Cranial Nerves I-III: Olfactory, Optic, Oculomotor

• Cranial nerves emerge directly from the brain, unlike spinal nerves from the spinal cord.
• These nerves relay information between the brain and the body, especially the head and neck.
• There are twelve cranial nerves, designated I-XII, ordered anterior to posterior on the brain.
• Cranial nerves originate from either the cerebrum or the brainstem.

Olfactory Nerve (I)

• This nerve is responsible for the sense of smell and is sensory.
• It originates from the olfactory epithelium in the nasal cavity.
• It passes through the cribriform plate of the ethmoid bone.
• The olfactory nerve terminates in the olfactory bulb.

Optic Nerve (II)

• The optic nerve carries visual information and is sensory.
• It originates from the retina of the eye.
• It passes through the optic canal.
• This nerve terminates in the lateral geniculate nucleus of the thalamus.

Oculomotor Nerve (III)

• It primarily controls most eye movements, including raising the eyelid, pupil constriction, and lens adjustment
• It is mainly motor.
• Originates from the midbrain.
• It passes through the superior orbital fissure.
• It innervates the superior, inferior, and medial rectus muscles, the inferior oblique muscle, and the levator palpebrae superioris muscle.

Trochlear Nerve (IV)

• Controls the superior oblique muscle for downward and outward eye movement.
• It is a motor nerve.
• Originates from the midbrain.
• It passes through the superior orbital fissure.
• It innervates the superior oblique muscle.

Trigeminal Nerve (V)

• This is the largest cranial nerve, featuring three major branches: ophthalmic (V1), maxillary (V2), and mandibular (V3).
• It has both sensory and motor functions.
• Originates from the pons.
• The ophthalmic nerve (V1) passes through the superior orbital fissure, carrying sensory information from the forehead, upper eyelid, and nose.
• The maxillary nerve (V2) passes through the foramen rotundum, carrying sensory information from the lower eyelid, cheek, nasal cavity, upper teeth, and palate.
• The mandibular nerve (V3) passes through the foramen ovale, controlling the muscles for chewing and carrying sensory information from the lower jaw, lower teeth, and tongue.

Abducens Nerve (VI)

• Controls the lateral rectus muscle, responsible for outward eye movement.
• It is a motor nerve.
• Originates from the pons.
• It passes through the superior orbital fissure.
• It innervates the lateral rectus muscle.

Facial Nerve (VII)

• Controls facial expression muscles and carries taste sensations from the anterior two-thirds of the tongue.
• It is both sensory and motor.
• Originates from the pons.
• It passes through the internal acoustic meatus and the stylomastoid foramen.
• It controls facial expression muscles, the stapedius muscle of the middle ear, and the lacrimal and salivary glands.
• It carries taste sensations from the anterior two-thirds of the tongue.

Vestibulocochlear Nerve (VIII)

• Carries information related to hearing and balance.
• It is sensory.
• Originates from the inner ear.
• Passes through the internal acoustic meatus.
• Has two divisions: the vestibular nerve (balance) and the cochlear nerve (hearing).

Glossopharyngeal Nerve (IX)

• Controls swallowing and carries taste sensations from the posterior one-third of the tongue.
• It is both sensory and motor.
• Originates from the medulla oblongata.
• Passes through the jugular foramen.
• Controls the stylopharyngeus muscle, which is involved in swallowing.
• Carries taste sensations from the posterior one-third of the tongue and general sensation from the pharynx.

Vagus Nerve (X)

• The longest cranial nerve, innervating many organs in the thorax and abdomen.
• It is both sensory and motor.
• Originates from the medulla oblongata.
• Passes through the jugular foramen.
• Controls the muscles of the pharynx and larynx and carries sensory information from the pharynx, larynx, and viscera.
• Plays a role in regulating heart rate, breathing, and digestion.

Accessory Nerve (XI)

• Controls the sternocleidomastoid and trapezius muscles, responsible for head and shoulder movement.
• It is motor.
• Originates from the medulla oblongata and the spinal cord.
• Passes through the jugular foramen.
• Innervates the sternocleidomastoid and trapezius muscles.

Hypoglossal Nerve (XII)

• Controls the muscles of the tongue.
• It is motor.
• Originates from the medulla oblongata.
• Passes through the hypoglossal canal.
• Innervates the intrinsic and extrinsic muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve).