15-chapter 12 - Chapter 12: The Nervous and Sensory System...

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Chapter 12: The Nervous and Sensory System Purpose Learn the major brain divisions, both embryonic and adult, in an evolutionary context. Learn the structures and their functions in the mammalian (sheep) brain. Learn the cranial nerves of vertebrates (name and number) and their innervations (omitting their branches). Understand the anatomy and function of the various stimulus receptors of vertebrates. Know the six extrinsic (extraocular) eye muscles and their associated cranial nerves. Learn the anatomy of the Bos eye Nerve structure and vocabulary afferent = sensory efferent = motor nerve = bundle of axons in PNS tract = bundle of axons in CNS ganglia = cluster of small bodies in PNS nuclei = cluster of cell bodies in CNS CNS = central nervous system = brain & spinal cord PNS = peripheral nervous system cranial vs. spinal nerves (based on point of origin) Mammalian Anatomy: The Cat -Nervous System and Sense Organs Chapters Ch. 12 supplement- Figs 12-2 and 12-3 Squalus eye, 12-4 Squalus external anatomy The Vertebrate Brain Evolution of the brain can occur in two ways: either new structures can be added to the brain or already existing structures can be made more complex. Only the latter method has been employed in vertebrates. Even taxa as distantly related as lampreys and mammals have the same basic brain components, although the components are developed to different degrees. In vertebrates, the three embryological divisions of the brain are the prosencephalon , mesencephalon , and rhombencephalon . In adults, the prosencephalon divides to give rise to the telencephalon and diencephalon , and the rhombencephalon divides to become the metencephalon and myelencephalon . The mesencephalon remains as a major division of the adult vertebrate brain. These divisions are depicted on the vertebrate brain models in our lab. You should use the chart at the end of this chapter to help you visualize both the embryological and adult brain divisions among the representative classes of craniates. You will be responsible for knowing both embryological and adult divisions of the vertebrate brains. You are also required to know the names and numbers of all 12 cranial nerves on the dog brain model. You should be able to identify the first 6 nerves on the preserved sheep brain. The twelve craniofacial nerves and their functions are depicted in Figure 12-1 (below).
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Figure 12-1. Mammalian craniofacial nerves and their functions. ( Adapted from Gilbert 1994. )
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Extrinsic (extraocular) eye muscles The six extrinsic eye muscles are a highly conservative feature in vertebrates. There is no variation in the number or arrangement of these muscles except in those burrowing taxa that have reduced or lost their eyes during their evolution ( e.g. , snakes, which apparently re-evolved eyes after losing them), and many birds, which have no room for them in their compact skulls. If you learn these six muscles in Squalus you then know them in most other vertebrates. There are two oblique
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15-chapter 12 - Chapter 12: The Nervous and Sensory System...

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