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maintain VS and intrinsic control of life processes
What does the reticular formation do and where is it located?
- -relay station for descending motor control
- -excludes that going down the pyramidal tract
What other term is used synonymously with brainstem
What does the vestibular formation do and where is it located?
- -coordinates eye and limb movement in response to body position
What is the cerebellum's function
-controls posture and coordinates muscle contraction on the ipsilateral side (same side)
Where is the diencephalon located?
What other structures are located within it?
sensory integrative center
Where is the basal ganglia located and what is its function?
- -planning and generating motor commands
- -motor signals generated here travel down the reticular formation and eventually to the muscle
- Not all fibers are blocked simultaneously with spinal anesthesia
- -first to be blocked are sympathetic fibers (small type C)
- -next are sensory
- -last are motor (large fibers)
With a spinal, which will be higher, sympathetic block or motor block?
Sympathetic block (up to 4 dermatomes higher)
- T4- nipples
- T10- umbilicus
Can a pt have a sympathetic and sensory block and still have muscle movement?
Yes the large motor fibers are difficult to block
Ascending pathway of the SC- sensory or motor?
Descending pathway of the SC- sensory or motor?
Where does sensory information enter the SC?
- Dorsal nerve roots
- -travels from peripheral nerve to dorsal (posterior) horn where it synapses with the SC
After sensory information enters the SC where does it go?
Travels via ascending pathways thru the SC to the brain
What 2 routes can the sensory information travel to the brain?
- 1) dorsal (posterior)
- 2 dorsal columns
- a) fasciculus gracilis
- b) fasciculus cuneatus
2) spinothalamic (anterior pathway)
- -descends to muscle which is then activated
- -brain to SC
Where do the descending motor pathways synapse?
In the anterior horn of the SC
What pathway (tract) do the motor impulses travel via?
3 main sensory pathways
- -spinothalamic (AKA anterolateral)
- -posterior dorsal columns (there are 2 columns but we think of them as 1)
Which 2 sensory tracts cross the SC?
- and dorsal columns
What type of sensory sensations does the spinothalamic (anterolateral) tract carry?
- -pain and temperature
- -travel via small fibers
path that pain impulses take (in the spinothalamic tract) to travel from periphery to the brain
What type of sensory sensations do the dorsal columns carry?
proprioception, "where is my limb?"
What type of sensory sensations does the spinocerebellar tract carry?
unconscious proprioception (ie walking without thinking, no conscious thought is required)
How does the spinocerebellar tract differ from the other 2 sensory SC tracts (spinothalamic and dorsal columns)?
- -does NOT cross the SC
- -so a cerebellar lesion causes weakness on THAT side
- -only travels as far as the midbrain (cerebellum)
Does a lesion of the spinothalamic and dorsal columns cause an issue of the ipsilateral or contralateral side?
contralateral side (remember it crosses the SC)
Where do the dorsal columns and spinothalamic tracts travel to (what part of the brain)?
Thalamus (sensory integrative center) and cerebral cortex
Where within the brain does the anterolateral (spinothalamic) tract synapse?
- -synapses in the thalamus (posterior ventrolateral nucleus)
- -then travels up into the brain
Where within the brain do the dorsal horns synapse?
-thalamus (ventral posterior nucleus)
What part of the brain regulates motor impulses ?
- Basal ganglia
- Brain stem
What path do motor impulses take (brain to periphery)
- -start in brain
- -travel thru brain stem
- -crosses SC
- -synapses in anterior horn
- -travel thru corticospinal tract (pyramidal)
Does the reticular formation relay pyramidal or extra-pyramidal impulses?
Pyramidal motor tract
- major motor pathway
- controls precise movement and laryngeal muscles
Extra-pyramidal motor tract
- maintains postural tone
- directs voluntary movement
Parts of the extra-pyradimal tract
- lateral vestibulospinal
How are the upper and lower motor neurons differentiated?
- UMN are above where the corticospinal tract synapses with the anterior horn
- LMN are below
What type of paralysis results with injury to the UMN?
spastic paralysis and hyperreflexia
- Occurs high (like in the brain)
- Ex: CP
- lesion interrupts signals between the brain and SC
What type of paralysis results with injury to the LMN?
flaccid paralysis and areflexia
- any interruption below L1 (below SC)
- doesn't have to do with the brain, is between SC and affected muscle
- stereotyped action in response to a peripheral stimuli
- SC contains neural circuits which produce reflexes
- Ex: knee-jerk, brain is not involved, only the SC is
SNS reflexes (pupils and heart)
- pupil dilation
- + inotropic and chronotropic effects on the heart
Where do the SNS fibers originate from?
Thoracic and lumbar
Where do the PNS fibers originate from?
Brainstem and sacral SC
Pathologic autonomic reflex
AKA mass reflex
AKA denervation hyperreflexia
AKA autonomic hyperreflexia
- occurs in presence of SC transection
- occurs when there is a stimulus to the skin or a visceral organ (below the level of SC injury)
- get simultaneous excitation of ALL segmental reflexes (SNS, PNS, massive excitation of the entire ANS)
At what level SC injury is autonomic hyperreflexia likely to occur at?
At what level is it unlikely?
- Likely - transection above T5
- Unlikely- lesion below T10
What type of anesthesia is appropriate for a pt with a T5 SC transection having a cystoscopy?
- GA or spinal even though the procedure is often done under LA
- a stimulus below the level of the transection will stimulate ANS
- need to not let the pt feel it
What needs to be considered for a pt with a SC injury?
The level of their injury (how stimulating the procedure is is less important)
What symptoms are seen with mass reflex
- bradycardia (due to carotid baroreceptor reflex)
How is mass reflex treated?
Treat HTN with direct acting VD (ex: nipride)
delivering a stimulus and looking at the result of that stimulus
Which type of EP is most sensitive to anesthetic drugs? Least sensitive?
- Most- visual EP
- Least- brain stem auditory EP
- (sensitivity implies that our drugs will change the EP)
What is SSEP
- somatosensory EP
- stimulate sensory system and see how it travels to the brain
- midrange sensitivity to anesthesia drugs
Can anesthesia drugs affect an EEG tracing?
Yes they will cause burst suppression and slowing
EEG rhythms: alpha
pt relaxed with eyes closed
EEG rhythms: beta
EEG rhythms: delta
EEG rhythms: burst suppression
- occurs during deep anesthesia
- spikes then flat inbetween
- also due to extreme hypothermia or hypoxia
For what procedure might we use EEG monitoring?
- monitors CBF and oxygenation
- EEG changes can indicate injury or that anesthetic level has changed
If EEG changes are noticed during a CEA what should be done?
- Communicate with EEG tech
- Raise BP to increase flow to brain
- 100% O2
If we're using SSEP and we stimulate the pt's left foot, are we monitoring the L or R side of the brain?
When looking at SSEP waveforms what are we looking at?
- Latency (wave frequency) and how long it takes for stimulus to get to the brain
- Amplitude (wave height) force
SSEP can tell us the functioning of what?
- Peripheral nerve
- Posterior column of the SC
Anesthetic management of a pt getting SSEP
- avoid giving a large amount of any 1 drug
- use infusions (steady state)
- avoid bolusing
- avoid versed
T or F, SSEP gives us information about the anterior part of the SC?
F, information about the posterior (sensory) portion only
What effect do our anesthesia drugs have on SSEP?
- All affect the SSEP waveform in a DOSE DEPENDENT manner!!
- volatiles, benzos, propofol, N20, opioids
NMB considerations when using MEP
use an infusion and maintain 2 / 4 twitches
a nerve stimulator is used and look to see if there is movement (of the foot for example)
wake up test
- if unsure of accuracy of MEP or SSEP tracings
- tell pt about possibility pre-op
- ask pt to wriggle toes
- maintain 2-3/ 4 twitches to avoid full movement of pt!
- ensure enough narcotic on board
NMB use and EMG
Rank order of response to stimuli
- memory (implicit then explicit)
- movement (purposeful then involuntary)
- sudomotor (tearing then sweating)
- HD (BP then HR)
EEG monitor configured to give us a number that corresponds with depth of anesthesia
T or F, pts are more likely to recall something unpleasant or threatening?
Awareness incidence- total
Awareness incidence- with NMB
Awareness incidence- without NMB
- so avoid NMB if surgeon does not require it
- large amplitude, low frequency wave
BIS- moderate sedation
- > 80
- small amplitude, fast frequency wave
T or F, BIS monitors analgesic level?
F, only measures level of hypnosis!!
With what pts is a BIS monitor recommended?
- Pt's with h/o awareness
- Is NOT the standard of care