Organisation of the Brainstem and Cranial Nerves

Question 1

Where are the colliculi found and what are their functions?

Answer 1

Roof (means dorsal in neuroanatomy) of the midbrain Superior – important for the coordination of eye and head movements at the same time (watching tennis on TV

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

The pons is the floor of the 4th ventricle

Question 3

Name an important unpaired, midline structure on the posterior aspect of the brainstem.

Answer 3

Pineal gland

Question 4

What is the role of this structure?

Answer 4

It produces melatonin, which is involved in regulating the circadian rhythm

Question 5

Which cranial nerve emerges from the back of the brainstem?

Answer 5

Trochlear nerve - the only nerve that emerges from the back of the brainstem.

Supplies one of the extrinsic muscles of the eye

Question 6

What is the role of this nerve? (CN IV)

Answer 6

It supplies the superior oblique muscle – one of the extrinsic muscles of the eye

Question 7

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

Answer 7

Dorsal Columns – sensory pathways – touch and proprioception

Question 8

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

Answer 8

Optic Chiasm Pituitary Stalk (infundibulum) Mammillary Bodies

Question 9

What are the mammillary bodies?

Answer 9

They are the inferior part of the hypothalamus – it is part of the limbic system

Question 10

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

Answer 10

Oculomotor Nerve (CN III)

Question 11

What are the cerebral peduncles? What is the significance of the word ‘peduncle’?

Answer 11

These are the descending motor tracts coming from the motor cortex. Peduncle is specifically a structure that has a functional AND structural role – it holds the cerebrum onto the brainstem

Question 12

Name the cranial nerve that emerges from the lateral aspect of the pons.

Answer 12

Trigeminal (CN V)

Question 13

What is the role of this nerve? (CNV)

Answer 13

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

Question 14

Which three nerves emerge at the pontomedullary junction (from medial to lateral)?

Answer 14

Abducens (VI), Facial (VII), Vestibulocochlear (VIII)

Question 15

Briefly state the role of each of these cranial nerves. (CN VI, VII, VIII)

Answer 15

Abducens – innervates the lateral rectus which is involved in abducting the eye

Facial – innervates the muscles of facial expression and is involved in taste sensation for the anterior 2/3 of the tongue

Vestibulocochlear – involved in balance and hearing

Question 16

Which three nerves emerge from the lateral medulla?

Answer 16

Glossopharyngeal (IX), Vagus(X) and Accessory (XI)

Question 17

Briefly state the role of each of these cranial nerves. (CN IX, X, XI)

Answer 17

Glossopharyngeal – sensory and motor innervation of the tongue and pharynx Vagus – main parasympathetic nerve descending down to the viscera Accessory – supplies the trapezius and sternocleidomastoid

Question 18

State the last cranial nerve – CN XII.

Answer 18

Hypoglossal Nerve – supplies the musculature of the tongue

Question 19

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 19

Pyramids (pyramids = motor, dorsal columns = sensory)

Question 20

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

Answer 20

90-95%

pyramidal decussation (part of the medulla)

Question 21

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

Answer 21

General Somatic Afferent - Sensation from the skin and mucous membranes

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

General Somatic Efferent - supply Skeletal muscles. The GSE fibres emerging from the brainstem would supply the Muscles for eye and tongue movements

General Visceral Efferent- Can be parasympathetic or sympathetic but the ones from the cranial nerves are the Preganglionic parasympathetic fibres (para=cranioscaral)

Question 22

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

Answer 22

Special Somatic Afferent- Vision, hearing and equilibrium

Special Visceral Afferent - Smell and Taste (comes from three nerves that converge on the nucleus solitarius)

Special Visceral Efferent- Muscles involved in chewing, facial expression, swallowing, vocal sounds and turning the head

Question 23

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

Answer 23

Sulcus limitans

Question 24

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

Answer 24

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 25

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

Answer 25

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 26

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

Answer 26

 Oculomotor (III) = midbrain

 Trochlear (IV) = midbrain

 Abducens (VI) = pons (though it emerges at the ponto-medullary junction)

 Hypoglossus (XII) = medulla

Question 27

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

Answer 27

 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 28

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

Answer 28

 Edinger Westphal = midbrain

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

 Vagus = pons

Question 29

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

Answer 29

Vestibulocochlear = pons and medulla

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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 33

What is the substantia nigra? Describe its clinical significance.

Answer 33

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 34

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

Answer 34

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 35

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

Answer 35

Midbrain –cerebral peduncles Pons – cerebellar peduncles

Question 36

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

Answer 36

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 37

What is the role of the inferior olivary nucleus?

Answer 37

It is involved in fine tuning motor function

Question 38

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

Answer 38

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 39

Name the two columns that make up the dorsal columns.

Answer 39

Gracilis – more medial – sensory information from the lower limb Cuneatus – more lateral – sensory information from the upper limb

Question 40

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

Answer 40

Thrombosis of vertebral artery or PICA (posterior inferior cerebellar art.)

◦Vertigo

◦Ipsilateral cerebellar ataxia

◦Ipsilateral loss of pain/thermal sense (face)

◦Horner’s syndrome

◦Hoarseness, difficulty in swallowing

◦Contralateral loss of pain/thermal sense (trunk and limbs)

Question 41

What are the symptoms of Horner’s Syndrome?

Answer 41

Ptosis Loss of sweating around the eye Hoarseness Difficulty Swallowing