Overview of Brainstem Organisation Flashcards
What structures constitute the brainstem and where does it extend from rostrally and caudally?
from the pyramidal decussation (region where medulla becomes the spinal cord) includes the medulla, pons and midbrain and ends at the Mammillary bodies
In what cranial fossa is the brainstem found?
posterior
How can we recognise the midbrain anatomically? (dorsal and ventral surface features)
dorsal surface = Superior and inferior Colliculi Ventral surface = Cerebral peduncles (huge white matter tracts)
What and where is the facial colliculus?
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.
How can we recognise the Pons anatomically?
dorsal surface has the facial colliculi. Ventral surface has cerebeller peduncles (superior, middle and inferior)
How can we recognise the medulla?
Dorsal surface -posterior columns, gracile-nuclei and cuneate tubercle. Ventral surface: inferior Olivary nuclei and pyramids descending to the pyramidal decussation
What is the tectum?
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
What is the tegmentum?
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
What are the broad regions of the brainstem (3 in midbrain, 2 in pons and medulla)
tectum (roof in midbrain), tegmentum, basis (ventral)
What is the basis region of the brainstem important in?
Ventral part of the brainstem and is involved in descending motor control -> region where the corticospinal tracts go
How and where do the cranial nerves exit the brainstem?
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
Where do sensory nuclei develop from embryologically?
Alar plate
Where do motor nuclei develop from embryologically?
Basal plate -> remember motor tracts are in the BASIS => basal
How are the cranial nerve nuclei positioned in the brainstem?
grouped based on similar functions in one of 6 columns on either side of the midline (3 sensory, 3 motor)
What are the 3 motor columns and are these medial or lateral?
medial
General somatic motor, Branchial motor
General visceral
What is the function of caudal part (pons and medulla) of the reticular formation?
survival reflexes and autonomic functions e.g. breathing, heart rate
In the brainstem where are sensory nuclei located?
laterally
In the brainstem where are the motor nuclei located?
close to the midline
What are the 3 sensory columns? are these laterally or medially located?
Lateral -General and special visceral,
General somatic,
Special somatic
What is the function of the rostral part (midbrain and upper pons) of the reticular formation?
maintain alert conscious state via modulation of forebrain activity (ascending reticular activating system)
What are the 3 major pathways traversing the brainstem?
Ascending 1. Dorsal column-medial lemniscus pathway 2. anterolateral pathway (pain) Descending 3.Corticospinal tract
Where does the dorsal column medial lemniscus pathway cross the midline?
in the medulla at the medial lemniscus
Where does the anterolateral (Pain) pathway cross the midline?
in the spinal cord
Where does the anterolateral (pain) system terminate?
3 pathways terminating in different regions- the thalamus, midbrain and reticular formation
Where does the corticospinal tract cross the midline? (descending pathway)
the pyramidal decussation (most caudal part of the medulla)
What does the dorsal aspect of the brainstem contain?
CN nuclei, Reticular formation (tegmentum)
What does the ventral region of the brainstem contain?
(basis)corticospinal tracts, cerebral peduncles, substantia nigra, red nuclei, cerebellar nuclei, cerebral peduncles, inferior olivary nuclei
What is ‘locked in’ syndrome?
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.
What is the rostral reticular information important in?
closest to brain -> modulates forebrain activity, contains the ascending reticular activating system -> controls alertness/conscious state
What is the caudal reticular formation involved in?
Survival reflexes (swalloing, vomitting, respiration, CV responses) and also chewing, crying and smiling
