Anatomy & Physiology I and II

Anatomy & Physiology Study Guide

©2018 Achieve Test Prep Page 129 of 367 The basal nuclei are bulks of gray matter that sit within each hemisphere deep to the bottom of the lateral ventricle. They are embedded in the white matter of the cerebrum, and the radiating projection fibers. Commissural fibers travel around or between these nuclei. The caudate nucleus has a large head and a slender, curving tail that follows the curve of the lateral ventricle. The head of the caudate nucleus lies in front of the lentiform nucleus . 12.6 The Cerebrum The cerebrum, the biggest region of the brain, contains motor, sensory, and association areas. All intellectual functions, including conscious thoughts, begin in the cerebral hemispheres. A large portion of the cerebrum processes information from somatic sensory and motor inputs. Gray matter in the cerebrum is found in the cerebral cortex and deeper basal nuclei. The white matter of the cerebrum lies deep to the neural cortex and around the basal nuclei. The Cerebral Cortex A blanket of neural cortex covers the paired cerebral hemispheres, which dominate the superior and lateral surfaces of the cerebrum. The two cerebral hemispheres are almost completely separated by a deep longitudinal fissure. Each cerebral hemisphere can be divided into lobes, or regions, named after the overlying bones of the skull. On each hemisphere, the central sulcus divides the anterior frontal lobe from the more posterior parietal lobe. Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite ( contralateral ) side of the body. For example, the motor areas of the left cerebral hemisphere control muscles on the right side, and the right cerebral hemisphere controls muscles on the left side. This crossing over has no known functional significance. The two hemispheres have different functions. The White Matter of the Cerebrum The interior of the cerebrum consists primarily of white matter. The axons can be roughly classified as association fibers, commissural fibers, and projection fibers. Association fibers interconnect areas of neural cortex within a single cerebral hemisphere. Arcuate fibers are short association fibers that curve in an arc to pass from one gyrus to another. Longer association fibers are organized into discrete bundles, or fasciculi . The frontal lobe connects to the other lobes of the same hemisphere by the longitudinal fasciculi. Commissural fibers permit communication between the cerebral hemispheres. Bands of commissural fibers linking the hemispheres include the anterior commissure and the corpus callosum. Projection fibers connect the cerebral cortex to the diencephalon, brain stem, cerebellum, and spinal cord. The entire collection of projection fibers is known as the internal capsule . 12.7 The Basal Nuclei While the cerebral cortex is consciously directing a multifaceted movement, or solving some intellectual puzzle, other centers of the cerebrum, diencephalon, and brain stem are processing sensory information and issuing motor commands outside the conscious knowledge. Many of these actions, which occur at the subconscious level, are directed by the basal nuclei, or cerebral nuclei. Structure