Brain stem and cranial nerves

Question 1

Define brain stem

Answer 1

The part of the CNS, exclusive of the cerebellum that lies between the cerebrum and the spinal cord

Question 2

What are the major divisions of the brain stem from top to bottom?

Answer 2

midbrain, pons and medulla oblongata

Question 3

What is the superior and inferior colliculus?

Answer 3

The roof of the midbrain.
Superior colliculus - controls the coordination of the eye and head
Inferior colliculus - Auditory reflexes

Question 4

What structure lies in the midline of the brain stem?

Answer 4

The pineal gland - secretes melatonin required for management of the circadian rhythm

Question 5

What cranial never emerges from the anterior surface of the brain stem?

Answer 5

Trochlear nerve (CN IV) emerges from the back of the brain stem. Only cranial nerve of dorsal origin.

Question 6

What does CN IV supply?

Answer 6

It supplies the superior oblique

Question 7

What are the two main sensory pathways in the dorsal column?

Answer 7

Touch

Proprioception

Question 8

How can the pons be identified?

Answer 8

It has transverse fibres going across it

Question 9

Describe the layout of the midbrain and the structures around it

Answer 9

See diagram and notes

Question 10

What cranial nerve emerges just emerges just above the transverse fibres of the pons?

Answer 10

CN III - oculomotor nerve

• Medial rectus
• Superior rectus
• Inferior rectus
• Inferior oblique

It emerges between the cerebral peduncles.

Question 11

What does the midbrain have that has a structural and functional role?

Answer 11

Cerebral peduncle - the main motor nerve fibres coming from the motor cortex to the spinal cord. Sensory fibres as well. It also holds the cerebrum to the brainstem. It travels behind the Pons and remerges below as pyramids. The fibres cross over at the base of the medulla called the pyramidal decussation. 90-95% of the fibres cross here.

Question 12

What cranial nerves emerge from the pons?

Answer 12

Lateral part of pons - Trigeminal (CN V)
Three cranial nerves emerge from the ponto-medullary junction. Going from most medial to lateral. Abducens (CN VI), Facial (CN VII) and Vestibulocohlear (CNVIII)

The emerge at the level of the pyramids before the decussation

Question 13

What is Bell’s Palsy?

Answer 13

Dysfunction of the facial nerve causing a loss of facial muscle tone

Question 14

What are the three CN that arise from the lateral part of the medulla?

Answer 14

Glossopharyngeal (CN IX) - Sensory and motor innervation to the tongue and pharynx
Vagus (CN X) - main parasympathetic nerve that projects down to the viscera
Accessory (CN XI) - supplies the sternocleidomastoid (allows turning of the head) and the trapezius

Question 15

What CN emerges separately from the other three cranial nerves of the medulla?

Answer 15

Hypoglossal Nerve (CN XII) - supplies the musculature of the tongue

Question 16

What are the functional subtypes of the cranial nerves?

Answer 16

GSA - sensation from the skin and mucous membranes
GVA - sensation from the GI tract, heart, vessels and lungs
GVE - preganglionic parasympathetic
GSE - muscles for eye and tongue movements

This order is also the order of the fibres from dorsal to ventral in an embryonic spinal cord

Question 17

What are also functional subtypes of the cranial nerves (S)?

Answer 17

SSA - Vision, hearing and equlibrium
SVA - Smell (CN I) and Taste (2 cranial nerves that go to the nucleus solitarius. Anterior 2/3 CN VII, posterior 1/3 CN IX)
SVE - Muscles involved in chewing, facial expressions, swallowing, vocal sounds and turning the head

Question 18

What is the sulcus limitans?

Answer 18

Separates the sensory nuclei from the motor nuclei

Question 19

Draw the arrangement of the nuclei of the cranial nerves

Answer 19

See diagram. Nucleus ambiguus - involved in laryngeal movements

Question 20

What appearance does the midbrain typically have?

Answer 20

Mickey mouse appearance

Question 21

What are the signs that you’re in the midbrain?

Answer 21

Inferior colliculus - low down in the midbrain
Cerebral aqueduct
Substantia nigra - Dopminergic neurones produce neuromelanin which gives it the distinct black colour
(cerebral peduncle)

Question 22

Where is the 4th ventricle in the region of?

Answer 22

The Pons

Question 23

The are the signs that you’re in the pons?

Answer 23

Transverse fibres
Cerebellar peduncles (main one is middle cerebellar peduncle)
Cerebral peduncles
4th ventricle

Question 24

Signs you are at the top of medulla?

Answer 24

Inferior olivary nucleus - connected to the cerebellum involved in fine tuning motor movements
4th Ventricle
Pyramids

Question 25

Signs you are in the lower medulla?

Answer 25

Round cross-section
Dorsal columns - smaller: gracilis (sensory information from the lower limb) more laterally: cuneatus (sensory information from the upper limb)
Central canal
Pyramidal decussation

Question 26

What causes lateral medullary syndrome?

Answer 26

Blockage of the vertebral artery or posterior inferior cerebellar artery

Question 27

What are possible symptoms of lateral medullary syndrome?

Answer 27

Vertigo - damage to vestibular nerve

Ipsilateral cerebellar ataxia - problem with gait on the same side of the body as the lesion due to damage to cerebellar peduncle

Ipsilateral loss of pain/thermal sense (face) - damage to trigeminal nerve

Contralateral loss of pain/thermal sense in the trunk and limbs - damage to spinothalamic tract above the decussation

Horner’s syndrome - damage to sympathetic tract/ambiguus

Hoarseness, difficulty in swallowing - damage to ambiguus