SM02 Mini3 Flashcards
explain the process of primary neurulation
- notocord (derived from epiblast cells) stimulates process
- neural plate formation on the ectoderm above the notochord
- neural groove/crest formation D20/21
- neural tube folding & closure starts in middle
- closing progesses caudally & cranially
- cranial closes first
- all closed by end of 4th week
- sonic hedgehog (SHH) differentiates ventral/motor neurons
- bone morphogenetic proteins (BMPs) differentiate dorsal/somatosensory neurons
derivatives of neuroectoderm
- ependymal cells: glial cells that line ventricles
- bipolar neuroblast→ multipolar neuroblast
- glioblasts→
- astrocytes→ fibrillar & protoplasmic
- oligodendrocytes
- NOT microglia
microglia are derived from
mesenchyme
b/c they are the macrophages of the brain
when does myelination occur?
mostly after birth
what are the primary brain vesicles?
prosencephalon
mesencephalon
rhombencephalon
prosencephalon develops into…
telencephalon & diencephalon
mesencephalon develops into…
the midbrain
rhombencephalon develops into…
metencephalon & myelencephalon
structures of the telencephalon
cerebral hemispheres
olfactory tract/bulb
basal nuclei
structures of the diencephalon
thalamus
hypothalamus
epithalamus
pituitary gland
pineal gland
optic vesicle/cups
structures of the metencephalon
pons & cerebellum
structures of the myelencephalon
medulla
spaces of the telencephalon
lateral ventricle x2
space of the diencephalon
thrid ventricle
space of mesencephalon
cerebral aquedcut
space of metencephalon
upper half of fourth ventricle
space of myelencephalon
lower half of fourth ventricle
thalamus is derived from
diencephalon
medulla is derived from
myelencephalon
pons is derived from
metencephalon
cerebellum is derived from
metencephalon
cerebrum is derived from
telencephalon
pituitary is derived from
diencephalon
cervical flexure
bend of primary brain vesicles between rhombencephalon & spinal cord
cephalic flexure
bend in the primary brain vesicles between the mesencephalon & rhombencephalon
pontine flexure
bend in secondary brain vesicles between metencephalon & myelencephalon
generates fourth ventricle
isthmus rhombencephalon
narrow portion of embryonic neural tube connecting rhombencephalon to mesencephalon
hemispheric sulcus
groove separating diencephalon from telencephalon
parts of the midbrain
dorsal to ventral
- tectum: composed of superior & inferior caliculus
- superior→visual
- inferior→ auditory
- tegmentum
- w/cerebral aqueduct in the middle
how are the derivatives of the metencephalon related?
pons is found ventrally
cerebellum is dorsal
sulcus limitans
groove that demarcates the border between sensory & motor neurons throughout the CNS
secondary neurulation
folding of the primary & secondary brain vesicles
what causes neural tube defects?
failure of the neural tube to close
OR
failure of cerebral hemisphere separation
techniques for prenatal neural tube defects
amniocentesis or ultrasound
week 3 major developments
neural groove & folds
3 primary vesicles
cervical & cephalic flexures
appearance of motor neurons
week 4 major developments
- neural tube closure
- begins D21/22
- rostal D24/25
- caudal D26/27
- neural crest cells begin migration
week 5 major developments
- optic vesicle formation
- pontine flexure
- 5 secondary vesicles visible
- sensory nerves grow into CNS
- formation of other minor structures
major developments of W6-7
telencephalon enlargement around diencephalon
basal ganglion prominent
secondary neurulation complete
cerebellum & optic nerve begin
insula formation
major developments of W8-12
neural proliferation & migration
cerebral & cerebellar cortex begin
anterior commissure & optic chiasm formation
internal capsule
reflexes appear
major developments of W12-16
neuronal proliferation & migration
glial differentiation
corpus callosum formation
major developments of W16-40
neuronal migration
cortical sulci formation
synpase formation
glial proliferation & start of myelination
spina bifida occulta
incomplete vertebra formation
usually benign
covered with a tuft of hair
spina bifida
neural tube fails to close caudally
associated w/folic acid deficiency of mother during pregnancy
meningocele
protrusion of the meninges
fluid filled sac
sub arachnoid space
can be seen caudally in spina bifida or proximally in encephalocele
spina bifida meningomyelocele
protrusion of meninges & axons (usually filum terminale)
may pull hind brain into foramen magnum causing hydrocele
encephalocele
herniation of the meninges and sometimes brain from openings in skull
- meningocele: just meninges (dura & arachnoid)
- meningoencephalocele: meninges & brain tissue
- meningohydroencephalocele: meninges, brain tissue, & ventricular lumen
anencephaly
neural tube fails to close rostrally
associated w/maternal type I diabetes
vault of skull fails to form
exposed brain tissue degenerates
holoprosencephaly
failure of L & R hemispheres to separate
- lobar: one central incisor
- semilobar: cleft palate
- alobar: cyclopia
usually fatal
related to SSH mutations, fetal alcohol syndrome
which neuroembryologic signaling protein is found dorsally? ventrally?
BMPs dorsally
SHH ventrally
neuroepithelium
thick pseudostratified epithelium
found as wall of neural groove& extends over entire thickness of wall
give rise to neuroblasts & gliablasts
what happens to neural ectoderm that is pinched off when the neural tube rolls up?
neural crest cells
develop into PNS
spina bifida w/rachischisis
neural tissue is exposed
often become necrotic
most severe type of spina bifida
what structures are important for air conduction in the auditory system?
the external ear: pinna & external auditory meatus
what structures are responsible for neural conduction of sound?
inner ear: vestibule & cochlea
and CN VIII vestibulocochlear nerve
and ascending: cochlear nucleus
otalgia
ear pain
medical term for external ear infection?
acute ototis externa
what are the coiled tubular glands found in the external auditory meatus?
cerminous glands
how is the outer ear formed?
from the auricular hillock
1st & 2nd pharyngeal arches
six bumps (3 from each arch) rotate counter clockwise to form pinna
how does the tympanic membrane form?
fusion of the ectoderm of the 1st pharyngeal groove and the endoderm of the 1st pharyngeal pouch
what is the pinna made of?
plate of elastic cartilage covered by thin skin
what is the embryologic origin of the auditory ossicles?
accumulation of ectoderm from the 1st & 2nd pharyngeal arches
forms cartilage
and later bone
how are the vestibule and cochlea formed?
otic vesicle of ectoderm pinches off and migrates inward
develops into otocyst
forms vestibule & cochlea
bone labyrinth forms from surrounding mesenchyme
where is perilymph found?
scala vestibuli & scala tympani of the cochlea
where is Reissner’s membrane?
between the scala vestibuli and the scala media
where is endolymph found?
scala media
what type of cells form Reissner’s membrane?
2 layers of simple squamous cells
what forms the spiral ligament?
thickened periosteal lining of bony labyrinth
connects to bailar membrane of scala media
where is the basilar membrane?
between the scala media and scala tympani
what is the tectorial membrane?
gelatinous membrane that extends over hair cell in the organi of Corti
where are Deiters’ cells found?
aka outer phalangeal cells
supporting cells of the outer hair cells in the organ of Corti
what cells are supported by the inner phalangeal cells?
inner hair cells
what is the main structural differences between the inner & outer hair cells?
- inner hair cells
- rounded
- found in the single row along the inner pillar cells
- row forms U shape
- outer hair cells
- more columnar in shape
- form three rows outward from the outer pillar cells
- rows are in V or W shape
whic type of cochlear hair cell has a larger efferent than afferent neuronal connection?
outer hair cells
where are the ampullae found?
one on each vestibular canal
where are the maculae found?
one on the utricle and another on the saccule
function of the macula
detect linear movement of the head & gravity
function of the ampulla
detection of angular momentum of the head
where is the cupula found?
in the ampulla
what are the main difference between the hair cell types found in the vestibule?
- type I
- round, bulbous cell body
- afferent axon surrounds cell body
- myelinated afferent axon
- type II
- columnar shape
- unmyelinated afferent axon
cerumen is a mixture of secretions from which glands?
ceruminous & sebaceous
umbo
pit of the concave tympanic membrane
caused by connection to malleus
how do the scala vestibuli and scale tympani communicate?
via the helicotrema
stria vascularis
richly vascularized pseudostratified epithelium
secretes endolymph
lateral border of cochlear duct
