Neurobiology Flashcards
function of neuroglia
myelination of neuronal axons, neurotransmitter uptake, neuronal growth factor synthesis, removal of extracellular debris, assistance with neuronal migration, BBB structure
neuroglia cells
microglia, astrocytes, Schwann cells, oligodendrocytes
function of astrocytes
regulate the balance of electrolytes (mainly potassium) in the extracellular space, provide nutrient support to neurons, stimulate endothelial cells to form tight junctions that compose the BBB, regulate neurotransmitter concentration, divide in response to injury (astrocytes or gliosis) and have limited phagocytic capacity
types of astrocytes
- fibrous astrocytes -> primarily in white matter
2. protoplasmic astrocytes -> primarily in gray matter
Bergmann cells
specialized astrocytes which surround and support the Purkinje cells of the cerebellum and Muller cells of the retina
oligodendrocytes
responsible for myelination of axons; single oligodendrocyte myelinations MULTIPLE axons
Schwann cells
responsible for PNS myelination; single Schwann cell myelinates one axon
microglia
derived from macrophages (MESODERMAL ORIGIN) and subsequently migrate into the CNS; phagocytosis and antigen presentation
are dendrites myelinated?
no
what is the name of the structure on a neuron that extends in a tubular fashion from the cell soma
axon hillock
what is the most excitable portion of the neuron
axon hillock
why is the axon hillock the most excitable portion?
high concentration of sodium channels
what structure is devoid of Nissel substance?
axon hillock
axon
efferent component of the neuron that conducts action potentials from the soma or axon hillock
unipolar neuron
simplest neuron; found only in the autonomic nervous system of vertebrates
bipolar neuron
associated with special senses (olfactory, vision, auditory, vestibular)
pseudounipolar neuron
two processes that fuse into one; comprise sensory ganglia of cranial nerves and spinal nerves (e.g. dorsal root ganglia)
multipolar neuron
most prevalent type of neuron; multiple dendrites
the ependymal cells that line the roof of the third and fourth ventricles, and the choroidal fissure of the lateral ventricles is called…
tela choroidea
tela choroidea
specialized secretory epithelium (choroid plexus) that synthesizes approximately 70% of the CSF
BBB of choroid plexus is unique….
epithelial instead endothelial
proteins and phospholipids that are destined for secretion are initially synthesized in the
rough endoplasmic reticulum
Rough ER sends products to the
Golgi complex
what happens in the Golgi complex
modifies proteins by adding polysaccharides, and processing includes glycosylation (O-linked and N-linked), proteoglycan formation, attachment of fatty acids, and sulfating of tyrosine and sugar residues
protein involved in fast anterograde transport
kinesin and ATP; 400 mm/day
drugs that interfere with microtubule structure and disrupt fast anterograde transport
vinblastine and colchicine
component A
slower than fast anterograde transport; 0.2 to 2.5mm/day; utilizes dynamic (GTP-dependent)
Component B
2-4mm/day; uses actin/myosin motor complex in the transport of cytosolic proteins, actin and spectrin
protein involved in retrograde axonal transport
dynein and ATP; 400mm/day
two types of synapses in the nervous system
electrical and chemical
electrical synapse
direct spread of action potential from the presynaptic neuron to the post-synaptic neuron; these neurons have direct cytoplasmic continuity with GAP JUNCTIONS CALLED CONNEXONS WITH PROTEIN SUBUNITS CALLED CONNEXINS
is electrical synapse unidirectional or bidirectional? slow or fast?
Fast; bidirectional
chemical synapse
more prevalent; pre and post-synaptic neuron separated by synaptic cleft; synaptic vesicles with neurotransmitters
is chemical synapse unidirectional or bidirectional? slow or fast?
unidirectional; slower than electrical
creation of acetylcholine
from choline and Acetyl CoA by enzyme choline acetyltransferase
what neurons use acetylcholine?
- spinal cord motor neurons at NMJ
- all PRE-ganglionic autonomic neurons
- all POST-ganglionic parasympathetic neurons
- POST-ganglionic sympathetic neurons to sweat glands
- nucleus basalis of Meynert
acetylcholine is metabolized by what enzyme
acetylcholinesterase
Dopamine, epinephrine and norepinephrine are all metabolized from the same molecule…
tyrosine
rate limiting enzyme in dopamine and norepinephrine synthesis
tyrosine hydroxylase; tyrosine -> L-DOPA
synthesis of dopamine from L-dopa via what enzyme
Aromatic amino acid decarboxylase
what prevents dopamine uptake into the synaptic vesicle
reserpine
where does norepinephrine synthesis take place?
in the synaptic vesicle
dopamine to norepinephrine via what enzyme
dopamine B-hydroxylase
where is norepinephrine found?
locus ceruleus, most post-ganglionic sympathetic neurons, pineal gland
norepinephrine uptake is blocked by what…
cocaine
norepinephrine is metabolized by what enzyme
catechol-O-methyl transferase (COMT) and monoamine oxidase (MAO)
synthesis of epinephrine from norepinephrine occurs in the adrenal medulla via what enzyme?
phenylethanolamine-N-methyl transferase
rate limiting enzyme in serotonin synthesis
tryptophan to 5HTP via tryptophan hydroxylase
5HTP to serotonin via what enzyme
5-hydroxytryptophan decarboxylase
describe process of synaptic vesicle exocytosis
depolarization -> calcium/calmodulin-dependent phosphorylation of synapse proteins release synaptic vesicle -> targets docking site at active zone of terminal bouton -> protein within wall called vesicle SNARE (v-SNARE or synaptobrevin) then binds to a target-SNARE (t-SNARE, syntaxin) -> protein complex fuses with wall of the synaptic vesicle and terminal bouton resulting in NT release
what does tetanus toxin cleave?
synaptobrevin
what does botulinum toxin cleave?
t-SNARES and v-SNARES
what subunit on G proteins interacts with effector enzymes?
alpha subunit
cholera toxin activates what G protein?
Gs
pertussis toxin activates what G protein?
Gi
G proteins activate adenylate cyclase to produce?
cyclic AMP
cAMP interacts protein kinase A and subsequently phosphorylates what…
serine and threonine residues on target proteins
nitric oxide is generated from what amino acid
arginine via nitric oxide synthase
nitric oxide synthase is activated by ca2+/calmodulin-dependent enzyme after stimulation of what receptor?
NMDA via glutamate
does nitric oxide stimulate cAMP or cGMP?
cGMP
what type of receptors do acetylcholine bind to?
nicotinic and muscarinic
subunits to nicotinic cholinergic receptors
5 subunits: two alpha, one beta, one gamma, one delta (a2byd)
alpha subunit binds how many ACH molecules?
one
how many ACH molecules are needed for activation of the channel?
two
a-bungarotoxin
binds the alpha subunit, effectively inhibiting nicotinic cholinergic channels
inhibitors of nicotinic cholinergic receptors
hexamethonium (ganglionic), succinylcholine (depolarizing), and D-tubocurarine (non-depolarizing)
subunits that make up muscarinic cholinergic receptors?
2 subunits: alpha and beta
what inhibits and stimulates muscarinic cholinergic channels?
inhibits -> atropine and scopolamine
stimulates -> bethanechol, carbachol, pilocarpine, methacholine
GABA-A subunits
5 subunits -> 2 alpha, 2 beta, 1 gamma
what subunits in GABA-A binds GABA, barbiturates, benzodiazepines?
GABA -> alpha, beta and gamma
barbiturates -> alpha and beta
benzodiazepines -> gamma
GABA-B channel
increases K+ conductance, thus generating inhibitory post-synaptic potential; activated by agonist baclofen
glycine channels
chloride channels that generate IPSP
glycine is synthesized in what cells?
Renshaw cells (spinal cord)
glycine channels are blocked by
strychnine
glycine release is inhibited by what toxin
tetanus
all norepinephrine receptors are metabotropic receptors that use G proteins and the second messenger….
cAMP
two sites of neurogenesis in the adult brain
- subependymal zone in the lateral wall of the lateral ventricles -> migrate through glial tubules to the olfactory bulb
- hippocampus -> subgranular layer of the dentate gyrus
what is the resting membrane potential in the neuron?
between -60 and -70mV; closest to K+ equilibrium potential (-75mV)
Na=K+ pump
3 Na out, 2 K in
how can you increase the conduction velocity of an axon?
- increase axon diameter
- increase transmembrane resistance
- decrease internal resistance
- decrease membrane capacitance
- myelination
proteins and phospholipids that make up myelin
- basic myelin protein
- myelin-associated glycoprotein
- proteolipid
- peripheral myelin protein 22
myelin increases what to increase conduction velocity
increases transmembrane resistance and reduces membrane capacitance
process of nerve regeneration after transection
synaptic transmission failure -> distal axon degeneration and phagocytosis (Wallerian degeneration) -> neuronal soma undergoes chromatolysis (peripheralization of rER and increased protein synthesis)-> end of proximal axon swells -> regeneration occurs when axons sprouts grow from the end of the proximal axonal segment and enter tissue remnants of distal stump
do larger axons have larger stimulation thresholds?
no, lower stimulation thresholds
larger axons are more sensitive to what….
hypothermia, compression and anoxia
local anesthetics induce conduction blocks in large or small axons?
both; smaller axons initially, then larger
Bell-magendie law
all sensory axons enter the dorsal root of the spinal cord, while all motor axons exits via the ventral root
Group I (Aa) fibers
largest, fastest conducting fibers (70-120m/s)
Two subgroups:
1) Ia -> primary muscle spindle afferent
2) Ib -> afferents from Golgi tendon organs
Group II (AB, Ay) fiber s
slower (30-70m/s); represent muscle spine secondary (flower-spray) afferents and cutaneous touch and pressure afferents
Group III (Ad) fibers
even slower (4-30m/s); conduct information regarding temperature, light touch and fast/sharp pain
Group I to Group III fibers. are all….
myelinated
Group B fibers
preganglionic autonomic fibers found only in the ventral root
Group C fibers
unmyelinated fibers that are much slower (0.4-2m/s) and mediate temperature and slow/burning pain.
Aa fibers
very rapid; spinal cord alpha motor neuron efferents to extrafusal musculature
Ay fibers
slower; impulses from y-motor neurons to intrafusal musculature (muscle spindles and GTO)
What fibers violate the Bell-Magendie Law?
C fibers
Meissner’s corpuscles
- transmit flutter via AB fibers
- small receptive fields
- rapid adaptation
Merkel’s disk receptors
- transmit pressure via AB fibers
- small receptive fields
- slow adaptation
Pacinian corpuscles
- transmit vibration via AB fibers
- large receptive field
- rapid adaptation
Ruffini endings
- sense skin stretch and transmit this modality via AB fibers
- large receptive fields
- slow adaptation
