SENSORY

Day 2Every single event in a basketball game has two effects: it usually causes one team to be

please, and one team to be discouraged. You can tell what is happening on the floor by listening to the sound. Because a basket made by one team is generally going to cause one set of fans to cheer, and the other set of fans to not cheer. If you walk in and you hear a greater intensity of sound coming from the right, you can tell Rutgers scored a basket. The same thing here, the brain is listening, saying which LSO is stronger. That is all I want to say about auditory function, and I want to talk a little bit about somatic function, then we can talk about muscular-skeletal.

Somatic function is probably something at some point in your elementary school education referred to your senses, and they included a sense of touch. There is something called touch, but it is not one of your senses, it is one of your somatic senses. Somatic senses are receptors that are distributed on the surface of the body and in the tissues of the body, and there is a whole variety of different types of somatic receptors. Some of them are mechanical and can respond to mechanical sensations, like a vibration or pressure. Mechanical receptors can activate, in some circumstances, touch receptors. The major touch receptors are phasynian corpusuls and meisners corpusuls. Then you also have what are called hair follicle receptors. These are all mechanical. If this is the surface of your skin, and this is epidermis, dermis, and this is hypodermis. This is the outer surface of your skin, and this is deep, and these are your muscles down here. A lot of our skin is what is called glabulus, which means it has hair, so we have tiny little hairs sticking out of the surface of your skin, fine fibers everywhere, and they all have free nerve endings wrapping around them. If you touch any of the fine hairs on the surface of your body, not touching your skin, just the hair, you will feel them, because they actually activate a sensory receptor that is wrapped around the hair follicle. You bend the hair itself and it activates the free nerve ending and that responds to very light touch.

There are place where the dermal part of your skin folds up into the epidermis, and in here are specialized receptors called the meisners corpusls, so the meisners are near the top of the skin for detecting light touch. Deep down, in the hypodermis, are very big receptors that respond to deep pressure. These are all mechanical sensations, detected by these various types of receptors.

Besides having these receptors that allow us to detect touch, we also have mechanical receptors that are integrated into our muscular-skeletal system. Say we have a muscle spanning two bones. One thing about the skeletal system is its stability is primarily maintained by having tension across the joint. The actual structure of the joint does not provide much stability at all. If you look at the top of your tibia, and looked at your femur, they are just sitting right on top of each other, the bone ending is not modified to create some kind of structural connection, they are just standing right on top of each other. The actual integrity of the joint, besides having things like ligaments and capsules, is maintained because of all the muscle tension that spans across the joint. The stability of the joint is determined by tension across the joint. We need to always have the right amount of tension in our muscles to maintain the stability of our joints. Integrated into our muscles are specialized modified muscle cells called muscle spindle fibers. Inside the muscle spindle fiber, there is a sensory neuron wound up on the inside of this, and if we need tension to maintain the integrity of a joint, we need a receptor that can tell how much tension there is in a joint. In this case, when the muscle spindle fibers stretches, indicating there is not

enough tension in the muscle, it sends a signal to the motor neurons inside the spinal cord and those motor neurons go out and they activate the muscle. It is a simply reflex. In addition to maintaining tension in the muscle, we also have to protect the muscle from applying too much force, primarily too much force on the connective tissues that attach that muscle to the bones. In our tendons are specialized receptors called the golgi tendon organs. When the golgi tendon organ is activated, that means there is too much force being applied to the muscle. Again, you are going to send signaling to the spinal cord, and the spinal cord is going to do two things, it will go back and inhibit the muscle that is applying the force, and it will cause the antagonist muscle, the muscle that opposes the given muscle, to be activated. If you are trying to make that last curl, and you are applying maximum force, sometimes you will drop the weight, because at that point in time, when you are trying to apply too much force, the golgi tendon organ will be activated and will inhibit the flexor, activate the extensor, and the limb will go back to its normal position, taking the force off that tendon so that the tendon is not damaged.

In addition to these types of receptors, we also have specialized receptors that can detect stimuli that are of sufficient magnitude that cause tissue damage. These are called nosiceptors. Nosier means pain. Nosiceptors detect stimuli that are of sufficient magnitude to cause injury, tissue damage. That could be mechanical force, that could be temperature, that could be chemical. The only defining characteristic is that that stimulus can cause tissue damage, and as a consequence the nosiceptors are activated and generally stop you from engaging in that behavior. One interesting thing about pain is that if your nosiceptors do not respond quickly enough to stop you from being exposed to the stimulus that causes pain, you will not feel pain for some extended period of time. Think about pain in a biological sense. Some large predatory animal is chomping on your ass, is it a good idea to feel pain while this assault on your ass is occurring? You must be running, screaming, and possibly defacating. If one escapes, then one can feel pain, one can say woe is me my ass hurts. But until that point in time, you shouldn’t feel pain at all. Pain is to interrupt behavior that could cause damage, but if damage is already caused, you do not feel pain right away because you also need to escape the source of the pain.

In addition to nosireceptors you also have thermoreceptors, and there are two basic types. You have cold receptors and hot receptors. These have overlapping ranges of function. The hot extend into a range of temperatures that also activate cold receptors. There are temperatures that we use both receptors to detect simultaneously, they are perceived as lukewarm. If you get outside of these ranges, and it is above the range where you detect hot into the range where the temperature could actually cause tissue damage, that is not perceived as hot, that is perceived as pain. Similarly, if it is too cold, you do not feel cold anymore, you feel pain.

We all perceive pain differently because pain has a cognitive component to it also. You have the ability to modulate pain in the spinal cord, the brain stem, and in the cortex itself. The actual norciceptor could be activated, and you could actually not perceive it because it is one of the few somatic sensations that can be modified cognitively. We all have difference tolerances for pain because we all process it differently at a cortical level, and we all have differing capacities to modulate it along the circuit.

You can activate almost any receptor mechanically, even a rod can be activated mechanically. If you hit a boxer hard enough in the head, they say they see stars, that is the mechanical force activating the rod, and they actually do see flashes of light because you activated their rods mechanically, so almost anything can be activated mechanically.