Cranial Nerves Ahmed Salam Lectures Medical Student “TSU” WWW.GREATASSIMPLEMEDICINE.COM

Olfactory System (CN I): G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Olfactory System (CN I): The olfactory pathway is composed of the olfactory epithelium of the nose, the fila olfactoria (olfactory nerve = CN I), the olfactory bulb and tract, and a cortical area (the paleocortex) extending from the uncus of the temporal lobe across the anterior perforated substance to the medial surface of the frontal lobe under the genu of the corpus callosum. WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT The sensory cells (olfactory cells) are bipolar cells whose peripheral processes terminate in the olfactory hairs of the olfactory epithelium. WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Olfactory pathway. The first neuron of the olfactory pathway is the bipolar olfactory cell; the second neurons are the mitral and tufted cells of the olfactory bulb. The neurites of these cells form the olfactory tract (2nd neuron), which lies adjacent to and just below the frontobasal (orbitofrontal) cortex. The olfactory tract divides into the lateral and medial olfactory striae in front of the anterior perforated substance; another portion of it terminates in the olfactory trigone, which also lies in front of the anterior perforated substance. The fibers of the lateral stria travel by way of the limen insulae to the amygdala, semilunar gyrus, and ambient gyrus (prepyriform area). This is the site of the 3rd neuron, which projects to the anterior portion of the parahippocampal gyrus WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT WWW.GREATASSIMPLEMEDICINE.COM

Function: G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Function: The afferent nerve fibers of the olfactory receptor neurons transmit nerve impulses about odors to the central nervous system where they are perceived by the sense of smell (olfaction). The functional components of the olfactory nerve include SVA, special visceral afferent, which carries the modality of smell. WWW.GREATASSIMPLEMEDICINE.COM

Examination: G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Examination: Damage to this nerve impairs the sense of smell. To simply test the function of the olfactory nerve, each nostril is tested with a pungent odor. If the odor is smelt, the olfactory nerve is likely functioning. On the other hand, the nerve is only one of several reasons that could explain if the odor is not smelt There are olfactory testing packets in which strong odors are embedded into cards and the responses of the patient to each odor can be determined. WWW.GREATASSIMPLEMEDICINE.COM

Lesions: G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Lesions: Lesions to the olfactory nerve can occur because of "blunt trauma", such as coup-contra coup damage, meningitis, and tumors of the frontal lobe of the brain. These injuries often lead to a reduced ability to taste and smell. Lesions of the olfactory nerve do not lead to a reduced ability to sense pain from the nasal epithelium. This is because pain from the nasal epithelium is not carried to the central nervous system by the olfactory nerve it is carried to the central nervous system by the trigeminal nerve. WWW.GREATASSIMPLEMEDICINE.COM

Visual System (CN II) G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Visual System (CN II) The retina is the receptor surface for visual information. Like the optic nerve, it is a portion of the brain, despite its physical location at the periphery of the central nervous system. Its most important components are the sensory receptor cells, or photoreceptors, and several types of neurons of the visual pathway. The deepest cellular layer of the retina contains the photoreceptors (rods and cones); the two more superficial layers contain the bipolar neurons and the ganglion cells. WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT WWW.GREATASSIMPLEMEDICINE.COM

Rods and cones: G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Rods and cones: When light falls on the retina, it induces a photochemical reaction in the rods and cones, which leads to the generation of impulses that are ultimately propagated to the visual cortex. The rods were long thought to be responsible for the perception of brightness and for vision in dim light, while the cones were thought to subserve color perception and vision in bright light. WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT WWW.GREATASSIMPLEMEDICINE.COM

Lesions along the Visual Pathway: G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Lesions along the Visual Pathway: Optic nerve lesions: The optic nerve can be damaged at the papilla, in its anterior segment, or in its retrobulbar segment, Lesions of the papilla (e. g., papilledema, caused by intracranial hypertension and by a variety of metabolic disorders), Lesions of the anterior segment of the optic nerve are often due to vasculitis WWW.GREATASSIMPLEMEDICINE.COM

G.S.M MEDICAL LECTURES/CN I and II AHMED SALAM MD STUDENT Lesions of the optic chiasm: such as those produced by a pituitary tumor, craniopharyngioma, or meningioma of the tuberculum sellae, The result is partial blindness for objects in the temporal half of the visual field of either eye. Optic tract lesions: cause homonymous hemianopsia, in which the hemifield of the same side is affected in each eye, The result is blindness in the left half of the visual field of each eye. WWW.GREATASSIMPLEMEDICINE.COM