CNS Flashcards
what is nervous tissue responsible for?
receptive, motor, and integrative functions
neurons transmit ____
electrochemical signals
neuroglia functions
insulate, nourish, support, and protect neurons
what is the major difference b/w the brain & the spinal cord?
the arrangement of gray and white matter
where is gray matter located in the spinal cord?
centrally located
how are gray and white matter arranged in the brain?
core of white matter and superficial layers of gray matter
where do most brain tumors originate?
glial origin
embryogenesis
form structural framework to guide migration of developing neurons
astrocytes
-present in the CNS
-branching cells with cytoplasmic processes ending in expansions called end-feet
end-feet of astrocytes
-expansions of astrocytes
-cover neurons, the inner surface of the pia mater, and every blood vessel of the CNS
glia limitans (glial limiting membrane)
joined end-feet processes coating the pia mater
functions of astrocytes:
-regulate interstitial fluid composition
-neurotransmitter metabolism
-potassium balance
-vascular end-feet interact with vascular endothelium to form blood-brain barrier
-distinguished by presence of glial fibrillar acidic protein
what are the two types of astrocytes?
-protoplasmic astrocyte
-fibrous astrocyte
protoplasmic astrocyte
-common in gray matter
-many branched processes
-look like bushes
fibrous astrocytes
-common in white matter
-long, unbranched processes
-help capillaries regulate interstitial fluid composition
-maintain blood-brain barrier via foot processes
components of blood-brain barrier
-CNS endothelium
-basal lamina
-pericytes
-end-feet of astrocytes
CNS endothelium fx in blood-brain barrier
unfenestrated capillaries joined by tight junction
basal lamina fx in blood-brain barrier
mechanical support and barrier to macromolecules
pericytes fx in blood-brain barrier
regulate endothelial cell morphology & may have macrophage activity and antigen presentation
what are the MAIN components of the blood-brain barrier?
tight junctions b/w endothelial cells
oligodendrocytes
-most numerous glial cells
-found in both gray & white matter
-nuclei small & dark-staining
oligodendrocyte
form myelin for multiple axons in CNS
demyelinating diseases
-affect the integrity of myelin
-can be immune-mediated, inherited, metabolic or virus-induced
multiple sclerosis (MS)
-immune-mediated disease
-multiple areas of demyelination in the CNS
Guillan-Barre syndrome
multiple areas of demyelination in the PNS
microglia
-elongate, with ramified dendritic morphology
-smallest & rarest
-phagocytic; derived from mononuclear phagocyte system
-found at synapses, somas, and along vasculature
-use cytokines to recruit leukocytes of the peripheral immune system when brain is damaged or an infectious agent encountered
-play crucial roles in important diseases
synaptic stripping
prune nerves near damaged tissue to promote growth/repair
AIDS effects on CNS
-increased microglial activity observed
-HIV-1 does not attack neurons but it does infect microglial cells that produce cytokines toxic to neurons
ependyma
-cuboidal epithelium
-lines ventricles & central canal of spinal cord
choroid plexus
-formed from modified ependymal cells
-secretes CSF
endothelial cells in CSF
LACK tight junctions & ARE fenestrated (opposite of normal endothelial cells in CNS)
formation of CSF
- endothelial cells have hydrostatic pressure that produces a net flow of water, solutes, and proteins that enter the surrounding loose CT
- fluid, solutes, and proteins enter the cell
- Na+, K+-ATPase. pumps Na+ into the lumen of the ventricle & produces a gradient that facilitates the diffusion of water from the cell into the extracellular space
PNS response to injury
connective tissue scar & Schwann cells form bridge b/w severed ends of nerves; if gap not too big, regeneration of axon possible; if damage too severe or old, axon may need to regrow its entire length
Step 1: Schwann cells multiply to physically bridge gap proliferate
Step 2: nerve axon sprouts neurites from proximal stump
Step 3: neurites grow into distal stump; contact reestablishes function
anterograde (Wallerian) degeneration
portion of axon distal to point of injury degenerates
what happens to an injured neuron?
cell body swells & becomes brightly eosinophilic, loses Nissl substance
result of severe injury to PNS
retrograde degeneration & death of cell body
CNS response to injury
-oligodendrocytes less efficient than Schwann cells; instead, neuroglial cells
how do glial cells prevent regeneration?
scar tissue proliferation; physically blocks contact b/w cell body & axon
neurons are stuck in which phase?
Go
-terminally differentiated; unable to be replaced
ALS
due to death of motor neurons controlling voluntary Mm
development of cerebellum
arose as a specialization of the vestibular system
cerebellum functions
mainly involved in the co-ordination of motor activities, posture and balance
structure of cerebellum
-cortex, with leaf-like folds called folia & medulla
medulla
consists of nerve fibers leading out of the cortex
molecular layer of cerebellum
-outermost layer of the cerebellar cortex
-relatively free of neuronal cell bodies
the vast complexity of the synaptic clefts b/w Purkinje cells & molecular layer provides what?
rapid & simultaneous processing of signals
why does the cerebellum need to process signals instantaneously?
b/c it is constantly fed inputs from the body and needs to be able to respond properly and quickly
pyramidal cells
pyramid-shaped neurons with long, slender axons, varying in size from small to large
Betz cells
largest cortical neuron
Stellate (granule) cells
small star-shaped neurons with short axons & dendrites
Cells of Martinotti
small neurons with long, horizontal axons
Fusiform cells
vertically oriented, spindle-shaped neurons with vertical axons
Horizontal cells of Cajal
horizontally orientated, spindle-shaped neurons with horizontal axons; least common type of neuron, found only in superficial layer
how many cortical layers are there in the cerebral cortex?
6
cortical layer I
-most superficial layer
-contains mostly dendrites & axons of cortical neurons
cortical layer II
-outer granule layer
-contains large number of small pyramidal cells & stellate cells
cortical layer III
-pyramidal cell layer
-contains stellate cells & medium pyramidal cells
cortical layer IV
densely packed stellate cells only
cortical layer V
-large pyramidal cells & a few stellate cells
-also contain cells of Betz
cortical layer VI
multiple size pyramidal cells & loosely packed stellate cells
