Organisation of brainstem and cranial nerves Flashcards
Where are the colliculi found and what are their functions?
Elevations of the midbrain tectum/roof located posteriorly, sitting on the roof plate of the midbrain
Superior colliculi: important in the coordination of reflex movements of the eye, head and neck
Inferior colliculi: important in auditory reflexes
Describe the location of the pons relative to the ventricular system
It forms a portion of the anterior wall of the 4th ventricle
Describe the location of the pineal gland
It develops from the roof of the diencephalon, midline structure, directly posterior to the third ventricle and colliculi
State the role of the pineal gland
Melatonin production (involved in regulating the circadian rhythm)
Which cranial nerve emerges from the back of the brainstem? Where does it arise from?
Trochlear nerve (CN 4) Arises from the trochlear nuclei in the posterior midbrain at the level of the inferior colliculi.
State the function of the trochlear nerves
Motor supply to the superior oblique muscle of the eye
Describe the location of the pituitary stalk/infundibulum, mammillary bodies and optic chiasm relative to each other
The mammillary bodies are bilateral round protrusions of the inferior part of the hypothalamus, immediately adjacent to the median eminence from which the pituitary stalk emerges. The optic chiasm lies immediately posterior to the proximal part of the pituitary stalk.
Which cranial nerve emerges from the midline just above the transverse fibres of the pons?
Oculomotor nerve (CN 3)
State the structures supplied by the oculomotor nerve, and the type of innervation
MOTOR
Superior branch: levator palpebrae and superior rectus muscles
Inferior branch: medial rectus, inferior rectus, and inferior oblique muscles - Eyeball movement
PARASYMPATHETIC
Ciliary and sphincter pupillae muscles - Pupillary constriction and accommodation
Name the cranial nerve that emerges from the lateral aspect of the pons
Trigeminal nerve (CN 5)
State the structures supplied by the trigeminal nerve, and the type of innervation
SENSORY (and MOTOR, provided by smaller root)
Face, scalp, cornea, nasal and oral cavities, cranial dura mater
Muscles of mastication, tensor, tympani muscle
Which three nerves emerge at the pontomedullary junction (from medial to lateral)?
Abducens, Facial, Vestibulocochlear (CNs 6, 7, 8)
State the function of the abducens nerve
Motor supply to the lateral rectus muscle for lateral movement of the eye ball
State the structures supplied by the facial nerve, and the functions
SENSORY
Anterior two-thirds of tongue - taste
MOTOR
Muscles of facial expression, stapedius muscle (tension on bones of middle ear)
PARASYMPATHETIC
Salivary and lacrimal glands via submandibular and pterygopalatine ganglia
State the function of the vestibulocochlear nerve
Involved in balance and hearing
Which three nerves emerge from the lateral medulla?
Glossopharyngeal, Vagus and Accessory (CNs 9, 10, 11)
Briefly state the role of cranial nerves 9, 10 and 11
Glossopharyngeal – sensory and motor innervation of the tongue and pharynx
Vagus – main parasympathetic nerve descending down to the viscera
Accessory – motor supply to the trapezius and sternocleidomastoid (shoulder and head movement)
Which cranial nerve emerges from the groove between the olive and pyramid of the medulla? State its role.
Hypoglossal nerve (CN 12)
Motor supply to intrinsic/extrinsic tongue muscles
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 - 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 - 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
Describe the arrangement of the different nuclei within the brainstem
Motor – Medial
Sensory – Lateral
Motor – arranged in columns GSE, SVE, GVE (medial to lateral)
Sensory – arranged in columns GVA/SVA, GSA, SSA (medial to lateral)
State the nuclei that are in the GSE 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 SVE group and describe their location within the brainstem.
Trigeminal = pons Facial = pons *Ambiguus = medulla Accessory = cervical spinal cord
*Nucleus ambiguus is a group of large motor neurones 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 group and describe their location within the brainstem.
Edinger Westphal (involved in PNS innervation of eye) = midbrain Salivatory = ponto-medullary border (there are THREE sets of salivatory nuclei) Vagus = pons
State the nuclei that are in the SSA group and describe their location within the brainstem.
Vestibulocochlear = pons and medulla
State the nuclei that are in the GSA group and describe their location within the brainstem.
Trigeminal = midbrain, pons, medulla and cervical spinal cord
State the nuclei that are in the GVA and SVA 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?
‘Mickey Mouse’
Ears of Mickey Mouse = cerebral peduncles
At the point where the cerebral peduncles meet the rest of the midbrain you find the substantia nigra
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.
A group of dopaminergic neurones.
In their normal metabolism they produce neuromelanin, which gives the black colour.
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?
4th ventricle at the dorsal aspect
Transverse fibres
Cerebellar peduncles bilaterally
Describe the appearance of a cross-section of the medulla. What are the key features seen?
Pyramids at the ventral aspect
Inferior olivary nucleus will be found lateral 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?
More round
Central canal in the middle
Dorsal columns
Pyramidal decussation may be seen
What is lateral medullary syndrome?
Thrombosis of vertebral arteries or posterior inferior cerebellar arteries
List the symptoms of lateral medullary syndrome
- 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)
Explain the symptoms of lateral medullary syndrome
Vertigo - disturbing the vestibular nucleus
Ipsilateral cerebellar ataxia - disturbing the inferior cerebellar peduncle
Ipsilateral loss of pain/thermal sensation on the face - disturbing the spinothalamic tract
Horner’s Syndrome– disturbing the sympathetic tract
Contralateral loss of pain/thermal sensation (trunk and limbs) - disturbing the spinothalamic tract
What are the symptoms of Horner’s Syndrome?
Ptosis
miosis
Loss of sweating around the eye
