Midbrain - Benifla Flashcards
What are the three divisions of the midbrain?
– 1.Tectum (Quadrigeminal plate) superior and
inferior colliculi – the post part. (chin of Mickey Mouse)
– 2.Tegmentum – Intermediate part – separated
from the tectum by the aqueduct. (cheeks of MM)
– 3.Crura cerebri – Anterior part – separated from
the tegmentum by the substantia nigra. (ears of MM)
Where do afferent and efferent fiibers from the superior colliculus go?
1.Retina via the optic
nerve, lateral
geniculate body of the
thalamus and superior
brachium.
2.Cerebral cortex: B-17,
8 ipsilaterally (occipital lobe)
3.Spinal cord – posterior
column
4.Inferior collicul
1.Crossed tectospinal
(cervical)
2.Uncrossed
tectobulbar
What are the components of the oculomotor nucleus?
What are the afferent and efferent fibers?
– 1.Paired lateral somatic cells
– 2.Dorsomedial visceral cells (the Edinger-Westphal
nucleus)
• Afferent fibers:
1.Cerebral cortex (motor cortex, precentral gyrus: B-4,6)
2.Superior colliculi
3.Reticular formation
4.Vestibular nuclei via MLF (balance)
5.MLF (eye movement)
6.Pretectal nucleus
• Efferent fibers:
– 1.Uncrossed somatic fibers (extraocular m, levator palpebrae m, ciliary body)
– 2.Uncrossed visceral
fibers-Preganglionic
parasympathetic
fibers that emerge
with the somatic root
fibers pass to the
ciliary ganglion
What is the pathway of the papillary light reflex?
Right Optic nerve –Right lateral geniculate body (no synapse)–>
(synapse at) right pretectal nucleus—>
Right (ipsilateral) Edinger-Westphal and Posterior commissure to Left Edinger Westphal nucleus
Each side’s EW to ciliary ganglion to sphincter of Iris to pupil on side of EW
Injury to optic nerve means sensory reflex injured but stimulation to unaffected side makes both pupils contract (normal reflex)
In cortical blindness, remains intact
What is the pathway of the Accomodation- Convergence Reflex?
Optic nerve
Optic tract
LGB
Visual cortex, occipital lobe (Brod- 17,18,19-includes decision to focus)
back to LGB
Pretectal nucleus
Third nuclei (motor and EW)
Cause bilateral medial rectus muscle ennervation, cilliary muscle (EW) and papillary constriction and curvature of the lens when an object comes close
Where do the afferent and efferent fibers of the Red Nucleus go and what does it do?
What is the effect of injury?
Anterior to the III n. and posterior to the substantia nigra
• Afferent fibers:
1. Crossed fibers from cerebellar nuclei
2. Uncrossed fibers from the precentral gyrus
• Efferent fibers:
1. Spinal cord – crossed (contralateral-decussate 3 times: cortex to cerebellum, cerebellum to red nucleus, RN to spinal cord)
2. Brain Stem
3. Cerebellum
Functional consideration:
Enhance flexor muscles activity during locomotion
Injury above causes loss of inhibition, decortication (abnormal flexion)
What is Benedickt syndrome?
Injury to red nucleus and oculomotor nerve due to a small infarct in the small vessels supplying brainstem.
Contralateral motor disturbances as tremor,
ataxia and ipsilateral III.n. palsy (midriasis, ptosis, loss f papillary light reflex, external strabismus)
– Result from unilateral lesion of III nerve and red nucleus.
– When involves the sensory tracts in the tegmentum there is also a contralateral hemianesthesia.
What are the components of the substantia nigra? What does it do?
Where do the afferent and efferent fibers go?
• GENERAL: Secretes dopamine (inhibition and disinhibition, sends information to different parts of basal ganglia) – The most voluminous nuclear mass. Divided into 2 parts:
1.Pars compacta – the posterior part.
2.Pars reticularis- the anterior part (striatum intermedium)
• AFFERENT FIBERS:
– Fibers from the:
1.Caudate nucleus
2.Putamen
• EFFERENT FIBERS:
– Fibers to the:
1.Caudate nucleus
2.Putamen
3.Thalamus
What is Weber’s syndrome?
Infarct of small arteries supplying small areas of brainstem with crus serebri and oculomotor nerve
Lesion of the ventral midbrain- III nerve and crus
cerebri
ipsilateral third nerve palsy with dilated pupil and
contralateral hemiplegia
What is Parinaud’s Syndrome?
Lesion of the dorsal midbrain, pretectum and posterior comissure.
• Upward gaze palsy
• Defective papillary light reflex (doesn’t constrict well, injury to consensual reflex, slower dilation)
• Lid retraction
• LID LAG (see white of conjunctive before covered by lid)
Due to increased intracranial pressure due to hydrocepahlous usually.
Inability of patient to lok upwards, eyes are “stuck”
What are the afferent and effererent fibers of the infeiror colliculus?
• AFFERENT
FIBERS:
1.From the cochlear nerve via the lateral lemniscus
2.Auditory cortex via the medial
geniculate body & the inferior brachium
3.Opposite inferior colliculus
• EFFERENT FIBERS:
– 1. Auditory cortex via the inferior brachium and
medial geniculate body
• FUNCTIONAL
CONSIDERATION:
– Serves as a relay nucleus in transmitting auditory impulses to the medial geniculate body which in turn projects to the primary auditory cortex.
Involved in ability to localize source of sound.
What is the effect of injury to the trochlear nerve?
Lack of contralateral intorsion (oculomotor still works to extort):
Head tilting: torticollis
Nucleus injury causes contralateral nerve defect and ipsilateral torticollis of the head
Nerve injury causes ipsilateral injury and contralateral torticollis of the head
Diplopia: double vision
Eye can’t move down, go downstairs with head looking down
What are the medial and lateral lemnisci?
• MEDIAL LEMNISCUS
– Ascent posterior to the substantia nigra, fibers from the nuclei gracilis and cuneatus
Fibers come from nuclei in medulla oblongada, convey impulses of proprioception to infeiror colliculus.
• LATERAL LEMNISCUS
– Is located dorsolaterally to the medial lemniscus. The principal ascending auditory pathway in the brain stem.
Part of auditory system.
What is the blood supply to the midbrain?
• Paramedian penetrating arteries (anterior)
• Short and long circumferential arteries
Crus cerebri and tegmentum Arising from the Basilar and PCA
Tectum- from SCA and PCA
