Figure 1 - Smooth muscle. Transverse section. Bar
These questions have (and still be) used in examinations. You should be able to answer them in about 10 minutes. You should not have to write more than a few lines for an component of a question.
| Question 1 | Top |
The slide below is a smooth muscle preparation with the cells cut in transverse section. The length of the smooth muscle cells is unknown and your task is to estimate cell length.
Cell length cannot easily be estimated from longitudinal sections because no cell is sectioned in the plane of any one section, and in any case where one cell ends and another cell begins is not easy to distinguish. However, the length of the nucleus can be measured with reasonable accuracy and it is not difficult to select only those which show a good full section and not merely grazing the nucleus. From a preparation sectioned longitudinally, the average length of the nucleus was 25 microns (50 nuclei were measured and the standard error of the mean was ± 2.5 microns).
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Figure 1 - Smooth muscle. Transverse section. Bar |
| Question 2 | Top |
A skeletal muscle is 15 cm in length when relaxed. Sarcomere length was 2.5 microns relaxed and 2.15 microns contracted. The speed with which actin slides past myosin is approximately 5 microns per second (fast muscle, light load). Calculate:
| Question 3 | Top |
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An athlete exercises maximally with all his muscle
for 5 minutes. His total muscle mass is a assumed to represent
40 % of his body mass of 70 kg. In the muscle tissues the activity
hydrolyses 20 mmol ATP kg-1 s-1, and this
is assumed to be the essential energy involved. The enthalpy
of the ATP reaction is 42 kJ mol-1. The specific
heat content of the body is 3.47 kJ kg-1 o C-1
. Calculate:
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Don't panic. This question requires nothing more than 'O'-level arithmatic (perhaps 'O'-level physics) that you will all have done. So, let's break this question down. The questions below prompt you for answers to specific questions that are each milestones to calculating the answers requested. If you get them correct then you should be able to enter the correct values in the last 2 questions.
The last bit. So you know how much heat energy is being produce by the muscle per second.
Now all that remains is to calculate how much this raises the total body temperature over the period of 1 minute.
| Question 4 | Top |
You are provided with length tension data from a published work (by Dr. Ranatunga and co-workers). The data consist of measurements of sarcomere length and both passive and total (active plus passive) force. You need to use the data to calculate:
In the 1960's A.F. Huxley and co-workers published a series of papers which established the sliding filament theory of muscle contraction. Somewhat refined, this mechanism is still accepted today. Central to this model was the characteristic length-active tension curve of striated muscle. In particular, the sarcomeric length-tension curve allowed one to estimate the length of the contractile proteins within the sarcomere. 15 years had to pass before these estimated could be confirmed by direct measurement. It is easy to get the passive length tension relation from a resting muscle. Similarly, it is not too difficult to arrive at a length vs total tension relation. The length vs active tension will be the difference between the two curves as shown in the figure 1.
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Figure 2 - Length tension relation for skeletal muscle |
It is possible (as shown in Gordon et al. (1966) to derive estimates from the active tension vs length relation so long as one is able to measure sarcomere length and not merely muscle length. The assumptions (interpretations) one has to make are shown in figure 2.
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Figure 3 - Cartoon to illustrate the relation between the contractile filaments and the active tension vs sarcomere length curve |
By studying these figures and applying the same methodology, you should be able to use the numbers in the file provided to estimate the filament lengths as outlined above.
References
Gordon, A.M., Huxley, A.F. & Julian, F.J. (1966) The variation in isometric tension with sarcomere length in vertebrate muscle fibres. J. Physiol. 184: 170-192
Elmubarak, M.H. & Ranatunga, K.W. (1984). Temperature sensitivity of tension development in a fast-twitch muscle of the rat. Muscle & Nerve, 7: 298-303
| Copyright (c) 1998 University of Bristol. All rights reserved.
Author: Phil Langton |
Last modified: 19 Feb 2001 09:31 Authored in CALnet |