Organisation of the Brainstem and Cranial Nerves Flashcards
Where are the colliculi found and what are their functions?
Roof (means dorsal in neuroanatomy) of the midbrain Superior – important for the coordination of eye and head movements at the same time (watching tennis on TV
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 this structure?
It produces melatonin, which is involved in regulating the circadian rhythm
Which cranial nerve emerges from the back of the brainstem?
Trochlear nerve - the only nerve that emerges from the back of the brainstem.
Supplies one of the extrinsic muscles of the eye
What is the role of this nerve? (CN IV)
It supplies the superior oblique muscle – one of the extrinsic muscles of the eye
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
Which cranial nerve emerges in the midline just above the transverse fibres of the pons?
Oculomotor Nerve (CN III)
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
Name the cranial nerve that emerges from the lateral aspect of the pons.
Trigeminal (CN V)
What is the role of this nerve? (CNV)
Touch and sensation throughout the head and neck It has a small root next to the larger one as it emerges out of the transverse fibres – this is the motor root providing motor innervation of the muscles of mastication
Which three nerves emerge at the pontomedullary junction (from medial to lateral)?
Abducens (VI), Facial (VII), Vestibulocochlear (VIII)
Briefly state the role of each of these cranial nerves. (CN VI, VII, VIII)
Abducens – innervates the lateral rectus which is involved in abducting the eye
Facial – innervates the muscles of facial expression and is involved in taste sensation for the anterior 2/3 of the tongue
Vestibulocochlear – involved in balance and hearing
Which three nerves emerge from the lateral medulla?
Glossopharyngeal (IX), Vagus(X) and Accessory (XI)
Briefly state the role of each of these cranial nerves. (CN IX, X, XI)
Glossopharyngeal – sensory and motor innervation of the tongue and pharynx Vagus – main parasympathetic nerve descending down to the viscera Accessory – supplies the trapezius and sternocleidomastoid
State the last cranial nerve – CN XII.
Hypoglossal Nerve – supplies the musculature of the tongue
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 (pyramids = motor, dorsal columns = sensory)
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%
pyramidal decussation (part of the medulla)
What are the four functional subtypes of the cranial nerves and what are their actions?
General Somatic Afferent - Sensation from the skin and mucous membranes
General Visceral Afferent- Sensation from the GIT, heart, vessels and lungs
General Somatic Efferent - supply Skeletal muscles. The GSE fibres emerging from the brainstem would supply the Muscles for eye and tongue movements
General Visceral Efferent- Can be parasympathetic or sympathetic but the ones from the cranial nerves are the Preganglionic parasympathetic fibres (para=cranioscaral)
What are the special subtypes of cranial nerves and what are their actions?
Special Somatic Afferent- Vision, hearing and equilibrium
Special Visceral Afferent - Smell and Taste (comes from three nerves that converge on the nucleus solitarius)
Special Visceral Efferent- Muscles involved in chewing, facial expression, swallowing, vocal sounds and turning the head
What structure separates the sensory (afferent) nuclei from the motor (sensory) 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
Sensory – Lateral
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 (III) = midbrain
Trochlear (IV) = midbrain
Abducens (VI) = pons (though it emerges at the ponto-medullary junction)
Hypoglossus (XII) = 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
What is the difference between the peduncles seen in the midbrain and the ones seen in the pons?
Midbrain –cerebral peduncles Pons – 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
What is the role of the inferior olivary nucleus?
It is involved in fine tuning motor function
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
Name the two columns that make up the dorsal columns.
Gracilis – more medial – sensory information from the lower limb Cuneatus – more lateral – sensory information from the upper limb
What is lateral medullary syndrome? Describe and explain the symptoms.
Thrombosis of vertebral artery or PICA (posterior inferior cerebellar art.)
◦Vertigo
◦Ipsilateral cerebellar ataxia
◦Ipsilateral loss of pain/thermal sense (face)
◦Horner’s syndrome
◦Hoarseness, difficulty in swallowing
◦Contralateral loss of pain/thermal sense (trunk and limbs)
What are the symptoms of Horner’s Syndrome?
Ptosis Loss of sweating around the eye Hoarseness Difficulty Swallowing
