Anatomy: Brainstem and CN (Midbrain)

Question 1

Label the external features of the midbrain

Answer 1

Question 2

Label this

Answer 2

Question 3

Label the ventral features of the midbrain

Answer 3

Each colliculi is related to the geniculate body via extensions called the brachium

Question 4

Label this

Answer 4

Question 5

Label the parts of the midbrain

Answer 5

Question 6

Label this

Answer 6

Question 7

What does the crus cerebri contain?

Answer 7

Crus Cerebri contains:
Corticopontine fibres –to pontine nuclei
Corticospinal and corticonuclear fibres (middle 2/3rd)

Question 8

Describe the structure of the substantia nigra

Answer 8

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

Question 9

What structures are found in the tegmentum aspect of the inferior colliculus?

Answer 9

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

Question 10

In the tegmentum the cerebellar peduncle also decussates. Explain this in more detail

Answer 10

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

Question 11

The nucleus of inferior colliculus is also known as…

Answer 11

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)

Question 12

What are the afferents (to CNS) vs efferents (to organ/muscle) of the inferior colliculus?

Answer 12

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.

Question 13

Describe the trochlear nerve

Answer 13

The trochlear nerve comes out dorsally, winding around the midbrain and then comes anteriorly to supply the superior oblique muscle

Question 14

How is the superior colliculus similar/different to the inferior colliculus?

Answer 14

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)

Question 15

What is the structure and function of the red nucleus?

Answer 15

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

Question 16

What are the afferents and efferents of the red nucleus?

Answer 16

Afferents
- Cerebellorubral fibres from deep nuclei of cerebellum
- Ipsilateral Corticorubral fibres
Efferents
-Ventral tegmental decussation (rubrospinal/rubrobulbar/rubroreticular fibres)

Question 16

What are the afferents and efferents of the red nucleus?

Answer 16

Afferents
- Cerebellorubral fibres from deep nuclei of cerebellum
- Ipsilateral Corticorubral fibres
Efferents
-Ventral tegmental decussation (rubrospinal/rubrobulbar/rubroreticular fibres)

Question 17

What are the afferents and efferents of the tectum in the SUPERIOR colliculus?

Answer 17

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

Question 18

Blood Supply of
Midbrain?

Answer 18

Question 19

What is congenital hydrocephelus and webers syndrome?

Answer 19

Congenital Hydrocephalus - Blockage of cerebral aqueduct