Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...

Spinal and Supraspinal Factors in Human Muscle Fatigue

Basal lamina grafts for reconnecting severed nerves are prepared from muscle by removing cellular material therefrom while preserving the tubular structure of the basal lamina. When connected to nerve stumps the basal lamina surfaces promote axon regeneration therethrough, eventually reestablishing nerve function through the regenerated graft.

Peripheral nerve regeneration

The selective elimination of axons, dendrites, axon and dendrite branches, and synapses, without loss of the parent neurons, occurs during normal development of the nervous system as well as in response to injury or disease in the adult. The widespread developmental phenomena of exuberant axonal projections and synaptic connections require both small-scale and large-scale axon pruning to generate precise adult connectivity, and they provide a mechanism for neural plasticity in the developing and adult nervous system, as well as a mechanism to evolve differences between species in a projection system. Such pruning is also required to remove axonal connections damaged in the adult, to stabilize the affected neural circuits, and to initiate their repair. Pruning occurs through either retraction or degeneration. Here we review examples of these phenomena and consider potential cellular and molecular mechanisms that underlie axon retraction and degeneration and how they might relate to each other in development and disease.

http://web.stanford.edu/group/luolab/Pdfs/Luo_OLeary_2005_AnnRevNeu.pdf

Axon retraction and degeneration in development and disease.

A wide range of insults can trigger axon degeneration, and axons respond with diverse morphology, topology and speed. However, recent genetic, immunochemical, morphological and pharmacological investigations point to convergent degeneration mechanisms. The principal convergence points - poor axonal transport, mitochondrial dysfunction and an increase in intra-axonal calcium - have been identified by rescuing axons with the slow Wallerian degeneration gene (Wld(S)) and studies with blockers of sodium or calcium influx. By understanding how the pathways fit together, we can combine our knowledge of mechanisms, and potentially also treatment strategies, from different axonal disorders.

Axon degeneration mechanisms: commonality amid diversity

Unlike other tissues in the body, peripheral nerve regeneration is slow and usually incomplete. Less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and current surgical techniques are similar to those described by Sunderland more than 60 years ago. Our increasing knowledge about nerve physiology and regeneration far outweighs our surgical abilities to reconstruct damaged nerves and successfully regenerate motor and sensory function. It is technically possible to reconstruct nerves at the fascicular level but not at the level of individual axons. Recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

/pdf/peripheral-nerve-reconstruction-after-injury-a-review-of-3g20ju057d.pdf

Peripheral nerve reconstruction after injury: a review of clinical and experimental therapies.

The object of the present observations is to describe certain alterations which take place in the elementary fibres of the nerve after they have been removed from their connection with the brain or spinal marrow. The following is a brief summary of the opinions and researches of modern physiologists on alterations of the nerve-tubes.

Experiments on the Section of the Glossopharyngeal and Hypoglossal Nerves of the Frog, and Observations of the Alterations Produced Thereby in the Structure of Their Primitive Fibres

In the ‘Proceedings of the Royal Society,’ No. 46, I have given a brief account of the effects of refrigeration of the ulnar nerve in man, by the application of ice. After repeated experiments on this nerve on myself, I never had occasion to witness any permanent disturbance in the nerve from the application of the ice, beyond a slight hyperæsthesia, which may have been partly due to the increased attention of the mind directed to the part whose functions were under investigation. The like immunity does not extend to experiments in which a much greater degree of cold is employed, as will be seen from the following instance.

/pdf/on-the-sensory-motory-and-vaso-motory-symptoms-resulting-3el0xzyp7q.pdf

On the Sensory, Motory, and Vaso-Motory Symptoms Resulting from Refrigeration and Compression of the Ulnar and other Nerves in Man. Second Communication

An Introduction to Human Physiology

The offices of these two nerves in the animal economy are of such importance as to render it a matter of practical interest to the physician, as well as to the physiologist, to obtain as clear an insight as possible into their functions. It would be impossible to point out any nerves presenting so many questions of daily importance to the practitioner as these, which govern the innervation of the stomach, the heart, the lungs, and the liver.

Experimental Researches on the Functions of the Vagus and the Cervical Sympathetic Nerves in Man

It has been shown by several previous observers (Holmgren, Dewar and M'Kendrick, Kuhne and Steiner) that the excised eyeball gives an electrical current, which under goes variation sat illumination, and that these variations of current are due solely to changes occurring in the retina. All the observers above named describe the variation to be positive at the commencement and at the end of illumination. Holmgren makes no distinct statement with regard to the state during illumination. Dewar and M'Kendrick seem to imply that the state during illumination is negative. Kuhne and Steiner distinctly assert that the state is positive during illumination, and that variations of the type described by Dewar and M‘Kendrick are characteristic of an injured, fatigued, or dying eyeball.

/pdf/on-the-retinal-currents-of-the-frog-s-eye-excited-by-light-3amappn6v8.pdf

Augustus Desire Waller

Papers

Experiments on the Section of the Glossopharyngeal and Hypoglossal Nerves of the Frog, and Observations of the Alterations Produced Thereby in the Structure of Their Primitive Fibres

On the Sensory, Motory, and Vaso-Motory Symptoms Resulting from Refrigeration and Compression of the Ulnar and other Nerves in Man. Second Communication

An Introduction to Human Physiology

Experimental Researches on the Functions of the Vagus and the Cervical Sympathetic Nerves in Man

On the Retinal Currents of the Frog's Eye, Excited by Light and Excited Electrically