The video discusses the effect of endocannabinoids on what is known as the descending pain modulation system, which is just a means by which the ascending pain signals in the spinal cord can be reduced (modulated), resulting in a reduction of pain. Of course modulation could also act in the reverse fashion to increase pain. This second figure, also from rnceus.com, illustrates the system from where the pain nerve (primary afferent pain neurons) enters the spinal cord to where it reaches the thalamus area of the brain and back to where the descending pathway interacts with the corresponding inhibitory interneuron. The enlarged section shows the interaction of the neurons at this junction. This is the area which the video animates in the second part, starting at 0:50. The enlarged section also lists some of the substances known to have an inhibitory effect on the transmission of pain but fails to include the cannabinoids, probably due to the more recent discovery of cannabinoid receptors.