Anatomy 3 - Cranial nerves (clinical testing) Flashcards
What is the forebrain ?
the anterior part of the brain, including the cerebral hemispheres, the thalamus, and the hypothalamus.
Label where each of the CN’s attach to the brain
- CN I - Forebrain
- II - Forebrain
- III - Midbrain
- IV - Midbrain
- V1, 2, 3 - Pons the lateral aspect of it, this is the only CN to connect to the pons
- VI - Pontomedullary junction
- VII - Pontomedullary junction
- VIII - pontomedullary junction
- IX - Medulla
- X - Medulla
- XI - emerges from the anterior rootlets of the first 5-6 cervical segments of the spinal cord
- XII - Medulla
What modality of nerves is carried by each CN ?
- CN I - Special sensory
- II - Special sensory
- III - Motor & parasympathetics
- IV - Motor
- V1, 2, 3 - V1 &2 just sensory, V3 - sensory & motor
- VI - Motor
- VII - Special sensory, motor & parasympathetics
- VIII - Special sensory
- IX - Special sensory, sensory, motor & parasympathetics
- X - Sensory, motor & parasympathetics
- XI - Motor
- XII - Motor
What is the function of CN I and describe its route to the brain
Function is to convey the sense of smell
- Cell bodies in the olfactory part of the nasal mucosa collect into bundles forming olfactors nerves ( R & L)
- The nerve fibres pass through tiny foramina in the cribriform plate of the ethmoid bone & enter the olfactory bulb in the anterior cranial fossa
- Axons from the olfactory bulb form the olfactory tract which conveys impulses to the brain by connecting to the forebrain
What is the function of the optic nerve (CN II) and describe its route to the brain
Function is to convey visual information
- Optic nerves pass posteromedially in the orbit exiting through the optic canal to enter the middle cranial fossa
- Here the optic nerves form the optic chaism, in the optic chiasm the optic nerve fibres from the nasal (medial) half of the retina decussate & join the other sides uncrossed nerve fibres from the temporal (lateral half) of the retina to form the optic tracts
- Optic tracts then terminate in the thalamus (this is where the optic nerves essentially connect with the forebrain)
- Axons are then relayed from the thalamus to the visual cortices of the occipital lobes of the brain
What is the function of the oculomotor nerve (CN III) and describe its route from the brain
Function is to provide motor innnervation to Sup, rectus, Inf. rectus, Medial rectus & inferior oblique (remember SO4, LR6, AL3) and the levator palpebrae superioris
It also supplies parasympathetics to the smooth muscles of the sphincter pupillae which causes constriction of the pupil & ciliary muscle to produce accommodation (allows lens to become more rounded) for nearer vision (the ciliary muscle contraction bit is always a mind fuck)
- Emerges from the midbrain
- Enters the orbit through the superior orbital fissure
- Supplies the muscles it innervates
- Parasympathetic from the nerve are carried to the ciliary ganglion and then innervate ciliary muscle and sphincter pupillae
What is the function and route of the trochlear nerve ?
Function is to supply the superior oblique muscle
- It arises from the lateral aspect of the midbrain
- Exits through the superior orbital fissure to then supply the SO
What is the function and route of the abducent nerve
Function is to innervate the lateral rectus muscle
- Emerges from the pontomedullary junction
- Enters orbit through superior orbital fissure and then supplies LR
Describe the route of CN V (trigeminal nerve)
Connects to the pons
Then extends forming trigemnial ganglion where the 3 branches then split off:
- V1 - exits through the superior orbital fissure
- V2 - exits via the foramen rotundum
- V3 - exits via the foramen ovalae
Describe the sensory supply of CN V1 and V2
CN V1 - opthalamic division:
- Supplies cornea, upper conjunctiva, mucosa of antero-superior nasal cavity.
- Frontal & ethmoid sinuses
- Skin of the dorsum of the nose, superior eyelid, forehead & scalp
- Ant & post cranial fossa
CN V2 - maxiallary division:
- Supplies conjunctiva of the inferior eyelid
- Mucosa of the postero-inferior nasal cavity
- Maxillary sinus
- Palate, anterior part of the superior oral vestibule, maxillary teeth
- Skin of the lateral external nose, inferior eyelid, anterior cheeck & upper lip
Describe the sensory and motor supply by CN V3 (mandibular division)
Sensory:
- Mucosa of the ant. 2/3rds of the tongue
- Floor of the mouth
- Inferior oral vestibule
- Mandibular teeth
- the skin over the mandible and temporomandibular joint (apart from the angle of the mandible – supplied by C2,3 spinal nerves)
- Part of the external ear (auricle, upper external auditory meatus, & tympanic membrane)
- Middle cranial fossa
Motor:
- Muscles of mastication
- Mylohyoid muscle
- Ant. belly of digastric
- Tensor tympani
- Tensor veli palatine
Describe the route of the facial nerve
- Emerges from the pontomedullary junction
- Exits via internal acoustic meatus
- Travels through petrous bone via facial canal - during course through facial canal it gives rise to greater petrosal nerve, chorda tympani nerve & the nerve to the stapidus
- The main part of the facial nerve continues through facial canal and exits via stylomastoid foramen
- After exiting the skull it runs just ant. to the ear
- It then continues to the parotid gland (doesnt innnervate it) the nerve then splits to supply the muscles of facial expression
Describe what the facial nerve supplies
- Greater petrosal nerve supplies the sublingual & submandibular salivary glands, also the lacrimal, nasal pharyngeal & palatine glands (mucous glands)
- Nerve to the stapidus - supplies the stapidus
- Chorda tympani - supplies special sensory (taste) to ant. 2/3rds of the tongue, also supplies parasympathetics to the submandibular & sublingual glands
- Rest of the facial nerve in the parotid gland - supplies muscles of facial expression
(Note there are a couple other divisions of the facial nerve but think it was too much detail refer to handwritten notes if needed)
Describe the route and function of the vestibulochoclear nerve (CN III)
Function is special sensory nerve of hearing & equilibrium
- It emerges from the pontomedullary junction
- Exits via the internal acoustic meatus and then spilts into the vestibular and chochlear nerves
Describe the route of the glossopharyngeal muscle (CN IX)
- Emerges from the lateral aspect of the medulla
- Exits cranium via the jugular foramen
- Follows the stylopharyngeus muscle
- Passes between the superior and middle pharyngeal constrictor muscles to reach the oropharynx & tongue
What does CN IX supply
General sensory to:
- the posterior 1/3rd of the tongue
- the mucosa of most of the nasopharynx
- the mucosa of all of the oropharynx
- the mucosa of some of the laryngopharynx (some overlap with CN X territory)
- the palatine tonsil
- the eustachian tube
- the middle ear cavity
special sensory to:
- The vallate papillae (with taste buds) of the posterior 1/3rd of the tongue
visceral afferent to
- the carotid sinus baroreceptors (for BP) & the carotid body chemoreceptors (for CO2 & O2 levels)
Somatic motor to:
- stylopharyngeus
parasympathetic (secretomotor) to:
- the parotid salivary gland
Describe the route of the vagus nerve
- Arises from the lateral aspect of the medulla
- Leaves cranium via jugular foramen
- Continues inferiorly in the carotid sheath to the root of the neck- where it gives off branches to palate, pharynx & larynx
- Supplies branches to the bronchi, bronchi & lungs
- Both R and L vagus nerves pass inferior to the lung roots and then onto the oesophagus
- The travel with the oesophagus through the diaphragm where they supply the oesophagus, stomach, & intestinal tract as far as the L colic flexure
Describe the function and route of the spinal accessory nerve
- Emerges from series of rootlets from the first 5 or 6 cervical segments of the spinal cord
- Exits cranium via jungular foramen
- Descends along the internal carotid artery
- Innervates the SCM and trapiezius
Go over this summary for CN testing
