Organisation of the Brainstem and Cranial Nerves Flashcards
Where are the colliculi found and what are their functions?
Roof of the midbrain
Superior: coordination of eye + neck movement
Inferior: auditory reflexes – turning head in direction of loud noise
Describe the location of the pons relative to the ventricular system.
Pons is the floor of the 4th ventricle
Name the unpaired, midline structure on the posterior aspect of the brainstem.
Pineal gland
What is the role of the pineal gland?
Produces melatonin (involved in regulating circadian rhythms)
Which cranial nerve emerges from the back of the brainstem?
Trochlear nerve
What is the role of the Trochlear nerve? (CN IV)
Supplies superior oblique muscle: 1 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 + proprioception
What 3 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?
The inferior part of the hypothalamus (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’?
Descending motor tracts from the motor cortex.
Peduncle = a structure that has a functional + 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 the Trigeminal nerve? (CNV)
Touch + sensation throughout the head + neck
It has a small root next to the larger one as it emerges out of the transverse fibres = motor root providing motor innervation of the muscles of mastication
Which 3 nerves emerge at the pontomedullary junction (from medial to lateral)?
Medially: Abducens (CNVI)
Lateral: Facial (CNVII)
(more) Lateral: Vestibulocochlear (CNVIII)
Briefly state the role of CN VI, VII, VIII
Abducens: innervates lateral rectus, allows lateral eye movement
Facial: innervates muscles of facial expression + taste sensation for anterior 2/3 of tongue
Vestibulocochlear: involved in balance + hearing
Which 3 nerves emerge from the lateral medulla?
Glossopharyngeal (CNIX)
Vagus (CNX)
Accessory (CNXI)
Briefly state the role of CN IX, X, XI
Glossopharyngeal: sensory + motor innervation of the tongue + pharynx
Vagus: main parasympathetic output to the viscera
Accessory: supplies the trapezius + sternocleidomastoid
State the last cranial nerve – CN XII.
Hypoglossal: supplies 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
If a problem occurs in the corticospinal tract it results in “pyramidal symptoms”
If problems in cerebellum/ other parts involved in motor control = “extrapyramidal symptoms”
What percentage of motor fibres cross to the contralateral side of the body in the brainstem and where does this changing of sides take place?
90-95%
At the base of the medulla
What are the 4 functional subtypes of the cranial nerves and what are their actions?
General Somatic Afferent: Sensation from skin + mucous membranes
General Visceral Afferent: Sensation from GIT, heart, vessels + lungs
General Somatic Efferent: Muscles for eye + tongue movements
General Visceral Efferent: Preganglionic parasympathetic
What are the special subtypes of cranial nerves and what are their actions?
Special Somatic Afferent: Vision, hearing + equilibrium
Special Visceral Afferent: Smell + Taste
Special Visceral Efferent: Muscles involved in chewing, facial expression, swallowing, vocal sounds + turning head
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?
Alar plate opens up, a ventricle forms
This opening of the alar plate results in motor nuclei being medial in the brainstem + the sensory nuclei lateral
Describe the arrangement of the different groups in columns within the brainstem.
Motor: Medial. Arranged in columns from medial to lateral in this order: GSE, SVE, GVE
Sensory: Lateral. 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 + Trochlear = midbrain
Abducens = pons (though emerges at the ponto-medullary junction)
Hypoglossal = medulla
State the nuclei that are in the special visceral efferent group and describe their location within the brainstem.
Trigeminal + Facial = pons
Ambiguus = medulla
Accessory = cervical spinal cord
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 (3 sets of salivatory nuclei)
Vagus = medulla
State the nuclei that are in the special somatic AFFERENT group and describe their location within the brainstem.
Vestibulocochlear = pons + medulla
State the nuclei that are in the general somatic AFFERENT groupand describe their location within the brainstem.
Trigeminal = in all 3 parts + 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 (+ a little bit in pons)
Describe the appearance of a cross-section of the midbrain. What are the key features seen?
‘Mickey mouse’ appearance
Ears= cerebral peduncles
Where the cerebral peduncles meet the rest of the midbrain = substantia nigra
Cerebral aqueduct in the middle (small diamond shape)
The 2 rounded protrusion on the opposite side of the cerebral peduncles = inferior colliculi
What is the substantia nigra? Describe its clinical significance.
A group of dopaminergic neurons
Produce neuromelanin, (gives black colour of the substantia nigra)
PD is caused by loss of these dopaminergic neurons so patients with PD 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
Most distinctive feature= 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 on the ventral aspect
Inferior olivary nucleus next to the pyramids
The 4th ventricle will still be visible
What is the role of the inferior olivary nucleus?
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
Central canal in the middle
Dorsal columns on the dorsal side
Pyramidal decussation (crossing of 90% fibres)
Name the 2 columns that make up the dorsal columns.
Gracilis: more medial – sensory info. from lower limb
Cuneatus: more lateral – sensory info. from upper limb
What is lateral medullary syndrome? Describe and explain the symptoms.
Group of symptoms caused by thrombosis of vertebral artery or posterior inferior cerebellar arteries (PICA)
Causes:
Horner’s Syndrome (disturbing sympathetic tract)
Vertigo (disturbing the vestibular nucleus)
Ipsilateral loss of pain/thermal sensation on the face (disturbing spinothalamic tract)
Contralateral loss of pain/thermal sensation (trunk + limbs– disturbing spinothalamic tract)
Ipsilateral cerebellar ataxia (disturbing inferior cerebellar peduncle)
What are the symptoms of Horner’s Syndrome?
Ptosis
Lack of sweating around the eye
Hoarseness
Difficulty Swallowing
What is the brainstem?
Part of the CNS, exclusive of the cerebellum
Lies between the cerebrum + spinal cord
What are the 3 major divisions of the brainstem?
Medulla oblongata
Pons
Midbrain
