Organisation of the Brainstem and Cranial Nerves

Question 1

Where are the colliculi found and what are their functions?

Answer 1

Roof of the midbrain
Superior: coordination of eye + neck movement
Inferior: auditory reflexes – turning head in direction of loud noise

Question 2

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

Answer 2

Pons is the floor of the 4th ventricle

Question 3

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

Answer 3

Pineal gland

Question 4

What is the role of the pineal gland?

Answer 4

Produces melatonin (involved in regulating circadian rhythms)

Question 5

Which cranial nerve emerges from the back of the brainstem?

Answer 5

Trochlear nerve

Question 6

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

Answer 6

Supplies superior oblique muscle: 1 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 + proprioception

Question 8

What 3 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

The inferior part of the hypothalamus (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

Descending motor tracts from the motor cortex.

Peduncle = a structure that has a functional + 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 the Trigeminal nerve? (CNV)

Answer 13

Touch + sensation throughout the head + neck
It has a small root next to the larger one as it emerges out of the transverse fibres = motor root providing motor innervation of the muscles of mastication

Question 14

Which 3 nerves emerge at the pontomedullary junction (from medial to lateral)?

Answer 14

Medially: Abducens (CNVI)
Lateral: Facial (CNVII)
(more) Lateral: Vestibulocochlear (CNVIII)

Question 15

Briefly state the role of CN VI, VII, VIII

Answer 15

Abducens: innervates lateral rectus, allows lateral eye movement
Facial: innervates muscles of facial expression + taste sensation for anterior 2/3 of tongue
Vestibulocochlear: involved in balance + hearing

Question 16

Which 3 nerves emerge from the lateral medulla?

Answer 16

Glossopharyngeal (CNIX)
Vagus (CNX)
Accessory (CNXI)

Question 17

Briefly state the role of CN IX, X, XI

Answer 17

Glossopharyngeal: sensory + motor innervation of the tongue + pharynx
Vagus: main parasympathetic output to the viscera
Accessory: supplies the trapezius + sternocleidomastoid

Question 18

State the last cranial nerve – CN XII.

Answer 18

Hypoglossal: supplies 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
If a problem occurs in the corticospinal tract it results in “pyramidal symptoms”
If problems in cerebellum/ other parts involved in motor control = “extrapyramidal symptoms”

Question 20

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 20

90-95%

At the base of the medulla

Question 21

What are the 4 functional subtypes of the cranial nerves and what are their actions?

Answer 21

General Somatic Afferent: Sensation from skin + mucous membranes
General Visceral Afferent: Sensation from GIT, heart, vessels + lungs
General Somatic Efferent: Muscles for eye + tongue movements
General Visceral Efferent: Preganglionic parasympathetic

Question 22

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

Answer 22

Special Somatic Afferent: Vision, hearing + equilibrium
Special Visceral Afferent: Smell + Taste
Special Visceral Efferent: Muscles involved in chewing, facial expression, swallowing, vocal sounds + turning head

Question 23

What structure separates the sensory nuclei from the motor 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

Alar plate opens up, a ventricle forms

This opening of the alar plate results in motor nuclei being medial in the brainstem + the sensory nuclei lateral

Question 25

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

Answer 25

Motor: Medial. Arranged in columns from medial to lateral in this order: GSE, SVE, GVE Sensory: Lateral. 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 + Trochlear = midbrain Abducens = pons (though emerges at the ponto-medullary junction) Hypoglossal = medulla

Question 27

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

Answer 27

Trigeminal + Facial = pons Ambiguus = medulla Accessory = cervical spinal cord

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 (3 sets of salivatory nuclei) Vagus = medulla

Question 29

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

Answer 29

Vestibulocochlear = pons + 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 3 parts + 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 (+ a little bit in pons)

Question 32

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

Answer 32

‘Mickey mouse’ appearance Ears= cerebral peduncles Where the cerebral peduncles meet the rest of the midbrain = substantia nigra Cerebral aqueduct in the middle (small diamond shape) The 2 rounded protrusion on the opposite side of the cerebral peduncles = inferior colliculi

Question 33

What is the substantia nigra? Describe its clinical significance.

Answer 33

A group of dopaminergic neurons Produce neuromelanin, (gives black colour of the substantia nigra) PD is caused by loss of these dopaminergic neurons so patients with PD 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 Most distinctive feature= 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 on the ventral aspect Inferior olivary nucleus next to the pyramids The 4th ventricle will still be visible

Question 37

What is the role of the inferior olivary nucleus?

Answer 37

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 Central canal in the middle Dorsal columns on the dorsal side Pyramidal decussation (crossing of 90% fibres)

Question 39

Name the 2 columns that make up the dorsal columns.

Answer 39

Gracilis: more medial – sensory info. from lower limb Cuneatus: more lateral – sensory info. from upper limb

Question 40

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

Answer 40

Group of symptoms caused by thrombosis of vertebral artery or posterior inferior cerebellar arteries (PICA) Causes: Horner's Syndrome (disturbing sympathetic tract) Vertigo (disturbing the vestibular nucleus) Ipsilateral loss of pain/thermal sensation on the face (disturbing spinothalamic tract) Contralateral loss of pain/thermal sensation (trunk + limbs– disturbing spinothalamic tract) Ipsilateral cerebellar ataxia (disturbing inferior cerebellar peduncle)

Question 41

What are the symptoms of Horner’s Syndrome?

Answer 41

Ptosis Lack of sweating around the eye Hoarseness Difficulty Swallowing

Question 42

What is the brainstem?

Answer 42

Part of the CNS, exclusive of the cerebellum | Lies between the cerebrum + spinal cord

Question 43

What are the 3 major divisions of the brainstem?

Answer 43

Medulla oblongata Pons Midbrain