Cranial Nerves Flashcards
Where do the majority of cranial nerves emerge from?
from the brain stem on the ventral surface of the brain
Which cranial nerves are different?
Where do they emerge from instead?
CN I and CN II, these emerge from the forebrain
CN XI emerges from the brainstem as well as the spinal cord
Which system are the nerves classified as part of?
Which cranial nerves are different and how?
They are classified as part of the peripheral nervous system
CN I and CN II are also considered as part of the central nervous system
Each nerve often has fibres performing …
many different functions
List the 12 cranial nerves in order
I - Olfactory II - Optic III - Oculomotor IV - Trochlear V - Trigeminal VI - Abducens VII - Facial VIII - Vestibulocochlear IX - Glossopharangeal X - Vagus XI - Accessory XII - Hypoglossal
List whether these cranial nerves are sensory, motor or both, in order
I - Sensory II - Sensory III - Motor IV - Motor V - Both VI - Motor VII - Both VIII - Sensory IX - Both X - Both XI - Motor XII - Motor
Describe the role of CN I
What effect may a lesion have?
CN I deals with sense of smell - the nerve fibres go through the roof of the nasal cavity to sit in the olfactory bulbs found right over the nasal cavity
Lesions cause anosmia and can affect taste too
Describe the role of CN II
What effect may a lesion have?
The optic nerves carry sensory input from the retina to the occipital cortex
Lesions cause blindness on the side of the eye that is affected
Describe the role of CN III
What effect may a lesion have?
It controls 4 of the 6 eye muscles - superior, inferior, medial and inferior oblique rectus muscles, it also constricts the lens and lifts the upper eyelid
Lesions can cause fixed rotation of the eye away from its normal position, a fixed dilated pupil and drooping of the eyelid
Describe the role of CN IV
controls the superior oblique rectus muscle
Describe the role of CN V
What effect may a lesion have?
It governs sensations of pain, touch and temperature changes in different areas of your face, also controls muscles of mastication
Lesions may cause facial numbness and paralysis and deviation of the jaw
Describe Trigeminal Neuralgia (TN)
a problem with CN V that causes severe facial pain - exact cause is often not known - the nerve sends pain messages to your brain due to
1 - pressure being exerted on the nerve from blood vessels in the head or from a tumour or cyst
2 - injury to the nerve from head trauma, surgery or stroke
3 - damage from other diseases, such as MS
TN can cause sudden, sharp or burning pain, normally occurs on one side of the face but can occur on both sides
Describe the role of CN VI
What effect may a lesion have?
The abducens sits right behind the trigeminal nerve at the midline - it controls the lateral rectus muscle
Lesions may lead to paralysis and there would be deviation of the eye towards the nose
Describe the role of CN VII
The facial nerve branches off into smaller nerves that supply muscles in 5 different parts of the face, the sensory component governs taste in the anterior 2/3rds of the tongue
Also the nerve of facial expression and supplies motor function to the salivary glands
Describe Bells Palsy
Due to lesion of CN VII
Typical symptoms include
1 - facial weakness
2 - drooping of the face because you can’t control the muscles of facial expression
3- lack of taste especially in the anterior 2/3rds of the tongue and dry mouth
It’s an idiopathic disease, we don’t know what causes it, can come on in pregnancy or with stress and it can just as easily go away without any known reason
