lecture 7 - medulla, CNs IX-XII

Question 1

describe the development of the internal features of the medulla oblongata

Answer 1

• alar plates move laterally forming the afferent (sensory) columns
• basal plates remain medially forming the efferent (motor) columns
• sulcus limitans separates motor columns & sensory columns

Question 2

what are some external features of the medulla?

Answer 2

• olives
• pyramids
• decussation
• anterior median sulcus
• CNs Ix-XII

Question 3

what are some internal features of the medulla?

Answer 3

• posterior median sulcus
• anterior median fissure
• fasciculus gracilis
• fasciculus cuneatus
• nucleus gracilis
• nucleus cuneatus
• CN V nucleus
• central canal
• pyramids
• decussation
• medial longitudinal fasciculus
• posterior spinocerebellar, anterior spinocerebellar and lateral spinothalamic tracts

Question 4

describe the pyramids at the level of the decussation of the pyramids

Answer 4

in the inferior portion of the medulla, they cross the midline plane and continue down the spinal cord as the lateral white column corticospinal tract

Question 5

describe the fasciculus gracilis and fasciculus cuneatus at the level of the decussation of the pyramids

Answer 5

• gracilis = medial
• cuneatues = lateral
• both come from the cord and climb posterior to the central gray matter (both appear as posterior extensions of the cenral gray matter)

Question 6

describe the substantia gelatinosa of the posterior gray column at the level fo the decussation of the pyramids

Answer 6

becomes continuous with the nucleus of the spinal tract of CN V

Question 7

describe the lateral and anterior white columns at the level of the decussation of the pyramids

Answer 7

same arrangement as the cord

Question 8

what is the decussation of the pyramids aka?

Answer 8

the great motor cross-over

Question 9

where does the decussation of lemnisci occur?

Answer 9

• in the inferior medulla a short distance above the decussation of the pyramids
• anterior to the central gray matter
• posterior to the pyramids

Question 10

what is the decussation of the lemnisci aka?

Answer 10

the great sensory cross-over

Question 11

describe the formation of the lemnisci at the level of the decussation of the lemnisci

Answer 11

• cuneatus nucleus and gracilis nucleus are the ends of the fasciculus cuneatus and the fasciculus gracilis
• the nuclei = the relay stations
• internal arcuate fibers cross the midline to form the medial lemnisci on the opposite side

Question 12

describe the location of the lemnisci at the level of the decussation of the lemnisci

Answer 12

• located btwn the olivary nuclei and behind the pyramids
• only begins at next section level
• oriented anteroposteriorly

Question 13

what is the function of the lemnisci?

Answer 13

to convey sensory information to the thalamus

Question 14

what is situated lateral to the arcuate fibers at the level of the decussation of the lemnisci?

Answer 14

nucleus of the spinal tract of CN V

Question 15

what is situated laterally to the nucelus of the spinal tract of CN V at the level of the decussation of the lemnisci?

Answer 15

the spinal tract (of CN V) itself

Question 16

where/what is the MLF (at the level of the decussation of the lemnisci)?

Answer 16

small tract of nerve fibers on both sides of the midline posterior to the medial lemnisci

Question 17

what is the function of the MLF?

Answer 17

connects vestibular and cochlear nuclei to the nuclei that control the external eye muscles (oculomotor, trochlerar and abducens)

Question 18

describe the reticular formation at the level of the decussation of the lemnisci

Answer 18

• obscured by the internal arcuate fibers
• consists of a diffuse group of nerve cells and fibers located behind the olivary nuclei
• extend through the pons and the midbrain

Question 19

where are the olives located?

Answer 19

at the inferior portion of the 4th ventricle

Question 20

what occurs at the level of the olives?

Answer 20

a dramatic increase in the amount of gray matter

Question 21

describe the olivary nuclear complex (inferior olivary nucleus) at the level of the olives

Answer 21

• nerve cells send dibers medially across the midline to enter the cerebellum through the inferior cerebellar peduncle
• gray matter is crumpled and opens medially
• gives rise to olives

Question 22

what is the function of the olivary nuclear complex?

Answer 22

voluntary muscle movement

Question 23

describe the vestibulocochlear nuclei at the level of the olives

Answer 23

made up of 4 vest nuclei:

• -medial, inferior, lateral and superior vestibular nuclei
• -at this level only medial and lateral can be seen

and 2 cochlear nuclei:

• -anterior = on the anterolateral part of the inferior cerebellar peduncle
• -posterior = on the peduncle lateral to the 4th ventricle

Question 24

describe the nucleus ambiguus at the level of the olives

Answer 24

• large motor nucleus deep in the reticular formation

- nerve fibers join CNs IX, X and XI

Question 25

describe the central gray matter at the level of the olives

Answer 25

contains:

• hypoglossal nucleus
• dorsal nucleus of CN X
• nucleus of tractus solitarius
• medial and lateral vestibular nuclei
• medial lemnisci
• medial longitudinal fasciculus
• inferior cerebellar peduncle
• spinal tract and nucleus of CN V
• anterior spinocerebellar tract
• anterolateral pathway (corticospinal tracts)

Question 26

what is the functional significance of the medulla?

Answer 26

reflex control of cardiovascular and respiratory systems

Question 27

why is there so much crossing over?

Answer 27

so that everything can fit in the body

Question 28

what is the largest and most important nucleus in the medulla?

Answer 28

inferior olivary