CSD 210 exam 3

what week does development of the CNS begin in embryology?

week three

in week three what are the three layers of the embryo?

ectoderm, endoderm, and mesoderm

what does the ectoderm form?

gives rise to the skin and outer connective tissues

what does the endoderm form?

the innermost part which gives rise to the organs

what does the mesoderm form?

it eventually forms into muscles

where does the neural ectoderm form?

at the dorsal portion of the embryo

what does the neural ectoderm form?

it gives rise to the future nervous system

what do the edges of the neural ectoderm form?

they give rise to the neural crest

how is the neural groove formed?

cells begin to bunch up and pressure forms, the neural ectoderm folds in at the top

what is the process of sinking and closing off of the neural groove?

cells continue to form the groove enlarges and the neural ectoderm sinks further down. it then proceeds to bulge in and drag the neural crest with it. eventually these two ends meet and close off to for the neural tube

how is the neural tube formed?

it is formed when the two edges of the neural crest meet and close off.

describe the neural tube

it is hallow with a fluid filled center

what will the neural tube eventually become?

future ventricles

what is important in the closing off of the neural groove?

it occurs in a pattern, which is important for future development

what is the first step in closing off of the neural groove?

the cervical region of the future spinal cord

what is the second step in closing off of the neural groove?

moves rostrally toward the anterior neurospace then caudally toward the posterior neurospace

what is the third step in closing off of the neural groove?

a massive cell proliferation occurs which proceeds the nervous system toward its next stage of development

what is the neural crest?

a group of cells that are derived from the crest of the neural folds

where are cells of the neural crest found?

on either side of the line of closure of the embryonic neural groove

what types of cells do the neural crest cells develop into?

sensory neurons, postganglionic neurons of the ANS, Schwann Cells (only in the PNS), and satellite cells of the PNS

what happens during the development of the neural crest?

cells communicate with the ectoderm toward formation of senses

what does the neural tube eventually become?

the brain and spinal cord

what does the ectoderm become?

the skin

what does the mesoderm develop into?

cranial vault and the vertebral column

should the cervical tube close before the anterior tube

yes

what does the cranial two-thirds of the neural tube become?

the brain

what does the caudal third become?

the spinal cord

in what order does the neural tube close?

middle, cranial, then posterior

What is the sulcus limitans?

a groove that appears in the lateral wall of the neural tube

What does the sulcus limitans do?

extends throughout and subdivides gray matter, sets up the foundational organization for the brain and spinal cord

what is the alar plate?

the zone dorsal to the sulcus limitans; becomes functionally divided for containing structures/pathways related to sensory processing

what is the basal plate?

the zone ventral to the sulcus limitans contains motor neurons and the motor processing structures/ pathways

posterior horn

the central process from sensory neurons from ascending sensory pathways

anterior horn

the cell bodies of motor neurons axons leave the spinal cord and innervate skeletal muscles

what are the three primary brain vesicles formed as the neural tube is closing off?

prosencephalon, mesencephalon, and rhombencephalon

in what week are the three primary brain vesicles forming?

week 5

what happens to the prosencephalon and rhombencephalon one weeks after they form?

the divide further into two secondary vesicles

what does the prosencephalon further divide into?

telencephalon and diencephalon

what does the rhombencephalon further divide into?

metencephalon and myelencephalon

what do bends and folds of the brain represent?

normal and correct development

where does the midbrain flexure occur?

ventrally

where does the cervical flexure occur?

ventrally at the junction between the hindbrain and spinal cord

where does the pontine flexure occur?

dorsally between these two flexures which results in thinning the roof of the hindbrain

what develops in the prosencephalon during week four?

the optic vesicles appear as two lateral bumps, this develops into the retinae and optic nerves. two larger protrusions appear behind and in front of the optical vesicles. this develops into the cerebral hemispheres which is now called the telencephalon vesicle.

each developing cerebral vesicle has what?

a lateral ventricle

what does the connection between the cerebral vesicles develop into?

lateral terminals

what is the lateral terminals the sight of?

closure of the rostral neurospace

what happens during telencephalon development?

massive cell proliferation

what happens on the basal part of the wall of the telencephalon?

further thickening which develops into the mass of neuron cell bodies called basal ganglia

what happens as cells continue to multiply and divide in the telencephalon

it folds down on top of the diencephalon and eventually fuses together

what is the area right over the telencephalon where it fuses together into the portion of the cerebral cortex called?

the insult

where does the diencephalon develop?

in the caudal forebrain. lateral to the third ventricle

what do both the thalamus and hypothalamus contain?

large amounts of cell nuclei

what happens when the mesencephalon doesn't form properly?

we see communication disorders

what does the mesencephalon become?

the midbrain

what does the rhombencephalon become?

the hindbrain

where does the fourth ventricle develop?

the rhombencephalon

where does the cerebellum develop in

Alar lamina

where does the pons develop?

Basal lamina

where does the medulla develop?

the myelencephalon

what are the three zones of the neural tube every where except the telencephalon

germinal zone, mantle zone, and marginal zone

germinal zone (NOT in telencephalon)

surrounds the ventricles and consists of cells which are born, divide and then get pushed out laterally

mantle zone (NOT in telencephalon)

when cells migrate here they lose their ability to divide and turn into neurons. from these neurons dendrites develop and axons spin off

marginal zone (NOT in telencephalon)

axons collect here become myelinated and travel. this structure is maintained with a central zone which is fluid filled, an area of gray matter where cell bodies are located and on the outside white matter where axons of cell bodies are found

what does the neural tube form the foundation of?

the spinal cord

what are the zones of the telencephalon?

germinal zone, intermediate zone, and outer cortical zone

germinal zone (IN telencephalon)

originally on the inside surrounding the lateral ventricles, with great cell proliferation it turns over on itself forcing it to become gray matter on the outside of the cerebral hemisphere

intermediate zone (IN telencephalon)

white matter is located here

outer cortical zone

is the six layer isocortex

spinal cord

as the neural tube closes its walls thicken and become stratified. the three layers become differentiated. the central canal becomes small in the spinal cord.

the PNS is derived from?

the neural tube

where are motor nuclei for all cranial and spinal nerves derived from?

the neural tube

how are the sensory nuclei formed from?

closing off the neural tube as neural crest cells separate from the closing neural tube

by week 25 the brain and spinal cord should have what?

a full set of neurons

what is teratogenesis?

abnormal development of an embryo that results in a deformed fetus

what does failure of the rostral or caudal neurospace to close result in?

a variety of congenital malformations

what is cranium bifidum?

the bone fusion posterior midline of skull does not occur. the brain and spinal cord protrudes through the opening.

spina bifida occulta?

most common and least severe. this represents the minimal degree of defect in which the halves of the vertebral arch fail to grow together at the midline. the skin of the back is epithelialized; a dimple, dermal sinus or hair growth.

spina bifida cystica?

most sever problem is characterized by a sac-like protrusion into the cleft between the unfused halves of the vertebral arch.

spina bifida with meningocele?

the sac contains only meninges and CSF (most commonly found in the lumbar area)

spina bifida with meningomyelocele?

the sac also contains tissues of the spinal cord or nerve roots. the spinal cord in not in the bottom where its supposed to be. (most commonly found in the lumbar area)

spina bifida with myeloschisis?

very rare and most severe; results in the failure of the neural tube to close over and extensive region of the spinal cord producing an exposed flat mass of neural tissue.

what is anencephaly?

cranial vault congenitally absent, cerebral hemispheres missing or reduced and attached to skull usually the brainstem is intact. infant will die in hours.

microcephaly

treatable but rare. the brain/ skull cap is small the face is normal the brain is underdeveloped. developmental deficits occur. Zika virus causes pregnant women to pass it onto their unborn babies.

Hydrocephaly

treatable if caught early. any abnormality involving expansion of the ventricular system of the brain. usually occurs from excess production of CSF or blockage from CSF flow. can result in enlarged head. brain atrophy, mental deficiency and convulsion. most common cause is fetal viral infection.

what are the three major functions of the brainstem?

conduit, cranial nerve, and integrative

what are the three parts of the brainstem?

medulla, pons, and midbrain

what does the conduit function do?

send information to and from, known as the information superhighway

what cranial nerves are housed in the brainstem

3-12

what does the integrative function do?

processes information and decides where it should go

medulla description

most inferior portion of the brainstem, transitions into the spinal cord is what connects the brainstem and spinal cord.

what cranial nerves are in the medulla

XII (hypoglossal) IX (glossopharyngeal) X (vagus) XI (accessory)

what are other structure(s) located on the lateral surface(s) of the medulla?

Olive

what are other structure(s) located on the posterior portion of the medulla?

Fasciculi cuneatus, cuneate tubercle, and fascicule gracilus

pons description

bulbous surface, located on its ventral surface. forms the center of the brainstem

what cranial nerves are on the pons?

V (trigeminal) VI (abducens) VII (facial) VIII (vestibulocochlear)

where is cranial nerve XII located in the medulla?

anterior towards lateral surfaces

where is cranial nerve IX, X, and XI located in the medulla?

off lateral grooves

where is cranial nerve V located in the pons?

enters at the midpons

where are cranial nerves VI, VII, and VIII located in the pons?

along the groove between the basis poutines and the medulla