Synaptic Transmission Flashcards
1
Q
numbers
A
- brains have 100 billion neurons
- each integrates with numerous others
- studied with microelectrod stimulations and recordings and mapping
- some spatially focused-precise timing, others are widely spread and diffuse-arousal, mood, motivation
2
Q
criteria for chemical neurotransmitters
A
- present in presynaptic terminal
- released in response to stimulation, release must be ca dependent
- specific receptors for the nt must be present on the postsynaptic cell
- mechanism to inactivate nt must be present
3
Q
electrical synapses
A
- speed and synchrony
- allow direct passive flow of electrotonic current between cells via gap junctions
- pores are larger than voltage or ligand gated, therefore unselective
- electrical synapses present in CNS but less common
- breathing
4
Q
chemical neurotransmission
A
- transmitter synthesized and stored in vesicles
- AP invades pre synaptic terminal
- depolarization of presynaptic terminal causes Ca channels to open
- influx of Ca
- Ca causes vesicles to fuse
- transmitter is released into synaptic cleft
- transmitter binds to receptors in post
- opening or closing of post synaptic channels
- post synaptic current causes excitatory or inhibitory PSP that changes the excitability of the postsynaptic cell
- removal of the nt by glial uptake or enzymatic degradation
5
Q
presynaptic terminals
A
-specialized structures that convert electrical signals propagated down the axon into chemical signals released from vesicles and transmitted across the synapse
6
Q
postsynaptic target cells
A
-contain nt receptors and respond rapidly if they are ionotropic or over longer time scales
7
Q
chemical synapses provide
A
- directionality
- amplification
- potential for excitation and inhibition
- potential for plasticity/remodeling
- integration in space and time
8
Q
Ca
A
- rise is necessary and sufficient for NT release
- steep gradient across presynaptic membrane because external Ca is 1mM and inside is 0.1uM
- electrical gradient
- blocking Ca channels prevents PSP because no NT
- lowering external Ca decreases size of PSP because fewer vesicles fuse
- entry rapid, clearance slower, Ca can build up
9
Q
facilitation
A
- rapid increase in synaptic strength that occurs when two or more AP invade the presynaptic terminal within a few milliseconds of each other
- second EPSP is larger because Ca was allowed to buildup for a little, more vesicles released, more nt, higher EPSP
- not temporal summation-number of AP and time constant
10
Q
one neuron can release one or more chemical transmitters
A
- small molecule-clear core, small vesicles synthesized in nerve terminals
- neuropeptides-dense core, large vesicles synthesized in cell body
- enkephalins and vasoactive intestinal peptide
- based on receptors, act rapidly (NMDA, AMPA), moderatly (metabotropic glutamate), or slowly
- peptides on fast axonal transport on MTs
11
Q
stimulation frequency
A
- influences transmitter release from different populations of synaptic vesicles
- low freq releases small molecules
- high releases both
- postsynaptic target has electron dense area with many receptors-postsynaptic density
- aligned with active zones
12
Q
active zones
A
- subset of vesicles containing small molecule NTs are docked at these sites
- preferentially released via localized influx of Ca
- high frequency has generalized increase- both types
13
Q
quanta
A
- release of NT is quantal
- AP in motorneuron is EPP
- EPP from simultaneous release of many quanta
- multiple MEPPS
- MEPPs size is fixed and constant
14
Q
post synaptic potentials
A
- result from conductance changes due to ion channel openings
- NT release
- receptor binding
- ion channels open/close
- conductance changes causes current flow
- PSP changes
- postsynaptic cell excited or inhibited
- summation determines whether an AP occurs
15
Q
synaptic potential changes
A
- local passive events
- become progressively smaller at greater distances from stimulus
- most dendrites don’t transmit APs
- temporal and spatial effects
- membrane capacitance, resistance, cytoplasmic resistance
- dendrites are long, thin and leaky
- need many APs
- decremental conduction
