fibres and innervation Flashcards
what type of fibres does CN I carry and what does it innervate
special sensory - smell
what type of fibres does CN II carry and what does it innervate
special sensory - vision
what type of fibres does CN III carry and what does it innervate
motor fibres - to extraocular muscles except superior oblique and lateral rectus
parasympathetic fibres - to ciliary muscle and pupillae constrictor
what type of fibres does CN IV carry and what does it innervate
motor fibres - to superior oblique muscle of eye
what type of fibres does CN V1 carry and what does it innervate
general sensory - to upper third of face (forehead, cornea, nose)
what type of fibres does CN V2 carry and what does it innervate
general sensory - to middle third of face (maxilla, upper lip, palate)
what type of fibres does CN V3 carry and what does it innervate
general sensory - to lower third of face (mandible, lower lip, anterior 2/3 of tongue)
motor:
- muscles of mastication
- mylohyoid
- anterior belly of diagastric (both inferior alveolar branch)
- tensor veli palatini (soft palate)
- tensor tympani (middle ear)
what are the muscles of mastication
massester, temporalis, medial pterygoid, lateral pterygoid
what type of fibres does CN VI carry and what does it innervate
motor fibres - lateral rectus muscle of eye
what type of fibres does CN VII carry and what does it innervate
motor fibres:
- muscles of facial expression
- posterior belly of digastric muscle
- stylohyoid muscle
- stapedius muscle (stapes bone in ear)
special sensory - taste to anterior 2/3 of tongue (chorda tympani)
general sensory - skin of external acoustic meatus (ear)
parasympathetic fibres - innervates all glands in head and neck except parotid (greater petrosal nerve innervates lacrimal and mucosal glands, chorda tympani innervates submandibular and sublingual glands)
what are the muscles of facial expression
- orbicularis oculi (around eyes)
- nasal muscles
- orbicularis oris (around mouth)
- buccinator (helps puff cheeks out)
- occipitofrontalis
describe the course of the facial nerve
- enters internal acoustic meatus with CN VIII
- exits IAM and enters facial canal
- forms geniculate ganglia in facial canal
- gives off greater petrosal nerve (parasymp), chorda tympani (taste), and nerve to stapedius
- exits skull via stylomastoid foramen
- gives off posterior auricular nerve (general sensory to ear), digastric and stylohyoid nerves
- passes through parotid gland
- gives off 5 branches to muscles of facial expression:
- temporal
- zygomatic
- buccal
- mandibular
- cervical
describe the course of the mandibular division of the trigeminal nerve
- gives off 4 branches in the infra-temporal fossa:
- buccal nerve
- auriculotemporal nerve
- lingual nerve
- inferior alveolar nerve (passes through mandibular foramen to innervate the lower teeth)
- superior alveolar nerve is branch of V2
what type of fibres does CN VIII carry and what does it innervate
special sensory - balance
special sensory - hearing
what type of fibres does CN IX carry and what does it innervate
special sensory - posterior 1/3 of tongue
parasympathetic - parotid gland
motor - stylopharyngeus muscle (pharynx)
general sensory - oropharynx, carotid body and sinus, posterior 1/3 of tongue, middle ear, eustachian tube
what are the carotid body and sinus?
both found at the bifurcation of the CCA
carotid body:
- chemoreceptor
- measures O2, CO2 and pH in the blood
- important modulator of cardiorespiratory function
carotid sinus:
- baroreceptor
- measures blood pressure in the CCA
what type of fibres does CN X carry and what does it innervate
parasympathetic - smooth muscle of trachea, bronchi, GI tract, cardiac muscle
special sensory - taste to epiglottis and base of tongue/palate
general sensory - skin of external acoustic meatus, laryngopharynx, larynx. visceral sensation to heart and abdominal organs
motor fibres:
- muscles of soft palate (except tensor veli palatini)
- muscles of pharynx (except stylopharyngeus)
- muscles of larynx (recurrent layrngeal nerve supplies all but cricothyroid muscle - innervated by superior laryngeal nerve) - both are branches of CN X
what are branches of the vagus nerve
- left recurrent laryngeal nerve (loops under aortic arch)
- right recurrent laryngeal nerve (loops under right subclavian artery)
- superior laryngeal nerve
- pharyngeal branches
- cardiac branches
- abdominal branches
what does the superior laryngeal nerve supply
cricothyroid muscle
the only intrinsic laryngeal muscle not innervated by the left recurrent laryngeal nerve
what type of fibres does CN XI carry and what does it innervate
what triangle of the neck is this nerve found in?
motor - to trapezius and sternocleidomastoid muscles
posterior triangle
what type of fibres does CN XII carry and what does it innervate
where on the skull base is the CN XII canal found?
motor - intrinsic and extrinsic muscles of the tongue
posterior cranial fossa, on the rim of the foramen magnum
what cranial nerves travel through the cavernous sinus?
what other important structure passes through this sinus?
- oculomotor nerve
- trochlear nerve
- ophthalmic and maxillary divisions of trigeminal nerves (V1 & V2)
- abducens nerve
- internal carotid artery
- (this sinus is important clinically as it is a site of thrombosis and spread of infection)
why does stroke spare the forehead?
each side of the upper part of the face is innervated by both hemispheres. (dual innervation)
fibres going from one hemisphere to the upper face either decussate to go the contralateral side or don’t decussate to go to ipsilateral side of upper face.
so lesion in one hemisphere due to stroke spares contralateral forehead because it is also innervated by the other hemisphere
fibres going to each side of middle and lower face come from one hemisphere only (all decussate)
why does bell’s palsy affect a whole unilateral side of the face?
it is a lower motor neuron disease so it simply affects all the motor neurons going to the face from the right or left facial nerve (CN VII) - is not concerned with the origin of the fibres
