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INTRODUCTION

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The brain is a highly complex and integrated organ that integrates and processes sensory and motor input. The brain can be categorized into the forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon). The forebrain is further broken into the cerebral hemispheres, thalamus, and basal nuclei.

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The cerebral hemispheres have three layers which include the cerebral cortex, subcortical white matter (largely the internal capsule), and the basal ganglia.

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The cerebral cortex is made up of gray matter and is a covering over the cerebral hemispheres. It is known as the center for higher intellectual processes. Sulci, or fissures, separate the cortex into the frontal, parietal, temporal, and occipital lobes. To increase the amount of surface area, the cortex has many gyri, or folds. There are many different types of nerve cells as well as layers of the cerebral cortex. Functionally, the cerebral cortex is divided into 47 different Brodmann areas.

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MOTOR

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The areas involved in motor movement include the primary motor cortex (Brodmann area 4), which is somatotopically organized as the motor homunculus. This area occupies the precentral gyrus. The area involved for each body part is proportional to the amount of complexity involved in movement, with the face, eyes, lips, mouth, and nose taking up at least half of the area. This area is responsible for voluntary movement on the opposite side of the body. Secondary areas involved in motor movement include the premotor cortex, supplementary motor area, frontal eye field, and posterior parietal motor area. All of these areas help prime and mediate complex movements, which are eventually relayed and carried out by the primary motor complex.

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SENSORY

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The primary somatosensory cortex (Brodmann areas 3, 1, and 2) is responsible for receiving sensory information from the opposite side of the body. It is located in the postcentral gyrus and, like the primary motor cortex, is somatotopically arranged as a homunculus.

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Vision input from the lateral geniculate nucleus goes to the primary visual cortex, which helps in processing color, motion, and three-dimensional vision. It is located on the lateral surface of the occipital lobe by the calcarine fissure. The primary visual cortex then sends signals to the visual association cortex, which helps in identifying objects, determining location, and determining visual significance based on prior experiences.

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The primary auditory cortex receives information from both ears from the medial geniculate body of the thalamus. It helps detect pattern alteration and location of sound. It also receives information from the lateral geniculate nucleus and is arranged in a tonotopic manner in regard to frequencies, with higher frequencies being located more caudally. Sensory association areas help integrate sensory information from various systems.

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SPEECH

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Wernicke and Broca areas are the two areas that are involved with language. They are interconnected by the arcuate fasciculus, which ...

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