All Problem questions are selected from your textbook. The first number of the problem refers to the chapter the question was taken from your textbook.

Layne, C.S. et al., The Effect of Long Duration Spaceflight on Postural Control during Self-generated Perturbations

Go to http://www.coe.uh.edu/~clayne/7340Reading.html and use the sheet to critique Dr. Layne's recent paper.

Textbook chapter problems

Problem 3.2 What would happen if there were no sodium inactivation mechanism?

Problem 3.3 What will happen if a myelinated fiber suddenly loses its sheath? What can you expect from such a fiber in a hot bath and in a cold bath? Note that ion diffusion proceeds much more quickly at high temperatures.

Problem 3.6 What will happen if you stimulate an axon with a strong electrical impulse somewhere in the middle of its length? In which direction will the action potential propagate? Why?

Problem 6.2 You want a large motor unit and a small motor unit to contract simultaneously. How would you time commands to the motorneurons?

Problem 6.4 Which motor units would you expect to find in abundance in a marathon runner, in a weight lifter, and in a swimmer.

Problem 6.5 You have invented a way to induce abrupt synchronization of motor units in human muscles. What types of athletes would you recommend this method to, and what types of athletes would you suggest not even try it?

Self-Test Problems 6. A person generates 5% of the maximal voluntary contraction force of a muscle. Then muscle force increases slightly so that only one new motor unit is recruited. What can you say about the properties of the motor unit? The same person generates 95% of the maximal voluntary contraction force. Again, muscle force increases slightly so that only one new motor unit is recruited. What can you say about the properties of this motor unit?

Readings

Thomas, C.K., et al. Embryonic cord transplants in peripheral nerve restore skeletal muscle function

1. List all of the words in the abstract you do not fully understand.

Textbook chapter problems

Problem 5.5 How will a secondary ending react to an increase in the activity of dynamic gamma motoneurons innervating the spindle?

Problem 5.6 When we voluntarily contract a muscle, its length decreases. However, the frequency of firing of the spindle endings in the muscle may remain constant. How can this happen?

Problem 23. 1 Does muscle and tendon elasticity affect signals from Golgi tendon organs? Do these receptors always accurately monitor muscle force? Why or why not?

Problem 23. 5 What kind of kinesthetic illusion can you expect if a joint flexor muscle is directly stimulated by an electrical stimulator?

Readings

Burke, R.E. Some comments on the organization of motoneurons

1. Develop a table relating motoneuron types to histochemically identified types. This table does not need to be an exhaustive listing of characteristics.

2. On page 168 Burke states - Recent quantitative biochemical work has confirmed earlier histochemical observations that virtually all of the muscle fibers innervated by a single motoneuron (i.e., belonging to a single muscle unit ) are essentially identical. It also appears likely that their mechanical properties are also the same.

What do you suggest is the functional significance of this finding?

Burke, D. and Gandevia, S.C. The human muscle spindle and its fusimotor control

1. Briefly describe the evidence that suggests that muscle spindle feedback provides servo-assistance during a voluntary muscle contraction.

Problem 7.1 How can you use an inhibitory neuron to increase the excitability of another neuron?

Problem 7.3 You stimulate a pool of Ia-interneurons. How will muscle force change for an agonist and for an antagonist? What kind of changes do you expect to see in the firing rate of a Renshaw cells?

Problem 7.6 What will happen if a presynaptic inhibitory mechanism is acting on a postsynaptic inhibitory synapse? What will happen if a presynaptic inhibitory mechanism is acting on another presynaptic inhibitory synapse.

Problem 8.1 What is missing in the suggested definition of reflex latency on page 65?

Problem 8.4 What will happen if two action potentials (one orthodromic and one antidromic) are moving toward each other and meet at a certain point on the axon?

Problem 8.5 What is the frequency of stimulation at which you may expect to see the M-response become smaller?

Problem 9.1 What kind of reflex effects can be expected from the action of Ib-afferents during a fast flexion movement against a constant external load?

Problem 9.4 If all the Ia-afferents are driven by vibration, why don't they induce monosynaptic reflexes in response to each vibration cycle?

Problem 9.5 Suggest an explanation for the suppression of H-reflexes during a tonic vibration reflex.

Readings

Ian McCloskey, D. Muscle, cutaneous and joint receptors in kinaesthesia

2. Briefly describe the evidence that suggests muscle receptors contribute to the conscious sensation of movement.

3. How can the phrases - the whole is greater than the sum of its parts and one plus one does not equal two be related to Ian McCloskey's article.

Ali, A.A and Sabbahi, M.A. H-reflex changes under spinal loading and unloading conditions in normal subjects

1. On page 665, the authors mention that H-reflex amplitude exhibits "wide variability between subjects even if the intensity of the electrical stimulation is held constant." Speculate on why this may be the case. (In this case, "subjects" refers to healthy individuals, see the two cited references).

2. The authors suggest that the H-reflex amplitude was inhibited during standing, loading and unloading relative to prone lying because the compressive forces on the spine are greater during the standing conditions. What are other possible explanations are there for these findings?

Readings

Perrier, J. et al. Cooperation of muscle and cutaneous afferents in the feedback of contraction to peroneal motoneurons

1a. In general, what do you think was the author's purpose in conducting this study?

1b. What is the hypothesis of the investigation.

2. How did the authors convince themselves that the afferent responses from the mechanical compression of the cat's foot were primarily the result of cutaneous receptors?

3. The authors describe "linear" and "nonlinear" interactions. Briefly explain HOW these different interactions could occur.

4. What do you think is the functional significance that cutaneous receptor inputs have multiple "access" routes to motoneurons?

Van Wezel, B.M.H. et al. AB fibers mediate cutaneous reflexes during human walking

5. What is the logic underlying this experiment?

6. What is the "well-known" 'reflex reversal' that is referred to in the article?

7. What evidence to the authors present that suggests that nociceptive and nonnociceptive cutaneous AB afferents use different reflex pathways?

Chapter 12

Problem 12.1 The difference between the latencies of the monosynaptic response and those of M2 is the same in the arm muscles and leg muscles. What does this finding tell us about the possible transcortical nature of M2?

Problem 12.3 You are carrying a bundle of firewood with extended arms. Suddenly it drops. What kind of reactions can you expect in your biceps and triceps?

Problem 12.6 Can you define the afferent source of the corrective stumbling reaction with the method of successive limb denervation, that is, eliminating afferent inputs from areas of the leg?

Readings

Bouisset, S., Zattara, M. To Which Biomechanical Necessities Do Anticipatory Postural Adjustments Related to Voluntary Movement Respond?

1. What do the authors mean when they state that "local anticipatory accelerations were organized according to a pattern that was specific to the forthcoming movement"?

Aruin, A.S., Latash, M. The role of motor action in anticipatory postural adjustments studies with self-induced and externally triggered perturbations

2. In the Discussion the authors maintain that "anticipatory postural adjustments were observed in all our experiments with self-initiated unloadings." What were their criteria to establish that anticipatory postural adjustments occurred?

On page 299 the authors state - "All this looks very confusing and suggests that the central nervous system is not as 'smart' as we used to think. In conditions of absolutely predictable and reproducible postural perturbations, it make an unnecessary and potentially harmful adjustments in the magnitude of anticipatory postural adjustments to the magnitude of the focal movement, leading to larger deviations of the center of pressure and leg joints."

3a. What evidence are they using support their claim.

3b. Do you "buy" their claim that their evidence suggest that the central nervous system is not as "smart" as we used to think.

3c. What assumption about movement control underlies their logic.

PS - take some time answering these questions

Shiratori, T., Latash, M. The roles of proximal and distal muscles in anticipatory postural adjustments under asymmetrical perturbations and during standing on rollerskates

4. On page 614, the Shiratori and Latash comment that Aruin et al, in a 1998 paper, suggested that anticipatory postural adjustments in unstable postural conditions could be due to the fact that the CNS considers APAs as additional sources of perturbation which may move the center of pressure out of the reduced area of support. Discuss this possibility in light of the Aruin and Latash article you read which maintains that APAs are "an inherent component of the "voluntary motor command" (page 299).

5. Identify one "flaw" in this study. This can be either something that is suspect in the methods or in the author's reasoning.

Readings

Turvey, M.T., Fitch, H.L., Tuller, B. The Bernstein Perspective: I,II,III

1. Briefly describe "address-specific" control.

2. Determine the number of degrees of freedom if the two lower limb, the two arms and the trunk are each considered independent elements within a locomoting system that has three dimensions but only one equation of constraint.

3. Briefly discuss context-conditioned variability as it related to human speech.

4. How are degrees of freedom, equations of constraint and coordinative structures related?

5. Briefly describe a behavioral feature of a mass-spring system.

6. What do the authors mean when they mention "the principle of relational invariance over metrical change?"

Gurfinkel, V.S., and Cordo, P.J. The scientific legacy of Nikolai Bernstein

1. What do you think Bernstein meant when he suggested that motor skills can be viewed as "morphological objects"?

2. What do you think may have been Berstein's greatest contribution to the field of prosthetics?

Turvey, M.T. and Kugler, P.N. An ecological approach to perception and action

1. Speculate on why the authors spend so many pages discussing the Cartesian Doctrine.

2. Briefly contrast Gibson's idea of reality with those subscribing to the Cartesian Doctrine.

3. How does the concept of time-to-contact relate to prospective control?

4. Briefly discuss the concept of affordances. Do you think affordances can be perceived without relying on a "mental state" in the Cartesian sense?

Chen, H., et. al., Age effects on strategies used to avoid obstacles

1. Relate the LSS and SSS to time-to-contact and the concept of affordances.

2. Which of the two stepping strategies was less "risky" and why. What evidence was used to support the author's claim?

McIlroy, W.E. and Maki, B.E. Age-related changes in compensatory stepping in response to unpredictable perturbations

1. Identify the discrepancy between the two papers in regards to their explanation of the different behaviors observed in their young and elderly subjects.

2. Discuss how decrements in perception could have resulted in the findings reported in the McIlroy and Maki paper.

3. Besides serving to move the body's center of mass, what could be another role of anticipatory postural adjustments?

Slobodan, J. Changes in movement symmetry associated with strengthening and fatigue of agonist and antagonist muscles

1. Do you "buy" the argument that increasing strength may be a reason why the authors found a change in the symmetry ratio after training? Why or why not.

2. What would be the value of generating symmetrical velocity profiles as a "basic organizing principle underlying movement generation".

a. Caldwell, G. E. and Li, L. How strongly is muscle activity associated with joint movements?

b. Bobbert, M.F. & van Soest, A.J. K. Two-joint muscles offer the solution, but what was the problem?

c. Gottlieb, G.L. Minimizing stress is not enough

1. Summarize each of the above three articles(a,b,c) in no more than 150 words.