22-09-23 - Cranial nerves: sensorimotor function Flashcards
(37 cards)
Learning outcomes
How many pairs of cranial nerves are there?
How are their nuclei laid out?
What 7 modalities do cranial nerves serve?
What structure do cranial nerves pass through?
What structures do cranial nerves innervate?
- There are 12 pairs of cranial nerves arise from the cerebrum or brain stem
- Their nuclei are essentially laid out from medial to lateral in the brainstem and sequentially, longitudinally in the midbrain, pons and medulla
- Cranial nerves serve 7 modalities :
- Motor:
1) Somatic efferent
2) Special visceral efferent to muscles derived from pharyngeal arches,
3) General visceral efferent (parasympathetic) - Sensory
1) Somatic afferent
2) Special visceral afferent (smell and taste)
3) General visceral afferent
4) Special somatic afferent (vision, hearing and balance) - Cranial nerves pass through the foramina on cranial bones
- With the exception of vagus, all cranial nerves innervate structures of the head and neck.
Olfactory Nerve (Cranial nerve 1 – CN1).
Where is the olfactory nerve region?
Where do olfactory nerves pass through and synapse?
What are cranial nerves anchored to when they enter the cranial cavity?
What forms the olfactory tract?
Where does the olfactory tract project to?
How is this unique?
- Olfactory Nerve (Cranial nerve 1 – CN1)
- The olfactory region is the upper third of the nasal cavity (superior nasal concha, roof of the nasal cavity and nasal septum)
- Olfactory nerves pass through the Cribriform Plate and synapse at the olfactory bulb –
- Olfactory nerves are anchored by dura mater when they enter into the cranial cavity
- Axons of neurons that synapse in olfactory bulb form olfactory tract
- The olfactory tract projects to the olfactory cortex first and then to the limbic system, hypothalamus and reticular formation
- These connections with the thalamus and the limbic system allow us to remember certain things when smelling certain smells
- Olfaction is unique in this regard, as it is the only sense that goes to the olfactory cortex before going to the thalamus – all other senses go from the thalamus first, then to the cortical centres
Olfactory Nerve (Cranial nerve 1 – CN1).
What do we need in the nasal cavity in order to smell?
What can basal cells differentiate to form?
Why is this unique?
What is anosmia? What can it be caused by?
How can the olfactory nerves potentially tear?
What can cause CSF Rhinorrhoea?
- Olfactory Nerve (Cranial nerve 1 – CN1)
- In the nasal cavity, we need to have moisture in order to fully appreciate smell
- This is because smell molecules must be absorbed in fluid to activate the receptors of bipolar neurons in the nasal cavity
- Basal cells differentiate to bipolar (olfactory) neurons every 40-60 days
- This is unique, as typically in adults, we do not get neuronal regeneration
- Anosmia is olfactory neuropathy caused by upper respiratory tract infection
- 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 leaking from the nose)
Trigeminal nerve (cranial nerve 5 – CN5).
How large is the trigeminal nerve?
How many nuclei/roots does the trigeminal nerve have?
Describe what each of these roots are for.
How large are these roots?
What are the 3 divisions of CN5?
- Trigeminal nerve (cranial nerve 5 – CN5)
- The trigeminal nerve is the largest cranial nerve
- CN5 has 4 nuclei (and 2 roots):
- Sensory roots to:
1) Mesencephalic nucleus
* From the temporomandibular joint and teeth
* For JPS and proprioception
2) Principal (pontine) nucleus
* For touch and pressure
3) Spinal nucleus
* Thin long nucleus
* For pain
* Goes into spinal cord
- Motor root from: Motor nucleus
- Supplies some muscles in the head derived from the first pharyngeal arch
- The Motor root is small as it innervates a couple of small muscles
- The sensory root is large, as it supplies general and conscious sensation to most of the face, head and associated orbital, nasal and oral cavities
- 3 divisions of CN5:
4) V1 and V2 – afferent (sensory only
* Feed into the brainstem
5) V3 – both afferent (sensory) and efferent (motor)
- If V3 is severed/injured, we would lose some sensation, an all motor function from CN5
- If V1 and or V2 is injured/severed, we will lose some sensation from CN5
Trigeminal nerve (cranial nerve 5 – CN5).
Where do the sensory and motor roots of CN5 emerge and run towards?
Where do the 3 divisions of CN5 emerge from?
Describe the root of each
- Trigeminal nerve (cranial nerve 5 – CN5)
- The sensory and motor roots of V emerge from the mid-pons and run towards the trigeminal ganglion.
- The three divisions of V emerge from the trigeminal ganglion:
1) The ophthalmic (V1) division - lateral wall of the cavernous sinus - superior orbital fissure - orbit
2) The maxillary (V2) division - lateral wall of the cavernous sinus - foramen rotundum - pterygopalatine fossa
3) The mandibular division (V3) - foramen ovale - infratemporal fossa
Ophthalmic division (V1 of CN5).
Is V1 sensory or moto? What fibres does it carry?
What branch does it give off?
What are the 3 main branches of the ophthalmic division of CN5?
What structures do these nerves supply?
What type of fibres do they each carry?
- Ophthalmic division (V1) of CN5
- The ophthalmic division (V1) of CN5 is a sensory only division
- It carries sympathetic fibres from the carotid plexus
- V1 Gives off meningeal branch near Trigeminal ganglion that supplies dura
- 3 main branches of the ophthalmic division (V1) of CN5:
1) Lacrimal nerve
* Supplies general sensation to the lacrimal gland, conjunctiva and upper eyelid in the vicinity of Lacrimal gland
* Also carries parasympathetic fibers of facial nerve (VII) to the lacrimal gland
* When we have blood shot eyes, it is the blood vessels of the conjunctive that are engorged
2) Frontal nerve
* Divides into supra-orbital and supratrochlear nerves
* Supplies the upper eyelid and conjunctiva, frontal sinus and the scalp as far back as vertex
3) Nasociliary nerve
* Gives off long ciliary nerve(s), anterior and posterior ethmoidal nerves, before continuing as infratrochlear nerve
* Provides sensation to the cornea of the eye
* Afferent limb of cornea reflex
* Can test this division by testing sensation on the tip of the nose
Frontal and nasociliary nerve diagrams
Maxillary division (V2) of CN5.
Is this branch motor or sensory?
What 2 sets of branches does V2 give of?
What 6 structures does V2 of CN5 supply?
- Maxillary division (V2) of CN5
- V2 of CN5 is sensory only
- 2 sets of branches maxillary division (V2) gives of:
1) Sends zygomatic and infra-orbital branches into the orbit via the inferior orbital fissure
* Infra-orbital nerve exits the orbit via infra-orbital canal via the infraorbital foramen
2) Sends palatine and superior alveolar branches to the palate and upper teeth
- 6 structures V2 of CN5 supplies:
1) Lateral forehead
2) Zygomatic region
3) Lower lid
4) Side of nose
5) Cheek (anteriorly)
6) Upper lip
Mandibular division (V3) of CN5.
Is this division sensory or motor?
What are the 4 branches of V3 of CN5?
What 5 structures does the sensory root of V3 supply?
What 5 structures does the motor root of V3 supply?
What is the skin over the angle of the mandible supplied by?
- Mandibular division (V3) of CN5
- V3 contains both sensory and motor fibres
- 4 branches of V3 of CN5:
1) Auriculotemporal
2) Masticatory
3) Lingual
4) Inferior alveolar branches - 5 structures the sensory root of V3 supplies:
1) Skin of anterior auricle and temple
2) Cheek, posteriorly
3) Lower lip and chin
4) General sensation from the anterior 2/3 of the tongue, and the floor of the mouth
5) The lower gums and teeth - 5 structures the motor root of V3 supply?
1) Muscles of Mastication: Lateral pterygoid, Medial pterygoid, Masseter and Temporalis
2) Tensor tympani (tenses ear drum)
3) Tensor veli palatini (tenses soft palate)
4) Mylohyoid
5) The anterior belly of Digastric (derived from 1st pharyngeal arch) - The skin over the angle of the mandible is not supplied by V3, but cervical plexus (spinal nerves)
Sensory and motor root supplies of V3 (mandibular division) of CN5 (in picture)
What does the jaw jerk reflex test?
What can an increased jaw jerk reflex indicate?
- The jaw jerk reflex or the masseter reflex is a stretch reflex used to test the status of a patient’s trigeminal nerve (cranial nerve V) and to help distinguish an upper cervical cord compression from lesions that are above the foramen magnum
- An increased jaw jerk reflex is characteristic of supranuclear involvement of the motor portion of the trigeminal nerve and, when exaggerated, may result in a sustained jaw clonus.
- Also, the jaw jerk reflex may be increased by anxiety, usually in association with diffuse physiological hyper-reflexia.
Oculomotor nerve (CN 3).
Which nucleus is the oculomotor nucleus?
Where is this located?
Is CN3 motor or sensory?
- Oculomotor nerve (CN 3)
- The somatic motor nucleus is the oculomotor nucleus, which is located in the midbrain
- CN3 contains somatic and autonomic motor fibres
Describe the 5 parts of the route of the oculomotor nerve (CN3).
How many nerves are there in the cavernous sinus?
- 5 parts of the route of the oculomotor nerve (CN3):
1) Passes between the posterior cerebral and superior cerebellar arteries, before lying close to the posterior communicating artery
* The axons of these neurons leave the brainstem anteriorly
* Aneurysms are more commonly seen in the posterior communicating artery
* Aneurysms of any of these arteries can compress CN3, leading to deficits
2) Runs anteriorly on the lateral wall of the cavernous sinus
3) After passing through the cavernous sinus, CN3 passes through superior orbital fissure and enters the orbit
4) Divides into Superior and inferior divisions (rami)
5) Passes through common tendinous ring of Zinn
* Area of attachment for some ocular muscles
- There are 4 nerves on the lateral wall of the cavernous sinuous and 1 in the middle
More occulomotor (CN3) diagrams (in picture)
Describe the 2 divisions of the oculomotor nerve (CN3).
What structures do they supply?
- 2 divisions of the oculomotor nerve (CN3):
1) Superior branch/rami
* Supplies levator palpebrae superioris (including sympathetics) – Elevates upper eye lid
* Supplies superior rectus – moves eye ball
2) Inferior branch/rami
* Supplies medial rectus, inferior rectus, and inferior oblique muscles
Trochlear nerve (CN4). Is this nerve motor or sensory?
Where is the CN4 nucleus?
Where does it exit the brainstem?
Why is this unique?
What structure does it enter?
- Trochlear nerve (CN4)
- CN4 is motor only
- CN4s nucleus is in the midbrain
- The nerve exits the brainstem from its posterior surface
- This is unique, as the trochlear nerve is the only cranial nerve that leaves the brainstem/brain on the posterior surface, with all others leaving laterally or anteriorly
- CN4 runs anteriorly around cerebral peduncle and enters the cavernous sinus
Trochlear nerve (CN4).
Where does CN4 pass through?
What muscle does it supply?
How does injury to the trochlear nerve affect patients?
How easily can the trochlear nerve be injured?
- Trochlear nerve (CN4).
- CN4 Passes through superior orbital fissure
- It supplies the Superior Oblique muscle
- Injury to the trochlear nerve results in the patient not being able to look medially and inferiorly
- Patient experience diplopia (double vision) while walking downstairs or reading a book
- The trochlear nerve can be easily injured
Abducent nerve (CN6).
Is CN6 motor or sensory?
Where is its nucleus located?
Where does CN6 exit the brainstem?
What structures does it then run through and enter?
What muscle does CN6 supply?
What occurs in CN6 injury?
How easy is it to injury CN6?
- Abducent nerve (CN6).
- CN6 is motor only
- Its nucleus is in the pons
- CN6 exits brainstem medially, between pons and medulla
- It enters the cavernous sinus, runs anteriorly in the cavernous sinus, and enters the orbit through superior orbital fissure
- CN6 supplies the lateral rectus muscle
- Injury to right abducent nerve would cause diplopia when looking right – the right eye would not abduct fully
- 2nd to the trochlear (CN4), The abducent nerve (CN6) is very easy to injured
Facial nerve (CN7). Is CN7 motor or sensory?
Where are its nuclei located?
Describe the 2 divisions of the CN7 motor nucleus.
What muscles do they each innervate?
What motor cortices are they connected to?
- Facial nerve (CN7)
- CN7 is a mixed nerve, with sensory and motor functions
- Its nuclei are located in the pons (motor nucleus, and nucleus solitarius (sensory))
- 2 divisions of the CN7 motor nucleus:
1) Superior division
* Innervates upper facial muscles
* This includes the upper eye lid muscles, and forehead muscles
* The superior division is connected to ipsilateral and contralateral motor cortices (both hemispheres)
2) Inferior division
* Innervates lower facial muscles inferior to the eye level e.g lower eye lid, and almost all muscles of facial expression
* The inferior division is connected to contralateral cortex only (1 hemisphere)
Facial nerve (CN7).
Where does CN7 leave the brainstem?
What structure does it immediately enter?
What are CN7 and CN8 for?
- Facial nerve (CN7).
- CN7 leaves the brainstem at the cerebellopontine angle
- It immediately enters the temporal bone through the internal acoustic meatus, with cranial nerve VIII and the labyrinthine artery
- CN7 is for hearing and CN8 is for hearing and balance
Facial nerve (CN7).
Where does CN7 enter after entering the temporal bone?
What cells bodies are located in the geniculate ganglion?
What structures does CN7 give off/receive in the facial canal?
Where does CN7 exit the temporal bone?
Why is the facial nerve at greater risk in newborns?
- Facial nerve (CN7).
- After entering the temporal bone, the facial nerve (CN7) Enters facial canal (has 2 bends, like a Z) within the temporal bone
- The cell bodies for taste fibres are in the geniculate ganglion (sensory ganglion for the facial nerve – CN7)
- CN7 sends a branch to the stapedius
- Just before exiting the temporal bone, CN7 gives off/receives the chroda tympani, which passes through the medullary cavity in order to join the facial nerve.
- The chorda tympani then goes backwards to the geniculate ganglion nerve where cell bodies are.
- CN7 exits the temporal bone through stylomastoid foramen (between the mastoid process and styloid process)
- In newborns, the mastoid process is not full developed, as newborns don’t use the SCM
- If delivery is via forceps, there is no protection of the facial nerve by the mastoid process, meaning it is at greater risk of injury
Facial nerve (CN7).
Where does the facial nerve send branches to after it leaves the temporal bone?
What occurs after CN7 enters the parotid gland?
What do the 5 branches of the CN7 plexus supply?
What are all of these muscles derived from?
- Facial nerve (CN7).
- After leaving the temporal bone, the facial nerve sends branches to supply Occipitalis and the auricular muscles
- After the CN7 enters the parotid gland, it divides to form a plexus within (superficial to the external carotid artery and retromandibular vein)
- 5 branches of the CN7 plexus supply:
1) Muscles of facial expression
2) Posterior belly of Digastric
3) Stylohyoid - All of these muscles are derived from the 2nd pharyngeal arch, making the facial nerve the nerve of the 2nd pharyngeal arch
Facial nerve (CN7). What are the 5 branches of the CN7 plexus?
What movements they each allow / what muscles do they supply?
What is a pneumonic for these branches?
What nerve supplies the skin over the CN7 plexus branches?
What structure does the CN7 plexus not supply?
- Facial nerve (CN7).
- 5 branches of the CN7 plexus:
1) Temporal branch
* Allows you to raise your eyebrows
2) Zygomatic branch
* Allows for mimes
3) Bucal branch
4) Marginal mandibular branch
* Close relationship with submandibular gland
* Do not confuse this with the mandibular branch, which is for the trigeminal (CN5)
5) Cervical branch
* For the platysma
- A pneumonic for these branches is Two Zebras Befriended My Cat
- The trigeminal nerve (CN5) supplies the skin over the branches of the CN7 plexus
- The CN7 plexus does not supply the angle of the mandible
