Lec 48 Disorders of Consciousness

Question 1

What is arousal vs awareness?

Answer 1

arousal = level of consciousness – are the lights on

awareness = content of consciousness – is anyone home

Question 2

What structures mediate arousal?

Answer 2

ascending reticular activating system (ARAS) [in ponto-mesencephalic junction]
thalamus
thalamo-cortical relays

Question 3

What happens to level of arousal and EEG if you transect the medulla? midbrain?

Answer 3

medulla = normal
midbrain = loss of arousal, desynchronized EEG

Question 4

Where are the source nuclei of the ARAS located? their NT?

Answer 4

nuclei in ponto-mesencephalic junction

NT = ACh

Question 5

What structures mediate awareness?

Answer 5

cerebral cortex

Question 6

What are the 6 states of conciousness?

Answer 6

Awake = full wakefulness

Drowsy = able to stimulate full arousal by non-noxious stimuli [saying their name]

lethargic = responds to non-noxious stimuli but unable to be brought to full arousal [say name]

obtunded = respond to non-noxious stimuli but more depressed level of consciousness

stuporous = noxious stimuli needed to raise level of arousal

coma = unresponsive to all stimuli

Question 7

What is the glasgow coma scale?

Answer 7

to asses arousal
assess eye opening, verbal responsivity, and motor responsitivity

score from 3 to 15 with 15 = fully awake 3 = coma or death

Question 8

What 3 principal features used to localize source of arousal dysfunction?

Answer 8

• respiratory pattern
• eye function
• motor responsitivity

“when you don’t know the where and whys, listen to breathing and look at the eyes”

Question 9

Match the type of respiratory pattern with the location of dysfunction

1. diffuse forebrain dysfunction
2. midbrain injury
3. rostral pons
4. caudal pons
5. medulla

A. ataxia
B. apneusis
C. hyperventilation
D. respiratory arrest
E. Cheyne-Stokes respiration

Answer 9

1. diffuse forebrain dysfunction
   - – E. Cheyne Stokes respiration [crescendo then decrescendo pattern]
2. midbrain injury
   - – C. hyperventilation
3. rostral pons
   - – B. apneusis [extended periods of apnea]
4. caudal pons
   - – A. ataxia [disorganized arrhythmic pattern]
5. medulla
   - - D. respiratory arrest

Question 10

What happens to the eyes in a thalamic lesion?

Answer 10

small, reactive, symmetric pupils

Question 11

What happens to the eyes in a pretectal lesion?

Answer 11

fixed, dilated pupils

Question 12

What happens to the eyes in a pontine lesion?

Answer 12

pinpoint pupils

Question 13

What happens to the eyes in a midbrain lesion?

Answer 13

fixed, mid size pupils

Question 14

What happens to the eyes in a herniation lesion?

Answer 14

• 1 fixed, dilated pupil

suggests mass effect = emergency

Question 15

What are afferent and efferent of corneal reflex?

Answer 15

afferent = V1 branch of CN V [CN V main nucleus in pons]

efferent = CN VII to orbicularis oculi [CN 7 nucleus in pon]

Question 16

What should you think if you see one fixed dilated pupil?

Answer 16

herniation! it might be an emergency

Question 17

What happens if you inject cold water into right ear canal?

Answer 17

eyes both turn to right with nystagmus to left

Question 18

What happens if you inject warm water into right ear canal?

Answer 18

eyes both move to left side with nystagmus to the right

Question 19

What happens if you have a lateral pontine lesion? to VOR function? when cold water injected in ipsilateral or contralateral side?

Answer 19

PPRF on side of lesion can’t function –> VOR not intact when head turned to contralateral side
ie. left lateral pons lesion. eyes do not move when head turned right

cold water in ipsilateral: no horizontal eye move
cold water in contralateral: normal eye move

Question 20

If you have a cortex lesion will you have VOR?

Answer 20

yes! –> you will have VOR but you won’t be able to control it

[in normal you have dolls eyes but can override it if you want to look in the direction of head turn. if no cortex can’t override so always have dolls eyes]

Question 21

If you have no cortex or brainstem will you have dolls eyes reflex?

Answer 21

nope!

Question 22

What happens if you have a bilateral midbrain lesion? to VOR function? when cold water injected in ipsilateral or contralateral side?

Answer 22

bilateral CN 3 nuclei can’t function so can’t use medial rectus to adduct

Question 23

If you have a right lateral pontine lesion what happens if:

• turn head to right
• turn head to left
• cold water into right ear
• cold water into left ear

Answer 23

• turn head to right –> both eyes shift left
• turn head to left –> eyes don’t move
• cold water into right ear –> eyes don’t move
• cold water into left ear –> eyes drift left

Question 24

If you have a bilateral midbrain lesion what happens if:

• turn head to right
• turn head to left
• tilt head back or forward
• cold water into right ear
• cold water into left ear

Answer 24

• turn head to right –> left eye goes, right eye doesn’t move
• turn head to left –> right eye goes, left eye doesn’t move
• tilt head back or forward: eyes do not move
• cold water into right ear –> right eye to right, left eye doesn’t move
• cold water into left ear –> left eye to left, right eye doesn’t move

symptoms are bc CN 3 nucleus disrupted and vertical movements regulated also in midbrain

Question 25

What happens to motor responsitivity in large cortical lesion?

Answer 25

lack of contralateral purposeful movement

Question 26

What happens to motor responsitivity in upper midbrain lesion?

Answer 26

decorticate/flexion posturing = abnormal stiff posturing with bent arms, clenched fists, legs out straight, arms bent in toward body and wrists and fingers bent and held on chest, can be unilateral or bilateral

Question 27

What happens to motor responsitivity in upper pontine damage?

Answer 27

decerebrate/extensor posturing = abnormal body posture w/ arms and legs straight out, toes pointed down, head and neck arched back, muscles held rigidly, can be unilateral or biltaeral

Question 28

What causes locked-in syndrome? clinical features?

Answer 28

cause: structural/functional brainstem transection just below mid-pons. ARAS above mid-pons = intact so preserved consciousness but disruption efferent paths
clinical: conscious, mute, quadriplegic, no conjugate lateral eye movements, preserved midbrain mediate movements (voluntary opening, vertical movement, convergence)

Question 29

Is there arousal in vegetative state? awareness?

Answer 29

arousal = variable, can be full
awareness = none

Question 30

How does minimally conscious state differ from vegetative?

Answer 30

both can have variable or full arousal

vegetative = no awareness; minimally conscious has partial/variable awareness

Question 31

What are characteristics of coma?

Answer 31

• complete awareness failure
• complete arousal failure
• eyes closed

Question 32

What are characteristics of vegetative state?

Answer 32

preserved capacity for arousal (spontaneous or stimulation induced)
sleep wake cycle
no awareness

Question 33

What are characteristics of minimally conscious state?

Answer 33

• preserved arousal and partial awareness

- see eye movements (tracking, stimulus fixation), ability to follow simple commands, and purposeful behavior

Question 34

What does brain death mean? signs?

Answer 34

no evidence of brain stem function
– absent midbrain reflexes = no pupillary reactivity

• absent pontine reflexes = no VOR or corneal reflex
• absent medullary reflexes = apnea