Bipn 140 Problem Set 1

Front 1

What is axoplasmic transport? Describe the experiment performed in the weiss lab that was used to discover this.

Back 1

The axoplasmic transport is the movement of materials inside the axon, both away from and towards the cell body. To discover this, a little piece of artery was bundled tightly around a bunch of axons making a cuff. They saw a build up of fluid inside the axon due to the blockage of the transportation of the cytoplasm along the length of the axon.

Front 2

What are the 3 way described in lecture used to detect axoplasmic transport?

Back 2

Direct visualization, arterial cuff /ligature, and radioactive tracers.

Front 3

What is the mechanism for slow axoplasmic transport?

Back 3

slow axoplasmic transport-bulk flow

Front 4

What is the mechanism for fast orthograde transport?

Back 4

fast orthograde transport- kinesin (motor molecule, uses microtubules)

Front 5

What is the mechanism for slow retrograde transport?

Back 5

intermediate retrograde transport- dynein (motor molecule, uses microtubules).

Front 6

How would slow axoplasmic transport, slow retrograde, and fast orthograde be affected by the addition of cochicine?

Back 6

Colchicine would make the microtubules, composed of tubulin and microtubule associated proteins, collapse and interrupt fast orthograde transport and intermediate retrograde transport

Front 7

What are the differences between sub-threshold and supra-threshold voltage changes in an axon, in terms of the relationship between stimulus and response

Back 7

Relationship between stimulus and response: the magnitude of a subthreshold change in is proportional to and graded with the magnitude of the stimulus; in contrast, the AP has a fixed amplitude i.e. all-or-none

Front 8

What are the differences between sub-threshold and supra-threshold voltage changes in an axon, in terms of how the intensity of the stimulus is encoded.

Back 8

The intensity of the subthreshold stimulus is encoded by the magnitude of the membrane potential while the suprathreshold stimulus is encoded by the magnitude of the membrane potential while the suprathreshold stimulus is encoded in the frequency of APs

Front 9

What are the differences between sub-threshold and supra-threshold voltage changes in an axon, in terms of how they change over distance.

Back 9

The subthreshold change in membrane potential will decay with distance from the site of initiation, whereas action potentials elicited by a suprathreshold change will be propagated w/o reduction over a long distance

Front 10

what active process helps establish the resting membrane potential?

Back 10

Na/K pump

Front 11

How can we determine the contribution of the Na/K pump to the maintenance of the negative resting membrane potential?

Back 11

To test the function of this active process, we would apply a Na/K pump ATPase blocker, such as strophanthadin or ouabin, in order to observe the relative positive change in resting membrane potential

Front 12

Mark is a PhD student studying the rat visual system. He is interested in an area in the visual cortex, and he wants to trace neurons from other brain regions that project to area (i.e. neurons with somas in some other brain regions and axon terminals in this area). What neuroanatomical method could mark employ?

Back 12

He can inject a fluorescent dye, which can be retrogradely transported back along axons, into this area of the visual cortex, after some time, when the dye has reached the somas, he can section the brain and see which regions have fluorescence. Alternatively he can inject a fluorescent dye that is lipophilic, inserts into the plane of the membrane, and diffuses back along the axons to the somas.

Front 13

Why does the peak membrane potential fail to achieve its ideal value?

Back 13

As the AP approaches ENa the driving force on Na+ ions becomes smaller and the Na+ conductance begins to decline, so that the increase in K+ conductance in combination w/ the large driving fore on K+ generates an outward current that opposes the inward Na+ current.

Front 14

What are rapid functions of glia in relation to neurons?

Back 14

1. Accelerating conduction of AP's along axons (myelin; oligodendrocytes and Schwann cells).

2. Potassium buffering: taking up K+ from the extracellular space, released by APs, providing signaling between neurons and astrocytes and preventing signaling between neurons

3. Electrical excitability and NT release, providing signals from astrocytes to neurons

4. NT uptake, terminating the action of transmitters on neurons.

Front 15

What are the different types of glia and whether they are located in the CNS or PNS

Back 15

PNS: Schwann cells

CNS: Oligodendrocytes, Astrocytes, Microglia, Ependymal cells, Radial glia

Front 16

What are the glial cells that direct the migration of neurons during early embryogenesis?

Back 16

radial glia

Front 17

A disfunction of what type of glial cell can lead to the NT glutamate, build up in the synaptic cleft up to toxic levels?

Back 17

astrocytes

Front 18

If an axon in the PNS is severed. It is observed that this axon is repaired and starts to grow. What is the glial cell involved?

Back 18

schwann cells

Front 19

What class of specialized macrophages is responsible for protection of the central nervous system?

Back 19

microglia

Front 20

Disruption in the blood brain barrier can lead to amyloid beta (a peptide believed to be responsible for the amyloid plaques observed in Alzheimer's Disease) From the blood plasma to enter the brain. A loss of function of which type of glial cell can lead to these observations?

Back 20

Astrocytes wrap around blood vessels and are responsible for the blood brain barrier

Front 21

What is the change in size of AP detected by the free nerve endings of dorsal root ganglion neurons when a cat first jumps down from a chair, which has a distance of 40 cm from the ground, and then jumps down from a balcony on the second floor that is 7 m above the ground?

Back 21

No change in AP.. An increase in the strength of the stimulus would not cause an increase in the size of the AP since and AP is an all-or-none event. But by increasing the strength of the stimulus the frequency of AP will increase.

Front 22

The cat has a kitten, which has a mutation that causes the free nerve endings of these neurons to have a lower threshold for initiation of AP. What will be the frequency of APs when both cat (a) and kitten (b) jump down from the balcony?

Back 22

well obviously the kitten will have a greater frequency of AP's because of its low threshold which makes APs easier to generate because of the less potential difference between the resting potential and threshold.

Front 23

Cat (a) has another kitten (c), which has mutation that increases its refractory
periods. Will there be a difference in the frequency of action potentials observed
between cat and kitten when they jump off the balcony? If so, how would the
frequency differ?

Back 23

A difference between the frequencies of action potentials of the two cats will be
observed. A lower frequency will be observed in kitten (c) because the longer
refractory period increases the time between consecutive action potentials, thus
decreasing the frequency.

Front 24

When you replace Ca++ outside the cell with X++ , an ion to which the membrane is not
permeable, action potentials are unaffected, but you are unable to release NT. What ion
do you think are responsible for the rising phase of the AP now?

Back 24

Cl- Actually, in an alien neuron, it is indeed possible that 2 voltage-gated ion
channels could be opening at the same time. Both voltage-gated Na channels AND voltage gated Cl- channels could be opening, and the peak of the action
potential could be an average of ECl- and ENa+

Front 25

How could you decrease the resistance, rm,
of the membrane? How could you
increase it?

Back 25

You could increase the number of open ion channels to decrease membrane resistance. To increase rm, you could myelinate the axon or make the channels very cold, so they could not open as in the Hodgkin experiment.

Front 26

While mammals myelinate their axons to increase conductance, invertebrates don’t.
What property do invertebrates use to increase conductance? Again, an equation we
discussed previously, how does this property increase the length constant?

Back 26

Invertebrates have larger diameter axons that increase  by decreasing ri.

Front 27

A patient suffers from hyperkalemia. Her extracellular potassium levels are elevated.
How would this affect her action potentialst?

Back 27

This would decrease the charge separation between the intra- and extracellular
compartments, essentially depolarizing the cell and opening some voltage-gated
Na
+
Channels (VGNa
+
Ch). If these elevated potassium levels are maintained, the
Na+ channels will become inactivated and are not able to open again because
they require repolarization in order to become deactivated. Deactivation is critical
because the VGNa
+
Ch cannot activate (open) without deactivation.

Front 28

The Na+/K+ Pump is said to be electrogenic. What does this mean?

Back 28

The Na+/K+ pump generates a charge imbalance by pumping in 2 K+ in for every 3 Na+ it pumps out. There is a net efflux of positive ions and the charge imbalance generates electrical potential/ electric field.