Well first off happy happy Mother’s Day to all mothers in the world! Especially to mine hehe, for being such a staunch supporter of me when no one believed in me when I said I wanted to be a vet. That meant bucket loads to me. Have a good one mom!
Sadly I am running out of time to write such posts. But it’s ok, because I can you entertained through the billions and gazillons of information I’m learning everyday. Well they keep me entertained. And today will be a nice little revision/interesting session, as we once again revisit our old friend, the cranial nerves. Yes I have finally gotten down to (trying to) learn them, all 12 of them. Or should I write that as XII of them. But ah well let’s cut the crap and get started.
CNI – Olfactory –> As its name suggests, it’s the sole nerve in the head that is responsible for your sense of smell. Lesions in this nerve will result in an impaired sense of smell (anosmnia).
CNII – Optic –> Once again, according to its name, this nerve helps with the sense of sigh by providing innervation to the eyes, specifically the retina. It is the sole nerve that provides visual imput, but it isn’t the sole nerve that gives us our sense of sight. Lesions in the optic nerve results in visual and pupillary light reflex (PLR, when you shine a light and your pupils contract) deficits.
CNIII – Oculomotor –> Not as easy to guess its function from its name, but we can still give it a try. Oculo – regarding the eye, motor – movement. This nerve supplies most of the muscles that move the eye within the periorbita. This is also the nerve that sends parasympathetic innervation to your pupl muscles, and in the brain it contributes to your sense of sight. Lesions in this nerve causes deficits in PLR and strabismus, which is just a fancy word meaning flickering of the eyeball.
CNIV – Trochlear –> Tricky unless you are good with your anatomy of the eye. This nerve only innervates the dorsal oblique muscle which is responsible for pulling the eye in when stimulated. Hence you can guess what will happen if this nerve is damaged – yes that’s right, strabismus again, but this time the eye will only flick laterally.
CNV – Trigeminal –> Arguably one of the most important nerves that innervate the face, the trigeminal (named so because it has 3 major branches, mandibular, maxillary and ophthalmic branches) nerve provides sensory innervation to the whole face. It deserves another post all to itself, so that’s what we’ll leave it at today. Lesions in the trigeminal nerve leads to facial sensory deficits and masticatory muscle paralysis (dropped jaw)
CNVI – Abducens –> Another small nerve that has got to do with the eye again. From its name we can guess it will innervate a muscle that abducts something, and since I already gave the clue that it’s the eyes, we can all predict that this nerve innervates the lateral rectus muscle of the eye. See, it’s not that bad. Because the bad ones come later. Anyhow damage to this nerve results in (dun dun dun) strabismus again, and also failure to retract the globe.
CNVII – Facial –> Now this has to be the most important cranial nerve. It basically supplies motor innervation to most, if not all the muscles of facial expression, and the glands. Hence if this nerve is somehow damaged, there will be serious consequences, including paralysis of facial muscles (drooping of ear, lip and eyelid) and decreased glandular secretions (i.e. tears and saliva production). In addition the facial nerve also supplies taste sensing cells in the tongue (rostral 2/3), so without this wonderful nerve, I won’t be having much of an appetite.
CNVIII – Vestibulocochlear –> What a mouthful, until you realise the components of that word all deal with the ear. Hence we can conclude this nerve innervates the ear, both the balancing and the hearing bits. You might think deafness resulting from lesions in this nerve might not be too serious, but if innervation to your body’s balancing centre is offline, you bet there will be great difficulties in balancing, resulting in head tilting, body twisting and rolling, amongst other clinical signs)
CNIX – Glossopharyngeal –> This nerve innervates a range of target tissues, as can be seen from its name. Glosso – having to do with the tongue, and pharyngeal – to do with the pharynx. It also supplies the sensation of taste to the caudal 1/3 of the tongue. Together with cranial nerve X, they help to innervate movement to these 2 regions of the head. Lesions can be hard to tell, because CNIX and CNX do such similar things.
CNX – Vagal –> Easy one to guess, because we all know vagal = parasympathetic (I hope we all know?). It also sends a bit of innervation to the muscles of the tongue and the pharynx, and a bit of sensory too. If your animal is not responding to stimuli meant to set off a parasympathetic response in the viscera, and if it happens to have dysphagia (difficulty swallowing) and respiratory noises (laryngeal paralysis), you can bet your money on this nerve being the point of lesion.
CNXI – Accessory –> This nerve doesn’t actually do much for the face. It supplies some of the major muscles in the neck, namely the brachiocephalic family and the trapezius muscle. Lesion in this nerve will cause these muscles to become paralysed and start to atrophy.
CNXII – Hypoglossal –> Ah the word glossal has popped up again, so this should be a clue to where it innervates. That’s right, the tongue! And this nerve innervates the extrinsic muscles to the tongue, and some intrinsic ones too. Examples include styloglossus, hyoglossus, genioglossus and geniohyoideus. With this information, we will know what to expect if this nerve is damaged, which is the paralysis and deviation of the tongue if its a unilateral lesion.
And voila! This is a short summary on the various functions of the cranial nerves. I haven’t even gotten into which of the 249857295748 foramens they come out from in the skull. But alas you may ask, how do we remember this 12 seemingly nonsensical words? That’s what mnemonics are for, and we have a pretty good one to help. But it’s a bit dirty, so I shall cross out the words that are slightly suggestive. You can fill in you own.
O O O To Touch And Feel V- Girls V- and H-
Hehe.
Ciao~
Posted in anatomy, neuroanatomy