Cerebral Cortex Layers скачать в хорошем качестве

Cerebral Cortex Layers

The 6 layers of the cerebral cortex look different depending on which stain is used to observe them, and each stain provides us with different insights into their structure. The golgi stain stains a limited number of cells at random in their entirety. This is useful because otherwise, neurons are so densely packed that It would be difficult to observe their structure. The Nissl stain stains ribosomal RNA on the rough endoplasmic reticulum dark blue, and hence shows cell bodies and proximal dendrites. The Weigert stain shows myelinated fibers and hence axonal distribution. Let’s describe some of the cell types are found in these 6 cortical layers. Pyramidal cells are some of the largest neurons in the brain, and have long apical dendrites that extend towards the cortex surface, as well as a set of basal dendrites. Betz cells are the largest pyramidal cells. Stellate cells are neurons with a star-like shape formed by their dendrites. Rosehip neurons are inhibitory neurons with a bushy appearance. Now, let’s cover the layers. Layer one is closest to the outer surface, and layer 6 is just above the white matter. The layers above layer IV, the internal granular layer, are called the supragranular layers, while the layers below are called the infragranular layers. Layer I is called the molecular, or plexiform, layer and has few neurons. Neurons that are found there include rosehip neurons, some spiny stellate cells and cajal-retzius cells. Other cells include subpial granular layer cells and glial cells. This layer is mostly made up of transverse fibers - extensions of the dendrites of pyramidal neurons. Layer II is called the external granular layer, and it contains lots of stellate neurons, as well as small pyramidal neurons. Layer III is called the external pyramidal layer, and it is predominantly occupied by small and medium-sized pyramidal neurons. There are also other neurons with vertically-oriented axons. Layer IV is called the internal granular layer. It is occupied by stellate and pyramidal cells. Layer V is called the internal pyramidal layer, and it features scattered Betz cells, which again, are large pyramidal cells. Layer VI is called the multiform, or polymorphic layer. This is the layer where cells of multiple forms merge with the white matter. The neurons in this layer differ in the shape and distribution of their axons and dendrites, as well as their physiological properties. Some of the cell types include pyramidal neurons and stellate neurons, as well as bipolar, or fusiform neurons. Now that we’ve discussed the layers, let’s do a brief overview of the connections formed by each layer. Layer I gets substantial input from the thalamus, specifically from matrix, or M-type thalamus cells. Neurons in the first three layers are the principal targets of interhemispheric corticocortical afferent fibers. So they receive communications from cortical neurons in the other hemisphere. Layer III is also the principal source of corticocortical efferents, meaning that it signals to other cortical neurons. Layer IV receives inputs from core, or C-type, thalamus cells. The infragranular layers primarily connect the cortex with subcortical regions. Betz cells in layer V are important for voluntary motor control, and this layer is especially well developed in motor cortical areas. Betz cells are found in the primary motor cortex of the frontal lobe and their axons travel through the internal capsule, then through the brain stem and spinal cord, forming the corticospinal tract. They also project to the basal ganglia, reticular formation, cerebellum, and other areas. Finally, layer VI has reciprocal connections with the thalamus. Now that we’ve discussed the connections formed by each layer, it is easier to understand what we observe with the Weigert stain. Exner’s plexus is the name for the fibers in the molecular layer. The band of bechterew is the name for the myelinated fibers in the superficial portion of layer III. The outer and inner bands of Baillarger are myelinated fibers coursing through layers IV and V respectively. Finally, there are the deep tangential fibers and vertical fibers. Note that not every region of the cortex has the same number of layers. For example, the primary olfactory cortex has only 3 histological layers.