BRAIN

A surface of the telencephalon is divided in few lobi: frontal, occipital and temporal. The cortex is formed by the grey matter that is arranged in the same way (isocortex). Phylogenetically youngest region of the cortex is known as the neocortex that consists of six layers (see Fig. 1).  Those portions of the neocortex that contain well distinguishable layers are called the homotypic isocortex. Under the pia mater, there is a superficial molecular layer containing few nervous cells and many nerve fibres. The second layer is outer (external) granular layer that contains densely arranged small pyramidal cells (granular cells). The third is the pyramidal layer that contains the medium-sized pyramidal neurons. Then the inner granular layer follows with many neurons. The fifth layer contains the largest neurons (ganglionic layer or inner pyramidal layer). The last cortical layer contains neurons of different shapes (multiform layer) that faces the white matter. 

This basic arrangement in six layers differs depending specialization of the brain region. For example, motor areas such as precentral gyrus have well-developed both pyramidal layers while inner granular layer is reduced. On the contrary, in sensory areas (postcentral gyrus postcentralis or visual cortex) granular layers are thick  while pyramidal layers are thin. Orientation in a slide of the brain incl. identification of pyramidal neurons is explained in practical classes "Nervous system".

Fig. 1 A. Three-dimensional reconstruction of the neocortex. A cortical surface is covered by the connective tissue pia mater. The left area shows cytoarchitectonics of the neocortex after cresyl violet staining. Dendroarchitectonics (right area) demonstrates neuron impregnation according to Golgi. Individual layers of the neocortex are labelled by roman numbers (left). Krstic, R. V. Human microscopic anatomy.		Fig. 1 B. Laminar arrangement of the neocortex. Immunoperoxidase detection of neurofilaments, intermediate filament of nervous cells, identifies perikarya of nervous cells, cytoplasmic processes as well as laminar arrangement of the neocortex. Microfotograph: Jaroslav Mokrý

NEURONS OF THE NEOCORTEX

Various types of neurons are found in different layers of the isocortex; they all are multipolar neurons. Characteristic neurons and their distribution are depicted in Fig. 2. Cajal horizontal cells (HC) are found in the molecular layer; they are association and intercalated elements with processes oriented horizontally. Outer granular layer (II) contains stellate cells (SC) and small pyramidal cells (PC). Outer pyramidal layer (III) contains basket cells (BC), fusiform cells (FC), stellate Martinotti cells (MC) and middle sized pyramidal cells (PC). The inner granular layer (IV) contains stellate cells that are densely packed while inner pyramidal layer (V) contains few large pyramidal cells (PyC). The largest pyramidal cells are known as Betz cells (almost 100 μm). The most characteristic cells of the multiform layer (VI) are stellate Martinotti cells (MC); this layer also contains small polymorph and fusiform cells.

Efferent (Eff) nerve fibres leaving the cortex are derived from the pyramidal neurons. Afferent (Aff) fibres modulate activity of pyramidal neurons via synapses on dendrites or via interneurons inside of the cortical columns.