Brainstem- Overview and Cranial Nerves

Question 1

Identify the main parts of the brainstem.

Answer 1

From superior to inferior:
Midbrain
Pons
Medulla Oblongata

Question 2

Describe the anatomical location of the brainstem.

Answer 2

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

Question 3

Identify the main components of the midbrain.

Answer 3

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)

Question 4

Identify the main components of the medulla.

Answer 4

Pyramids (extensions of corticospinal tract)

Question 5

What structure connects cerebrum and cerebellum ? How so ?

Answer 5

PONS “connects the cerebrum to the cerebellum through the cerebral peduncle”

Question 6

Identify all the links between cerebellum and brainstem.

Answer 6

MIDBRAIN
-Superior cerebellar
peduncle

PONS
-Middle cerebellar
peduncle

MEDULLA
-Inferior cerebellar
peduncle

Question 7

Identify the main nuclei present in the brainstem.

Answer 7

• 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)

Question 8

Where in the spinal cord are autonomic nuclei present ?

Answer 8

Autonomic nuclei are present between ventral and dorsal horns

Question 9

Give examples of UMN lesions.

Answer 9

Cerebral infarct

Corticospinal tract lesion

Question 10

Give examples of LMN lesions.

Answer 10

Peripheral nerve lesions

Nerve root lesion

Question 11

Identify the sensory cranial nerves.

Answer 11

CN1 (olfactory)
CN2 (optic)
CN8 (vestibulocochlear)

Question 12

Identify the motor cranial nerves.

Answer 12

CN3 (Oculomotor)
CN4 (Trochlear)
CN6 (Abducens)
CN11 (Accessory)
CN12 (Hypoglossal)

Question 13

Identify mixed cranial nerves.

Answer 13

CN5 (Trigeminal)
CN7 (Facial)
CN9 (Glossopharyngeal)
CN10 (Vagus)

Question 14

Which part of the brainstem do the cranial nerves originate from ?

Answer 14

4 from midbrain and above
4 from the pons
4 from the medulla

Question 15

Which part of the brainstem do the cranial nerves originate from ?

Answer 15

4 from midbrain and above
4 from the pons
4 from the medulla

EXCEPT trigeminal sensory nucleus (goes all way up and down brainstem)

Question 16

Describe arrangement of somatic motor nuclei.

Answer 16

Orbital muscles:

• Midbrain: III (most eye movement muscles), IV (Superior oblique muscle, to depress eye)
• Pons: VI (for lateral rectus)

Tongue:
- XII (medulla)

Question 17

What is the Edinger-Westphal nucleus ? Which other nucleus is this close to ?

Answer 17

PSNS nucleus (also technically the second CN3 nucleus) that supplies pupillary constrictor fibers. Close to third cranial nerve (oculomotor) nucleus.

Question 18

What kinds of defects will a medial brainstem problem result in ?

Answer 18

Will affect somatic motor nuclei, and therefore may be resulting problems with eye (CN3, 4, 6) or tongue (CN12) movements

Question 19

Describe arrangement of somatic sensory nuclei.

Answer 19

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

Question 20

What kinds of defect will a lateral brainstem problem result in ?

Answer 20

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)

Question 21

Describe arrangement of autonomic nuclei in brainstem.

Answer 21

• 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’)

Question 22

Identify examples of PSNS effects, and SNS effects.

Answer 22

PSNS: Constricts pupils, stimulates salivation, inhibits heart

SNS: Dilates pupils, inhibits salivation, accelerates heart

Question 23

Describe a possible pathological result of a lesion in the autonomic motor pathways.

Answer 23

Horner’s syndrome

Question 24

Distinguish between the way parasympathetic and sympathetic fibers exit the CNS.

Answer 24

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)

Question 25

Describe a possible pathological result of a lesion in the autonomic motor pathways.

Answer 25

Horner's syndrome - Miosis (constriction) - Ptosis - Anhydrosis

Question 26

Identify possible pathologies causing abnormal, reduced, or absent pupillary light reflex.

Answer 26

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

Question 27

Describe the pathway of the fibers which are affected in Horner's Syndrome.

Answer 27

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

Question 28

Identify possible causes of Horner's Syndrome.

Answer 28

- 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)

Question 29

Identify the main features of Horner's syndrome.

Answer 29

- Ptosis - Miosis - Anhydrosis

Question 30

Describe the location of the Edinger Westphal nucleus.

Answer 30

In proximity to third CN Relatively medial Higher up than third cranial nerve

Question 31

Identify the main features of Horner's syndrome.

Answer 31

- Ptosis - Miosis - Anhydrosis

Question 32

Describe the location of the Edinger Westphal nucleus.

Answer 32

In proximity to third CN Relatively medial Higher up than third nerve

Question 33

State examples of special sensations.

Answer 33

 Hearing  Balance  Sight

Question 34

Which cranial nerves carry special sensations ?

Answer 34

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

Question 35

Identify the main tracts going through the brainstem.

Answer 35

``` 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

Question 36

How will a brainstem lesion affecting the DCML pathway present (e.g. medial lesion in brainstem) ?

Answer 36

A brainstem lesion affecting this pathway will cause a contralateral loss of JPS

Question 37

Which pathways might be affected by a medial lesion of the brainstem ? Lateral ?

Answer 37

Medial: DCML Lateral: Spinothalamic

Question 38

How will a brainstem lesion affecting the spinothalamic pathway present (e.g. lateral lesion in brainstem) ?

Answer 38

A brainstem lesion will cause a contralateral loss of pain and temperature

Question 39

What is the spinal equivalence of the medial lemniscus pathway ? spinal lemniscus pathway ?

Answer 39

- Medial Lemniscus: Dorsal columns | - Spinal Lemniscus: Spinothalamic tract

Question 40

How will a brainstem lesion affecting the spinocerebellar pathway present ?

Answer 40

A brainstem lesion produces an ipsilateral spino-cerebellar tract defect

Question 41

Describe the function of the medial longitudinal fasciculus.

Answer 41

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

Question 42

How may lesions of the MLF manifest ? What is a possible cause of a MLF lesion ?

Answer 42

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.

Question 43

Identify the nuclei and tracts which are present medially in the brainstem. State whether or not they cross.

Answer 43

MEDIALLY: - Medial lemniscus (X) - Motor tracts- somatic (X) - MLF (X) -Somatic motor nuclei (3, 4, 6, 12)

Question 44

Identify the nuclei and tracts which are present laterally in the brainstem. State whether or not they cross.

Answer 44

LATERALLY - Spino-cerebellar (I) - Spino-thalamic (X) -Sympathetic (I) -Somatic sensory nuclei (of trigeminal nerve)

Question 45

Describe effects of a lesion in the lateral aspect of the medulla.

Answer 45

- 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)

Question 46

Describe effects of a lesion in the medial aspect of the brainstem.

Answer 46

- 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)

Question 47

Describe arterial supply of the brainstem.

Answer 47

"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)"

Question 48

Identify pathologies which may affect arterial supply to the brainstem.

Answer 48

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

Question 49

Describe the main signs and symptoms of lateral medullary syndrome of Wallenburg, as well as a possible cause of it.

Answer 49

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

Question 50

How can you localise the site of nerve damage ?

Answer 50

By determining the: Cranial nerves effected (level, side and horizontal level) Tracts effected (side and lateral position)

Question 51

What is internal organisation of the brainstem based on ?

Answer 51

On the spinal cord

Question 52

Name the nuclei associated with somatic motor, somatic sensory, visceral motor, and visceral sensory for each of these: - Trigeminal - Facial - Glossopharygeal - Vagus

Answer 52

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)