Answers to the crosswords on membrane physiology

To check out the answers for the crosswords on membrane physiology, visit PhysioBytes (click here)

Sodium-Potassium pump and action potentials

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Regulation of ACh release at neuromuscular junction

An interesting question was raised a few days ago by a couple of you regarding the neuromuscular junction (NMJ).
Is there any mechanism that regulates the amount of ACh released at the NMJ?
One of the most important factors that determine the amount of ACh release at the NMJ is off course the ECF Ca++ concentration. A fall in ECF [Ca++] will decrease ACh release as the Ca++ influx that occurs during a presynaptic potential is dependent on the out-to-in gradient for Ca++.
Other than that, in many of the central neural synapses there are additional presynaptic mechanisms that influnce neurotransmitter release. Receptors for the very neurotransmitter released at a synapse are often present on the presynaptic membrane. Such receptors are refered to as autoreceptors. The nerutransmitter released during synaptic transmission, in addition to its primary action on the postsynaptic side, also binds to these presynaptic autoreceptors and brings about changes in the presynaptic mechanisms thus influencing further release of neurotransmitters. For instance, consider the synapses in the sympathetic nervous system. Nor-adrenaline is a neurotransmitter employed by sympathetic nerve endings and acts upon different types of nor-adrenergic post synaptic receptors. A particular type of adrenergic receptor, the alpha2 adrenergic receptor, is found on the presynaptic membrane of these nerve terminals. The nor-adrenaline released during sympathetic activation acts on these presynaptic autoreceptors to reduce further release nor-adrenaline. Thus this is an example for a feed back regulation of neurotransmitter release. In some cases such feedback regulation may increase neurotransmitter release rather than decrease it. Such mechanisms are believed to be important in maintaining the sensitivity of the post-synaptic emmbrane to neurotransmitters and regulating the efficiency of synaptic transmission.
Coming back to the NMJ, it was traditionally believed that such feedback regulation of neurtransmitter release does not occur at the NMJ. But recent studies suggest that the release of ACh at NMJs may also be influenced by a feedback effect of ACh on presynaptic autoreceptors which belong to the muscarinic class of cholinergic receptors.It remains to be seen how important such regulation is and whether it has clinical significance.

Sloppy work

I must admit that I have been a little sloppy of late. Errors in the crossword, mix-ups in the problems and missing -ve signs in the solutions to problems...! Well I have corrected whatever that was brought to my notice. Nice to know that some of you have looked at these things carefully and have taken the time to give me some feedback.I hope this continues and more of you join in the action.

Hodgkin & Huxley

I simply can't stop admiring the contribution of Dr. Allan Hodgkin and Dr. Andrew Huxley to the field of Neuroscience. Their amazing work with squid axons is an classical example of the success of the experimental approach in biology. It is also illustrative of the multidisciplinary approach to neurscience that has yielded rich dividends. Their description of the ionic basis of action potentials in neuronal membranes is indeed a major landmark in the history of Neuroscience. The quantitative model (a mathematical description) of the action potential that they developed marks the birth of computational neurobiology which has added an exciting element to the field of neuroscience. It is indeed very rare that such a precise and convincing explanation is discovered for a fundamental phenomenon. The early 1950s were indisputably some of the most exciting yeras for science in general and bilology in particular. Even as Hodgkin and Huxley where discovering the basis of the electrical signals that the brain uses to perform its amazing feats, Watson and Crick were cracking the structure of DNA - the very essence of life. More than 50 years after these seminal discoveries, scientists still continue to expolre their implications for the understanding of life and all its mysteries. For those who are interested in reading more about these great men of science, may I recommend a visit to the following sites...
More about Hodgkin
More about Huxley

Crossword corrections

Just realized that there are a few errors in the croosswords - thanks to few blessed souls who have actually tried it!
1. (1) Across was meant to be "A change in the membrane potential that makes it less NEGATIVE". But it does'nt really matter - it does'nt mess up the rest of puzzle anyway...
2. The answer to (3)Down has two alternate spellings...that may create some trouble...Heres a clue - the fifth letter in (3)Down is "A"

I have made the corrections in the version on PhysioBytes

Answers? we'll wait for another couple of days to give the lazybones another chance...

Crosswords

I hope there are some crossword enthusiasts amongst you. When I was in the hostel during mu under-graduate years, the only reason I used to get up early in the morning was to lay my hands first on the crosswords in the newspaper that was delivered to the hostel reading room. There were quite a few crossword nerds in our hostel and so there was always stiff competition!
Try this simple crossword on membrane potentials - it may even help you review the topic. Visit PhysioBytes (you'll find links at the top as well as on the side bar of this page)for the crossword.