LM 3.0: Development of the Nervous System

Question 1

from where does the nerve system develop in an embryo?

Answer 1

from the ectoderm

Question 2

from where does the neural tube develop in an embryo?

Answer 2

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…

Question 3

what do the neural plate and tube give rise to?

Answer 3

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

Question 4

on what day of development do the cranial and caudal neuropores close?

Answer 4

cranial neuropore is closed on the 25th day of the embryogenesis

caudal neuropore is closed on the 27th day

Question 5

what happens do the neural tube as development continues?

Answer 5

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

Question 6

what gives rise to the PNS?

Answer 6

the neural crest gives rise to the PNS

PNS = cranial, spinal, autonomic ganglia and nerves

Question 7

what are the various neuroepithelial cells present in the neural tube during embryologic development?

Answer 7

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

Question 8

what are the stages of neuroepithelial cell differentiation?

Answer 8

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

1. apolar neuroblast –> neuron with an axon and dendrites
2. glioblast –> astroblast or oligodendroblast
3. ependyma –> epithelium of choroid plexus

Question 9

what do multi-polar neuroblasts differentiate into?

Answer 9

multi-polar neuroblasts form axon and dendrites and then become neurons

Question 10

what do glioblasts differentiate into?

Answer 10

glioblasts become astrocytes that later become protoplasmic and fibrillar astrocytes after migrating into the mantle and marginal zones

glioblasts also become oligodendroblasts and oligodendrocytes

Question 11

what is the function of oligodendrocytes?

Answer 11

oligodendrocytes form myelin sheaths around axons

the ependymal cell layer is formed from neuroepithelial cells around the ventricles and canals

Question 12

what is the order of neuroepithelial cell differentiation?

Answer 12

1. 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

2. then, other neuroepithelial cells differentiates into glioblasts

glioblasts migrate from the ventricular zone into the mantle and marginal zones and become astrocytes and oligodendrocytes

3. 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
4. lastly, microglial cells from neural crest cells migrate into the marginal and mantle zones

Question 13

what are the steps in cerebral cortex formation?

Answer 13

1. first, neuroblasts in the ventricular zone sprout fibers that form the marginal zone under the outer surface
2. 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

3. 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

Question 14

what are the layers of the brain during development??

Answer 14

OUTER SURFACE
marginal zone

cortical plate

intermediate zone

subventricular zone

ventricular zone (radial glial cell)

INNER SURFACE

Question 15

which layer in the development of the brain gives rise to the white matter?

Answer 15

the intermediate zone

it is devoid of neurons and comprised of mostly axons

Question 16

what are the steps for how the neural crest differentiate into the PNS?

Answer 16

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

1. neural crest –> neural crest cells –> spinal ganglion –> spinal nerve
2. neural crest –> neural crest cells –> melanocytes
3. neural crest –> neural crest cells –> ganglion of sympathetic trunk –> celiac ganglion, or renal ganglion or plexus in intestinal tract or suprarenal gland

Question 17

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?

Answer 17

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

Question 18

what is the sulcus limitans?

Answer 18

the part that separates the dorsal alar plate from the ventral basal plate

Question 19

what are the alar plates?

Answer 19

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

Question 20

what are the basal plates?

Answer 20

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

Question 21

what peripheral nerve systems are connected to the spinal cord?

Answer 21

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

Question 22

what is the function of Schwann cells?

Answer 22

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.

Question 23

what is the sympathetic nervous system?

Answer 23

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.

Question 24

what is the parasympathetic nerve system?

Answer 24

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.

Question 25

where do the meninges come from embryonically?

Answer 25

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

Question 26

what is the continuation of the pia mater past the conus medullar is called?

Answer 26

film terminale

this binds o the first coccygeal vertebra

Question 27

how does the length of the spinal cord change through development?

Answer 27

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

Question 28

what are the 3 primary vesicles fo the brain?

Answer 28

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:

Question 29

what are the 5 secondary brain vesicles that form during development?

Answer 29

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

Question 30

what is the function of the medulla?

Answer 30

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

Question 31

how does the myelencephalon become the medulla oblongata?

Answer 31

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.

Question 32

where are the pons and cerebellum embryologically derived?

Answer 32

metencephalon

Question 33

what is the function of the cerebellum?

Answer 33

coordination of fine movement

Question 34

what is the function of the pons?

Answer 34

provide a pathway for nerve fibers that connect the cerebral and cerebellar cortices to the spinal cord

Question 35

how is the cerebellum developed?

Answer 35

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.

Question 36

how does the inside of the cerebellum develop?

Answer 36

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.

Question 37

where if the midbrain embryologically derived from?

Answer 37

mesencephalon

Question 38

how does the midbrain develop?

Answer 38

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.

Question 39

how does the diencephalon develop?

Answer 39

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.

Question 40

how does the pituitary gland develop?

Answer 40

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

Question 41

what is spina bifida occult?

Answer 41

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

Question 42

what is spina bifida meningocele?

Answer 42

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.

Question 43

what is spina bifida meningomyelocele?

Answer 43

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