Structure of the Cortex

• 12-1 What four lobes make up the cerebral cortex, and what are the functions of the motor cortex, somatosensory cortex, and association areas?

If you opened a human skull, exposing the brain, you would see a wrinkled organ, shaped somewhat like the meat of an oversized walnut. Without these wrinkles, a flattened cerebral cortex would require triple the area—roughly that of a large pizza. The brain’s left and right hemispheres are filled mainly with axons connecting the cortex to the brain’s other regions. The cerebral cortex—that thin surface layer—contains some 20 to 23 billion of the brain’s nerve cells and 300 trillion synaptic connections (de Courten-Myers, 2005). Being human takes a lot of nerve.

Each hemisphere’s cortex is subdivided into four lobes, separated by prominent fissures, or folds. Starting at the front of your brain and moving over the top, there are the frontal lobes (behind your forehead), the parietal lobes (at the top and to the rear), and the occipital lobes (at the back of your head). Reversing direction and moving forward, just above your ears, you find the temporal lobes. Each of the four lobes carries out many functions, and many functions require the interplay of several lobes (Figure 12.1).

frontal lobes

the portion of the cerebral cortex lying just behind the forehead; involved in speaking and muscle movements and in making plans and judgments.

parietal [puh-RYE-uh-tuhl] lobes

the portion of the cerebral cortex lying at the top of the head and toward the rear; receives sensory input for touch and body position.

occipital [ahk-SIP-uh-tuhl] lobes

the portion of the cerebral cortex lying at the back of the head; includes areas that receive information from the visual fields.

temporal lobes

the portion of the cerebral cortex lying roughly above the ears; includes the auditory areas, each receiving information primarily from the opposite ear.

Figure 12.1 The cortex and its basic subdivisions

Flip It Video: Structure and Function of the Cortex

The diagram shows the brain from the side (as a person looks to the left). The frontal lobe is highlighted in blue and is located at the front of the brain. The parietal lobe is highlighted in green and located at the top, back of the brain. The temporal lobe is highlighted in purple and located below the two regions above and centered behind the ear. Lastly, the occipital lobe is highlighted in pink and located at the rear of the brain. The diagram shows a dorsoventral cross-section of the brain (through the middle, from top to bottom). This cross-section shows that the brain has left and right hemispheres.

FYI

The people who first dissected and labeled the brain used the language of scholars—Latin and Greek. The words they chose are actually graphic descriptions: For example, cortex means “bark,” cerebellum is “little brain,” and thalamus is “inner chamber.”