Olfactory Nerve Anatomy Quiz

Olfactory Nerve

• The olfactory nerve (CN I) is the first and shortest cranial nerve.
• It's a special visceral afferent nerve, transmitting information about smell.
• The anatomical pathway of the olfactory nerve involves the transmission of special sensory information from the nasal epithelium to the primary olfactory cortex in the brain.
• Smell is detected by olfactory receptors in the nasal epithelium.
• Axons (fila olfactoria) from olfactory receptors group into bundles of true olfactory nerves.
• These nerves pass through foramina in the cribriform plate of the ethmoid bone, entering the cranial cavity.
• Once inside the cranial cavity, the fibres enter the olfactory bulb, which rests in the olfactory groove of the anterior cranial fossa.
• The olfactory bulb contains specialized neurons called mitral cells.
• Olfactory nerve fibers synapse with mitral cells, forming glomeruli.
• Second-order nerves then extend posteriorly into the olfactory tract.
• The olfactory tract travels posteriorly on the inferior surface of the frontal lobe.
• The tract divides into medial and lateral striae.
• Lateral stria convey axons to the primary olfactory cortex, located in the uncus of the temporal lobe.
• Medial stria carries axons across the medial plane to the opposite side's olfactory bulb.
• The primary olfactory cortex transmits nerve fibers to other brain areas like the piriform cortex, amygdala, and secondary olfactory cortex.
• These areas are crucial for olfactory memory and perception.
• The olfactory mucosa plays a role in both smell and taste.
• It is composed of pseudostratified columnar epithelium and contains basal cells, which are stem cells; supporting cells called sustentacular cells; and olfactory receptor cells (bipolar neurons).
• The dendritic processes of olfactory receptor cells extend to the epithelial surface, bearing olfactory cilia that respond to odors in the air.
• The axons (central process) of receptor cells extend in the opposite direction into the olfactory bulb.

Optic Nerve

• The optic nerve (CN II) is the second cranial nerve, responsible for transmitting special sensory information for vision.
• It's responsible for transmitting visual information from the retina to the primary visual cortex of the brain.
• The optic nerve is made up of axons from retinal ganglion cells, which receive signals from photoreceptors (rods and cones).
• The optic nerve exits from the bony orbit through the optic canal in the sphenoid bone.
• Within the middle cranial fossa, it forms the optic chiasm.
• At the chiasm, fibers from the nasal (medial) half of each retina cross over to the contralateral optic tract, and fibers from the temporal (lateral) halves of each retina remain ipsilateral.
• The left optic tract contains fibers from the left temporal and right nasal retin,as.
• The right optic tract contains fibers from the right temporal and left nasal retinas.
• Each optic tract heads to its corresponding cerebral hemisphere and relays information to the lateral geniculate nucleus in the thalamus.
• Axons from the LGN then project to the visual cortex via optic radiations.
• Optic radiations split into upper and lower optic radiations.
• Upper optic radiations carry impulses from superior retinal quadrants (inferior visual field).
• Lower optic radiations carry impulses from inferior retinal quadrants (superior visual field).
• Each pathway connects to the visual cortex.

Oculomotor Nerve

• The oculomotor nerve (CN III) is the third cranial nerve.
• It provides motor and parasympathetic innervation to some structures within the bony orbit.
• The motor component innervates most extrinsic eye muscles: levator palpebrae superioris, superior rectus, inferior rectus, medial rectus, and inferior oblique.
• Parasympathetic fibers innervate the sphincter pupillae muscle and the ciliary muscles.
• Sympathetic fibers, running with the oculomotor nerve, innervate the superior tarsal muscle (raising the eyelid).
• The oculomotor nerve originates from the oculomotor nucleus in the midbrain, ventral to the cerebral aqueduct.
• It emerges from the anterior aspect of the midbrain.
• The nerve then travels through the cavernous sinus.
• Within the cavernous sinus, it receives sympathetic branches from the internal carotid plexus, these branches run alongside the nerve.
• The nerve exits the cranial cavity via the superior orbital fissure.
• The nerve divides into superior and inferior branches.
• Motor component innervations to muscles are supplied via these branches.
• The superior branch innervates the superior rectus and levator palpebrae superioris.
• The inferior branch innervates the inferior rectus, medial rectus, and inferior oblique muscles.
• Parasympathetic fibers are carried to the ciliary ganglion, then to the eye to innervate the sphincter pupillae (pupil constriction) and ciliary muscles (lens accommodation).

Trochlear Nerve

• The trochlear nerve (CN IV) is the fourth cranial nerve.
• It's the smallest cranial nerve by the number of axons.
• It has a purely somatic motor function.
• It arises from the trochlear nucleus, located in the posterior aspect of the midbrain.
• It's the only cranial nerve that exits the posterior aspect of the midbrain.
• The nerve passes through the cavernous sinus, and enters the orbit via the superior orbital fissure.
• It innervates the single superior oblique muscle.
• The superior oblique muscle is responsible for depression and intorsion of the eyeball.