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Neuroscience and Mental Health > 3. Organisation of the brainstem and cranial nerves > Flashcards

3. Organisation of the brainstem and cranial nerves Flashcards

1
Q

Define the brainstem

A

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

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2
Q

What are the three major divisions of the brainstem from the top to the bottom?

A
  • Midbrain
  • Pons
  • Medulla Oblongata
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3
Q

How can you identify the roof of the midbrain?

A
  • Area with four lumps

* Colliculi - “low lying hills”

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4
Q

What is the ventral floor of the 4th ventricle?

A

Pons

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5
Q

What is the pineal gland?

A
  • One of the few midline structures (not bilateral like most others in the brainstem)
  • Releases melatonin
  • Regulation of circadian rhythm (24hr cycle)
  • Can be entrained by light - skull too thick so trained with vision
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6
Q

What is the Superior Colliculus for?

A

Midbrain nucleus for coordination of eye and head movements at the same time

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7
Q

What is the Inferior Colliculus for?

A

Midbrain nucleus for auditory reflexes e.g. looking in the direction of a bang

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8
Q

Which cranial nerves emerge from the back of the brainstem

A

Only trochlear nerves (IV) - supplies superior oblique muscle of the eyes

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9
Q

Where are the dorsal columns involved in?

A
  • Touch
  • Proprioception (space perception)
  • Sensory from lower limbs medial to sensory from upper limbs
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10
Q

Why is it easy to identify the pons?

A

Transverse fibres going across it

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11
Q

What structure is at the top of the midbrain?

A

Optic chiasm

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12
Q

What structure is immediately behind the optic chiasm?

A

Pituitary stalk (infundibulum)

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13
Q

What can you see behind the infundibulum?

A

Inferior part of the hypothalamus - mammillary bodies (part of limbic system)

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14
Q

What happens to mammillary bodies in chronic alcoholics?

A
  • Becomes dark

* Neovascularisation

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15
Q

Which nerves emerge just above the the transverse fibres of the pons?

A

Oculomotor nerves (III)

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16
Q

What is the cerebral peduncle?

A
  • Structure above the transverse fibres of the pons
  • Main motor fibres coming from motor cortex to the spinal cord
  • Also has structural role - holding cerebrum onto the brainstem
17
Q

What does Pons mean, and what does it do?

A
  • Pons = bridge

* Joins two halves of cerebellum together

18
Q

Which nerves emerge from the lateral parts of the pons?

A 
• Trigeminal (V)
• Divide into:
- Opthalmic
- Maxillary
- Mandibular
19
Q

What is the function of the Trigeminal nerve?

A
  • Touch and sensation throughout the head and neck

* Very small root next to large one as Trigeminal also has a motor function - mastication

20
Q

Which nerves emerge below the pons (ponto-medullary junction) from medial to lateral?

A
  • Abducens (VI) - supplies the lateral rectus muscle, causing abduction from midline
  • Facial (VII) - innervates muscles involved in facial expression
  • Vestibulocochlear (VIII) - balance and hearing
21
Q

What is Bell’s Palsy?

A
  • Dysfunction of facial nerves
  • Loss of facial muscle tone
  • May be due to post-infection inflammation
  • Usually temporary
22
Q

Which nerves emerge from the lateral medulla?

A
  • Glossopharyngeal (IX) - sensory and motor innervation of tongue and pharynx
  • Vagus (X) - main parasympathetic nerve that projects down into the viscera
  • Accessory (XI) - supplies the sternocleidomastoid and trapezius
23
Q

Which nerves emerge more anteriorly/medially from the medulla?

A
  • Hypoglossal nerves (VII)

* Supplies the musculature of the tongue

24
Q

Describe the pyramids of the medulla?

A
  • Structures on the anterior surface of the medulla
  • Continuation of corticospinal tracts
  • Fibres come down from the cortex through the peduncles, behind the transverse fibres, and re-emerge as pyramids
  • 90-95% of fibres cross over at “pyramidal decussation” at the base of the medulla - contralateral motor control
25
Q

What are the four functional subtypes of the cranial nerves?

A
  • General Somatic Afferent (GSA) - sensation from skin and mucous membranes (V)
  • General Visceral Afferent (GVA) - sensation from GI tract, heart, vessels and lungs
  • General Somatic Efferent (GSE) - muscles for eye and tongue movements (III, IV, VI, XII)
  • General Visceral Efferent (GVE) - pre-ganglionic parasympathetic: Edinger Westphal - input into eye, 3 pairs of salivatory nuclei at ponto-medullary border, Vagus (X)
26
Q

What are the 3 “special” subtypes of cranial nerves?

A
  • Special Somatic Afferent: vision, hearing and equilibrium - optic and vestibulocochlear
  • Special Visceral Afferent: Smell (olfactory) and taste (anteriorly facial, posteriorly glossopharyngeal, Nucleus Solatarius)
  • Special Visceral Efferent: muscles involved in chewing (V), facial expression (VII), swallowing, vocals (nucleus ambiguus for IX + X) and head turning (XI)
27
Q

How does information enter and leave the embryonic spinal cord?

A
  • Enters via dorsal root

* Leaves via ventral root

28
Q

How are the afferent and efferent nuclei arranged in the embryonic rhombencephalon (brainstem)?

A

• As the alar plate opens up creating a ventricle…

  • afferent nuclei are more lateral (sensory)
  • efferent nuclei are more medial (motor)
29
Q

Describe the general appearance of the midbrain (cross-section), and what structures can you see here?

A 
• Mickey mouse appearance
• Cerebral aqueduct always visible
• Cerebral peduncle varies in appearance
• Inferior colliculus low down in midbrain
• Most obvious sign - Substantia Nigra
- dopaminergic neurones
- normally produce neuromelanin - black pigment
- gets darker through life
(pale - sign of Parkinson's)
30
Q

Describe the identifiable features pons?

A
  • 4th ventricle
  • Transverse fibres
  • Cerebral peduncles - holding cerebrum onto brainstem
  • Cerebellar peduncles - holding cerebellum onto back of brainstem (main one is middle cerebellar peduncle)

As you go down, the features change:
• Pyramids start to be seen
• Bulge in the sides - inferior olivary nuclei (connected to cerebellum - fine tuning motor)

31
Q

Describe the cross-section and identifiable features of the lower medulla?

A

• Junction with the spinal cord is very round
• Dorsal columns seen
- gracillis (smaller and more dorsal/medial - sensory from lower limb)
- cuneatus (larger and more lateral - sensory from upper limbs)
• Central canal
• Crossing over of fibres at pyramidal decussation

32
Q

What is Lateral Medullary Syndrome?

A

Thrombosis of vertebral artery or posterior inferior cerebellar artery (PICA), resulting in:
• vertigo
• ipsilateral cerebellar ataxia: problem with gait on the same side of the body as the lesion
• ipsilateral loss of pain/thermal sense (face)
• Horner’s Syndrome - loss of sympathetic innervation to the head and neck
- ptosis (droopy eye lid)
- lack of sweating around the eye
- hoarseness
- difficulty swallowing
• Contralateral loss of pain/thermal sense in the trunk and limbs

33
Q

Why can thrombosis of the PICA cause vertigo?

A

Vestibular nucleus in medulla is disturbed

34
Q

Why can thrombosis of the PICA cause a loss of balance?

A

Inferior cerebellar peduncle (involved in providing proprioceptive information coming up) is disturbed

35
Q

Why can thrombosis of the PICA cause a loss sensation on the face and contralateral side of rest of body?

A

Spinal nucleus of trigeminal in medulla is disturbed

36
Q

Why can thrombosis of the PICA lead to Horner’s syndrome?

A

Sympathetic fibres in medulla are disrupted

37
Q

Why can thrombosis of the PICA lead to hoarseness and difficulty swallowing?

A

Nucleus ambiguus is disrupted

38
Q

Why can thrombosis of the PICA lead to contralateral loss of pain/thermal sense in the trunk and limbs?

A
  • Spinothalamic tract is disturbed

* Has already crossed over before reaching medulla - therefore contralateral

Neuroscience and Mental Health (17 decks)

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