Anatomy & Physiology I and II

Anatomy & Physiology Study Guide and the pituitary gland. The processing centers and nuclei of the brain stem relay information headed to or from the cerebrum or cerebellum. The brain stem includes the mesencephalon, pons, and medulla oblongata. The mesencephalon , or midbrain, processes visual and auditory information and controls reflexes triggered by these stimuli. Some centers in this region help maintain consciousness. The pons of the brain attaches the cerebellum to the brain stem. Pons also contains nuclei involved with somatic and visceral motor control. The spinal cord attaches to the brain at the medulla oblongata . Information is relayed to the thalamus and to other centers in the brain stem by the medulla oblongata. Main centers that regulate autonomic functions, such as heart rate, blood pressure, and digestion, send instructions from this region of the brain. 12.2 Embryology of the Brain The central nervous system (CNS) is developed from the embryological layer called ectoderm . During initial development, this layer curves into a hollow cylinder known as the neural tube . In the cephalic section of the neural tube, three prominent enlargements develop to become the primary brain vesicles . The three primary brain vesicles are identified for their relative regions: the prosencephalon, or “forebrain”; the mesencephalon, or “midbrain”; and the rhombencephalon, or “hindbrain.” The prosencephalon and rhombencephalon are further split into secondary brain vesicles. The prosencephalon forms the telencephalon and the diencephalon. The telencephalon will form the cerebrum of the adult brain. The portion of the rhombencephalon adjacent to the mesencephalon forms the metencephalon . The dorsal portion of the metencephalon will become the cerebellum, and the ventral portion will develop into the pons. The portion of the rhombencephalon closer to the spinal cord forms the myelencephalon , which will become the medulla oblongata. 12.3 Ventricles of the Brain During embryonic development, the hollow cavity within the cerebral hemispheres, diencephalon, metencephalon, and medulla oblongata, called the neurocoel, expands to form chambers called ventricles . Each cerebral hemisphere contains a large lateral ventricle. These ventricles are divided by a thin medial partition known as the septum pellucidum . Each ventricle communicates with the third ventricle of the diencephalon through an interventricular foramen . The mesencephalon has a slender canal known as the aqueduct of midbrain (also called the mesencephalic aqueduct, aqueduct of Sylvius, or cerebral aqueduct). This passageway connects the third and fourth ventricles. The fourth ventricle continues into the medulla oblongata; then it narrows and becomes continuous with the central canal of the spinal cord. The ventricles are covered with cerebrospinal fluid (CSF). The CSF continuously circulates through the CNS from the ventricles and central canal into the subarachnoid space of the surrounding cranial meninges. ©2018 Achieve Test Prep Page 126 of 367