HNS04 Brainstem Flashcards
Brainstem 3 components
上—>下:
- Midbrain
- Pons
- Medulla oblongata
Major functions of Brainstem
- ALL Ascending (sensory) and Descending (motor) pathways pass through brainstem
- Nuclei of most cranial nerves are located in brainstem —> control head and neck region
- Most important life centre e.g. heart beat, breath, BP, ascending activating system area located in brainstem (the reticular formation)
***Surface anatomy of brainstem
- Thalamus (Diencephalon)
- **Lateral geniculate body
- **Medial geniculate body
- Pineal gland - 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)
- Pons
- Superior cerebellar peduncle
- Middle cerebellar peduncle
- Inferior cerebellar peduncle
- Fourth ventricle (Rhomboid fossa)
—> CN5
—> CN6-8 at boundary
- Medulla oblongata
- Cuneate tubercle
- Gracile tubercle
- Corticospinal tract
- Olive
- Decussation of pyramid
—> CN9-12
Medulla oblongata external features
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)
Pons external features
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)
Midbrain external features
Anterior:
- Mammillary body
- Occulomotor nerve (CN3)
- Interpeduncular fossa
Lateral:
- Cerebral peduncle
Posterior:
- Superior colliculi (vision + motor)
- Inferior colliculi (hearing + motor)
- Trochlear nerve (CN4)
Medulla oblongata internal features
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)
Pons internal features
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)
Midbrain internal features
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
***Functions of Medulla oblongata
- Connect with spinal cord with ascending + descending nerve tracts
- CN5, 9-12 nuclei
- Discrete nuclei in internal gray matter
- Regulates **HR, vessel diameter, **respiration, ***swallowing, vomiting, hiccupping, coughing, sneezing
- ***Pyramids: descending nerve tracts on anterior surface
—> Inferiorly fibres decussate —> each half of brain controls opposite half of body -
**Olives: rounded, protrude from anterior surface
—> Nuclei within help regulate balance, coordination, modulation of **sound from inner ear
***Functions of Pons
Bridge of ascending and descending fibre tracts
Nuclei
- CN5-9: posterior portion
- ***Pontine: anterior portion, relay between cerebrum and cerebellum (Pontocerebellar fibres —> Middle cerebellar peduncle —> Cerebellum)
- ***Sleep centre
- ***Respiratory centre coordinates with centre in medulla
***Functions of Midbrain
Nuclei:
- CN3-5 (Trigeminal nucleus widely distributed within whole brainstem)
- ***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 - ***Red nuclei of tegmentum
—> unconscious regulation and coordination of motor activities - ***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)
***Reticular formation
- ***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:
- ARAS
- VTA, Substantia nigra (Dopaminergic)
- Locus coeruleus (Noradrenergic)
- Raphe nucleus (***Serotonergic)
- Pontine (ACh) - Descending tracts
- Red nucleus —> **Rubrospinal tract
- Reticular nuclei —> **Reticulospinal tract (Medial / Lateral)
- Lateral Vestibular nucleus —> ***Lateral Vestibulospinal tract
***Ascending Reticular Activating System (ARAS)
Diffuse neurons in Reticular formation
- Locus coeruleus
—> Norepinephrine system —> ***Fight/flight response - Raphe nucleus
—> Serotonin system —> Functions of ***basal ganglia, Emotion - Pontine
—> ACh system —> ***Sleep/wake cycle, Wakefulness - Substantia nigra / Ventral Tegmental Area (VTA)
—> Dopamine system —> **Dopaminergic neurons of basal ganglia, Cognitives, **Memory, Incentive feelings
Common disorders of Brainstem (Occlusion of PICA)
Occlusion of PICA supplying lateral aspect of medulla
—> Wallenberg syndrome
- CN5 —> Ipsilateral analgesia + thermoanaesthesia of face
- Spinothalamic tract —> Contralateral analgesia + thermoanaesthesia below neck
- Ambiguus nucleus, CN9, 10 —> Ipsilateral paralysis of palatal + laryngeal muscles
- Sympathetic nerve injury —> Horner’s syndrome, drooping of eyelid, pupil constriction
