Axonal Propagation And Synaptic Transmission Flashcards
Driving force for Na and K at RMP
Larger driving force for Na. RMP -70mV is closer to Ek (Na influx)
What is an EPSP
Transient depolarization of postsynaptic neuron due to increased conductance of the postsynaptic membrane to Na/K in response to NT binding
What is an IPSP
Transient hyper polarization of postsynaptic neuron (most often) due to increased Cl conductance of post synaptic membrane in response to NT binding
What are two ions can cause an IPSP
Cl in
K out
Where does synaptic integration occur? Why this location?
Occurs at axon hillock
Highest density of Nav channels therefore lowest threshold for spike initiation
Where to record for synaptic integration? How do inputs add?
Recorded from cell body of neuron
Additive inputs- spatial and temporal
Two ways of summation
Spatial summation- come from different spatial location and sum at hillock
Temporal summation- come from same spatial location and sum at hillock
- summation occurs if that arrive at the same time (close enough to each other at hillock)
What is the shunting effect? What does it relate to?
Synaptic integration
The amplitude of a signal closer to the hillock will be larger by the time it reaches vs a signal farther from the hillock (amplitude decrease with time)
- if signals do sum at hillock they may not have a large enough amplitude to cause an EPSP
What channels are on Nodes of Ranvier
Nav channels- densely populated
Kv
Function of Nodes of Ranvier
Produce saltatory conduction
- regenerate AP makes it look like AP jumps from node to node (b/c myelin this is only location we can see AP)
3 reasons why the APs are regenerated at the nodes
- Membrane conductance is high
- Membrane resistance is low
- Nav and Kv density is high
What is propagated between the nodes of Ranvier in the axon? 2 reasons How?
Passive potentials
1. Membrane resistance is high (no channels and myelin)
2. Membrane capacitance is low (charge separation is larger due to layers of myelin- charges are free to move b/c they are not attracted to anything with other side of membrane so far away)
What is a benefit if myelin
Don’t need channels down whole axon
How to improve conductance
Increase diameter (decrease Ra)
Myelinate the axon (increase Rm)
Remember: length constant - Rm/Ra
How myelination increases, what happens to Rm and capacitance. Explain capacitance effect cause and why importance
Rm increases
Capacitance deceases
- availability of charges to move
- distance between charge separation
Important to facilitate the spread of passive potential
What makes myelin in CNS and PNS
CNS- oligodendrocytes
PNS- Schwann cells
What are the two types of synapses
Chemical and electrical
How is info sent from dendrite to hillock
Passively propagated
Difference between summed signal hitting sub threshold vs suprathreshold? Where does summation occur
Subthreshold- no AP
Suprathreshold- AP occurs and propagates down axon
- sum at hillock
What happens to signal at synapse
Electrical signal converted to chemical signal then back to electrical
Where are electrical synapses found, what is there importance
Exist in CNS- function unclear
- provide low resistance pathway between cells that allows current to flow
- electrical synapses are fast, bi-directional, but lack gain (doesn’t add to the effect, just a hole)
- important in electrical coupling of networks in diff CNS regions
Provide examples of types of NT: small molecules, gaseous, amines
Small mcs- glutamate, GABA, acetylcholine
Gaseous- NO
Amines- dopamine, serotonin, NE
Reminder- steps of synaptic transmission
- NT is synthesized and packaged into vesicles
- AP arrives at presynaptic terminal
- Voltage gated Ca channels open, Ca enters
- Rise in Ca triggers fusion of synaptic vesicles with presynaptic membrane
- NT diffuse across synaptic cleft and bind to its receptor on postsynaptic cell, this activates postsynaptic cell
- NT breaks down, is re-uptake into presynaptic cell, diffuse away from synapse
Name excitatory NT and where they are found
Glutamate- in brain
ACh- PNS at NMJ (NAChR) and autonomic ganglia (MAChR), CNS in basal ganglia and spinal cord
Inhibitory NTs and location
GABA- in brain
Glycine- in spinal cord
When do dopamine and serotonin act
Dopamine- motivation, motor function, reward, pleasure
Serotonin- mood, appetite, sleep
When is gating direct and indirect
Direct: ionotropic
- ligand gated ion channel
- NMDA, AMPA- ionotropic glutamate receptor, NAChR, GABAa/c
Indirect: metabotropic
- G protein coupled receptor
- metabotropic glutamate receptor, MAChR, GABAb
Cys-loop channel structure (glycine, NAChR, serotonin)
- pentamer- 5 subunits
- each subunit has 4 transmembrane domains
- NT binds to N terminus
- M3 transmembrane domain creates pore- permeable to Na/K
Ionotropic glutamate receptors structure (AMPA, NMDA)
- tetramer- 4 subunits
- ## each subunit has 3 transmembrane domains
AMPA vs NMDA binding differences
AMPA- ligand gated channel
NMDA- required glu and gly to bind, exhibit voltage dependent Mg block (depolarization required to open channel), permeable to Ca
EPSC vs EPSP speed and type of potential
EPSC (current)- faster, active potential (ionotropic channels open and close)
EPSP (potential)- slower, passive potential
Explain an experiment to measure a post synaptic potential
Pg 19
Pre and post neuron- stimulate pre with an AP to cause NT release, record from post
Repeat experiment at different voltages
- Na movement at -90, -80, -70mV
- AP generation at -60mV, -42
- if voltage provided starts above threshold Nav inactivate so no AP just EPSP -32, -14 (Na in)
- -14, +3 reversal potential
- k movement at +10, +30mV out = IPSP (K has higher driving force since close to ENa)
What is a reversal potential
- RP is when the current through a channel physically reverses
Point of no net flux
Na in and K out at same rate (offset each other) - RP close to 0mV for non specific ion channel (ex. NAChR)
- RP close to Eion if voltage gated ion channel
What is the benefit of “synaptic recycling” (reusing vesicles)? Name 2 ways vesicles can be saved for re-use
Benefit- maintain membrane size, composition, and enhance efficiency (vesicles aren’t added or formed using membrane)
- kiss and run and endocytosis involving clathrin-coated pits
