In this video I'll be talking about reflexes. It's not just a single by Duran Duran, but it's a neural pathway that controls a reflex. This is one that you're probably all familiar with. This is a something that you often get tested, when you go to the doctor. A reflex arc is a neural pathway that controls a reflex. Most sensory neurons have a synapse within the spinal cord, allowing for reflexes to take place without the involvement of the brain, which speeds up the process. This pathway can be described as a reflex arc, which is made up of five components. The first one is a receptor, a stretch receptor, which is stimulated by stretching of the muscle tendon and that stimulates that muscle spindle. The next part is the afferent pathway which consists of this pseudo-unipolar sensory neuron that brings that information into the gray matter of the spinal cord. Here is the synapse which is the integration between the sensory line and the motor line, and then illustrated in black is the multipolar neuron, a motor neuron that causes a reflex muscle contraction when it's activated at that integration site, the synapse. So we have a sensor and an afferent pathway, carrying information into the spinal cord where the synapse is, and then an efferent pathway causing change in an effector, in this case producing a reflex muscle contraction. So here it's the patellar reflex. We have a muscle spindle which is sensitive to stretch, and it's there in one of the quadriceps muscles, and it detects movement of the patellar ligament and of the patella, and that sensory neuron sends a message to the spinal cord where the synapse is, and the motor neuron causes contractions of that muscle of the quadriceps group. So that sensory neuron is afferent, pseudo-unipolar, it has its cell body in the dorsal root ganglion, so that's in the peripheral nervous system. And then the motor neuron is efferent and multipolar, with its cell body in the central nervous system, and in this particular reflex, it's monosynaptic, meaning only one synapse. So there's no interneuron that's present here. I'll talk a little bit more about this spinal reflex. The stretch reflex, the best known spinal reflex, which is the patellar reflex. This is a reflex of proprioception, which helps to maintain posture and to maintain balance. It allows you to keep your balance without any real effort or conscious thought. The stretch reflex is the contraction of a muscle that occurs in response to its stretch. It's not controlled by the higher functioning center the brain, and it's a monosynaptic response that's transmitted to the spinal cord. Our body needs to be able to respond without our cortical input from the cortex of the brain. So this stretch reflex is an example of a circuit that skips the brain and follows the simple neural loop connecting the muscle to the spinal cord and back. This enables a rapid response and this particular response is crucial, for example if the muscle is working against a load and shortening during contraction, and a subsequent extra load is added, then the muscle is able to recognize the stretch immediately and can compensate with a stronger contraction. Posture is also a very important consequence of the stretch reflex. It's relevant, as leaning to one side will result in the muscle spindles of the leg and the spinal muscles of the opposite side being stretched, and this is quickly countered by the stretch reflex, which will keep us upright. Another example is if we encounter a sudden change in the ground that we're standing or walking on, if we have to prevent ourselves from falling over due to the force of gravity, we need really rapid correction mediated by the stretch reflex. The motor neurons travel from the spinal cord itself and return to the muscle in a loop of neural circuitry. When we make conscious movements, we send impulses from our brains down our spinal cords and then back to the brain for cerebral processing.