section 2, part 2 internal anatomy Flashcards
list 3 things that can cause the BBB to break down
- brain tumors
- bacterial invasion
- ischemia (most common cause)
explain what the pathology of a stroke stems from
from loss of tissue oxygenation but also from introduction of toxins to the brain and from ion fluxes (because the BBB has been broken down)
in ischemia, why is there swelling in the brain?
because ischemia directly damages Na+ and K+ pumps, so there is ionic influx–> cells fill with water–> brain swelling
how does CSF decrease the weight of the brain on the skull
by giving the brain buoyancy
what is the total volume of CSF?
140 mL
what is the average rate of CSF formation /day
500 ml/day
entire volume of CSF is turned over 3-4 times/day
CSF is primarly secreted by___?
the choroid plexus
what type of epithelium surrounds the choroid plexus?
cuboidal or columnar epithelium
CSF is in equilibrium with what?
the brain extracellular fluid
compared to the blood plasma, is CSF more or less acidic?
more acidic
what color should the CSF be?
clear with no RBCs and few or no WBCs
where is the choroid plexus found?
- floor of the inferior horn
- body of the lateral ventricle
- roof of 3rd ventricle
- inferior part of the roof of the 4th ventricle
where is the CSF made (which ventricle)?
in the lateral ventricle and roof of 3rd ventricle
how does most CSF exit the 4th ventricle?
through 3 foramina:
foramen of magendie (middle)
foramina of luschka (1 on either side of magendie)
where are the arachnoid villi located?
in the walls of the dural sinuses. this is where the majority of the CSF is absorbed into the venous system
what could cause an obstructing or non-communicating hydrocephalus
a tumor that blocks the flow of CSF
which place is most common for a CSF blockage?
wherever the ventricular system narrows
intraventricular foramen, cerebral aqueduct or at the outlet of 4th ventricle
what causes communicating hydrocephalus?
when the arachnoid villi are disease and absorption fails
where can increased intracranial pressure be seen?
when inspecting the fundus of the eye with an ophthalmoscope
the retinal vessels of optic nerve are engorged and optic nerve is dilated
(papilledema)
what are some additional symptoms of increased intracranial pressure?
headache N/V cognitive impairment decreased level of consciousness impair vision and 6th nerve palsies
if increased intracranial pressure causes the frontal lobe function to be impaired, what is common symptom?
characteristic unsteady gait where the feet barely leave the floor (magnetic gait) as well as incontinence
above what level of WBC in the CSF is concerning for a pathology?
about 4/mm^3 (can increase 1000x in acute bacterial meningitis)
in patients with MS what is characteristic of the CSF composition?
the gamma globulin content of the CSF is disproportionately increased to more than 13% of the total protein
if there is RBCs in the CSF, what does this indicate?
hemorrhagic stroke
what 3 fibers can the deep white matter in the cerebrum be classified into?
- association fibers
- commissural fibers
- projection fibers
what is the role of the association fibers?
connect different areas of cortex in same hemisphere
what is the role of the commissural fibers?
connect homologous areas of cortex of 2 hemispheres
what is the role of the projection fibers?
connect areas of cortex to lower areas of neuraxis
what are the 4 long association fiber tracts?
- superior longitudinal fasciculus (aka arcuate fasciculus)-largest one
- inferior longitudinal fasciculus
- uncinate fasciculus
- cingulum
where does the superior longitudinal fasciculus extend to and from?
extends from frontal lobe arcing inferiorly into the temporal lobe and posteriorly to the occipital lobe
what areas does the superior longitudinal fasciculus connect?
broca’s motor speech area, Wenicke’s area and auditory cortex
where does the inferior longitudinal fasciculus extend to and from?
extends from occipital lobe to the temporal lobe along the inferior aspect of the hemisphere deep to the occipitotemporal gyrus
where does the uncinate fasciculus run?
deep to the limen insulae (the anterior border of the insula)
what two areas does the uncinate fasciculus connect?
the frontal and temporal cortices
*it is thought that it connects the orbital frontal cortex-based reward & punishment centers with temporal lobe based memory representations
what does the cingulum connect?
structures of the limbic system (subcallosal gyrus, cingulate gyrus, parahippocampal gyrus and uncus)
where does the cingulum run?
it runs on the medial aspect of the hemisphere deep to the cingulated gyrus
which structure is hypothesized to be involved in the process of learning to avoid painful stimuli?
the cingulum because its connections with areas of the thalamus (that receive pain fibers via the spinothalamic tract)
are the association fiber systems direct one way?
HELL NO!
what is the largest commissural fiber tract?
the corpus callosum
what is the function of the corpus callosum?
interconnect homologous areas of cortex in the two hemispheres in a spatially oriented fashion
what part of the corpus callosum are the frontal lobes connected through?
the genu of the corpus callosum
what part of the corpus callosum are the parietal lobes connected through?
the body of the corpus callosum
what part of the corpus callosum are the occipital lobes connected through?
the splenium (this facilitates binocular vision)
what is the function of the anterior commissure?
it connects the anterior poles of the two temporal lobes containing the primary olfactory cortices
what is the function of the hippocampal commissure
it is comprised of axons of the fornix that cross where the two fornices approach one another between the splenium and the posterior part of the thalamus
connects the two hippocampi
what is the function of the posterior commissure?
connects two sides of rostral midbrain
involved in pupillary light reflex
essential for maintaining upward gaze
in the cerebral hemispheres, the axons of the projection fibers are collectively knwon as what?
the corona radiata
what is the importance of the thalamic radiations in the corona radiata?
they interconnect the thalamic nuclei and their cortical targets
they include sensory projections from the sensory nuclei of teh thalamus to their respective cortical centers in the parietal, occipital & temporal lobes
as the axons of the corona radiata pass mediate to the lenticulate nucleus, what are they called?
the internal capsule
for axons whose targets are the brainstem & spinal cord, they descend onto the anterior aspect of the midbrain as what?
the crus cerebri
what 3 types of fibers do the internal capsule and crus cerebri contain?
- cortcospinal fibers
- corticobulbar fibers
- corticopontine fibers
what are corticospinal fibers?
they are axons originated in the pre and post central gyri that go to the dorsal & ventral horn neurons in the spinal cord
what are the corticobulbular fibers?
motor axons that control cranial nerve nuclei in the brain stem
what are corticopontine fibers?
axons from the motor cortex that go to the pontine nuclei (in the base of the pons) which then is projected to the contralateral cerebeller hemisphere
