Lewis Wetzel was born in 1763 to a frontier family living in the Ohio River basin. Intermittent warfare persisted between the native Americans and the westward expanding settlers, and that ongoing conflict resulted in Lewis losing his father, sister and brother to Indian raids in 1786–testimony to the ferocity of the engagements. The young man growing up under these circumstances had to develop frontier skills simply to survive, and of course use of firearms was essential. The rifle of that day was a muzzle loading device requiring a series of complicated (certainly compared to modern firearms) procedures in order to eventually arrive at a primed and effectively loaded weapon. First a correct measure of gunpowder was poured into the barrel, then a lead ball was inserted and tamped down tightly with a metal ramrod. The hammer was then set in the half cock position and a few grains of powder were introduced into the flash pan just below the level of the touch hole. The cover of the flash pan was lowered, the hammer now pulled back to the full cocked position, and finally the rifle was ready to fire. Armies practiced this drill continuously in a series of standard movements while at rest in order to provide a steady rate of synchronized fire.
Lewis, however, had honed his abilities to a far more remarkable degree, and he became adapt at loading his rifle while sprinting, carrying spare lead balls in his mouth. When chased by Indians, Wetzel would fire at his opponent, then run away with what appeared to be an empty weapon. But Lewis was reloading on the run, and would suddenly wheel about and shoot again at his suddenly astonished-and very unhappy- pursuers. So numerous were these deadly encounters, he became known to the local tribes as “Death Wind”.
Even as firearms must be reloaded to continue functioning, our multiple biologic systems must also have the ability to return to a primed state to perform repeated biochemical activities. Once a nerve has completed its bio electrical impulse transfer to the next nerve across the connecting synapse, this system must be reset to a virgin condition. Neuro transmitting molecules that have been released from the initiating nerve to the receiving nerve have to be cleared from the synaptic space, while each of the nerves have to normalize to a pre transmission state. These are complicated processes but without them the nerve only fires once. This would be akin to using dueling pistols instead of semi automatic weapons. Throughout our bodies, literally trillions of biochemical reactions are proceeding constantly, but in order to keep this system flowing after each reaction there has to be a resetting mechanism. Otherwise, everything grinds to a halt within moments. Not exactly a good business model for building life forms.
We also see this with the periodic firing of the sinoatrial node in our heart. Astonishingly we have a spark plug sitting in the center of our chest in exactly the perfect position for initiating and propagating a heartbeat that will pump blood through lungs which oxygenate hemoglobin molecules in our red blood cells, then eventually send this life sustaining blood through a massive series of progressively tapering tubes to every corner of our body. And the spark plug has to fire with exactly the correct timing. Too fast or too slow–well these are disease states that require intervention. Our spark plug has to fire within exact parameters. I have been summoned to the hospital to attend patients with extremely slow heart rates, requiring placement of a temporary pacemaker wire into the heart’s ventricle and then attaching the other end to a pulsing battery, returning the heart to normal rates. Alternatively, extremely rapid rates require administration of IV medications and at times electrical cardioversion with those paddles you have all seen on televised medical shows.
As with nerve synapses, after each impulse from the sinoatrial node, this system has to clear and return to a pre firing condition, and it has to be done fast. If we do not have the ability to reset the node, then we are at a literal dead end. One heartbeat. Try existing on that. There is no time to slowly develop this system–it all has to exist together. Multiple genes are involved in producing the architecture of our heart and circulatory system. Indeed, there are specific separate genes involved solely in the formation of the sinoatrial (SA) node and its function. The SA node covers only a few square millimeters in our heart and the cells are extremely specialized. Once the cells have discharged their bioelectrical spark, they have to reset quickly–physiologists refer to this as the “membrane clock”. Between heartbeats sodium and potassium ions influx through specialized channels resulting in a gradual buildup of electrical potential. When the proper threshold is reached, a large influx of calcium ions is triggered which causes a rapid spread through the conducting tissues along the heart’s septum (middle-divides the heart chambers) to the atrial ventricular node (AV). This is located at the inferior portion of the septum and has arisen separately through its own multiple specialized genes during the heart’s formation. This node acts as an electrical transformer and splits the propagation of the impulse to both sides of the heart allowing contraction of the ventricles (large chambers) to occur simultaneously. If this sounds complicated consider that this description is simplistic. This system is actually much more complex.
The SA node is not the only repetitively firing pacemaker in the body. Our respiration is rhythmic and central for life, and located in the brainstem is an apparatus known as the Pre Botzinger Complex (PBC). This behaves much like the SA node in terms of building a bio electrical action potential, but this fires at a slower rate of 14-18 times per minute. Once the PBC fires, a signal is sent to the dorsal respiratory group (DRG) which is also located in the brainstem, and there the bio current is processed and propagated through the phrenic nerve which terminates in the diaphragm–the main breathing muscle separating abdomen and chest. When the signal is received the diaphragm contracts resulting in breathing. Even while asleep this system maintains a regular breathing pattern which has been set at the optimum rate for proper respiratory function in order that our tissues can continue to receive adequate oxygenation. How is it that 2 separate electrical pacemakers in the body are set individually at the perfect location and frequencies to ensure the necessary heart and respiratory rates to maintain life? In addition, animal studies are now indicating that the PBC responsible for respiratory rate may have a back door involvement in heart rate and blood pressure management as well.
There is also a ventral respiratory group (VRG) in the brainstem which is involved in forced breathing–unlike the heart, we can voluntarily over ride the respiratory frequency cycle. In additional, the brainstem respiratory group controls the depth of respiration. The entire system has a feedback loop from chemo receptors which measure oxygen, carbon dioxide, and pH levels in the blood, as well as from stretch receptors in the lung. Finally, the hypothalamus in the brain adjusts our breathing in response to input from temperature, pain, emotions and exercise.
Stop and think about this–the entire system spans anatomic locations from the brain’s cerebrum and brainstem to control rhythmic processes which are expressed in the heart and lungs and involve incredibly complicated feedback loops with continuous input.
God’s Human Biology Chapter 20 “The Matrix” discusses the propagation of a biochemical current along a nerve. At the microscopic level, the nerve terminates in a synapse, the site of neuro transmission of a signal to an adjacent nerve. This is an enclosed protected space equipped with the ability to release molecular neurotransmitters from the initiating nerve to interact with the receiving nerve’s binding sites. There are a variety of neuro transmitting molecules and each requires its own specific binding site. Small sacs on the releasing side contain these neurotransmitters and these fuse with the presynaptic membranes when the action potential traveling down the nerve releases calcium ions at this location. Fusion of the sac with the membrane creates an opening to release neurotransmitters which cross the synaptic cleft joint to the biting sites on the post synaptic nerve membrane. Just as Lewis Wetzel would have been a dead man if he could only fire once without reloading, these nerves would only have the ability to have 1 interaction without the ability to clean up the neurotransmitters and return to a pristine state in preparation for the next wave of activity. To complicate matters further the process of recycling is different for each neurotransmitter. Acetylcholine for example, must be degraded by an enzyme into component parts acetate and choline. Each of these is individually reabsorbed through active channels into the presynaptic nerve ending. Other neurotransmitters are each handled specifically and these events happen with fractional second timing. Any frontier rifleman would be envious.
Muscle contraction also requires a fire and reload mechanism. This sequence begins with a bio electrical stimulation conducted through nerves terminating in a neuromuscular junction–similar to a synapse-with the neurotransmitter acetylcholine released and binding to receptors on the opposing muscle membrane. This causes microscopic channels to open permitting the influx of positively charge sodium ions which build until an action potential is triggered and travels along the membranes covering the muscle. Calcium ions are then directed to flow into muscle cell cytoplasm and bind to troponin proteins. Tropomyosin, which has been bound to actin filaments, is now physically detached and change the troponin’s configuration, in turn leaving the actin binding sites exposed; these are now free to bind to myosin filaments which crosslink and contract. ATP ( Chapter 29 “Fuel”) then binds to the myosin which releases from actin, the calcium ion flow then reverses, troponin returns to its original shape, tropomyosin again covers the binding sites on actin, myosin returns to its inert but available state, and the muscle relaxes. Whew. The entire apparatus is now reloaded and ready for the next command to fire.
Do all these systems-sinoatrial node pacemaker, respiratory rate initiation, nerve synapse operation, muscle contraction-sound complicated? Because they should. All are ridiculously complex and many are inter dependent requiring vast numbers of cooperating integrated activities. Extensive biochemical activities are required to initiate and conduct sub cellular actions and all have to reset rapidly and prepare for the next round of excitation. The human body had to figure out this vast network of nerves and muscles within a timeframe that does not allow for slow development. The chances of this happening by random undirected mutations over time would be akin to having a planetary sized roulette wheel that spits out repeated sequential landings on double O. Ain’t gonna happen.