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NB505 - Focus Areas Exam One


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What drug can be used to turn off voltage gated Na+ channels?
ttx (tetrodotoxin)
What durg can be purfused into a neuron to turn off voltage-gated Na+ channels?
What drug can be used to block electrical junctions?
Octanol (alcohol)
What drug shuts off NMDA channels?
What drug shuts off GABA channels?
What are the fundamental points of the Stuart and Sakmann paper?
1) APs backpropagate
2) The backpropagated wave uses active propagation as Na+ channels in the dendrites help to sustain the wave.
3) The "APs" in the dendrites caused by the backpropagating AP are not all-or-nothing.
What are the fundamental points in the Galarreta and Hestrin paper?
1) Inhibitory henrons are critical in the coordination of cortical activity.
2) Electrical synapses between inhibitory cells => synch of firing
Give three characteristics of electrically coupled cells regarding firing, frequency/coupling and coupling ratios.
1) Electrically coupled cells tend to fire all-or-none.
2) Low-freq signals => higher coupling ratios.
3) Coupling ratios are usually small, e.g. in the 1 to 10% range.
Within the hippocampus, what type of cells will be heavily connected via electrical junctions and which will not?
1) Interneurons will be heavily electrically connected.
2) Pyramidal electrical coupling is sparse.
What are the fundamental points of the Gibson et al. paper?
1) In the neocortex there is an inhibitory network of Fast Spiking (FS) neurons which are electrically coupled.
2) In the neurocortex there is an inhibitory network of Low-Threshold (LTS) neurons that are electrically coupled.
3) There is no electrical coupling between FS-LTS.
What are the distinctions between sodium generated APs and calcium generated APs?
1) All-or-none
2) Distinct threshold for AP
3) Short duration - ~ 1 ms
1) Longer duration - 10s of ms
2) Not all-or-none
3) No distinct threshold
What would be seen in intra-dendritic recordings during APs in cerebellar Purkinje cells and hippocampal pyramidal cells?
Purkinje cells have a low number of Na+ voltage-activated channels in the dendrites so backpropagated APs will only see passive propagation.

Hippocampal pyramidal cells have Na+ voltage-activated channels in the dendrites so there will be active backpropagation of APs.
What are the three different tests to tell if two neurons are electrically connected?
1) Direct (probe in each cell)
2) Indirect (send signals back along axons and see what is coupled to what)
3) Tracer coupling (inject a dye and see if it goes from one cell to another)
Contrast electrical vs. chemical synapses.
distance between cells: 3.5 nm (elec) vs. 20-40 nm (chem)

Cytoplasmic continuity (elec) vs. none.

Gap-junction channels (connexons) vs. pre-synaptic vesicles, active region, post-synatpic receptors.

Ion current (elec) vs chemical transmitter

Usually bi-directional (elec) vs. unidirectional.
Trace the electrical pathway within the hippocampus.
Performant pathway => granule cells => CA3 pyramidal cells via mossy fibers => CA1 pyramidal cells via Shaffer collaterals.
What are the two things needed to get LTP in the hippocampus?
Synaptic stimulus coincides with strong depolarization.
State how to form a LTP in the hippocampus and the details of what happens.
1) Apply low freq stimulus => high freq stimulus (50-100 stimulii at a rate of 100/sec) => how freq stim.
2) Apply stimulus to multiple inputs in the dendritic tree. AMPA channels form EPSPs.
3) Get temporal and spacial summation => AP.
4) AP backpropagates => strong depolarization => NMDA channels turn on => Ca++ entry => LTP.
What are the four basic firing patterns?
Slow regular
Fast regular
fast irregular
What two nucleii make up the magnocellular cells?
supraoptic nucleii
paraventricular nucleii
Where are magnocellular cells located - soma and terminals? Where are the hormones dumped?
They are located in the hypothalimus and there terminals are in the posterior pituitary. The hormones are dumped directly into the bloodstream.
What hormones are released by the magnocellular cells?
Oxytocin and vassopressin.
Contrast the release of oxytocin to vassopressin
Oxytocin: released in pulses. The magnocellular cells burst in sync to produce a pulse of oxytocin.

Vassopressin: Release is graded and async.
Given the timeline/signals for release of oxytocin during nursing of rat pubs.
Signal from suckling => sync bursting in magnocellular cells => release of pulse of oxytocin into the blood stream => release of milk (about 10 seconds later).
Give the timeline/signals for the release of oxytocin during uterus contractions.
Contraction signal from uterus => sync bursting in magnocellular cells => release of oxytocin into blood stream => stimulation of contractions.
Give the drivers and targets for release of vasopressin.
Decrease osmolarity => async stim. magnocellular cells => releases vasopressin.

Decrease blood volume or BP => async stim. Magno. cells => release of vasopressin.

Target: constriction of arterial smooth muscle; reabsorption of water by kidneys.
What is one major hormone released by the parocellular cells? G___

What is one of the hormones that this causes to be released? L___

What is a characteristic of firing of the parocellular cells?
GnRH (gonotrophic releasing hormone).

Leuteinizing hormone (LH).

They fire in sync (neuron to neuron) bursts.
What is the anatomy of the parvocellular cells?
PV cells are located in the hypothalamus and send a process into the median eminence where hormone is released into the portal vascular system and subsequently affects the anterior pituitary.
Looking intracellularly, what will be seen in a parvocellular cell when GnRH is about to be released?
The frequency of APs associated with a burst increase.
What is a DAP and what is its significance?
DAP - depolarizing after potential. If an AP occurs their will be a sharp depolarization followe by a fast repolarization with a slower repolarization tail. During this tail, the membrane is still depolarized and this is a DAP. If multi APs occur together and temporally sum, then the DAP will show a rising membrane potential which can lead to a plateau. During this time period, the membrane is closer to threshold and it is possible for a burst of APs to occur.
What is an example of the use recurrent inhibitory feedback circuits?
Allow pyramidal cells to be extensively interconnected w/o leading to positive feedback that could result in a seizure if unchecked.
What drug blocks AMPA channels?
What are modern approaches to studying the electrophysiological mechanisms of mammalian hypothalamic neuroendocrin cells.
There are various transgenic mice breed to express a given protein for a hypothalmic cell. For instance, eGTP breed into transgenic mice to be able to distinguish GnRH cells. Use fluorescene to see these. Use biocytin to see cell being probed.
What neurotransmitters are normally associated with neuroendocrine cells?
glutamate and GABA-A
What are two of the key parameters measured in EEGs?
Amplitude and frequency.
What can induce paroxysmal depolarization?
Block inhibition
What is observed during a myoclonic seizure?
Rapid contraction of muscles (rapid and short)

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