Cranial Nerves 2 Flashcards
What is the path of the sensory component of the trigeminal nerve?
Sensory neurons (1st order) from the 3 subdivisions (V1, V2, V3) synapse with cell bodies in trigeminal ganglion (except proprioception) –> terminate on sensory nuclei of the trigeminal nerve (2nd order) –> 3rd order neurons terminate in primary sensory cortex
What is the sensory function of the trigeminal nerve?
It is the main somatosensory nerve for the head (skin + mucosa + teeth). It detects pain, temperature, discriminative touch and proprioception.
What is the motor function of the trigeminal nerve?
Muscles of mastication (movement of temperomandibular joint)
1) Masseter, temporalis, lateral and medial pterygoids
2) Tensor tympani – prevents ear drum from vibrating too much dampens sound
3) Tensor veli palatini – prevents food from entering nasopharynx, opens auditory tube
4) Mylohyoid and digastric muscle
What is the path of the motor component of the trigeminal nerve?
Arises from the brainstem –> travel inferior to the trigeminal ganglion (do not enter) –> merge with sensory fibres of the mandibular nerve
Describe the V1 subdivision of the trigeminal nerve.
Ophthalmic nerve (V1) – sensory
1. Path: lateral wall of the cavernous sinus (inferior to CN4) –> exit cranial cavity/enter the orbit via the superior orbital fissure
2. Branches carry sensation from the cornea + mucosa of upper nasal cavity + skin of upper eyelid and forehead
a. Supraorbital
b. Supratrochlear
Describe the V2 component of the trigeminal nerve.
Maxillary nerve (V2) – sensory
1. Path: lateral wall of cavernous sinus (inferior to V1) exit cranial cavity via foramen rotundum enter pterygopalatine fossa where it breaks up into branches
2. Branches carry sensation from mucosa of nasal cavity + upper jaw and teeth + maxillary sinuses + skin of the lower eyelid, nose, and upper lip.
a. infraorbital nerve
b. superior alveolar plexus
Describe the V3 segment of the trigeminal nerve.
Mandibular nerve (V3) – sensory + motor
1. Path: exits the cranial cavity via foramen ovale –> enter the infratemporal fossa (medial to the temporomandibular joint) –> breaks up into small branches
2. Branches supply the mucosa of cheek and temporal region skin
a. auricular temporal nerve
b. lingual nerve (sensory to anterior 2/3 of tongue)
c. inferior alveolar plexus: enters the mandible to supply the mucosa and teeth of the lower jaw and skin of the cheek
Patients with trigeminal nerve lesions will have…
a. Decreased sensation to the face
b. Increased pain
c. Impaired chewing
d. Trigeminal neuralgia: condition that causes painful sensations similar to an electric shock on one side of the face
Where does the facial nerve arise from?
Pontomedullary junction
What are some motor functions of the facial nerve?
i. Muscles of facial expression
ii. Stapedius muscle (in middle ear)
iii. Posterior belly of digastric + stylohyoid muscles
iv. Facial motor nucleus (pons), loops around the abducens colliculi
What are the parasympathetic functions of the facial nerve?
Glands of the head (except parotid): lacrimal, submandibular, sublingual, mucous membranes
What are the sensory functions of the facial nerve?
Taste from anterior 2/3 of tongue
What is the general path of the facial nerve?
Emerges from pontomedullary junction –> enters internal acoustic meatus –> travels toward ear along with CN8
What is the motor pathway of the facial nerve?
i. Facial motor nucleus branch travels through the facial canal exits the skull through the stylomastoid foramen enter the parotid gland (does not supply) branches into nerves supplying muscles of facial expression
1. gives off a branch to the stapedius muscle in the middle ear before exiting the skull
What is the parasympathetic pathway of the facial nerve?
ii. Superior salivatory nucleus branch splits into 2 branches
1. one travels forward to synapse on the pterygopalatine ganglion hitchhike on branches of the maxillary nerve lacrimal glands
2. one forms a branch called the chorda tympani passes through the floor of the ear and hitchhike on the lingual nerve submandibular + sublingual salivary glands
What is the sensory pathway of the facial nerve?
iii. Solitary tract forms the chorda tympani –> passes through the floor of the ear and hitchhike on the lingual nerve –> anterior 2/3 of the tongue (taste)
What does injury to the facial nerve look like?
a. Loss of taste to anterior 2/3 of tongue
b. Loss of function of muscles of facial expression droopy mouth (Bell’s palsy), unable to close eyes (ipsilateral)
c. Distorted taste
d. Loss of control of submandibular and sublingual salivary glands
e. Hyperacusis – sensitivity to noise because of the loss of stapedius dampening of the auditory ossicle chain
Where does the vestibulocochlear nerve originate from?
Pontomedullary junction
What are the functions of the VC nerve?
a. Vestibular (balance) – from otolith organs (utricle, saccule) and semicircular canal
b. Cochlear (hearing) – from Organs of Corti in cochlea (has hair-like structures)
What is the pathway of CN8?
Enters the cranial cavity via the internal acoustic meatus –> enters the brainstem in the pontomedullary junction (lateral to CN7) –> goes to the vestibular + cochlear nuclei
What are the effects of injury to CN8?
Hearing loss, loss of balance, dizziness, nausea, nystagmus (involuntary, rapid eye movement)
