BME 402 Homework 4 Due 11am Monday 3/5/06
Be able to derive the cable equation like we did in class using Kirchhoff’s current law.
Know the definition of the space constant
and the input resistance R
for an infinite
uniform cable and how these depend on diameter, and know what the steady state voltage
profile looks like in a uniform cable for various boundary conditions (i.e. if the cable
terminates in a fatter or thinner cable or a closed end, or two or more daughter branches).
Know the d
law for matched input conductances at branch points. Understand why the
speed of voltage propagation in a cable depends more on R
. Understand why
myelin speeds the propagation of AP’s and why action potentials block when myelin is
disturbed. Be able to briefly discuss at least one myelin-related disease.
Be able to compare and contrast electrical synapses (gap junctions) and chemical
synapses, in terms of where in the nervous system they occur, their approximate
dimensions, their physical components (know the basic vocabulary), their transmission
delays, their directionality, and their functional uses. In particular, be able to explain
what advantages accrue to chemical synapses that justify their much greater complexity.
Be able to name at least 8 neurotransmitters, and be able to say a couple of
interesting/informative things about each (such as where they are found, whether
excitatory or inhibitory or both, whether they are involved in direct or 2
gated transmission or both, what diseases are associated with their imbalances, what
drugs or blockers act on their receptors, etc.). Know what is meant by “reversal
potential”, and what this corresponds to in an electric circuit representation, and what the
reversal potentials typically are for excitatory and inhibitory synapses (and what ions are
Be able to draw the basic structure of the NMJ including the single axon (and know
where the parent neuron lives), its multiple release sites on the endplate, as well as a cross
sectional view of the pre- and post-synaptic terminals. Know some approximate
numbers: how many vesicles are typically released, how many channels are typically
activated, how large is the typical EPSP in the muscle fiber. Know what neurotransmitter
is used, and what ions carry the synaptic current. Be able to draw what the synaptic
response looks like under both current and voltage clamp including the approximate time
course. Know several things that can go wrong with the NMJ, including the names of at
least one toxin that blocks the ACh receptor, another that interferes with pre-synaptic
release, and a drug that acts on acetylcholinesterase. Be able to desribe how the
symptoms of at least one disease arise from dysfunction at the NMJ.