User:Ldorn15/sandbox

Leeches are comprised of several segmented ganglia, which, they utilize to achieve swimming behavior. A study demonstrated when the head and tail ganglia were torn apart from each other, swimming behavior still occurred. Another study has been completed that led to the conclusion that neural activity that controls swimming coordination is central rather than peripheral. There are five functional classes of neurons involved in leech swimming, mechanosensory, motor, oscillator, gating and trigger. Physiological experiments have been conducted to determine that leech swimming behavior is controlled by a neuronal central pattern generator or, CPG. The results obtained from these experiments show that the CPG consists of linked segmental oscillators that have a specific way of connecting. Excitatory potentials from gating neurons reach the CPG which regulates the frequency of oscillations. The higher the level of activity from the neuron in which the excitatory potential came from, the greater the oscillation frequency and the greater the swimming behavior. The swimming behavior of leeches is the result of the wave-like movement of the body from the front to the rear end of the leech. The waves produced by the leeches effect the efficiency as well as the stability of their swimming behavior. For example, if the leech produces a larger thrust while swimming it leads to an overall instability in their body but a greater efficiency in the swimming behavior. On the other hand, a smaller thrust would allow the leech to be more stable and have more control but it would prevent the swimming behavior from being very efficient. The neural circuit of the leech is comprised of three levels, two of which are "command-like" neurons. A study was conducted to examine the responses of this neural circuit when in the presence of stimuli that caused whole-body shortening of the leeches. The results indicated that the neurons in the upper level of the neural circuit were excited by these stimuli along with stimuli that induced swimming, whereas neurons in the lower level were inhibited during the shortening process. Therefore, it is evident that, at higher levels of the neural swim circuit, there is no control in choosing between swimming and shortening behavior. Swimming behavior in leeches is stimulated by pressure, light-dark waves, or moderate to strong contact with something else. These stimuli that activate swimming behavior are converted into a signal by many different classes of sensory neurons including the sensillar movement receptors and light-sensitive organs. The stimulation of these sensory neurons causes trigger and command neurons to be activated through direct or polysynaptic connections with other neurons.