ICL 2.3: Overview of the Human Brain Flashcards
what is the grey matter of the brain?
aka the cerebral cortex!! it’s the outer most layer of the brain
it’s the neuron cell bodies
ex. ganglia and nuclei
what is the white matter of the brain?
aka the cerebral white matter; it’s the inner layer of the brain under the cerebral cortex
the myelinated axons from the neuron cell bodies
what are the 3 poles of the brain?
- frontal pole
- temporal pole
- occipital pole
they are found in the anterior, middle and posterior cranial fossas, respectively
what would the brain of someone with Alzheimer’s or dementia look like?
the gyri and sulci wouldn’t be tight
the sulci would be dilated and the gyri would be small and atrophied
which sulcus seperates the frontal and parietal lobes?
central sulcus
what would cause the brain to be flattened?
edema
edema in the cranial cavity could cause the lobes of the brain to become squished against the skull and appear flattened
what are the gyri of the frontal lobe?
- superior frontal gyrus (closest to midline)
- middle frontal gyrus
- inferior frontal gyrus
- precentral gyrus
slide 14; go look at the picture
what are the subdivisions of the inferior frontal gyrus?
- pars opercularis
- pars triangularis
- pars orbitalis
what are the sulci of the frontal cortex?
- superior frontal sulcus
- inferior frontal sulcus
- precentral sulcus (superior and inferior)
what is the importance of the central sulcus?
it separates the frontal lobe from the parietal lobe but more importantly it separates functional areas!
the motor cortex fibers all originate from the frontal lobe while all the sensory information we receive is in the parietal lobe
so when a patient has a tumor one of the things the surgeon will do is identify the central sulcus to find the somatosensory cortex of the parietal love vs. the motor cortex of the frontal lobe
what are the gyri of the parietal lobe?
- postcentral gyrus
- superior parietal lobule
- inferior parietal lobule
the inferior parietal lobule is comprised of the supramarginal gyrus and the angular gyrus
how can you locate the specific gyri of the inferior parietal lobule?
the inferior parietal lobule is composed of the supramarginal gyrus and the angular gyrus
if you follow the superior temporal gyrus it will lead you to the supramarginal gyrus
if you follow the superior temporal sulcus it will lead you to the angular sulcus
what are the sulci of the parietal lobe?
- postcentral sulcus
2. intraparietal sulcus
what are the gyri of the temporal lobe?
- superior temporal gyrus
- middle temporal gyrus
- inferior temporal gyrus
- fusiform gyrus (underneath)
what are the sulci of the temporal lobe?
- superior temporal sulcus
2. inferior temporal sulcus
what is the tentorium cerebelli?
it’s the dural reflection that the occipital lobe sits on
it covers the cerebellum
what is the insula?
aka the insular cortex
you can find it deep to the frontal and temporal lobes and it’s like a second mini brain = “hidden lobe”
people think that pain and auditory elements are processed here as well
what structure separates the left and right hemisphere?
longitudinal cerebral fissure
which structure separates the temporal lobe from the frontal and parietal lobes?
lateral sulcus aka fissure of sylvius
if you dissected through the lateral sulcus you’d find the insural cortex
what is the function of Broca’s area?
execution and fluency of speech
what is the function of Wernicke’s area?
comprehension of speech
what is conductive aphasia?
Broca’s area and Wernicke’s area have to be in constant communication in order for you to understand what is being said to you and respond back
so if there’s a disruption between them then you get conductive aphasia
which sulcus splits the occipital lobe into superior and inferior portions?
calcarine sulcus
which sulcus separates the occipital and parietal lobes?
parieto-occipital sulcus
you can only see on a sagittal cut of the brain
what are commissures? what are the two commissures of the brain?
- corpus callosum
- anterior commissure
commissures are points of connection between the right and left hemispheres so that they can communicate
what is the corpus callosum?
a commissure of the brain that’s a large bundle of axons connecting left and right cerebral hemispheres
when tumors metastasize from one side of the brain to the other it’s because they use the corpus callosum to get there
a thin corpus callosum indicates white matter atrophy or degeneration of myelin
side note: on a coronal section you will only see the corpus callosum once but in the sagittal section you’ll see the whole curve
what is the anterior commissure?
a small bundle of axons that passes between the two cerebral hemispheres joining the grey matter of the anterior poles of the temporal lobes
what is the internal capsule? what is it bordered by?
a collection of myelinated fibers
it has 3 subdivisions and unique fibers travel through each division each with their own function
it is bordered by the caudate nucleus, globus pallidus, thalamus, and putamen
go look at the picture
what is the basal ganglia?
caudate nucleus + putamen + globus pallidus
it helps you execute smooth rhythmic movement
ex. Huntington’s is a disease of the basal ganglia and so they have lots of movement problems
what are the subdivisions of the internal capsule?
- anterior limb
- genu
- posterior limb
only in an axial image would you be able to see all 3 of these
which fibers are located in the genu of the internal capsule?
corticobulbar fibers
these are involved in motor function
which fibers are located in the posterior limb of the internal capsule?
corticospinal fibers
involved in motor supply
what is the diencephalon?
fancy word for the thalamus + hypothalamus
what dura covers the hypophyseal fossa?
diaphragma sellae
what controls the pituitary gland?
the hypothalamus
so the hypothalamus is super close to the pituitary gland, it’s only seperated by the pituitary streak
this means the hypothalamus is in close proximity to the sellea turcica
what part of the brain must all afferent sensory information pass through?
the thalamus
ALL information that comes from the outside world has to stop at the thalamus and then the thalamus sends it out to the right area of the brain to be processed
so basically the thalamus is a relay station and it has specific nuclei that will route information to specific areas of the brain
what structure separates the thalamus from the hypothalamus?
hypothalamic sulcus
what are the 3 subdivisions of the brainstem?
- midbrain
- pons
- medula
what are the 4 ventricles in the brain?
2 lateral ventricles
3rd ventricle
4th ventricle
note: the lateral ventricle is found in every aspect of the brain; the frontal, temporal and occipital horn!
what is the function of the ventricles of the brain?
CSF flows through the ventricles!
it flows from the ventricles of the brain to the subarachnoid space in the spinal cord
lateral ventricle –> 3rd ventricle –> 4th ventricle –> subarachnoid space
CSF leaves 4th ventricle via foramen of magendie (caudal end) & foramina of Luschka (lateral angles of ventricle) to enter subarachnoid space
what structure connects the lateral ventricle with the 3rd ventricle?
interventricular formamen
what structure connects the 3rd ventricle to the 4th ventricle?
cerebral aqueduct
what structure resides inside the lateral ventricle?
the choroid plexus
this produces CSF
what separates the anterior horn of the lateral ventricle into left and right?
septum pellucidum
how could a brain tumor beneath the tentorium cerebelli effect the brain?
the tentorium cerebelli is the dura matter that separates the cerebellum from the occipital lobe
if there’s an infratutorial tumor below the tentorium cerebelli it’s putting pressure on the ventricles; specifically the cerebral aqueduct –> most pediatric brain tumors are infratutorial while most adult ones are supratutorial
the problem is that just because there’s a tumor doesn’t mean that the brain will stop making CSF so the 3rd ventricle will probably get huge since the tumor is compressing on the cerebral aqueduct and not allowing it to drain
so what happens is the brain tissue starts to compressed against the skull and get damaged…
the take-home message is that if you have a block at either connection between the ventricles you will end up with serious problems
how is the cerebral cortex organized?
the cerebral cortex is the grey matter of the brain and it’s organized into 6 layers
all the layers communicate with each other
layer 3 and 5 are the important ones
what is the function of layer 3 of the cerebral cortex?
cortical-cortical connections
aka commissural and association fibers
so layer 3 is important for developing connections so that different parts of the brain can communicate with each other
what is the function of layer 5 of the cerebral cortex?
it sends output to subcortical structures like the pons, brainstem, basal ganglia, and spinal cord
so it’s what helps form pathway like the corticospinal pathway and corticobulbar pathway
it’s composed of long projection fibers out of the cerebral cortex
the neurons in the cortex of the brain are considered UPPER motor neurons
what are the two upper motor neuron pathways?
- motor cortex (M1)
2. premotor cortex (M2)
what is the function of the motor cortex?
part of the frontal lobe that evokes movement of individual muscles, and is arranged in a somatotopic fashion (homunculus)
most axons of the Pyramidal tract originate here.
what is the function of the premotor cortex?
part of the frontal lobe that evokes mass movements involving postural adjustments both ipsilaterally and
contralaterally
most extrapyramidal pathways originate in the premotor cortex
lesions in this area result in spasticity of contralateral antigravity muscles due to the loss of inhibition provided by upper motor neurons in this area
describe the pathway of the motor homunculus
M1 in the frontal lobe –> posterior limb of the internal capsule –> midbrain –> pons –> mid medulla –> caudal medulla
once the signal reaches the caudal medulla, the fibers cross over before ending the spinal cord
so if you had an upper motor neuron lesion in the cortex of the brain, your symptoms and muscle weakness would be on the contralateral side of the body!!
if in turn, you had a lower motor neuron lesion in the ventral horn of the spinal cord, your deficits would be ipsilateral
what are the 3 types of pyramidal cells?
- projection
- association
- commissural
the white matter in the brain consists of large numbers of myelinated axons (fibers) carrying electrical signals between areas of within the brain and between the brain and the rest of the body –> functionally, there are three major types of white matter fibers in the CNS: Projection Fibers, Association Fibers, and Commissural Fibers
what is a projection fiber?
project OUTSIDE of cortex – to the thalamus or basal ganglia or brainstem or spinal cord
what is an association fiber?
send axons to another cortical region in the SAME hemisphere
what is a commissural fiber?
send axons to cortical regions in the OPPOSITE hemisphere
what is a very important example of association fibers?
association fibers connect different parts of the same cerebral hemisphere
for example, Broca’s area and Wernicke’s area connected by the arcuate fasciculus which is a type of association fiber
because of this connection patients with lesions in either Broca’s or Wernicke’s area will have impaired repetition = conduction aphasia
damage to the arcuate fasciculus impairs the transmission of information between Wernicke’s area andBroca’sarea; this injuryleads to impaired repetition
thus, the patient can comprehend the speech but cannot transmit the information the speech production centers in Broca’s area to allow repetition to occur
are neurons glial cells?
NO
glial cells are supporting cells
what is an astrocyte?
part of the CNS
- structural support
- transport of substances from blood to neurons
- react to injury
most brain tumors are astrocytomas
what is an oligodendrocyte?
part of the CNS
- they form the myelin sheaths around axons in the CNS – multiple axons per oligodendrocyte
this means that the loss of just one oligodendrocyte is a big deal because that means no myelin for 50-100 axons
- provide nutritive functions in gray matter
what is a microglia?
- immune function; basically a macrophage – have lots of lysosomes, inclusions and vesicles that release damaging and neuroprotective chemicals
- react to injury
they’re small, elongated nuclei with twisted processes
what is an ependymal cell?
part of the CNS
they line ventricles
they’re a single layer of cuboidal-to-short columnar epithelium that line the ventricles of the brain and the central canal of the spinal cord
they’re bound by junctional complexes on the apical side
they also have cilia and microvilli that facilitate the movement and absorption of the CSF
what are satellite cells?
part of the PNS
they have support functions similar to astrocytes
what are Schwann cells?
the cells in the PNS that form myelin around the axons on the pNS
what happens when an astrocyte reacts to an injury?
you could end up with severe astrogliosis
normally the astrocyte cell body is flat which means there’s nothing going on but when they’re activated by injury they start to plump up
if there’s a ton of damage to axons like with a patient who has MS and there’s a lot of myelin degeneration around the axon, the astrocytes will occupy the empty space left behind by the myelin and this is how you end up with a glial scar in the brain tissue
how can you histologically identify an oligodendroglioma?
the tissue will be composed of round cells with blue nuclei and a rim of clear cytoplasm
so the oligodendrocytes look like they’re surrounded by cytoplasm and they usually aren’t…
