40 Fun Facts About Cranial Nerves

Brain freeze, the ice-cream headache felt in the forehead, is pain carried by which cranial nerve?

The trigeminal nerve is thought to sense blood vessels in the palate tightening and then swelling after sudden cold, and the brain misreads the pain as coming from the forehead.

The vagus nerve, which reaches from the skull to the colon, is named from a Latin word meaning what?

Wandering is the literal meaning of the Latin vagus, and the same root gives English the words vagrant, vagabond and vague.

Which condition, named for a Scottish surgeon, is a sudden one-sided paralysis of the facial nerve?

Bell's palsy usually shows as a facial droop that comes on within 72 hours, and most people start to improve within about two weeks.

The facial nerve controls the stapedius, the smallest skeletal muscle in the body, found where?

The middle ear holds the stapedius, which steadies the tiny stapes bone; when it is paralysed, normal sounds seem very loud.

Excessive vagus nerve activity during emotional stress can cut the heart's output and cause what?

Fainting of this vasovagal kind is typically set off by the sight of blood, pain or long standing, and people come round without any treatment.

The point where the optic nerve leaves the retina creates which feature of every healthy eye's vision?

A blind spot forms because the disc where the nerve exits has no light-detecting cells, but the brain fills the gap from surrounding detail and the other eye.

A pacemaker-like implant under the collarbone pulses the vagus nerve to treat which condition?

Epilepsy that drugs cannot control is the main use: the generator sends regular electrical pulses to the nerve in the neck, and it is also approved for stubborn depression.

The eighth cranial nerve, which shares a bony canal with the facial nerve, carries which two senses?

Hearing and balance travel together because the eighth nerve is two bundles in one: a cochlear nerve for sound and a vestibular nerve for equilibrium.

A shoulder shrug tests the eleventh cranial nerve because that nerve powers which large muscle?

Trapezius is the shrugging muscle, so when its nerve is injured the shoulder droops and lifting the arm out to the side becomes difficult.

The Rinne and Weber tests, two screening checks for deafness, both rely on which simple instrument?

A tuning fork, usually vibrating at 512 Hz, lets the examiner compare sound carried through air with sound carried through bone to tell two kinds of deafness apart.

Which cranial nerve raises the upper eyelid and controls most of the muscles that move the eyeball?

The oculomotor nerve also carries the fibres that narrow the pupil, so complete damage leaves the eye turned down and out with a wide pupil.

Which cranial nerve, the smallest by number of nerve fibres, controls just one muscle of the eye?

The trochlear nerve is also the only cranial nerve to emerge from the back of the midbrain, and it runs the longest course inside the skull.

Which cranial nerve controls only the muscle that swings the eye outward, away from the nose?

The abducens nerve works the lateral rectus alone, so when it fails the unopposed medial rectus pulls the eye in toward the nose.

Which cranial nerve senses blood pressure at the carotid sinus and the touch that sets off gagging?

The glossopharyngeal nerve has just one muscle to command, the stylopharyngeus, which lifts the throat during swallowing and speech.

Which cranial nerve arises from nerve cells in the upper spinal cord rather than in the brain?

The accessory nerve climbs through the foramen magnum and then leaves again, making it the only cranial nerve to both enter and exit the skull.

Damage to which cranial nerve makes the tongue curve toward the injured side when it is stuck out?

The hypoglossal nerve moves nearly every tongue muscle, so losing one side leaves the healthy side pushing the tip across unopposed.

Damage to the third cranial nerve can leave the upper eyelid drooping, a sign known by what name?

Ptosis appears because the third nerve powers the muscle that lifts the lid, and the pupil on that side is often widened as well.

Which eye muscle, its tendon looped through a pulley, is the fourth cranial nerve's only target?

The superior oblique pulls the eye downward best when it is turned in, so examiners test it by asking the patient to look toward the nose and then down.

Which gland is threaded by the facial nerve but takes its orders from the ninth cranial nerve?

The parotid gland, the largest of the salivary glands, sits in front of each ear; the facial nerve splits into its branches inside it without supplying it.

The twelfth cranial nerve exits through a canal just above the condyles of which skull bone?

The occipital bone hides this canal on each side, and quirks of development sometimes leave a person with more than two of them.

Besides ophthalmic and maxillary, which division of the fifth cranial nerve alone has motor fibres?

Mandibular is the only division that moves muscles as well as feeling touch, and it leaves the skull through its own opening, the foramen ovale.

The fifth cranial nerve powers the masseter and temporalis, the main muscles used for which action?

Chewing relies on four muscles on each side, the masseter, the temporal muscle and two pterygoids, and the same nerve also tenses the eardrum.

The facial nerve's chorda tympani branch carries taste from which part of the tongue?

Front two-thirds is this nerve's territory for taste, yet ordinary touch from the very same area travels in a different nerve altogether.

Which skull-base opening lets the ninth, tenth and eleventh cranial nerves all leave together?

The jugular foramen also passes the large vein that drains blood from the brain, and it is usually slightly larger on the right side than on the left.

Olfactory nerve fibres pass to the roof of the nose through tiny holes in which part of the ethmoid?

The cribriform plate also supports the olfactory bulbs, and with age its openings can close up and pinch the fibres passing through.

Fibres from the inner half of each retina cross sides at which X-shaped structure beneath the brain?

The optic chiasm lets each half of the brain's visual cortex receive the same half of the visual field from both eyes.

Optic neuritis, a painful inflammation of the optic nerve, is often an early sign of which disease?

Multiple sclerosis first shows itself as this eye inflammation in roughly one in five patients, and up to half develop it at some point.

Which term means loss of smell, a common result of head injuries that damage the olfactory nerve?

Anosmia after a head injury can be permanent, and because smell feeds flavour, people who have it often find their sense of taste dulled as well.

The first two pairs of cranial nerves, for smell and sight, emerge from which part of the brain?

The cerebrum gives rise to only those two pairs; the rest emerge lower down, mostly from the brainstem.

The Roman numerals given to the twelve pairs of cranial nerves follow which ordering principle?

Front-to-back position on the brain decides the number, so the nerve of smell, emerging furthest forward, is first and the tongue's motor nerve is last.

The facial nerve, which works the muscles of expression, is which numbered pair of cranial nerves?

Seventh in the sequence, this nerve emerges from the pons, threads a bony canal in the temporal bone and then splits into five branches across the face.

Smell from the olfactory nerve is the one sense that reaches the cortex bypassing which relay hub?

The thalamus has a relay nucleus for each of the other senses, passing sight, sound, taste and touch on to their own areas of cortex.

Damage to the third, fourth or sixth cranial nerve usually causes which visual symptom?

Double vision, which doctors call diplopia, arises because those three nerves steer the eyeball, so when one fails the two eyes no longer line up on the same target.

Which physician of the Roman Empire named only seven pairs of cranial nerves?

Galen's count of seven was revised to nine by an English anatomist in 1664, and the modern total was not settled until 1778.

Which benign brain tumour is more properly known as a vestibular schwannoma?

Acoustic neuroma is the older name for a growth of the Schwann cells that insulate a nerve from the inner ear; about 95% affect one side only, bringing deafness, ringing and vertigo.

The optic nerve is technically a tract of the brain, its myelin made by which cells?

Oligodendrocytes, not the Schwann cells found in ordinary nerves, insulate its fibres, and like the rest of the brain it has little power to regrow after injury.

Which slender nerve, first discovered in shark brains, is sometimes called cranial nerve zero?

The terminal nerve was found in humans only in 1913, long after the classical list was fixed, so it never received a regular number of its own.

Which English anatomist, namesake of a brain artery circle, counted nine pairs of cranial nerves?

Thomas Willis published his count in 1664 and was the first to number the cranial nerves in the order anatomists still use.

The left vagus nerve sends a branch under which great vessel before it climbs back to the voice box?

The aortic arch hooks the left branch far lower than the right one, and in giraffes the resulting detour is about 4.6 metres long.

The third, fourth and sixth cranial nerves all enter the eye socket through which sphenoid opening?

The superior orbital fissure is the gap between the lesser and greater wings of the sphenoid, and the first branch of the fifth nerve passes through it as well.