As we mentioned, we have our central nervous system as well as our peripheral nervous system. The central nervous system, as we just went through, we have brain and in the brain, we have telencephalon. We have diencephalon, cerebellum, brain stems. We just study the full details of the brain stems. This lecture it contains midbrain, pons, and medulla. Also, we have in the CNS system, we have the spinal cord. Peripheral system, we have several nerves. We have cranial nerves, 12 pairs and we have 31 pairs of spinal nerves. Also, we have some nerves can sense or sent the information of our visceral system, so we have visceral sensory nerves and we have our visceral motor nerves. And then the biggest system of these two system is the symphatic parts and the parasymphathic part. In our spinal chord system, there are two very important concepts. One is the reflex and then the other is the reflex arc. The reflex is a reaction of the organism by the nervous system in response to a stimulus. There is a stimulation applied to our muscle or our body and then our nervous system will make a response according to the stimulation. Reflex arc, there five basic component in our reflex arc. One is the receptor and the other is the sensory neuron. The information from the sensory neuron will get into our CNS system and from the CNS system, the CNS system will process the information, the sensory information, will make a decision and then the decision or response will send it back to the motor neuron. And then the motor neuron will control the effector, sometimes it's our muscle. For example, this reflex here, if we hit our muscle or tendon here and then this [INAUDIBLE] or this information will ascend into the spinal cord, the sensory area by the sensory neuron. And then the sensory neuron will make one relay here at the spinal cord. And then the spinal cord will know this information and then make a decision, what kind of things the muscle will do in response to this stimulation. The information will send out through this blue line through this red line here by the motor neuron to the effector is the muscle in the leg, and then will make the leg either contraction or other response.