Cranial nerves
Cranial nerves are found paired as ganglia in the medulla oblongata at the base of the brain (Fig 7-55). Pairs of cranial nerves already leave the brain while inside the cranial cavity. The cranial nerves are numbered in Roman numerals in the order they exit from the brain from front to back.
The cranial nerves can be divided into three groups, classified according to their function:
- Sensory nerves (I, II, VIII, IX)
- Nerves responsible for eye movement (III, IV, VI)
- Pharyngeal arch nerves (V, VII, IX, X, XI)
I. Olfactory nerve (nerve of smell, nervus olfac-torius; also known as fila olfactoria): Consists of processes of the olfactory epithelium of the nasal mucosa and extends to the olfactory bulb as a protuberance of the forebrain (proencephalon); it is not regarded as a true cranial nerve.
II. Optic nerve (N opticus; also known as fasciculus opticus): A protuberance of the diencephalon as a fiber tract at the rear of the eyeball; it is encased in meninges and is hence part of the brain. With its terminal branches, it supplies the retina of the eye.
III. Oculomotor nerve (N oculomotorius): A cranial nerve emerging from the midbrain whose fibers mainly supply the eye muscles; the parasympathetic fibers control narrowing of the pupils.
IV. Trochlear nerve (N trochlearis): A nerve emerging dorsally from the midbrain that supplies the outer muscles of the eye.
V. Trigeminal nerve (N trigeminus; see detailed description later in this chapter).
VI. Abducens nerve (N abducens): A motor nerve that supplies the outer muscles of the eye.
VII. Facial nerve (N facialis): Responsible for supplying the muscles of facial expression, parts of the sense of taste, the salivary glands of the mandible, and the lacrimal glands.
VIII. Vestibulocochlear nerve (N vestibuloco-chlearis): A sensory nerve arising in the pons of the myelencephalon responsible for supplying the organ of balance and the cochlea in the ear.
IX. Glossopharyngeal nerve (N glossopharyn-geus): The main nerve of taste for the tongue; responsible for movement of the esophagus and for the parotid gland.
X. Vagus nerve (N vagus): Supplies the muscles of the larynx and is responsible for the digestive tract as far as the curvature of the large intestine.
XI. Accessory nerve (N accessorius): A motor cranial nerve that supplies the sternocleidomastoid muscle in the neck and functions as a supplementary nerve to cranial nerve X.
XII. Hypoglossal nerve (N hypoglossus): runs as a motor nerve from the medulla oblongata to the tongue and ensures tongue movement.