Brainstem and Cranial Nerves Flashcards
Motor functions of the brainstem include. . .
control of ocular, pupillary, facial, laryngeal, pharyngeal, and visceral musculature.
Ascending neurotransmitter-specific projection pathways of the brainstem
- substantia nigra (dopamine)
- locus coeruleus (norepinephrine)
- median raphe nuclei (serotonin)
- pedunculopontine nuclei (acetylcholine)
The somatosensory pathways for the extremities and torso mostly travel ___ witihn the brainstem.
The somatosensory pathways for the extremities and torso mostly travel posteriorly witihn the brainstem (the exception being the medial lemnisci from the dorsal column pathway)
In general, the motor cranial nerve nuclei are ___ , and their cranial nerves emerge ___
In general, the motor cranial nerve nuclei are closest to the midline, and their cranial nerves emerge medially/anteriorly
(CN 4 is an exception in that it exits posteriorly).
The motor cranial nerve nuclei innervating skeletal muscle are at the ___
The motor cranial nerve nuclei innervating skeletal muscle are at the midline:
CNs 3, 4, and 6 (innervating extraocular muscles) and CN 12 (innervating tongue muscles).
The motor cranial nerve nuclei innervating branchial muscles are located ___:
The motor cranial nerve nuclei innervating branchial muscles are located laterally to the midline: CN 7 (facial muscles), CN 5 (jaw muscles), and CNs 9 and 10 (muscles of the larynx/pharynx)
The sensory and special sensory cranial nerve nuclei are located ___:
The sensory and special sensory cranial nerve nuclei are located more lateral than the motor cranial nerve nuclei: sensory nuclei of CN 5, vestibular and cochlear nuclei (CN 8), and nucleus solitarius (for taste and visceral sensation)
Cranial nerve nuclei diagram
The reticular acitivating system is located. . .
. . . in the upper pons and midbrain.
CN nuclei order (with exceptions)
Brainstem blood supply
With the exception of ___, all cranial nerves project ipsilaterally
With the exception of CN 4, all cranial nerves project ipsilaterally
Lesions of the medial brainstem cause predominantly ___ symptoms and signs, whereas lesions of the dorsolateral brainstem cause predominantly ___ symptoms and signs
Lesions of the medial brainstem cause predominantly motor symptoms and signs, whereas lesions of the dorsolateral brainstem cause predominantly sensory, special sensory, and cerebellar symptoms and signs
Unilateral medial medullary infarction syndrome
Causes ipsilateral tongue weakness (CN 12) and contralateral extremity weakness (due to involvement of the not-yet-crossed corticospinal tract)
Caused by occlusion of anterior spinal artery
Lateral medullary infarction syndrome
Ipsilateral loss of facial pain/temperature sensation (spinal tract and nucleus of CN 5) and contralateral pain/temperature sensation loss in the extremities (due to involvement of the already-crossed anterolateral tract) as well as vertigo (vestibular nuclei), nausea/vomiting and ataxia (inferior cerebellar peduncle and cerebellum), dysarthria and dysphagia (nucleus ambiguus), and ipsilateral Horner’s syndrome
Caused by occlusion of vertebral artery or PICA
Locked-in-syndrome
- Patient is awake and conscious, but cannot move or communicate with the exception of blinking and vertical gaze
- Ventral pontine lesions cause loss of all motor function controlled by the pons (resulting in quadriplegia, bilateral facial weakness, horizontal gaze palsy)
- But, the patient may still be awake and able to blink and look vertically if the dorsal pons, midbrain, and structures superior to it (i.e., thalami, cerebral hemispheres) are spared.
- It is important to distinguish the locked-in state from coma, since a locked-in patient is conscious
The portion of the reticular-activating system responsible for maintaining consciousness and arousal is in the . . .
The portion of the reticular-activating system responsible for maintaining consciousness and arousal is in the dorsal pons (pontine tegmentum) and midbrain.
The sensory ganglion of CN 5 is called the ___, which resides in ___
The sensory ganglion of CN 5 is called the gasserian ganglion, which resides in Meckel’s cave
(mnemonic: ganglion for cranial nerve V resides in Meckel’s cave).
Trigeminal nerve path diagram
How divisions of CN V enter the skull
V1 and V2 pass through the cavernous sinus, whereas V3 does not pass though the cavernous sinus. V1 exits the skull through the superior orbital fissure, V2 through the foramen rotundum, and V3 through the foramen ovale.
Additional functions of trigeminal (apart from those learned in Foundations anatomy)
- Supplies sensation to the dura
- Supplies touch sensation to the interior of the mouth
- Innervates one palate muscle, one ear muscle (both have tensor in the name), and the muscles of mastication
- Note that this is why the jaw-jerk reflex is afferent and efferent CN V
Brainstem reflexes involving the trigeminal
- Corneal reflex (CN V -> CN VII)
- Jaw-jerk reflex (CN V -> CN V)
Isolated facial sensory loss is most likely to be due to , , ,
. . . a lesion of the trigeminal nerve, the entry zone of the nerve in the pons, or a small cortical lesion. This is because lesions at all other sites would likely cause other deficits due to involvement of adjacent structures (other cranial nerves, cortical signs, etc)
Numb chin sign
Numbness of the chin (numb chin sign) should raise concern for metastatic malignancy affecting the mandibular (V3) division of the trigeminal nerve in the skull base or the distal trigeminal branches in the mandible
Breast cancer and lymphoma are among the most common malignancies causing the numb chin sign. The differential diagnosis includes dental etiologies and systemic causes of trigeminal neuropathy (e.g., Sjögren’s syndrome, sarcoidosis).
Evaluation should include panoramic dental x-ray, CT scan or bone scan of the jaw (to evaluate the mandible), CT scan of the head (to evaluate for a skull base lesion), and/or MRI of the brain with contrast (to evaluate the trigeminal nerve itself).
Trigeminal neuralgia
- In trigeminal neuralgia, brief lightning-like paroxysms of pain shoot through the face. These may be spontaneous or may be triggered by contacting the face (like brushing teeth)
- May be idiopathic, or it can be caused by multiple sclerosis, a compressive vascular loop, any etiology of trigeminal pathology, or it may begin after dental work. If trigeminal neuralgia is present in a young woman and/or bilaterally, multiple sclerosis should be considered and MRI obtained
- In idiopathic trigeminal neuralgia, facial sensation is generally normal.
- Antiepileptics are used for pain control in trigeminal neuralgia, with the most supportive evidence being for carbamazepine
Light touch vs pain sensation in the trigeminal
Light touch sensation from the face is transmitted primarily to the main sensory nucleus of 5 (also called the chief or principal sensory nucleus of 5) at the level of entry in the pons
Pain and temperature sensation from the face descend to the medulla in the spinal tract of 5 along with its associated spinal nucleus of 5. The spinal nucleus and tract of 5 extend as inferiorly as the upper cervical spine. The output of the spinal nucleus of 5 crosses to join the contralateral spinothalamic tract from the body and ascends to the ventral posterior medial (VPM) nucleus of the thalamus
Facial sensation information projects to the ___ nucleus of the thalamus, and sensation from the limbs and trunk travels to the ___ nucleus of the thalamus
Facial sensation information projects to the ventral posterior medial (VPM) nucleus of the thalamus, and sensation from the limbs and trunk travels to the ventral posterior lateral (VPL) nucleus of the thalamus
Other roles of CN VII (apart from those discussed in Foundation anatomy)
- Innervation of lacrimal and nasal glands
- Innervation of submandibular and sublingual salivary glands (but not the parotid salivary gland)
- Taste to the anterior two thirds of the tongue
- Somatic sensation for the external auditory meatus (interior of the external ear)
Facial nerve pathways diagram
- The geniculate ganglion is the main ganglion for all sensory and special sensory CN 7 functions (taste to anterior two thirds of the tongue, sensation around the ear).
- The greater petrosal nerve innervates the lacrimal and nasal glands (by way of the sphenopalatine ganglion, also known as the pterygopalatine ganglion).
- The nerve to the stapedius innervates the stapedius.
- The chorda tympani transmits taste from the anterior two thirds of the tongue and provides innervation to the salivary glands (submandibular and sublingual). Taste information travels to the nucleus solitarius in the medulla. (Mnemonic to recall that the nucleus solitarius is responsible for taste: nucleus solitastiest)
Facial weakness diagram
A: The facial nerve receives input from the contralateral motor cortex as well as an ipsilateral projection to the upper face. B: A lesion of the facial nerve will interrupt all input to both the upper face and lower face. C: A lesion of the motor cortex will cause contralateral lower facial weakness with preserved motor function of the upper face due to the ipsilateral “backup” to the upper face.
If facial weakness is due to an upper motor neuron lesion, . . .
If facial weakness is due to an upper motor neuron lesion, only the lower face is affected: The patient is unable to smile on the affected side (contralateral to the brain lesion), but can still close the eye and raise the eyebrow.
Each CN 7 contains the information from the contralateral motor cortex for the whole face and a “backup” for the upper face from the ipsilateral hemisphere.
Bell’s palsy
- Refers specifically to idiopathic facial nerve palsy (lower neuron, not upper)
- more common in diabetics and during the third trimester of pregnancy
- Facial weakness usually emerges over hours
- Some patients report facial numbness as a way of describing the feeling of the face being weak, although true facial numbness due to trigeminal involvement is uncommon.
- Patients often report that sounds are louder on the affected side (hyperacusis) due to weakness of the stapedius muscle
- Taste may be lost on ipsilateral anterior 2/3 of the tongue as well
- Most patients begin to recover from Bell’s palsy by 1 month and recover completely over subsequent months. A short course of oral steroids can increase the degree and speed of recovery.
- An important supportive measure in patients with Bell’s palsy is to protect the eye with artificial tears and patching
Kallman’s syndrome
anosmia and absence of gonadotropin-releasing hormone (GnRH) secreting neurons
CN 9 and 10 work together to:
- Innervate musculature of the pharynx and pallate
- transmit visceral afferent information from vascular baroreceptors
Additional functions of CN 9 (not discussed in Foundations anatomy)
- Innervates the parotid salivary gland
- Suppliest taste to the posterior third of the tongue
- Touch sensation in the inner ear
- Visceral sensation in the carotid body
Additional functions of the vagus nerve (not discussed in Foundations anatomy)
- Muscles of the larynx
- Somatic sensation in the dura mater of the posterior fossa aside from the tentorium (the rest of the dura is CN V)
- Somatic sensation in the pharynx
- Taste in the pharynx
- Visceral sensation from the aortic arch
- Autonomic visceral functions
Muscles innervated by CN XI
Sternocleidomastoid
Trapezius
Pathways innervating the upper and lower facial muscles (cartoon)
Afferent limb of pupillary light reflex
The bulk of visual information does not travel to the brainstem, however, in order to have pupillary reflexes, some small fibers do, and they specifically travel to the midbrain.
Nuclei of occulomotor cranial nerves
CN 3 and 4 have nuclei in the midbrain and CN 6 has its nuclei in the pons.
They are all located medially (following the pattern of motor structures being medial within the brainstem)
Nuclei of hypoglossal nerves
Located in the middle medulla
Trigeminal nerve nuclei and paths
Light touch fibers have nuclei (the chief nuclei of V) in the posterior pons, close to the middle cerebellar peduncles.
Pain and temperature travel separately in the spinal tract of V, going down from the pons into the medulla and even lower into the cervical spine, decussating, and coming back up to join the anterolateral tracts.
“Bronchial motor” stuctures
Due to an embryological difference, the nuclei of nerves that innervate bronchial structures are slightly more lateral than those that innervate other motor structures.
These fall in between the “pure motor” core of the brainstem and the sensory region towards the lateral/posterior regions.
Cranial nerve ___ does not have a nucleus in the brainstem at all
Cranial nerve XI does not have a nucleus in the brainstem at all
Cranial nerve “chalk talk” diagram
Lateral medullary syndrome summary
Ventral pontine syndrome summary
Ventral midbrain syndrome summary
Lesions in CN III cause the common physical exam sign of. . .
. . . ptosis! This is in addition to their roles in occulomotor movement.
It innervates the levator palpebrae, the muscle controlling eyelid movement.
What is going on in this patient?
Baroreceptor and chemoreceptor information carried by cranial nerves
Nucleus solitarius
Receives information for both taste and baroreception/chemoreception from cranial nerves VII, IX, X
Two nuclei of the vagus nerve
- Both located in the medulla
- Nucleus ambiguus:
- Controls motor functions of vagus
- Dorsal nucleus of the vagus:
- Controls parasympathetic autonomic functions
Spinal trigeminal nucleus
At the base of the medulla, fibers from ___ merge to join the anterolateral tract.
At the base of the medulla, fibers from the sensory portion of the trigeminal nerve carrying pain and temperature information merge to join the anterolateral tract.
They also decussate as they approach the anterolateral tract, so that information is organized by side.
In the pons, fibers from ___ merge to join the medial lemniscus
In the pons, fibers from the sensory portion of the trigeminal nerve carrying fine touch and proprioception information merge to join the medial lemniscus
They also decussate as they approach the medial lemniscus, so that information is organized by side.
Brainstem CN nuclei diagram with axial cross-sections
Brainstem CN nuclei diagram
Tongue deviation . . .
. . . points to the side of the neurologic deficit!
What is going on in this radiology study?
Vestibular schwannoma
You can tell because it surrounds the 8th cranial nerve
These are fairly common. Present w/ cranial nerve 8 signs.
If they are bilateral, suspect NF type 2
Medial medullary syndrome
The medial medulla is supplied by ____.
The lateral medulla is supplied by ____.
The medial medulla is supplied by the anterior spinal artery.
The lateral medulla is supplied by the posterior inferior cerebellar artery.
Lateral medullary syndrome cartoon
To find the nucleus solitarius in the medulla, look for. . .
. . . the donuts!
They will be in the dorsal medial portion, just lateral to the hypoglossal nuclei
