Organisation of the Brainstem and Cranial Nerves Flashcards
Where are the colliculi found and what are their functions?
Roof of the midbrain Superior – important for the coordination of eye and head movements at the same time Inferior – auditory reflexes – turning your head in the direction of a loud noise
Describe the location of the pons relative to the ventricular system.
The pons is the floor of the 4th ventricle
Name an important unpaired, midline structure on the posterior aspect of the brainstem.
Pineal gland
What is the role of the pineal gland?
It produces melatonin, which is involved in regulating the circadian rhythm
Which cranial nerve emerges from the back of the brainstem?
Trochlear nerve
What structure defines the medulla in the dorsal aspect and what pathways are found within this structure?
Dorsal Columns – sensory pathways – touch and proprioception
What three significant structures can be seen superior to the pons when viewing the brainstem from an anteroinferior view?
Optic Chiasm Pituitary Stalk (infundibulum) Mammillary Bodies
What are the mammillary bodies?
They are the inferior part of the hypothalamus – it is part of the limbic system
What are the cerebral peduncles? What is the significance of the word ‘peduncle’?
These are the descending motor tracts coming from the motor cortex. Peduncle is specifically a structure that has a functional AND structural role – it holds the cerebrum onto the brainstem
The motor fibres coming down from the motor cortex come via the cerebral peduncles then disappear behind the transverse fibres of the pons. What structure do they re-emerge as, inferior to the transverse fibres?
Pyramids
What percentage of motor fibres cross to the contralateral side of the body in the brainstem and where does this changing of sidestake place?
90-95%
What are the four functional subtypes of the cranial nerves?
General Somatic Afferent General Visceral Afferent General Somatic Efferent General Visceral Efferent
What are the special subtypes of cranial nerves?
Special Somatic Afferent
Special Visceral Afferent
Special Visceral Efferent
What structure separates the sensory nuclei from the motor nuclei in the spinal cord and brainstem?
Sulcus limitans
What happens in the formation of the rhombencephalon and how does this affect the arrangement of the nuclei?
The alar plate opens up and a ventricle forms This opening of the alar plate results in the motor nuclei being medial in the brainstem and the sensory nuclei are lateral
Describe the arrangement of the different groups in columns within the brainstem.
Motor – Medial (left) Sensory – Lateral (right) Motor – arranged in columns from medial to lateral in this order: GSE, SVE, GVE Sensory – arranged in columns from medial to lateral in this order: GVA/SVA, GSA, SSA
State the nuclei that are in the general somatic efferent group and describe their location within the brainstem.
Oculomotor- midbrain Trochlear-midbrain Abducens- pons Hypoglossus-medulla
State the nuclei that are in the special visceral efferent group and describe their location within the brainstem.
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
State the nuclei that are in the general visceral efferent group and describe their location within the brainstem.
Edinger Westphal = midbrain Salivatory = ponto-medullary border (there are THREE sets of salivatory nuclei) Vagus = pons
State the nuclei that are in the special somatic AFFERENT group and describe their location within the brainstem.
Vestibulocochlear = pons and medulla
State the nuclei that are in the general somatic AFFERENT groupand describe their location within the brainstem.
Trigeminal = in all three parts and in the cervical spinal cord
State the nuclei that are in the general visceral AFFERENT and special visceral AFFERENT groups and describe their location within the brainstem.
Solitarius – mainly in the medulla (but a little bit in the pons)
Describe the appearance of a cross-section of the midbrain. What are the key features seen?
It has a distinctive ‘mickey mouse’ appearance Ears of Mickey Mouse are the cerebral peduncles 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 protrusion on the opposite side of the cerebral peduncles are the inferior colliculi
What is the substantia nigra? Describe its clinical significance.
The substantia nigra is a group of dopaminergic neurons In their normal metabolism they produce neuromelanin, which gives the black colour of the substantia nigra Parkinson’s disease is caused by loss of these dopaminergic neurons so patients with Parkinson’s will have a pale substantia nigra
Describe the appearance of a cross-section of the pons. What are the key features seen?
The 4th ventricle will be seen at the dorsal aspect of the pons The most distinctive feature are the transverse fibres On either side you will see the middle cerebellar peduncles
Describe the appearance of a cross-section of the medulla. What are the key features seen?
Pyramids will be seen on the ventral aspect The inferior olivary nucleus will be found next to the pyramids The 4th ventricle will still be visible
Describe the appearance of a cross-section of the lower medulla. What are the key features seen?
It will be more round The central canal will be seen in the middle The dorsal columns will be seen on the dorsal side The pyramidal decussation may be seen
Distribution of cranial nuclei in embyonic plate
Afferent dorsal and efferent ventral Visceral more towards centre
