Synaptic Transmission Flashcards
dendrites
tapered processes arising from the cell body that greatly increases the receptive surface. The membranes contain receptors for transmitters and voltage gated ion channels that can amplify the graded synaptic signal. primary areas for receiving and integrating complex information from thousands of synapses.
cell soma
surrounds nucleus and contains the ER, golgi, etc. performs house keeping functions such as protein synthesis, degradation and processing.
axon
single thin process arising from the cell body at the axon hillock. transmits all or none action potentials to the terminals after integrating transmitter mediated bioelectrical changes received in the dendrites and cell body
presynaptic terminals
specialized structures that convert electrical signals propagated down the axon (action potentials) into chemical signals (neurotransmitter).
synapse
point of contact between pre and post synaptic neuron/target cell.
axoplasm
contains parallel arrays of microtubules and neurofilaments that provide structural stability and a means to transport materials back and forth between the cell body and presynaptic terminals.
kinesin
microtubule motor that mediates fast antegrograde transport of mitochondria and vesicles from soma to terminals.
dynein
mediates fast retrograde transport of degraded vesicular membranes and absorbed toxins/viruses/growth factors from terminal to soma
electrical synapses
provide speed and synchrony. how electrical response in one cell is transmitted to another cell. fast and bidirectional. allows direct passive flow of electrotonic current between cells via gap junctions
gap junctions
compromised of intramembrane channel proteins called connexions. critical for synchronous electrical coupling in visceral smooth muscle and cardiac muscle.
criteria for chemical neurotransmitters
present in presynaptic terminal, released in a voltage and calcium dependent manner, specific receptors present in the post synaptic target cell, means to inactivate the transmitter
steps in synaptic transmission
transmitter molecules are synthesized and packaged in vesicles, action potential arrives at the presynaptic terminal, depolarization of terminal opens voltage gated calcium channels, increased calcium in terminals trigger vesicle fusion, transmitter diffuses across cleft and binds to postsynaptic receptors, postsynaptic response occurs, transmitter molecules are cleared/inactivated by enzymatic degradation, uptake or diffusion
active zones
a specialized site on the presynaptic terminal where vesicles that are docked to be preferentially released in response to invasion of the terminal by an action potential, activation of voltage sensitive calcium channels, and influx of calcium.
functional magnetic resonance imaging (fMRI)
measures changes in regional blood flow associated with changes in local cerebral glucose metabolism.
exocytosis
process of neurotransmitter release from the presynaptic terminal.
endocytosis
prevents out of control enlargement of the presynaptic membrane. how vesicle membrane that has fused to the presynaptic membrane is recycled.
botulinum toxin
causes muscle weakness by cleaving SNAP-25 (A&E) or synaptobrevin (B) proteins in the presynaptic terminal of alpha motor neurons.
ionotropic receptor
contain ion channel as part of their structure and transmitter binding triggers a rapid response.
ligand binding site and ion channel
metabotropic receptor
commonly linked to G proteins that transduce a slower biochemical signal.
ligand binding site linked to G protein
nicotinic AChR
ligand gated channel on the post synaptic membrane. end result is muscle contraction in skeletal muscle
example of ionotropic receptor
muscarinic AChR
coupled to a heterotrimeric G protein. end result is decreased heart rate in cardiac muscle.
example of metabotropic receptor
How are postsynaptic potentials (PSPs) produced?
conductance changes due to ion channel openings (and sometimes closings) lead to ionic current flow through the channels that in turn lead to changes in the membrane potential.
Excitatory PSP (EPSPs)
increase the probability that an action potential will be triggered
Inhibitory PSP (IPSPs)
decrease probability that an action potential will be triggered
glutamate
major excitatory neurotransmitter and binds to ionotropic and metabotropic receptors. binding of glutamate to specific ligand gated ion channels in the target cell produces both fast and slow depolarizing responses (EPSP) because distinct receptors are activated.
GABA
major inhibitory transmitter and binds to ionotropic and metabotropic receptors. binding of GABA to specific ligand gated ion channels in the target cell produces hyperpolarizing responses called IPSP.
cable theory takes into account
membrane capacitance, membrane resistance, and longitudinal cytoplasmic resistance between different parts of the neuron
decremental conduction
large amount of potential is lost by leakage through the membrane before EPSP can reach the cell soma
occurs because dendrites are long and their membranes are thin and leaky to electric current.
What determines the probability that an action potential will be generated?
temporal and spatial summation
process of temporal stimulation
two action potentials on one synapse. when the membrane has a longer time constant, some of the depolarization from the first EPSP is still present when the second occurs, and the individual depolarizations can summate.
process of spatial summation
two action potential on two different synapses. when the cell membrane has a longer space constant, the EPSP from synapse 1 is able to propagate further along the membrane and can summate with the EPSP from synapse 2, resulting in more depolarization to propagate to the soma and axon hillock.
