Swimming Phase Research Articles

The adaptation of a reflex response to the ongoing phase of locomotion in fish.

The reflex response to stimulation of the tail fin has been studied in the swimming fish, by bilateral electromyographical (EMG) recordings in several segments along the body. The response varies with the phase of swimming. When the muscles on one side (segment) are active, a large response will occur on this side but no response on the contralateral side at the same level. When the other side becomes active an identical stimulus will cause an activation of this side but no response on the previously active side. When the movements were filmed a powerful mechanical effect was demonstrated with an augmentation of the ongoing movement, that would result in an instantaneous increase in speed. The stimulus causes in addition a shortening of the duration of the swimming cycle and its components. Most of the results were obtained on spinal dogfish, which also exhibits spontaneous locomotion after a spinal transection. Mainly electrical bipolar stimulation of the tail fin was used. Identical stimuli applied in different phases on an ongoing movement, thus give a reflex response that changes dramatically with the phase of the movement. This phase dependent reflex reversal is functionally meaningful; it is fast and due to spinal mechanisms.

Neuronal organization of escape swimming inTritonia

1. Escape swimming behavior inTritonia diomedea consists of two major components: an initial reflexive withdrawal followed by a series of alternating ventral and dorsal flexions. The basic mechanism of generating motor neuron activity, therefore, switches from reflexive to centrally programmed. 2. Three classes of cerebral interneurons and some of their synaptic connections have been identified. 3. Reflexive withdrawal interneurons (RWI) receive direct input from sensory afferents and synapse with motoneurons in the pedal ganglion (DFN, VFN). This class of interneuron is excited during reflexive withdrawals and inhibited during the swim phase. 4. Swim interneurons (SI) are excited during reflexive withdrawals and burst during the swim phase. 5. The third set of interneurons (C2) are shown to be necessary for the normal initiation and maintenance of the cyclical swim phase. Activity in C2 neurons appears to retrigger the swim oscillator network cycle-by-cycle. 6. C2 neurons inhibit the RWI neurons during swimming thus freeing motoneurons to respond predominantly to inputs from the SI and C2 neurons. The switch from reflexive to programmed motor output is, therefore, mediated centrally by two identified C2 neurons.

Upper extremity contraction moments and their relationship to swimming training

A rationale is presented for relationships between the contraction moments at the shoulder and elbow joints and the forces acting on the adjacent body segments during the propulsive phase of front crawl swimming. It was hypothesised that the magnitude of the contraction moments necessary to sustain large hydrodynamic forces would be such that with swimming training the contraction moments would increase, and that the faster swimmers would have larger contraction moments. In order to reduce the complexity of the kinetic analysis it was assumed the contraction moments could be measured using a device which allowed for rotation without translation and provided an appropriate resistance moment. The contraction moment produced bending strain on a lever arm and the signal was integrated to give impulse and work output. Tests were carried out on a sample of 42 boys. Half of the group underwent a period of swim training and it was found that the medium ability swimmers did increase the initial segments of the impulse and work output curves. Tests on the remaining swimmers showed that the higher ability swimmers had impulse and work output curves which were significantly greater than for the lower ability swimmers.

CHANGES IN THE ACTIVITY OF ACID PHOSPHATASE AND THE APPEARANCE OF METAMORPHOSING POTENCIES OF THE LARVAE OF THE ASCIDIAN, HALOCYNTHIA RORETZI.

In the swimming phase of the larvae of the ascidian, Halocynthia roretzi, changes in the activity of acid phosphatase (AcP-ase) were studied cytochemically with respect to the appearance of metamorphosing potencies. The AcP-ase activity in the larvae before and soon after hatching is weakly visible only in and around the nuclei of the epithelial, muscular and notochordal cells. 6 hr after hatching the enzyme activity begins t o appear weakly in the microblasts around the proximal end of the notochordal sheath, whereas the activities which were found in the previous stages disappear. In the larvae which passed for 12 hr after hatching, the activity of AcP-ase is distinctly shown in the microblasts and also in the other 2 mesodermal cells, meso- and macro- blasts. The microblasts of this stage are closely attached to the notochordal sheath at the proximal end. At the same time, many large granules which appear similar to lysosomes are found in the microblast by an electron microscopy. The 6th hour's larvae after hatching can be induced slowly to resorb its tail by the treatment with a nile blue solution, but the time which it takes for tail resorption is gradually shortened depending on the age of the larva up until 12 hr after hatching. From these results, i t was concluded that the appearance of the AcP-ase activity in the microblasts was parallel with the appearance of the potency of metamorphosis of the larvae after hatching. Possible roles of the microblasts at onset of meta- morphosis would seem to play a role in the rupture of the notochordal sheath and in the succeeding regression of the tail tissues.