116 Lecture 9.S10

116 Lecture 9.S10 - CBNS 116 Lecture 9 - Brainstem III:...

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CBNS 116 Lecture 9 - Brainstem III: Cranial nerves III - XII and their nuclei Lecture notes by Todd Fiacco ASSIGNMENT: In Nolte read Chapter 12: “Cranial nerves and their nuclei”. FOR NEXT LECTURE: No new assignment. The next reading assignment (for 5/6) will be “hypothalamus and pituitary”, Nolte Ch. 23 pp. 580-591. TODAY'S LECTURE: The big picture: The cranial nerves are the somatosensory and motor nerves for the head. Thus, they are the head’s equivalent of the spinal nerves of the spinal cord. Remember that in addition to these basic sensory and motor functions, much of the parasympathetic innervation of the head and viscera emerges from the brainstem (the cranio of craniosacral outflow; CNs III, VII, IX, X). Furthermore, some cranial nerves carry additional, special modalities of information. During development, much of the musculature of the head is derived from the branchial arches , the primordial gill arches (that develop into gills in fish). Thus several cranial nerves (V, VII, IX, X, XI) carry branchial motor , or special motor , innervation to these structures. In addition, the head contains specialized sensory structures (for vision, auditory, balance, olfaction, and taste), and information reaches the CNS from these structures in specific cranial nerves carrying special sensory information (I, II, VII, VIII, IX, X). Thus the cranial nerves together carry a total of 6 different modalities: 1) general somatosensory, 2) general motor, 3) autonomic (visceral) sensory, 4) autonomic (visceral) motor, 5) special (branchial) motor, and 6) special sensory information. All of the cranial nerves except I & II carry their information to, or send their information from, the brainstem. The best way to learn the cranial nerves is to organize them by modality , as Nolte tries to do in Chapter 12. I. Generally speaking, sensory cranial nerve nuclei are located laterally in the brainstem, while motor nuclei lie medially [slide 44]. We will look at cranial nerve function by modality, moving from medial to lateral. II. Cranial nerves III*, IV, VI, and XII are somatic motor nerves , and their nuclei lie along the midline of the brainstem. (*CN III also contains a small amount of preganglionic parasympathetic fibers to the pupillary sphincter muscle to constrict the pupil and to the
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ciliary muscle to focus the lens for near vision during “rest and digest” activity [like when you’re relaxing reading a book]. It is nevertheless classified as a somatic motor nerve). A. CN III ( oculomotor nerve ) innervates 4 of the 6 extraocular muscles for voluntary eye movements. This includes all of the extraocular muscles except the superior oblique (CN IV) and lateral rectus (CN VI). (A useful mnemonic to differentiate between CNs IV and VI is to use the pseudo-chemical formula SO 4 LR 6 , where SO is the superior oblique and LR is the lateral rectus). One clinically important eye muscle innervated by CN III is the medial rectus, which is responsible for moving the eye medially (like when we
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This note was uploaded on 10/31/2010 for the course CBNS 116 taught by Professor Todda.fiacco during the Spring '10 term at UC Riverside.

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116 Lecture 9.S10 - CBNS 116 Lecture 9 - Brainstem III:...

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