Cells of the Nervous System (Week 1--Micevych) Flashcards Preview

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Flashcards in Cells of the Nervous System (Week 1--Micevych) Deck (27):
1


Anatomical organization of nervous system


CNS: brain and spinal cord

PNS: cranial nerves, spinal nerves and associated ganglia

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Functional organization of nervous system


Sensory (afferent) for receiving signals

Motor (efferent) component for transmitting impulses to effector organs throughout the body

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Basolateral and apical sides of neuron


Basolateral: cell body and dendrites

Apical: axon and terminals

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Cell body/soma of a neuron


Actively synthesizing proteins!

Prominent nucleus (pale) and nucleolus (dark) with dispersed chromatin (because actively being transcribed)

Lots of rough ER and polysomes called Nissl bodies

Golgi complex synthesizes receptors, enzymes, peptide transmitters

Numerous mitochondria

Inclusions (not organelles, just aggregations of things) including melanin granules, lipofuscin pigment (older people have more), lipid droplets

Neurosecretory cells in hypothalamus also have secretory vesicles in cell body

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Dendrites of a neuron

Cytoplasmic projections of cell body with same organelles (except nucleus)

Specialized for receiving impulses

Highly branched

Specialized zones that receive inputs are equipped with membrane receptors, gap junctions, and associated signal transduction machinery

Some dendrites have spines for input

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Dendritic spines


CNS dendritic specialization for receiving input/synapses (axon terminals make contact with spine)

Little bumps on dendrite shaft that look like mushrooms

Spines help focus the signal (to small area of dendrite)

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Axon of a neuron


Single process (can branch AFTER leaving cell body)

Often myelinated (CNS by oligodendrocytes and PNS by Schwann cells)

Axon begins as axon hillock (initial segment) which has no Nissl bodies and is not myelinated; this area initiates action potentials

Axon shaft has smooth ER, mitochondria, vesicles, actin filaments, microtubules, intermediate filaments (neurofilaments), MAPs (1,3,5), motoric proteins (kinesin anterograde and dynein retrograde)

Axon ends with terminal bouton (end bulb or axon terminal) which converts electrical impulses into release of chemical messengers (NTs)

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Tau proteins

Stabilize microtubules

Pathologically contribute to neurodegenerative diseases (tauopathies include Alzheimer's disease and frontotemporal dementia)

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Types of axon damage


Closed head injury (concussion) can cause axon damage via:

Stretching

Twisting

Compression

Reaction to damage

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Axonal transport


Need transport to get things up and down the axon which can be up to 100cm long!

Fast transport: vesicles move 50-400mm/day, propelled by molecular motor proteins

Kinesin moves to + end, anterograde (toward axon terminal/synapse)

Dynein moves to - end, retrograde (toward cell body)

Slow transport: nonmembrane organelles (proteins, ribosomes, cytoskeletal components) move 0.3-8mm/day because intermittent and bidirectional movement

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Chemical synapse vs. electrochemical synapse


Chemical synapse: where NTs released; space that separates terminal bouton from receiving cell dendrite, cell body or axon

Electrochemical synapse: gap junction

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Morphology of neurons


Unipolar: single process, only during development

Bipolar: two processes from cell body (one dendrite and one axon); in olfactory epithelium and vestibular and cochlear ganglia

Pseudounipolar neurons: have only one process emanating from cell body that divides into peripheral and a central branch which are BOTH axonal; terminal portion of peripheral end often branched and contains secretory vesicles; in cranial sensory and spinal (dorsal root) ganglia

Multipolar neurons: most common type; pyramidal, motoneuron, Purkinje cells

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Classification of neurons based on function


Sensory (afferent): primarily in PNS, for transmission of sensory input

Motor (efferent): originate in CNS and activate peripheral effectors (muscles, glands)

Interneuron: only in CNS; integrators that establish networks of neuronal circuits

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Glia


Provide metabolic and mechanical support for neurons and are active participants in nervous system (synthesize and release NTs, sop up NTs to clean area)

In CNS, have astrocytes, oligodendrocytes, microglia and ependymal cells

In PNS have Schwann cells, satellite cells

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Astrocytes


Found in both gray and white matter

Protoplasmic astrocytes more prevalent in gray matter

Fibrous astrocytes more prevalent in white matter

Reactive astrocytes activated by injury and create glial scar

Elaborate process that extend between blood vessels and neurons and ends of processes form end feet that cover large areas of surface of blood vessels

Astrocytes coupled by gap junctions

Contain GFAP

Help form BBB (regulate tight junctions between endothelium of brain capillaries)

Move metabolites away from neurons

Regulate ion concentrations (membranes have high gK so buffer extracellular K+ during repititive activity)

Regulate NT concentrations (have uptake machinery for NTs)

Synthesize neurosteroids (role in reproduction, neuroprotection)

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Reactive astrocytes


Activated by injury, form glial scar

Seen in many conditions: infarction, MS, infection

Presence of reactive astrocytes called astrogliosis or gliosis

Edge of infact has glial scar, or dense astrogliosis

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Oligodendrocytes


In CNS

Make myelin

One oligodendrocyte can wrap up to 10 axons in myelin

Develop late in development and much of myelination occurs post-embryonically

Essential for proper CNS function (remember demyelinating diseases MS, transverse myelitis, Guillain-Barre)

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Schwann cells


In PNS

Make myelin

Can form two types of covering for cells in periphery: myelinated and unmyelinated (all neurons are supported by Schwann cells but only some are wrapped several times to be myelinated)

Flattened cell with flat nucleus, some polysomes, some rER, small Golgi apparatus, few mitochondria

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Node of Ranvier

Interruption in myelin

At regular intervals

Note: astrocytes cover Nodes of Ranvier (sop up extra K+??)

Saltatory conduction from one Node of Ranvier to the next

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Internode


Space between Nodes of Ranvier, so where axon IS myelinated

(aka myelin packet)

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Differences between myelin in CNS vs. PNS

Different proteins (PLP vs. P0)

Fewer Schmidt-Lanterman clefts in CNS

No basal lamina in CNS

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Schmidt-Lanterman clefts (incisures)


Cone-shaped, oblique clefts in the internodal myelin sheath

Schwann cell cytoplasm trapped between layers of plasmalemma

Provide cytoplasmic channel of communication from outside of myelin to interior

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Microglia


Macrophages of the CNS

Derived from yolk sac myeloid progenitors

Small cells (8-12um) with long processes

If CNS is damaged, microglia enlarge, become motile and phagocytic

Note: usually not many circulating monocytes in CNS, but if pathology has opened BBB, can have some

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Ependymal cells

Line brain ventricles and central canal of spinal cord

Secrete CSF

Cuboidal to low columnar, ciliated, form continuous sheet--the ependyma

Ependyma is remnant of embryonic proliferative neuroepithelium

Where they cover choroid plexus, form choroid plexus epithelium

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Choroid plexus


Site of formation of CSF from blood!

Evagination of pia and ependymal layers into ventricular spaces

Contain blood vessels that supply fluid and electrolytes to CSF

Choroid plexus epithelium is made of specialized ependymal cells

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Satellite cells


Found in sensory ganglia (DRG) and autonomic ganglia

Multipotent glial cells that can differentiate into oligodendrocytes, Schwann cells and astrocytes

Ensheath neuronal cell bodies to provide support (but not myelin)

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Does CSF have proteins in it?


No, not much!

That's how you can tell wheher BBB or choroid plexus is compromised

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