Basic Neuroanatomy Flashcards
macroglia
astrocytes, oligodendrocytes, and ependymal cells
glial cells
classified as macroglia and microglia
provide support and protection for neurons
outnumber neurons 10 to 1 in the central nervous system
astrocytes
largest glial cell
astrocyte support functions
regulates interstitial fluid
modulates signals that regulate blood flow in response to neuronal activity
provides structural support; astrocytes are essential components of the blood brain barrier and of glial-limiting membranes (aka glial limitans) that line the pia mater and parenchymal vasculature
provides nutritional support via glycogen storage
protects against the death of neurons by activating antioxidant pathways
astrocyte enzyme
glutamate synthase
glutamate synthase
important for the removal of excess glutamate and GABA from synapses
also plays a role in the detoxification of ammonia
astrocyte angiogenic factors
VEGF
VEGF
decreases the stability of the blood-brain barrier with inflammatory conditions and CNS tumors
immunohistochemical staining to identify astrocytes
stain for glial fibrillary acidic protein (GFAP)
glial fibrillary acid proteins (GFAP)
make up intracellular intermediate filaments located in astrocytic processes
reactive astrocytes
become reactive and hypertrophic from injury, infection, or chronic neurodegeneration
upregulate GFAP, proliferate, and form a glial scar that surrounds damaged CNS tissue
oligodendrocytes
responsible for the formation of myelin in the central nervous system
myelin
provides electrical insulation that allows for saltatory conduction, the speed of which is determined by the length of the internodal myelin segments. larger axonal diameters conduct faster than smaller diameters
identify myelinated fibers on microscope with
Luxol fast blue (LFB) staining
lack or paucity of LFB staining can suggest demyelinating disease
leukodystrophy and oligodendrocyte
typically involve metabolic and lysosomal pathways that are necessary for normal oligodendrocyte function
progressive multifocal leukoencephalopathy (PML) and oligodendrocytes
likely involves lytic infection of oligodendrocytes to induce demyelination
oligodendroglioma
primary brain tumors
classic ‘chicken wire’ appearance on histopathology and fried egg appearance
astrocyte-oligodendrocyte crosstalk
communication occurs by direct cell-cell gap junctions, as well as secreted signaling molecules
importance of astrocyte-oligodendrocyte communication is made apparent in primary astrocytopathies such as Alexander disease and osmotic demyelination syndrome
Alexander disease
rare leukodystrophy caused by mutations in GFAP gene resulting in accumulation of abnormal filaments (Rosenthal fibers) in astrocytes leading to oligodendrocyte death and demyelination
Infantile Alexander Disease
presents with megalencephaly, seizures, spasticity, and developmental delay
osmotic demyleination syndrome
astrocyte death is observed before oligodendrocyte death and demyelination
ependymal cells
produces and facilitates the movement of CSF
lines the ventricles and central canal of the spinal cord
resembles the cuboidal or columnar epithelium with some cilia and microvilli on histopathology
ependymal cells on histopathology
resembles the cuboidal and columnar epithelium with some cilia and microvilli
microglia
primary immune cell of the central nervous system
- responsible for antigen presentation
- activates in response to tissue damage and ischemic injury. once activated, becomes a motile, phagocytic cell (adept for neuronophagia) which forms reactive oxygen species and secretes cytokines and proteases
microglia derived from
smallest and rarest glial cell
derived from bone marrow/monocytes and enter the CNS in the perinatal period
- all other glial cells and neuronal cells are derived from neural tube cells
neuronal cells
responsible for receiving, integrating, and propagating information to other cells
parts of neuronal cells
dendrites
cell body
axons
dendrites
receive information from other neurons at synapses
changes in dendritic spines are critical for neural plasticity that occurs during development and learning
cell body
the main synthetic and trophic center of the cell, it contains the nucleus and most organelles
easily identified by a large central and euchromatic nucleus with a prominent nucleolus
basophilic clumps of polyribosomes are called Nissl bodies
Nissl bodies
basophilic clumps of polyribosomes
axons
conducts information to muscles, glands, and neurons
axons terminate at synapses
pyramidal cells
prototype cerebral neuron, present in the cortex and hippocampus, with large triangular cell bodies
stellate cells
described as GABAergic inhibitory interneurons that control Purkinje cell activity in the cerebellum
Betz cells
upper motor neuron cells that are the largest neurons of the cerebral cortex
- predominant neurons affected by motor neuron disease, such as amyotrophic lateral sclerosis
Purkinje cells
large distinct neurons in the cerebellum with a prominent pink cell body and extensive dendritic tree
these degenerate in various cerebellar degeneration syndromes (e.g. alcohol, chronic phenytoin use, or anti-Yo paraneoplastic syndromes)
identify neurons on microscope slides
silver staining, which impregnate neurofilaments
intracellular neurofibrillary tangles
suggest a neurodegenerative disease such as Alzheimer’s disease
Wallerian degeneration
caused by severe damage of the axons of the nerves
axonal fibers distal to the area of injury degenerate, while proximal fibers survive
neurofibrillary tangles
tend to occur in the amygdala, hippocampus, and temporal association cortices
senile (amyloid) plaques
tend to occur in the neocortex of the frontal, parietal, and temporal lobes
neuron action potential
blood brain barrier
highly selective barrier that maintains CNS homeostasis
CNS microvasculature contains continuous non-fenestrated blood vessels that tightly regulate the flow of proteins, ions, and cells between blood and parenchyma and is responsible for the influx of nutrients and the efflux of waste, toxins, and drugs
integrity of the blood brain barrier
depends on close apposition of astrocytic endfeet to blood capillaries, endothelial cells, and a thick basement membrane
- endothelial cells form the inner walls of the blood vessel and create tight junctions which function as a fairly impermeable barrier. transport occurs via either active or passive transport
simple diffusion of blood brain barrier
gases (CO2, O2), water, and non-polar, small, lipophilic molecules (ethanol, nicotine, diazepam)
transport through blood brain barrier
larger, polar, and/or hydrophilic molecules such as glucose, electrolytes, and amino acids
aquaporin 4
channels targeted in neuromyelitis optica (NMO) are present in astrocytic foot processes
pericytes and smooth muscle cells
integral neighboring cells of the blood brain barrier
damage to the blood brain barrier causes
can occur secondary to ischemic, traumatic, inflammatory, infectious, or metabolic derangements and leads to vasogenic edema
cytotoxic edema
results from cellular swelling, membrane breakdown, and cell death
vasogenic edema and cytotoxic edema
sometimes seen together. in the case of ischemic stroke, cytotoxic edema is seen in the hyperacute/acute phase, but vasogenic edema due to consequent damage to the blood-brain barrier can develop as soon as 6+ hours later, and reaches its peak at 1-2 days post-insult
areas that lack a blood-brain barrier
area postrema
pineal gland
posterior pituitary
choroid plexus
less significant: median eminence, subfornical organ, organum vasculosum, subcommissural organ, and lamina terminalis
area postrema
chemoreceptor trigger zone for vomiting
found int he dorsomedial medulla oblongata
pineal gland
solid organ that is located in the roof of the third ventricle and secretes melatonin
cysts are common here and can lead to obstructive hydrocephalus
posterior pituitary gland
responsible for the secretion of oxytocin and vasopressin
choroid plexus
produces CSF
ependymal cells lining the lateral and third ventricles form the choroid plexus and are responsible for CSF production
ependymal cells pathology
malignancy (ependymomas/subependymomas), ependymal cysts, and infection (ependymitis)
arachnoid granulations
small pouches of arachnoid mater that project through the dural wall of the major venous sinuses
- most CSF is reabsorbed into the superior sagittal sinus
volume of CSF
150mL of CSF is present in the ventricles and subarachnoid space at any given time
volume of CSF produced daily
500mL
route of CSF following production
enters the third ventricle via the interventricular foramen of Monro, then flows through the cerebral aqueduct and into the fourth ventricle. CSF leaves the fourth ventricle into the subarachnoid space through the medial foramen of Magendie and the lateral foramina of Luschka
foramen of Magendie
connects to the cisterna magna
foramen of luschka
connects to the cerebellopontine cistern
hydrocephalus
can occur with excess production of CSF, blockage of CSF circulation, or deficiency in CSF reabsorption
Obstructive hydrocephalus
occurs with mass lesions that compresses the flow of CSF
most common cause of hydrocephalus
common causes of obstructive hydrocephalus
pineal region tumors, intraventricular lesions, Chiari malformations, and aqueductal stenosis
non-obstructive hydrocephalus
occurs with impairment of CSF reabsorption through arachnoid granulations, which most often follows subarachnoid hemorrhage, venous sinus thrombosis, or meningitis
congenital aplasia of arachnoid granulations can also cause hydrocephaly in children with cranial dysplasia
intraventricular lesion locations
lateral ventricle
third ventricle
fourth ventricle
lateral ventricle intraventricular lesions
subependymoma, choroid plexus tumors
third ventricle
colloid cyst, subependymal giant cell astrocytoma, central neurocytoma
fourth ventricle
ependymoma, medulloblastoma
ventriculitis
possible complication of meningitis
on MRI, ventriculitis appears as fluid levels within the cortical sulci and within the posterior horns of the lateral ventricles
- T1 sequences with contrast will show extensive enhancement of the ependyma
