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Cerebral Cortex

Explanations > Brains > Parts > Cerebral Cortex

Description | Areas | Internal structure | See also

Description

The cerebral cortex surrounds the cerebral hemispheres much like the rippled bark of a tree ('cortex' actually means 'bark').

It has fissures (large grooves) and sulci (small grooves, singular: sulcus) and gyri (bulges, singluar gyrus). This folding triples the surface area to about 2350 cm² (about 2.5 square feet), on which the mat of neurons and glia lies. The large concentration of myelin here has led it to be called white matter. Grey matter is made up of of neurons cell bodies, glial cells and blood vessels.

Areas

Hemispheres

There are two almost separate hemispheres to the cortex which are connected by the corpus callosum, one of which (usually left) is dominant.

Lobes

The frontal lobe is the largest lobe, being around the front half of the cortex. It is involved in voluntary motor activities, memory, personality, planning and judgement. It contains Broca's area in the dominant hemisphere, which is concerned with speech.

The parietal lobe runs across the top rear of the cortex. it is involved in perception of peripheral sensation and spatial orientation. It is separated from the frontal lobe by the central sulcus that runs across the top of the head.

The occipital lobe is at the lower rear of the cortex. It is involved with vision. It is largely separated from the parietal lobe by by the lateral fissure.

The temporal lobes are at the lower sides of the cortex. It includes areas involved in speech and includes Wernicke's area in the dominant hemisphere.

Sensory areas

The primary visual cortex is at the rear, on the inner surface of the occipital lobe, on the calcarine fissure.

The primary auditory cortex is on the lower surface of the lateral fissure, at the top of the temporal lobe.

The primary somatosensory cortex is a vertical strip just caudal (rear) of the central sulcus, in the parietal lobe. Sensory information from the body goes to the contralateral hemisphere, except for smell and taste.

The secondary somatosensory cortex is a small area near the lateral fissure that is involved in general sensation.

Movement

The primary motor cortex is a strip just in front of the primary somatosensory cortex, in the frontal lobe.  Perhaps unsurprisingly, corresponding sense and motor areas are next to one another (feet, fingers, face, etc.).

Just forward (rostral) of the primary motor cortex is the pre-motor cortex (or motor association cortex), and controls the primary motor cortex. This does the thinking about moving (the primary motor cortex does the actual moving).

Other areas

Forward of the pre-motor cortex in the frontal lobes is the pre-frontal cortex (PFC), and is involved in planning, strategy and general thinking about the future, particularly in the orbito-frontal cortex (OFC), which sits just behind the eyes.

The insula is an internal area only visible by section. It is thought to be involved in emotion and autonomic responses.

Association areas are not involved in sensing or moving. and are mainly found in the frontal, parietal and temporal lobes. They are thought to be responsible for reasoning, abstract thinking, spoken and written language, judgement, planning and socialization.

The overall main cortex, including all the lobes is called the neocortex, due to its evolutionary recency. Underneath the neocortex is the limbic cortex (or cingulate cortex) which is involved in emotion and memory. Cingulum is Latin for 'belt'.

Brodmann's map is a numbered topographic map of the cortex with 47 parts. This is often used for referencing smaller areas.

Internal structure

Layers

The cortex has six different layers the deeper you go, called I to VI. The thickness of each layer varies with the cortex area. Sensory areas are granular, with well-developed layers II and IV but small layers III and V. The reverse is of true in the motor cortex, with agranular texture, developed III and V and thinner II and IV.

Columns

Cutting through the cortex reveals columns of neurons, where each column has a similar function.

See also

Left and right brain