Bovine biology series
Part - 24 Brain
The brain
In the coming months we will examine the head area of animals, the brain, eyes, nasal passages, nose, ears, jaw and teeth or palate, and the tongue. After we complete the head area we'll investigate the nervous system. Actually the nervous system, through the brain and spinal cord are all related, physiologically.
This month, we examine the brain.
I doubt many of us have ever seen the brain of a cow. Usually when a cow is posted, her internal body - cavity organs are inspected.....the rumen and intestines and liver and lungs and heart, etc. We gaze at the reproductive tract, or perhaps the musculature of the legs. Sometimes we look at the secretory tissue of the udder. But the brain? No, generally we leave this alone, for in the role of pathological investigation, the head remains intact.
And yet the head, specifically, the skull or cranium contains the brain, an organ responsible for the control of many body functions. As such, to investigate the cause of disease or trauma resulting in death, simply looking at the brain by opening up the skull serves little purpose. For the functions of the brain are still largely hidden from us and the visual observation of this organ during a post-mortem tells us little about its role in the end of life.
When I write here that the functions of the brain are largely a mystery, I do so in giving this organ its reverential role of that which science cannot fully explain. In many diseases of the body having to do with the brain, such as Alzheimer's or Multiple Sclerosis, science has just scratched the surface in determining prevention and treatment of these disorders. Even in the areas of depression, athletic performance, motor skills, memory, creativity and the realm of the subconscious, again, the science that is known about these areas is barely expressed, as if the tip of the iceberg is all that we know.
But that does not limit or constrain us. For every day the medical and scientific communities are gaining ground, learning more about the brain, its functions and how treatments may hold off pathological maladies.
My sister, for instance, was recently diagnosed with Multiple Sclerosis. A vibrant and busy woman of 40 years, she is now the carrier of a disease that resides in her brain, at the end of nerve cells. Here, something has impaired the ability of the nerve cells to transmit stimuli and thus properly cause messages to travel throughout the body. But the knowledge of MS is greater today than just five years ago; new medicines and new strategies for diet, exercise and therapy have helped ease the etiology of MS. I do not know what Madeline is going through, obviously, because the workings and improper workings of her brain are known only to her through feelings, moods, emotions and thought, but I do know she is in good hands, as her clinicians and neurologists can help her deal with her own homeostasis. At least that is my fervent belief.
The human brain weighs about three pounds; the mature cow’s brain is just over one pound. In terms of relative weight, in a man weighing 180 pounds, the brain is 1.67 percent of his body weight. In a 1400 pound cow, however, the brain is 0.08 percent of her body weight. Thus, a cow's brain is about 20 times smaller than man's on a body weight equivalent basis.
I did not realize this relationship was so dramatic, that is, a twenty to one difference in relative brain weight. As animals have higher need for coordination, thought complexity and metabolic control, the brain inside becomes larger in order to meet these needs.
We may examine the brain as three different regions: the forebrain, midbrain and hindbrain. The forebrain (also called the cerebrum and cerebral cortex) is the portion just beneath the forehead and behind the eyes. It serves the role in sensory and motor function, but primarily is responsible for the processing of information. As I sit here writing, my cerebrum is going full blast, processing words and ideas and creativity. It is controlling the nerve impulses that move my fingers over the keyboard; it signals nerves to move my eye muscles as I follow the words displayed on the screen, and it signals my ears to tune in the sound of a radio. All the while it is processing many other subconscious bits of information.
The cerebral cortex is by weight the largest portion of the forebrain. It is divided into the left side and right side. The left side controls speech, language, and analysis - calculations. The right side serves as the creative site, where artistic ability and spatial perception. Memory is placed in the forebrain too, as both factual bits of information and learned skills are accumulated here. The factual bits of information can be drawn from the forebrain by consciously thinking about them. Learned skills, learned by repetition, are implanted in memory cells of the forebrain too. These skills, however, do not need conscious recall. Walking or tying our shoes are done rather automatically. That is why bad habits once learned and placed in the brain, are so hard to break.
Two parts of the brain, the thalamus and the hypothalamus are found in the forebrain. These two organs are responsible for integration of sensory perception as determined by nerves and external stimuli. The thalamus collects such stimuli and sends it to the cerebrum for further processing and interpretation. The hypothalamus, while weighing just a fraction of an ounce, is largely in control of homeostasis. It is an endocrine gland, secreting posterior pituitary hormone and the releasing hormones for the anterior pituitary gland. The hypothalamus controls the body's basil metabolic rate, or internal thermostat. As such, it determines or regulates hunger and eating. Another function is helping regulate sexual response and mating behaviors, the flight or fight response, and the overall sense of pleasure.
The pituitary gland (another endocrine gland) is part of the forebrain too. We know the role of this gland in releasing oxytocin upon the sensory stimuli of the milking procedure. A signal is heard and literally felt when the cow enters the milking parlor and she is handled by the milker. By touching her teats and udder, the cows' nerves interpret this message and electrically send a signal to the hypothalamus, which sends a message to the anterior pituitary gland to release oxytocin into the bloodstream. The 30 to 90 second period of release to arrival at the target tissue, the myoepithelial cells (smooth muscles) surrounding the alveoli of the secretory gland, causes milk to be squeezed out of the alveoli lumen into the ducts that eventually drain into the gland cistern, the teat cistern. The milking machine can now be put on.
The midbrain is the cap, or end point of the spinal cord that flows the spine in the back. The midbrain, then, obviously has something to do with sensory perception. It also serves as a projection center by sending coded sensory messages along certain neurons to the forebrain for processing. The animals' visual and hearing systems are routed to the midbrain.
The hindbrain is also the end point of the spinal cord (brain stem). It is this part of the brain that is intimately connected with the enervation of the spinal cord. The three major functions of the hindbrain are homeostasis, movement coordination and signal conduction. The lower part of the hindbrain, named the medulla oblongata, control several autonomic (involuntary) functions, including breathing rate by moving the diaphragm muscles up and down in response to blood oxygen content and effort or work demand, heart and blood vessel activity, in response to an animals state of activity, recovery, or rest. Swallowing and digestion are controlled in the hindbrain too.
The hindbrain portion known as the cerebellum is responsible for coordination of movement. The cerebellum is a remarkable part of the brain in that it controls how we sit, or walk, or run, or lay in bed as we sleep. The cerebellum is the end point of a whole series of nerves attached to the muscles and joints of the skeletal system. As an arm or leg is moved, the cerebellum facilitates the move by working with other nerves in the region to ease the movement of the whole body. For instance when we run, the left forward leg and right forward arm are in concert. Back in forth the arms and legs go each opposite of the other. Why? Well, the cerebellum is working to keep our body in balance. So we do not fall down. Thus the cerebellum makes us appear fluidlike, and we attain equilibrium. Another example is the eye to hand coordination. The typing action that I am doing this very moment is controlled by the cerebellum, my left hand working the left side of the keyboard, the right hand working the other side, and my eyes following the words on the screen.
The total volume of blood in a cow is 60 ml/Kg, or about ten gallons (85 pounds, 6 percent of body weight). At any one time, approximately 15 percent, or one and a half gallons (13 pounds) of blood are found in the brain itself. The brain has a tremendous vascular system, as evidenced by its obligations to serve many functions. The percentage removal rate of glucose from the blood into the brain tissue can be as high as 40 percent. Thus the brain is an organ with a high fuel demand. But we do expect it to do a great deal for us. Many of which are done without any conscious thought.
The brain is truly a remarkable organ.
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