Welcome back! In this final lesson of our module on the normal horse, we'll look at the horse's nervous system including it's remarkable vision. When we are through you'll be able to describe normal responses of the nervous system and list the ways in which we, as caretakers, can respond safely to cues from the nervous system. The horses fine tuned nervous system is a highly complex apparatus consisting of the communicating network of the brain, the spinal cord and nerves. This system governs conscious and unconscious actions of the body including coordination, digestion, blood vessel tone, glandular secretions, and vital signs. The nervous system is very susceptible to the effects of inflammation. And compression of the nervous system or compartmentalization in any way can create stumbling and paralysis. While we can't cover this system in depth, it is important to understand that there are physical consequences to unseen nervous system responses to stimuli. For example, when a horse experiences a perceived threat to his life or well-being, he reacts from a place of fear. This may initiate digestive upset, sweating or fleeing in panic. This is not desirable, but it is a normal nervous system response of flight. For your horse's own well-being and for your safety it is important to understand how a horse proceeds and reacts to its surroundings. Understanding a horse's normal behavior will give you clues when his vision or nervous system are not working properly. For example, an anxious horse will not eat or drink, whereas a normal horse lives to eat. As we have discussed It is our responsibility as horse caretakers who have domesticated horses, to be sure to provide them with a safe environment that is compatible with their anatomy and functions so they can exhibit normal behavior. The horses' vision and nervous system highlight the critical intersection of anatomy, function, and behavior. Let's start with vision, horse's eyes are located at the outer edge of the upper facial bones and protrude beyond the eyelids more than a human eye. This placement of the eyes also creates some blind spots for the horse directly in front of his head and directly behind his rump. A normal horse has amazing peripheral vision that allows it to see over 300 degrees of its horizon. This adaptation occurred such that the horse could respond to any predators that might be approaching it while it's head is down grazing. Knowing how the horse's vision works and where it's blind spots are, there are precautions we can take. For instance, the best way to approach a horse is towards the left shoulder at a 45-degree angle. And as we approach, we should be talking, so that the horse can hear us and see us coming. Horses are trained from a young age to be handled on their left side. It is never a good idea to approach a horse from the directly behind or directly in front as this is their blind spot. If you approach them in the blind spot, you you may startle them and they may spook away from you or kick at you. The most important point is that you do not approach a horse from directly behind it, because you may be the target of their powerful kick. Here's an interesting tip. When leading a horse from sunny outdoors into a barn, be patient. The horse may hesitate because it takes some times for the large pupils to dilate for him to be able to see what is in front of him. This location of wideset large eyes also means the eye balls are very vulnerable to injury. Eye care and concerns are a common reason for a veterinary examination. And it is not uncommon for horses to scratch their large exposed eye in their surroundings. In a normal horse at rest the cornea of the eye should be clear and glistening and the area around the eye should be dry. The eyelids are usually wide open. If the horse is relaxed and drowsy, the eyelids may drupe slightly. But upon announcing your presence, the lids will open. The area above the eye socket will have a slightly sunken appearance. As horses age, this sunken appearance will increase as the lose periorbital fat. A common injury to the eye is an abrasion to the cornea, which presents as a horse that is tearing, squinting, and clamping its eye closed. Lacerations to the eyelid are also common. These both require the care of a veterinarian. Lid laceration repair is extremely important to maintain the normal anatomy of the lid, such that it can easily roll over the eye and perform the functions of both protection of the cornea and lubrication of the eye itself. The horse's nervous system is triggered by stress. Such as being separated from a buddy or the herd. And this can cause an instant change in the horse's behavior, as the horse's blood pressure rises and the stress hormones are released. You may not even notice the buddy is gone, but your horse's nervous system has already begun to fire and the horse will react quickly. We'll describe this behavior and the reasons for it in greater detail in a later lesson. This separation anxiety can lead to panic and the horse may exhibit defensive behaviors in an effort to save itself. This may include running away, kicking and biting. The horse may temporarily forget that you are the kind human who feeds him everyday. If you are in the path of escape you may be knocked over or injured, thus it is important to realize when the horse is becoming excited and to know and plan a way to get away if the horse does both. When a horse is panicked or in significant fear mode, their nervous system causes the release of a large amount of adrenaline similar to what is released in the human body. And that adrenaline may create such a strong reaction that the horse fails to take care of his own safety and may run through a fence or try to jump out of a stall if he feels that he is safer away from whatever is causing the fear response. The horse may be so concerned with his situation that he won't eat, or drink, or care for himself. If you are witnessing this scenario, stay calm and pause. Pay attention and look at their ears. Ears that are pinned back are a sign of a defensive mood. Flared nostrils and increased respiratory rate are another sign of the nervous system being on high alert in this circumstance. It is especially important to avoid cornering a horse if you are seeing signs of panic. Try to assess the surroundings to determine what is causing the disturbance and remedy the situation before the behavior turns into a physical problem, such as colic or a self-inflicted injury. Just as in humans, the horse's brain sends signal out to the rest of the body through the spinal cord and peripheral nerves. When a horse is excited it sends signals to its legs to move via muscular contraction. It also sends signal to its heart to increase rate and increase oxygen delivery. The peripheral nerves in the feet tell the brain where the horse's feet are and thus give it coordination. So it's a highly wired technical system that relies on feedback. And when it is healthy, the horse is incredibly coordinated and fast. When the nervous system is unhealthy, when those connections are not being made adequately either because of some form of inflammation or compression, then the horse's responses will not match the signalling from the brain. In many cases, horses that have a neurologic deficit, will manifest this with stumbling, in-coordination, a weak gait, or inability to navigate their surroundings or control basic facial function like eyelid tone, nasal tone, or ear tone. If you notice, when you look at your horse's face, that there's an asymmetry to the face, or that your horse is stumbling or drugging its toes, or that you have excessive hoof wear in one of the hooves. These can be signs that the horse is suffering from some form of neurologic impairment. When you see a horse that is panicking, some questions that you might ask are, Is his friend missing? Did the other horses get fed but not him? Is there a strange animal or smell nearby or a strange object or shape that the horse is not familiar with, such as an umbrella, a sheet blowing in the wind or some new lawn furniture? Has a strange person been near the horse? As a safety reminder, knowing how the vision and nervous system of the horse impact their behavior reminds us to be especially careful when approaching and leading a horse in normal and unusual circumstances. That concludes our discussion of the equine nervous system. We have covered a lot in this module and next week we'll turn our attention to the topics of hydration and nutrition, two of the most important aspect of the equine welfare. We'll look at nutritional requirements as well as types of feed and how the horse processes food. See you there.
