“Thirty-one pairs of spinal nerves enter and leave the spinal cord. Each of these nerves has a ‘top’ part and a ‘bottom’ part, called the dorsal root and the ventral root, respectively. Actually, the dorsal root would be at the top of your CNS if you were a quadruped (walked on all fours); think of the dorsal fin of a shark. The dorsal root brings sensory information into the spinal cord, whereas the ventral root takes out motor impulses from the spinal cord to the skeletal muscles. This statement of the functions of the dorsal and ventral roots is called the Bell-Magendie law, named for two 19th-century physiologists credited with its discovery. As sometimes happens, the men got into a huge battle over who deserved credit for the discovery. French physiologist François Magendie’s experimental work was more definitive than that of British physiologist Sir Charles Bell, but Bell’s name is usually listed first, so you see who won the battle.”

“The Bell-Megendie law summarizes two of the three main functions of the spinal cord. Specifically, the spinal cord receives sensory information from the body below the head by way of the dorsal roots of the spinal nerves. Also, it relays motor impulses from the brain to the skeletal muscles by way of the bentral roots. The third function of the spinal cord is that it is responsible for several spinal reflexes. Your Knee jerk, or patellar reflex, is an example of a spinal reflex. To elicit this reflex, your doctor taps your crossed leg just below your kneecap, and you respond reflexively by kicking out your lower leg.”