116 Lecture 7.S10

116 Lecture 7.S10 - CBNS 116 Lecture 7 Brainstem I...

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CBNS 116 Lecture 7 - Brainstem I: Organization, key landmarks and cross sections Lecture notes by Todd Fiacco ASSIGNMENT: Read Nolte Chapter 11: “Organization of the brainstem”. FOR NEXT LECTURE: Begin reading Nolte Chapter 12: “Cranial nerves and their nuclei”. Although the material in these chapters is challenging, aside from part of Chapter 23 on the hypothalamus and pituitary, they are the only 2 chapters assigned during the middle third of the course so you will have extra time to study the material. TODAY'S LECTURE: The big picture: The brainstem is the most caudal part of the brain and is a very important transitional structure situated between the spinal cord caudally and the diencephalon and telencephalon rostrally. In some ways it resembles the spinal cord, but the clear-cut organization of the spinal cord with the white matter on the outside and the gray matter on the inside is lost in the brainstem. For example, rather than having continuous columns of cells (such as Clarke’s column and intermediolateral cell column), the gray matter of the brainstem is discontinuous, forming distinct nuclei. The brainstem can be thought of as the “heart” of the central nervous system. Although the brainstem is the most evolutionarily ancient brain region, it is the most important in terms of survival. This is because the brainstem contains centers regulating attention, alertness, and sleep (consciousness), respiratory control, cardiovascular control, pain modulatory control, as well as ingestion, defecation, and urination. It also contains all of the fiber pathways by which the cerebellum communicates with the spinal cord and brain. In addition, the brainstem is home to modulatory neurotransmitter systems that project to all other brain areas, and also contains nuclei of all cranial nerves with the exception of olfactory (I) and optic (II) (although it contains an important structure involved in visual orientation, the superior colliculus). Thus the brainstem is an important control center for eye movements (CNs III, IV, VI) and autonomic control of heart rate and blood pressure (CNs IX, X). Via the cranial nerves, the brainstem is the spinal cord equivalent of somatosensory, autonomic, and motor control of the head, while also subserving the special senses of hearing, equilibrium, and taste. Based on this host of important functions, it is easy to surmise that even small lesions occurring in the brainstem can have devastating consequences.
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I. Overall organization of the brainstem [Lecture Images part 2, slides 2-22]. A. The brainstem consists of three parts: From caudal to rostral, they are the medulla , pons , and midbrain . Each of these parts is typically further subdivided into caudal and rostral portions. The brainstem has characteristic surface features that help make sense of its internal organization [slides 2-5]: 1) The medulla has closed and open portions. The closed medulla is the caudal half that contains a central canal continuous with that of the spinal cord. The open
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116 Lecture 7.S10 - CBNS 116 Lecture 7 Brainstem I...

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