Anatomy: Brainstem and CN (Midbrain) Flashcards
Label the external features of the midbrain
Label this
Label the ventral features of the midbrain
Each colliculi is related to the geniculate body via extensions called the brachium
Label this
Label the parts of the midbrain
Label this
What does the crus cerebri contain?
Crus Cerebri contains:
Corticopontine fibres –to pontine nuclei
Corticospinal and corticonuclear fibres (middle 2/3rd)
Describe the structure of the substantia nigra
Pars compacta (darker bit)–dorsal, deeply pigmented, cell rich, small/medium sized neurons, rich in melanin pigment
Pars reticularis (lighter bit) –ventral, less pigmented, large multipolar but cell poor zone, rich in iron content
What structures are found in the tegmentum aspect of the inferior colliculus?
Tegmentum contains the:
Periaqueductal gray; this also contains the trochlear Nucleus and nerve, Mesencephalic Nucleus/Tract (unipolar neurons)
Lemnisci, Reticular formation, central tegmental tract
MLF - medial longitudinal fasciculus / Tectospinal tract
In the tegmentum the cerebellar peduncle also decussates into ascending and descending fibres
In the tegmentum the cerebellar peduncle also decussates. Explain this in more detail
Fibres derived from the deep nuclei of cerebellum decussate into ascending and descending fibres
Ascending fibres terminate in red nucleus, thalamus, midbrain Reticular formation (RF)
Descending fibres terminate in inferior olivary nucleus and RF of pons and medulla
The nucleus of inferior colliculus is also known as…
tectum is the region of the midbrain posterior to the cerebral aqueduct of Sylvius. It contains the nuclei of the superior and inferior colliculi.
These colliculi help process visual (superior colliculi) or auditory stimuli (inferior colliculi)
What are the afferents (to CNS) vs efferents (to organ/muscle) of the inferior colliculus?
Afferents:
Lateral lemniscus, carrying auditory impulses
Commissural fibres from contralateral IC
Efferents:
Through inferior brachium to Medial Geniculate Body
Commissural fibres to contralateral IC and to ipsilateral Superior colliculus
The inferior colliculus is the relay station within the auditory pathway.
Describe the trochlear nerve
The trochlear nerve comes out dorsally, winding around the midbrain and then comes anteriorly to supply the superior oblique muscle
How is the superior colliculus similar/different to the inferior colliculus?
Features Common with previous section: Crus cerebri, substantia nigra, lemnisci (not Lateral lemniscus)
Additional features
Oculomotor + Edinger Westphal + pretectal nuclei
Red nucleus
Tegmental decussations
– Ventral (rubrospinal)
– Dorsal (tectospinal)
What is the structure and function of the red nucleus?
Red-pink in fresh cut, ovoid mass 5mm
Rich in iron
Motor function, monitors cerebellar function
Corticorubral and rubrospinal fibres form an alternate descending pathway along w the pyramidal system for flexor muscle tone
What are the afferents and efferents of the red nucleus?
Afferents
- Cerebellorubral fibres from deep nuclei of cerebellum
- Ipsilateral Corticorubral fibres
Efferents
-Ventral tegmental decussation (rubrospinal/rubrobulbar/rubroreticular fibres)
What are the afferents and efferents of the red nucleus?
Afferents
- Cerebellorubral fibres from deep nuclei of cerebellum
- Ipsilateral Corticorubral fibres
Efferents
-Ventral tegmental decussation (rubrospinal/rubrobulbar/rubroreticular fibres)
What are the afferents and efferents of the tectum in the SUPERIOR colliculus?
Afferents:
a) From Retina via retino-tectal fibres
b) Cortico-tectal fibres from visual cortex via superior
brachium for visual reflexes
c) From ipsilateral IC
d) Spinotectal fibres –sensory info from cutaneous nerve
endings of limbs to turn head and eye towards the cutaneous stimuli
Efferents:
a) Tecto-spinal tract to cervical part of spinal cord to turn
the head and eye towards auditory and cutaneous stimuli
b) Tecto-bulbar tract to III, IV, VI nuclei for scanning eye
movement and VII n for reflex closure of eyes
Blood Supply of
Midbrain?
What is congenital hydrocephelus and webers syndrome?
Congenital Hydrocephalus - Blockage of cerebral aqueduct
