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Flashcards in Neurology Deck (33):
1

Neural Development

-Notochord induces overlying ectoderm to differentiate into neuroectoderm & form the neural plate
-Neural plate gives rise to neural tube & neural crest cells
-Notochord becomes nucleus pulposus of the intervertebral disc in adults
-Alar plate (dorsal): sensory -same orientation
-Basal plate (ventral): motor as spinal cord

2

Regional Specification of Developing Brain

Forebrain - Telencephalon -cerebral hem./lat. vent.
- Diencephalon - thalmus, 3rd ventricle

Midbrain - Mesencephalon-midbrain/aqueduct

Hindbrain - Metencephalon pons (upper part of 4th)
cerebellum
- Myelencephalon medulla (lower part of
4th ventricle)

3

Neural Tube Defects

-neuropores fail to fuze (4th week), persistent connection b/w amniotic cavity & spinal canal
-Associated with low folic acid intake before conception & during pregnancy
-Elevated alpha-fetoprotein in amniotic fluid & maternal serum
-inc. AChE in amniotic fluid is a helpful confirmatory test (fetal AAChE in CSF transudates across defect into the amniotic fluid)

4

Spina Bifida Occulta

-Failure of bony spinal canal to close, but no structural herniation
-usually seen at lower vertebral levels
-Dura is intact
-Associated with tuft of hair or skin dimple at level or bony defect

5

Meningocele

-Meninges (but not the spinal cord) herniate through spinal canal defect

6

Meningomyelocele

-Meninges & spinal cord herniate through spinal canal defect

7

Anecephaly

Forebrain Anomalies
-Malformation of anterior neural tube resulting in no forebrain, open calvarium "frog-like appearance"
-Clinical findings: inc. AFP; polyhydramnios (no swallowing center in brain)
-Associated with maternal diabetes (type I)
-Maternal folate supplementation dec. risk

8

Holoprosencephaly

Forebrain Anomalies
-Failure of left & right hemispheres to separate; usually occurs during weeks 5-6
-Complex multifactorial etiology that may be related to mutations in sonic hedgehog signaling pathways
-Moderate form has cleft lip/palate, most severe form results in cyclopia

9

Chiari II (Arnold-Chiari Malformation)

Posterior Fossa Malformations
-Significant cerebellar tonsillar & vermian herniation through foramen magnum with adueductal stenosis & hydrocephalus
-Often presents with thoraco-lumbar myelomeningocele & paralysis below the defect

10

Dandy-Walker

Posterior Fossa Malformations
-Agenesis of verebellar vermis with cystic enlargement of 4th ventricle (fills the enlarged posterior fossa)
-Associated with hydrocephalus & spina bifida

11

Syringomyelia

-Cystic enlargement of central canal of spinal cord
-Crossing fibers of spinothalmic tract are typically damaged first
-Results in a "cape-like" bilateral loss of pain & temperature sensation in upper extremities (fine touch sensation is preserved)
-Syrinx = tube, as in syringe
-Associated with Chiari I malformatio (> 3-5mm cerebellar tonsillar ectopia)
-Most common at C8-T1

12

Tongue Development

-1st branchial arch forms anterior 2/3 (thus sensation via CN V3, taste via CN VII)
-3rd & 4th arches form posterior 1/3 (thus sensation & taste mainly via CN IX, extreme posterior via CNX)
-Motor innervation is via CN XII
-Muscles of the tongue are derived from occipital myotomes

Taste: CN VII, IX, X (solitary nucleus)
Pain: CN V3, IX, X
Motor: CN XII

13

CNS/PNS Origins

-Neuroectoderm - CNS neurons; ependymal cells (inner lining of ventricles, make CSF), oligodendroglia; astroctes

-Neural crest - PNS neurons, Schwann cells

-Mesoderm - Microglia (like Macrophages, originate from Mesoderm)

14

Neurons

-Signal-transmitting cells of the nervous system
-Permanent cells-do not divide into adulthood (and, as a general rule, have no progenitor stem cell population)
-Signal-relaying cells with dendrites (receive input), cell bodies, & axons (send output)
-Cell bodies and dendrites can be stained via teh Nissl substance (stains RER). RER is not present in the axon
-If an axon is injured, it undergoes Wallerian degeneration-degeneration distal to the injury & axonal retraction proximally; allows for potential regeneration of axon (if in PNS)

15

Astrocytes

-Physical support, repair, K+ metabolism, removal of excess neurotransmitter, maintenance of blood-brain barrier
-Reactive gliosis in response to injury
-Astrocyte marker-GFAP

16

Microglia

-CNS phagocytes, mesodermal origin, not readily discernible in Nissl stains, have small irregular nuclei & relatively little cytoplasm
-Scavenger cells of the CNS, respond to tissue damage by differentiating into large phagocytic cells
-HIV-infected microglia fuse to form multinucleated giant cells in the CNS

17

Myelin

-inc. conduction velocity of signals transmitted down axons
-Results in saltatory conduction of action potential b/w nodes of Ranvier, where there are high conc. of Na+ channels
-CNS-oligodendrocytes
-PNS-Schwann cells
-Wraps & insulates axons, inc. space constant & inc. conduction velocity

18

Oligodendroglia

-Each myelinates multiple CNS axons (up to 50 each).
-In Nissel stains, they appear as small nuclei with dark chromatin & little cytoplasm
-Predominant type of glial cell in white matter
-These cells are destroyed in multiple sclerosis
-Looks like fried eggs on H&E staining

19

Schwann Cells

-Each myelinates only 1 PNS axon
-also promote axonal regeneration, derived from neural crest
-Inc. conduction velocity via saltatory conduction b/w nodes of Ranvier, where there are high conc. of Na+ channels
-These cells are destroyed in Guillain-Barre syndrome
-Acoustic neuroma: type of schwannoma
-Typically located in internal acoustic meatus (CN VIII)

20

Free Nerve Ending

-C-slow, unmyelinated fibers
-A(delta)-fast, myelinated fibers
-Location: all skin, epidermis, some viscera
-Senses: pain & temperature

21

Meissner's Corpuscles

-Large, myelinated fibers, adapt quickly
Location: Glabrous (hairless) skin
Senses: Dynamic, fine/light touch; position sense

22

Pacinian Corpuscles

-Large, myelinated fibers
Location: Deep skin layers, ligaments, & joints
Senses: vibration, pressure

23

Merkel's Discs

-Large, myelinated fibers, adapt slowly
Location: Hair follicles
Senses: Pressure, deep static touch (shape, edges), position sense

24

Peripheral Nerve

-Endoneurium-invests single nerve fiber layers (inflammatory infiltrate in Guillain-Barre)
-Perineurium (permeabiligy barrier) - surrounds a fascicle of nerve fibers. Must be rejoined in microsurgery for limb reattachment
-Epineurium-dense connective tissue that surrounds entire nerve (fascicles & blood vessels)

endo = inner peri = around epi = outer

25

Neurotransmitters: NE

Change in Disease: inc. in anxiety, dec. in depression
Locations of Synthesis: Locus ceruleus (pons)

26

Neurotransmitters: Dopamine

Change in Disease: inc. in schizophrenia, dec. in Parkinson's, dec. in depression

Locations of Synthesis: ventral tegmentum & SNc (midbrain)

27

Neurotransmitters: 5-HT

Change in Disease: dec. in anxiety, dec. in depression

Locations of Synthesis: Raphe nucleus (pons)

28

Neurotransmitters: ACh

Change in Disease: dec. in Alzheimer's; dec. in Huntington's, inc. in REM

Locations of Synthesis: Basal nucleus of Menert

29

Neurotransmitters: GABA

Change in Disease: dec. in anxiety; dec. in Huntington's

Locations of Synthesis: Nucleus accumbens

30

Locus Ceruleus

-stress & panic

31

Nucleus accumbens & septal nucleus

-reward center, pleasure, addiction, fear

32

Blood-Brain Barrier

-Prevents circulating blood substances from reaching the CSF/CNS. Formed by 3 structures:
1) tight junctions b/w nonfenestrated capillary endothelial cells
2) basement membranes
3) astrocyte foot processes

-glucose & aa cross slowly by carrier-mediated transport mechanisms
-nonpolar/lipid-soluble substances cross rapidly via diffusion
-a few specialized brain regions with fenestrated capillaries & no blood-brain barrier allow molecules in the blood to affect brain function (area postrema-vomiting after chemo-OVLT-osmotic sensing) or neurosecretory products to enter circulation (neurohypophysis-ADH release)

-infarction and/or neoplasm destroys endothelial cell tight junction leads to vasogenic edema
-Hypothalamic imputs & outputs permeate the BBB
-helps prevent bacteria infection from spreading into the CNS, also restricts drug delivery to the brain

33

Barriers other than the BBB?

-blood-testis barrier
-maternal-fetal blood barrier of placenta