Lec.10 DEV'T OF CNS AND PNS Flashcards
The central nervous system (CNS) develops from the ____ once the latter has become specified into surface ectoderm and neuroectoderm.
The peripheral nervous system (PNS) develops in association with the CNS as the communication system between the CNS and the rest of the body.
ectoderm
____, a signaling molecule.
They signal the notochord to induce overlying ectodermal cells to differentiate into neuroectoderm.
Signaling molecules that act between cells within a close range are referred to as ____
Many of these are involved in induction and in ____
Sonic hedgehog
paracrine factors or morphogens
embryonic cell patterning
Cells from the primitive node invaginates and move towards the cranial end of the embryo.
the flattened tube will form the ____
They will eventually form the ____
notochordal plate
notochord
The development of the neural plate, a thickening of the ectoderm that represents the primordium of the nervous system, is induced by the notochord.
Subsequently, the neural plate folds and forms the ____
neural tube
*Neural Plate
The notochord, which is in close proximity to the midline neural plate during this stage, releases ____
Much of the surface ectoderm during gastrulation produces ____ this prevents the dorsal ectoderm from forming neural tissue.
sonic hedgehog molecules
Bone Morphogenetic Protein-4 (BMP4)
*Neural Plate
During neurulation, cells of the developing notochord secrete ____ and ____
These two molecules are neural inducers that block the inhibitory influence of BMP4 and thus allow the ectoderm dorsal to the notochord to form neural tissue.
noggin and chordin
*Neural Tube
Before neurogenesis, the neural plate and the neural tube are composed of a single layer of neuroepithelial cells (neuroepithelium).
Shortly after induction, the neuroepithelium organizes into a ____
pseudostratified epithelium
*Neural Tube
The nuclei shift extensively within the ____ as the cell cycle progresses.
These nuclei will migrate within the cytoplasm towards the lumen of the ____
The orientation of the mitotic spindle during this division is important for the fate of the daughter cells.
cytoplasm
neural tube
*Neural Tube
If the cleavage plane is perpendicular to the apical (inner) surface of the neural tube, the two daughter cells slowly migrate towards the _____ of the neural tube.
Here, they will prepare for another round of _____
periphery (edge)
DNA synthesis
*Neural Tube
If the cleavage plane runs parallel to the inner surface of the neural tube, the two daughter cells have different fates.
The daughter cell that is closer to the inner surface migrates away and remains a proliferative _____ that is still capable of mitosis.
progenitor cell
*Neural Tube
The daughter cell that is closer to the basal surface inherits a high concentration of the Notch receptor (regulates cell differentiation) and is now called a ____
These are the precursor cells of neurons and produces cell processes that will become axons and dendrites.
neuroblast
*Cell Lineages
During development, neural cells that are capable of self renewal and pluripotent / multipotent (stem cells) undergo many mitotic divisions.
They will be maturing into ____, which give rise to either neuronal or glial progenitor cells.
progenitor cells
*CNS Cells
Nerve cells
Neuroblasts, once formed, lose their ability to divide.
During further differentiation, several small cytoplasmic processes extend from their cell body. One of these processes elongates rapidly, forming the _____ Some forms branches (arborization) and become the ____
These cells can be now called multipolar neuroblasts that eventually become mature ____
primitive axon.
primitive dendrites.
multipolar neurons
*CNS Cells
Glial cells
The other major cell lineage from progenitor cells are the ____
They are formed by ____ after the production of neuroblasts ceases.
glial progenitor cells (glioblasts)
neuroepithelial cells
*CNS Cells
Glial cells
These cells can split into several lines.
One of the options for a glioblast is to become the ____
This will lead to either oligodendrocytes (forms myelin sheath) or astrocytes (aid in homeostasis and synapse formation).
O2-A progenitor cell.
*CNS Cells
Glial cells
The glioblast can also become ____ which forms the radial glial cells.
They act as guide wires in the brain for the migration of young neurons.
radial progenitor cells
*CNS Cells
Glial cells
The radial glial cells can differentiate into ____ Another type of glial cell of the CNS does not originate from the neuroepithelium.
These microglial cells, which act as motile macrophages after damage to the CNS.
astrocytes, specialized glial cells, ependymal cells and neurons.
*Spinal Cord Dev’t
With the beginning of cellular differentiation in the neural tube, the _____ thickens and appears layered.
Once cells in the neuroepithelial layer cannot proliferate further, they differentiate to become the ____ of the central canal and the ventricular system of the brain.
neuroepithelium
ependyma
*Spinal Cord Dev’t
The ventricular zone is surrounded by the ____
As the spinal cord matures, the intermediate / mantle layer becomes the ____
As the neuroblasts continue to develop axons and dendrites, a peripheral marginal layer is formed that will later become the ____ of the spinal cord.
intermediate layer
grey matter.
white matter
*Spinal Cord Dev’t
Continuous addition of neuroblasts to the intermediate layer thickens the neural tube ventrally and dorsally on each side.
The ventral thickenings are referred to as the ____
The dorsal thickenings on the other hand are called the ____
basal plates
alar plates
*Spinal Cord Dev’t
The left and right alar plates are connected dorsally by the ____
The two basal plates are connected by the
____
These plates do not contain neuroblasts, they only primarily connect one side to the other.
roof plate.
floor plate
*Root Ganglia & Spinal Nerves
Neural crest cells migrate from the edge of the neural folds and give rise to ____ of the spinal nerves.
They also give rise to other types of ganglia cells, Schwann cells, melanocytes, odontoblasts, and mesenchyme of the pharyngeal arches.
sensory or spinal ganglia (dorsal ganglia)
Initially, the spinal cord runs the entire length of the embryo.
Later, however, the vertebral column and the dura grow more rapidly than the spinal cord, leaving the posterior end of the cord terminating in the ____
This phenomenon is called ____
In adult animals the spinal cord terminates at the level of L2 to L3, depending on the species.
vertebral column
ascensus medullae spinalis
*Brain Dev’t
The anterior two-thirds of the neural tube develop into the ____
Fusion of the neural folds in the anterior region, and closure of the anterior neuropore, result in the formation of the ____
Brain
three primary brain vesicles
*Brain Dev’t
An expansion at the most rostral end of the neural tube forms the first brain vesicle, the ____
The optic vesicles grow out as evaginations from each side of the prosencephalon.
The two enlarged regions of the brain after the prosencephalon become the ____ and ____
prosencephalon or forebrain.
mesencephalon and rhombencephalon.
*Brain Dev’t
The prosencephalon partly divides into two vesicles, the ____
The anterior part of the forebrain, the telencephalon, forms the _____
telencephalon and
diencephalon.
cerebral hemispheres and the olfactory bulbs.
*Brain Dev’t
Although the cerebral hemispheres expand greatly during early pregnancy, their external surface remains smooth.
Later, they undergo folding and several major ____ and ____ begin to appear.
At the end of ____, the surface of each hemisphere becomes folded and develops the species-specific sulci (grooves) and gyri (elevations).
sulci and fissure
end of pregnancy
*Brain Dev’t
The posterior part, the diencephalon, gives rise to the epithalamus which includes the: ____
The diencephalon also forms the neurohypophysis and optic cups.
epiphysis
thalamus
metathalamus
hypothalamus
*Brain Dev’t
The ____ (midbrain) remains structurally relatively simple.
The midbrain functions as a relay system, transmitting information necessary for vision and hearing.
It also plays an important role in motor movement, pain, and the sleep/wake cycle.
mesencephalon
*Brain Dev’t
The rhombencephalon divides into the metencephalon and myelencephalon.
Metencephalon becomes ____
Myelencephalon becomes the ____
pons and cerebellum.
medulla oblongata.
*Brain Dev’t
The ____ represents the anterior portion of the rhombencephalon and develops into the pons and cerebellum.
The cerebellum, an alar plate derivative, is involved in coordination of movements.
metencephalon
*Brain Dev’t
How well the cerebellum is developed at birth is closely correlated with the age at which the animal is able to stand and walk.
In what animal?, much of the differentiation of the cerebellar cortex occurs postnatally; kittens and puppies do not walk in a coordinated manner for
carnivores
*Brain Dev’t
In what animals? the cerebellum is much more differentiated and functional at birth.
They are able to stand and walk within an hour of birth.
calves and foals
*Brain Dev’t
____ or the future medulla oblongata will serve as a channel between the spinal cord and the brain.
The medulla also contains important centers for the regulation of respiration and heartbeat.
Myelencephalon
*Brain Dev’t
The roof plate of the myelencephalon is reduced to a single layer of ependymal cells that is covered by mesenchymal cells forming the ____
Proliferation of the vascular mesenchyme produces a sac-like invaginations that will form a ____, which produces the cerebrospinal fluid.
pia mater
choroid plexus
*Brain Flexures
Differential growth of the five secondary brain vesicles gives rise to flexures (bending)
As head folding occurs, the mesencephalon bends ventrally to produce the ____
A second more gradual ventral bend between the hindbrain and the spinal cord is termed the ____
midbrain flexure (cephalic flexure).
cervical flexure.
*Brain Flexures
In the rhombencephalon a slight dorsal bending, the ____, occurs.
This flexure is located in the future pontine region and causes a thinning of the roof of the hindbrain.
pontine flexure
*Ventricular System
spinal cord, the lumen of the neural tube expands in the developing brain region.
As certain parts of the brain take shape, the lumen of the neural tube expands into well- defined ____, connected by thinner channels.
Ventricles produce ____
ventricles
CSF
*Peripheral Nerves
The peripheral nervous system (PNS), consists of the cranial, spinal, and visceral nerves and the cranial spinal, and autonomic ganglia.
PNS is comprised of____ nerve fibers that conduct impulses away from the CNS and ____ fibers that conduct impulses towards the CNS.
efferent (motor) nerve fibers
afferent (sensory) fibers
*Peripheral Nerves
Efferent as well as afferent nerves of the PNS can also be classified as being ____
This subdivision is based on whether a peripheral nerve terminates in tissues derived from the ____ (i.e. visceral tissue), or ____ (i.e. body wall tissue).
somatic or visceral.
splanchopleura
somatopleura
*Peripheral Nerves
General somatic efferent fibers are concerned with voluntary muscles derived from the ____
Special somatic afferent fibers are concerned with vision, hearing, and balance.
somatopleura
*Peripheral Nerves
____ fibers control the movement of: voluntary muscles derived from the pharyngeal arches
involuntary muscles and glands in the pulmonary and digestive tracts
the cardiovascular system
Visceral efferent fibers
*Cranial Nerves
By convention, ____ are used to designate the cranial nerves, with cranial nerve I being the most rostral and cranial nerve XII the most caudal.
One of the major differences between cranial and spinal nerves is the tendency of many cranial nerves to be either afferent or efferent rather than mixed.
roman numerals
Cranial nerves can be classified into three categories:
nerves with ____ (afferent)
____ that innervate pharyngeal arch derivatives
nerves with exclusively general somatic ____
special sensory function
mixed nerves
efferent fibers
what cranial nerves constitute the cranial nerves with special afferent functions.
Cranial nerves I (olfactory),
II (optic)
VII (vestibulocochlear)
cranial nerves that are classified as mixed nerves with both special visceral efferent and afferent components.
Cranial nerves V (trigeminal),
VII (facial),
IX (glossopharyngeal),
X (vagus),
XI (accessory)
cranial nerves that are general somatic efferent nerves.
Cranial nerves III (oculomotor),
IV (trochlear),
VI (abducent),
XII (hypoglossal)
____: receive sensory information from the skin, skeletal muscles and joints.
____: receive sensory information from the viscera (organs).
____: receive sensory information from the ectodermal retina, cochlear and vestibular apparatus.
____: receive sensory information from the endodermal nose and tongue.
GSA (general somatic afferent)
GVA (general visceral afferent)
SSA (special somatic afferent)
SVA (special visceral afferent)
____provide motor innervation to skeletal muscles.
____: provide secretomotor function to smooth muscle and glands.
____: provide motor innervation to skeletal muscles of the pharyngeal arches.
GSE (general somatic efferent):
GVE (general visceral efferent)
SVE (special visceral efferent)
*Autonomic Nervous System
The ____regulates many of the involuntary functions of the body.
It has a central regulatory role in the innervation of smooth muscle, cardiac muscle, exocrine, and endocrine glands.
autonomic nervous system (ANS)
The efferent portion of the autonomic system nerves (the general visceral efferent fibers) can be divided into:
The ____, originating from the thoracolumbar region.
The ____, originating from the cranial and sacral regions.
sympathetic nervous system
parasympathetic nervous system
