Cerebral cortex

Cerebral cortex

1. CEREBRAL CORTEX Aditya Johan .R, M.Fis

2. The cerebral cortex is the outer covering of gray matter over the hemispheres This is typically 2- 3 mm thick, covering the gyri and sulci

3. Most of the cerebral cortex is neocortex. There are phylogenetically older areas of cortex termed the allocortex These more primitive areas are located in the medial temporal lobes and are involved with olfaction and survival functions such as visceral and emotional reactions

4. In turn, the allocortex has two components: the paleocortex and archicortex . The paleocortex includes the piriform lobe, specialized for olfaction, and the entorhinal cortex. The archicortex consists of the hippocampus, which is a three-layered cortex dealing with encoding declarative memory and spatial functions

5. The neocortex represents the great majority of the cerebral cortex. It has six layers and contains between 10 and 14 billion neurons Layer I is the molecular layer, which contains very few neurons layer II the external granular layer layer III the external pyramidal layer layer IV the internal granular layer layer V the internal pyramidal layer layer VI the multiform, or fusiform layer

6. Functionally, the layers of the cerebral cortex can be divided into three parts The supragranular layers consist of layers I to III. The supragranular layers are the primary origin and termination of intracortical connections, which are either associational (i.e., with other areas of the same hemisphere), or commissural (i.e., connections to the opposite hemisphere, primarily through the corpus callosum)

7. The internal granular layer, layer IV, receives thalamocortical connections, especially from the specific thalamic nuclei. This is most prominent in the primary sensory cortices The infragranular layers, layers V and VI, primarily connect the cerebral cortex with subcortical regions. These layers are most developed in motor cortical areas. The motor areas have extremely small or non-existent granular layers and are often called "agranular cortex". Layer V gives rise to all of the principal cortical efferent projections to basal ganglia, brain stem and spinal cord. Layer VI, the multiform or fusiform layer, projects primarily to the thalamus

8. There are several identifiable cell types in the cerebral cortex. The pyramidal cells are the main cell type within layers III and V. These cells can be extremely large in layer V of the motor cortex, giving rise to most corticobulbar and corticospinal fibers The largest of these neurons are called "Betz cells"

9. BROADMAN AREA

10. Prefrontal Cortex The prefrontal cortex is extremely well developed in humans There are two main portions of this cortex The dorsolateral prefrontal cortex (DLPC; mostly areas 9 and 10) and the orbitomedial prefrontal cortex (especially areas 11 and 12) The DLPC is primarily involved in executive functions. These include working memory, judgment, planning, sequencing of activity, abstract reasoning and dividing attention. The orbitomedial prefrontal cortex is involved in impulse control, personality, reactivity to the surroundings and mood

11. Somatosensory Cortex Primary somatosensory cortex (areas 3,1,2) is located in the post central gyrus Neurons within each cortical site (particularly layer IV) are arranged in columns representing specific body regions The secondary somatosensory cortex (area 40) is in the lower parietal lobe This responds to sensory stimuli bilaterally, although with much less precision than the primary cortex The somatosensory association cortex (areas 5 and 7) is directly posterior to the sensory cortex in the superior parietal lobes This receives synthesized connections from the primary and secondary sensory cortices.

12. Visual cortex The primary visual cortex (area 17) also called the striate cortex Lesions of the occipital lobe would cause cortical blindness and difficulty tracking objects the visual association areas (areas 18 and 19), where signals are interpreted and form is recognized Selective lesions of these association areas will produce an inability to recognize objects even when they may be seen

13. Auditory Cortex The primary auditory cortices (area 41) are on the transverse temporal gyri, extending into the lateral fissures These gyri are situated on the upper part of the superior temporal gyri Unilateral cortical lesions do not effect hearing because of completely bilateral sound representation There are auditory association areas surrounding the primary auditory cortex (area 42). These areas are involved in the interpretation of sound. In the dominant hemisphere the cortex surrounding the auditory cortex (area 22) is required for understanding language (Wernicke's area)

14. Lesions of the opercular and triangular portions of the inferior frontal gyrus (areas 44 and 45), called Broca's area in the dominant hemisphere, produce expressive or motor aphasia. These patients have difficulty in generating spoken or written language

15. Motor Cortex The primary motor cortex (area 4) is in the precentral gyrus. This is the origin of most of the corticospinal tract and a large number of cortical bulbar fibers This also has projections to the thalamus and basal ganglion Lesions produce spastic contralateral weakness, which is most prominent in the distal extremities The premotor cortex (area 6) is immediately anterior to the motor cortex and has many of the same connections as the motor cortex. This region receives input from the sensory association cortex as well as feedback from the basal ganglia via the VA and VL of the thalamus

16. Association and Commissural Fibers

17. Association and Commissural Fibers Regions of the cerebral cortex are tied together by bundles of white matter fibers There are association bundles that connect one part of the cortex to another These association fibers typically arise from layer III and terminate in layers I and II Commissural fibers connect one hemisphere with the other. The largest commissural connection is the corpus callosum Damage to this pathway can produce a "split brain "in some individuals, where an individual may literally appear to have two minds

18. HOMUNCULUS MOTOR AND SENSORY