ICL 6.1: Brainstem Structure and Organization Flashcards
Where is the brainstem located int the cranium?
Posterior cranial fossa
It’s bordered the foremen magnum, tentorium cerebelli, clivus and occipital bones
What is the rhomboid fossa?
a rhombus-shaped depression that is the anterior part of the fourth ventricle
This anterior wall aka rhomboid fossa is formed by the back of the pons and the medulla oblongata, constitutes the floor of the fourth ventricle
So the 4th ventricle is located at the level of the medulla and the pons and they’re what forms the ventricular floor aka rhomboid fossa
What is the lateral recess?
a projection of the fourth ventricle which extends from the rhomboid fossa into the inferior cerebellar peduncle of the brainstem
What forms the roof othe 4th ventricle?
Midline portion of the cerebellum
What is the obex?
The point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord
The obex occurs in the caudal medulla
The decussation of sensory fibers happens at this point.
how does the CSF leave the 4th ventricle?
- foramen of Magendie at the caudal end
2. foramen of Luschka at the lateral angels of the ventricle
what are cisterns?
spaces formed by openings in the subarachnoid space
these cisterns are filled with cerebrospinal fluid
what are the important cisterns in the brain?
- interpeduncular cistern (in front of the midbrain)
- prepontine cistern (rostral to the pons)
- cerebellomedullary cistern (under the cerebellum)
- superior cistern (above the cerebellum)
slide 5
what are the 3 components of the brainstem?
rostral
1. midbrain
- pons
- medulla oblongata
caudal
what can be found in the brainstem?
it contains ascending and descending pathways to and from thalamus, hypothalamus, cerebral cortex and cerebellum, cranial nerve nuclei, SC
it also contains cranial nerve nuclei/fiber that allow nuclei to communicate
the reticular formation is also found in the brainstem!!
what are colliculi?
a collection of cell bodies that receive information about our auditory and visual system
they’re located in the dorsal midbrain
what are is the summary of the internal features of the midbrain?
- joins thalamus rostrally
- central core = tegmentum and tectum
- contains mammillary bodies
- CN III, IV motor nuclei
- superior/inferior colliculi
- crus cerebri (cerebral peduncles)
- interpeduncular fossa
- joined by paired superior cerebellar peduncle
what are is the summary of the internal features of the pons?
- extends from pons-medulla junction
- consists of pontine tegmentum and basilar pons
- CN Nuclei (V, VI, VII, VIII)
- superior salivatory nucleus
- joined by paired middle cerebellar peduncles
what are is the summary of the internal features of the medulla oblongata?
- at the level of the foramen magnum
- level of where pyramidal decussation happens (caudal portion)
- CN Nuclei (IX, X, XI XII), portions of CN V
- joined by paired inferior cerebellar peduncles
what are the 2 parts of the midbrain?
- tectum
- tegmentum
the tegmentum allows for a lot of synaptic activity between different neurons and it spans the whole length of the brainstem
what are cerebellar peduncles?
there is a superior, middle and inferior peduncle and these are what attach the cerebellum to the brainstem!
the superior cerebellar peduncle attaches the cerebellum to the midbrain and thalamus
the middle cerebellar peduncle attaches the cerebellum to the pons
the inferior cerebellar peduncle attaches the cerebellum to the medulla and spinal cord
where is the midbrain located?
between the diencephalon and pons
what are the anatomical features of the midbrain?
- two cerebral peduncles on the ventral side (so like kinda on the bottom side of the tegumentum on top of the pons)
- cerebral aqueduct runs through the midbrain
- superior and inferior colliculi of the tectum
- substantia nigra
- red nucleus
the midbrain is composed of the tectum and tegmentum
slide 37 cross section go look
what is the function of the cerebral peduncles?
aka cruz cerebri
they are located on the ventral side of the midbrain and they contain:
- descending fibers that go to the cerebellum via the pons
- descending pyramidal tracts
in-between the cerebral peduncles is the interpeduncular fossa/cistern!
what is the tectum?
the “roof” of the midbrain – it lies above the transverse plane of the cerebral aqueduct
it’s made up of 2 superior colliculi that control reflex movements of the eyes and 2 inferior colliculi that is a relay stations for auditory fibers –> the colliculi literally look like bumps on the midbrain
where is the the tegmentum located and what does it contain?
the ventral area of cerebral aqueduct and dorsal to the substantia nigra
it contains:
1. CN III and IV nuclei at different levels
- red nucleus
- substantia nigra
- decussation (fibers) of superior cerebellar peduncle
what major longitudinal pathways pass through the tegmentum?
- DCML
- spinothalamic tract
- medial longtidinal fasciculus
- descending motor pathways and autonomics
- projection pathways of the reticular formation
what can the superior and inferior colliculi be used as markers for?
the 3rd CN is at the level of the superior colliculi of the midbrain while the 4th CN is at the level of the inferior colliculi of the midbrain
what is the red nucleus?
the red nucleus is at the level of the superior colliculus of the midbrain
it’s dorsal to the substantia negri
it contains numerous blood vessels and a high iron content
what is the function of the red nucleus?
the red nucleus takes information from the cerebrum and cerebellum and communicates with the medulla and also the contralateral part of the cerebellum
so it receives information from the cerebrum and cerebellum then sends out fibers that synapse on the ipsilateral inferior olivary nucleus in the medulla which then projects fibers to the contralateral cerebellar cortex
helps control muscle tone and posture
what tract arises from the red nucleus?
rubrospinal tract
what is the substantia nigra?
part of the midbrain that is ventral to the red nucleus
it’s really dark because its neurons contain melanin
it secretes dopamine to inhibit the excitatory neurons of the basal ganglia (motor control system)
what are the two parts of the pons?
- basilar pons (ventral)
2. pontine tegmentum
which tracts run through the basilar pons?
- corticospinal tracts
- corticobulbar tracts
- corticopontine tracts
these tracts specifically run through the basilar pons
which structures are in the pontine tegmentum?
- spinothalamic tracts
- medial lemnisci
- medial longitudinal fasciculi
- reticular formation and pathways
which nerves are contained in the pons?
sensory and motor nuclei for 4 cranial nerves
CN 5 = trigeminal
CN 6 = abducens
CN 7 = facial
CN 8 = auditory/vestibular
which nerve would be impacted most by an enlargement of the 4th ventricle?
CN 6 = abducens nerve
it’s the closes to the 4th ventricle so if there was a tumor or enlargement, CN 6 would be the first impacted which would effect your ability to move the eye since it innervates the lateral rectus muscle
what are the anatomical features of the medulla oblongata?
- medullary pyramids
- decussation of the pyamids
- decussations of the DCML pathway
- inferior olivary nuclei
what are the medullary pyramids?
medullary pyramids are formed by the large motor corticospinal tracts
right about the medulla-spinal cord junction, these fibers decussate
where do the fibers of the corticospinal tract decussate?
caudal medulla
fibers of the corticospinal tract cross the midline (contralateral) and descend in the spinal cord as lateral corticospinal tracts
where do the fibers of the DCML pathway decussate?
caudal medulla
but rostral to the pyramidal decussation of the corticospinal tract
what is the inferior olivary nuclei?
it receives fibers from cerebellum, red nucleus, basal ganglia and cerebral cortex
it then sends fibers to the opposite cerebellar hemisphere via the inferior cerebellar peduncle
which nerves are found in the medulla oblongata?
CN 8-12
CN 8 = auditory/vestibular
CN 9 = glossopharyngeal
CN 10 = vagus
CN 11 = accessory
CN 12 = hypoglossal
what are relay nuclei?
relay nuclei are important in terms of creating synaptic connections with sensory fibers
- the nucleus gracilis and nucleus cuneatus which are part of the medulla
they pass sensory information to the thalamus
- olivary nuclei
they relay info from the spinal cord, cerebral cortex, and the brainstem to the cerebellar cortex
what are the 3 major afferent pathways?
- trigeminothalamic tract
- DCML
- spinothalamic tract
what are the 2 major efferent pathways?
- corticobulbar tract
2. corticospinal tract
what is the corticobulbar tract?
efferent motor pathway
this pathway doesn’t decussate till it gets to the brainstem but there’s also some fibers that stay on the same side
so its nuclei are dually innervated by fibers in both the left and right cerebral cortex
what part of the brainstem is the reticular formation?
tegumentum of the midbrain
the reticular formation and the tegmentum are superimposed on each other
what is the reticular formation?
It forms a diffuse, multi-synaptic, net-like meshwork (reticulum) of widely interconnected neurons in the tegmentum (midbrain, dorsal pons, medulla)
the RF is involved in nearly every aspect of brain function including the following:
- Homeostasis
- Consciousness
- Arousal
- Pain
- Primitive motor control
- Muscle tone
- Behavioral mechanisms
what is ARAS?
ARAS = ascending reticular activating system which is found in the midbrain portion of the reticular formation
the midbrain RF gives rise to an ascending barrage of diffuse, non-specific sensory data called the ARAS
acting like a battery, the ARAS stimulates the cerebral cortex and maintains the conscious state
so if there was a midbrain lesion that compressed on the ARAS of the RF, the patient would probably be in a coma or at least result in stupor
what is the function of the reticular formation in the pons-medulla area?
vital Centers are located in the medulla and pons and control cardiovascular respiratory, and other homeostatic mechanisms
so if you can’t guess, lesions in these centers are fatal
examples of RF mediated reflexes: Aortic Body, Carotid Body, Aortic Sinus, Carotid Sinus, Respiratory, Cough, Swallowing, Salivary and Vomiting
review: which CNs are found in each part of the brainstem?
midbrain = CN 3, 4
pons = CN 5, 6, 7, 8
medulla = CN 9, 10, 11, 12
what is the blood supply to the midbrain?
- posteromedial group
- posterior cerebral artery
- superior cerebellar artery
- basilar artery
slide 36
what is the blood supply to the pons?
- superior cerebellar artery
- paramedial and circumferential branches
- anterior inferior cerebellar artery
- basilar artery
slide 36
what is the blood supply to the medulla?
- anterior inferior cerebellar artery
- anterior posterior spinal artery
- posterior inferior cerebellar artery
- vertebral artery
slide 36
what is the arterial supply of the lateral areas of the brainstem and the cerebellum?
- the posterior inferior cerebellar artery supplies the lateral medulla and posterior inferior aspect of the cerebellum
- the anterior inferior cerebellar artery supplies the lateral aspect of the pons and anterior inferior aspect of the cerebellum
- the superior cerebellar artery supplies the lateral midbrain and superior surface of the cerebellum
