Development of the Brain (Dennis) Flashcards
Describe neurulation
Week 3: Notochord induces posterior aspect of embryo to form neural plate and neural groove
Week 4: Neural tube forms from 5th somite (neurulation)
Cranial 2/3 (up to 4th pair of somites) part of the neural tube becomes …
Caudal 1/3 part of the neural tube becomes…
- future brain
- future spinal cord
When does cranial neuropore close?
When does caudal neuropore close?
- 25 days
- 27 days
How does the brain proper develop?
Neural folds in the cranial region will fuse while the rostral neuropore will close to form the primary brain vesicles
What are the primary brain vesicles?
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
What happens at week 5?
Secondary vesicles form
Describe the development of secondary brain vesicles:
Forebrain divides into telencephalon and diencephalon
Hindbrain divides into metencephalon and myelencephalon
Label the parts of the developing brain
OK
What does the developing brain do morphologically at week 5?
-Grows rapidly and bends ventrally (unequal)
-The bending produces the midbrain/mesencephalic flexure (midbrain) and cervical flexure (midbrain-SC junction)
Unequal growth produces the pontine flexure
What is the significance of these flexures?
Cervical
Pontine
- divides the hindbrain from the spinal cord
- divides the hindbrain into the metencephalon (rostral) and myelencephalon (caudal)
What does the myelencephalon form?
What does the metencephalon form?
What does the cavity of the hindbrain form?
- medulla oblongata
- pons and cerebellum
- 4th ventricle and central canal in the medulla
Describe what happens to the caudal part of the myelencephalon
Neuroblasts in alar plate migrate to the marginal zone to form the nuclei gracilus and cuneatus (sensory nuclei)
Pyramids with CST fibers form at the ventral side
Describe what happens to the rostral part of the myelencephalon
Pontine flexure causes wall of medulla to move laterally and the roof plate is thinned
After this movement, alar plate becomes lateral to the basal plate (sensory is lateral to motor)
What do the neuroblasts at the basal plate of medulla form?
Motor neurons form three separate circles/columns - GSE, SVE, GVE
What do the neuroblasts of the alar plate of medulla form?
Sensory neurons form the lateral circles/columns: GVA, SVA, GSA, SSA
Somatic efferent column
CNs: III (in mesenscephalon)
IV, VI, XII (in rhombencephalon)
Special/branchial efferent column
Rhombencephalon has V, VII, IX, X, XI
Visceral efferent column:
Rhombencephalon has salivatory and dorsal nucleus of vagus Mesencephalon has the Edinger-Westphal nucleus (III)
General visceral afferent column:
Has the nucleus that receives info via CN IX and X
Special afferent column:
Has the nucleus of the tractus solitarius, which receives taste impulses via CN VII, IX and X
General afferent column:
Receives general facial sensation (CN V and VII)
Oral, nasal and auditory cavities (CN V, VII, IX and X)
Special somatic afferent column:
Has cochlear and vestibular nuclei (VIII)
Metencephalon forms the …
Pons and cerebellum
What does the pontine flexure do specifically?
Pushes the walls of the pons laterally, spreads gray matter in floor of 4th ventricle
Each basal plate has neuroblasts that develop into motor nuclei
Cerebellum development
Forms from the dorsal part of the alar plate
Cerebellar swellings project into the 4th ventricle and fuse in median plane
Describe the formation of the choroid plexus
Ependymal roof of the 4th ventricle is covered by pia forming the tela choroidea. This structure invaginates the 4th ventricle to form the choroid plexus
Epithelium of the choroid plexus is derived from …
Stroma of the choroid plexus is derived from …
Neuroepithelium
Mesenchymal cells
What are the median and lateral apertures?
Evaginations of the 4th ventricle at 3 different locations. Formation of these apertures allow the CSF to enter the subarachnoid space from the 4th ventricle
What happens to the Alar plate neuroblasts in the midbrain?
Migrate to the tectum to form the superior and inferior colliculi
Cerebral peduncles are formed from …
Cerebral aqueduct formed from ….
Fibers growing from the cerebral cortex
Narrowing of the neural canal
Describe how the diencephalon develops:
Lateral walls of the 3rd ventricle will have swellings that form the thalamuses (thalamus, hypo and epi)
Functions of the epithalmic sulcus and hypothalmic sulcus
Separates the thalamus from the epithalamus and hypothalamus respectively
Describe how the thalamus develops
Bulges from the walls of the 3rd ventricle, fuses at midline and forms the interthalamic adhesion
Describe how the hypothalamus develops
It arises from neuroblasts in the intermediate zone . Develops endocrine and homeostatic nuclei and forms Mammillary bodies on the ventral surface
Describe how the pineal gland develops:
Forms a median diverticulum at the caudal part of the roof of diencephalon
Cells proliferate and form the cone shaped gland
Describe the development of the pituitary gland
Rathke’s pouch (hypophyseal diverticulum) grows upward from the stomedeum while the neurohypophyseal diverticulum grows downward from the diencephalon > cells of both diverticulum proliferate to form certain parts > Neuroepithelial cells differntiate into pituicytes and nerve fibers grow into the pars nervosa from the hypothalamus
Parts of the hypophyseal diverticulum:
Parts of the neurohypophyseal diverticulum:
Pars anterior and pars tuberalis
Median eminence, infundibulum and pars nervosa
Hypophyseal diverticulum comes from which lobe and which tissue type?
Neurohyophyseal diverticulum comes from which lobe and which tissue type?
- Anterior lobe, oral ectoderm
- Posterior lobe, neuroectoderm
Telencephalon:
What do the telencephalic/cerebral vesicles become?
What does the median cavity of the Telencephalon become>
Median cavity of the telencephalon forms the 3rd ventricle while the two telencephalic/cerebral vesicles are the primordia of the cerebral hemispheres.
What does the closure of the rostral neuropore induce?
Appearance of the optic vesicles (primordia of the retinae and optic nerves)
How doe the hemispheres and the 3rd ventricle communicate?
Via the interventricular foramina
Describe the development of the hemispheres:
From the primordia, hemispheres become more C shaped. Medial wall of the hemisphere becomes very thin and choroid plexus appears at this site.
Hemispheres expand and cover the entire thing and meet at midline
Falx cerebri develops from …
Mesenchyme trapped in the longitudinal fissure as the hemispheres develop
Holoprosencephaly (HPE):
Cause
Clinical
Incomplete separation of the hemispheres caused by defects in forebrain development = facial anomalies
Could result in cyclopia, premaxillary agenesis and other facial deformities
Cerebral commissures are
Nerve fibers connecting the cerebral hemispheres
Lamina terminalis forms
Septum pellucidum as it is stretched
Anterior commissure connects
Hippocampal commissure connects
Olfactory bulb with hemispheres
Hippocampal formations
Corpus callosum connects
Hemispheres along their length
Anterior develops before posterior
Agenesis of corpus callosum:
Absence of corpus callosum
Seizures and mental deficiency, but can be asymptomatic. Mostly associated with congenital syndromes
Describe the growth of cerebral hemispheres into sulci and gyri:
Cortex is smooth at first. It infolds and forms the gyri which basically increases surface area
Birth brain is only at 25% volume, reaches final size at age 7
Zones of the cerebral hemisphere:
Ventricular, intermediate and marginal. Subventricular appears later
Describe the histogenesis of the cerebral cortex:
Neurons migrate from deeper layers to form the superficial layers to form cortical layers (inside out development)
Lissencephaly
Incomplete neuronal migration to cerebral cortex at month 3 or 4
Smooth cerebral surface with gyri abnormality. Enlarged ventricles and malformed corpus callosum. Patient is normal at first but later develop seizures, mental deficiency and spastic quadriplegia
Pachygyria
Agyria
Neuronal heterotopia
- broad, thick gyri
- lack of gyri
- cells in weird positions compared to normal brain
Microcephaly
Reduction of brain growth due to inadequate pressure from growing brain. Caused by genetics, radiation, infection or alcohol abuse.
Calvaria and brain is small but face is normal sized.
