manieren van signaaloverdracht:
a. via de bloedbaan endocriene cell → bloedbaan → target cell
b. actie potentiaal (neuroon) neuron → axon → actie potentiaal → target cell
Neuronal communication
neuron = zenwuwcel (altijd 1 axon en 1 of meerdere dendrieten)
signaal axon → dendriet (gekoppeld via dendritic spines) begin = axon hillock
actiepotentialen: snelle en onomkeerbare elektrische signalen
excitable: can generate action potentials
neuron diversity
- number of neurites unipolar, bipolar, multipolar (2x a, 1d | 1d, 1a | meerdere d)
- shape of dendrites purkinje, pyramidal, stellate
- length of axon
- function afferent | efferent (p → zenuwst. | z → periderie)
- transmitter secretion
anaxonic neuron: mainly in the brain
Non-neuronal cells in the brain:
- astrocyte cell glyacel - signaal overdracht beinvloeden + contact bloedvat
(bloed-hersen barriere)
- microglial cell glyacel - immuunsysteem hersenen
- oligodendrocyte glyacel - aanleg myaline + voorkomt kortsluiting
Myelination
brain oligodendrocytes produce layers of myelin that wrap around the neuronal axons and
act as a layer of insulation for the transmission of electric action potentials down the
neuronal axon (faster)
Multiple sclerosis (MS) : impaired nerve signal conduction due to inflammation of the
myelin sheath → bewegingsaandoening
Actiepotentialen
intracellular recordings - meten van de spanning tussen binnen en buitenkant cel
resting membrane potentials -70mV
Na+, CI- buiten de cel | K+ binnen de cel
kalium en natrium kanaal altijd open; kalium naar buiten, natrium naar binnen
+ NA/K pomp (bij -90mV is de cel in evenwicht voor K+ = equilibrium potential)
Neuronal stimulation
depolarization: -70mV → -65mV Na+ naar binnen
hyperpolarized: -70mV → -80mV K+ naar buiten
—> repolarization
ligand-gated ion channels (LGIC)
open when a ligand binds → influx of a specific ion type
Neurotransmitter bindt —> open —> depolarisatie (bij positieve lading)
Acetylcholine = activerend depolariserend
GABA = remmend hyperpolariserend |CI- binnen
voltage-gated ion channels (VGIC)
open in response to change in membrane potential → massive influx of ion type
= open bij drempelwaarde (-60mV)
Toxins:
- CTX sodium channel blockers
- STX sodium channel blockers
- TTX sodium channel blockers
- PTX Turns Na\K pump into a channel
,Generation of action potentials
action potential propagation
Initial segment: Na stroomt naar binnen → Na diffundeert → volgende plek op axon
depolariseert → nieuw actiepotentiaal → etc.
Na gaat maar 1 kant op door negatieve membraanspanning na actiepotentiaal
, Action potential propagation in myelinated axons
- Knopen van Ranvier
Neuronal integration:
- 1 enkele actieve synaps kan geen actiepotentiaal veroorzaken
- 1 snel vurende synaps kan wel een actiepotentiaal veroorzaken
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