L56 Consciousness Flashcards
define consciousness
the ability to be aware of oneself and ones place in the environment
the ability to respond appropriately to environmental stimuli
*easy to define, but no one knows how it works
what does consciousness depend on?
synchronization of cortical neurons that fire around 40Hz
what does consciousness result from?
important functions of brain activity
- memory
- learning
- distinguishing self from non-self
- re-entry
define re-entry
the recursive comparison of info by different brain regions
where is the re-entry mechanism located?
in circuits of the thalamocortical system
define coma
nonsleep, loss of consciousness that (unlike syncope) lasts for an extended period of time
what are the levels of unconsciousness?
- lethargic
- obtunded
- stuperous
- comatose
define lethargic
pt can be fully aroused
define obtunded
pt cannot be fully aroused
define stuporous
sleep like status
define comatose
no purposeful response to stimuli
what does the brainstem play an important role in?
condition of consciousness
attentive vigilance
wake-sleep rhythm
lesions to what can impair consciousness?
thalamus
midbrain
or both cerebral hemispheres
describe the brainstem and its link to consciousness
- Cells of the midbrain (reticular formation) receive ascending info from the spinothalamic track and other
- They are projected via 2 branches to higher cortical centers
- To the thalamus→ activating and modulating
thalamic relay nuclei and intralaminar nuclei
- To the lateral hypothalamic area→ which is joined by ascending output from hypothalamic and basal forebrain cells
define the transmission mode
- resting potential is near firing threshold
- cholinergic input from pons and basal forebrain is present
- EEG shows DEsynchronized pattern - LOW voltage, HIGH frequency
wakefulness and awareness
define Burst mode
- neurons hyper polarized by inhibitory GABA from reticular formation input
- EEG shows Synchronized wave patterns - HIGH voltage, LOW frequency
deep sleep and coma
what is coma?
A deep state of unconsciousness; unable to move or respond to environmental stimuli
Raw definition→ not opening eyes, not obeying commands and not uttering understandable words
what are the common causes of coma?
Commonly caused by head injury or complications to another disease (ie: brain tumor or ↑ICP)
what brain structure is involved in Vegetative state?
cortex/higher centers
Describe Vegetative state
-A complete loss of higher brain function (cortex) however maintain breathing and circulatory functions
-Spontaneous movements can occur such as eye opening to painful external stimuli but are unable to
respond to commands, to speak or respond meaningfully to environmental stimuli
-Pt may cry, grimace or laugh but this is not the result of them interpreting and responding meaningfully.
what brain structure is involved in brain death?
all brain including the brainstem
describe brain death
Denotes the irreversible loss of all brain functions
determined by
-No electrical brain activity (isoelectric EEG)
-Absence of brain→ no movement, response to stimuli, breathing or brainstem reflexes
what are common causes of brain death?
- Anoxia (suffocation; can be drug, respiratory disease, etc)
- Ischemia (vascular occlusion)
- Intracranial Hemorrhage
- Trauma
- Brain Tumors
- ↑ICP and uncal herniation
what brain structure is involved in Locked-in-syndrome
pons
describe Locked-in-syndrome
- Blockage of basilar artery causing massive infarction to pons
- Causes total paralysis of voluntary muscle except for vertical eye movement muscles and opening lid
- Pts are fully aware but cant move and communicate via vertical eye movements and opening the eyelid
what causes loss of consciousness?
- damage to the reticular formation in the midbrain
- damage to either branch of the ascending arousal system
- impairment of thalamus
- bilateral impairment of the cerebral hemispheres
what is the Glasgow coma scale
scored between a 3 and 15
what 3 parameters are evaluated in the GCS
best eye response
best verbal response
best motor response
what is the criteria to grade best eye response?
(4) 1 - no eye opening 2 - eye opening to pain 3 - eyes opening to verbal command 4 - eyes open spontaneously
what is the criteria to grade best verbal response?
(5) 1 - no verbal response 2- incomprehensible sounds 3 - inappropriate words 4 - confused 5 - orientated
patients who score less than or equal to 8 on GCS are what?
90% in coma
patients who score greater than or equal to 9 on GCS are what?
not in coma
what is the critical score of GCS?
8
what score describes moderate severity of the GCS
9-11
what score describes minor injury of the GCS?
12-15
where is the lesion associated with Cheyne-Stokes respirations?
forebrain lesions
where is the lesion associated with apneusis (inspriatory cramps) respirations?
lesion in pons
where is the lesion associated with hyperventilation respirations?
lesion in midbrain
where is the lesion associated with ataxic breathing respirations?
lesion in lower pons/upper medulla
what damage is associated with decorticate posturing?
damage to upper midbrain (bilteral)
what damage is associated with decerebrate posturing?
damage to upper pons or lower midbrain (bilateral)
with respect to the pupillary light response, what does small reactive pupils indicate?
- diffuse forebrain impairment (metabolic encephalopathy)
- pontine injury
- sedative drugs (opiates)
with respect to the pupillary light response, what does mid positional pupils and loss of response indicate?
-structural injury (almost always) damage of CN III at level of midbrain
with respect to the pupillary light response, what does unilateral pupillary dilation indicate?
- injury of CN III at the exit of brainstem
- unilateral compression (aneurysm of post. communicating a., tumor, increased ICP –> uncial herniation)
with respect to the pupillary light response, what does large, unreactive pupils indicate?
pressure in pretectal area (pineal tumor)
with respect to oculomotor responses, describe metabolic encephalopathy?
- dolls head maneuver - eyes roll counter head movement
- cool water in ear - eyes turn to same side = brainstem intact
with respect to oculomotor responses, describe a right pontine lesion?
Dolls Test
- Head to right→ normal (eyes to left)
- Head to left→ no movement at all
COWS
- Cold in right→ no movement
- Cold in left→ normal (eyes to left)
gaze paralysis to the right, because right PPRF and /or right CN VI is lesioned
with respect to oculomotor responses, describe a midbrain lesion?
Dolls Test
- Head to left→ right eye normal but left is unresponsive
- Head to right→ left eye normal but right is unresponsive
COWS
- Cold in right→ right eye normal but left is unresponsive
- Cold in left→ left eye normal but right eye is unresponsive
*This lesion involves both occulomotor nuclei causing loss in Medial Rectus, thus loss of aDduction
