Brain vs. Spinal Cord Anatomically, the Brain

Brain vs. Spinal Cord

Anatomically, the brain or central nervous system (CNS) is distinct from the spinal cord. The CNS is encased in the skull, while one end of the spinal cord is attached at the base of the brain and the other end extends down the spinal column to the lumbar region. A rough visual and functional analogy would be the cables from the keyboard, mouse, internet connection, and monitor (spinal column) connecting to the processor inside a computer (CNS).

The CNS and spinal cord are functionally distinct as well. The spinal cord collects the nerve fibers carrying peripheral sensory information and relays it to the CNS. These sensory nerve fibers are called afferent or ascending fibers. There are four main types of information transmitted through afferent fibers: mechanoreceptors (touch), proprioreceptors (muscle movement), thermoreceptors (temperature), and nocioceptors (pain). The information provided by these afferent fibers would be analogous to the information being communicated from the mouse, keyboard, and internet to the computer's processor.

The information coming in from all the different afferent fibers is kept segregated as it transitions through the spinal cord and enters the CNS. Very little processing occurs in the spinal cord; however, the cognitive experience of these inputs is unified, which suggests the processing of the sensory information is accomplished simultaneously or in parallel within the CNS. Once this information has entered the CNS, it is acted upon through comparison with past memories of similar sensory experiences. The relevant memories, and any associated expectations concerning reward and punishment, will influence how the information is processed, perceived, and responded to behaviorally. For example, if a person steps in a mud puddle by accident and they begin to feel the cold liquid seeping through their expensive shoes, the CNS will compare this to similar past experiences. If this comparison results in negative connotations, they may respond with a grimace, a verbal expletive, and a look downward at their foot. By comparison, a young child experiencing this for the first time might enjoy it and begin to stomp around in the mud puddle to recreate the experience repeatedly.

The product of CNS sensory information processing is behavior. This includes motor control, thinking, and emotional content. When motor control is involved, such as getting up out of a chair, the decision to stand up is packaged into information and transmitted by motor neurons into the periphery. The fibers that transmit this information are called efferent fibers. External signs of emotional behavior would be voicing an expletive or a scream of joy when stepping into a puddle. Thinking behavior could include the person with a mud covered expensive shoe beginning to contemplate whether the shoe can be saved or thrown away.