Lecture 8: Brain Development Flashcards
What parts of the CNS form during primary neurulation?
Future brain and lumbar spinal cord
What is the embryologic origin of the CNS
Ends of the neural plate fusing to form the neural tube
What part of the neural tube forms the brain?
Neural tube cranial to 4th somites
What are the three primary brain vesicles ?
- Prosencephalon: forebrain
- Mesencephalon: midbrain
- Rhombencephalon: hindbrain
What primary brain vesicles divide in the 5th week?
Forebrain (Prosencephalon)
Hindbrain (Rhombencephalon)
What does the prosencephalon give rise to?
- Telencephalon: cerebral hemipsheres, anterior 3rd ventricle & lateral venticles
- Diencephalon: thalami structures and 3rd ventricle
What are derivatives from the mesencephalon?
Midbrain and cerebral aqueduct
What does the rhombencephalon give rise to?
- Metencephalon: pons, cerebellum, and upper part of 4th ventricle
- Myelencephalon: medulla and lower part of 4th ventricle
What does the midbrain flexure divide?
Midbrain and forebrain
Flexes forward
What does the cervical flexure divide?
Hindbrain and spinal cord
Flexes forward
What does the pontine flexure divide?
Divides hindbrain into rostral metencephalon and caudal myelecephalon (pons/cerebellum and medulla)
Extending
What are some structures formed in the myelencephalon (medulla oblongata)?
- Alar Plate - lateral
- Nucleus Gracilus and Cuneatus
- Sensory modalities
- PCML Fibers
- Basal Plate - medial
- Motor modalities
- Pyramids (white matter dealing with motor tracts)
- Corticospinal Tract fibers
- Olivary Nuclei
What gives rise to sensory neurons that remain contained within the CNS?
Alar plate
What is the embryological origin of motor neurons that leave the CNS to go out to skeletal muscle?
Basal plate
Between the Alar and basal plates, which are lateral and which are medial?
Basal plates (motor) - medial
Alar plates (sensory) - lateral
What is the olivary nuclei
Neuroblasts that migrate ventrally from the alar plates in the medulla
What gives rise to the cerebellum?
Dorsal parts of the alar plates
What is cerebellar swellings
Cerebellum projects into 4th ventricle and overlaps pons, medulla and rostral part of the 4th ventricle
What coveres the ependymal roof of the 4th ventricle?
Pia Mater
What is tela choroidea?
Pia mater + ependymal roof
What forms the choroid plexus
Proliferation and investing of the tela choroidea into the 4th ventricle
How do the median and lateral apertures form?
The roof of the 4th ventricle evaginates, forming outpockets that rupture.
What gives rise to the superior and inferior colliculi?
where are they found?
Neuroblasts from alar plate that migrate to the tectum
Midbrain
Colliculi deal with vision/hearing, which are sensory
What gives rise to the tegmental nuclei?
What are some examples of tegmental nuclei?
Neuroblast of basal plate in the midbrain
- Red Nuclei
- Reticular Nuclei
- CN III Nuclei
- CN IV Nuclei
What gives rise to substantia nigra?
Where is it located in the brain?
Basal or alar plate that migrate ventrally
Midbrain
How and where is the cerbreal aqueduct formed
Midbrain
Narrowing of the neural canal
How and where are the cerebral peduncles (crus cerebri) formed?
Midbrain
Fibers growing from the cerebral cortex
What structures does the diencephalon give rise to
Thalamus, hypothalamus, epithalamus & pineal gland
Are diencephalon structures grey or white matter?
Grey Matter
Where do mammilary bodies come from
Form on ventral surface of hypothalamus
What major structure is the caudate nucleus located adjacent to?
Lateral ventricle
What embryological layer gives rise to the anterior lobe of the pituitary gland?
Hypophyseal diverticulum (Rathke’s pouch) from roof of stomodeum (primitive mouth)
- When it fuses with posterior pituitary gland, Rathke’s stalk degenerates
What embryological layer gives rise to the posterior lobe of the pituitary gland?
Neurohypophyseal diverticulum from floor of diencephalon
downgrowth of diencephalon (neuroectoderm)
What is Infundibulum
Derived from neurohypophyseal diverticulum. It’s the stalk of the pituatry that allows it to stay connected to the brain
How is the falx cerebri formed
Meschyme trapped in the longitudinal fissure of the telencephalon
What is holoprosencephaly?
SHH dysfunction that results in incomplete separation of cerebral hemispheres during development that can result in facial anomalies
Patient presents with epilepsy, headache, abnormal movements. Upon examination, he has a reduced frontonasal prominence and a cleft lip as well as some developmental delay. What disorder does he most likely have?
Holoprosencephaly
What are cerebral commissures
examples
Groups of nerve fibers interconnecting the cerebral hemispheres
- Lamina ternminalis
- Anterior Commissure
- Hippocampal comissure
- Corpus Callosum
Lamina Terminalis
Largest cerebral commissure. Others form within it. Extends from roof of diencephalon to optic chiasm.
Anterior Commissure
Interconnects the two parietal lobes
Hippocampal commissure
Interconnects the hippocampi within each hemishere
What can happen if there is agenesis of corpus callosum?
Seizures and mental deficiency
What are the layers of the cerebral cortex?
From top to bottom:
- Marginal Zone
- Intermediate Zone
- Subventricular Zone
- Ventricular Zone
Where are the older and newer neurons in the cerebral cortex?
- Older Neurons: Deeper (Layer VI)
- Newer Neurons: Superificial (Layer I)
Incomplete neuronal migration during 3-4 months can result in what brain disorder and what are the consequences
Lissencephaly (smooth brain).
Seizures, profound mental deficiency & mild spatic quadriplegia
Types of Lissencephaly
Pachygria (broad, thick gyri)
Agyria (lack of gyri)
Neuronal heterotopia (cells in aberrant positions compared to a normal brain)
What is Lissencephaly characterized by?
Ventriculomegaly (englarged ventricles)
malformation of corpus callosum
Microcephaly
Neurodevelopmental disorder where calvaria and brain are small, but face is normal sized
What can cause microcephaly?
- Autosomal recessive primary microcephaly
- Ionizing Radiation
- Infectious Agents’
- Cytomegalovirus
- Rubella
- Toxoplasma gondii
- Maternal Alcohol Abuse
