I recall the same "everything coming together" feeling, but for me it didn't happen until Applied Biochemistry in grad school.
I recall the final exam being only a single question, with a bunch of blank lined pages to write your answer, and the question was something like "You just ate a ham sandwich. What happens to it?" A good answer needed to include everything down to the molecular/chemical level and tie it together all the way up to the macro scale, and I finally felt like that class had prepared me to tell the story.
Oh man, where do I even start? Sensory input from the inner ear to balance, the networks that handle feedback from afferent signals from the periphery, efferent pathways to control motor movement. I don't even know all the details but it's mind bogglingly complex. Do I explain the molecular basis of action potentials? The modulating effects of inhibitory feedback within the networks? I feel like all of that barely scratches the surface of the insane complexity of neuronal networks
And how does one even begin to talk about our desire and internal drive to do things like ride a bicycle
Assume an experienced rider, as learning is different.
Intention is set, requiring the basal ganglia and fore brain and either a notion of free will, determinism, or whatever you fancy.
The area ahead is scanned and mapped for a clear path via retina- optic nerve - visual cortex and particularly the dorsal parietal pathway.
Initial organised motor signal sequences originate in pre and pre pre motor areas, hitting motor strip of the brain, particularly those homoncular areas corresponding to legs, arms and torso. Basal ganglia loops prime these circuits into action and help maintain their engagement.
Activated motor strip neurons pass through the internal capsule, down the pyramidal tracts, the spinal cord, and meet a lower motor neuron in the anterior horn, which then carries the baton and traverses out if the cord (still the central nervous system) into the body and to the final destination: a muscle. Electrical depolarisation along the axon hops rapidly between nodes of ranvier, enabled by insulation myelination. At the terrminal synaptic bouton lower motor neurons branch across a muscle body. Each neurons innervated patch is a motor unit; multiple combine into a motor pool. Depolarisation triggers fusion of vesicles to the membrane endplate and release of acetylcholine into the thin synapse. Rapid diffusion moves thr snall molecukes to the muscle membrane, the sarcolemma, who then bind to the membrane spanning Nm nicotinic receptors which open and allow a rapid flooding of sodium into the muscle cell syncitium and efflux of potassiun into the extra cellular matrix. Depolarisation of that muscle allows further calcium released from the sarcoplasmic reticulum to activate protein machinery; myosin and actin run across each other and fibres contract. With enough activity concentric movement is achieved across the associated joint.
In a manner similar to walking, various spinal reflexes and the spinal locomotor pattern generator create a local, fast framework for actualisation of the impulses.
Feed back on state of the musculature ascends the spine via dorsal root ganglia and the dorsal horn. Amongst these are proprioceptive afferents, rapidly feeding back state of tension in muscle fibres from golgi tendon organs along highly myelinated type 1a fibres. These signals pass into the cerebellum where they are co processed with signals from the eyes and vestibular system.
The cerebellum modulates
the intensity of descending motor activity by comparing expected to perceived muscle state. It also orchestrates balance by integrating general body state, visual cues and vestibular information. In this way the small and large oscillations of riding the bike are maintained and constrained into an orderly process.
Experienced riders can dedicate higher function, i.e Executive frontal areas to other tasks, or to refined modulation of thr task to overcome specific issues.
Beginners must use all their frontal powers to focus attention on the task, painstakingly sequence actions, and reflect on the numerous errors and their consequences. Learning is slow, multi system, and largely independent of autobiographical memory.
You forgot the metabolic cycles of the signalling molecules and their receptor proteins, as well as the ion pumps important for those reactions. I think that is really what the professor was going for. Also, perhaps, some [partial] description of the learning process as it impacts a single neuron.
It took me a long time to figure out how I made a turn on a bicycle. No, it's not just turning the steering wheel in the direction you want to turn. You actually slightly turn it the other way, then the bike tilts into the turn you want to make, and you turn the steering wheel into the turn to stop the tilt from turning into a crash.
It all happens so subtly, and your body does it perfectly with no input from the brain other than "I want to turn".
It is a fun one to show new or inexperienced riders. "Now that we are coasting, what do you think a slight push forward of your left hand will do to the bike?"
My finger gently depresses the black plastic key. As the machine begins to pull in data from the net I shift my weight back in the chair and look up over the top of screen, out the window at the lunch hour foot traffic passing silently by beyond the steam tinted cafe window. The overheavy graphics begin to render, but my gaze is caught by a momentary glimpse between the rushing cars of a woman in a red dress on the far side of the street...
... it'll be fun if you start from what happens when the enter key is pressed- the mechanics and electronics involved in submitting that URL (and some chemistry and physics behind what your eyes see on the screen), the physical transmission of the signal from your computer to through the interwebs and some error correction protocols to ensure your signals are still useful.
Maybe toss a line or two in about the complexities of running a large data center and how your response time varies based on some sorcery.
Then you go the extra mile and weave a tale of electrons wrestling with their universe of invisible electromagnetic wave overlords that determine their fate while they embark on a treacherous journey to convey information thousands of kilometers across with blistering speed. Tell them of the aged electron saw a family member get attacked by a stray cosmic ray and the fright of the pack when one simply tunneled out of existence...
Not during an interview, though. The interviewer would see it as trolling (at best), and you would fail the interview. And for a good reason! Because as an engineer (and an intelligent person in general) you must be able to separate what is essential from the non-essential for the subject in question. For instance, the physics or the physiology of the process of pushing a key on a keyboard is probably not what the question was about, nor do those things in fact have much to do with typing, even (which you can do on a touchscreen or using the mouse).
This answer reminds me of the blog post of the guy asked to implement a linked list iirc during an interview, and he does it all in Haskell's type system.
When we start looking at life at the level of physics, chemistry, and biochemistry, the absolute beauty of the system begins to appear. The complexity is on a scale that's difficult to imagine or even unimaginable even to those trained in the fields, and there is a feeling of wonder that words can't capture
Going over quantum electrodynamics to explain how to make microcircuits would be fun, that was our first class specific to electrical engineering for me some 30 plus years ago.
I recall the final exam being only a single question, with a bunch of blank lined pages to write your answer, and the question was something like "You just ate a ham sandwich. What happens to it?" A good answer needed to include everything down to the molecular/chemical level and tie it together all the way up to the macro scale, and I finally felt like that class had prepared me to tell the story.