Natures wonders: fruit fly complex nerve controls (Introduction)

by David Turell , Sunday, June 30, 2024, 18:22 (78 days ago) @ David Turell

Not so simple:

https://www.sciencedaily.com/releases/2024/06/240626152203.htm

"Although a fly's motor neurons are few, it performs remarkable aerial and terrestrial feats. A wiring diagram recently created of the motor circuits in the central nervous system of the fruit fly is providing detailed information on how the nerve coordination of leg movements differs from that controlling the wings. Such studies reveal the unexpected complexity of the fly's tiny motor system. They also advance the understanding of how the central nervous system in animals coordinates individual muscles to carry out a variety of behaviors.

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"Although fruit flies seem like simple creatures, the researchers said that their motor system contains "an unexpected level of complexity."

"'A typical fly motor neuron receives thousands of synapses from hundreds of presynaptic premotor neurons," the scientists observed. "This number is on par with the scale of synaptic integration in pyramidal cells of the rodent cortex."

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"All such movements, from postural reflexes that enable a fly to hold its position steady, to traversing obstacles or changing flight direction, originate through electrical signals from motor neurons. These signals are conducted through threadlike projections from the motor neuron to stimulate muscles.

"A fly's six legs are managed by just 60 to 70 motor neurons, the researchers pointed out. In a cat, they noted, about 600 motor neurons supply a single feline calf muscle. Only 29 motor neurons govern the power and steering muscles of a fruit fly wing. In comparison, a hummingbird's pectoral muscle is supplied by 2,000 motor neurons.

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"The scientists explained that motor units are composed of a single motor neuron and the muscle fibers that it can excite. Various motor units, activated in different combinations and sequences, collaborate to achieve a myriad of movement behaviors.

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"One of the studies employed automated tools, machine learning, cell-type annotation, and electron microscopy to identify 14,600 neuronal cell bodies and about 45 million synapses (signal-transmission junctions) in the ventral nerve cord of a female fruit fly. The ventral nerve cord in flies is analogous to the spinal cord in vertebrates. They scientists went on to apply deep learning to automatically reconstruct the anatomy of the neurons and their connections throughout the female fly.

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"Multiple innervations might offer more flexibility and explain why an insects' limbs can operate with precision despite having so few motor neurons.

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"The scientists also examined the fly's wing motor system, which has roughly three sections grouped by function: powering the wing flapping, steering the insect, and adjusting wing motion.

"The investigation of the connectivity of the premotor neurons enabled the researchers to compare the organization of premotor circuits for two types of limbs. The leg and the wing in fruit flies each have a distinct evolution and biomechanics."

Comment: the appearance of neurons in evolution during the Cambrian changed everything. This shows how simple organisms are all highly complex. Even at the Archaeal level the metabolism is not simple. Not by chance.