Chapter 4.4: Electrical and Chemical Synapses Flashcards
Synapse
Junction between excitable cell and target cell.
axon terminal synapse
pre synaptic terminal terminates at the axon terminal.
axonal varicosities
pre syn terminal ends along unmyelinated axons in specialized compartments (bulges)
en passent synapse
one neuron joins another but not at the axon terminal
dendritic spine synapse
small bulge in dendrite that receives input from a single axon.
dendrodendritic synapse
dendrite to dendrite
axoaxonic synapse
axon terminal to axon hillock
axodendritic synapse
axon terminal to dendrite. most common
axosomatic synapse
axon terminal to soma
2 mechanisms of info flow from synapses
1) electrical (DIRECT): rapid AP flow between adjacent cells by using GAP JUNCTIONS. seen in cardiac muscles at the intercalated disks
2) Chemical (INDIRECT): 2 cells are not directly connected to one another. Can occur Neuron to neuron or neuron to muscle. the gap is too large for gap junction electical signalling, and the neurons use chemical messengers to communicate instead.
Limitations to electrical info flow across synapse
1) the post synaptic cells must be very close together in order for connexins to form gap junctions
2) communication in BOTH DIRECTIONS COULD HAPPEN
3) single type of communications; just exerts a change of membrane potential. there is noneuro transmitter release.
advantages to chemical indirect info flow across a synapse
1) they are a UNIDIRECTIONAL method of info propagation because the NTs only travel on direction
2) allows for multiple types of communication; can cause depolarization or hyperpolarization.
2 Types of inhibition
1) post synaptic inhibition
2) presynaptic inhibition
post synaptic inhibition
inhibition at the POST syn cell by the presyn cell. Usually because a neurotransmitter opens hyperpolarizing channels in the post syn cell.
Presynaptic inhibition
inhibition at the pre syn cell ( from a neuron that is synapsed on it) that prevents it from communicating with the post syn cell.
presynaptic facilitation. HOw does this happen?
when the release of transmitter is enhanced through the persistent Ca2+ elevations in the presynaptic terminus, triggering vesicle release, or when another neuron contributes to the depolarizing events on a post syn cell, helping the pre syn cell execute its excitation of post syn cell.
pre and post synaptic ____ and presynaptic ____ allow fine tuning control of the post synaptic cell
pre and post synaptic inhibition and presynaptic facilitation allow for the fine tuning control of the post synaptic cell.
the __ ____ ____ is the total potential in the post synpatic neuron after the addition of all EPSPs and IPSPs that have occurred around the same time
Grand Post Synaptic Potential
2 methods for EPSPs to bring a membrane to threshol
1) temporal summation: summation of multiple EPSPs from the SAME SYNAPSE.
2) spatial summation: summation of EPSP and IPSP inputs from more than one synapse. EPSPs from different synapse. the different inputs need to fire essentially simultaneous in order to get summated at the axon hillock together.
Cancellation
when EPSPs and IPSPs get summated together from different synapses and essentially cancel each other out.
why does the axon hillock have the lowest threshold?
because it has the largest density of voltage-gated Na+ channesl. the action potential originates at the axon hillock.
convergence
many presynaptic neurons converge onto one post synaptic neuron
divergence
axon terminals of one neuron can synapse with multiple post synaptic neurons.
how do neurotransmitters work?
typically trigger the opening of specific ion channels to bring out membrane potential changes in post synaptic cell (EPSP or IPSP). Can also open 2nd messenger systems via metabotropic receptors.
T/F Neuropeptides are larger than neurotransmitters
True . they are larger. around 10 AA-long chains
T/F: neuropeptides are packaged in synaptic vesicles
false. They are packaged in DENSE CORE VESICLES which are released into the synapse.
neuromodulators
messengers that do not bring about EPSPs or IPSPs themselves, but can bring long term changes that enhance or depress the actions at a synapse. Can bind at non synaptic sites and activate 2nd messenger systems
Example of a neuropeptide. What does it do?
Substance P. It is involved with the delivery of pain perception. Substance P and glutmate is released from the afferent PAIN FIBER in response to a painful stimulus.
Substnace P and Glu bind to receptors on the DORSAL HORN INTERNEURONS which conveys the into to the thalamus for pain perception, as well as the RETICULAR FORMATION for awareness, and hypothalamus, to bring awareness and behavioral emotional responses to pain.
how do endorphins affect substance P?
endorphins are amino acid chains that are released from the brain, spinal cord and pituitary and adrenal medulla. it blocks pain via PRESYNAPTIC inhibition of the afferent pain fiber.
It prevents the afferent pain fiber from stimulating the dorsal horn interneurons by preventing the output of substance P and glutamate. without the stimulation of the interneurons, the thalamus or reticular formation cannot be stimulated to bring on the awareness of pain.
