5 Flashcards
(115 cards)
1
Q
What is the junction between the pons and medullary called?
A
Ponto-medullary junction
2
Q
What are the four nerves originating from the pons?
A
- Trigeminal (V)
- Abducens (VI)
- Facial (VII)
- Vestibulocochlear (VIII)
3
Q
Describe the abducens nerve (CN 6)
A
- purely motor nerve
- innervates one muscle that abducts the eyeball: lateral rectus (extra-ocular muscle)
- originates from lower pons (Ponto-medullary junction), the runs vertically upwards before being able to pass into cavernous sinus
- DOES NOT run through lateral wall of cavernous sinus
- then enters into ORBIT via SUPERIOR ORBITAL FISSURE
Clinical points
- tested using eye movements (tests CN 3, 4, 5), such as look left look right, eye that doesn’t move is the affected one
- patients present with diplopia (double vision)
- microvascular complication (diabetes/hypertension) can affect the nerve (most common cause)
- susceptible to injury in raised ICP (e.g. due to bleed, tumour, severe headache)
- nerve can be easily stretched in raised ICP since it emerges anteriorly, at ponto-medullary junction before running under the surface of the pons upwards towards cavernous sinus; brainstem is pushed downwards causing tension to be pushed downwards, stretching the nerve
4
Q
What is the pathway of the facial nerve (CN 7)
A
- originates from lower pons (ponto-medullary junction)
- then enters petrous bone via INTERNAL ACOUSTIC MEATUS
- splits into THREE branches within the petrous bone
- branches exit through base of skull in STYLOMASTOID FORAMEN
5
Q
Other than innervation the muscles of facial expression, what else do the extracranial branches of the facial nerve innervate?
A
- innervates posterior belly of digastric
- innervates stylohyoid muscle
6
Q
Describe the functions of the facial nerve (CN 7)
A
- Special sensory: TASTE for anterior 2/3 of tongue
- Autonomic (parasympathetic): lacrimal glands (tears), mucosal glands in nose and roof of mouth, salivary glands (all EXCEPT parotid gland)
- facial nerve runs through parotid gland but DOESNT supply anything to it
- Motor: muscles of facial expression (and scalp)
- nerve to stapedius (in middle ear) which protects ear from sound damage
- General sensory: small area of external ear
- ex. When you eat something and dont like it, sensed by facial nerve
7
Q
Why is the facial nerve known as a mixed cranial nerve?
A
- has different types of nerves (cell bodies) within the brainstem
- has nerves carrying special sense taste
- has autonomic fibres to glands (salivary, lacrimal, mucosal in nose and palate)
- has nerves carrying motor to muscles of facial expression
- has a very small area of sensory innervation within ear
8
Q
What is the genicular ganglion?
A
- where the cell bodies of sensory nerves are located
- for the facial nerve
9
Q
What is the nervous intermedius?
A
-contains sensory and parasympathetic axons
10
Q
How are motor and sensory nerves different in appearance?
A
- motor nerves has the cell body closer to the end of an axon
- sensory nerves have the cell body in the middle of the axon
11
Q
What are the two roots at the cerebellopontine angle for the facial nerve?
A
Motor root and nervus intermedius
12
Q
What are the three branches of the facial nerve that arise in the petrous bone?
A
- Greater petrosal
- Chorda tympani
- Nerve to stapedius
13
Q
Which branch of the facial nerve exits first as we leave the geniculate ganglion?
A
The greater petrosal
14
Q
What does the greater petrosal nerve innervate?
A
-carries parasympathetic fibres to lacrimal, nasal and palatine glands
15
Q
What does the chorda tympani nerve do?
A
- innervates tongue and most salivary glands
- but NOT parotid gland
- allows parasympathetics to reach salivary glands but also carries special sensory TASTE to the anterior 2/3 of tongue
16
Q
What does the nerve to stapedius do?
A
- motor branch that attaches to stapes in ear
- dampens down the vibrations of sounds to stapes so it doesn’t damage it
17
Q
Why is it important to know what area of the facial nerve is damaged?
A
- because it could affect different functions of the face
- if lesion is more proximal, then everything is affected
- will experience dry eyes, droopy face, taste is messed up
- if lesion is more distal, then only muscles of facial expression would be affected
18
Q
What are the clinical points of the facial nerve?
A
- clinical testing is mainly by testing muscles of facial expression (smiling, frowning)
- also test corneal reflex
- CN 7 lesions can present with a variety of signs and symptoms depending on where along the nerve route the pathology is
- important to ask about other symptoms such as hyperacusis (no protection to stapedius), dry eyes, altered taste
- middle ear pathology (in petrous bone) can sometimes involve the facial nerve
- close relationship with vestibulocochlear nerve within posterior cranial fossa and both enter internal acoustic meatus
- extracranial branches of facial nerve have close relationship with parotid gland
19
Q
What is facial nerve palsy (ex. Bell’s palsy)
A
-absence of the muscles of facial expression on one side
20
Q
What is the corneal reflex?
A
- to see if eye closes or not
- afferent limb of reflex is innervated by the opthalmic division of trigeminal nerve
- efferent limb of reflex is innervated by the facial nerve
- if facial nerve is affected then eye will be unable to close
21
Q
Describe the passage of the vestibulocochlear nerve (CN 8)
A
- originates from lower pons (ponto-medullary junction)
- enters into internal acoustic meatus
- becomes vestibulocochlear nerve
- splits and one part goes into cochlea while the other goes into semicircular canals (vestibular system)
22
Q
What is the function of the vestibulocochlear nerve?
A
- is a special sensory nerve
- used for hearing and balance
23
Q
What are the clinical points of the vestibulocochlear nerve?
A
- crude hearing test (whisper 99 in each ear)
- more formal hearing test i.e. pure tone audiometer if investigating hearing loss
- enquire pt. Amount balance
- damage involving cochlea, cochlear component of vestibulocochlear nerve, or brainstem nucleus causing hearing loss (sensorineural)
- pathology involving semicircular canals, vestibular component of vestibulocochlear nerve, or brain nucleus causes DISTURBANCE OF BALANCE (VERTIGO)
- acoustic neuroma
- presbyacusis
24
Q
What is presbyacusis?
A
- Old-age related hearing loss
- typically corrected with hearing aids
25
What is an acoustic neuroma?
- benign tumour involving vestibulocochlear nerve
- as it enlarges, it compresses the nerve
- tumour of the Schwann cells surrounding (vestibular component) of CN 8
- could potentially squash facial nerve as well
- could also rise superiorly and compress trigeminal nerve
- physical presence causes compression of the whole nerve and more or less CNs in close proximity
26
What are the symptoms and signs of an acoustic neuroma?
- unilateral hearing loss
- tinnitus
- vertigo
- numbness, pain or weakness down one half of face
27
What are the four nerves from the medulla?
- Glossopharyngeal (IX)
- Vagus (X)
- Accessory (XI)
- Hypoglossal (XII)
28
What nerves from the medulla exit via the jugular foramen with the IJV?
- Glossopharyngeal (IX)
- Vagus (X)
- Accessory (XI)
29
Where does the hypoglossal nerve exit to?
-exits through the hypoglossal canal?
30
Do all the medulla cranial nerves exit base of skull and enter into the superior part of the carotid sheath? Which nerve stays the longest?
- Yes they all do
| - CN 10 (vagus) stays the longest
31
What are the functions of glossopharyngeal nerve (CN 9)
- Main function: sensory supply of oropharynx, posterior 1/3 tongue and middle ear
- General sensation: (palatine) tonsils and oropharynx, middle ear and tympanic membrane (inner surface), sensory from carotid body and sinus
- special sensory: taste and general sensation of posterior 1/3 tongue
- Autonomic: carries parasympathetic innervation to parotid gland
- Motor: supplies ONE muscle (stylopharyngeus) which assists in swallowing since nerve runs over surface of this muscle
32
Why do we sometimes feel ear pain when we have a sore throat?
- no pathology in ear
| - felt because glossopharyngeal nerve supplies sensory to both throat area and middle ear and tympanic membrane
33
What are the clinical points of glossopharyngeal nerve?
- tested in conjunction with vagus nerve (CN 10), when asking pt. To swallow
- gag reflex (sensory limb): only tested if concerns around swallowing and integrity of nerves involved in this reflex
- stimulate the back of throat, and if pt. Feels it they will wretch or gag
- feeling the stimulation is by glossopharyngeal but wretching in response is the vagus nerve
- taste is not formally tested
- isolated regions of CN 9 is very rare
34
What is the pathway of the vagus nerve (CN 10)?
- originates from medulla
- then goes into jugular foramen
- then enters carotid sheath
- goes through neck, into thorax and abd; gives many branches on its route
35
What is the function of the vagus nerve (CN 10)?
- General sensory: sensory to lower pharynx and WHOLE larynx
- sensory to small part of EXTERNAL ear and tympanic membrane
- Motor: muscles of soft palate, pharynx and larynx
- swallowing and coughing innervated by vagus nerve
- Autonomic: parasympathetics to thoracic (eg. Heart, tracheobronchial tree) and abd viscera
36
What branch of the vagus nerve should I remember?
- recurrent laryngeal nerve
- right one turns under right subclavian
- left one turns under arch of aorta
37
What are the clinical points of the vagus nerve?
- note patient’s speech, cough and ability to swallow
- note movement of uvula and soft palate when saying “aaah”
- gag reflex (efferent limb)
- isolated lesions of CN X are rare
- injury to its branches ex. Recurrent laryngeal nerve following thyroid surgery can cause hoarseness and dysphonia (difficulty in speaking)
38
What is the function of the spinal accessory nerve (CN 11)?
- Motor nerve
- motor to SCM and trapezius
- originates from medulla and takes little rootlets from cervical spine to join it
39
Describe the passage of the spinal accessory nerve
- originates from medulla
- emerges through jugular foramen
- passes deep to SCM and provides its motor innervation
- runs posterolaterally across posterior triangle (superficially)
- enters deep to trapezius and provides its motor innervation
40
What are the clinical points of the spinal accessory nerve?
- Test: shrug shoulders against resistance (trapezius)
- Test: turn head against resistance (SCM)
- spinal accessory nerve runs inferiorly through neck in posterior triangle (i.e. quite superficial)
- wont affect SCM b/c already gave branches off
- susceptible to injury in this area (SCM) (ex. In lymph node biopsies, surgery, stab wound)
41
What is the function of the hypoglossal nerve (CN 12)?
- Motor nerve
- innervates muscles of the tongue (all except one)
- left hypoglossal does left half of tongue and right does right half
- goes through hypoglossal canal
42
What is the passageway of the hypoglossal nerve?
- Originates from medulla and enters hypoglossal canal
- CN 12 runs medial to angle of mandible
- crosses internal and external carotid arteries in neck
- runs under chin to the muscles of the tongue
43
What are the clinical points of the hypoglossal nerve?
- Test: inspection and movement of tongue
- rare for pathology
- damage to CN 12 causes weakness and atrophy of tongue muscles on IPSILATERAL Sade
44
In what week of development do the pharyngeal arches become apparent?
-from week 4 of developing embryo
45
What are the pharyngeal (or branchial) arches?
- sequence of ridges that form in the lateral walls of the embryonic pharynx
- towards the cranial end of the neural tube
- complex tissue system
- embryonic head and neck
- involves many systems of the body, notably the brain, CVS (heart and great vessels), and special sensory organs
46
Is the face formed in the embryo at week 4?
- no distinguishing external features
| - BUT head and neck represent 0.5 length of embryo
47
What does each arch represent?
- rep. A body segment
- each arch has a neurovascular plan
- develops muscles and skeletal elements
48
What does each arch consist of?
- large mesenchyme core (with some neural crest cells that migrate in)
- covered by ectoderm on its external surface
- covered by endoderm on the internal surface
49
Where do the pharyngeal arches arise from and how many are there?
- arise from neck region of embryo
- 5 in total, numbered 1 to 6
- i.e. 5th does not form in humans
- lots of cell division occurs
50
What parts constitute the building blocks of the face from the head and neck region?
- frontonasal prominence which is a single unpaired midline structure
- and pharyngeal arches
- two maxillary prominences (swelling)
- two manidibullar prominences (swellings)
51
What is mesenchyme?
Primitive embryonic CT
52
What does each arch have?
An associated artery, nerve and cartilage bar
53
What is between each arch on the external surface? Describe them
- pharyngeal groove or pharyngeal cleft
- clefts usually disappear EXCEPT the first one which is between the first and second arch
- this cleft becomes the EXTERNAL AUDITORY MEATUS of the ear
54
What is between each arch on the internal surface?
- pharyngeal pouches
- glandular structures arise from these pouches
- parathyroids, thymus and tonsils
- first pouch is the largest and becomes the tympanic cavity
- second pouch becomes palatine tonsil
- third pouch becomes inferior parathyroid and thymus
- fourth pouch becomes superior parathyroid and C cells of thyroid
55
What is the pharyngeal apparatus?
-collection of the pharyngeal arches, grooves (clefts), and pouches
56
Describe the size of the pharyngeal arches?
- first one is largest and gets progressively smaller
| - 4th and 6th are not visible
57
What is the cartilaginous bar of the first pharyngeal arch also known as?
- Meckel’s cartilage
| - gives rise to mandible, malleus and incus bones
58
What do the 4th and 6th arches give rise to?
-thyroid, arytenoids and cricoids (remain cartilaginous)
59
What cranial nerves associate with the pharyngeal arches?
- CN V, VII, IX and X (5, 7, 9, 10)
- have mixed sensory and motor functions
- supply the derivatives of the pharyngeal arches
- CN XI and CN XII have relationship with pharyngeal arch system
60
Why does the recurrent laryngeal nerve of the ages become looped under arch of aorta and subclavian artery?
- due to rearrangement of developing structures
- each pharyngeal arch becomes associated with an aortic arch blood vessel
- appears very organized at first but then embryo develop and structures start to derive from the pharyngeal arches
61
What are the muscular derivatives of the first pharyngeal arch?
- muscles of mastication (CN 5)
- mylohyoid
- anterior belly of digastric*
- tensor tympani
- tensor Veli palatine
62
What are the muscle derivatives of the second pharyngeal arch?
- muscles of facial expression (CN 7)
- stapedius
- stylohyoid
- posterior belly of digastric
63
What are the muscle derivatives of the third arch?
-stylopharyngeus (muscle of pharynx)
64
What are the muscle derivatives of the 4th arch?
- criciothyroid
- levator palatine
- constrictors of pharynx
65
What are the muscle derivatives of the sixth arch?
-intrinsic muscles of the larynx?
66
What are the cartilages of the first arch?
- Meckel’s cartilage
| - Maxillae and zygomatic bones
67
What are the skeletal/cartilages of the second arch?
- Reichert’s cartilage
- superior part of hyoid
- stapes
- styloid process
- stylohyoid ligament
68
What are the skeletal/cartilages of the third arch?
-inferior part of body of hyoid
69
What are the cartilages of the third and fourth arch?
-epiglottis
70
What are the cartilages of the fourth and 6th arch?
-cartilages of the larynx
71
How do the cartilages of the arches start off?
- each arch starts off as a simple rod-shaped cartilaginous structure
- work to keep gills rigid and allow for gas exchange
- rod-like bars get remodelled to make appropriate structure
72
What are the arteries of the first and second pharyngeal arch?
-dont have any, they disappear
73
What is the artery for the third arch?
Internal carotid
74
What is the artery for the fourth arch?
-aortic arch (left) and subclavian artery (right)
75
What are the arteries for the sixth arch?
-pulmonary arteries?
76
What is the nerve for the first arch?
Trigeminal (V)
77
What is the nerve for the second arch?
Facial nerve (VII)
78
What is the nerve for the third arch?
Glossopharyngeal (IX)
79
What is the nerve for the fourth and sixth arches?
Vagus (X)
80
What happens is the pharyngeal clefts do not close up properly?
- branchial cyst or branchial fistulae could occur
- SCM can help identify as it is a key landmark
- marks where normal fusion occurs
- if there is a lump anterior to SCM then it could possibly be a branchial cyst
81
What drives development of the face?
- expansion of the cranial neural tube
- appearance of a complex tissue system associated with:
- cranial gut tube
- outflow of the developing heart
- development of sense organs and the need to separate the resp. Tract from the GI tract
82
What is the first evidence of face development?
-appearance of a depression in the ectoderm on the ventral aspect of the head
83
What is a stomadaeum?
- site of future mouth
| - buccopharyngeal membrane
84
What parts of the face will the frontonasal prominence form?
-forehead, bridge of nose, upper eyelids and centre of upper lip (philtrum)
85
What parts of the face will the laterally paired maxillary prominences form?
- middle third of face
- upper jaw
- most of lip and sides of nose
- cheeks
86
What parts of the face will the paired mandibular prominences form?
- lower third of face
| - lower jaw and lower lip
87
What is the facial primordia?
- consists of first pharyngeal arch (maxillary and mandibular prominences)
- FNP which surrounds ventro-;arterial part of forebrain
- primordia of eyes begin development on lateral side of head
88
What is the first evidence of nose formation?
-appearance of two ectodermal thickenings (nasal placodes) on either side of midline on ventrolateral aspect of FNP
89
What is a placode?
- name given to an area of ectoderm that starts to thicken and differentiate itself from its surrounding tissue to give rise to sensory structure
- also an optic placode from which future ear develops
90
After the nasal placodes are formed, what happens next?
- placodes invaginate and form deep pits known as NASAL PITS
- nasal pits eventually become nostril
- horseshoe-shaped ridge forms around entrance to each nostril
- “arms” of the horseshoe are the medial and lateral nasal prominences
- deepening nasal pits are separated by the oronasal membrane
- oronasal membrane disappears so that the oral and nasal cavities become one continuous space
91
What is the oronasal membrane?
-thing sheet cells that separate the deepening nasal pits which lie dorsal to the stomodaeum
92
After the separation of the nasal pits, what happens next?
- development of the palate
- involves the maxillary prominences and the medial nasal prominences
- medial nasal prominences merge in the midline, separating the nostrils from the mouth and creating the intermaxillary segment
- maxillary prominences fuse with medial nasal prominences
- nasal prominences form the philtrum of upper lip and a small midline component of the palate (primary palate or premaxillary portion)
- palatal shelf grows from each maxillary prominence vertically downwards, on either side of tongue, towards the midline
- they fuse with each other and with primary palate
- fusion creates secondary palate which separates nasal cavity from oral cavity
- mandible grows large enough for tongue to “drop”
93
What is cleft lip and palate?
| Vl
Lateral cleft lip
-failure of fusion of medial nasal prominence and maxillary prominence
Cleft lip and cleft palate
-above combined with failure of palatal shelves to meet in midline
- can be due to genetics and environmental factors, mostly congenital abnormalities
- can be diagnosed antenatally with ultrasound or after delivery
- if left uncorreted, will cause problems with feeding and perch
- most common facial birth defect
- doctor will take neonatal exam before discharge, including feeling the hard palate with a gloved finger to check for the presence of cleft
- clefts can be corrected with surgery
- cleft lips at around 3 months (for cosmetic reasons)
- palate repairs are later at 9-12 months
94
How do the ears develop?
- external auditory meatus develops from first pharyngeal cleft
- middle ear cavity and ossicles develop from first pharyngeal pouch and cartilages of first and second arches respectively
- auricles develop from proliferation within first and second pharyngeal arches surrounding the meatus
95
Explain the positioning of the ears
- external ears develop initially in the neck
- as mandible grows, the ears ascend to the side of head to lie in line with the eyes
- all common chromosomal abnormalities have associated external ear anomalies
96
What is fetal alcohol syndrome?
- no known safe alcohol consumption during pregnancy
- facial Skeleton derived from neural crest cells populating the pharyngeal arches
- neural crest migration as well as development of the brain are known to be extremely sensitive to alcohol
- incidence of FAS and ARND= 1/100 births
- alcohol extremely toxic to developing neurons and neural crest cells
97
What parts of the face does the medial nasal prominence form?
Philtrum, primary palate, mid upper jaw
98
What part of the face does the lateral nasal prominence form?
Cheeks, lateral upper lip, secondary palate, lateral upper jaw
99
What consequence will occur if olfactory nerve is damaged?
Loss of olfaction
100
What will happen if optic nerve or oculomotor nerve is damaged?
Fixed dilated pupil
101
What will happen if optic branch of facial nerve is damaged?
Inability to close eye
102
What will happen if opthalmic division of trigeminal nerve or facial nerve is damaged?
Loss of blink reflex
103
What will happen if there interruption to sympathetic innervation to eyelid?
Partial drooping of eyelid (partial ptosis)
104
What will happen if oculomotor nerve is damaged
Complete drooping of eyelid (complete ptosis)
105
What will happen if maxillary division of trigeminal nerve was damaged? (Trigeminal neuralgia)
Intermittent sharp shooting pain over cheek
106
What will happen if opthalmic division of trigeminal nerve is damaged? (Opthalmic shingles)
Ulcerated lesions over eyelids and cornea
107
What will happen if facial or glossopharyngeal nerve is damaged?
Altered taste sensation
108
What nerves are damaged in numbness of tongue?
Lingual nerve (branch of mandibular division of trigeminal)
109
What nerve was damaged in difficulty swallowing?
Vagus and a bit of glossopharyngeal, minor role)
110
What nerve is damaged in hoarseness of voice?
Vagus nerve
111
What nerve is damaged in weakness of tongue?
Hypoglossal nerve
112
Into what three “spaces” do the 3 branches of the trigeminal nerve arise?
- Opthalmic: into superior orbital fissure
- Maxillary: through foramen rotundum into pterygopalatine fossa
- Mandibular: through foramen ovale into infratemporal fossa
113
Which cranial nerves pass into the orbit?
-oculomotor, optic, and opthalmic branch of trigeminal
114
What is the cavernous sinus? What are its borders?
- potential space involving blood vessel
- floor: endosteal layer of dura mater that overlies the base of the greater wing of sphenoid bone
- roof: meningeal layer of dura mater that attaches to the anterior and middle cricoid processes of sphenoid bone
- anterior: superior orbital fissure
- posterior: petrous part of temporal bone
- medial: body of sphenoid bone
- lateral: meningeal layer of dura mater running from roof to the floor of middle cranial fossa
115
What goes through the cavernous sinus?
O TOM CAT
| Oculomotor, Trigeminal, Opthalmic, Maxillary, Carotid, Abducens, Trochlear
