Porth's Essentials of Pathophysiology, 4e

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Organization and Control of Neural Function

C h a p t e r 3 4

Central sulcus

Parietal lobe

Frontal lobe

Parieto-occipital fissure

Occipital lobe

Transverse fissure

Lateral sulcus

Temporal lobe

A

Premotor (6) Supplementary motor (6,8)

Somatosensory (3, 1, 2)

Frontal eye field (part of 8)

Premotor (6) Motor (4)

Motor (4)

Somatosensory (3, 1, 2)

Vestibular

Somatosensory association (5, 7)

Somatosensory association (5, 7) Second

somatosensory

Visual (17)

(18) (19)

Visual (17)

(18) (19) Visual association

Visual association

Auditory association (42, 22)

Auditory (41)

B

C

FIGURE 34-16. Cerebral hemispheres. (A) Lateral view of the cerebral hemispheres showing the frontal, parietal, occipital, and temporal lobes. (B) Left lateral view of the motor and sensory areas of the cerebral cortex. (C) Areas of the motor and sensory cortex in a brain that has been sectioned in the median plane.

Irritation or stimulation can result in vivid hallucina- tions of long-past events. Occipital Lobe. The occipital lobe lies posterior to the temporal and parietal lobes. It contains the primary visual cortex (area 17), stimulation of which causes the experience of bright lights called phosphenes in the visual field. Just superior and inferior is the visual association cortex (areas 18 and 19), which is required for gnostic visual function, by which the meaningful- ness of visual experience, including experiences of color, motion, depth perception, pattern, form, and location in space, occurs. The neocortical areas of the parietal lobe, between the somatosensory and the visual cortices, have a func- tion in relating the texture, or “feel,” and location of an object with its visual image. Between the auditory and visual association areas, the parieto - occipital region is necessary for relating the meaningfulness of a sound and image to an object or person.

Limbic System. The medial aspect of the cerebrum is organized into concentric bands of cortex, the limbic system (from the Latin limbus , “border”), which sur- rounds the connection between the lateral and third ventricles. The innermost band just above and below the cut surface of the corpus callosum is folded out of sight but is a three-layered cortex ending as the hip- pocampus in the temporal lobe. Just outside the folded area is a band of transitional cortex, which includes the cingulate and the parahippocampal gyri (Fig. 34-17). The limbic lobe has reciprocal connections with the medial and the intralaminar nuclei of the thalamus, with the deep nuclei of the cerebrum, and with the hypothalamus. Overall, this region of the brain is involved in emotional experience and in the control of emotion-related behavior. Stimulation of specific areas in this system can lead to feelings of dread, high anxi- ety, or exquisite pleasure. It also can result in violent behaviors, including attack, defense, or explosive and emotional speech.