Neurology- embryology, neural tube defects, sleep Flashcards
What does the neural plate give rise to?
neural tube and neural crest cells
What causes the differentiation of ectoderm into neuroectoderm?
Signals from the notochord induce the overlaying ectoderm to differentiate into the neuroectoderm and form the neuroplate
-begins at about 18 days
What is the derivative of the notochord in adults ?
nucleus pulposus of the intervertebral discs
Recall: nucleus pulposus is inner gel-like center, surrounded by outer thick fibrous, anulus fibrosus
From what structure do the primary vesicles develop?
neural vesicles are the result of rapid growth of the cranial region of the neural tube
What are the primary vesicles?
There are three primary vesicles
- Prosencephalon - forebrain
- Mesencephalon-Midbrain
- Rhombencephalon- hindbrain
What are the secondary vesicles?
There are five secondary vesicles:
- Prosencephalon–> telencephalon & diencephalon
- Mesencephalon –> mesencephalon
- Rhombencephalon –> metecephalon, myelcephalon
Telencephalon
- neocortex, basal ganglia, limbic system, olfactory system
- lateral ventricles
Diencephalon
- thalamus, hypothalamus, subthalmus, epithalamus
- third ventricle
Mesencephalon
- midbrain
- cerebral aqueduct
Metencephalon
- pons, cerebellum
- upper fourth ventricle
Myelcephalon
- medulla
- lower fourth ventricle
What cell types develop from the neuroectoderm?
CNS neurons, ependymal cells, oligodendroglia, astrocytes
What cell types develop from the neural crest cells?
PNS neurons, schwann cells
Microglia develop from what germ layer?
Mesoderm
hint: like macrophages
From what structure does the spinal cord develop?
From the caudal portion of the neural tube
Alar plate
posterior portion of neural tube –> sensory structures of spinal cord
“alar is like alarm for sensory”
Basal plate
the anterior portion of the spinal cord —> motor structures of the spinal cord
What separates the basal plate from the alar plate?
Sulcus limitans
Spina bifida occulta
: failure of posterior vertebral arch to close but no structural herniation; usually in lower vertebral levels, dura is intact
-associated w/tuft of hair or dimple at the level of the bony defect
- neural tube defect = elevated AFP in amniotic fluid and maternal serum, elevated AChE in amniotic fluid
- associated with low folic acid intake before conception and during pregnancy
Meningocele
:meninges but not the spinal cord herniate through the bony defect
- neural tube defect = NORMAL AFP, elevated AChE in amniotic fluid
- associated with low folic acid intake before conception and during pregnancy
Meningomyelocele
:meninges and spinal cord herniate through spinal defect
- neural tube defect = elevated AFP in amniotic fluid and maternal serum, elevated AChE in amniotic fluid
- associated with low folic acid intake before conception and during pregnancy
Anencephaly
: malformation of anterior neural tube resulting in no forebrain, open calvarium (skull)
- elevated AFP, polyhydraminos (no swallowing center in brain)
- associated with maternal DM I
- maternal folate supplementation decreases the risk
Holoprosencephaly
:failure of left and right hemispheres to separate; occurs in 5-6 wk
- may be related to sonic hedgehog signaling pathway
- moderate form has cleft lip/palate, most severe form results in cyclopia
Arnold Chiari malformation (Chiari II)
: significant herniation of cerebellar tonsils and vermis through foramen magnum with aqueductal stenosis and hydrocephalus.
- often associated with meningomyelocele and paralysis below the defect
Dandy Walker
:angenesis of cerebella vermis and cystic enlargement of the 4th ventricle; huge dilated 4th ventricle in posterior fossa
-associated with spina bifida and hydrocephalus
Cerebral aqueduct stenosis
:congenital stenosis of the cerebral aqueduct which leads to hydrocephalus
- presents are enlarging head circumference in an infant
Wallerian degeneration
:degeneration distal to injury and axonal retraction proximally; allows for regeneration of axon if in the PNS
Nissl substance
stains RER of dendrites, RER not in axons
Astrocytes
: physical support, repair, K metabolism, removal of excess NT, component of BBB, glycogen fuel reserve buffer
- reactive gliosis (proliferation and hypertrophy) in response to neuronal injury
- astrocyte marker GFAP (glial fibrillary acidic protein)
- derived from neuroectoderm
Microglia
:CNS phagocytes; respond to tissue damage by differentiating into large phagocytic cells
- derived from mesoderm; part of the mononuclear phagocyte system
- HIV infected microglia fuse to form giant cells in CNS
Nodes of Ranvier
unmyelinated portions of axons that contain high concentrations of Na channels
-myelin + nodes of ranvier = saltatory conduction
What is the effect of myelin on signal conduction?
Increases the space constant and conduction velocity
Oligodendroglia
:myelinates the axons of neurons of the CNS.
- each oligodendrocyte can myelinated many axons
- predominant type of glial cell in the white matter
- Fried egg appearance on H & E stain
Schwann cells
:myelinated axons in PNS
-each schwanna cell myelinates only 1 PNS axon
What are the components of the BBB?
- tight junctions between non-fenestrated capillary endothelial cells
- thick basement membrane
- astrocyte foot processes
How do glucose and amino acids cross the BBB?
cross slowly via carrier-mediated transport
What kind of substances readily cross the BBB by diffusion
non-polar/lipid soluble substances cross the BBB rapidly via diffusion
What are the circumventricular organs?
:structures in the brain that lack normal BBB; allow blood-borne substances to be in contact with the brain and these organs can communicate with the periphery via hormones
“Mild SOAP”
1. Median eminence: part of the hypothalamic-hypophyseal portal system; allows hypothalamus secrete releasing/inhibitory molecules into portal system to reach anterior pituitary
2. Subfornical organ: wall of 3rd ventricle; contains receptors for angiotensin II –> induces thirst
3. Organum vasculosum of laminal terminalis (OVLT): osmotic sensing
4. Area postrema: wall of 4th ventricle, close to nucleus solitarius; chemorecpetor trigger zone for vomiting in response to GI toxins including after chemo
5. Pinel gland: 3rd ventricle; senses darkness to secrete melatonin
6. Posterior pituitary: oxytocin and ADH
Vasogenic edema
:results from the destruction of tight junctions of the endothelial cells that make up the BBB
-often destroyed in infarction or neoplasm —> leakage of fluid and intravascular proteins into extracellular space of brain
What regulates the circadian rhythm?
The hypothalamus via the suprachiasmatic nucleus (“need sleep to be charismatic”)
SCN –> norepinephrine release –> pineal gland –> melatonin
-SCN is regulated by retinal light sensing cells
What hormones are released as a result of circadian rhythm control?
noctural ACTH, prolactin, melatonin, norepinephrine
What controls extraocular movements during REM sleep?
PPRF (conjugate gaze center)
How often does REM sleep occur? How does it change throughout the night?
occurs every 90 minutes and increases through the night
What drugs are associated with decreased REM sleep and delta wave sleep?
EtoH, benzodiazepines, barbituates
-Norepinephrine associated with decreased REM sleep
How do you treat bedwetting?
oral desmopressin acetate (DDAVP) which mimics ADH; preferred over imipramine d/t adverse effects
What drug class if useful for night terrors and sleep walking?
benzodiazapines
What is the EEG wave pattern of the sleep cycle?
“BATS Drink Blood”
Beta, Alpha, Theta, Sleep spindles and K complexes, Delta, Beta
EEG sleep: beta
: highest frequency, lowest amplitude
-during awake eyes open
EEG sleep: alpha
Awake eyes closed
EEG sleep: Theta
Non-REM stage N1; light sleep (5% of sleep cycle)
What stage does bruxism occur? What waveform is expected on EEG?
Bruxism= teeth grinding
EEG: sleep spindles and K complexes (45% of sleep cycle)
What EEG waveform is seen in the deepest non-REM sleep stage?
:delta- lowest frequency, highest amplitude =slow wave sleep (25% of sleep cycle)
-when sleep walking, night terrors, and bedwetting occur
What happens during REM sleep?
loss of motor tone, increase in brain O2 use, increase in variable pulse and blood pressure
-when dreaming and clitoral tumescence (engorgement) occur
Tongue development
- Anterior 2/3 develops from 1 & 2 branchial arches _> sensation from V3, taste via CN VII
- posterior 1/3 develops from 3 & 4 branchial arches -> sensation and taste mainly from IX, extreme posterior va CN X
- motor innervation from CN XII
- muscles of the tongue derived from occipital myotomes
