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
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.
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
Pathways innervating the upper and lower facial muscles (cartoon)
Cranial nerve “chalk talk” diagram
Lateral medullary syndrome summary
Ventral pontine syndrome summary
Ventral midbrain syndrome summary
What is going on in this patient?
Baroreceptor and chemoreceptor information carried by cranial nerves
Spinal trigeminal nucleus
Brainstem CN nuclei diagram with axial cross-sections
Brainstem CN nuclei diagram
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
Lateral medullary syndrome cartoon
