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Y2 LCRS 2 - Neuroscience and mental health > Organisation of the Brainstem and Cranial Nerves > Flashcards

Organisation of the Brainstem and Cranial Nerves Flashcards

1
Q

What are the parts of the brainstem?

A

Superior to inferior:

  • Midbrain
  • Pons
  • Medulla oblongata
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2
Q

What is a characteristic of nearly all the structures within the brainstem?

A

They are bilateral

EXCEPTION: midline structures

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3
Q

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

A

Pineal gland

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4
Q

What is the role of the pineal gland?

A

It produces melatonin, a hormone which is involved in regulating the circadian rhythm (24-hour biological cycle - includes sleep-wake cycle)

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5
Q

Where are the colliculi found and what are their functions?

A

The collliculi form the roof of the midbrain (misnamed because it is actually the back of the midbrain)

There are 2 paired colliculi (rounded swellings):

  • Superior – important for the coordination of eye and head movements at the same time (e.g. while watching tennis)
  • Inferior – auditory reflexes (e.g. turning your head in the direction of a loud noise immediately)
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6
Q

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

A

The pons is the floor of the 4th ventricle

NOTE: ventricle = fluid (CSF) filled cavity so it has certain borders which are surrounding brain structures (these are then lined by ependymal cells)

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7
Q

Which is the only cranial nerve emerges from the back of the brainstem?

A

Trochlear nerve (CN IV)

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8
Q

What is the role of the trochlear nerve?

A
  • General somatic efferent nerve
  • Supplies the superior oblique muscle – one of the extrinsic muscles of the eye
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9
Q

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

A

Dorsal columns

  • Ascending sensory pathways (DC-ML)
  • Carry information about touch and proprioception
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10
Q

What three significant structures are found near the midbrain? Describe their positions.

A
  • Optic Chiasm
    • A midline structure in the brain
    • Where the right and left optic nerves converge and 50% of the fibres within each nerve cross to the contralateral side of the brain
  • Pituitary Stalk (infundibulum)
    • Just behind the optic chiasm
  • Mammillary Bodies
    • Behind and slightly above the infundibulum
    • Just in front of midbrain

NOTE: these structures are not part of the midrain

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11
Q

What are the mammillary bodies?

A

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

  • The hypothalamus is made up of lots of nuclei (groups of cell bodies)
    • The mamillary bodies are a paired structure
    • One mamillary body on either side of the midline making up the inferior part of the hypothalamus
  • Each mammillary body consist of two groups of nuclei (medial and lateral) within the hypothalamus
  • FUNCTION: mainly involved in memory
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12
Q

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

A

Oculomotor Nerve (CN III)

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13
Q

What is the function of the oculomotor nerve?

A

Nerve contains:

  • General somatic efferent fibres
    • Innervates 4 out of 6 of the extrinsic eye muscles
    • Innervates the muscle which allows eyelid movement
  • General visceral efferent fibres
    • Innervates constrictor pupillae (circular muscle of the iris)
    • Innervates ciliary muscles to control the thickness of the lens
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14
Q

What are the cerebral peduncles? What is their significance’?

A
  • These are the descending motor tracts coming from the motor cortex
  • They have a functional AND structural role – it holds the cerebrum onto the brainstem
    • Paired structure - one on each side of the brainstem
    • Make up the anterior (front) portion of the midbrain
    • Stretches from cerebrum to pons, connectin to the two
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15
Q

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

A

Trigeminal (CN V)

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16
Q

What is the role of the trigeminal nerve?

A
  • General somatic afferent - touch and sensation throughout the head and neck (large sensory root)
  • Special visceral efferent - motor innervation of the muscles of mastication/chewing (small motor root next to larger one as it emerges out of pons)
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17
Q

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

A
  • Abducens (CN VI)
  • Facial (CN VII)
  • Vestibulocochlear (VN VIII)
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18
Q

State the role of each of the cranial nerves emerging at the ponto-medullary junction.

A

Abducens:

  • General somatic efferent
  • Innervates the lateral rectus muscle (one of the extrinsic muscles of the eye) which is causes abduction of the eye from the midline → outward gaze

Facial:

  • General somatic efferent - innervates the muscles of facial expression
  • Special visceral afferent - Involved in taste sensation for the anterior 2/3 of the tongue

Vestibulocochlear:

  • Special somatic afferent
  • Involved in balance and hearing
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19
Q

Which three nerves emerge from the lateral medulla?

A
  • Glossopharyngeal (CN IX)
  • Vagus (CN X)
  • Accessory (CN XI)
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20
Q

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

A

Glossopharyngeal:

  • Sensory and motor innervation of the tongue and pharynx

Vagus:

  • Main parasympathetic nerve descending down to the viscera

Accessory:

  • General somatic efferent
  • Supplies the trapezius (allows movement of the scapula) and sternocleidomastoid (allow turning of the head)
21
Q

State the last (12th) cranial nerve.

A

Hypoglossal Nerve (CN XII)

22
Q

What is the role of the hypoglossal nerve?

A
  • General somatic efferent
  • Supplies the musculature of the tongue
23
Q

What are the pyramids?

A

The motor fibres coming down from the motor cortex come via the cerebral peduncles then disappear behind the transverse fibres of the pons

Inferior to the transverse fibres, these motor fibres re-emerge as the pyramids on the anterior surface of the medulla

NOTE: name due to pyramidal shape created by fibres (not pyramidal cells)

24
Q

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

A
  • 90% of fibres undergo pyramidal decussation - these fibres form the lateral corticospinal tract
  • This takes place at the anterior meddian fissure of the medulla
  • This point of dessucation marks the lower limit of the pyramids
25
Q

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

A

General visceral afferent (GVA):

  • Sensory input from visceral organs of the body
    • e.g. GI tract, heart, BVs, lungss

General somatic afferent (GSA):

  • Afferent neurones which are sensory to the body wall (skin), fascia, mucous membranes, muscles and joints
    • (e.g. “Touch”: fine touch, pain, temperature, proprioception, vibration)

General visceral efferent (GVE):

  • Autonomic neurones in the CNS (All autonomic neurones are motor)
    • Preganglionic parasympathetic fibres come are part of cranial nerves sacral spinal nerves
    • Preganglionic sympathetic fibres are part of thoracic and lumbar spinal nerves

General somatic efferent (GSE):

  • Efferent neurones which are motor to skeletal muscles
    • E.g. muscles which control eye and tongue movements
26
Q

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

A

REMEMBER: special afferent means all the senses except for touch

Special visceral afferent (SVA):

  • Neurones carrying information relating to smell and taste
    • Develop in associaton with GI tract (viscera = internal organs)

Special somatic afferent (SSA):

  • Neurones carrying information relating to vision, hearing and balance

Special visceral efferent (SVE):

  • Motor to muscles of facial expression, mastication and laryngeal muscles
  • Motor to the trapezius and sternocleidomastoid
    • Smiling, snacking, singing, sternocleidomastoid
    • Special becuase they provide motor function to skeletal muscles of a different origin within the embryo
27
Q

Summarise which cranial nerves contain which fibre types.

A
28
Q

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

A

Sulcus limitans

29
Q

Describe the structure of the developing spinal cord.

A
  • The grey matter has split into two different types
    • Alar plate (dorsal)
    • Basal plate (ventral)
  • ​​​Neurones within the alar plate develop into afferent neurones
  • Neurones within the basal plate develop into efferent neurones
30
Q

In th embyonic spinal cord, describe the arrangement of the different types of nuclei

A

Dorsal to ventral:

  • GSA
  • GVA
  • Divided by sulcus limitans
  • GVE
  • GSE

NOTES:

  • Visceral nuclei closer to the sulcus limitans than the somatic nuclei
  • No special efferent/afferent fibres shown in the spinal cord as these are related to sructures in the head and neck so exclusive to brainstem
31
Q

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

A
  • In the brainstem, the roof plate proliferates and expands
  • This means that the alar plates on either side move apart
  • This results in the:
    • efferent (motor) nuclei being medial
    • afferent (sensory) nuclei being lateral

NOTE: rhombencephalon = developing hindbrain (pons, medulla, cerebellum) - the picture below shows a cross section of the embryonic rhombencephalon

32
Q

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

A

Efferent (motor) – medial

Afferent (sensory) – lateral

Medial to lateral:

  • GSE
  • SVE
  • GVE
  • Divided by sulcus limitans
  • GVA/SVA - nuclei overlap
  • GSA
  • SSA
33
Q

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

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

NOTE: some CNs are mixed so contain nuclei of more than one group (e.g. have efferent and afferent nuclei)

34
Q

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

A
  • 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

NOTE: some CNs are mixed so contain nuclei of more than one group (e.g. have efferent and afferent nuclei)

35
Q

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

A

 Edinger Westphal = midbrain  Salivatory = ponto-medullary border (there are THREE sets of salivatory nuclei)  Vagus = pons

36
Q

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

A

Vestibulocochlear = pons and medulla

37
Q

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

A

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

38
Q

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

A

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

39
Q

Be able to label this diagram.

A

Image shows cross section of brainstem showing various nuclei

  • Nucleus solitarius comes from 3 CNs - smell and taste (SVA)
  • Edinger Westphal nucleus - parasympathetic portion of oculomotor nerve (GVE)
    • innervates sphincer pupillae and ciliary muscle
  • Nucleus ambiguus comes from 3 CNs - innervates muscles of soft palate, pharynx and larynx; strongly associated with speech and swallowing (GSE)
40
Q

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

A
  • It has a distinctive ‘Mickey Mouse’ appearance
    • Upside down Mickey Mouse when anterior end is closest to you on an image
    • Ears of Mickey Mouse are the cerebral peduncles - at the anterior end
  • 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 protrusions on the opposite side of the cerebral peduncles are the inferior colliculi (for this cross section; on another cross section you may see superior colliculi)
41
Q

What is the substantia nigra? Describe its clinical significance.

A
  • The subtantia nigra is a nucleus which is part of the basal ganglia (group of subcortical nuclei)
  • It is made up of dopaminergic neurones which produce high levels of neuromelanin as part of their normal metabolic reactions, therefore it is dark
  • Important in movement
    • The nigro-striatal pathway is important in control of muslce movement
    • In Parkinson’s disease many of the dopaminergic neurones of the substantia nigra are lost leading to loss of control
    • You can see this as PD patients will have a pale substantia nigra
  • The substantia nigra also has other functions - e.g. plays a role in the feeling of reward
42
Q

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

A
  • The 4th ventricle will be seen at the dorsal (posterior) aspect of the pons
  • The most distinctive feature are the transverse fibres
  • On either side you will see the middle cerebellar peduncles
    • ​The middle cerebellar peduncles are tracts which connect the pons and cerebellum
    • The fibres originate in the pontine nuclei, cross the midline and so go to the opposite hemisphere of the cerebellar cortex (contralateral)
    • These tracts are made up of the transverse fibres of the pons
43
Q

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

A

Midbrain – cerebral peduncles

  • Connects to primary motor area of cerebral cortex

Pons – cerebellar peduncles

  • Connects to cerebellar cortex
44
Q

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

A
  • Pyramids will be seen on the ventral (anterior) aspect
  • An inferior olivary nucleus will be found next to each pyramid
  • The 4th ventricle will still be visible
45
Q

What is the role of the inferior olivary nucleus?

A
  • It is involved in fine tuning motor function
  • The neurones of the nucleus connect to the cerebellum (important role in motor control)

NOTE: inferior olivary nucleus is underneath the superior olivary nucleus, which together make up the olivary body (olive)

46
Q

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

A
  • It will be more round
  • The central canal will be seen in the middle
    • 4th ventricle narrows to form central canal
  • The dorsal columns will be seen on the dorsal (posterior) side
  • The pyramidal decussation may be seen
47
Q

Name the two columns that make up the dorsal columns.

A

Fasciculus Gracilis:

  • More medial
  • Sensory information (touch and prociception) from the lower limbs

Fasciculus Cuneatus:

  • More lateral
  • Sensory information (touch and prociception) from the upper limbs
48
Q

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

A
  • It is a collection of symptoms due to ischeamia in the lateral part of the medulla → disturbances in the nuclei or tracts affected from lack of blood supply
  • It is caused by an occlusion (usually due to thrombosis) in the (left or right) vertebral or posterior inferior cerebellar artery (PICA)
  • It causes:
    • Horner’s Syndrome - go over definition
      • disturbing the sympathetic tract
      • causes symptoms like ptosis (droopy eyelid), decreased sweating, miosis (pupil constriction)
    • Vertigo (the feeling that everything around you is spinning)
      • because of disturbing the vestibular nucleus
    • Ipsilateral loss of pain/thermal sensation on the face
      • disturbing the spinothalamic tract (or spinal trigeminal tract)
      • the trigeminal nerve carrying sensory information from the face descends to a point within the medulla before it decussation
      • ipsilateral because disurbance of the tract before decussation
    • Contralateral loss of pain/thermal sensation on the trunk and limbs
      • disturbing the spinothalamic tract
      • contralateral because crossing over happened in the spinal cord before it gets to the medulla
    • Ipsilateral cerebellar ataxia (lack of coordination of voluntary muscle movements)
      • disturbing the inferior cerebellar peduncle (connects medulla and cerebellum)
    • Hoarseness, difficulty swallowing
      • disruption of nucleus ambiguus

Y2 LCRS 2 - Neuroscience and mental health (23 decks)

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