Lab - External Anatomy and Blood Supply of the Brain Flashcards
how to decide if the lesion is peripheral, or in the spinal cord, or in the brain?
- symptoms in the head (like facial weakness) usually rule out spinal cord (except Horner’s)
- increased tone usually rules out strictly peripheral pathology
if the lesion is in the brain, how to decide the level?
shift your diagnosis rostrally (anteriorly) to accommodate additional reported symptoms
-do NOT shift down/caudally
what level should the lesion be assumed?
lesion is at the level of the highest symptom
- lower symptoms are due to damage to sensory and motor tracts as they passed through midbrain
- assume a single lesion
what can you guess about the lesion if symptoms occur suddenly?
probably caused by a stroke, except if caused by obvious trauma
- either hemorrhagic or ischemic
- treatments are different, but symptoms are largely identical
what can you guess about the lesion if symptoms progress gradually over time and are unilateral?
likely caused by tumor
-often accompanied by increased intracranial pressure, though large hemorrhagic strokes can also present with increased intracranial pressure
what can you guess about the lesion if symptoms progress gradually over time and are bilateral?
usually caused by disease process
what side are symptoms on, and what kind of symptoms are there, if the lesion is in the spinal cord?
all sensory and motor symptoms are on the same side as the lesion except loss of pain and temperature
what side are symptoms on, and what kind of symptoms are there, if the lesion is in the brain?
lesion is on the same side as the highest symptom (the one which located the level)
-lower symptoms occur on the opposite site
what side are symptoms on, and what kind of symptoms are there, if the lesion is in the forebrain?
all sensory and motor symptoms are on the opposite side of the body (olfactory loss is the exception)
what side are symptoms on, and what kind of symptoms are there, if the lesion is in the cerebellum (or its input or output tracts)?
all symptoms are on the same side of the lesion
what 3 diagnoses can motor symptoms be reduced to?
- failure to move (indicates lesion of descending motor pathways)
- tremor, incoordination (usually implicate cerebellum)
- involuntary, uncontrollable movement (implicates basal ganglia)
what is the telencephalon made of?
cerebral hemispheres (cortex, white matter, and basal ganglia)
what is the diencephalon made of?
thalamus and hypothalamus
what is the mesencephalon made of?
midbrain
what is the metencephalon made of?
cerebellum and pons
what is the myelencephalon made of?
medulla
what is the forebrain made of?
telencephalon and diencephalon
what is the hindbrain made of?
metencephalon and myelencephalon
cerebellum, pons, and medulla
what is the brainstem made of?
midbrain, pons, and medulla
which cranial nerves originate in the medulla?
what do they collectively control?
what symptoms suggest that the medulla has been compromised?
IX (glossopharyngeal), X (vagus), XI (spinal accessory), XII (hypoglossal)
- collectively control breathing and heart rate
- ataxic or disrupted breathing (death), or irregular heartbeats suggest medulla has been compromised
which cranial nerves originate in the pons?
what symptoms suggest that the pons have been compromised?
V (trigeminal), VI (abducens), VII (facial)
-loss of sensation in face, eye deviated medially, or weakness in facial muscles
where is cranial nerve 8? what are symptoms?
vestibulocochlear is in transition between pons and medulla
-ipsilateral deficits in hearing or balance
what is the only cranial nerve that begins on the posterior side?
IV (trochlear)
which cranial nerves originate in the midbrain?
what symptoms suggest that the midbrain has been compromised?
III (oculomotor), IV (abducens)
- dilated pupil or eye whose movements are restricted
- levels of consciousness are controlled by circuits in tegmentum of midbrain, so coma usualloy indicates forebrain or midbrain involvement
which cranial nerves originate in the forebrain?
what symptoms suggest that the forebrain has been compromised?
I (olfactory), II (optic)
-loss of smell or more commonly loss of vision indicates forebrain disease, along with changes in “mental” functions, memory, language, and affect
regional functions of cerebral cortex
participates in many sensory, motor, and “cognitive” processes
- is the largest component of our brain (85% by weight)
- surface is convoluted into gyri and sulci, which define general functional regions
- interconnected with other side of brain via commissures, including parts of corpus callosum, and anterior commissure
what is the neocortex?
what makes up most of the cerebral cortex
- contains neurons organized in 6 layers/laminae that are numbered from surface of brain to deep white matter
- -each layer has distinctive morphology
- -changes in organization between different cortical areas is related to functional specialization
how many divisions of cortex have been defined by histological differences?
50 different subdivisions
- cortical layer IV is made of small stellate neurons with locally ramifying axons, prominent in sensory cortices and receive input from thalamus
- layer V is made of large pyramidal cells whose axons leave cortex to descend to brainstem and spinal cord; prominent in brainstem and spinal cord
how are connections of group of neurons between different laminae organized?
in a vertical/columnar fashion so that cells with similar function span all cortical layers w/in columns
occipital lobe functions
associated with visual system; damage causes visual deficits
- visual info from thalamus to cortex comes first to primary visual cortex (area V1 or area 17)
- -this area includes part of lingual and cuneate gyri, and within deep folds of calcarine sulcus
- most of the cortex is on medial hemisphere
- visual info then spreads to other parts of occipital cortex, then to areas in parietal and temporal lobes (18 and 19)
what do lesions in occipital lobe cause?
blind spots (scotomas) in half of visual field contralateral to lesion
how are sides of the visual cortex interconnected?
each side of the visual cortex is interconnected with the ohter side via the splenium of the corpus callosum
what is the postcentral gyrus part of what and what does it do?
part of parietal lobe associated with somatosensory system
- analogous to area V1 of occipital cortex (where somatosensory information from thalamus first reaches cerebral cortex)
- also called area S1 or Brodmann’s areas 3,1,2
what does damage to the postcentral gyrus do?
somatic sensory deficits (loss of touch, limb position) on opposite side of the body
-due to topographic localization of sensory info within the gyrus, damage to a portion of it will result in sensory loss to only a part of the opposite side of the body and will help to localize damage
what is the superior parietal lobule part of what and what does it do?
part of parietal lobe associated with guiding movement
what does damage to the superior parietal lobule do?
lesions sometimes cause “apraxia” (inability to bring limb under sensory or cognitive control)
-patient might not be able to point to an object when asked, even though can see clearly and limbs not paralyzed
what is the inferior parietal lobule part of what and what does it do?
part of parietal lobe and associated with several cognitive functions
- in “dominant” left hemisphere, concerned with language
- in right hemisphere, pathology leads to spatial disabilities
- -may get lost in own home, “neglect” the left side of his body
what gyri are part of the dominant hemisphere of inferior parietal lobule?
supramarginal gyrus is part of “Wernicke’s” area to understand language
angular gyrus is gateway through which visual information reaches Wernicke’s area
-damage to this area affects the ability to read
how are the parietal lobe and posterior parts of the frontal lobe interconnected?
these parts are interconnected through body of corpus callosum
what is Heschl’s gyrus/gyri part of? what does it do? what happens if there’s damage in one hemisphere versus both?
temporal lobe (AKA transverse temporal gyrii, Brodmann’s areas 41 and 42)
- primary sensory cortex for audition, but since info from both ears is processed bilaterally in the brain, damage to this area in only one hemisphere produces little deficit
- damage in both hemispheres causes inability to understand spoken language, since auditory info is cut off from Wernicke’s area
what is the superior temporal gyrus part of? what does it do?
temporal lobe; associated with audition and posterior portion and superior surface lying within lateral sulcus (planum temporale, posterior to Heschl’s gyrus)
-makes up part of Wernicke’s area in dominant hemisphere (understand language)
what are the middle, inferior, and occipito-temporal (fusiform) gyri part of? what do they do? what do bilateral lesions do?
temporal lobe; associated with vision, particularly visual memory and perception
-lesions cause prosopagnosia (inability to identify or recognize faces)
what are the parahippocampal gyrus and uncus part of? what do they do? what does bilateral damage cause?
temporal lobe
- medial surface has special association with memory
- bilateral damage can lead to severe amnesia
what regions receive terminations of olfactory tract?
uncus, anterior part of parahippocampal gyrus, subcallosal gyrus
how are the anterior parts of the temporal lobes and olfactory lobes interconnected?
they are interconnected via the anterior commissure
what is the precentral gyrus part of? what does it do?
frontal lobe; AKA primary motor cortex of area 4 (Brodmann), major source of axons that extend to spinal cord and other motor areas for control of voluntary movements
what does damage to the precentral gyrus do?
weakness (paresis) and movement deficits on opposite side of the body
what are the superior and middle frontal gyri (posterior portions) part of? what do they do?
frontal lobe; includes “secondary motor” and “premotor” areas that contribute to organization of voluntary movements, including eye movements (frontal eye fields)
what does damage to superior and middle frontal gyri do?
damage to this part of the brain can result in apraxia
-if damage is in dominant hemisphere, ability to write may be impaired
what is the inferior frontal gyrus (posterior portion) a part of? what does it do? what happens if it’s damaged?
frontal lobe; in dominant hemisphere, it’s called “Broca’s area” and is needed for programming of speech and writing
-if damaged, patients lose ability to generate fluent speech, although can understand verbal or written statements
what is the prefrontal cortex part of? what does it do?
frontal lobe (rostral portions of superior, middle, and inferior frontal gyri) -far more developed in humans, and functions are hard to delineate but may be for person's personality, planning and sequencing of tasks, etc.
what does damage to prefrontal cortex do?
personality changes that may be subtle or profound
-patients sometimes develop compulsive, repetitive behaviors (related to impaired ability to plan complex behaviors)
how are frontal lobes interconnected?
via genu of corpus callosum
where does information about speech travel?
enters temporal cortex in Heschl’s gyrus, spreads to Wernicke’s area, then relayed to frontal lobe (Broca’s area in inferior frontal gyrus) where commands for speech are organized
what is Wernicke’s area made of?
posterior parts of superir temporal gyrus and supramarginal gyrus
where does visual information directly related to reading travel?
from occipital lobe, enters Wernicke’s area via angular gyrus
Wernicke’s aphasia
receptory or sensory aphasia
- involves inability to understand language and to speak coherently, but can think words properly
- in most cases, it’s associated with damage to Wernicke’s area
Broca’s aphasia
expressive or motor aphasia
-associated with impaired ability to generate speech (or writing) and usually involves damage to Broca’s area
what are the 2 major origins of CNS circulation? what provides anastomoses between them?
posterior circulation: vertebral arteries (branches of subclavian arteries)
anterior circulation: internal carotid arteries
anastomoses via posterior communicating arteries
-allow one circulation to perfuse the other if the latter occludes gradually from arterial disease
-since these are so small, anastomoses will not protect the brain from a sudden stroke in one of the two circulations
what areas of the brain do vertebral arteries supply? what are some branches?
posterior circulation; supplies brainstem, cerebellum, and pard of cerebral cortex
- gives rise to small arteries that travel down spinal cord
- -2 posterior spinal arteries + 1 anterior spinal artery
- -travel length of spinal cord and reinforced by segmental branches from aorta
- as vertebral arteries extend along base of medulla, each gives rise to many medial and lateral branches that penetrate medulla
- also produce proiminent branches that supply dorsolateral medulla and medial parts of cerebellum (including nuclei) via posterior inferior cerebellar arteries
what is the basilar artery? what are its branches
where the vertebral arteries join near the junction of the medulla and pons
- at or just beyond this junction, a pair of branches arise which supply undersurface of cerebellar cortex and central areas of pontine tegmentum (anterior inferior berebellar arteries)
- then gives off several small pontine arteries that supply medial and lateral parts of pons
- at rostral end of pons, two more large branches (superior cerebellar arteries) supply superior surface of cerebellar cortex and dorsolateral areas of pontine tegmentum
- at rostral end of basilar artery, perforating branches contribute to blood supply of crus cerebri, posterior thalamus, and mibrain
posterior cerebral arteries
bifurcation of basilar artery (distal to perforating branches)
- travel along medial surface of temporal of occipital lobes
- send branches to midbrain, posterior parts of thalamus and internal capsule (posterior choroidal arteries)
- each artery gives rise to a branch that connects the posterior circulation to anterior via posterior communicating artery
- -gives rise to important perforating branches in thalamus, midbrain, and crus cerebri
what is the distribution and major symptoms of a lesion in the anterior spinal artery?
ventral 2/3 of spinal cord - branch in spinal cord: paralysis, loss of pain and temperature sense below occlusion
medial medulla - branch in medulla: contralateral sensory loss and paresis, ipsilateral tongue paralysis
what is the distribution and major symptoms of a lesion in the posterior inferior cerebellar artery?
dorsolateral medulla and pons, medial cerebellum, cerebellar cortex
-Wallenburg’s syndrome: vertigo, loss of balance, ipsilateral “cerebral signs”, loss of facial pain sensation, hoarseness
what is the distribution and major symptoms of a lesion in the anterior inferior cerebellar artery?
inferior surface of cerebellar cortex, dorsolateral pons
-ipsilateral “cerebellar signs” (tremor, ataxia), facial paralysis, ipsilateral hearing loss, loss of pain and temperature over face ipsilaterally
what is the distribution and major symptoms of a lesion in the basilar branches
pons, anterior midbrain (crus cerebri)
- paralysis and loss of sensation in face, body, and limbs
- can also affect eye movements and cause diplopia
what is the distribution and major symptoms of a lesion in the superior cerebellar artery?
superior surface of cerebellum, dorsolateral corner of rostral pons
-ipsilateral cerebral signs, contralateral pain and temperature loss, Horner’s
what is the distribution and major symptoms of a lesion in the posterior cerebral artery?
occipital lobe, medial portions of parietal and temporal lobes, anterior and posterior midbrain, crus cerebri, posterior thalamus
- if unilateral: blindness in visual field contralateral to affected side, alexia (left)
- if bilateral (like “top of the basilar”): bilateral blindness, memory loss, somatosensory loss, coma and death
what is the distribution and major symptoms of a lesion in the posterior communicating branches?
anterior midbrain, crus cerebri, thalamus
-contralateral paresis, coma and death
what is the distribution and major symptoms of a lesion in the middle cerebral artery?
lateral surface of cortex, insula
-contralateral paralysis, sensory loss, apraxia, aphasia, partial blindness
what is the distribution and major symptoms of a lesion in the anterior cerebral artery?
medial surface of parietal and frontal lobes
-contralateral parallysis and sensory loss in leg and foot, sometimes apraxia
what is the distribution and major symptoms of a lesion in the lenticulostriate artery?
basal ganglia, amygdala, internal capsule, anterior thalamus
-possibly involuntary movements (basal ganglia), paralysis, sensory deficits over entire half of body, homonymous visual field deficits (internal capsule)
what is the distribution and major symptoms of a hemorrhage in the anterior choroidal artery?
hippocampus, anterior choroid plexus, posterior internal capsule
-hemorrhage may cause paralysis, sensory deficits, visual field defect (internal capsule)
