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Cranial Nerves Brooke Roby Anatomy and Physiology II, PCC Vocabulary: 1. Cranial- pertaining to the brain 2. Nerve- a bundle of neuronal axons and or dendrites and associated connective tissue coursing together outside the central nervous system. 3. Axon- the usually single, long process of a nerve cell that propagates a nerve impulse toward the axon terminals. 4. Dendrite- a neuronal process that carries electrical signals usually graded potentials, toward the cell body. 5. Synapse-the functional junction between two neurons or between a neuron and an effector, such as a muscle or gland; may be electrical or chemical. 6. Sensory neurons- neurons that carry sensory information from cranial and spinal nerves into the brain and spinal cord or from a lower to a higher level in the spinal cord and brain. Also known as afferent neurons. 7. Motor neuron- neurons that conduct impulses from the brain toward the spinal cord or out of the brain and spinal cord into cranial or spinal nerves to effectors that may be either muscle or glands. Also called efferent neurons. 8. Mixed-contains both sensory and motor neurons Introduction: Understanding cranial nerves are very important because each has a specific function in the body. Without nerves are body will receive no impulses from the brain, which means our bodies will not function. There are 12 pairs of cranial nerves and each arises from a different location and has a specific function. Understanding and remembering where each arises from and the function it has may be very difficult. There are so many cranial nerves and spinal nerves that it is hard to keep them all straight and remember them all. Explanation: There are twelve cranial nerves. They are all named with a name, which tells a nerve’s function, and a Roman numeral, which tells which nerve it is. The first is Cranial Nerve I, which is the olfactory nerve. If you know what olfactory is, this one will be easy to remember. Olfactory has to do with a person’s sense of smell. This nerve is entirely sensory. It covers the upper part of the nasal cavity and the bottom surface of the cribiform plate. Olfactory nerves end in the brain in paired masses of gray matter called the olfactory bulbs. The next cranial nerve is Cranial Nerve II, the Optic Nerve. This is also a simple on to know because optic means eye, or vision of the eye. It also is entirely sensory. This nerve conducts impulses for vision. The third cranial nerve is Cranial Nerve III, the oculomotor nerve. Oculo=eye, and motor=a mover. This cranial nerve is mixed which means it contains both sensory and motor neurons. There are a few branches of the oculomotor nerve. This nerve innervates the superior rectus, which is an eyeball muscle, and it also innervates the upper eyelid. The second branch is the inferior branch innervates the ciliary muscle of the eyeball, and the circular muscle which is around the iris (the colored part of the eye). This second branch also innervates the inferior rectus muscle of the eye. Cranial Nerve IV is the trochlear Nerve. This nerve is mixed, and innervates the superior oblique muscle of the eye, which also controls the movement of the eye. These axons convey nerve impulses for proprioception. Cranial Nerve V is the trigeminal nerve, and likes its name has 3 branches, ophthalmic, maxillary, and mandibular. This cranial nerve conveys impulses for touch, pain, and temperature sensations and proprioception. It is also involved in chewing. It is a mixed nerve. Cranial nerve VI is also mixed, and is called the abducens nerve. It is involved in movement of the eye, and propriception. It works with nerve III and IV. The next cranial nerve is Cranial Nerve VII, the facial nerve. Like its name states, it is involved in facial expressions, taste and secretion of saliva and tears. It is a mixed nerve. Cranial nerve VIII is the vestibulocochlear nerve, which is also mixed. The cochlear is a spiral, snail like shape, structure in the inner ear. It conveys impulses related to equilibrium, conveys impulses for hearing. The Glossopharyngeal nerve is cranial nerve IX. Glosso = tongue, and –pharyngeal = throat. It has to do with taste and somatic sensation from the back 2/3 of the tongue. It also functions by elevating the pharynx during swallowing and speech. Cranial nerve X is the vagus nerve and is also a mixed nerve. Its sensory function is taste and it somatic motor function is swallowing, coughing, and voice production. Cranial nerve XI is the accessory nerve. This mixed nerve’s spinal part mediates movement of the head and shoulders. The final cranial nerve is cranial nerve XII. The hypoglossal nerve is responsible for the tongue during speech and swallowing. Summary: In order to remember the order of these nerves it is best to come up with a saying, such as: Old Opie Octopus Trocanter Tripped And Fell Very Gracefully Vanashing Always Head-over-heels This will help to remember the order. Knowing the functions takes some time and it is best to practice and practice. If you break down most of the names it can help you to put the function with the name. Good Luck!