clinical relevance of middle cranial fossa (cranial nerves) (A19) Flashcards
3 types of cranial fossae
- anterior (more superior)
- middle (a little bit more inferior)
- posterior (most inferior)
bones that form the floor of the anterior cranial fossa
- frontal
- ethmoid (cribiform plate + crista gali)
- part of sphenoid
bones that form the floor of the middle cranial fossa
- sphenoid
- temporal
bones that form the floor of the posterior cranial fossa
- temporal
- occipital
nerve modalities
- modality = type of nerve fibre contained within a nerve
- CN’s can carry just one modality, but a lot of nerves carry a mix of modalities
- types of modalities:
- > somatic sensory
- > somatic motor
- > parasympthetic
- > special sensory
- > mixed
- > visceral afferent
somatic sensory nerve modality function
- take sensory info from skin etc back towards the brain
- eg. mental nerve
mental nerve
- sensory nerve innervation to skin on chin
- nerve modality=somatic sensory
- mental nerve is a branch of the inferior alveolar nerve which is a branch of the mandibular division of trigeminal nerve
somatic motor nerve modality function
- to skeletal muscle
- eg. spinal accessory
spinal accessory innervation
- trapezius
- SCM
parasympathetic nerve modality function
- part of autonomic nervous system- ‘rest and digest’
- most of the parasympathetic nerves have motor function/make you do something (secretomotor to glands etc, motor to smooth muscle)
- eg. to glands (mucous/lacrimal/salivary)
vagus nerve
- parasympathetic innervation
- goes down to abdomen
special sensory nerve modality function
-from special sence organs-carrying one of the senses (sight, taste, smell etc)
mixed nerves modality function
- carry more than 1 modalities
- eg. CNV/trigeminal (somatic sensory and somatic motor)
visceral sensory (afferent) modality function
- afferent= means the same thing as sensory
- sensory innervation coming from an organ
- from carotid body/sinus, pharynx, larynx, trachea, bronchi, lungs, heart, GI tract
- only really found in glossopharyngeal and vagus nerves
modalities of cranial nerves
- CNI = special sensory
- CN II = special sensory (optic = eyesight)
- CN III = mixed (somatic motor, parasympathetic)
- CN IV = somatic motor
- CN V = mixed (somatic motor, somatic sensory)
- CN VI = somatic motor
- CN VII = mixed (somatic motor for facial expression, somatic sensory, special sensory for taste, parasympathetic)
- CN VIII = special sensory
- CN IX = mixed (somatic motor, somatic sensory, special sensory, parasympathetic)
- CN X = mixed (somatic motor, somatic sensory, special sensory, parasympathetic)
- CN XI = somatic motor
- CN XII = somatic motor
CN I
- olfactory nerve
- modality = special sensory
- long bits at anterior of inferior brain is the olfactory tract with the olfactory bulb on the end
- olfactory receptor cells pass through cribriform plate (like a sieve) and sit at top of nasal cavity and travel along and down medial wall
- olfactory mucosa = roof of nasal cavities (you can only smell something if molecule is dissolved in fluid/mucous in nose)
CN II
- optic nerve
- modality = special sensory
- exits cranial cavity by passing through optic canal (foraminae)
- optic chiasm = joining of the 2 optic nerves and is really closely related to the pituitary stalk
- crossing of visual fields:
- > when you look at something in the middle you see the nasal visual field view
- > temporal visual fields are what you see at the sides
- > sight that has been picked up both from nasal and temporal fields cross before hitting the retina, so that temporal visual fields will hit the retina at the medial aspect (nasal at the lateral aspect) at the back of the eye
- > as these signals pass through the optic nerves to chiasm, the lateral (nasal) field from retina stays on the same side to visual cortex, but anything on the medial aspect at retina (temporal field) crosses over at chiasm, meaning at the back of the visual cortex, the temporal field has crossed over to the opposite side of the brain)
- visual cortex is in occipital lobe of brain
special sense of taste
from CN VII, CN IX and CN X (only a tiny bit contributed by vagus nerve)
pupil
- black hole in centre of eye
- light passes through the pupil and then the focusing lens
- what you see through
- covered in clear cornea (the transparent layer forming the front of the eye)
iris
coloured part of eye covered by clear cornea (the transparent layer forming the front of the eye)
2 muscles of the (coloured part of the eye)
- sphinctor pupillae
- dilator pupillae
sphinctor pupillae
- iris associated circular smooth muscle
- controlled by parasympathetics (‘rest and digest)
- > constrict the pupil
- parasympathetic nerve fibres reach the eye/sphinctor pupillae via CN III (occulomotor nerve)
- sphinctor pupillae close over the pupil when contracted/squeee the pupil closed
- covered by clear cornea
dilator pupillae
- iris associated radial smooth muscle
- radiate out from pupil
- supplied/controlled by sympathetics (‘fight or flight’)
- > dilate the pupil
- as there is no sympathetic innervation from the cranial nerves, sympathetic nerve fibres reach the orbit by following arteries/hitch hiking a ride on the arteries, especially the internal carotid (and opthalmic artery)
- covered by clear cornea
clinical testing of CN II (optic nerve)
- pupillary light reflex (shine light in patients eye)
- tests if optic nerve has picked up that there’s alot of light
- both eyes should constrict due to cross over at chiasm
- sensory limb of the reflex = CN II/optic nerve which spreads to the other side at chiasm causing consensual light reflex (opposite pupil to the one light is shone on constricts, direct light reflex = pupil that light is directly shone into constricts)
- motor limb of the reflex = CN’s III/oculomotor nerves which allow parasympathetics to travel to the sphinctor pupillae muscles of both eyes
CN III
- oculomotor nerve
- modality = mixed (somatic motor and parasympathetic)
- > somatic motor innervation to the extra-ocular skeletal muscles and to the levator palpebral superioris (elevates the eyelid)
- > parasympathetic innervation to the sphinctor pupillae muscle associated with the iris (constricts pupils)
extra-ocular muscles
- skeletal muscles
- within orbit but external to the eye itself
CN IV
- trochlear nerve
- modality = somatic motor
- only has one function = supplies one tiny eye muscle/ superior oblique extra-ocular muscle
- very delicate nerve
- only cranial nerve to emerge from the posterior aspect of the midbrain
- called the trochlear nerve as the muscle comes across through the CT/connective tissue tube which is joined onto bone, goes through a trochlea/pulley and attaches onto eye at an oblique angle (the little pulley=trochlea, so trochlear nerve is related to that muscle which passes through trochlea)
CN VI
- abducent nerve
- modality = only somatic motor (similar to trochlear nerve)
- > to only one skeletal muscle: the lateral rectus muscle (extra- ocular) (rectus = straight muscle), helps to abduct the eye/take the eye away from midline
- arises on inferior aspect of the brain at the junction between the pons and the medulla
CN V
- trigeminal nerve
- modality = mixed (somatic sensory and somatic motor)
- 3 division of trigeminal:
- > Va/opthalmic (modality= sensory innervation to the skin of upper face including front of eyeball)
- > Vb/maxillary (modality= sensory innervation to the skin of the mid-face)
- > Vc/mandibular (modality= mixed; sensory to the skin of most of the lower face, ‘motor to the muscles of mastication’, ABD/anterior belly of digastric, mylohyoid and 2 ‘tensors’)
- separate motor root joins with sensory part of Vc at the foramen ovale
- only crania nerve to emerge directly from the pons
- right at the tip of the trigeminal nerve on inferior aspect of the brain is the tiny motor root
- although trigeminal does cutaneous (relating to or affecting skin) innervation, also supplies sensory innervation deep to those
nerves which pass through superior orbital fissure
- trochlear
- occulomotor
- CNVa (opthalmic division of trigeminal)
joining of separate motor root of CN V to sensory root
-the separate motor root nerve which lies beneath the trigeminal sensory ganglion (joins mandibular sensory division of trigeminal) next to the big sensory ganglion at the foramen ovale
ganglion
where the nerve cell bodies are and synapse
great auricular nerve
C2,C3
which cranial nerves enter/exit cranial cavity via foraminae in anterior cranial fossa
-CN I
which cranial nerves enter/exit cranial cavity via foraminae in middle cranial fossa
- CN II
- CN III
- CN IV
- CN Va,Vb,Vc
- CN VI
which cranial nerves enter/exit cranial cavity via foraminae in posterior cranial fossa
- CN VII
- CN VIII
- CN IX
- CN X
- CN XI
- CN XII
which foraminae does the olfactory nerve (CN I) enter/exit cranial cavity via
cribiform plate
which cranial nerves enter/exit cranial cavity via superior orbital fissure
- CN III
- CN IV
- CN VI
- CN Va
which foraminae does the optic nerve (CN II) enter/exit cranial cavity via
optic canal
which foraminae does the oculomotor nerve (CN III) enter/exit cranial cavity via
superior orbital fissure
which foraminae does the trochlear nerve (CN IV) enter/exit cranial cavity via
superior orbital fissure
which foraminae does the abducent nerve (CN IV) enter/exit cranial cavity via
superior orbital fissure
which foraminae does the opthalmic division of trigeminal (CN Va) enter/exit cranial cavity via
superior orbital fissure
which foraminae does the maxillary division of trigeminal (CN Vb) enter/exit cranial cavity via
foramen rotundum
which foraminae does the maxillary division of trigeminal (CN Vc)/and motor root of trigeminal enter/exit cranial cavity via
foramen ovale
location of pituitary stalk
- within diaphragm sellae
- pituitary gland is located inferior to diaphragm sellae
trigeminal sensory ganglion
- within middle cranial fossa
- all the sensory fibres from Va, Vb and Vc join together here and the cell bodies of Cn V’s peripheral sensory neurones are found here
- > V motor root lies beneath the sensory ganglion and passes through the foramen ovale alongside Vc
which foraminae does the middle meningeal artery enter/exit cranial cavity via
foramen ovale (within middle cranial fossa)
relationship between CN V and cavernous sinus
- cavernous sinus is close to trigeminal
- some branches of the trigeminal nerve pass through cavernous sinus (Va and Vb?) via the lateral wall
posterior aspect of coronal section of cavernous sinus (structures within)
- between dura and bone
- alot of nerves pass through the lateral wall of the cavernous sinus/dura (occulomotor/CN III, trochlear/CN IV, CNVa, CNVb)
- internal carotid artery and abducent nerve/CN VI pass through cavernous sinus
- Vc is situated on the outside of the cavernous sinus
greater and lesser petrosal nerve
- pass through bone
- lie close to trigeminal nerve
- wrapped round middle meningeal artery at foramen spinosum (?)
- lesser petrosal nerve goes from CN IX/glossopharyngeal nerve to parotid gland?
- petrosal form glossopharyngeal and goes down to supply parotid gland, where it hitches a ride with one of the branches of the trigeminal nerve
motor innervation of the parotid gland
- parasympathetic innervation from glossopharyngeal nerve to the parotid gland
- lesser petrosal branch of the glossopharyngeal nerve synapses at the otic ganglion (pre-ganglionic parasympathetic nerves synapse) and postganglionic fibres are carried in/hitch a ride on the auriculotemporal nerve (sensory branch of CN V3) and gives off the parotid branch which supplies the parotid gland with secretomotor fibres
auriculotemporal nerve
-sensory branch of mandibular division of trigeminal (CNV3)
