Section 1 Flashcards
Symptoms in the head (e.g., facial weakness) usually rule out what?
spinal cord (Horner’s is the exception).
Increased tone usually rules out what?
pathology that is strictly peripheral
If in the brain, what level is the lesion?
Shift your diagnosis rostrally to accommodate additional reported symptoms. Do not shift down (caudally).
If the symptoms occur suddenly, they are most probably caused by what?
a stroke, except if caused by obvious trauma.
Strokes can be either
hemorrhagic or ischemic (thrombus).
If the symptoms progress gradually over time and are unilateral, they are likely caused by a
tumor.
Tumors often are accompanied by
increased intracranial pressure, although large hemorrhagic strokes can also present with increased intracranial pressure.
Symptoms caused by a disease process develop gradually and are usually
bilateral in nature with no increased intracranial pressure.
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.
If the lesion is in the brain stem:
The lesion is on the same side as the highest symptom (the one which located the level); lower symptoms will occur on the opposite side.
If the lesion is in forebrain,
all sensory and motor symptoms are on the opposite side of the body (olfactory loss is the exception).
If the lesion is in the cerebellum (or its input or output tracts)
all symptoms are on the same side as the lesion.
Reduce all somatosensory words (loss of pain, position sense, temperature, joint sense, etc.) into
one symptom, “sensory loss of the … [e.g., left trunk and limbs].” Somewhere along its course the ascending sensory pathways have been cut.
Reduce all motor symptoms to one of three diagnoses:
1) Failure to move: includes “paralysis, paresis, weakness, hypertonus, spastic, flaccid.” All of these indicate lesion of descending motor pathways (motor cortex, internal capsule, descending motor tracts, etc., motor neurons.). 2) Tremor, incoordination, usually implicate cerebellum 3) involuntary, uncontrollable movement implicates basal ganglia
telencephalon =
cerebral hemispheres (cortex + white matter + basal ganglia)
diencephalon =
thalamus + hypothalamus
mesencephalon =
midbrain
metencephalon =
cerebellum + pons
myelencephalon =
medulla
forebrain =
telencephalon + diencephalon
hindbrain =
metencephalon + myelencephalon (i.e. cerebellum + pons + medulla)
brainstem =
midbrain + pons + medulla
The glossopharyngeal, vagus, hypoglossal, and spinal accessory nerves originate largely in the
medulla
Collectively, what do the glossopharyngeal, vagus, hypoglossal, and spinal accessory nerves do?
they control breathing and heart rate (among other things) so that ataxic or disrupted breathing (death), or irregular heartbeats suggest that the medulla has been compromised by the patient’s illness.
ataxic or disrupted breathing (death), or irregular heartbeats suggest that
the medulla has been compromised by the patient’s illness.
Cranial nerves 5, 6 and 7 originate in the
pons,
so that loss of sensation in the face, or an eye deviated medially, or weakness of the facial muscles is often indicative of
pontine dysfunction.
Cranial nerve eight originates in
the transition between the pons and medulla, and
CN 8 symptoms include
ipsilateral deficits in hearing or balance.
Cranial nerves 3 and 4 originate from the
midbrain.
Midbrain dysfunction often shows as
a dilated pupil or an eye whose movements are extremely restricted (Cn 3).
Additionally, levels of consciousness are controlled by circuits in the
tegmentum of the midbrain so a coma usually indicates forebrain or midbrain involvement.
Cn 1 and 2 are
forebrain nerves.
Loss of smell or the more common loss of vision indicates
forebrain disease.
Changes in “mental” functions, memory, language, affect also indicate
forebrain disease.
The cerebral cortex
participates in many sensory, motor, and “cognitive” processes and is the largest component of our brain, about 85% of the brain by weight.
The surface of the cortex is
highly convoluted into gyri and sulci, which are similar from person to person and define general functional regions.
The cerebral cortex is interconnected with the other side of the brain via
commissures, including different parts of the corpus callosum, and the anterior commissure.
Most of the cerebral cortex is made up of
neocortex
Neocortex
contains neurons organized in six layers or laminae that are numbered from the surface of the brain to the deep white matter.
Each layer (of the neocortex) has
neurons with distinctive morphology.
Changes in the organization of these laminae (number of neurons, cell packing density, perikaryal size, etc.) between different cortical areas is related to
their functional specialization; altogether over 50 subdivisions of the cortex have been defined by these histological differences
For instance cortical layer IV is made up of
small stellate neurons with locally ramifying axons.
In sensory cortices
(somatosensory, visual, auditory) this layer is prominent and receives input from the thalamus.
Layer V is
prominent in motor cortex and contains large pyramidal cells, whose axons leave the cortex to descend to the brainstem and spinal cord.
Layer IV is
difficult to detect in motor cortex.
In addition to this laminar organization, connections of groups of neurons between different laminae are
organized in a vertical or columnar fashion, so that cells with similar function tend to span all cortical layers within these columns.
In sensory and motor regions of cortex, this columnar organization is
represented topographically across the surface of the cortex.
Sensory cortex
(post-central gyrus) a map of the body’s surface spreads over this region such that columns of neurons representing the face is located within this gyrus in a region near the lateral fissure, the arm more superiorly, and the leg and foot representation ar
Occipital lobe
Its functions are associated with the visual system and damage to it result in visual deficits.
Visual information
(from the thalamus) to the cortex comes first to the primary visual cortex (often called “area V1” or “area 17”).
V1
This region of the occipital cortex includes a portion of the lingual and cuneate gyri and within the deep folds of the calcarine sulcus.
Most of the primary visual cortex is on
the medial surface of the hemisphere
Visual information after the primary visual cortex
then spreads to other portions of the occipital cortex and to areas in the parietal and temporal lobes (e.g. areas 18 and 19).
Lesions in the occipital lobe usually cause
blind spots (called “scotomas”) in the half of the visual field contralateral to the lesion.
Each side of the visual cortex is
interconnected with the other side via the splenium of the corpus callosum.
Parietal Lobe parts
- Postcentral gyrus 2. Superior parietal lobule 3. Inferior parietal lobule
- Postcentral gyrus -
This area is associated with the somatosensory system.
Post central gyrus is analogous to
area V1 of the occipital cortex in that it is the site where somatosensory information from the thalamus first reaches the cerebral cortex.
Post central gyrus is also called
area “SI” or Brodmann’s areas 3,1, 2
Damage to Brodmann’s area leads to
somatic sensory deficits (e.g. loss of touch, limb position) on the opposite side of the body.
Because of the topographic localization of sensory information within the postcentral gyrus, damage to a portion of it (e.g. anterior cerebral artery infarct damaging the medial aspect of the cortex) will result in
sensory loss to only a portion of the opposite side of the body and help to localize the damage.
Superior parietal lobule -
This region is associated with guiding movement.
Lesions of the superior parietal lobule
will sometimes cause “apraxia”. This is an inability to bring the limb under sensory or cognitive control.
Example of apraxia
a patient may not be able to point to an object when asked, even though he can see it clearly, and his limbs are not paralyzed.
Inferior parietal lobule –
This region is associated with several cognitive functions.
Inferior parietal lobule in the “dominant” hemisphere
(usually the left) it is concerned with language.
The supramarginal gyrus is
part of “Wernicke’s area” and is needed to understand language
The angular gyrus
is the gateway through which visual information reaches Wernicke’s area.
Damage to the angular gyrus
area affects the ability to read.