Brainstem- Overview and Cranial Nerves Flashcards
Identify the main parts of the brainstem.
From superior to inferior:
Midbrain
Pons
Medulla Oblongata
Describe the anatomical location of the brainstem.
Lies in the posterior cranial fossa, between spinal cord; cerebellum and cerebral hemisphere.
ANTERIORLY
- Clivus
- Nerves and vessels
POSTERIORLY
- Cerebellum and attachments
INFERIORLY
- Foramen magnum and spinal cord
SUPERIORLY
- Tentorium and diencephalon
Identify the main components of the midbrain.
Corpora quadrigemina (two superior and two inferior coliculi, have to do with movements of the eyes and head in response to visual and auditory stimuli)
Identify the main components of the medulla.
Pyramids (extensions of corticospinal tract)
What structure connects cerebrum and cerebellum ? How so ?
PONS “connects the cerebrum to the cerebellum through the cerebral peduncle”
Identify all the links between cerebellum and brainstem.
MIDBRAIN
-Superior cerebellar
peduncle
PONS
-Middle cerebellar
peduncle
MEDULLA
-Inferior cerebellar
peduncle
Identify the main nuclei present in the brainstem.
- Cranial nerve nuclei
- Vital and non-vital centers (e.g. involved in breathing, HR)
- Reticular formation (diffuse network of interconnected neurons, with different NT systems e.g. Noradrinergic system based in locus cœruleus, 5HT system in Raphe nucleus, as well as ACh and Dopaminergic systems)
- Motor coordination (e.g. red nucleus, substantia nigra, inferior olivary nucleus)
Where in the spinal cord are autonomic nuclei present ?
Autonomic nuclei are present between ventral and dorsal horns
Give examples of UMN lesions.
Cerebral infarct
Corticospinal tract lesion
Give examples of LMN lesions.
Peripheral nerve lesions
Nerve root lesion
Identify the sensory cranial nerves.
CN1 (olfactory)
CN2 (optic)
CN8 (vestibulocochlear)
Identify the motor cranial nerves.
CN3 (Oculomotor) CN4 (Trochlear) CN6 (Abducens) CN11 (Accessory) CN12 (Hypoglossal)
Identify mixed cranial nerves.
CN5 (Trigeminal)
CN7 (Facial)
CN9 (Glossopharyngeal)
CN10 (Vagus)
Which part of the brainstem do the cranial nerves originate from ?
4 from midbrain and above
4 from the pons
4 from the medulla
Which part of the brainstem do the cranial nerves originate from ?
4 from midbrain and above
4 from the pons
4 from the medulla
EXCEPT trigeminal sensory nucleus (goes all way up and down brainstem)
Describe arrangement of somatic motor nuclei.
Orbital muscles:
- Midbrain: III (most eye movement muscles), IV (Superior oblique muscle, to depress eye)
- Pons: VI (for lateral rectus)
Tongue:
- XII (medulla)
What is the Edinger-Westphal nucleus ? Which other nucleus is this close to ?
PSNS nucleus (also technically the second CN3 nucleus) that supplies pupillary constrictor fibers. Close to third cranial nerve (oculomotor) nucleus.
What kinds of defects will a medial brainstem problem result in ?
Will affect somatic motor nuclei, and therefore may be resulting problems with eye (CN3, 4, 6) or tongue (CN12) movements
Describe arrangement of somatic sensory nuclei.
V (trigeminal) -From posterior horn of the spinal cord to the midbrain -Head’s somatic sensation: Midbrain - proprioception Pons – discrim. touch Medulla – pain and temp
What kinds of defect will a lateral brainstem problem result in ?
If have lateral lesion, may have problem with sensation
coming from face on that part of the body (because facial nerve nuclei may be affected)
Describe arrangement of autonomic nuclei in brainstem.
- Ambiguous nucleus: Motor (somatic motor: speech, swallowing)
- Solitarius nucleus: Sensory (visceral sensory: taste, gag, involuntary reflexes)
- Salivatory nuclei
- Dorsal nucleus of the vagus (in medulla)
- Edinger Westphal nucleus (accessory third cranial nerve nucleus but contains autonomic fibers, ‘pre-ganglionic nucleus’)
Identify examples of PSNS effects, and SNS effects.
PSNS: Constricts pupils, stimulates salivation, inhibits heart
SNS: Dilates pupils, inhibits salivation, accelerates heart
Describe a possible pathological result of a lesion in the autonomic motor pathways.
Horner’s syndrome
Distinguish between the way parasympathetic and sympathetic fibers exit the CNS.
PSNS:
- -“PSNS fibres exit the CNS by two routes. The two regions where their neuron cell bodies are located are the medulla which constitutes the cranial half of the system, as well as the sacral segment of the spinal cord (sacral half of the system)”
- The cranial half of this system includes:
1) Certain cranial nerves in the cranium, namely the preganglionic parasympathetic nerves (CN III, CN VII, and CN IX) usually arise from specific nuclei in the central nervous system (CNS) (including Edinger-Westphal nucleus, superior salivatory nucleus, inferior salivatory nucleus) and synapse at one of four parasympathetic ganglia: ciliary, pterygopalatine, otic, or submandibular. From these four ganglia the parasympathetic nerves complete their journey to target tissues via trigeminal branches (ophthalmic nerve, maxillary nerve, mandibular nerve)
2) The vagus nerve does not participate in these cranial ganglia as most of its parasympathetic fibers (arising from Dorsal nucleus of the vagus and Nucleus ambiguus) are destined for a broad array of ganglia on or near thoracic viscera (esophagus, trachea, heart, lungs) and abdominal viscera (stomach, pancreas, liver, kidneys, small intestine…)
SNS:
“Sympathetic neurons exit the CNS through the spinal nerves located in the lumbar/thoracic regions of the spinal cord” (between T1-L2)
Describe a possible pathological result of a lesion in the autonomic motor pathways.
Horner’s syndrome
- Miosis (constriction)
- Ptosis
- Anhydrosis
Identify possible pathologies causing abnormal, reduced, or absent pupillary light reflex.
If lesion in midbrain, may not get any light response, or may get a problem with either direct or consensual response:
• Aneurysm on posterior communicating artery (runs next to the nerve), can compress third nerve so may get third nerve palsy. Because third nerve controls most of eye muscles except abduction and depression of eye, eye is turned out and down. At the same time, if constrictor fibers are affected (because constrictor fibers are on outside of third nerve), then pupil is dilated.
→ Presentation: Pain + sudden onset double vision + eye depressed and out + dilated pupil
• Diabetes can also cause CN3 palsy, where smallest blood vessels are affected. Hence, inner fibers of nerve are more likely to be affected (so more likely to have sparing of those constrictor fibers).
→ Presentation: Pain + sudden onset double vision + eye depressed and out + WITHOUT dilated pupil
Describe the pathway of the fibers which are affected in Horner’s Syndrome.
Output from hypothalamus:
- Responsible for facial sweating, eyelid
elevation, vasomotor and pupil dilation
- Descends mainly uncrossed, including through the sympathetic pathways in the brainstem laterally
- Then fibers ascend in cervical SNS chain and join carotid artery, before going into the eye along with the CN3
Identify possible causes of Horner’s Syndrome.
- A lesion of the pathway in postero-lateral brainstem will produce an ipsilateral Horner’s syndrome (e.g. MS
- Ischemia in carotid artery thrombosis (affecting sympathetic fibers)
- Lesions of cervical sympathetic chain such as thyroid carcinoma, thyroid surgery
- Lesions of spinal root of T1 (apical carcinoma of lung e.g. Pancoast tumor, cervical ribs)
Identify the main features of Horner’s syndrome.
- Ptosis
- Miosis
- Anhydrosis
Describe the location of the Edinger Westphal nucleus.
In proximity to third CN
Relatively medial
Higher up than third cranial nerve
Identify the main features of Horner’s syndrome.
- Ptosis
- Miosis
- Anhydrosis
Describe the location of the Edinger Westphal nucleus.
In proximity to third CN
Relatively medial
Higher up than third nerve
State examples of special sensations.
Hearing
Balance
Sight
Which cranial nerves carry special sensations ?
VIII (vestibulocochlear): 8th CN nucleus in pons responsible for hearing and balance
II (optic)
Medial and lateral geniculate bodies are responsible for hearing and sight respectively
Identify the main tracts going through the brainstem.
DESCENDING 1) Motor tracts Cortico-bulbar Cortico-spinal 2) Sympathetic
ASCENDING
Spino cerebellar
Spino thalamic (Spinal lemniscus)
Medial lemniscus
LINKING
Cerebellar peduncles
Medial longitudinal fasciculus
How will a brainstem lesion affecting the DCML pathway present (e.g. medial lesion in brainstem) ?
A brainstem lesion affecting this pathway will cause a contralateral loss of JPS
Which pathways might be affected by a medial lesion of the brainstem ? Lateral ?
Medial: DCML
Lateral: Spinothalamic
How will a brainstem lesion affecting the spinothalamic pathway present (e.g. lateral lesion in brainstem) ?
A brainstem lesion will cause a contralateral loss of pain and temperature
What is the spinal equivalence of the medial lemniscus pathway ? spinal lemniscus pathway ?
- Medial Lemniscus: Dorsal columns
- Spinal Lemniscus: Spinothalamic tract
How will a brainstem lesion affecting the spinocerebellar pathway present ?
A brainstem lesion produces an ipsilateral spino-cerebellar tract defect
Describe the function of the medial longitudinal fasciculus.
Tract in the brainstem which links up some of the nuclei
E.g.
-If want to move eyes to the right, signal comes
from L frontal eye field (area 8).
-Subsequently, need to pull on right lateral rectus (CNVI, Abducens), and left medial rectus (CNIII, occulomotor). MLF links those two together.
-Signal comes down to opposite lateral gaze center, which is next to sixth nerve nucleus, in pons (pontine gaze center).
-To get to opposite third nerve, signal has to cross over through the MLF
How may lesions of the MLF manifest ? What is a possible cause of a MLF lesion ?
Internuclear ophtalmoplegia:
when the patient attempts lateral gaze, slowed or absent adduction of the ipsilateral eye (can be uni or bilateral).
MLF is one of the first pathways to myelinate, and one of the first to demyelinate in MS.
Identify the nuclei and tracts which are present medially in the brainstem. State whether or not they cross.
MEDIALLY:
- Medial lemniscus (X)
- Motor tracts- somatic (X)
- MLF (X)
-Somatic motor nuclei (3, 4, 6, 12)
Identify the nuclei and tracts which are present laterally in the brainstem. State whether or not they cross.
LATERALLY
- Spino-cerebellar (I)
- Spino-thalamic (X) -Sympathetic (I)
-Somatic sensory nuclei (of trigeminal nerve)
Describe effects of a lesion in the lateral aspect of the medulla.
- Ataxia ipsilaterally (spinocerebellar pathway is lateral and does not cross)
- Pain and temperature loss on other side (spinothalamic pathway is lateral and cross early on)
- Sympathetic issues ipsilaterally (sympathetic tracts are lateral and do not cross)
Describe effects of a lesion in the medial aspect of the brainstem.
- JPS loss (contralateral if it crossed already, ipsilateral if not)
- Somatic motor tracts issues, (esp. corticospinal tracts going down (that would be above where they cross))
- Internuclear ophtalmoplegia contralaterally (because MLF is present medially and crosses)
Describe arterial supply of the brainstem.
“The brainstem is supplied by the vertebrobasilar circulation
(two vertebral arteries join up to form basilar artery) and their branches, small branches of the posterior cerebral artery (PCA, from basilar artery), and the anterior spinal artery (the two vertebral arteries also provide branches to the anterior spinal artery)”
Identify pathologies which may affect arterial supply to the brainstem.
1) Posterior Inferior Cerebellar Artery Infarct may cause Lateral Medullary Syndrome (causes lateral medullary syndrome, and therefore affects sympathetic, spinocerebellar, spinothalamic pathways, and somatic sensory nuclei)
2) “Ischemia of the anterior spinal artery may cause Anterior Spinal Artery Syndrome”, which affects medial lemniscus, corticospinal tract, MLF, and somatic motor nuclei
3) Posterior communicating artery aneurysm may press on third nerve
Describe the main signs and symptoms of lateral medullary syndrome of Wallenburg, as well as a possible cause of it.
Possible cause: Posterior Inferior Cerebellar Artery Infarct
- Ptosis and small pupil (affects ipsilateral sympathetic tracts)
- Loss of pain and temperature sensation on same side of face, and opposite side of body (affects ipsilateral spinothalamic above decussation point, and contralateral spinothalamic below decussation point)
- Ataxia (affects ipsilateral spinocerebellar tracts)
- Dysphagia
How can you localise the site of nerve damage ?
By determining the:
Cranial nerves effected (level, side and horizontal level)
Tracts effected (side and lateral position)
What is internal organisation of the brainstem based on ?
On the spinal cord
Name the nuclei associated with somatic motor, somatic sensory, visceral motor, and visceral sensory for each of these:
- Trigeminal
- Facial
- Glossopharygeal
- Vagus
Somatic motor, somatic sensory, visceral motor, and visceral sensory:
- Trigeminal (Motor nucleus 5, /, /, Sensory nucleus 5)
- Facial (Facial nucleus, S. salivary nucleus, Nucleus solitarius, Sensory nucleus 5)
- Glossopharygeal (Nucleus ambiguus, I. salivary nucleus, Nucleus solitarius, Sensory nucleus 5)
- Vagus (Nucleus ambiguus, Dorsal motor nucleus, Nucleus solitarius, Sensory nucleus 5)
