LM 3.0: Development of the Nervous System Flashcards
from where does the nerve system develop in an embryo?
from the ectoderm
from where does the neural tube develop in an embryo?
the neural plate invaginates along the central longitudinal line, forming a neural groove and neural folds
then the neural folds fuse in the middle and thus form the neural tube!
during neural tube folding, neural crest cells next to the neural tube migrate ventrolaterally to both sides of the neural tube and form cranial and spinal ganglia and other peripheral nerve systems
go look at the picture…
what do the neural plate and tube give rise to?
the anterior two thirds of the neural plate and tube becomes the brain
the posterior one third become the spinal cord
the lumen of the neural tube becomes the ventricular system of the brain
on what day of development do the cranial and caudal neuropores close?
cranial neuropore is closed on the 25th day of the embryogenesis
caudal neuropore is closed on the 27th day
what happens do the neural tube as development continues?
the walls of the neural tube are thickened during the formation of the brain and the spinal cord
the cavity inside the neural tube becomes the ventricles of the brain and the central canal of the spinal cord
what gives rise to the PNS?
the neural crest gives rise to the PNS
PNS = cranial, spinal, autonomic ganglia and nerves
what are the various neuroepithelial cells present in the neural tube during embryologic development?
neuroepithelial cells in the ventricular zone are dividing and connected to each other via tight junctions
then neuroepithelial cells in the ventricular zone differentiate into neuroblasts and migrate into mantle zone
lastly, the neuroepithelial cells in the marginal zone are terminally differentiated
what are the stages of neuroepithelial cell differentiation?
ventricular zone –> intermediate mantle zone –> marginal zone
neuroblasts in the mantle zone gradually differentiate into apolar, bipolar, unipolar, and multipolar neuroblasts
neural tube –> neuroectoderm –> apolar neuroblast or glioblast or ependyma
- apolar neuroblast –> neuron with an axon and dendrites
- glioblast –> astroblast or oligodendroblast
- ependyma –> epithelium of choroid plexus
what do multi-polar neuroblasts differentiate into?
multi-polar neuroblasts form axon and dendrites and then become neurons
what do glioblasts differentiate into?
glioblasts become astrocytes that later become protoplasmic and fibrillar astrocytes after migrating into the mantle and marginal zones
glioblasts also become oligodendroblasts and oligodendrocytes
what is the function of oligodendrocytes?
oligodendrocytes form myelin sheaths around axons
the ependymal cell layer is formed from neuroepithelial cells around the ventricles and canals
what is the order of neuroepithelial cell differentiation?
- first, neuroepithelial cells in the ventricular zone differentiate into neuroblasts that migrate outward to form the mantle zone
mature neurons in the mantle zone becomes the gray matter –> the axons outgrowing from the mantle zone neurons form peripheral marginal zone that becomes the white matter
- then, other neuroepithelial cells differentiates into glioblasts
glioblasts migrate from the ventricular zone into the mantle and marginal zones and become astrocytes and oligodendrocytes
- after the differentiation of neuroepithelial cells into neuroblasts and glioblasts is completed, neuroepithelial cells along the central canal become ependymal cells that form ependymal layer of the central canal of the spinal cord
- lastly, microglial cells from neural crest cells migrate into the marginal and mantle zones
what are the steps in cerebral cortex formation?
- first, neuroblasts in the ventricular zone sprout fibers that form the marginal zone under the outer surface
- then, many neuroblasts migrate outward and form an intermediate zone between the marginal zone and the ventricular layer
some neuroblasts in the intermediate zone form a cortical plate between marginal zone and intermediate zone
the subventricular zone is formed between ventricular zone and intermediate zone
- then, the subplate layer is formed between the intermediate zone and the cortical plate
the cortical plate and subplate together form the definitive cerebral cortex
the intermediate layer forms the white matter of the cerebral cortex
what are the layers of the brain during development??
OUTER SURFACE
marginal zone
cortical plate
intermediate zone
subventricular zone
ventricular zone (radial glial cell)
INNER SURFACE
which layer in the development of the brain gives rise to the white matter?
the intermediate zone
it is devoid of neurons and comprised of mostly axons
what are the steps for how the neural crest differentiate into the PNS?
neural crest cells migrate along the lateral sides of the neural tube and form sympathetic ganglia at the dorsolateral aspects of the aorta
then the sympathetic ganglia are connected to each other by longitudinal fibers, which is called sympathetic trunks
some neural crest cells migrate to the aorta and form the celiac and mesenteric ganglia
neural crest cells also form terminal ganglia or plexus on the heart, lungs, and gastrointestinal tract
- neural crest –> neural crest cells –> spinal ganglion –> spinal nerve
- neural crest –> neural crest cells –> melanocytes
- neural crest –> neural crest cells –> ganglion of sympathetic trunk –> celiac ganglion, or renal ganglion or plexus in intestinal tract or suprarenal gland
during the development of the spinal cord from the neural tube, what are the two different plates formed at the ventral and dorsal aspects of the neural tube?
at the ventral side, the basal plates containing motor nerves are formed
at the dorsal aspects, the alar plates containing sensory nerves are formed
the roof and floor plates are formed above and below the neural tube canal
what is the sulcus limitans?
the part that separates the dorsal alar plate from the ventral basal plate
what are the alar plates?
the alar plates containing afferent sensory nerves form the dorsal gray horns of the spinal cord
the structure that comes between two alar plates is called dorsal septum
what are the basal plates?
they contain efferent motor nerves form the ventral and lateral gray horns of the spinal cord
the structure that comes between two basal plates is called ventral septum
what peripheral nerve systems are connected to the spinal cord?
At the ventral side of the spinal cord, somatic motor neurons sprout their axons through the marginal zone and form the ventral motor root. Somatic motor axons from the ventral roots form preganglionic fibers along with the axons from the sympathetic neurons in the intermediate horn
On the other hand, in the dorsal area, neural crest cells form sensory neurons in dorsal root ganglia. The sensory neurons in the dorsal root ganglia sprout two processes
what is the function of Schwann cells?
Schwann cells developed from neural crest cells wrap up the axons that exit from the spinal cord
Schwann cells form myelin sheaths around the axons of somatic motor neurons and preganglionic autonomic motor neurons of the PNS
Schwann cells also wrap up the axons of postganglionic motor neurons.
what is the sympathetic nervous system?
sympathetic motor nerves from the spinal cord connect to the peripheral organs from T1-L2
The preganglionic sympathetic fibers enter the sympathetic trunk and form synapses with peripheral sympathetic neurons.
Preganglionic fibers in the sympathetic ganglia also ascend or descend in the sympathetic trunk to reach their targets.
Ganglionic neurons in the sympathetic trunks sprout postganglionic fibers that also pass through the sympathetic trunk, reach, and form synapses at glands, vascular smooth muscle, peripheral blood vessels, hair, etc.
what is the parasympathetic nerve system?
The preganglionic parasympathetic fibers arise from the nuclei in the brain stem and in the sacral region of the spinal cord.
The parasympathetic pathways have long preganglionic fibers and short postganglionic fibers or plexus.
The parasympathetic nerves leave the brain stem via the cranial 3rd, 7th, 9th, and 10th nerves that are oculomotor, facial, glossopharyngeal, and vagus nerves.
Another sets of parasympathetic fibers leave from the spinal cord at the levels of Sacral 2 through Sacral 4.
where do the meninges come from embryonically?
the mesenchyme around the neural tube thickens and forms the spinal meninges
the outer layer becomes the dura mater and the inner layer forms the pia-urachnoid that consists of pia mater and urachnoid
the pia-urachnoid is also called leptomeninge. The spaces within the pia-urachnoid fuse with each other to form the subarachnoid space
what is the continuation of the pia mater past the conus medullar is called?
film terminale
this binds o the first coccygeal vertebra
how does the length of the spinal cord change through development?
it starts as the entire length of the vertebral column
then it shrinks to around S1 at 24 weeks
when you’re a newborn it stops around L3
but when you’re an adult the conus medlars is around the L1 level
what are the 3 primary vesicles fo the brain?
Initially, the primitive brain has three primary vesicles, forebrain, midbrain, and hindbrain; in other words, prosencephalon, mesencephalon, and rhombencephalon
Later, the primitive brain forms five vesicles:
what are the 5 secondary brain vesicles that form during development?
The prosencephalon is split into telencephalon and diencephalon
The mesencephalon stays as it is
The rhombencephalon is split into metencephalon and myelencephalon
THEN
telencephalon –> cerebrum
diencephalon –> thalamus, hypothalamus, epithalamus
mesencephalon –> midbrain
mesencephalon –> pons and cerebellum
myelencephalon –> medulla oblongata
what is the function of the medulla?
The medulla relays impulses between the spinal cord and the brain
it contains the brain parts that regulate respiration, heartbeat, and some reflex movements
it develops from the myelencephalon
how does the myelencephalon become the medulla oblongata?
The pontine flexure pushes the lateral walls outward, making roof plate thinner. The sensory nuclei in the alar plate are differentiated into three afferent incoming nerve groups.
General visceral afferent receives impulses from the viscera. Special visceral afferent receives impulse from taste fibers. Special somatic afferent receives signal from the ear.
The motor nuclei in the basal plate are differentiated into three groups. General somatic efferent sends impulse to the hypoglossal nerve in the tongue.
Special visceral efferent sends impulse to branchial nerve that goes through the neck, the shoulder, and the arm. General visceral efferent sends impulse to the vagus and pharyngeal nerves.
where are the pons and cerebellum embryologically derived?
metencephalon
what is the function of the cerebellum?
coordination of fine movement
what is the function of the pons?
provide a pathway for nerve fibers that connect the cerebral and cerebellar cortices to the spinal cord
how is the cerebellum developed?
the cerebellum develops by thickening the dorsal parts of the alar plates
The dorsolateral parts of the alar plates are bending to form rhombic lips
The rhombic lips are folding under the mesencephalon.
Upon deepening of the pontine flexure, the rhombic lips are compressed, thus forming the cerebellar plates: extraventricular and intraventricular.
Later, the vermis and two hemispheres show up in cerebellar plates. Then, the nodule and the lateral flocculonodular lobes are separated from the vermis and two hemispheres.
how does the inside of the cerebellum develop?
The primitive cerebellar plate containing the mantle and marginal layers develop between the mesencephalon and the roof plate of the 4th ventricle.
Neuroepithelial cells migrate to the surface of the cerebellum, forming the external granule layer.
Later, cells in the external granule layer migrate inward toward the Purkinje cells and becomes various cell types in the cerebellum. The dendate nuclei are formed above the fourth ventricle.
where if the midbrain embryologically derived from?
mesencephalon
how does the midbrain develop?
The narrowed cerebral aqueduct connects the 3rd and 4th ventricles. The superior and inferior colliculi are formed from the alar plate on the roof or tectum of the mesencephalon.
The tegmentum such as red nuclei, cranial nerve nuclei, and reticular nuclei are formed from the basal plate. The substantia nigra is also formed from the basal plate.
Nerve fibers from the cerebrum pass through the cerebral peduncles, in other words, crus cerebri, down to the brain stem and the spinal cord.
how does the diencephalon develop?
After the optic vesicles appear on the forebrain, the cerebral hemispheres grow dorsally and rostrally. The cranial and anterior part of the forebrain, including cerebral hemispheres, is called telencephalon.
The caudal and posterior parts together is called the diencephalon. On the lateral walls of the diencephalon, three swellings develop and become epithalamus, thalamus, and hypothalamus.
The epithalamic sulcus separates the thalamus from the epithalamus. The hypothalamic sulcus separates the thalamus from the hypothalamus.
The thalamus on each side bulges into the middle space of the third ventricle and fuses to form massa intermedia, also called as interthalamic adhesion. In the hypothalamus, various nuclei having different neuroendocrine functions are developed.
The hypothalamus is the brain center that controls overall endocrine activities in the body. A pair of pea-sized mammillary bodies (that connects amydala and hippocampus to thalamus) are formed on the ventral side of the hypothalamus.
The pineal gland develops on the roof of the diencephalon.
how does the pituitary gland develop?
The pituitary gland that connects the hypothalamus to peripheral endocrine systems also develops in the diencephalon.
The pituitary gland develops from two different origins. The ectodermal roof of the primitive oral cavity, also known as Rathke’s Pouch, grows up into the diencephalon. The neuroectoderm of the diencephalon grows downward to Rathke’s Pouch and joins the upgrowing ectoderm.
The upgrowing oral ectoderm becomes the adenohypophysis that consists of pars anterior and pars tuberalis.
Later, the physical connection of the adenohypophysis with oral cavity is lost. The down-growing neuroectoderm, called as infundibulum, becomes neurohypophysis that consists of median eminence, infundibular stem, and pars nervosa.
Later, the adenohypophysis becomes the anterior pituitary lobe and the neurohypophysis becomes the posterior pituitary lobe
what is spina bifida occult?
Defective closures in the middle of the neural tube cause congenital malformations in the spinal cord
Spina bifida occulta occurs in the sacrolumbar region and is covered by skin
what is spina bifida meningocele?
Defective closures in the middle of the neural tube cause congenital malformations in the spinal cord
Spina bifida meningocele is caused by the protrusion of the meninges of the spinal cord while the spinal cord is still inside of the body.
what is spina bifida meningomyelocele?
Defective closures in the middle of the neural tube cause congenital malformations in the spinal cord
In spina bifida meningomyelocele, both meninges and spinal cord are protruded to outside of the back. In myeloschisis, spinal cord is exposed to the outside of the back
