Term
| Explain the relationship between "bursting" "thalamic neurons and EEG synchronization. |
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Definition
1) During sleep, EEG is synchronized
- Input from Reticular Thalamic neurons (RTNs) onto thalamocortical neurons leads to hyper-polarization and activation of T-type Calcium channels, which cause depolarization and AP firing (Bursts).
2) During arousal, EEG is de-synchronized
- Lack of inhibitory input from RTNs prevents bursting from thalamocortical neurons and allows them to faithfully transmit sensory signals (transition mode). |
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Term
| What is the structure of the ascending reticular activating system (ARAS)? |
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Definition
Arise in rostral pons and midbrain and terminate in thalamus.
- Cholinergic cells within pedunculopontine and dorsolateral tegmental nuclei (NA and 5-HT also important) reduce inhibitory drive of RTNs.
- Active during wakefulness, preventing thalamocortical "bursting"
- Reduction in activity causes lack of responsiveness during sleep
- Lesions cause coma |
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Term
| How does stupor/coma relate to activity with the ARAS? |
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Definition
Lesion of these ACh-releasing cells that project from the rostral pons to the reticular thamalic nucleus (RTN) prevents their role in inhibiting RTN fibers that cause bursting in thalamocortical cells.
The result is increased cortical synchronization, thalamocortical bursting and coma. |
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Term
| What types of lesions can produce coma/stupor? |
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Definition
1) Extensive, bilateral lesions to thalamus, cortex or thalamocortical axonal systems.
2) Focal lesion to ARAS
Largest group of etiologies involve no visible lesion
Those with visible lesions may include
- Mass lesion (tumor, hemorrhage, abscess)
- Structural lesion of thalamus, midbrain or pons with direct injury to ARAS (infarcts or small hemorrhages)
- Widespread bilateral damage to cortex and white matter (hypoxia, meningitis or encephalitis) |
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Term
| What are the 8 major components of a neurological workup for a comatose patient? |
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Definition
GARPEMS M
1) General evaluation
2) Alertness
3) Respirations
4) Pupils
5) Eye movements
6) Motor responses
7) Synthesis
8) Management |
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Term
| What important components are included in the General Medical evaluation of a comatose patient? |
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Definition
1) Hypothermia (hypoglycermia, hypothyroidism, drugs)
2) Hyperthermia (infection, heat stroke, anti-ACh drugs)
3) Hypertension (HTN encephalopathy, ICH, intracranial HTN)
4) Hypotension (Shock, blood loss, sepsis)
5) Skin lesions (Purpura) |
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Term
| What important components are included in the "Level of Alertness" evaluation of a comatose patient? |
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Definition
NCLSC
1) Normal consciousness
2) Confusion and delirium (often precede coma)
3) Lethargy (mild, sleep-like state, can be brought to wakeful state)
4) Stupor (vigorous stimulation required to bring to wakeful state)
5) Coma (Un-arousable, but motor responses may persist) |
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Term
| What important components are included in the "Respirations" evaluation of a comatose patient? |
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Definition
1) Cheyne-Stokes
-Bilateral dysfunction of brain at level of hemispheres or diencephalon)
- can be structural or toxic-induced.
2) Central Neurogenic Hyperventilation
- Usually midbrain, sometimes Pons.
3) Apneustic respirations (inspiratory cramps)
- Pontine (rare, but localizing)
4) Ataxic respirations
- Lower pontine or medullary dysfunction |
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Term
You examine a patients respirations and discover Crescendo-decrescendo periodic respirations with apneic pauses.
Where is the most likely brain lesion? |
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Definition
Cheyne-Stokes respirations
- Bilateral hemispheric or diencephalic |
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Term
You examine a patients respirations and discover sustained steady hyperventilation with respiratory alkylosis
Where is the most likely brain lesion? |
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Definition
Central Neurogenic Hyperventilation
- Usually midbrain (sometimes Pons) |
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Term
You examine a patients respirations and discover Inspiratory cramps.
Where is the most likely brain lesion? |
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Definition
Apneustic respirations
- Rare- Pons |
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Term
You examine a patients respirations and discover that they are uncoordinated in rate and rhythm of breathing
Where is the most likely brain lesion? |
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Definition
Ataxic respirations (impending failure).
- Lower pontine or medullary dysfunction |
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Term
A patient presents with mid-position pupils that are poorly reactive. He also exhibits sustained, steady hyperventilation.
What is going on? |
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Definition
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Term
A patient presents with "pin-point" reactive pupils. He also exhibits inspiratory cramps suggesting apneustic respirations.
What is going on? |
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Definition
Pontine lesion (apneustic respirations are rare)
**Opiates also cause point-point pupils, but not inspiratory cramps** |
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Term
True or False:
Metabolic diseases are characterized by intact eye movements and pupillary responsiveness. |
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Definition
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Term
A patient presents with Cheyne-Stokes respirations and a right hemiparesis. Eye movements are normal, but the patient is stuporous.
What is going on? |
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Definition
Left hemisphere hemorrhage
- Eye movements are normal because lesion has not expanded to brainstem |
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Term
| What are management strategies to handle a comatose patient? |
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Definition
1) Circulation, airway and respirations
2) Check glucose
3) Start IV and run tox screen
4) IV thiamine if possible (avoid B1 deficiency)
5) Neuro exam and imaging
6) Nalaxone for narcotics
7) LP if meningitis, encephalitis or SAH is expected.
8) EEG for seizure
9) Support temp and catheterize bladder. |
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