Say we see a mosquito, and our brain tells us 'hey that's a mosquito, you should kill it.' Then we move our hands and slap/clap it.

The initial visual stimulus is translated to an action potential via the phototransduction cascade. Light hits retinal, bla bla, glutamate release is decreased, turns a few cells on and off, which eventually sends the action potential down the optic nerve through the lateral geniculate nucleus and to the 'final' target, the occipital cortex.

Then, something happens from this point in the occipital cortex, which eventually 'translates' to action potentials beginning in an upper motor neuron (UMN). This UMN located in the motor cortex of the brain, propagating its message eventually reaching the muscle.

The question is, what happens in this intermediate phase, where visual input lands on the occipital cortex, and then eventually translates to an action potential being propagated at the UMN located in the motor cortex? Do neurons directly synapse from the occipital cortex to the motor cortex? Is there a particular neurotransmitter responsible for communication between neurons of the occipital lobe and motor cortex, or whatever lies in between (glutamate, acetylcholine, etc)?

And finally, the hardest question... light provides a simple stimulus which translates to an action potential, making it the 'origin' of the action potential in this case. But if we close our eyes, and imagine a mosquito, we'll still have activity in our occipital cortex, and willingly provoke the same motor response. What was the stimulus for this visualization, if light wasn't the firestarter? Does some other molecule isomerize cis-retinal to trans-retinal, or affect some other step down the photoreception cascade?


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