Monday, December 31, 2012

Getting the Picture

Do you get the picture? This familiar idiom asks if the listener understands a situation clearly. In terms of understanding literal visual pictures, that is, understanding the meaning of the information our eyes provide, we sometimes come up short teaching the role of mental processes involved with seeing. Stated another way, even in early grades students may begin to understand the connections between body senses and the mind’s ability to make sense of messages our body receives from the outside world. Sensory information means nothing without a sentient, conscious, operating mind. I recall repeating to my classes that our eyes merely receive information via light energy: “But it is our brain which figures it all out. The brain really does the seeing.”

Science instructors teaching light and sight units may rely too much on analogies between our eyes and a camera. For example, the camera has a lens to capture light from billions of data points--light producing points--in our environment. Billions of rays of light from multiple light data points in our surrounding world enter the camera through a tiny opening. Based on our students’ unspectacular discovery that light rays travel through the medium surrounding us in straight lines, simple diagrams of the camera phenomenon may be drawn. Light rays coming from the top of our field of vision enter the camera and fall on the bottom of the image sensor. Meanwhile, light rays from the bottom of our field of vision enter the camera’s tiny opening and fall on the top of the image sensor. Students discover image inversion. Holding a magnifying glass at arm’s length illustrates the inversion phenomenon.

Students discover that a tiny, extremely finely-detailed, focused picture of our sight field falls on our retina inverted and reversed. The student may ask, “Is this how we see?” No, this is just the beginning of our discovery! The remaining wonders revolve around nerve impulses, more technically termed called action potentials. These nerve impulses, tiny electrical charges, are integrated from information received from over 100 million photoreceptor cells in the retina on which the tiny image is focused. Integration consists of processing the information and transmitting it through approximately one million optic nerve fibers to the part of the brain called the visual cortex, a small area in the back of the brain. Some integration takes place in the retina. The main processing of information, however, takes place in the visual cortex.

Biology (7th edition), an Advanced Placement, 1231 page text authored by Neil A. Campbell and Jane B. Reece, is one of many wonderful resources for advanced students of biology. Campbell and Reece summarize their section on “Processing Visual Information” as follows:

Point-by-point information in the visual field is projected along neurons onto the visual cortex. How does the cortex convert a complex set of action potentials representing two-dimensional images focused on our retinas into three-dimensional perceptions of our surroundings? Researchers estimate that at least 30% of the cerebral cortex—hundreds of millions of interneurons in perhaps dozens of integrating centers—take part in formulating what we actually “see.” Determining how these centers integrate such components of our vision as color, motion, shape, and detail is the goal of an exciting, fast-moving research effort.

Our concern for today’s population revolves around their primary focus on the operational functions of camera technology, to name one example. Seldom do they discuss how their technological marvels actually work or what historic discoveries led to our present level of achievement. Instead, their conversations center on how such innovative technology enriches their entertainment experience. They master operational skills easily, but their fascination for how their technological marvels actually work may take a back seat.

“Getting the picture” of everyday human vision is far more gripping. Do we comprehend the wonder of our ability to immediately recognize and process the events portrayed in our visual field? Do we consider how our memory of past events instantly integrates with events observed in the present? Campbell and Reece, authors of Biology, observe, “Each neuron may communicate with thousands of other neurons in complex information-processing circuits that make the most powerful electronic computers look primitive.”

Samuel F. B. Morse’s first telegraph message was transmitted on May 24, 1844 between Washington and Baltimore. The message contained a phrase from Numbers 23:23: “What hath God wrought?” If Morse’s simple, technologically primitive electronic message deserved an epiphany giving credit to God, how much more may we apply the exultation to the wonders of “neurons in complex information-processing circuits” in the human body “that make the most powerful electronic computers look primitive.” The process of human sight is an occasion to give glory to God.

Monday, December 24, 2012

Visions of Design

Discussion of the more technical aspects of eye anatomy, including the path of light through the eye--cornea, aqueous humor, lens, and vitreous humor, along with the amazing retina and how it functions--turns out to be tedious for a portion of our population. Their interest may extend only to maintaining eye health with proper care, including dietary practices promoting healthy vision, or how the eye examination may lead to a prescription for corrective lenses. When I visit the ophthalmologist, I sometimes apologize for asking many questions concerning eye function. Doctors in other specialties are also recipients of my “What? Why? How?” queries. Seldom are my requests dismissed. Medical professionals are humbly proud of their professional expertise. They are anxious to share their knowledge of the wonderful workings of their body system specialties.

Curiosity which surpasses our doctor’s office questions may be satisfied by in-depth personal searches. This material is available to laypersons in televised special programs, textbooks, magazines, or internet postings. My interest in more detailed scientific and medical information is driven by desire to share knowledge of the wonders of divine design features evident wherever we look. This blog expresses our conviction that science topics are a powerful apologetic for our Christian beliefs in the reality of God as Creator. The “Theology of Creation” is an under stressed topic in many churches. Here is a link to a previous post under that title:

Each medical specialty dealing with a body system or sub-system is rich with information about the Creator’s design features. The denial of plentiful supernatural design features of the human body appears to be a position of irrationality. This post closes with a brief discussion of the workings of the retina of the human eye. Perhaps it serves to inform readers how much more knowledge is available apart from knowing the familiar truth about rods and cones.

The retina serves to transmit point by point information from the outside world to rods and cones and neurons in the retina called ganglion cells. Each atom or molecule of objects in our visual field is the source of a point of light. One friend described visible objects in our external field of vision as “consisting of trillions of data points.” Separate data from these points fall on different parts of the retina, thanks to the precision optics of our eyes. The human retina receives a great abundance of information. 100 million rod cells and 5 million cone cells collect light information from the trillions of data points in our external world. We may agree that the information received by our retina exceeds information produced by our “pixel-rich” cameras and printers.

The energy of photons falling on our retinal rods and cones triggers the production of “all or none” action potentials--electrical impulses triggered in the neurons which lead from the rods and cones known as photoreceptors to other types of cells in the retina: (1) The “all or none” electrical impulses travel to cells in the retina termed bi-polar cells. All bipolar cells are neurons which, in turn, (2) transmit impulses to ganglion cells. Ganglion cells also occur in the retina. All messages then travel as action potentials from ganglion cells to centers in the brain for processing into a meaningful picture. This transfer of information occurs through the optic nerve. The optic nerves, in two sections, eventually terminate in brain centers. For review, we present this flow chart:

Photoreceptors (rods and cones) à bi-polar cells à ganglion cells à axons of the ganglion cells (the optic nerve) à brain centers.

The optic nerve consists of approximately one million nerve fibers carrying only “all or none” electrical impulses to the brain. Before the electrical impulses travel through the axons of the ganglion cells, two other types of cells in the retina, horizontal cells and amacrine cells, help integrate the information received from the rods and cones. They join with bi-polar and ganglion cells to accomplish the integration. This is information processing at an early level. The most extensive information processing and integration occurs in the brain.

Perhaps the information discussed, cursory as it is, arouses a generous portion of wonder, along with the desire to investigate these topics on your own. We trust readers recognize the futility of a naturalistic explanation for the thousands of wonders surrounding us at every level, both in the living world and the material cosmos. In the world of life, particularly human life, we must also consider the problems posed by the belief that naturalistic evolution, even theistically guided evolution, brought these wonders into existence. 

Tuesday, December 18, 2012

Retinal Function

As we review the biological principle of “Form fits Function,” there is no better example than the remarkable sense of human light detection. Without the functional retina, the innermost layer of our eyeball, we would possess no vision. Most of the eight million extant species on our planet share with humans some degree of ability to detect light, ranging from simple detection of the mere presence of light in primitive organisms to the detailed color images perceived by birds of prey such as hawks. The visual acuity in such animals exceeds even that of humans.

The principle of “Form fits Function” amounts to a commentary on the ubiquitous design features of our universe. More specifically, it argues powerfully for the deliberate work of God whose activity in creating the multiplicity of living things was highlighted by the last product of creation--man in his image. In short, our lives operate successfully because this biological principle applies to virtually every phase of our physical experience. With respect to our sense of vision, we must not fail to understand extraordinary retinal tissue function.

The close range and distant matter surrounding us releases a constant flow of electromagnetic radiation. Visible light is but one type of radiation. That light ranges from dim to intense, along the familiar spectrum of colors. The retinal cells, termed rods and cones, detect light energy under dim conditions and color under bright conditions. There are four other types of retinal cells which possess other functions in the sight process. Rods and cones, however, are the key players in the drama.

All rods and cones contain a light-absorbing molecule called retinal which bonds to a protein called an opsin. In rods the visual pigment called rhodopsin is formed by this bond. When light, especially bright light, enters the eye we see clearly for a time. But the rhodopsin is changed somewhat and the rods become unresponsive. That explains why moving quickly from a bright environment to a dark room causes us to experience temporary difficulty seeing clearly while the rods regenerate.

Cone cells come in three classes. Three types of opsins, known as photopsins are each sensitive to a different color. One cone cell is sensitive to red light, another is sensitive to green light, and the third responds to blue light. Some cone cells are sensitive to an overlap of color wavelengths and together those wavelengths will produce intermediate colors when the brain organizes the image later in the visual process. In this way we may perceive every color on the visible light spectrum.

When we learned about rods and cones in elementary grades, our teachers may have wisely guarded her students against information overload. There was far more to the story. For example, what sort of signals do rods and cones send to the brain through the neurons? How does the light message arrive at the brain? After all, it is our brains which actually “see.” In the retina there are bipolar, horizontal, ganglion, and amacrine cells. They are the next players on stage, paving the way to discovery of “the rest of the story,” a phrase made famous by Paul Harvey, radio commentator for over fifty years.

The retina could not function as an entity apart from the energy of light flowing from the objects around us. The form of light and the function of the eye’s retina are complementary. This is one of hundreds of examples of the complementarity of design features present in our environment everywhere we look. Who is the author of these exquisite complementary design features? Our belief in the Designer is strengthened by recognizing the many form/function relationships evident everywhere in our created sphere.


Monday, December 17, 2012

Form Fits Function

In the current series of posts on human sight, this title may seem irrelevant at first glance. An explanation is in order. Perhaps you have been asked whether you would select the sense of sight or hearing should you be forced to do without one or the other. The question is irrelevant to our experience, but may trigger personal speculation and introspection on how highly valued and treasured all our sensory gifts are. Among the five major senses of the human body, sight probably ranks as the sense we would least like to do without. With this introduction, we look more closely at the elements of form and function related to vision.

There is an important physiological basis for judging that sight may be the paramount body sense, even though we may dislike prioritizing in this manner. According to estimates, 70% of the sensory neurons in our body are located in the retina. The retinal tissue is just over 1000 square mm in area. Roughly, this converts to the area of a teaspoon. In this small area there are well over 100 million rod cells and four million cone cells. This gives 150,000 cones per square millimeter in the central retina, the area providing clear, color vision of our central visual field. Cone cells function for humans in bright light. In the periphery of the human retina, there are many more rod cells which provide us with effective colorless vision even in extremely dark conditions.

Form fits Function is a principle of life science articulated in most modern biology textbooks. It is applicable throughout the living world. The principle applies to molecules, cells, issues, organs, and complete organisms. Among biology books, this principle could appropriately appear in every chapter covering the relationship between biological entities and their purpose. The principle applies to the hundreds of tasks accomplished within an individual organism, to the relationship of that organism to other organisms, and to the relationship of an organism to its environment.

In our current discussion of the phenomenon of sight, there is appropriate application of Form fits Function to the mechanism of the sensory detection of light by the human retina. The light reaching our eyes from nearby or distant objects arrives as billions of photons streaming from billions of data points from the light-giving object. We might say that each atom of those light-giving objects, complete with its vibrating electrons, is the source of a light data point. From each data point flows photons of electromagnetic light energy. Therefore, we have the form of plentiful light generation and effective transmission of light energy through space. What remains is the function of light detection, that is, our sensory organs of light detection. Initially, light is transmitted through the layers and substances of our eye—the cornea, aqueous humor, lens, and vitreous humor. However, the most spectacular functional organ, or, if you will, body tissue, is the specialized retina with its millions of rods, cones, and other specialized cells. These cells are triggered by photons to begin their work of sensing messages of light to the brain.

The form of light, billions of electromagnetic waves called photons, fits the function of the billions of retinal cells with their ability to detect billions of light data points. Beyond the retina, data will be sent to the brain as billions of simple electrical “all or none” pulses of voltage. The most fascinating aspect of “seeing” has yet to be discussed in an upcoming post.

Who is the author of the principle of “Form fits Function?” This blog has consistently proposed that our cosmos is a creation of the God of the universe, the Creator of all things, the God of Judeo-Christian scripture. He has designed all things after His will. We interpret scientific information in this light.

Monday, December 10, 2012

From Eye to Brain

Human sight is an ultimate production of the brain. As I look across the room from my computer keypad there would be no cognizance of the scene without my brain’s interpreting ability. My brain provides conscious awareness of the reality of the scene. Without a functioning mind sight does not occur. Light is a physical phenomenon present whether there is an observer or not, but sight is a subjective phenomenon based on external physical light stimuli. We need a human being to enjoy the subjective experience of human sight.

The transmission of information from the retina via cell extensions called axons through the optic nerve to the brain is one of the most fascinating processes related to the sight sequence. Each optic nerve contains over one million nerve fibers. We may understand the function of optic nerves by comparing how digital photographs are transmitted through a USB cable from a camera to computer storage files. Our digitally literate young people easily grasp this example of modern digital communication. Their personal photographs are transmitted as millions of tiny electrical impulses. The impulses carry the photograph to the computer, they explain. Older citizens might have a bit more trouble understanding how the process works.

These electrical impulses are called “action potentials,” tiny, repeated changes in voltage. Each change is like a light switch being turned on or off. There is no “in between.” In our eyes, 100 million rod cells and four million cone cells sense photons of light. Nerve cell endings then transmit millions of “all-or-nothing” electrical messages to the brain. Each of two optic nerves, one from each eye, contains about one million neural conduits. Our brain receives many millions of on or off electrical messages through the optic nerve each moment from the retina where the external image is projected and focused. The process works with divine simplicity.

The more than 100 million tiny rod and cone cells perceive varied light stimuli and send millions of different electrical messages from each data point projected on the retina. Millions of data points produce a plentiful trove of digital information. In a computer analog, the computer is able to convert received digital information from multiple data points into a high resolution image. The high resolution photographic image will possess no meaning for us until we observe and interpret it as though we were observing the image in real life.

The simplicity of digital messaging, either in technological applications or in the body’s own central nervous system, is belied by the presence of a multitude of physical constants and physical laws set in place by the Creator. Digital signaling, however, is governed by simple “ons” or “offs.” Scientists have figured out a way to use these on or off signals in hundreds of modern applications unheard of several generations ago.

Digitally literate young people have no have trouble mastering the underlying principle of digital technology. Neither do they stumble at the operational logic needed for mastering their ubiquitous remote units and computer driven devices. Our legitimate apprehension for modern users of technology, young or old, is the loss of wonder, amazement, and reverent awe of the Creator. He is the author of physical constants and laws of nature operating in our bodies and in our technology. God has enabled seven billion souls to benefit from application of physical constants and laws authored in his divine mind.

Our prayer is that we would give glory to God for these wonders. He designed the simple beauty of our body’s nervous system, including the concluding steps of the marvelous sequence of sight. Psalm 139:13-14 (NLT) declares: “You made all the delicate, inner parts of my body and knit me together in my mother’s womb. Thank you for making me so wonderfully complex! Your workmanship is marvelous—and how well I know it.”

Wednesday, December 5, 2012

Sight's Missing Link

One entire chapter of John’s gospel is devoted to a remarkable story of physical and spiritual healing. The ninth chapter of John chronicles the story of the man blind from birth whose sight was restored by one of Jesus’ transcendent miracles during his three year public ministry. The story is remarkable for different reasons. Physical blindness was overshadowed by the spiritual blindness of some characters in this scripture account. The healing of the victim’s physical and spiritual blindness and unbelief of the assembled spiritual leaders who witnessed the mighty miracle creates one of scripture’s most powerful multidimensional lessons.

Visual blindness is a malady of overarching significance as we consider a catalog of possible physical deficiencies. For the vast majority of sighted people, imagining life without vision is difficult. Nearly two million United States residents are afflicted with total blindness. Their adaptation to blindness is a tribute to their spirit and ability to adjust to a major life challenge. The absence of remote sensing visual capability, however, is a profound loss.

We may only imagine what caused the man’s blindness. Perhaps there was a congenital abnormality which triggered changes in the retina causing death of the photoreceptors. Infantile glaucoma is an elevation of internal eye pressure which causes damage to the optic nerve. The Bible story does not tell any details about the sight mechanism of the man blind from birth. It is likely he never saw any light at all, much less any images. His deficiency occurred in step 3 of the sight sequence. All his life he was surrounded by (1) plentiful light generation from light-producing objects and (2) transmission of light to his physical body. His physical eyes (3) were unable to process light for reasons we are not told. There was no reception of the light-generated electrical impulses through his optic nerve. But (4) his mind functioned normally, never having processed light images from the outside world. He was able to carry on a discussion of his healing, however, including the acknowledgement of Jesus as the divine Healer.

Normal vision surpasses the capability of the finest cameras. Former president George H. W. Bush popularized the expression “a thousand points of light” in a political speech while accepting his party’s nomination for president in 1988.
In a physical and poetic sense, visual information about our distant and close-up environment could be characterized as a million points of light. One may understand the literal meaning of this imagery by reviewing the physics of digital photography. Modern photographs are composed of “pixels,” the smallest picture element on a visual display. To produce a quality 9X12 inch photograph with a color printer, one needs the resolution of a million pixels (one megapixel). Human eyes define images with great resolution. With the processing our brains provide, our vision is far superior to images captured by high quality cameras.

Information in anatomy reference books provides details of the eye’s physical structure. Light passes through the cornea, the watery aqueous humor, the pupil, and the gelatinous vitreous humor inside the eyeball. The image is finally formed on the retina like pictures on the screen at a slide show. Images are transferred to the brain through the optic nerve for processing and eventual recognition. The man “blind from birth” in the 9th chapter of John provides a fascinating case study. Before Jesus healed him his disciples posed questions to Jesus on whose sin was responsible for his blindness. Was it his own sin or the sin of his parents? Jesus replied it was neither. God’s power was available and evident. The circumstances provided opportunity for manifestation of God’s power.

By human standards we live in an imperfect world. This universe was not created according to our idealized concept of perfection. It was created with an overlay of gradual decay according to the laws set in place by God himself. Ultimately the laws governing this universe will be replaced by the New Creation described in Revelation 21-22.