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.
At floor of 4th Ventricle
Name an important unpaired, midline structure on the posterior aspect of the brainstem. What is its role?
Pineal gland, produces melatonin, which is involved in regulating the circadian rhythm
Which cranial nerve emerges from the dorsal aspect of the brainstem? What is its role?
Trochlear nerve – CN IV
The Trochlear nerve innervates a single muscle, the superior oblique muscle (an extrinsic muscle of the eye), contralateral to its nucleus.
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?
Part of limbic system, inferior parts of hypothalamus
Which cranial nerve emerges in the midline just above the transverse fibres of the pons?
Oculomotor Nerve (CN III)
What are the cerebral peduncles?
These are the descending motor tracts coming from the motor cortex. They are peduncles as they have 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. What is its role?
Trigeminal (CN V)
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 (chewing)
Which three nerves emerge at the pontomedullary junction (from medial to lateral)? What are their roles?
Abducens (CN VI) - Innervates the lateral rectus which is involved in abducting the eye
Facial (CN VII) - Innervates the muscles of facial expression and is involved in taste sensation for the anterior 2/3 of the tongue
Vestibulocochlear (CN VIII) - Involved in balance and hearing
Which three nerves emerge from the lateral medulla? What are their roles?
Glossopharyngeal (CN IX) - sensory and motor innervation of the tongue and pharynx
Vagus (CN X) - main parasympathetic nerve descending down to the viscera
Accessory (CN XI) - supplies the trapezius and sternocleidomastoid
Which cranial nerve traverses a foramen in the occipital bone?
CN XII – Hypoglossal nerve, supplies motor innervation to muscles of 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
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 pyramidal decussation
What are the four general subtypes of cranial nerves and 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
Muscles for eye and tongue movements
General Visceral Efferent
Preganglionic parasympathetic
What are the special subtypes of cranial nerves and what are their actions?
Special Somatic Afferent (CN II & CN VIII)
Vision, hearing and equilibrium
Special Visceral Afferent (CN I, CN VII, CN IX, CN X)
Smell and Taste (comes from three nerves that converge on the nucleus solitarius)
Special Visceral Efferent (CN V, CN VII, CN IX, CN X, & CN XI)
Muscles involved in chewing, facial expression, swallowing, vocal sounds and turning the 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?
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 = midbrain Trochlear = midbrain Abducens = pons (though it emerges at the ponto-medullary junction) 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 group and 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 – Cerebella 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 (Note this column traverses the entire cord anteriorly)
Cuneatus – more lateral – sensory information from the upper limb (This column begins around T1/C8 level and traverses anteriorly)
What is lateral medullary syndrome? Describe and explain the symptoms.
It is a constellation of symptoms caused by an occlusion in the vertebral arteries or the posterior inferior cerebellar arteries (PICA)
It causes:
Horner’s Syndrome– disturbing the sympathetic tract
Vertigo– because of disturbing the vestibular nucleus
Ipsilateral loss of pain/thermal sensation on the face–disturbing the spinothalamic tract
Contralateral loss of pain/thermal sensation on the trunk and limbs– disturbing the spinothalamic tract
Ipsilateral cerebellar ataxia– disturbing the inferior cerebellar peduncle
Hoarseness / Difficultly swallowing (From Nucleus Ambiguus)
Contralateral loss of pain thermal sensation in limbs and trunk.
What are the symptoms of Horner’s Syndrome?
Ptosis (drooping eyelid) Loss of sweating around the eye Miosis Retraction of eyeball (ALL UNILATERAL)
