Overview of Brainstem Organisation

Question 1

What structures constitute the brainstem and where does it extend from rostrally and caudally?

Answer 1

from the pyramidal decussation (region where medulla becomes the spinal cord) includes the medulla, pons and midbrain and ends at the Mammillary bodies

Question 2

In what cranial fossa is the brainstem found?

Answer 2

posterior

Question 3

How can we recognise the midbrain anatomically? (dorsal and ventral surface features)

Answer 3

dorsal surface = Superior and inferior Colliculi Ventral surface = Cerebral peduncles (huge white matter tracts)

Question 4

What and where is the facial colliculus?

Answer 4

elevated ‘hill’ located on the dorsal surface of the pons in the floor of the 4th ventricle. It is formed by fibres of the motor nucleus of the facial nerve as they loop over the abducens nucleus.

Question 5

How can we recognise the Pons anatomically?

Answer 5

dorsal surface has the facial colliculi. Ventral surface has cerebeller peduncles (superior, middle and inferior)

Question 6

How can we recognise the medulla?

Answer 6

Dorsal surface -posterior columns, gracile-nuclei and cuneate tubercle. Ventral surface: inferior Olivary nuclei and pyramids descending to the pyramidal decussation

Question 7

What is the tectum?

Answer 7

the tectum is the roof of the brainstem - the dorsal aspect - it is only found in the midbrain and is made up of the inferior and superior colliculi

Question 8

What is the tegmentum?

Answer 8

area of the brainstem ventral to the ventricles, it is continuous with the spinal cord - it is in all parts of the brainstem and contains the CN nuclei and the reticular formation

Question 9

What are the broad regions of the brainstem (3 in midbrain, 2 in pons and medulla)

Answer 9

tectum (roof in midbrain), tegmentum, basis (ventral)

Question 10

What is the basis region of the brainstem important in?

Answer 10

Ventral part of the brainstem and is involved in descending motor control -> region where the corticospinal tracts go

Question 11

How and where do the cranial nerves exit the brainstem?

Answer 11

exit the ventral surface (except CN IV) in order rostro-caudal. First 4 (CNI-IV) exit above the pons (with I and II not associated with the brainstem), next 4 exit in the pons, last 4 exit the medulla

Question 12

Where do sensory nuclei develop from embryologically?

Answer 12

Alar plate

Question 13

Where do motor nuclei develop from embryologically?

Answer 13

Basal plate -> remember motor tracts are in the BASIS => basal

Question 14

How are the cranial nerve nuclei positioned in the brainstem?

Answer 14

grouped based on similar functions in one of 6 columns on either side of the midline (3 sensory, 3 motor)

Question 15

What are the 3 motor columns and are these medial or lateral?

Answer 15

medial
General somatic motor, Branchial motor
General visceral

Question 16

What is the function of caudal part (pons and medulla) of the reticular formation?

Answer 16

survival reflexes and autonomic functions e.g. breathing, heart rate

Question 17

In the brainstem where are sensory nuclei located?

Answer 17

laterally

Question 18

In the brainstem where are the motor nuclei located?

Answer 18

close to the midline

Question 19

What are the 3 sensory columns? are these laterally or medially located?

Answer 19

Lateral -General and special visceral,
General somatic,
Special somatic

Question 20

What is the function of the rostral part (midbrain and upper pons) of the reticular formation?

Answer 20

maintain alert conscious state via modulation of forebrain activity (ascending reticular activating system)

Question 21

What are the 3 major pathways traversing the brainstem?

Answer 21

Ascending 
1. Dorsal column-medial lemniscus pathway
2. anterolateral pathway (pain)
Descending
3.Corticospinal tract

Question 22

Where does the dorsal column medial lemniscus pathway cross the midline?

Answer 22

in the medulla at the medial lemniscus

Question 23

Where does the anterolateral (Pain) pathway cross the midline?

Answer 23

in the spinal cord

Question 24

Where does the anterolateral (pain) system terminate?

Answer 24

3 pathways terminating in different regions- the thalamus, midbrain and reticular formation

Question 25

Where does the corticospinal tract cross the midline? (descending pathway)

Answer 25

the pyramidal decussation (most caudal part of the medulla)

Question 26

What does the dorsal aspect of the brainstem contain?

Answer 26

CN nuclei, Reticular formation (tegmentum)

Question 27

What does the ventral region of the brainstem contain?

Answer 27

(basis)corticospinal tracts, cerebral peduncles, substantia nigra, red nuclei, cerebellar nuclei, cerebral peduncles, inferior olivary nuclei

Question 28

What is ‘locked in’ syndrome?

Answer 28

Stroke causing damage to ventral pons, patient survives and is aware (as vital survival centres in medulla are preserved) but can only use CN III and IV so is able to move their eyes only.

Question 29

What is the rostral reticular information important in?

Answer 29

closest to brain -> modulates forebrain activity, contains the ascending reticular activating system -> controls alertness/conscious state

Question 30

What is the caudal reticular formation involved in?

Answer 30

Survival reflexes (swalloing, vomitting, respiration, CV responses) and also chewing, crying and smiling