Organisation of the Brainstem and Cranial Nerves Flashcards
Where does the brainstem lie? What are its major divisions?
Brainstem = a part of the CNS exclusive of the cerebellum which lies between the cerebrum and spinal cord.
Major divisions:
- Medulla oblongata
- Pons
- Midbrain
Label this.
Where are the colliculi found and what are their functions?
Roof of the midbrain - 4 bumps (“low lying hill”)
- Superior colliculi – important for the coordination of eye and head movements at the same time
- Inferior colliculi – auditory stimulus reflexes (for survival) e.g. turning your head in the direction of a loud noise
Describe the location of the pons relative to the ventricular system.
The pons makes up the floor of the 4th ventricle
Name an important unpaired, midline structure on the posterior aspect of the brainstem.
Pineal gland
Everything in the brainstem is bilateral except the pineal gland.
What is the role of the pineal gland?
It produces melatonin, which is involved in regulating the circadian rhythm
- Disrupted in people who work shifts
- Melatonin release is controlled by connections from retina to the pineal gland
Which cranial nerve emerges from the back of the brainstem?
Trochlear nerve CNIV - the only cranial nerve to emerge posteriorly from the brain stem
What is the role of CNIV?
It supplies the superior oblique muscle – one of the extrinsic muscles of the eye
It is one of the three nerves supplying the eyes
What structure defines the medulla in the dorsal aspect and what pathways are found within this structure?
Dorsal Columns – sensory pathways –fine touch and proprioception
Label this.
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? What causes them to become dark?
“little breats” - involved in housekeeping, homeostasis and memory
They are the inferior part of the hypothalamus, part of the diencephalon – it is part of the limbic system
- Become dark due to chronic alcoholism causing neovascularisation.
Which cranial nerve emerges in the midline between the cerebral peduncles?
Oculomotor Nerve (CN III)
What are the cerebral peduncles? What is the significance of the word ‘peduncle’?
Peduncle is specifically a structure that has a functional (are the descending motor tracts coming from the motor cortex) AND structural role (it holds the cerebrum onto the brainstem)
Name the cranial nerve that emerges from the lateral aspect of the pons. What are its 3 branches?
Trigeminal (CN V) (motor and sensory) - ophthalmic, maxillary and mandibular nerves.
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, Facial, Vestibulocochlear (CN6,7,8)
Briefly state the role of each of these cranial nerves CN VI, VII, VIII (which emerge at the pontomedullary junction.
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, Vagus and Accessory - CN9, 10, 11
Briefly state the role of each of these cranial nerves - CN IX, X, XI (which emerge from the lateral part of the medulla)
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. What is the function?
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 = continuation of the corticospinal tract which re-emerges
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%
Decussation (crossing over) occurs at the most caudal end of the pyramids.
What are the four functional subtypes of the cranial nerves and what are their actions?
- General Somatic Afferent (GSA)
- Sensation from the skin and mucous membranes
- General Visceral Afferent (GVA)
- Sensation from the GIT, heart, vessels and lungs
- General Somatic Efferent (GSE)
- Muscles for eye and tongue movements
- General Visceral Efferent (GVE)
- Preganglionic parasympathetic
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 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
- (Generally they remian in a classical organisation with the GSE remaining more medial and the GVE more 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 GSE (general somatic efferent) group and describe their location within the brainstem.
Midbrain – oculomotor; trochlear.
Pons – abducens (emerges in pontomedullary junction, so fibres move down before emerging up)
- These are all the eye movement nerves.
Medulla – hypoglossal
State the nuclei that are in the SVE (special visceral efferent) group and describe their location within the brainstem.
Pons – trigeminal motor (muscles of mastication); facial
Medulla – nucleus ambiguus (involved in laryngeal movements)
Cervical spinal cord – accessory
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 GVE (general visceral efferent) group and describe their location within the brainstem.
This is the parasympathetic
Midbrain – Edinger Westphal nucleus (follow the oculomotor nerve and provides parasympathetic innervation to the eye)
Ponto-medullary border – salivatory (3 of these nuclei- prompt salivation)
Medulla – vagus motor (gut motility)
State the nuclei that are in the SSA (special somatic AFFERENT) group and describe their location within the brainstem.
Pons and medulla - Vestibulocochlear (balance and hearing; most lateral)
State the nuclei that are in the GSA (general somatic AFFERENT) group and describe their location within the brainstem.
Midbrain(mesencephalon), pons, medulla and cervical spinal cord, - trigeminal = (in all 3 parts and spinal cord)
State the nuclei that are in the GVA and SVA (general visceral AFFERENT and special visceral AFFERENT) groups and describe their location within the brainstem.
Medulla (and a bit in th pons)- nucleus solitarius for taste sensation
Label this cross-section of the midbrain.
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 - looks more like spinal cord
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 - transverse fibres all cross at pyramidal decussation
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? List 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
- Vertigo
- Ipsilateral loss of pain/thermal sensation on the face
- Contralateral loss of pain/thermal sensation on the trunk and limbs
- Ipsilateral cerebellar ataxia
- Hoarseness, difficulty swallowing
Describe the reasons behind the symptoms of lateral medullary syndrome.
- Horner’s Syndrome– disturbing the sympathetic tract which passes here
- 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
What is Horner’s syndrome?
Loss of sympathetic drive to the face
What are the symptoms of Horner’s Syndrome?
Ptosis
Loss of sweating around the eye
Hoarseness
Difficulty swallowing
