The Cranial Nerves

There are twelve pairs of cranial nerves that originate from the brain. The cranial nerves are given a number which indicates the order in which they arise from the brain (cranial nerve I is anterior most and cranial nerve XII is posterior most). Each cranial nerve is also given a

Figure 23.4 Frontal Section of the Brain

Corpus callosum Fornix Gray matter Hypothalamus Insula Lateral ventricle Longitudinal cerebral fissure Pituitary gland Thalamus Third ventricle White matter name which indicates its function or distribution within the body. Ten of the twelve pairs originate from the brain stem. Cranial nerves that originate from the medulla are the: vestibulocochlear VIII (cochlear branch), glossopharyngeal IX, vagus X, spinal accessory XI, and hypoglossal XII. Cranial nerves that originate from the pons are the: trigeminal V, abducens VI, facial VII, and vestibulocochlear Vm (vestibular branch). Cranial nerves that originate from the midbrain are the: oculomotor HI and trochlear IV. The remaining two cranial nerves are the: olfactory I (which arises in the olfactory mucosa of the nose) and the optic II (which arises in the retina of the eye). Olfactory nerve I has two structures which make it up; these are the olfactory bulb and the olfactory tract.

Optic nerve II passes to the optic chiasma and from here the neurons pass through the optic tracts on there way to the lateral geniculate nucleus in the thalamus.

Figure 23.5 Inferior External View of the Brain

Abducens nerve VI Accessory nerve XI (spinal accessory) Facial nerve VII Glossopharyngeal nerve IX Hypoglossal nerve XII Longitudinal fissure Mammillary body Medulla Oculomotor nerve III Olfactory bulb Olfactory nerve I Olfactory tract Optic chiasma Optic nerve II Optic tract Pituitary gland Pons Trigeminal nerve V Trochlear nerve IV Vagus nerve X Vestibulocochlear nerve VIII

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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