Manatee Brain

Cerebral Cortex

Drawing of manatee brain and its postulated sensory and motor areas.

Vis = visual cortex; Aud = auditory cortex; SI = main somatosensory cortex; SII = second somatosensory cortex; MI = main motor cortex.

The drawing of the manatee brain shown above indicates the sensory and motor areas of cerebral cortex as suggested by the external morphology as well as by the microscopic appearance of the manatee cortex. This picture indicates the well accepted notion that cerebral cortex is the target region where the sensory environment is mapped in an orderly topographic fashion.

The cerebral cortex consists of collections of cellular regions arranged as a sheet which covers the entire forebrain in mammals. It is generally subdivided into two general zones: the neocortex and the paleocortex, which merge into transitional cortical zones together where they adjoin.

Neocortex
The neocortex is a seven-layered sheet of neurons which may be quite elaborately convoluted into an extensive array of gyri which may contain a large number of independently developed cortical areas. These cortical areas are richly interconnected with each other and with the thalamus, basal forebrain and even more distant brainstem targets. These connections are usually very specific and often reciprocal. Neocortex lies on the dorsal, dorsomedial, dorsolateral, frontal, caudal and ventrolateral portions of each hemisphere. The cortical regions in the two hemispheres are connected to each other via a large fiber bundle known as the corpus callosum. The major sensory inputs from the environment or the body itself project to cerebral neocortex in ways that represent the real features of the external world.

Paleocortex
The paleocortex consists of cortical regions on the midline around the corpus callosum, ventrally beneath the basal ganglia and amygdala, rostrally just behind the anterior olfactory nuclei and caudally adjacent to the hippocampus. The general subdivisions of the paleocortex are the entorhinal, pyriform and limbic regions.

These regions of cerebral cortex can be seen from the coronal series of sections displayed in the brain atlas and in the array of sections cut in coronal, horizontal and sagittal planes which are displayed below. These sections were all stained to show fiber stains, and cerebral cortex is revealed as the paler grey sheet overlying the forebrain.

The cell bodies themselves are revealed below as purple dots in a coronal section through the center of the manatee's brain stained with thionin.

Cerebral cortex viewed at greater magnifications are displayed below. The strips of cortex shown here are taken from several different cortical areas from front to back of the brain: