects predispose to hydrocephalus?
Cord gets tethered at site of defect
Spine grows and cord cant move within the vertebral canal so the brainstem containing the 4th ventricles gets pulled down through Foramen magnum becoming occluded so CSF builds up
What condition is caused by failure to close the neural tube in the cranial direction?
Anencephaly
What condition is caused by the failure of closure in the caudal direction (involves the spine/spinal cord)?
Spina bifida
What structure is failing to develop when the neural tube fails to zip up/fuse in the cranial or caudal direction?
Posterior vertebral arches
What is craniorachischisis?
Most severe neural tube defect where the tube completely fails to fuse both cranially and caudally
It is embryonically fatal since neither brain or spinal cord forms
What are some conditions caused by failure of the cranial neuropore to fuse?
Anencephaly
Cranial bifida
Cranial meningocele
What are the 4 main neural tube defects caused by failure of the caudal neuropore to fuse?
Spina bifida occulta
Spina bifida cystica
Meningocele
Myelomeningocele
Which neural tube defect involves the h spinal cord and so has neurological problems and which defect doesn’t?
Meningocele or myelomeningocele
Meningocele doesn’t involve spinal cord only meninges
Myelomeningocele involves spinal cord
What is myelocele?
Spinal cord fails to develop so the lumen of the neural tube is exposed to the outside world and is associated with a CSF filled cyst
Why are children with myelocoele at risk to meningitis and have neurological deficits?
Spinal cord doesn’t form properly
Neural tissue is exposed to the world
What is a Myelomeningocele?
CSF fillled cyst containing the spinal cord (meninges and neural tissue)
The vertebral body doesn’t fully close
Child will likely have neurological deficits
A type of spinal bifida cystica
What is a meningocele?
Presence of a CSF fille cyst that contains only the meninges
Type of spinal bifida cystica
How does myelomeningocele and meningocele present differently?
Meningocele transilluminates very well whereas Myelomeningocele doesn’t
Meningocele normally has good neurological prognosis whereas Myelomeningocele doesn’t
What are the 2 types of spina bifida c ystica?
Meningocele
Myelomeningocele
What is it called when the meninges herniate out of the fontanelles of the skull?
Cranial meningocele
What is spina bifida occulta and how does it present?
Hidden spina bifida where the vertebral arches fail to fuse
Site has an overlying tuft of hair and nothing else is really affected
How do you prevent neural tube defects?
Take folic acid 400mg daily from 3months before conception until week 12 of pregnancy
What other structure can folate deficiency lead to anomalies in except neural tube defects?
Palatial anomalies
What are neural crest cells?
Cells at the Lateral border that during neuraltion dissociates from their neibouring cells to form neural crest cells (they migrate from the neural tube)
What cells are derived from neural crest cells?
All neurones who’s cell bodies are in the PNS:
-primary sensory neurones
-autonomic postganglionic neurones
-enteric neurones
Schwann cells
Cells of adrenal medulla
Meloncytes
Leptomeninges
Head mesenchyme
What are the leptomeninges?
Arachnoid and pia mater
What tissue receives significant contribution from neural crest?
Thymus
Thyroid
Spiral septum of heart
Parts of teeth
Where do neural crest cells migrate from in the embryo?
Dorsal part
As neural crest cells migrate dorsal to ventral what structures do they leave behind?
Dorsal root ganglia
Sympathetic ganglia
Preaortic ganglia (receive input from splanchnic nerves)
Adrenal medulla (chromaffin cells)
Gut wall enteric nervous system
What are the 2 main neural crest cell defects?
Hirschsprungs disease
Di George Syndrome
What is Hirschsprung’s disease?
Neural crest cell defect
Lack of enteric nerves in sections of large intestine leading the Denervation of smooth muscle causing hypomotility and constipation
What is Di George syndrome?
Neural crest cell defect
Immunodeficiency due to involvement of thymus (neural crest cells have big contribution)
Facial anomalies (cleft/lip palate, low set ears, small jaw)
Heart anomalies
Hypocalcaemia (parathyroid involve
