Medical brain notes 24

  Structure of the Cerebral Cortex          Because of the presence of a large number of sulci, only about one third of the total area of cerebral cortex is seen on the surface of the brain. The total area of the cerebral cortex has been estimated to be about 2000 cm 2 .         Like other masses of grey matter the cerebral cortex contains the cell bodies of an innumerable number of neurons along with their processes, neuroglia and blood vessels. The neurons are of various sizes and shapes. They establish extremely intricate connections with each other and with axons reaching the cortex from other masses of grey matter. In spite of a very large volume of work done on the subject, it is not yet possible to explain the neuronal patterns within the cerebral cortex in terms of function. In any case such considerations are beyond the scope of this book. Neurons in the Cerebral Cortex     ...

  Neurons in the Cerebral Cortex          Cortical neurons vary in size, in the shape of their cell bodies, and in the lengths, branching patterns and orientation of their processes. Some of these are described below (Fig. 15.1). 1.   The most abundant type of cortical neurons are the  pyramidal cells . (In contrast all other neurons in the cortex are referred to as non-pyramidal neurons). About two thirds of all cortical neurons are pyramidal. Their cell bodies are triangular, with the apex generally directed towards the surface of the cortex. A large dendrite arises from the apex. Other dendrites arise from basal angles. The axon arises from the base of the pyramid. The processes of pyramidal cells extend vertically through the entire thickness of cortex and establish numerous synapses. The axon of a pyramidal cell may terminate in one of the following ways. a.           ...

  Laminae of Cerebral Cortex          On the basis of light microscopic preparations stained by methods in which the cell bodies are displayed (e.g., Nissl method) and those where myelinated fibres are stained (e.g., Weigert method) the cerebral cortex is described as having six layers or laminae (Fig. 15.2). From the superficial surface downwards these laminae are as follows.          1 . Plexiform or molecular layer.  2 . External granular layer.  3 . Pyramidal cell layer.  4 . Internal granularlayer.  5 . Ganglionic layer  6 . Multiform layer.          The plexiform layer is made up predominantly of fibres although a few cells are present. All the remaining layers contain both stellate and pyramidal neurons as well as other types of neurons. The external and internal granular layers are made up predominantly of stellate (granular) cells...

  Further Consideration of Functional Areas of the Cerebral Cortex          The classical concept of the functional areas of the cerebral cortex has been presented on before. Recent work has shown that these concepts need modification in some areas and elaboration in others.          According to classical teaching the cerebral cortex has been divided into the following: a)             Motor areas a.                When these areas are stimulated electrically movements occur in various parts of the body. Anatomically, these areas give origin to projection fibres that form the corticospinal and corticonuclear tracts. b)             Sensory areas a.              ...