NEUROSCIENCE Flashcards
(154 cards)
1
Q
The axons of the neurons in the grey matter are myelinated by what type of cell?
A
Oligodendrocytes
2
Q
Neural crest cells will become what?
A
The peripheral nervous system, both somatic and autonomic. Neural crest cells migrate throughout the body, becoming the ganglia of the sensory tracts as well as the autonomic ganglia.
3
Q
The neural tube will become what?
A
The central nervous system.
4
Q
What does endoderm form?
A
The gut tube (colon, stomach, intestines) and the lungs.
5
Q
What does the ectoderm form?
A
Skin (epidermis), hair, nervous system (neurons, glial cells, ependymal cells).
6
Q
What does the mesoderm form?
A
Blood vessels, bones, meninges, lymphatics, musculoskeletal system.
7
Q
What do the terms rostral, caudal, ventral and dorsal mean?
A
Towards the head (rostral), towards the tail (caudal), belly-side (ventral), and backside (dorsal).
8
Q
What is the trilaminar disc comprised of?
A
The trilaminar disc consists of ectoderm, endoderm, mesoderm, and the medodermal notochord. Ectoderm is the sheet of cells on top with the amnion above it. Endoderm is the sheet of cells on the bottom, with the yolk sac below it. Between ectoderm and endoderm is the sheet of mesoderm cells.
9
Q
What does the mesodermal notochord become, and is its role in neurulation?
A
It is a tube that will, in the adult, form intervertebral discs, padding for the vertebra. Early on in neurulation, the notochord is responsible for inducing embryogenesis of the entire nervous system.
10
Q
What are the support cells of dorsal root ganglia?
A
The support cells of dorsal root ganglia of the peripheral sensory neurons are Schwann cells that myelinate and satellite cells that nurture axons.
11
Q
The axons of the neurons in the grey matter are myelinated by what type of cell?
A
Oligodendrocytes
12
Q
From superficial to deep, what it the order of meninges?
A
The layers of meninges are the dura mater, the arachnoid mater, and the pia mater.
13
Q
What are the support cells of the central nervous system?
A
Astrocytes (that keep the blood-brain barrier tight), the oligodendrocytes (that do the myelinating), the ependymal cells (that line ventricles), and the microglial cells (that act as resident macrophages)
14
Q
What are Nissl bodies?
A
These are darkly staining structures in the cytoplasm around the nucleus, pathognomonic for a neuron’s cell body.
15
Q
Name a few of the neurotransmitters.
A
Acetylcholine, nitric oxide, vasoactive intestinal peptide, and norepinephrine.
16
Q
Neuron cell bodies are often very active in building what?
A
Protein; most neurotransmitters are proteins, and transmembrane proteins are required to receive or deliver a stimulus.
17
Q
In general, what are the roles of astrocytes?
A
Astrocytes likely supply the neurons with nutrients from the bloodstream, reinforce the CNS barrier with the ependymal cells, modulate the blood-brain barrier, modulate potassium, and modulate neurotransmitters.
18
Q
What is the role of ependymal cells?
A
Ependymal cells are the only true epithelium of the CNS and keep the CSF out of the parenchyma, and sometimes secrete CSF (choroid plexus) or reabsorb it (arachnoid granulations).
19
Q
What is the role of oligodendrocytes?
A
Oligodendrocytes are responsible for myelinating axons in the central nervous system. Unlike the Schwann cells that myelinate the peripheral nerves, one oligodendrocyte myelinates many axons.
20
Q
What is the role of microglial cells?
A
Microglial cells are phagocytes and antigen-presenting cells - they are the resident macrophages of the CNS.
21
Q
What is the only glial or neuronal cell derived from mesoderm?
A
Microglial cells.
22
Q
From superficial to deep, what is the order of meninges?
A
The layers of meninges are the dura mater, the arachnoid mater, and the pia mater.
23
Q
What is cavernous sinus syndrome?
A
This is caused by a pituitary tumor, an ascending infection, or a thrombosis. Headache and papilledema are common problems, but there can also be symptoms such as internal strabismus (due to impairment of the oculomotor nerve), sensory loss or the lower face, and Horner’s syndrome.
24
Q
The two lateral ventricles connect to the third ventricle via the ______.
A
Interventricular foramen (formerly foramen of Monro).
25
The third ventricle is connected to the fourth ventricle by the ______.
Cerebral aqueduct (formerly cerebral aqueduct of Sylvius).
26
Describe the flow of CSF.
CSF is generated from the choroid plexus, drained by arachnoid granulations, and contained by the ventricles (within the cranium), spinal canal (within the spine), and subarachnoid space.
27
What is the role of arachnoid granulations?
Arachnoid granulations take excess CSF and put it back into the systemic circulation, back into the venous blood, via the dural sinuses.
28
What is an obstructive (noncommunicating) hydrocephalus?
This is caused by a structural lesion that occludes the flow of CSF by blocking the passages from ventricle to ventricle. Any ventricles proximal to the obstruction are dilated which causes the CSF level to increase. This increase in CSF level leads to an increase an intracranial pressure which may lead to herniation.
29
What is a communicating (nonobstructive) hydrocephalus?
This is caused by impaired CSF reabsorption by arachnoid granulations. This classically occurs seconday to post-hemorrhage or post-meningitis effects on where the arachnoid granulations are. With nowhere for the CSF to go, the ventricles dilate, though unlike obstructive, in which only the proximal ventricle dilates, communicating hydrocephalus sees all ventricles dilate.
30
What is hydrocephalus ex vacuo?
This is caused by atrophy; progressive loss of tissue results in excess CSF to fill the cranial cavity. Hydrocephalus ex vacuo happens commonly in an elderly patient with dementia.
31
What is normal-pressure hydrocephalus?
This is a reversible cause of dementia where there is ventricular enlargement, but normal intracranial pressure. A patient with NPH thus does not show signs of increased ICP and will develop symptoms insidiously. Recall "wobbly, wacky, and wet," which represents the classic symptoms of a broad-based gait, cognitive changes, and urinary incontinence.
32
What cranial nerves pass through the cavernous sinus?
The abducens (CN VI), oculomotor (CN III), trochlear (CN IV), and trigeminal (CN V) nerves (as two separate branches (opthalmic branch CN V/I and maxillary branch CN V/II)
33
What is cavernous sinus syndrome?
This is caused by a pituitary tumor, an ascending infection, or a thrombosis. Headache and papilledema are common problems, but there can also be symptoms such as internal strabismus (due to impairment of the oculomotor nerve), sensory loss or the lower face, and Horner's syndrome.
34
Describe a subarachnoid hematoma.
Affected individuals complain of the "worst headache of their life." Although it is possible to get these bleeds from trauma, we see them as being secondary to medical disease - either hypertensive emergency or a rupture of a berry aneurysm. Affected individuals are stricken by an excruciating headache that has a rapid onset and cresendos quickly ("thunderclap").
35
What is Cushing's triad?
Bradycardia, hypertension and irregular respirations (Cheyne-Stokes breathing).
36
What is the main sign of increased ICP?
Headache that is worse in the morning and with actions that increase ICP (cough, sneeze, and Valsalva maneuver).
37
Besides headaches, what are other signs of ICP?
Projectile vomiting without nausea, papilledema, seizures, and a cranial nerve VI palsy (inability to abduct an eye past midline).
38
What are ways to treat increased ICP?
Raising the head of the bed, hyperventilation, mannitol, craniotomy, and decompressive craniectomy.
39
Describe an uncal herniation.
The medial aspect of the temporal lobe (uncus) herniates under the tentorium cerebelli which causes compression of the ipsilateral oculomotor nerve (CN III) resulting in ipsilateral pupil dilation and extraocular muscle paralysis. As the herniation progresses, the uncus compresses the brainstem away from the lesion causing loss of bodily sensation on the entire ipsilateral side (hemiparesis).
40
Describe a tonsillar herniation.
The cerebellar tonsils herniate through the foramen magnum which pushes the contralateral medulla up against bone causing compression of the medulla. This causes respiratory and cardiovascular arrest.
41
Describe a central hernia.
Caused by diffuse cerebral edema (often in patients with significant trauma), the progression of expanding edema forces the top of the brainstem and posterior cerebrum through the tentorial notch. This shears blood vessels and compresses the eye nerves and nuclei bilaterally, resulting in bilateral pupil dilation and bilateral extraocular palsies.
42
Describe an epidural hematoma.
Most often caused by damage to the middle meningeal artery due to strong, blunt force trauma to the side of the head. The patient will have a trauma, with either a loss of consciousness or not, but after a brief lucid interval, there is a rapid progression to coma and death.
43
Describe a subdural hematoma.
This is a bleed below the dura mater (subdural) and above the arachnoid layer. These patients present with an insidious headache progressing to encephalopathy (often mistaken as dementia). Shearing of the bridging veins in this kind of hematoma is seen in children and the elderly.
44
Describe a subarachnoid hematoma.
Affected individuals complain of the "worst headache of their life." Although it is possible to get these bleeds from trauma, we see them as being secondary to medical disease - either hypertensive emergency or a rupture of a berry aneurysm. Affected individuals are stricken by an excruciating headache that has a rapid onset and cresendos quickly ("thunderclap").
45
What are the positive and negative symptoms of schizophrenia?
Positive symptoms include delusions, hallucinations, disorganized speech, and disorganized behavior. Negative symptoms include flat affect, poverty of speech, poverty of movement, anhedonia, and cognitive delay.
46
What are the components of the basal ganglia?
Caudate nucleus, putamen, nucleua accumbens, and globus pallidus.
47
What neurotransmitter activates the thalamus and therefore stimulates movement?
Dopamine
48
Describe the direct pathway of the basal ganglia.
The direct pathway results in the disinhibition of the thalamus, and therefore allows movement. It does so through dopamine from the substantia nigra.
49
Describe the indirect pathway of the basal ganglia.
The indirect pathway results in the inhibition of the thalamus through acetylcholine, which prevents movement.
50
What is the mesolimbic pathway?
This pathway involves connections from the ventral tegmental area to the forebrain, and plays roles in emotion and reward and is responsible for the positive symptoms of schizophrenia. If you give a patient dopamine therapy, this pathway may elicit hallucinations.
51
What is the mesocortical pathway?
This pathway involves connections from the ventral tegmental area to the prefrontal cortex. It plays a role in cognition, executive function, and the negative symptoms of schizophrenia.
52
Whare are the signs and symptoms of Parkinson's disease.
Patients present with less movement, termed bradykinesia. Bradykinesia is characterized by the mask-like face (diminished facial expression), shuffling steps, a resting pill-rolling tremor, and cogwheel rigidity (movement is interrupted periodically: normal movement with abrupt pauses).
53
What causes Parkinson's disease?
It is a degenerative disease of the nigrostriatal dopaminergic system. The patient progressively loses the substantia nigra (the dopamine machine). The progressive loss of dopamine leads to worsening symptoms since dopamine is movement and the disease claims the dopamine-secreting cells.
54
What is Lewy body dementia?
If a patient presents with severe dementia and progresses to Parkinonism, the diagnosis is Lewy body dementia.
55
What are the positive and negative symptoms of schizophrenia?
Positive symptoms include delusions, hallucinations, disorganized speech, and disorganized behavior. Negative symptoms include flat affect, poverty of speech, poverty of movement, anhedonia, and cognitive delay.
56
When do babies lose their primitive reflexes?
Babies have primitive reflexes when they are born that abate within the first year of life as their frontal lobe develops, and their spinal cord becomes fully myelinated.
57
What happens if a stroke lesioned Broca's area?
The patient would be able to hear, understand, and formulate the thought of speaking, but then be unable to actually speak.
58
The anterior cerebral artery is responsible for which areas?
The feet and the legs.
59
The middle cerebral artery is responsible for which areas?
The face, hands, and Broca's area.
60
What are the symptoms of an upper motor neuron lesion?
The patient will have increased muscle tone, hyperreflexia, and up-turning toes.
61
What are the symptoms of a lower motor neuron lesion?
The patient will have decreased muscle tone and hyporeflexia, and the muscle will eventually atrophy and there may be the presence of fasciculations.
62
What causes a lower motor neuron lesion?
A lower motor neuron lesion may be temporary (e.g., demyelination) or permanent (trauma, transection, stroke of the spinal cord).
63
Where are the nuclei of lower motor neurons located?
The anterior horn of the spinal cord.
64
Along what tract do upper motor neuron axons travel within?
Upper motor neuron axons will travel within the lateral corticospinal tract until they reach their vertebral level.
65
The motor cortex controls the _____ body.
Contalateral.
66
When do babies lose their primitive reflexes?
Babies have primitive reflexes when they are born that abate within the first year of life as their frontal lobe develops, and their spinal cord becomes fully myelinated.
67
Sensations carried by the STT are activated by ________.
Nociceptors (chemical, thermal, and mechanical).
68
What is the role of the dorsal column-medial lemniscus system?
This system carries general sensation, including proprioception (understanding the body's spatial location and speed of movement), vibration, touch, pressure, and tickle senses.
69
How does a STT lesion present?
STT lesions always present with contralateral loss of pain and temperature except at the site of the lesion.
70
What happens if there is a spinal cord lesion that affects both the DCMLS and STT?
There will be ipsilateral general touch sensation loss and contralateral pain and temperature sensation loss.
71
Where is the primary somatosensory cortex located and what is its function?
It is located in the parietal lobe just posterior to the central sulcus, and it facilitates integration with vision, audition, and balance. It also handles spatial orientation and word choice for speech.
72
The middle cerebral artery perfuses the area of the brain that is responible for?
The face, hands and trunk (the MCA territory).
73
The anterior cerebral artery perfuses the area of the brain that is responsible for?
The genitals, feet, part of the legs (the ACA territory).
74
The sensory tracts of the DCLMS bring the perception of sensation to the ______ brain.
Contralateral.
75
The cell body of the peripheral sensory neuron is located in the _________.
Dorsal root ganglion outside of the spinal cord.
76
Sensations carried by the DCLMS are activated by ________.
Mechanoreceptors.
77
Sensations carried by the STT are activated by ________.
Nociceptors (chemical, thermal, and mechanical).
78
In trauma, iatrogenic injury during repair of the thoracoabdominal aorta (dissection, hematoma, aneurosym), or systemic hypotension, the ______ artery can be compromised.
The Adamkiewicz artery
79
What is cauda equina syndrome?
This happens when the nerve roots of the cauda equina are compressed, causing saddles anesthesia (S3-S5), with anesthesia of the genitals, perianal region, and anus. In addition to anesthesia, there may also be landinating leg pain. Treatment is emergent surgical decompression of the nerve(s) causing the symptoms. You will also see hyporeflexia, reduced tone, and possibe paralysis because this acts as a lower motor neuron lesion.
80
What is amyotrophic lateral sclerosis?
This is a motor-only lesion where both upper motor neurons in the frontal cortex and lower motor neurons in the anterior horn are affected. You would have symptoms of both upper motor and lower motor neuron lesions in the extremities, and also dysarthria and dysphagia because ALS also affects all skeletal muscles.
81
What is Brown-Sequard syndrome?
This happens when there is a perfect hemisection of the spinal cord and there is contralateral loss pain and temperature sensation below the lesion, ipsilateral upper motor neuron symptoms below the lesion, and ipsilateral touch sensation is lost below the lesion.
82
What tracts are affected in anterior spinal artery syndrome?
The lateral corticospinal and lateral spinothalmic tracts.
83
What are the symptoms of anterior spinal artery syndrome?
At the lesion, there is bilateral loss of temperature, bilateral lower motor neuron symptoms, and normal regular sensation. Below the level of the lesion, there is bilateral loss of temperature, bilateral upper motor neuron symptoms, and normal regular sensation.
84
How does B12 deficiency affect the DCMLS?
Recall that B12 is necessary for myelin synthesis. Initially, there will be severe bilateral impairment of proprioception and vibration sensation (dorsal columns affected). If allowed to go on untreated, it will claim more of the spinal cord, leading to ataxia (spinocerebellar tracts affected) and bilateral spastic weakness (corticospinal tracts affected). Sensation to temperature and pain remain unaffected.
85
What is the etiology of a syringomyelia?
This is almost always a childhood disease, occuring in patients who already have malformations of their foramen magnum, such as Dandy-Walker or Chiari malformation type 1. Acquired syringomyelia can occur following spinal surgery or as a product of infection - either meningitis or encephalitis.
86
What are the symptoms of syringomyelia and why?
Bilateral segmental loss of pain and temperature in a "cape-like" distribution. It is bilateral because both the left and right second-order neurons' axons decussate here at the anterior commissure. Of note, only the STT is compromised, so the sensations of pain and temperature are compromised.
87
What is tabes dorsalis?
Tabes dorsalis is caused by tertiary syphilis, and causes a lack of proprioception and light touch and vibration sensations bilaterally indicates that the lesion is in the spinal cord and involves a loss of the bilateral DCMLS.
88
In trauma, iatrogenic injury during repair of the thoracoabdominal aorta (dissection, hematoma, aneurosym), or systemic hypotension, the ______ artery can be compromised.
The Adamkiewicz artery
89
Describe a PCA stroke.
There is contralateral homonymous hemianopsia with macular sparing.
90
What is the circle of Willis?
It is located in the midbrain and is an anastomosis between three anatomic arterial origins - the left internal carotid artery, the right internal carotid artery, and one basilar artery.
91
What are the major watershed areas and what is the significance?
The ACA-MCA territories and the MCA-PCA territories are the major watershed areas. The significance of a watershed area is that it is the most vulnerable to reduced perfusion.
92
What are the categories of strokes?
Ischemic and hemorrhagic.
93
What are the three etiologies of an ischemic stroke?
Thrombotic, embolic, and lacunar.
94
What are embolic strokes caused by?
They are caused by atrial fibrillation or by atherosclerosis, rupture and thrombosis, then embolism somewhere else (most commonly the carotid arteries).
95
What is a transient ischemic attack (TIA)?
It is an episode of reversible neurologic dysfunction, and is caused by focal ischemia (acute rupture and thrombosis of a plaque) that goes away on its own. There must also be the absence of acute infarction, as evidence by MRI, and no lasting neurologic deficit.
96
What is a cerebrovascular accident (CVA)?
This usually means ischemic infarction - permanent damage caused by the rupture and thrombosis of a plaque.
97
Describe a ACA stroke.
There is lower extremity motor function and sensation loss. There will be also upper motor neuron lesion signs and symptoms on the contralateral side.
98
Describe a MCA stroke.
There is upper extremity motor function and sensation loss. There will be also upper motor neuron lesion signs and symptoms on the contralateral side. As well, there can be aphasia or hemineglect.
99
Describe a PCA stroke.
There is contralateral homonymous hemianopsia with macular sparing.
100
What nerves are responsible for the taste sensation and the swallowing reflex?
Both the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X).
101
What is cranial nerve VIII and its function?
It is the vestibulocochlear nerve and is a purse sensory nerve. It connects the vestibular system (balance) and the bones of audition (hearing) to the brain.
102
What is cranial nerve XII and its function?
It is the hypoglossal nerve and is a purely motor nerve. This nerve innervates all the intrinsic muscles and all but one of the extrinsic muscles (genioglossus, styloglossus, and hypoglossus) of the tongue.
103
What cranial nerves are midbrain and above?
CN I through IV (CN I handles smell, and CN II, III and IV innervate the eye).
104
What cranial nerves are pons?
CN V through VIII (and they innervate the face, the ears, and some of the eye).
105
What cranial nerves innervate the mouth and below?
CN IX through XII.
106
What structures pass through the foramen magnum?
Brainstem, vertebral arteries, and CN XI.
107
The anterior cranial fossa contains what?
It contains the cribriform plate, through which the many branches of the olfactory nerve penetrate.
108
Describe why cranial nerve V (the trigeminal nerve) is both a motor and sensory nerve?
This nerve provides cutaneous innervation to the face (V1 - forehead, bridge of nose, eyelids, V3 - mandible, lower lip, lower half of cheek, and temples) and provides motor inntervation to the masseter, temporalis, and pterygoids.
109
Describe the role of the vagus nerve.
All visceral autonomics (sensory and motor) of the parasympathetic system are carried in the vagus nerve. It is also responsible for peristalsis and swallowing.
110
What nerves are responsible for the taste sensation and the swallowing reflex?
Both the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X).
111
What connects the third and fourth ventricles, and where is this structure located?
The cerebral aqueduct which is located within the midbrain.
112
Describe how the medulla is responsible for reflexive actions.
In cardiac, it receives information from baroreceptors and alters autonomic output to adjust the heartrate. In pulmonary, it receives information from those same baroreceptors regarding oxygen content of blood and moderates the respiratory center. The vomiting center is also located in the medulla (or at least the site that initiates emesis).
113
Describe the roll of the cerebellum.
It helps smooth out and coordinate movement and does so incredibly quickly.
114
What is the Rule of 4's?
4 cranial nerves in the midbrain or above (CN I, II, III, IV), 4 in the pons (CN V, VI, VII, VIII), 4 in the medulla (CN IX, X, XI, XII), and 4 are medial (II, III, VI, XII) because they are motor-only neurons.
115
If the anterior inferior cerebellar artery (AICA) is affected, what cranial nerves are also affected?
CN VI, VII, and VIII
116
If the posterior inferior cerebellar artery (PICA) is affected, which cranial nerves are also affected?
CN XII, XI, X, and IX
117
All fibers entering the cerebellum, except those from the olivary nucleus, are called _____.
Mossy fibers.
118
Every input that enters the cerebellum takes two branches, what are they?
One is stimulatory to a neuron in the deep nucleus; the other is stimulatory to granule cells.
119
If the basilar artery is affected, which cranial nerve is also affected?
CN V
120
What part of the brain houses the corticospinal tracts and the substantia nigra?
The basis pedunculi which is the anterior portion of the midbrain.
121
What connects the third and fourth ventricles, and where is this structure located?
The cerebral aqueduct which is located within the midbrain.
122
Proprioception, vibration and touch defects are always _______ to the brainstem lesion.
Contralateral.
123
Describe the symptoms of a basilar stroke.
Locked-in syndrome; quadriparesis, paralysis of the facial muscles, 5/6 extraocular muscles work and the eyelid can lift; there is loss of sensation of the entire body, though facial sensation may remain intact
124
Describe the symptoms of a AICA stroke.
Ipsilateral CN VII affected (facial paralysis, decreased salivary output, loss of taste on anterior 2/3 of tongue); vertigo, vomiting, nystagmus, deafness; ipsilateral loss of pain and temperature of the face; contralateral loss of pain and temperature of the body; ipsilateral Horner's syndrome
125
Describe the symptoms of a PICA stroke.
Ipsilateral IX and X affected (impaired gag reflex, impaired swallowing reflex, loss of dysphagia, dysarthria); vomiting, nystagmus; ipsilateral loss of pain and temperature of the face; contralateral loss of pain and temperature of the body; ipsilateral Horner's syndrome
126
Describe the symptoms of a ASA stroke.
Contralateral hemiparesis, contralateral hemiplegia, and tongue deviation towards the side of the lesion.
127
Describe the symptoms of a SCA stroke.
Ipsilateral cerebellar gait ataxia, limb ataxia, and vertigo.
128
Describe the symptoms of Weber Syndrome.
Better termed superior median midbrain syndrome and symptoms include contralateral hemiparesis (upper and lower extremities, and face) due to the loss of the medial lemniscus, ipsilateral oculomotor palsy due to loss of the oculomotor nucleus, ipsilateral miosis due to the loss of the E-W nucleus, and some contralateral upper motor neuron lesions of the corticbulbar tract.
129
If there are any ipsilateral symptoms, there must be a lesion of a ______.
Brainstem nucleus.
130
If you have a lesion of the corticobulbar tract, the defect will be on the _______ side.
Contralateral.
131
If you have a lesion of the corticobulbar tract, the symptoms will be on the _______ side of the brainstem lesion.
Ipsilateral.
132
Proprioception, vibration and touch defects are always _______ to the brainstem lesion.
Contralateral.
133
Most schwannomas occur at the ______.
Cerebellopontine angle, where they are attached to the vestibular branch of CN VIII. Patients often present with tinnitus and hearing loss.
134
What are common symptoms of brain cancers?
Increased intracranial pressure, obstructive hydrocephalus, focal neurological deficit, or seizure.
135
What is the most common cause of an intracranial cancer in the brain?
Metastasis from somewhere else; the brain is a common metastatic site for lung cancer (the most common metastasis to the brain), melanoma, renal cell carcinoma, and breast cancer.
136
How do metastatic lesions appear on brain imaging?
They are multiple in number and are described as well-circumscribed lesions that occur at the grey-white junction with surrounding vasogenic cerebral edema.
137
What is the most common group of primary brain tumors?
Gliomas which include astrocytomas, oligodendrogliomas, and ependymomas.
138
Describe glioblastoma multiforme (GBM).
It shows ring-enhancing lesions on MRI, follows a serpignious border, and has central necrosis or cystic change. GBM is highly malignant when diagnosed and is commonly found in the cerebral hemispheres and can cross the corpus callosum. Classically, this demonstrates a "butterfly glioma pattern." Histology demonstrates a pseudopalisading pleomorphic tumor. This cancer will stain GFAP positive.
139
Describe what a oligodendroglioma is.
It is a glial cancer derived from oligodendrocytes and is slow-growing. It typically forms in the frontal lobe and, being a supratentorial tumor, it is primarily found in adults in their 40s and 50s. On histology, it has a "fried egg" appearance, and you can also see calcification and a chicken-wire fence appearance.
140
Describe what an ependymoma is.
It is a cancer of the ependymal cells, the cells of the choroid plexus that make CSF. It is a pediatric tumor and is classically found below the tentorium cerebelli in the fourth ventricle. It grows within the fourth ventricle, resulting in the obstruction of the cerebral aqueduct, which in turn causes obstructive hydrocephalus. Increased intracranial pressure is a predominant symptom with others including headache that is worse in the morning, emesis without nausea, relieft from symptoms while being upright, and worsened symptoms with any increase in intracranial pressure (e.g., cough, sneeze, Valsalva maneuver).
141
Describe a medulloblastoma.
This is a malignant embryonal tumor and is a pediatric malignancy of the cerebellum. Patients present with either cerebellar signs or obstructing hydrocephalus. Medulloblastoma is representative of a primitive neuroectodermal origin and consists of small blue cells. These form Homer-Wright rosettes.
142
Describe what a meningioma is.
Meningiomas are a benign growth of the epithelium of the arachnoid layer and commonly involve deletions of chromosome 22, which harbors the NF2 gene. Patients with neurofibromatosis type 2 can have meningiomas. It is a slow-growing tumor and is classically seen in a young adult female with seizures.
143
Most schwannomas occur at the ______.
Cerebellopontine angle, where they are attached to the vestibular branch of CN VIII. Patients often present with tinnitus and hearing loss.
144
When is phenobarbital used?
This is often an outpatient medication used as an anticonvulsant. It is never the first-line medication and never the preferred treatment. It should only be used for seizures in a patient with severe disease and as an adjunct to other failed medications.
145
What is GABA?
GABA (gamma-aminobutyric acid) is an inhibitory neurotransmitter.
146
What is benzodiazepines affect on GABA channels?
They increase the frequency with which GABA channels open.
147
What is barbiturates affect on GABA channels?
They increase the duration for which GABA channels are open.
148
What is the most common excitatory signal used in the CNS?
Glutamate.
149
In general, compare and contrast GABA and glutamate.
GABA is inhibitory and causes hyperpolarization, while glutamate is stimulatory and causes depolarization.
150
Describe the role of glumate and GABA in astrocytes.
In most astrocytes, glutamate produces depolarization by increasing conductance of cations (Na+, Ca2+, and K+), whereas GABA hyperpolarizes cells by opening Cl- channels.
151
Why is there a risk of developing tolerance when benzodiazepiones are used chronically or abused?
The reason is the changes in the GABA-glutamine microenvironment. Excessive GABA receptor inhibition is met with synaptic plasticity - GABA receptor expression decreases, whereas glutamate receptor expression increases.
152
Describe the benzodiazepine withdrawal symptoms.
Diastolic hypertension and tachycardia are usually the first signs, then diaphoresis, shaking tremors, anxiety and restlessness, nausea, visual or tactile hallucinations, and possibly seizures.
153
What are the short-acting benzodiazepines?
Alprazolam (Xanax), midazolam (Versed), diazepam (Valium), and lorazepam (Ativan).
154
When is phenobarbital used?
This is often an outpatient medication used as an anticonvulsant. It is never the first-line medication and never the preferred treatment. It should only be used for seizures in a patient with severe disease and as an adjunct to other failed medications.
