Week 6: Cranial Nerves Flashcards
What are the “special sense” nerves?
- Cranial nerve 1 = Olfactory nerve (I)
- Cranial nerve 2 = Optic nerve (II)
- Cranial nerve 8 = Vestibular nerve (VIII)
What are the Somatic motor nerves in the eye?
- Cranial nerve 3 = Oculomotor nerve (III)
- Cranial nerve 4 = Trochlear nerve (IV)
- Cranial nerve 6 = Abducens nerve (VI)
What are the somatic motor nerves of the tongue?
- Cranial nerve 12 = hypoglossal nerve
- speech
What are the rest of the body nerves?
- Cranial nerve 9 = Glossopharyngeal nerve (IX) , swallowing
- Cranial nerve 10 = Vagus nerve (X) , heartbeat/digestion/metabolism
- Cranial nerve 11 = Spinal nerve (XI)
Face and jaws nerves?
- Cranial nerve 7 = Facial nerve (VII) (smile, close eyes forcefully)
- Cranial nerve 5 = Trigeminal (V) (sensory and jaw)
What are cranial nerves?
Nerves that come from the brainstem in brain and pass through the skull to destination origin that they’re concerned with, relate to the foramen of the skull, 12 in total
What are the somatic motor nerves and their target muscle (that they’re attached to)?
Cranial nerve 4 - trochlear nerve - superior oblique (exit is the superior orbital fissure / sphenoid, keyhole in skull cavity)
Cranial nerve 6 - Abducens nerve - Lateral rectus
Cranial nerve 3 - superior, medial and inferior rectus, inferior oblique, Levator palpebrae superioris
Parasympathetic nerve blood supply which controls pupil and accommodation which controls pupillary muscle (sympathetic system will make pupil dilated so can let in more light and see clearly / parasympathetic nerve system makes ciliary body and pupil contract so can focus on small details)
What is the olfactory bulb?
N. Of cells underneath the frontal cortex of the brain which pick up smells coming though sinuses so thats the smell area and one on each side of the head and they’re going to help you with smell
What eye does the right oculomotor nerve from the brain?
The left eye
Look at picture : View of cranial nerves as they emerge from brainstem
Idk
Where does the 3rd cranial nerve start and go to? (And parasympathetic motor fibres)
- ocularmotor nerve
- starts in the midbrain and inside nucleus is command centre for OM nerve
- When nerve comes out of brainstem and gets to superior orbital fissure, nerve splits in 2 branches; Inferior division & Superior division
- superior division goes up to eyelid and superior rectus
- Inferior division goes towards medial rectus and down towards inferior rectus and inferior oblique
- Parasympathetic motor fibres which are going towards the ciliary body and head towards the pupil
Where do all the signals from the 3rd cranial nerve start?
Oculomotor nucleus where signals and command start, cushioned by neural tissue. However if there was a bleed or tumour in this region, px will also present with some external signs that indicate their is something wrong in the brainstem.
- might see this in px who has cancer or tumour, they get tremors in one side of body and will also have problems moving their eyes in all directions
- might have hemiplegia which is one half of the body is paralysed because red nucleus is responsible for sending signals out to body for movement so if damages, will get combo of eye that cant move in some directions plus might be unsteady on their feet and tremor with hands e.c.t.
What is the circle of Willis?
- round structure, key point where lots of blood coming up and all the vessels are all going to different parts
- post cerebral artery + carotid artery + basilar artery
Why is pituitary gland important?
Maintaining hormonal control, problems here can affect vision in different ways
What is the PCA and role?
Posterior communicating artery, allows blood to transfer from the front of the Willis to the back the Willis
Prone to aneurisms which is when you get blooming or swelling in this area, it starts to compress on the third cranial nerve (Oculomotor nerve) then all signals passing through eye will be blocked and eye will stop moving properly.
-these px will present with a pupil that is dilated, vision might be okay but cant move eye in many directions, which is emergency cause aneurism, and if it bursts then person will die
Why is it an emergency if you see a px with eye that cant move up/down/left/right and dilated pupil?
They have an aneurism and if it bursts they will die
What muscles will be affected if tumour grows on branches of oculomotor nerve?
Medial rectus, inferior rectus, inferior oblique, superior rectus, superior palpille,
What happens if a tumour is in the SOF?
Superior orbital fissure, space where further division to each muscle, only affect one muscle so know problem in orbit
What does the Edinger-Westphal nucleus control?
The pupillary sphincter and the ciliary muscle
What does the Oculomotor nucleus control?
Controls the rectus muscles (including superior, inferior and medial), the inferior oblique muscle and the palpebrae superioris (4/6 muscles)
What is the bath ways of the two axons that join together and head out the brain just behind the optic nerve?
Headed fo the eye, along the way the nerve splits into two branches, the superior and inferior branches, heading to the top and the bottom of the eye respectively,
What is the ciliary ganglion?
Little signal centre that sends info via short ciliary nerves that go to lens and ciliary body and pupil and eye itself
When you get aneurism it presses on pupillary fibres (red and yellow on diagram) and you get dilated pupil
What is the nucleus role?
Subdivided with individual areas responsible for individual muscles. A nuclear lesion of the third cranial nerve (oculomotor nerve) will cause bilateral ptosis due to the close proximity of the SR nuclear control.
Disorders in nucleus can result in congenital palsy in one of muscles.
If something happens in middle, will stop superior rectus in both eyes from functioning- can lead to droopy eyelids so cant look up
What is the function of the Trochlear Nerve?
- Only has to send signal to one muscle, superior oblique muscle
- Axons run dorsally and cross the midline before emerging from the brainstem so the nucleus for 4th nerve on right side controls left superior oblique (and nucleus on the left side of brainstem controls the right side of superior oblique muscle)
- Thus a lesion of the trochlear nucleus affects the contractural (opposite) eye
- Smallest nerve in terms of n. Of axons it contains also longest.
- Only CN that exists from the dorsal aspect of the brainstem which makes it supseptable to injury form blows to back of the head in particular whiplash injury
What is crossing over of nerves sometimes referred to as?
The crossing of the right and left corticospinal tract is known as decussation.
Other than the optic nerve (CN2) and Trochlear nerve CN(4) are only cranial nerves that decussate
What gives nerve supply to superior oblique?
Superior orbital fissure
Where is the nucleus of the trochlear nerve located?
In the caudal mesencephalon beneath the cerebral aqueduct. Immediately below the nucleus oft the oculomotor nerve (CN3) in the rostral mesencephalon
What muscle does the Abducens nerve affect?
Lateral rectus muscle is controlled by the Abducens nerve (CN6)
- Abducens = abduct = lateral rectus muscle moves eye outwards
- nerve leaves the pons quite low down
What is the pathway of the Abducens nerve?
- leaves the brainstem at junction of pons and medulla (medial to facial nerve)
- in order to reach eye, it runs superiorly and then bends anteriorly
- nerve enters subarachnoid space where it emerges from the brainstem
- runs a upwards (between pons and clivus) and then pierces the dura mater to run between the dura and skull through the Dorello’s canal.
- At the tip of the petrous temporal bone it makes a shape turn forward to enter the cavernous sinus.
- In the cavernous sinus it runs alongside the internal carotid artery.
- Then enters the orbit through the superior orbital fissure and innervates the lateral rectus muscle of the eye
What does the long pathway of the Abducens nerve mean?
Makes it vulnerable to injury at many levels.
E.g. fractures of the petrous temporal bone can selectively damage the nerve, as can aneurysms of the intracavernous cartons artery. Mass lesions that push the brainstem downward can damage the nerve by stretching it between the point where it memerges from the pons and the point where it hooks over the petrous temporal bone.
What happens when px has infection in ear and it works its way upto vestibular nucleus which then gives rise to infection in brainstem?
Combined 6th and 8th CN palsy
What is Moebius syndrome?
6th and 7th facial palsy so can smile or make facial expressions, cant move eye outwards
Where is the nucleus of the Abducens nerve?
- located in the pons, on the floor of the fourth ventricle at the level of the facial colliculus. The facial nerve loops round it.
- Lesions affecting the dorsal pons at the level of the abducens nucleus can also affect the facial nerve, producing an ipsilateral facial palsy together with a lateral rectus palsy
How many cranial nerves serve eye muscles?
3
How many divisions does the 3rd cranial nerve split into? And where do they go to?
(Oculomotor nerve)
-2; Upper division (Superior rectus and Levator)
Lower Division (Medial rectus, Inferior rectus, Inferior oblique, pupil and ciliary body)
What muscle does the Trochlear nerve attach to ?
Superior oblique ONLY (decusses and dorsal exit)
CN 4
What muscle does the Abducens nerve attach to ?
Lateral Rectus muscle ONLY
Long path and nucleus in pons
CN6
What is the CN1?
Olfactory nerve, associated with smell, least sensitive as brain eventually forgets about smell
What is the function and functional components of the Optic nerve?
CN2
- function: sensory
- Functional components: Special sensory fibres transmit vision
- close to pituitary gland (goes straight from eye to brain)
What is the protective layering system of the Optic nerve?
- Stops signal leaking out
- Dura, Arachnoid, pia (mater)
- 3cm in orbit
What happens if the central artery of the retina is cut
Loose vision (as no blood supply)
Look at diagram of all CN nerves and muscles
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