4. Brainstem Flashcards
Describe the dorsal-ventral patterning in the development of the brainstem?
- Alar plates produces neurones of the sensory (somatic) pathways
- Basal plates produce voluntary (somatic) motor neurones
- The intermediate region (sulcus limitans) produces motor and sensory neurones of the visceral (autonomic) pathways
Describe the medio-lateral patterning in the development of the brainstem?
- Neural tube expands outwards stretching the roof plate out into a broad membrane (ependyma)
- Brings the sensory nuclei (alar) to lie lateral to the motor regions (basal)
- Some alar plate neurones migrate ventrally to form special nuclei in the base of the pons and medulla
What are the functions of the brainstem?
- Passage or ascending/descending tracts connecting the spinal cord to high centres.
- Contains reflex centres associated with control of respiration, cardiovascular system and consciousness
- Contains the important nuclei of cranial nerves III to XII (i.e. all cranial nerves, except first two, are connected to brainstem)
Describe the features present on the ventral Medulla?
Pyramids
o First two superior swellings from the interior part of the medulla
o From here the pyramidal tracts (corticospinal tract carrying the main motor nerves)
Olives
o Contains the olivary nucleus
Decussation of the pyramids
o Fibres passing one side to the other
o Corticospinal tract decussate here. The motor fibres cross here
Number of cranial nerves (9-11/12)
Describe the features present on the dorsal Medulla?
Cerebellum forms ‘roof’ of pons & upper medulla (to see requires removal of cerebellum)
• 3 pairs of peduncles (“stalks” of neurons) to see posterior brainstem(Superior, middle, inferior.)
• Posterior surface: dorsal median sulcus (continuous with that of cord)
• Dorsal columns (fasciculus gracilis & cuneatus) continue to nucleus gracilis & cuneatus
Where does the Medulla join the spinal cord?
At the opening of the foramina magnum, at the level of C1
What is the significance of the olives?
They contain the inferior olivary nuclear complex, an important part of the cerebellar circuitry
What route does the spinocerebellar tract take through the brainstem
Does not cross
Lies lateral to the cuneate fasciculus
Exits through the the inferior cerebellar peduncle
Describe the origins of the pyramids and their role in motor decussation?
- Descending motor tracts enter the brainstem from the hemispheres via the cerebral peduncles.
- Pass through the pons into the medulla
- In the medulla, they are grouped together and close to the surface so that they form the pyramids on the surface
Describe the features present on the ventral Pons?
Ventral Pons: Dominated by transverse fibres (pontocerebellar fibres); pontine nuclei to cerebellum (via middle cerebellar peduncle)
Describe the features present on the dorsal Pons?
Trochlear nerve (CNIV) merges from posterior surface (only one) between pons & midbrain
Describe the features present on the ventral Mid-brain?
Midbrain: Huge column of descending fibres on either side - cerebral peduncles (crura cerebri); separated by interpeduncular fossa – Mammillary bodies
Describe the features present on the dorsal Mid-brain?
Trochlear nerve (CNIV) merges from posterior surface (only one) between pons & midbrain
Midbrain: Marked by 4 paired elevations:
– Superior colliculi: Part of visual system
– Inferior colliculi: Part of auditory system
Describe the internal features of the Pons?
– Posterior part – the tegmentum (Latin “covering”)
– Anterior part – basis pontis (basal part)
– Basal part – numerous transversely oriented pontocerebellar fibres originating from scattered pontine nuclei
Describe the internal features of the Midbrain?
– Tectum (tectal plate): posterior; forms ‘roof’ of midbrain
– Tegmentum
– Basal portion (composed of crura cerebri [cerebral peduncles])
Draw and label a transverse segment of the midbrain
Tectum
What constitutes the tectum in the midbrain?
Tectum in midbrain is composed of four colliculi – 2 superior (visual reflexes) and 2 inferior (auditory information)
What is contained within the tegmentum of midbrain?
o Upper tegmentum contains the paired red nucleus (involved in motor control; iron gives it pink hue)
o (Corticorubral and rubrospinal tracts together form an indirect corticospinal tract)
What is the Substantia Nigra
Pigmented (melanin) mass of neurons – role in muscle tone/activity - degeneration is associated with Parkinson’s disease
List the Cranial Nerves which emerge from the brainstem and draw/describe their locations.
(III, IV) Oculomotor & Trochlear nerves – leave the midbrain
(V) Trigeminal nerve – leaves the side of the pons by two roots
(VI) Abducens nerve – leaves in the groove between medulla and pons
(VII) Facial nerve – leaves the upper medulla by two roots
(VIII) Vestibulocochlear (auditory) nerve
(IX, X) Glossopharyngeal & Vagus nerves – leave the medulla dorsal to the olive
(XI, XII) Accessory & Hypoglossal nerve – leave between the pyramids and olives by many roots; XII supplies the muscles of the tongue
Each one gets fibres from nuclei in the brainstem depending on what it supplies
