Exam 1 (Lecture 3) - Brain Stem

Question 1

Brain Stem

Answer 1

1) Neural tube
- brain stem derives from the
mesen-, meten-, and
myelencephalon

    1) mesencephalon = midbrain
    2) metencephalon = pons
    3) myelencephalon = medulla obl.

2) Partially covered by the cerebrum & cerebellum.

3) Gives rise to cranial nerves III-XII (10 nerves).

4) Lesions cause a wide range of clinical signs.

Question 2

Dorsal Brain Stem

Answer 2

1) midbrain (most rostral)
- rostral colliculus = visual reflexes
(body & ocular/ pupillary dilation)
- caudal colliculus = auditory reflexes
(startle reflex)
- gives rise to CN IV (trochlear) =
caudal border

2) pons
- cerebellar peduncles (3 tracts made
of cerebellar afferent and efferent
fibers)

3) medulla oblongata
- caudal to the cerebellar peduncles
- rostral to the spinal cord

Question 3

Ventral Brain Stem

Answer 3

1) midbrain
- crus cerebri (cerebral motor tracts
that originate in cerebrum’s primary
motor cortex

2) pons
- basilar pons
- gives rise to CN V (PNS); at junction
of pons and medulla oblongata

3) medulla oblongata
- pyramids (continuation of crus
cerebri tract)
- trapezoid body
- gives rise to CN VI-XII (PNS)

Question 4

Inner Structure of the Brain Stem

Answer 4

1) Nuclei - neuronal cell bodies
- grey matter
- segmental, various sizes/shapes
- sensory or motor

2) Tracts
- white matter
- ascending and descending tracts

3) Local circuits

4) Reticular Formation
- mixture of grey and white matter

Question 5

Naming a Motor Nucleus that Gives Rise to a Cranial Nerve

Answer 5

1) Somatic Motor Nuclei (innervate skeletal muscle)
- named after the cranial nerve
carrying their motor fibers to
skeletal muscle (exception is the
nucleus ambiguus)

2) Visceral Motor Nucleus (smooth or cardiac muscle)
- named after the cranial nerve
carrying its parasympathetic fibers

**For the sensory nuclei; there are no rules for naming them.

Question 6

Reticular Formation

Answer 6

1) Mixture of the grey & white matters
- critical for consciousness (ascending
reticular activating system)
- monitors info coming in & going out
- visceromotor centers that control:
- micturition
- respiratory
- cardiovascular
- swallowing
- vomiting

Question 6

Deviation of Tongue Due to Hypoglossal Nerve Injury

Answer 6

1) Protruding tongue
- tongue will deviate toward the
lesion side whether it is an acute or
chronic lesion

2) Resting tongue (deviation depends on length of denervation)
- when totally denervated, muscles
lose their tone
- if recent: tongue will deviate
away from the lesion side
- if innervation doesn’t come
back: tongue will deviate toward
lesion side (muscle has
atrophied & been replaced by
scar tissue = less elastic; so
muscle contracts pulling tongue
to lesion side

Question 6

Hypoglossal Nerve (CN XII) and its Central Nucleus

Answer 6

1) Innervates intrinsic and extrinsic tongue muscles
- movement of tongue = is the
outcome of innervation
- styloglossus, genioglossus, &
hyoglossus

2) Bilateral nerve (L & R)