Cranial nerves: sensorimotor function Flashcards
What are cranial nerves?
There are 12 pairs of cranial nerves and they arise from the cerebrum or brain stem
Their nuclei are essentially laid out from medial lateral in the brainstem and sequentially, longitudinally in the midbrain, pons and medulla
They serve 7 modalities
Motor - somatic efferent, special visceral efferent to muscle derived from branchial arch, general visceral efferent (parasympathetic)
Sensory - Somatic afferent, special visceral afferent (smell and taste), general visceral afferent, special somatic afferent (sight, hearing and balance)
They pass through the foramina on cranial bones
With the exception of vagus, all cranial nerves innervate structure of head and neck
Where are the different cranial nerves located ?
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What are the features of the olfactory nerve (I) ?
Olfactory region - upper 1/3rd of the nasal cavity (superior nasal concha, roof of nasal cavity and nasal septum)
Olfactory nerves pass through the Cribriform Plate and synapses at the olfactory bulb
- Anchored by dura mater
Axons of neurons in olfactory bulb form olfactory tract
Project to the olfactory cortex FIRST and then to the limbic system, hypothalamus and reticular formation
Basal cells can differentiate to bipolar (olfactory) neurons - regeneration in adult human
What is Anosmia ?
Anosmia;
- Olfactory neuropathy caused by upper respiratory tract infection (kills bipolar neurons)
- Trauma, causing the brain and olfactory bulb to move may tear the olfactory nerves
Fractures of the cribriform plate may cause CSF rhinorrhoea (blood stained CSF laking from the nose)
What are the features of the trigeminal nerve (V) ?
The largest cranial nerve
Has 3 divisions; V1, V2, V3
- V1 and V2 afferent only
- V3 is both afferent and efferent
Supplies general, conscious sensation to most of the face, head and associated orbital, nasal and oral cavities
Has 4 nuclei (and 2 roots)
- Sensory roots: to mesencephalic nucleus, principle (pontine) nucleus, spinal nucleus
- Motor root - from motor nucleus
The sensory and motor roots emerge from the mid-pons snd run towards the trigeminal ganglion
What are the 3 divisions of the Trigeminal V ganglion ?
3 divisions of the Trigeminal V ganglion;
- The ophthalmic (V1) division -> lateral wall of cavernous sinus -> superior orbital fissure -> orbit
- The maxillary (V2) division -> lateral wall of the cavernous sinus -0> foramen rotundum -> pterygopalatine fossa
- The mandibular division (V3) -> foramen ovale -> infratemporal fossa (mixed)
What are the features of the opthalamic nerve (V1)?
Sensory only division
Carris sympatheitc fibres from the carotid plexus from T1+2
Gives off meningeal branch near Trigeminal ganglion that supplies dura
Has 3 main branches;
- Lacrimal
- Frontal (biggest)
- Nasociliary
What are the 3 different branches of the Ophthalmic Nerve (V1) and their functions?
Lacrimal nerve
- Supplies goral sensation to the lacrimal gland, conjunctiva and upper eyelid in the vicinity of the lacrimal gland
- Also carries parasympathetic fibres of facial nerve (VII) to the lacrimal gland
Frontal nerve;
- Divides into supra-orbital and supra-trochlear nerves
- Supplies the upper eyelid and conjunctiva, frontal sinus and the scalp as far back as the vertex
Nasociliary nevre;
- Gives off long ciliary nerve(s), anterior and posterior ethmoidal nerves, before continuing as infratrochlear nerve
- Sensation to the cornea of the eye -> afferent limb of corona reflex
- Tip of the nose
What are the features of the Maxillary nerve (V2)?
Sensory only division
Sends zygomatic and infraorbital branches into the orbit via the inferior orbital fissure
Infraorbital nerve exits the orbit via infraorbital canal -> infraorbital foramen
Sends palatine and superior alveolar branches to the palate and upper teeth and upper gum
Supplies;
- Lateral forehead
- Zygomatic region
- Lower lid
- Side of nose
- Cheek (anteriorly)
- Upper lip
What are features of the mandibular nerve (V3)?
Contains both sensory and motor fibres
Gives off auricotemporal, masticatory, lingual and inferior alveolar branches
Supplies;
- Skin of Auricle and Temple
- Cheek, posteriorly
- Lower lip and chin
- General sensation to the anterior 2/3rd of tongue, and floor of the mouth
- The lower gums and teeth
The skin over the angle of the mandible is not supplied by V, but by cervical plexus
Supplies;
- Muscles of Mastication: lateral, Pterygoid, Medial Pterygoid, Masseter and Temporalis
- Tensor typmani
- Tensor veli palatini
- Mylohyoid
- The anterior belly of digastric
How does the Jaw Jerk work?
A tendon hammer is tapped on crevice above chin to test trigeminal nerve
What are the features of the Oculomotor nerve (III)
Oculomotor nucleus in midbrain
Motor only (somatic and visceral)
Passes between posterior cerebral and superior cerebellar arteries, before lying close to the posterior communicating artery
Runs anteriorly on the lateral wall of the cavernous sinus
Passes through superior orbital fissure and enters orbit
Divides into superior and inferior divisions (rami)
Passes through common tendinous ring of Zinn
What are the features of the trochlear nerve (IV)?
-Motor only
- Nucleus in midbrain
- Nerve exits brainstem from its posterior surface (breaks rule of cranial nerves)
- Runs anteriorly around cerebral peduncle
- Enters cavernous sinus
- Passes through superior orbital fissure
- Supplies Superior Oblique
What can injury to the Trochlear nerve cause?
Injury to the Trochlear nerve results in the patient no being able to look medially and inferiorly
Patient experience diplopia (double vision) while walking down stairs or reading a book
What are the features of Abducent Nerve (VI) and what does injury here cause?
- Motor only
- Nucleus in pons
- Exits brainstem medially between pons and medulla
- Enters cavernous sinus (Only cranial nerve in here, rest on lateral wall)
- Enters orbit through superior orbital fissure
- Supplies lateral rectus
Injury to right abducens nerve would cause diplopia (double vision) when looking right - the right eye would not abduct fully - abducent paralysis
What are the features of the facial nerve (VII)?
Mixed nerve; nuclei in pons
Motor nucleus; Nuc. Solitarius (sensor)
Motor nucleus has a superior and inferior divisions which innervate upper and lower facial muscle respectively
The superior division (upper facial) is connected to the ipsilateral and contralateral motor cortices
the inferior division (lower facial) is connected to the contralateral cortex only
What journey does the facial nerve (VII) take?
The motor root emerges in the angle between the lower pons and the cerebellum - the cerebellopontine angle
Enters the temporal bone at the internal acoustic meatus, with VII and the labyrinthine artery
Enters facial canal within the temporal bone
The cell bodies for taste fibres are in the geniculate ganglion
Sends a branch to stapedius
Receives (gives off!) chords tympani
Exits through temporal bone through stylomastoid foramen
Sends branches to supply occipitals and auricular muscles
Enters the parotid gland and divides too form a plexus within (superficial to the external carotid artery and retromandibular vein)
5 nerves branch off and supply the muscles of facial expression, posterior belly of digastric and stylohyoid
- Remember by Two Zebras Befriended My Cat
(temporal, zygomatic, buccal, mandibular, cervical)
What occurs in facial nerve injury?
At cerebellopontiine angle;
- Balance and hearing problems
- Ipsilateral facial muscle paralysis
- Hyperacusis (pain on loud sounds)
- Taste disturbances
- Reduced lacrimal secretion
Within the petrous temporal bone, depending on exact location;
- Reduced lacrimal secretion
- Hyperacusis (pain on loud sounds)
- Taste disturbance
- Ipsilateral facial muscle paralysis
Distal to the stylomastoid foramen;
- Ipsilateral facial muscle paralysis
- Dry eye, drooling
What is the difference between Central and Peripheral facial palsy ?
Central facial palsy;
- Upper motor neuron lesion
- Can raise eyebrows, cannot blow cheeks
Peripheral facial palsy;
- Lower motor neuron lesion
- Cannot raise eyebrows or blow cheeks
What is the cornea reflex?
The corneal blink reflex is caused by a loop between the trigeminal sensory nerves (ophthalmic division) to the trigeminal sensory nucleus and they send out motor impulses through the facial motor nucleus which causes obicularis oculi to contract and shut eyelid.
What is the function of the Glossopharyngeal (IX)?
Mixed nerve; nuclei in medulla
Motor nucleus is Nuc. ambiguus, sensory nucleus is Nuc. Solitarius
Tympanic branch to middle ear, tympanic membrane and mastoid air cells
Receives;
- General sensation from middle ear, oropharynx, palatine tonsil, inferior aspect of soft palate, posterior 1/3 tongue
- General visceral sensation from carotid sinus and carotid body
- Special visceral sensation (taste) from posterior 1/3 tongue
Motor supply to stylopharyngeal m.
What are the features of the Vagus (X)?
Mixed nerve; nuclei in medulla
Nuc. ambiguus (motor)
Nuc. solitarius (sensory)
Leaves brainstem, passes through jugular foramen with IX and XI
General somatic sensation from deep auricle and parts of the external acoustic meatus (Hence why cleaning ear with cotton bud can cause gagging reflex)
General visceral sensation from the laryngopharynx and larynx
Motor supply to the started muscles of the pharynx and larynx
(Muscles from 4th and 6th pharyngeal arches will be supplied from)
How does the gag reflex work?
Sensation is felt by the receptors in the back of tongue/pharynx and this sends the impulse along a glossopharyngeal nerve (IX) to the brainstem to synapse in nucleus solitarius and uses the vagus nerves to trigger muscle contraction in the pharynx, tongue and oesophagus. It also has a branch that synapses in the spinal cord and joins thee upper thoracic ganglia to contract the stomach.
There is general somatic sensation from deep auricle and parts of the external acoustic meatus which can trigger this pathway when cleaning ear with cotton bud
What is the function of the accessory nerve (XI)?
Motor only
Spinal root; from C1-5
Cranial root; from nuclei. ambiguus
Spinal root enters cranial cavity, through foramen magnum
- joins with cranial root
Both roots exit skull via jugular foramen as accessory nerve
Crosses the posterior triangle in the investing layer of fascia, surrounded by lymph nodes
Spinal accessory supplies trapezius and sternocleidomastoid
What is the function of the hypoglossal nerve (XII)?
Motor only
Hypoglossal nucleus in medulla
Exits the brainstem anterior to olive
Emerges from the hypoglossal (anterior condylar) canal
Descends the neck, passing lateral to both the internal and external carotid arteries and associated with a loop of cervical nerves that supply the strap muscles of the neck
Enters oral cavity under the tongue, between mylohyoid and hypoglossus to supply all the tongue muscles except palatoglossus
If the hypoglossus was injured what would you expect to see?
Ipsilateral tongue weakness, therefore the tongue deviates to the side of the lesion
Give a general summary of all the cranial nerves?
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Give a general summary of the tongue?
Posterior 1/3;
- Taste by glossopharyngeal
- General sensation by glossopharyngeal
Anterior 2/3;
- taste by chords timpani of Nerves Intermedius (facial)
- General sensation by lingual nerve of V3
Motor supply to all muscles is Hypoglossal (XII) except palatoglossus
Give a general summary of the pharynx ?
Pharynx (sensory)
Oropharynx, palatine tonsil, inferior aspect of soft palate, posterior 1/3 tongue; Glossopharyngeal (IX)
Laryngopharynx, vallecula and epiglottis; Vagus (X)
Soft palate; V2 glossopharyngeal
Nasopharynx; maxillary (V2)
