Synapses Flashcards
what are the 3 different kinds of synapses?
-Axon + cell body (Axosomatic)
-Axon + dendrite (axodendritic)
-Axon + axon (axo-axonic)
What happens in depolarization?
- The action potential triggers voltage gated Na+ channels to open
- Na+ rushes in, inside of axon becomes less negative and reaches threshold
- voltage gated Ca+ channels open, Ca+ moves in (down its concentration gradient)
- Ca+ triggers synaptic vesicles with neurotransmitters in it to fuse with membrane and release neurotransmitter into synaptic cleft
- below threshold Ca+ channels close, Ca+ pumps will now pump Ca+ out (using energy)
where are voltage gated Na+ channels? voltage gated Ca+ channels?
Voltage gated Na+ channels traverse whole axon, but Ca+ channels are only on the tip
_________ are channels where ligand binds to protein, it opens and lets an ion through
Ionotropic channel (ligand- gated channel)
Ionotropic channels are _____, while metabotropic channels are _____
fast, slow
______ are channels where ligand binds and there is a signaling cascade in the cell
Metabotropic channel (usually GPCR)
can ligands have both metabotropic or ionotropic effect ?
YES: GABA-a: binds to ionotropic, but GABA-B binds to metabotropic
____________ is the enzyme that catalyzes the creation of Ach
Choline acetylase/Choline acetyltransferase
________ is the enzyme that breaks down Ach
Acetylcholinesterase (ACE)
where are the degradative enzymes usually located?
post-synaptic cell
what is end-plate potential?
when Ach binds to ligand gated channels on muscle fiber → channels open → Na rushes in → graded potential (graded potential in muscle fiber)
contrast neuron-muscle junction and neuron-neuron junction
- Neuron-Muscle junction:
Large area for neurotransmitters
LARGE depolarization
~60mV change
Graded potential
-Neuron-Neuron junction:
has small area
depolarization is small
only 1mV change
Ach channel is a ________ cation channel
monovalent
what determines the direction of monovalent cations through the Ach channel?
Concentration gradient
Charge difference
More Na+ ______ neuron, More K+ _____ neuron bc Na+/K+ pump
outside, inside
At rest _____ driving force is much greater than ____
Na+
K+
(-) DF for (+) ion = going ____ cell
INTO
(+) DF for (+) ion = going ____ of cell
OUT
________ has ligand gated channels that bind Ach and allow Na+ to enter
End plate region
what are the steps at end plate regions?
Ach binds to Ach ligand gated channel → Na+ goes in at end plate region → Na+ diffuses and causes depolarization within the muscle fiber → if you reach threshold outside end plate, voltage gated Na+ channels open → AP fires → muscle fiber contracts
Normal threshold = _____ depolarization from rest, but graded potentials are usually _____mV
~15mV
~60mV
why is graded potential so much higher than threshold?
it Exceeds threshold dramatically to ensure that the muscle fires
________ blocks degradation of AcH
Eserine
- causes Ach concentration to increase
_______ blocks Ach ligand gated channels
Curare
- will never reach threshold since ACH cant trigger channels
Neuron-neuron synapses can be _______, but neuron-muscle synapses are ALWAYS _____
inhibitory or excitatory
ALWAYS excitatory
where are small neurotransmitters assembled?
in the terminal
where are large neurotransmitters assembled?
in cell body but then transported down axon for release
what are some examples of large neurotransmitters and what are their functions?
Endorphins and Enkephalin (natural painkillers)
Inhibiting degradative enzymes → _______ neurotransmitters concentration
INCREASES
____ = degradative enzyme on presynaptic neuron
MAO
____ = degradative enzyme on post-synaptic cell
COMT
What are the 3 ways to deal with Neurotransmitters?
Reuptake
Diffuse away into interstitial fluid
Degradation
which ways are used to get rid of small vs large neurotransmitters?
LARGE: diffusion, degradation
SMALL: reuptake, diffusion, degradation
what is IPSP? what can cause this?
- input on post-synaptic neuron that reduces likelihood of AP firing
-K+ rushes out → more negative → farther from threshold
-Cl- channel opens → Cl- rushes in → more negative → farther from threshold
what is EPSP? what can cause this?
-input on post-synaptic that increases likelihood of AP firing
-Na+ rushes in → more positive → closer to threshold
- is a graded potential
when can a depolarizing IPSP happen?
just depends on the driving forces and equilibrium potentials; driving force can switch
EX: Cl- below Equilibrium potential causes depolarization, but once it hits Eq. potential it causes mV to decrease
** look on summary, its confusing**
