Module 3 Lecture 1 Flashcards
what is Ramón y Cajal’s law of dynamic polarization
neurons are directional; they take in input and send output
synapse definition
where two neurons come in very close proximity to communicate with each other
- any given neuron is likely both pre- and postsynaptic
what theory did Golgi have about neural communication
reticular theory; thought the nervous system was one continuous web, and not a bunch of cells communicating
Cajal’s neural theory
that there are distinct cells that talk to each other
two classes of synapses
- chemical: one neuron secretes NT that activates receptors on another neuron
- electrical: neurons are in electrical continuity with each other via interlocking proteins w/ ion channels
what forms the gap jxn in electrical synapses
2 connexons
where were gap jxns first found
in the crayfish lateral giant interneuron
- if you give a crayfish an aversive stimuli, they have an escape reflex that takes a tiny amount of time to execute; mediated by electrical synapses
gap jxn structure
- each is made of 6 connexin subunits, each with 4 TM regions
- large, non-selective pores
- synchronization of electrical & second messenger signals
- has binding sites for PKA, PKC, MAP kinase, calmodulin
how did the Long 2002 experiment impact our understanding of electrical synapses
- they simultaneously patch clamped onto two neurons in the inferior olive of mice with connexin-36 KO
- found that connexin-36 KO mice show impaired synchrony in membrane potential changes
where are gap jxns found in mammals
hippocampus
gap jxn function in mammalian hippocampus
involved in the neurons that deal with conceptual learning & memory during hippocampal sampling of features
- may be responsible for hippocampal pattern recognition
what did Negeshi (1980) contribute to electrical synapses
showed how electrical synapses can be regulated
- dye infused into horizontal cells of Eugerres plumieri usually spreads rapidly to other horizontal cells
- dopamine, through PKA activation, can reduce this spreading
role of PKA in gap jxns
phosphorylates connexins and lowers conductance
what did Galvani’s frog leg experiment (~1790) contribute
he connected spinal muscles to spinal nerve; muscles twitched when electricity was applied to either the nerve or the muscle
- called it animal electricity
what is a negative Schwankung
the AP waveform
- observed by Dubois-Reymond and Julius Bernstein
what was the significance of the rheotome
allowed Dubois-Reymond and Bernstein to compare the voltage inside a cell to the voltage outside, and quantify the difference over time
- not precise enough to show an overshoot, and they had no sense of a refractory period
Bernstein’s breakdown theory (1902)
depolarization of the cell membrane above some threshold leads to a transient breakdown of the ionic barrier between inside & outside of a cell, making the cell permeable to all ions equally
flaws of Bernstein’s breakdown theory
- implies AP should peak at 0 mV
- membrane gets a lot more permeable, but doesn’t get equally permeable to all ions
- there are more ions involved than just 1
what was the first human EEG
Hans Berger’s Edelmann String Galvanometer
- couldn’t get detailed or high resolution about electrical signals
- they were really good at picking up on seizures
what happens when you deliver muscarine to a heart prep
heart slows
what was the first theory for what is released by the vagus nerve onto the heart
muscarine and adrenaline
what is actually released by the vagus nerve onto the heart
acetylcholine and norepinephrine
“Vagusstoff” and “accelleronstoff”
what was the significance of the isolated heart prep
allowed for the study of nerve stimulation of the heart
isolated heart experiment methods
- dissect the heart, attach it to a perfusing line
- record from the heart to observe contractions while stimulating still-attached nerves
results of the isolated heart experiment
activation of parasympathetic vagus function slows the heart down
- still not known whether muscarine is what is released from the vagus nerve
results of the perfusate heart experiment
the heart connected to the perfusate of the first heart showed a slowing effect
- concluded that vagus nerve is releasing some substance that has an effect on the heart
how long does it take for vagus nerve stimulation to take effect?
150 ms – very slow
methods for NMJ prep
patch onto the nerve in the middle of the mouse soleus muscle; stimulate or measure from the nerve, measure from the muscle to see what’s going on
- flaw: everytime the muscle twitched, the setup was destroyed
curare function
inhibits ability to get an AP
- you still get EPPs after treating with curare, but you only observe depolarization
delay time for NMJ vs cardiac
100x smaller than cardiac response to vagal stimulation; muscle response is within 1 ms
- Eccles now considered that this could work in CNS
how did Eccles determine that Cl- currents mediate inhibition of motor neurons
he stimulated an inhibitory interneuron synapsing on a motor neuron, and observed that removing Cl- from the bath gets rid of the hyperpolarizing inhibitory synaptic input
what would you expect from Eccles’ interneuron experiment if there was only electric synaptic transmission
inhibition would not cause much hyperpolarization, but would make it harder to cause depolarization
- you would not expect there to be different patterns for excitation vs inhibition due to different ion concentrations, but rather a decrease or increase in the same ion (like K+)
