The receptors for salty and sour are believed to be ion sensors. MSG stimulates receptors corresponding to unami. PROP causes an intense bitter sensation in "supertasters." Sweet and bitter receptors are believed to be similar to odorant receptors because molecules dock on transmembrane receptors in order to initiate an action potential.

Assuming that a food critic or wine taster most values their ability to perceive the flavors and aromas of these consumable items, then a loss of their sense of smell—olfactory loss—would be the greatest of these misfortunes they could suffer. The vestibular sense is that which informs us as to the orientation of our bodies in space. The semicircular canals contribute to this sense, and are housed within the inner ears. The loss of this sense might not compromise a food critic or wine taster as severely in their professional life. The striate cortex is a key component of the visual cortex, and damage therein would likely result in partial or total blindness. This would not hinder the food critic or wine taster's abilities to perceive their foods or wines however.

There are about three hundred and fifty receptor types involved in olfaction. Each receptor responds to more than one molecule, but with different strengths. Receptors make their first synapse with glomeruli, but each glomerulus receives input from only one type of receptor.

The Moro reflex (also called the "startle reflex") generally lasts in newborns until the age of six months. When startled, a newborn exhibiting the Moro reflex will throw its head back and its arms and legs out simultaneously, cry, then pull its limbs back in.

The somatosensory system is a sense system based around information about the physical body. This includes the senses of touch, of heat, of pain, pressure, and vibration; of orientation and balance; and of muscular movement. The tactile and skin senses, the vestibular sense, and the kinesthetic sense comprise it. The tactile sense is that of touch. Other skin senses include detection of heat, pain, pressure, and vibration. The vestibular sense is that which detects the body's orientation in space, and contributes to our sense of balance and motion. The kinesthetic sense is based off the movements and positions of our muscles, and may also be referred to as proprioception. This sense is how we can close our eyes yet remain aware of where our limbs are positioned in space, or why we don't need to follow our legs and arms with our eyes to direct them while we walk or reach for objects out of view. The other answer choices do not involve correct groupings of senses to summarize the somatosensory system.

An action potential describes the event of an electrical impulse being activated by a given neuron once it is sufficiently polarized. We may think of an experience such as pain. If I prick my finger with a needle, I feel a small amount of pain. If, however, I unfortunately lose my fingertip due to a mechanical accident of some sort, I will feel much more pain. This difference in pain is not due to the strength of any one given action potential. An action potential either leads to an electrical impulse or it does not (in other words, it is all-or-none). There are no gradients in strength or degree; however, the number of action potentials occurring across neurons can have a cumulative effect (e.g., greater number of nerve cells involved in the more serious injury of losing a finger tip equates to a greater experience of pain).

While potassium—alongside sodium—plays a vital role in the functioning of neurons and in the exchange of neurotransmitters, it is not a neurotransmitter. Rather, it is involved in the shifting of polarity in the neuron that leads to an action potential. In other words, the amount of potassium present in a given neuron directly impacts meeting the threshold of an action potential. Serotonin, dopamine, and norepinephrine are neurotransmitters released by these action potentials.

In reading popular articles on brain science or, perhaps, by watching a documentary on brain injuries, we might have come across the terms sensory and motor neurons. Just as they sound, a sensory neuron passes along sensory information. Motor neurons, which are located close to the spine, assist with our motoric abilities (e.g., walking, grasping, pushing). Interneurons play the role of circuitry connectors between sensory and motor neurons. Because of this, they are also sometimes referred to as relay neurons. Finally, “outer neurons” are not one of the three major classifications of neurons. In fact, there are no such things as outer neurons.

The tiny space between a synapse of one neuron and the synapse of another is called the synaptic gap. It is also known as the synaptic cleft. It is in this space where neurotransmitters can be exchanged between neurons. It is important to note that not all neurotransmitter molecules emitted by a given synapse or necessarily received by the synapse across the synaptic gap. Multiple variables are at play. The gap is not needed for the neurons to have space to grow nor is the brain kept moist via these clefts.

This question is closely associated with the nature vs. nurture debate. Let us be reminded that both nature and nurture are at play in development including neuronal development. With that in mind, we can successfully conclude that the false statement in this series is, “by birth, neurons are fully developed including axons, dendrites and myelin.” While most of the neurons we will have throughout our life are present at birth, these neurons are in nascent form. That is, they are still building neural pathways and connections while other neural pathways and connections are being pruned away if left unused. This process is most prolific in the first three years of life, but continues across the lifespan.