Brainstem LN Flashcards
What does the brain stem consist of?
-midbrain
-pons
-medulla oblongata
how long is the medulla, where does it rest and where does the junction of spinal cord and medulla begin?
-about 3 cm long
-rests on the midline part of the occipital bone and is covered dorsally by the cerebellum
-The junction of the spinal cord and medulla is level with the foramen magnum
Where is the fourth ventricle relative to the medulla?
Dorsal surface contains the caudal half of the fourth ventricle
What is the surface of the medulla marked by?
several bulges or eminences, outlined by sulci –> one of such eminences is the pyramid which consists of corticospinal fibres also called pyramidal tract
Where is the olive in medulla?
lateral to the pyramid, is an oval swelling that marks the position of the inferior olivary nucleus
What is the inferior cerebellar peduncle?
A body of white matter that connects the medulla with the cerebellum and form the side wall of the caudal half of the fourth ventricle
Where does the gracile and cuneate fasciculi continue from the spinal cord?
continue into the medulla
What tuberculum cinereum?
-lateral to the cuneate fasciculus and tubercle marks the position of the trigeminal spinal tract and nucleus
What is the obex?
The apex of the V-shaped boundary of the inferior part of the fourth ventricle, which is folded caudally over the most rostral 1 to 2 mm of the central canal
How many cranial nerves are attached to the medulla?
-4 (CN 9-12)
-further 3 emerge at the junction between the medulla and pons (CN 6 -8 )
What is the length of the pons?
about 2.5 cm long
Describe the basal part of the pons
-indented along its ventral surface in the midline by a shallow groove, the basilar sulcus (accommodates the basilar artery)
-The basal pons blends laterally into the middle cerebellar peduncles
- the attachment of the trigeminal nerve marking the transition between the pons and the peduncles
-the basal pons serves as a large synaptic relay station, providing a connection from the cortex of each cerebral hemisphere to the opposite cerebellar hemisphere
in the pons fibres from the cerebral cortex terminate…
ipsilaterally on neurons that compose the pontine nuclei
What is the tegmentum of pons?
-dorsal part of pons
-similar to much of the medulla and midbrain in that it contains ascending and descending tracts and nuclei of cranial nerves
What is the dorsal face of the pons formed by?
The floor of the fourth ventricle
What is the most rostral part of the pons known as?
Isthmus of the brain stem (situation immediately below the cerebral peduncles and inferior colliculi of the midbrain)
Where does the diamond-shaped floor of fourth ventricle (rhomboid fossa) lie?
On dorsal aspect of the brain stem
What happens to fourth ventricle as we move toward the obex caudally and the aqueduct of the midbrain rostrally?
Narrows
Does the floor median sulcus divide into symmetrical or asymmetrical halves?
symmetrical
What does the sulcus limitans divide each half into?
medial and lateral areas
What is the V-shaped interval between the converging peduncles bridged by? and what does the remainder of the roof consist of?
-The superior medullary velum, a thin sheet of white matter
-remainder of roof consists of a thinner pial ependymal membrane, the inferior medullary velum
What is the foramen of Magendie? and what does it provide?
-A median aperture of the fourth ventricle formed by a deficiency of variable size in the inferior medullary velum
-this hole provides the principal communication between the ventricular system and the subarachnoid space
What do the lateral walls of the fourth ventricle include?
The inferior cerebellar peduncles, which curve from the medulla into the cerebellum on the medial aspects of the middle peduncles
What is the foramen of Luschka? and where is it situated?
-2 lateral apertures of the fourth ventricle which are channels through which cerebrospinal fluid enter the subarachnoid space
- situated at the junction of the medulla, pons, and cerebellum (the cerebellopontine angles)
where is the choroid plexus of the fourth ventricle suspended from?
The inferior medullary velum
What does choroid plexus do?
Tissue that secretes CSF
Where is most of the CSF produced in? and where does it travel
-In lateral and third ventricles and flows into fourth ventricle by way of the cerebral aqueduct where more CSF is produced
-The choroid plexus makes a small addition to the volume of the CSF in the cavity of the fourth ventricle and directly into the subarachnoid space of the pontocerebellar angle
What is the length of the mibrain and where does the ventral surface extend?
-about 1.5cm long
-ventral surface extends from the pons to the mamillary bodies of the diencephalon
What is the basis pedunculi (crus cerebri)?
is the robust column of white matter on each side of the midbrain. It is composed of corticospinal, corticobulbar, and
corticopontine fibres.
What is the interpeduncular fossa?
-deep depression between the basis pedunculi columns (aka the posterior perforated substance because of the many small penetrating blood vessels at this region)
What is the lateral surface of the midbrain formed by?
mainly by the cerebral peduncle
What does the cerebral peduncle comprise?
comprises the basis pedunculi and some internal structures, the substantia nigra, and the tegmentum
describe the dorsal surface of the midbrain
-has four rounded elevations, the paired inferior and superior colliculi (also called the corpora quadrigemina)
-These colliculi make up the tectum (they mark the extent of the midbrain on the dorsal surface)
-fibres that connect the inferior colliculus with the medial geniculate body (part of the thalamus) form a ridge known as the inferior brachium
What does the superior brachium contain?
-fibres proceeding from the cerebral cortex and the retina to the superior colliculus
What is the superior colliculus involved in?
control of movements of the eyes and head in response to visual and other stimuli.
What are the ascending pathways of brainstem?
-medial lemniscus system
-spinothalamic tract
-spinotectal (or spinomesencephalic) tract
-spinoreticular fibres
-spinocerebellar tracts
What are the descending tracts of the braimstem?
-corticospinal (pyramidal) tract
-central tegmental tract/rubrospinal tract
-tectospinal tract
Where does the medial lemniscus tract terminate in brainstem?
-in the gracile nucleus, the gracile fasciculus is concerned with sensations from the leg and lower trunk
- and in cuneate nucleus, cuneate fasciculus carries signals from upper trunk, arm and neck
where do the myelinated axons of the cells in gracile and cuneate nuclei go after terminating here in the medial lemniscus system?
-follow a curved course to the midline as internal arcuate fibres then;
-After crossing the midline in the
decussation of the medial lemnisci, these fibres turn rostrally in the medial lemniscus
where is the medial lemniscus tract?
it is conspicuous tract occupying the interval between the midline and the inferior olivary nucleus in the medulla.
What happens after medial lemniscus system traverses the pons and midbrain(lateral area of tegmentum of midbrain)?
- tract ends in the lateral division of the ventral posterior nucleus of the thalamus (for general somatic sensation)
What is the spinothalamic tract for?
-pain, temperature, and touch on the opposite side of the body continues into the medulla without appreciable change in position
What is the spinotectal tract for?
-conveys somaesthetic data to the superior colliculus and the reticular formation of the midbrain also continues into the medulla without appreciable change in position.
-end on the central posterior and other thalamic nuclei
What is the spinal lemniscus?
-spinothalamic and spinotectal tract merge to form spinal lemniscus
-spinal lemniscus traverse thelateral area of medulla dorsal to the inferior olivary nucleus
-dorsolateral to medial lemniscus
Where does the spinoreticular tract in ventral and lateral white matter spinal cord continue into?
into brains where the axons synapses with cells of the reticular formation
What information does the spinoreticular fibres transmit?
data from the skin and internal organs
some spinoreticular fibres are collateral branches of fibres of….
the spinothalamic tract
What do the dorsal and ventral spinocerebellar tracts carry information about?
unconscious proprioceptive signals from the lower limbs
where does the uncrossed dorsal (posterior) of the spinocerebellar tract originate ?
-in the nucleus thoracicus (nucleus dorsalis or Clarke’s column) of the thoracic and upper lumber segments of the spinal cord
describe the crossing of the central tract of spinocerebellar tract and origin
-largely double crossed (crosses midline, travels superiorly and then crosses back over)
-most of its cells of origin are in the lumbosacral enlargement of the spinal cord
where does the dorsal spinocerebellar fibres enter after traversing medulla?
The inferior cerebellar peduncle– to cerebellum
where does the ventral spinocerebellar fibres enter after traversing medulla?
keeps traveling through pons and enters the cerebellum by way of the superior cerebellar peduncle
Where are the cell bodies of the corticospinal tract located?
in area of cerebral cortex that occupies adjoining regions of frontal and parietal lobes
Where do the axons of corticospinal (pyramidal) tract traverse in the brain?
traverse subcortical white mater, the internal capsule, and the brainstem
in medulla each corticospinal tract is…
a compact body of white matter in the pyramid (located in medulla), each pyramid contains roughly 1 million axons of varying size
where do most decussation occur in most people, and where in the rest of people for corticospinal tract?
decussation of the pyramids (85%), and the rest continue into the ventral funiculus of funiculus of the cord as the central corticospinal tract
where or the corticospinal fibres termine in the spinal cord before descending?
in base of dorsal horn, intermediate gray matter and the ventral horn
where does the corticospinal tracts origin and what does this mean?
they have motor function because many axons of cortical origin arise in the primary somatosensory area
What is the widest and most rapidly conducting neurons in the corticospinal tract?
from giant pyramidal cells of Betz in the primary motor area, their fibres end in synaptic contact with the cells bodies of spinal motor neurons
Corticospinal tracts also modulate the transmission of sensory signals to the brain, (they form synapses with neurons in the gracile and cuneate nuclei and in the dorsal horn of the spinal cord). true or false?
true
describe the central tegmental/rubrospinal tract
-arise from the ipsilateral red nucleus and other gray area of the midbrain, terminates in the inferior olivary complex
-A tiny bundle of axons from the
contralateral red nucleus continues caudally as the rubrospinal tract.
-Rubrospinal tracts occupy a position ventral to the lateral corticospinal tract.
-In humans, this tract ends in the upper two cervical segments of the spinal cord.
describe the tectospinal tract
-This originates in the superior colliculus of the midbrain
-The fibres cross at that level to the opposite side of the brain stem.
-The tract is insignificantly small in humans.
- Tectobulbar fibres go from the superior colliculus to the reticular formation of the pons and upper medulla.
- They are involved in the reflexive control of eye and head movements as a result of auditory or visual stimuli.
what does the pretectal area consist of?
-four pairs of small nuclei which are rostral to the lateral edge of the superior colliculus
What does the olivary pretectal nucleus receive fibres from? and where do axons go from the pretectal nucleus
- receives fibres from both retinas by way of the ipsilateral optic tract and the superior brachium
-from here axons go to the Edinger-Westphal (EW) nucleus of each side.
What is the EW nucleus source of? and what does this mean?
-preganglionic parasympathetic fibres in the oculomotor nerve
-Thus, the pretectal area is included in a reflex pathway for constriction of the pupils in response to increased intensity of light
The pretectal area has connections that implicate it in pathways for the control of eye movements, including convergence. true or false
true
Describe the red nucleus and associated tracts
-The egg-shaped red nucleus extends from the caudal limit of the superior colliculus into the
subthalamic region of the diencephalon. It has myelinated axons.
- It is more vascular than the surrounding tissue (named for its pinkish hue in a fresh specimen).
- Afferent fibres from the contralateral cerebellum reach the red nucleus by way of the superior
cerebellar peduncle and its decussation
Describe the substantia nigra
-Is a large nucleus situated between the tegmentum and the basis pedunculi throughout the midbrain
- It extends into the subthalamic region of the diencephalon.
-the dopaminergic neurons of the pars compacta give it its black colour
