Cranial nerves and brainstem Flashcards
1
Q
What is the brainstem?
A
Includes the midbrain, the pons and the medulla oblongata and continues downwards to form the spinal cord
2
Q
What is the function of the brainstem?
A
Converys motor and sensory information from the body and autonomic and motor information from higher centers to peripheral targerts
3
Q
What is the function of the olfactory nerve?
A
Smell
Innervation of the olfactory sensory neurons embedded in the olfactory epithelium in the upper nasal cavity
4
Q
What is CNI
A
The olfactory nerve
5
Q
Which nerve provides somatosensory innervation to the nasal cavity
A
Trigeminal nerve (opthalmic and maxillary divisions)
6
Q
What is CNII
A
Optic nerve
7
Q
What is the function of the optic nerve?
A
Vision
Transmits visual information from the retina to the brain
8
Q
Which cranial nerves control eye movement?
A
CN III
CN IV
CNVI
9
Q
What is CNIII?
A
Oculomotor nerve
10
Q
What does the oculomotor nerve do?
A
Innervates 4 of the 6 external muscles:
- Inferior oblique
- Superior rectus
- medial rectus
- inferior rectus
11
Q
What is CN IV?
A
Trochlear nerve
12
Q
What is the function of the trochlear nerve?
A
Innervates the superior oblique muscle
13
Q
What is CNVI?
A
The abducens nerve
14
Q
What is the function of the abducens nerve?
A
Innervation of the lateral rectus muscle
15
Q
Which intrinsic eye muscles are innervated by the oculomotor nerve?
A
- Spincter pupillae (pupil constriction)
- Ciliary muscle (accommodation)
16
Q
Where do CN III, IV, VI enter the orbit?
A
Through the superior orbital fissure
17
Q
What are the symptoms of oculomotor palsy?
A
Ptosis
outward and slightly downward deviation of the eye
dilated and fixed pupil
18
Q
What are the symptoms of a trochlear palsy?
A
- torsional (rotational) diplopia
- compensatory tilted head
19
Q
What are the symptoms of an abducens palsy?
A
- reduced abduction
- eye positioned medially
20
Q
What symptom does a palsy in CN III, IV, VI have in common?
A
Diplopia (double vision)
21
Q
What is CN V?
A
Trigeminal nerve
22
Q
What is the function of the trigeminal nerve?
A
- sensory: innervation of face, teeth, tongue, oral and nasal cavity, sinuses
- motor: innervation of the muscles of mastication
23
Q
What test can be performed on the sensory innervation of the trigeminal nerve?
A
Lightly touch the skin in 3 divisions of the trigeminus of your patients face with a piece of cotton wool or blunt object
- mental foramen (jaw)
- infra-orbital foramen (nose)
- supraorbital foramen (eye)
24
Q
Where is the trigeminal ganglion localised?
A
Occupies a cavity (meckel’s cave) in the dura mater, covering the trigeminal impression near the appex of the petrous part of the temporal bone
25
What is the trigeminal ganglion?
A sensory ganglion of the trigeminal nerve (CNV)
26
What are the functions of the trigeminal ganglion?
Contains the sensory cell bodies of the 3 branches of the trigeminal nerve:
- opthalmic
- mandibular
- maxillary
27
What are the three branches of the trigeminal nerve?
- opthalmic
- Maxillary
- Mandibular
28
Name a nerve branch of the opthalmic nerve
supra-orbital nerve
29
Name a nerve branch of the maxillary nerve
infra-orbital nerve
30
Name a nerve branch of the mandibular nerve
Mental nerve
31
Which cranial nerves are involved in the corneal reflex?
- Trigeminal nerve (sensory afferent, opthalmic division)
| - Facial nerve (efferent - orbicularis oculi)
32
What is CNVII?
The facial nerve
33
What are the functions of the facial nerve?
- motor: innervation of the muscles of facial expression
- taste: sensation on the anterior 2/3 of the tongue
- parasympathetic functions on the head
34
How can you test the motor functions of the facial nerve?
Ask patient to:
- raise eyebrows
- frown
- smile
- puff out cheeks and resist pressure
- tightly close eyes and resist opening
Cornea reflex:
- using sterile cotton lightly apply a wisp to the cornea (approach from the side to avoid visual stimulation) = patient should blink in response to stimuus
35
What is the sensory limb of the cornea reflex?
the opthalmic branch of the trigeminus [v1]
36
What is the motor limb of the cornea reflex?
mediated by the facial nerve
37
What large glands are innervated by the facial nerve?
- submandibular glands
- sublingual glands
- lacrimal glands
38
What is CNVIII
The vestibulocochlear nerve
39
What is the function of the vestibulocochlear nerve?
hearing and balance
innervation of the inner ear, cochlea and the vestibular organ
40
How is the hearing function of the vestibulocohclear nerve performed?
Whisper voice test:
- each ear is tested individually, starting with the ear with better hearing.
- During testing the non-test ear is masked by gently occluding the auditory canal with a finger
- the examiner stands at arm's length (~0.6 m) behind (to prevent lip-reading) the seated patient and whispers a combination of numbers and letters, and then asks the patient to repeat the sequence.
- the examiner should quietly exhale before whispering to ensure as quiet a voice as possible.
- the patient is considered to have passed the screening test if they repeat at least 3 out of 6 numbers or letters
correctly
- audiometry: objective measurement of hearing threshold across the audible frequency range.
41
What is CN IX?
The glossopharyngeal nerve
42
What is CN X?
The vagus nerve
43
What is the function of the glossopharyngeal and vagus nerves?
- innervation of the pharynx, larynx, soft palate and back of the tongue
- sensory motor and parasympathetic functions
Important for speech and swallowing
44
Why are CN IX and X tested and described together?
Isolated lesions of one but not the other are essentially unknon
45
What are obvious features of a lesion on CN IX and X?
- absent gag reflex
| - uvula deviated away from the lesion
46
How are CN IX and X tested?
- speech: ask the subject to speak; watch for huskiness of the voice and difficulties in producing sounds
(dysphonia) .
- swallowing: ask the subject to swallow, ask and watch if there are any difficulties (dysphagia).
observe the position of the palate and the uvula through the open mouth
watch for symmetrical position and movements
uvula deviates to the side opposite to nerve lesion.
- gag reflex: the back of the throat (pharynx) is touched with a tongue blade, this evokes the gag reflex
in most people.
47
What are the features of a vagus lesion on the right side?
- asymmetric arch of the palate (lower on the right)
| - uvula deviates to the left
48
Which large gland is innervated by the glossopharyngeal nerve?
- parotid gland (via the petrosal nerve)
49
What is CNXI?
The accessory nerve
50
What is the function of the accessory nerve?
Motor innervation of the trapezius and sternocleidomastoid muscles
51
How is the accessory muscle tested?
Place your arms firmly on the shoulder of your patient
They should be able to raise their shoulders against the resistance
52
What is CNXII?
The hypoglossal nerve
53
What is the function of the hypoglossal nerve?
Motor innervation of the intrinsic and extrinsic muscles of the tongue
54
How do you test the hypoglossal nerve?
As the patient to stick their tongue out.
The tip of the tongue will deviate to the weak side, if there is a lesion present
Check movements can be made in all directions without difficulty
55
Which nerves provide taste and somatosensory innervation to the tongue?
- anterior 2/3:
lingual nerve
mandibular division of CNV
chorda tympani from the facial nerve (taste)
- posterior 1//3 is innervated by the glossopharyngeal nerve (both somatosensory and taste sensation)
56
Which cranial nerves are involved in the gag reflex?
- afferent glossopharyngeal
| - efferent vagus nerve
57
Describe the test for CNI?
Equipment: At least two different items to smell.
Smell the odour samples, one at a time with each nostril (the other nostril should be blocked)
record what the samples are.
Control: Even if olfactory function is lost, irritants (e.g. ammonia) can still be detected by the pain receptors in
the nasal mucosa.
NB: testing of the olfactory nerve is rarely done in clinical practice. An alternative is just to ask the patient if
they have noticed any problem with their sense of smell.
58
Describe the test for CN II
1. Visual acuity
Equipment: printed material – e.g. book, newspaper.
Ask patient to cover one eye.
Hold the printed material approximately 18 inches away and have them read two sentences. Repeat the
procedure using the other eye.
In clinical practice you might want to formally test visual acuity by using a Snellen chart
2. Visual fields
3. Pupil reflexes
4. Fundoscopy
59
Describe the test for CNIII, CNIV and CNVI
These Nerves are usually tested together.
Equipment: nil
- To examine the extraocular muscle movements, hold your forefinger about 18 inches away from patient’s
eyes.
Ask them to follow your finger with his/her eyes as you draw the letter “H”.
Their eyes should move together as they follow your finger with their eyes.
Always ask if they experienced any double vision.
Their head should not move. I
t can be helpful to gently place your other hand on their head for this test.
- Test eye movements:
your subject should sit upright - hold the subject’s head still with one hand
Observe normal position (e.g. deviation of one eye, strabism) and lack of spontaneous movements (e.g.
nystagmus) of the eyes with forward gaze.
Eye movements: move an object (e.g. pencil) slowly horizontally and then vertically ~30 cm in front of the
eyes.
Your subject should follow the object (tip of the pencil) with his/her eyes without moving the head.
Eye movements should be free in all directions; the two eyes should move together in a coordinated fashion.
Minimal nystagmus at the extreme positions is considered normal.
60
How do you test for CNV function?
Equipment: Cotton wool ball
There are sensory and motor components.
To test for the sensory function (ophthalmic, maxillary, and mandibular sensations), have patient close both
eyes.
Lightly touch his/her forehead, cheek, and jaw, on both sides of the face, using a cotton ball.
Have them tell you when they feel the cotton touching them.
Pain sensation can then be tested in the same areas by using the pin end of a “neurotip” – these are single use
and should be disposed of in a sharps bin.
To evaluate the motor components, you will examine the masseter and temporalis muscles.
For temporalis, put your fingertips on your lab partner’s temples and ask him/her to clench his/her teeth.
To assess the masseter muscles, place your fingertips on his/her jaw and ask them to clench their teeth.
The muscles should feel strong and even on both sides of their head and face.
Finally perform the jaw jerk on the patient by placing your left index finger on their chin and striking it with a
tendon hammer.
The reflex will cause a slight protrusion of the jaw, although frequently the reflex is not visible. It is normal to
have an absent or minimal response.
The corneal reflex should also be examined in a full cranial nerve examination, as the sensory supply to the
cornea is from the trigeminal nerve.
In OSCE examinations, you would usually tell the examiner you would like to test the corneal reflex as an
additional test.
To perform the test, lightly touch the cornea with a small wisp of the cotton wool. You should touch the edge
of the cornea, with the patient looking away so they don’t see the cotton wool. The corneal reflex should
cause the patient to shut their eyelids.
61
How do you test for facial nerve function?
Equipment: nil
To test the motor control of the muscles of facial expression, have patient raise their eyebrows, frown, smile
and puff out their cheeks.
Have them tightly close their eyes and resist your attempts to (gently) open them.
62
How do you test for CNVIII function?
Equipment: Ticking watch, tuning fork
To test for hearing, stand a couple of steps behind your partner’s right side.
Whisper several numbers and see if they can repeat them.
Hold a ticking watch from a distance, slowly bring towards ear and have your partner tell you when he/she can
hear it. (Repeat the test on the left side.)
In addition, Rinne’s and Weber’s tests can be done if you have a tuning fork.
These tests are used to differentiate conductive and sensorineural hearing loss
To carry out the Rinne test, place a sounding tuning fork on the patient’s mastoid process and then next to
their ear and ask which is louder.
A normal patient will find the second position louder.
To carry out the Weber’s test, place the tuning fork base down in the centre of the patient’s forehead and ask
if it is louder in either ear. Normally it should be heard equally in both ears.
Try the tuning fork tests again with your partner covering one ear. This will mimic a conductive hearing loss.
63
How do you test for CNIX?
Equipment: Cotton applicator and tongue depressor
The test is called a gag reflex
As with the corneal reflex, it is generally only done if you suspect it may be abnormal, or there are other
neurological signs.
To perform a gag reflex, hold down the tongue with a tongue depressor and touch the back of the throat
gently with a cotton swab.
64
How do you test for CNX function?
Equipment: Tongue depressor
A simple test is to ask the patient to say “aah” and look for movement of the uvula. There should be no
deviation. You may need to use a tongue depressor.
In addition, normal speech is a good indication that muscles of the pharynx are working.
65
How do you test for CNXI function?
Accessory XI
Equipment: None
Test the strength of the sternocleidomastoid muscle by placing your hand against your partner’s cheek and
having them turn their head as you apply resistance. Note the force they are able to apply against your hand.
To assess the strength of the trapezius muscle, place your hands on patient’s shoulders and have him/her
shrug their shoulders as you apply resistance. Is the muscular strength equal on both sides?
66
How do you test for CNXII function?
Equipment: None
Have your lab partner stick out their tongue.
Observe the tongue for any signs of wasting or fasciculations (small involuntary muscle twitches).
If the tongue deviates to either side, it suggests a weakening of the muscles on that side.
67
What features can be found in the brainstem?
- autonomic centres for cardiovascular, respiratory and gastrointestinal control
- groups of neurons and tracts of cranial nerves
- tracts ascending to the thalamus and cortex from the spinal cord and cerebellum
- several tracts descending to he spinal cord and the pyramidal tract from the motor cortex runs through
- the brainstem reticular formation, continuous with the interneurones of the spinal cord, has major integrative functions
- it is he source of modulatory neurotransmitters affecting the function of neurones in the spinal cord and the cerebral cortex
- interaction between the brain stem and cerebral cortex is essential for consciousness
68
Describe the midbrain
```
- mesencephalon
extends rostrally (frontwards) from the pons-midbrain junction to join the diencephalon (thalamus)
```
69
Which cranial nerves exit from the midbrain?
- oculomotor nerve (CNIII)
| - trochlear nerve (CNIV)
70
Where does the oculomotor nerve exit the brain?
exits the anterior aspect of the midbrain
71
Where does the trochlear nerve exit the brain?
exits the posterior aspect of the midbrain
72
What is the posterior aspect of the midbrain characterised by?
superior and inferior colliculi
73
What is the anterior aspect of the midbrain chracterised by?
the crus cerebri and interpeduncular fossa
74
Describe the pons
The anterior part of the metencephalon
extends from the pons-medulla junction to an imaginary line drawn from the exit of the trochlear nerve posteriorly to the rostral edge of the basilar pons anteriorly
actually consists of two portions:
- pontine tegmentum
- basilar pons
75
Describe the basilar pons
- bulbous
| - characteristic of the anterior aspect of the pons
76
Describe the pontine tegmentum
- located internally
- contains portions of the trigeminal nuclei and the vestibular nuclei, facial motor nucleus, superior salivatory nucleus and the abducens nucleus
77
Where does the trigeminal nerve exit?
Emerges from the lateral aspect of the pons
78
Which nerves exit at the pons-medulla junction
- abducens (CN VI)
- facial (CN VII)
- vestibulocochlear (CN VIII)
79
How is the cerebellum connected to the brainstem?
3 large paired bundles of fibers:
- The inferior cerebellar peduncle
- the middle cerebellar peduncle
- the superior cerevellar peduncle
cerebellum is not part of the brainstem
80
What is the inferior cerebellar peduncle?
paired bundle of fibers that connects the cerebellum to the medulla oblongata
81
what is the middle cerebellar peduncle
(brachium pontis)
paired bundle of fibers that connects the cerebellum to the basilar pons
82
What is the superior cerebellar peduncle?
paired bundle of fibers that connects the cerebellum to the midbrain
83
Describe the medulla oblongata
Myelencephalon
at the level of the foramen magnum where the spinal cord merges into the most caudal portion of the brain
slightly cone shaped and enlarges in diameter as it extends rostrally from the medulla-spinal cord junction towards the pons-medulla junction
84
Which cranial nerves are associated with the medulla oblongata?
- hypoglossal
- parts of accessory
- parts of vagus
- parts of the glosspharyngeal
85
Which cranial nerve nuclei are found in the medulla oblongata?
- hypoglossal
- vagal
- glossopharyngeal
& portions of the trigeminal nerve
86
What are the ventricular spaces of the brainstem?
- the cerebral aquaduct in the mesencephalon
| - fourth ventricle in the rhomencephalon
87
What is the cerebral aquaduct?
- narrow channel
| - connects the third (diencephalon cavity) and fourth (rhombencephalic cavity) ventricles
88
What differentiates the cerebral aqueduct from the ventricles?
- does not contain choroid plexus
| - walls are formedby a continous mantle of cells collectively called the periaqueductal gray
89
What is the roof of the midbrain called?
the tectum
90
What is the fourth ventricle?
the cavity of the rhombencephalon
91
Where is the fourth ventricle?
- rostral portion between the pons and cerebellum
- caudal portion located in the medulla
The lateral recesses extend around the brainstem at the pons-medulla junction and end at the foramen of luschka, which opens into the lateral cerebellomedullary cistern
92
name the structures the fourth ventricle connects with?
Continuous:
- rostrally with the cerebral aqueduct
- caudally wth the central canal of the caudal medullaand cervical spinal cord
- laterally with the subarachnoid space via the midline forame of magendie and the two lateral foramina of luschka
93
Where is the foramen of magendie located?
in the causal roof of the ventricle and opens into the dorsal cerebellomedullary cistern (cistern magna)
94
Which cranial nerves are not attached to the brainstem?
- olfactory
- optic
- accessory
95
What is the red nucleus?
A structure in the rostral midbrain that is involved in motor coordination
96
Describe the red nucleus
The red nucleus is pale pink, which is believed to be due to the presence of iron in at least two different forms:
hemoglobin and ferritin
97
What symptoms would result from a lesion of the red nucleus
resting tremor, abnormal muscle tone and choreoathetosis
