Brainstem and Cranial Nerves

Question 1

Where are the colliculi found and what are their functions?

Answer 1

Roof of the midbrain
Superior – important for the coordination of eye and head movements at the same time
Inferior – auditory reflexes – turning your head in the direction of a loud noise

Question 2

Describe the location of the pons relative to the ventricular system.

Answer 2

At floor of 4th Ventricle

Question 3

Name an important unpaired, midline structure on the posterior aspect of the brainstem. What is its role?

Answer 3

Pineal gland, produces melatonin, which is involved in regulating the circadian rhythm

Question 4

Which cranial nerve emerges from the dorsal aspect of the brainstem? What is its role?

Answer 4

Trochlear nerve – CN IV

The Trochlear nerve innervates a single muscle, the superior oblique muscle (an extrinsic muscle of the eye), contralateral to its nucleus.

Question 5

What structure defines the medulla in the dorsal aspect and what pathways are found within this structure?

Answer 5

Dorsal Columns – sensory pathways – touch and proprioception

Question 6

What three significant structures can be seen superior to the pons when viewing the brainstem from an anteroinferior view?

Answer 6

Optic Chiasm
Pituitary Stalk (infundibulum)
Mammillary Bodies

Question 7

What are the mammillary bodies?

Answer 7

Part of limbic system, inferior parts of hypothalamus

Question 8

Which cranial nerve emerges in the midline just above the transverse fibres of the pons?

Answer 8

Oculomotor Nerve (CN III)

Question 9

What are the cerebral peduncles?

Answer 9

These are the descending motor tracts coming from the motor cortex. They are peduncles as they have a functional AND structural role – it holds the cerebrum onto the brainstem

Question 10

Name the cranial nerve that emerges from the lateral aspect of the pons. What is its role?

Answer 10

Trigeminal (CN V)
Touch and sensation throughout the head and neck
It has a small root next to the larger one as it emerges out of the transverse fibres – this is the motor root providing motor innervation of the muscles of mastication (chewing)

Question 11

Which three nerves emerge at the pontomedullary junction (from medial to lateral)? What are their roles?

Answer 11

Abducens (CN VI) - Innervates the lateral rectus which is involved in abducting the eye
Facial (CN VII) - Innervates the muscles of facial expression and is involved in taste sensation for the anterior 2/3 of the tongue
Vestibulocochlear (CN VIII) - Involved in balance and hearing

Question 12

Which three nerves emerge from the lateral medulla? What are their roles?

Answer 12

Glossopharyngeal (CN IX) - sensory and motor innervation of the tongue and pharynx
Vagus (CN X) - main parasympathetic nerve descending down to the viscera
Accessory (CN XI) - supplies the trapezius and sternocleidomastoid

Question 13

Which cranial nerve traverses a foramen in the occipital bone?

Answer 13

CN XII – Hypoglossal nerve, supplies motor innervation to muscles of tongue

Question 14

The motor fibres coming down from the motor cortex come via the cerebral peduncles then disappear behind the transverse fibres of the pons. What structure do they re-emerge as, inferior to the transverse fibres?

Answer 14

Pyramids

Question 15

What percentage of motor fibres cross to the contralateral side of the body in the brainstem and where does this changing of sides take place?

Answer 15

90-95% at pyramidal decussation

Question 16

What are the four general subtypes of cranial nerves and their actions?

Answer 16

General Somatic Afferent
Sensation from the skin and mucous membranes

General Visceral Afferent
Sensation from the GIT, heart, vessels and lungs

General Somatic Efferent
Muscles for eye and tongue movements

General Visceral Efferent
Preganglionic parasympathetic

Question 17

What are the special subtypes of cranial nerves and what are their actions?

Answer 17

Special Somatic Afferent (CN II & CN VIII)
Vision, hearing and equilibrium

Special Visceral Afferent (CN I, CN VII, CN IX, CN X)
Smell and Taste (comes from three nerves that converge on the nucleus solitarius)

Special Visceral Efferent (CN V, CN VII, CN IX, CN X, & CN XI)
Muscles involved in chewing, facial expression, swallowing, vocal sounds and turning the head

Question 18

What structure separates the sensory nuclei from the motor nuclei in the spinal cord and brainstem?

Answer 18

Sulcus Limitans

Question 19

What happens in the formation of the rhombencephalon and how does this affect the arrangement of the nuclei?

Answer 19

The alar plate opens up and a ventricle forms
This opening of the alar plate results in the motor nuclei being medial in the brainstem and the sensory nuclei are lateral

Question 20

Describe the arrangement of the different groups in columns within the brainstem.

Answer 20

Motor – Medial
Sensory – Lateral
Motor – arranged in columns from medial to lateral in this order: GSE, SVE, GVE
Sensory – arranged in columns from medial to lateral in this order: GVA/SVA, GSA, SSA

Question 21

State the nuclei that are in the general somatic efferent group and describe their location within the brainstem.

Answer 21

Oculomotor = midbrain 
Trochlear = midbrain 
Abducens = pons (though it emerges at the ponto-medullary junction) 
Hypoglossus = medulla

Question 22

State the nuclei that are in the special visceral efferent group and describe their location within the brainstem.

Answer 22

Trigeminal = pons

Facial = pons

Ambiguus = medulla

Accessory = cervical spinal cord

NOTE: ambiguus is a group of large motor neurons situated deep in the medullary reticular formation. It contains cell bodies of nerves that innervate muscles of the soft palate, pharynx and larynx – strongly associated with speech and swallowing

Question 23

State the nuclei that are in the general visceral efferent group and describe their location within the brainstem.

Answer 23

Edinger Westphal = midbrain

Salivatory = ponto-medullary border (there are THREE sets of salivatory nuclei)

Vagus = pons

Question 24

State the nuclei that are in the special somatic AFFERENT group and describe their location within the brainstem.

Answer 24

Vestibulocochlear = pons and medulla

Question 25

State the nuclei that are in the general somatic AFFERENT group and describe their location within the brainstem.

Answer 25

Trigeminal = In all three parts and in the cervical spinal cord

Question 26

State the nuclei that are in the general visceral AFFERENT and special visceral AFFERENT groups and describe their location within the brainstem.

Answer 26

Solitarius – mainly in the medulla (but a little bit in the pons)

Question 27

Describe the appearance of a cross-section of the midbrain. What are the key features seen?

Answer 27

It has a distinctive ‘mickey mouse’ appearance
Ears of Mickey Mouse are the cerebral peduncles
At the point where the cerebral peduncles meet the rest of the midbrain you find the substantia nigra
You will see the cerebral aqueduct in the middle (small diamond shape)
The two rounded protrusion on the opposite side of the cerebral peduncles are the inferior colliculi

Question 28

What is the substantia nigra? Describe its clinical significance.

Answer 28

The substantia nigra is a group of dopaminergic neurons In their normal metabolism they produce neuromelanin, which gives the black colour of the substantia nigra
Parkinson’s disease is caused by loss of these dopaminergic neurons so patients with Parkinson’s will have a pale substantia nigra.

Question 29

Describe the appearance of a cross-section of the pons. What are the key features seen?

Answer 29

The 4th ventricle will be seen at the dorsal aspect of the pons
The most distinctive feature are the transverse fibres
On either side you will see the middle cerebellar peduncles

Question 30

What is the difference between the peduncles seen in the midbrain and the ones seen in the pons?

Answer 30

Midbrain – Cerebral Peduncles

Pons – Cerebella Peduncles

Question 31

Describe the appearance of a cross-section of the medulla. What are the key features seen?

Answer 31

Pyramids will be seen on the ventral aspect
The inferior olivary nucleus will be found next to the pyramids
The 4th ventricle will still be visible

Question 32

What is the role of the inferior olivary nucleus?

Answer 32

It is involved in fine tuning motor function

Question 33

Describe the appearance of a cross-section of the lower medulla. What are the key features seen?

Answer 33

It will be more round
The central canal will be seen in the middle
The dorsal columns will be seen on the dorsal side
The pyramidal decussation may be seen

Question 34

Name the two columns that make up the dorsal columns.

Answer 34

Gracilis – more medial – sensory information from the lower limb (Note this column traverses the entire cord anteriorly)
Cuneatus – more lateral – sensory information from the upper limb (This column begins around T1/C8 level and traverses anteriorly)

Question 35

What is lateral medullary syndrome? Describe and explain the symptoms.

Answer 35

It is a constellation of symptoms caused by an occlusion in the vertebral arteries or the posterior inferior cerebellar arteries (PICA)

It causes:
Horner’s Syndrome– disturbing the sympathetic tract

Vertigo– because of disturbing the vestibular nucleus

Ipsilateral loss of pain/thermal sensation on the face–disturbing the spinothalamic tract

Contralateral loss of pain/thermal sensation on the trunk and limbs– disturbing the spinothalamic tract

Ipsilateral cerebellar ataxia– disturbing the inferior cerebellar peduncle

Hoarseness / Difficultly swallowing (From Nucleus Ambiguus)

Contralateral loss of pain thermal sensation in limbs and trunk.

Question 36

What are the symptoms of Horner’s Syndrome?

Answer 36

Ptosis (drooping eyelid)
Loss of sweating around the eye 
Miosis 
Retraction of eyeball 
(ALL UNILATERAL)