Questions

Neurophysiology – A conceptual approach, 5th ed. (Carpenter and Reddi)

Pg.3

1. ‘… tree-like dendrites that enormously increase the surface area of many neurons’Is the increased surface area important? I don’t think a plain surface area increase (per se) is the main point for function, instead the structure of the nerve dendrites increase the reach (but maximizing space economy, a huge nerve soma will not be useful even though its reach has increased) and also increase the number of connections (this point is related to the surface area). Is there any citation or paper for this? Also, conceptually, is there a difference in nerve endings (or are they just excitatory or inhibitory)? If we have one big round nerve, with all the previous connections feeding into it, will there be a difference in overall effect? (Of course there’s a space problem, but what about conceptually?)

Pg.10

1. Where are all the numbers coming from?

‘The connections that actually determine the brain’s behavior must be something of the order of 1015.‘‘yet it is smaller than your brain by at least two orders of magnitude.’

2. Are neuron-neuron connections like logic gates (binary response)?

Pg.18

1. I think that the diagram is wrong. The oil barrier is located on a myelin sheath, so in effect, it doesn’t make a bit of difference. The passive conduction within the nerve cytosol is still going on, and will still be at threshold and fire an action potential UNLESS the node of Ranvier is covered as well. Only if the node is covered, the passive conduction will decay below threshold before it can reach the next node. The explanation is fine, as practically, the oil drop will probably cover the node.

Pg.23

1. ‘the membrane, having the properties of a capacitor, tends to accumulate these cations on the outer surface.’How does this work?

Pg.31

1. Proof that the Potassium channel system is a fourth order system, and the Sodium channel system is a third order system. The book describes ion blocking as an explanation. But VG channels also can be activated via conformational changes (and ball and chain mechanisms). Which is this, then?

2. The end bit + the first part of pg. 32 says that conformation is involved. How does this explain the order of the system?

Pg.34

1. If the gradual depolarization is brought above threshold, what happens? If we do it slow enough, there won’t be positive feedback of channels, will there? Because the number of inactivated Sodium channels is too high to permit positive feedback.

Pg.38

1. Are there disadvantages of Frequency Coding? Of course in the real world and radios, there is always noise. But ‘If you add interference to a signal it masses up its amplitude but hardly affects its frequency at all’. Why are we assuming that noise only comes in the form of amplitude? Is this the case in real life (both in radio and in the human body)?

Pg.39

1. Are all stimuli ENCODED by receptor channels? Keep this in view while looking at touch, pain, etc.

Pg.40

1. What’s this about optimization?

Pg.52

1. ‘Vesicles appear to obey a kind of all-or-nothing law in that they either empty completely into the synaptic cleft, or not at all’What about the kiss-and-run theory? That does not completely empty the vesicles! Also, how

plausible are these theories? For some reason I think the kiss-and-run theory seems more possible unless we have a HUGE amount of vesicles. The passage also mentions that 200-300 vesicles are released per AP. Couldn’t we run out relatively quickly, then?

Pg.89

1. ‘what you feel is a tight constriction round the meniscus, even though the pressure is of course greatest at the fingertip.’While this is true that the pressure is the greatest at the fingertip, the pressure difference is really small. Should we be able to discern between the two? And therefore, in the end, the whole finger feels the pressure (more or less equal). And that is why the greatest difference is felt at the boundary.

Pg. 92

1. Why does anoxia affect the largest fibres first? Metabolism? Or easier to compress? The latter seems odd.

2.