HNS04 Brainstem

Question 1

Brainstem 3 components

Answer 1

上—>下:

1. Midbrain
2. Pons
3. Medulla oblongata

Question 2

Major functions of Brainstem

Answer 2

1. ALL Ascending (sensory) and Descending (motor) pathways pass through brainstem
2. Nuclei of most cranial nerves are located in brainstem —> control head and neck region
3. Most important life centre e.g. heart beat, breath, BP, ascending activating system area located in brainstem (the reticular formation)

Question 3

***Surface anatomy of brainstem

Answer 3

1. Thalamus (Diencephalon)
   - **Lateral geniculate body
   - **Medial geniculate body
   - Pineal gland
2. Midbrain
   - Superior colliculi
   - Inferior colliculi
   (Superior colliculi + Inferior colliculi —> Corpora quadrigemina)
   - Cerebral peduncle (all nerve fibres from cerebrum to spinal cord)
   - Mammillary body (anterior)

—> CN2-4 (3 at boundary)

3. Pons
   - Superior cerebellar peduncle
   - Middle cerebellar peduncle
   - Inferior cerebellar peduncle
   - Fourth ventricle (Rhomboid fossa)

—> CN5
—> CN6-8 at boundary

4. Medulla oblongata
   - Cuneate tubercle
   - Gracile tubercle
   - Corticospinal tract
   - Olive
   - Decussation of pyramid

—> CN9-12

Question 4

Medulla oblongata external features

Answer 4

Anterior:

• Anterior median fissure
• Pyramid
• Decussation of pyramid (corticospinal tract R/L crossing)

Lateral:

• Olive
• Cuneate tubercle (upper body sensation)

Posterior:
- Posterior median fissure
- Gracile tubercle (lower body sensation)
(- Stria medullares)

Question 5

Pons external features

Answer 5

Anterior:
- Basilar sulcus

Lateral:

• Trigeminal nerve (CN5)
• Middle cerebellar peduncle (signals from cerebrum to cerebellum)

Posterior:
- Superior cerebellar peduncle (signals from cerebellum to cerebrum)
- Inferior cerebellar peduncle (signals from spinal cord to cerebellum)
- Fourth ventricle
(- Median sulcus
- Sulcus limitans
- Stria medullares)

Question 6

Midbrain external features

Answer 6

Anterior:

• Mammillary body
• Occulomotor nerve (CN3)
• Interpeduncular fossa

Lateral:
- Cerebral peduncle

Posterior:

• Superior colliculi (vision + motor)
• Inferior colliculi (hearing + motor)
• Trochlear nerve (CN4)

Question 7

Medulla oblongata internal features

Answer 7

Anterior (descending / motor pathways):

• Anterior gray column
• Medullary pyramids (Pyramidal decussation of Corticospinal tract (descending))

Upper Anterior:

• Inferior olivary nucleus
• Medial Lemniscus (convey mechanical sensation; ascending pathway to thalamus)
• Corticospinal tract

Posterior (ascending / sensory pathways):

• ***Fasciculus Cuneatus (upper body sensation) —> Nucleus Cuneatus (2nd neurons located in here)
• ***Fasciculus Gracilis (lower body sensation) —> Nucleus Gracilis
• Internal arcuate fibres (Decussation for Dorsal column-medial lemniscal pathway)
• Trigeminal nucleus
• Hypoglossal nucleus
• Fourth ventricle

Upper Posterior:
- Vagus nucleus, Vestibular nucleus, Ambiguus nucleus (upper region between medulla and pons)

Centre:
- Reticular formation

Upper Lateral:
- Spinothalamic tract (pain sensation)

Question 8

Pons internal features

Answer 8

Anterior:

• ***Pontine nucleus (giving rise to Pontocerebellar fibres —> then connects to Middle cerebellar peduncle)
• Corticospinal tract (descending pathway, patches within Pontine nucleus)

Posterior:

• Abducens nucleus (CN6)
• Facial nucleus (CN7)
• Medial lemniscus (horizontal arrangement)
• Reticular formation
• ***Superior cerebellar peduncle

Lateral:

• ***Inferior cerebellar peduncle
• ***Middle cerebellar peduncle

Upper Centre:
- Trochlear nucleus (CN4)

Question 9

Midbrain internal features

Answer 9

Anterior (Tegmentum):

• Interpeduncular fossa
• Occulomotor nerve (CN3)

Posterior (Tectum):

• Superior colliculi
• Inferior colliculi

Lateral:

• ***Cerebral peduncle (collect all fibre communicating from cerebrum to lower brain, major region for descending pathway)
• ***Substantia nigra (deep to cerebral peduncle, region of basal ganglia)
• Medial lemniscus
• Corticospinal tract

Centre:

• ***Cerebral aqueduct
• ***Periaqueductal gray (modify pain sensation)
• Occulomotor nucleus / Edinger-Westphal nucleus
• Reticular formation
• ***Red nucleus (motor control)

Tegmentum + Tectum separate by line drawn across colliculi —> Anterior + Posterior part

Question 10

***Functions of Medulla oblongata

Answer 10

1. Connect with spinal cord with ascending + descending nerve tracts
2. CN5, 9-12 nuclei
3. Discrete nuclei in internal gray matter
4. Regulates **HR, vessel diameter, **respiration, ***swallowing, vomiting, hiccupping, coughing, sneezing
5. ***Pyramids: descending nerve tracts on anterior surface
   —> Inferiorly fibres decussate —> each half of brain controls opposite half of body
6. **Olives: rounded, protrude from anterior surface
   —> Nuclei within help regulate balance, coordination, modulation of **sound from inner ear

Question 11

***Functions of Pons

Answer 11

Bridge of ascending and descending fibre tracts

Nuclei

1. CN5-9: posterior portion
2. ***Pontine: anterior portion, relay between cerebrum and cerebellum (Pontocerebellar fibres —> Middle cerebellar peduncle —> Cerebellum)
3. ***Sleep centre
4. ***Respiratory centre coordinates with centre in medulla

Question 12

***Functions of Midbrain

Answer 12

Nuclei:

1. CN3-5 (Trigeminal nucleus widely distributed within whole brainstem)
2. ***Tectum: 4 nuclei that form mounds on dorsal surface of midbrain
   —> each separate part is a colliculus
   —> 2 superior colliculi: visual reflex, receive information from inferior colliculi, eyes, skin, cerebrum
   —> 2 inferior colliculi: hearing
3. ***Red nuclei of tegmentum
   —> unconscious regulation and coordination of motor activities
4. ***Substantia nigra:
   —> pigmented with melanin
   —> interconnected with basal nuclei of cerebrum

Tracts:

• Tegmentum
  —> Ascending tracts such as spinal + medial lemniscus from spinal cord to brain (Spinothalamic tract)
• Descending
  —> ***Cerebral peduncle from cerebrum through brainstem to spinal cord (Corticospinal tract)

Question 13

***Reticular formation

Answer 13

• ***Diffusely interconnected neurons in brainstem (different from more distinct nuclei associated with cranial nerves)
• Integrate sensory, motor, visceral, limbic functions —> project throughout CNS
• Important influence on Autonomic regulation of vital organ system, behaviour, somatic motor activities, sleep cycles, alertness, pain modulation

Major subsystem:

1. ARAS
   - VTA, Substantia nigra (Dopaminergic)
   - Locus coeruleus (Noradrenergic)
   - Raphe nucleus (***Serotonergic)
   - Pontine (ACh)
2. Descending tracts
   - Red nucleus —> **Rubrospinal tract
   - Reticular nuclei —> **Reticulospinal tract (Medial / Lateral)
   - Lateral Vestibular nucleus —> ***Lateral Vestibulospinal tract

Question 14

***Ascending Reticular Activating System (ARAS)

Answer 14

Diffuse neurons in Reticular formation

1. Locus coeruleus
   —> Norepinephrine system —> ***Fight/flight response
2. Raphe nucleus
   —> Serotonin system —> Functions of ***basal ganglia, Emotion
3. Pontine
   —> ACh system —> ***Sleep/wake cycle, Wakefulness
4. Substantia nigra / Ventral Tegmental Area (VTA)
   —> Dopamine system —> **Dopaminergic neurons of basal ganglia, Cognitives, **Memory, Incentive feelings

Question 15

Common disorders of Brainstem (Occlusion of PICA)

Answer 15

Occlusion of PICA supplying lateral aspect of medulla
—> Wallenberg syndrome

1. CN5 —> Ipsilateral analgesia + thermoanaesthesia of face
2. Spinothalamic tract —> Contralateral analgesia + thermoanaesthesia below neck
3. Ambiguus nucleus, CN9, 10 —> Ipsilateral paralysis of palatal + laryngeal muscles
4. Sympathetic nerve injury —> Horner’s syndrome, drooping of eyelid, pupil constriction

Question 16

Common disorders of Brainstem (Occlusion of Vertebral artery)

Answer 16

Occlusion of branches of Vertebral artery supplying medial aspect of medulla
—> Medial Medullary syndrome

1. Medial lemniscus —> Contralateral impaired sensation of position, movement, tactile discrimination
2. Corticospinal hemiparesis —> Contralateral hemiparesis
3. CN 12 —> Ipsilateral paralysis of tongue muscle with deviation to the paralysed side when tongue is protruded

Question 17

Other common disorder of Brainstem

Answer 17

1. Blockage of cerebral aqueduct
   —> prevent flow of CSF from ventricles to subarachnoid space
   —> Hydrocephalus + Cerebral lesion (through compression)
2. Degeneration of neurons in Substantia nigra
   —> Parkinsonism
3. Damage of reticular formation
   —> loss of many important life functions e.g. lesion may cause sleep / coma due to interruption of ascending activating system

Question 18

Summary: Structures in Medulla

Answer 18

External:
Anterior:
- Anterior median fissure
- Pyramid
- ***Decussation of pyramid (corticospinal tract R/L crossing)

Lateral:

• Olive
• ***Cuneate tubercle (upper body sensation)

Posterior:
- Posterior median fissure
- ***Gracile tubercle (lower body sensation)
(- Stria medullares)

Internal:
Anterior (descending / motor pathways):
- Anterior gray column
- ***Medullary pyramids (Pyramidal decussation of Corticospinal tract (descending))

Upper Anterior:

• Inferior olivary nucleus
• ***Medial Lemniscus (convey mechanical sensation; ascending pathway to thalamus)
• ***Corticospinal tract

Posterior (ascending / sensory pathways):

• ***Fasciculus Cuneatus (upper body sensation) —> Nucleus Cuneatus (2nd neurons located in here)
• ***Fasciculus Gracilis (lower body sensation) —> Nucleus Gracilis
• Internal arcuate fibres (Decussation for Dorsal column-medial lemniscal pathway)
• Trigeminal nucleus
• Hypoglossal nucleus
• Fourth ventricle

Upper Posterior:
- Vagus nucleus, Vestibular nucleus, Ambiguus nucleus (upper region between medulla and pons)

Centre:
- Reticular formation

Upper Lateral:
- Spinothalamic tract (pain sensation)

Cranial nerve —> CN9-12

Question 19

Summary: Structures in Pons

Answer 19

External:
Anterior:
- Basilar sulcus

Lateral:

• Trigeminal nerve (CN5)
• ***Middle cerebellar peduncle (signals from cerebrum to cerebellum)

Posterior:
- **Superior cerebellar peduncle (signals from cerebellum to cerebrum)
- **Inferior cerebellar peduncle (signals from spinal cord to cerebellum)
- ***Fourth ventricle
(- Median sulcus
- Sulcus limitans
- Stria medullares)

Internal:
Anterior:
- ***Pontine nucleus (giving rise to Pontocerebellar fibres —> then connects to Middle cerebellar peduncle)
- Corticospinal tract (descending pathway, patches within Pontine nucleus)

Posterior:

• Abducens nucleus (CN6)
• Facial nucleus (CN7)
• Medial lemniscus (horizontal arrangement)
• Reticular formation
• ***Superior cerebellar peduncle

Lateral:

• ***Inferior cerebellar peduncle
• ***Middle cerebellar peduncle

Upper Centre:
- Trochlear nucleus (CN4)

Cranial nerve:
—> CN5
—> CN6-8 at boundary

Question 20

Summary: Structures in Midbrain

Answer 20

External:
Anterior:
- Mammillary body
- Occulomotor nerve (CN3)
- Interpeduncular fossa

Lateral:
- ***Cerebral peduncle

Posterior:

• ***Superior colliculi (vision + motor)
• ***Inferior colliculi (hearing + motor)
• Trochlear nerve (CN4)

Internal:
Anterior (Tegmentum):
- Interpeduncular fossa
- Occulomotor nerve (CN3)

Posterior (Tectum):

• ***Superior colliculi
• ***Inferior colliculi

Lateral:

• ***Cerebral peduncle (collect all fibre communicating from cerebrum to lower brain, major region for descending pathway)
• ***Substantia nigra (deep to cerebral peduncle, region of basal ganglia)
• Medial lemniscus
• Corticospinal tract

Centre:

• ***Cerebral aqueduct
• ***Periaqueductal gray (modify pain sensation)
• Occulomotor nucleus / Edinger-Westphal nucleus
• Reticular formation
• ***Red nucleus (motor control)

Tectum + Tegmentum separate by line drawn across colliculi —> Anterior + Posterior part

Cranial nerve —> CN2-4 (3 at boundary)

Question 21

Cerebral peduncle

Answer 21

Collect all fibre communicating from cerebrum to lower brain, major region for descending pathway

Question 22

Cranial nerve nuclei in Brainstem

Answer 22

Midbrain: CN3-5
Pons: CN5-9
Medulla: CN5, 9-12