Week 8 - Intracranial Regulation & ICP Flashcards
define cranium
- the collective bone structure that encloses the brain
- AKA the skull
what does intracranial mean?
- refers to all components inside the skull
- the brain, circulatory system, and dura mater
define intracranial regulation
- mechanisms of conditions that impact intracranial processing & function
- focuses on conditions that specifically affect the contents of the cranium
describe the scope of ICR
ranges from
- normal & optimal function to
- impairment
what does brain function depend on
- a constant supply of blood delivering O2 and nutrients
what specific nutrient provides fuel for the brain?
- carbs = bg important
what 2 organs does the brain rely on for perfusion
- lungs
- heart
what is the function of the skull
- composed of multiple bones that acts as a rigid, noncompliant protective covering for the brain
what 3 components are found within the skull? what are their %?
- brain tissue (80%)
- blood (10%)
- CSF (10%)
what is intracranial pressure
- the sum of the pressure exerted by the 3 components in the skull (tissue, blood, and CSF)
what is the monra-kelli doctrine
- the total volume inside the skull cannot change, since the skull is noncompliant (it does not stretch)
- therefore, a change in one compartment must be compensated by a decrease in another component
ex. if blood increased, then CSF will have to decrease to make room, etc.
what are the meninges
- a tough protective membrane made of 3 layers that surrounds the brain and spinal cord
what are the 3 layers of the meninges
- duramater (outer layer)
- arachnoid mater
- pia mater
what is the space between the arachnoid layer & pia mater called? what does it contain?
- subarachnoid layer
- contains CSF
what is the dura mater attached to?
- the skull
what is the CSF? what is its function? (2)
- cerebrospinal fluid
- cushions & supports the brain & other structures (such as the spinal cord) of the CNS & provides nutrients
describe how the Monro-Kelli compensation changes over time; what does this result in?
- at first, small increases in the volume can be compensated and ICP remains the same (or close to)
- but as the intracranial volume continues to increase, the compensatory mechanisms fail
- results in increased ICP
what is normal ICP? what is considered intracranial HTN?
- normal <15 mmHg
- >20 HTN
what can cause increased ICP? (6)
- brain hemorrhage
- trauma
- edema
- infection
- tumours
- excessive amt of CSF
what can increased ICP cause? (3)
- obstruct cerebral blood flow (can compress blood vessels)
- destroy brain cells
- displace brain tissue (herniation)
describe how the brain can compensate for increased ICP
- can move CSF to another location
- vasconstriction of cerebral arteries to decrease blood flow into the brain
what is the fnxn of the brainstem? what is the 3 parts?
controls life-sustaining processes
- midbrain
- pons
- medulla
what is the function of the medulla (3)
plays important role in vital functions:
- CVS
- resp
- reflexive actions
what reflexive actions is the medulla responsible for (4)
- swallowing
- coughing
- sneezing
- vomiting
what causes the early signs of increased ICP
- pressure on the brainstem & meninges
- hypoxia to sensitive cortical neurons
list the 4 early signs of increased ICP
- decreased LOC
- severe headache
- vomitting
- papilledema
what causes decreased LOC during increased ICP
- pressure on the reticular activating system
- hypoxia of cortical neurons which
what is the RAS? where is it found? what does it do?
- network of neurons found in the brainstem
- responsible for arousal, awareness, and sleep-wake cycle
what does pressure on the RAS cause
- decreased responsiveness & arousal
what does hypoxia of the cortical neurons cause
- altered cognition
how does increased ICP cause a headache (2)
- due to stretch on the dura mater –> pain receptors
- stretch on blood vessels
how does increased ICP cause vomitting?
- due to pressure on the emetic center (in the medulla)
what does vomitting do to increased ICP look like? (3)
- may be projectile
- rapid
- w/o nausea
what is papilledema
- swelling of the optic nerve
how does increased ICP cause papilledema
- compresses the optic nerve, and the retinal veins & arteries
what is Cushing’s reflex/triad? what does it include?
- set of signs indicative of increased ICP
1. increased systolic BP (and widened pulse pressure)
2. decreased HR
3. decreased RR
describe how increased ICP causes increased systemic BP
- as ICP rises, we get ischemia to the brain
- this ischemia and lack of O2 is detected by the CVS control center in the medulla
- this triggers efferent signals from the vasomotor area causing systemic vasoconstriction
= increased bp to try and perfuse the brain
describe how increased ICP causes decreased HR
- the rise in BP initiates a baroreceptor reflex which lowers the HR ( only effect the HR, not blood vessel constriction)
describe how increased ICP causes decreased RR (3)
unknown but 3 proposed mechanisms:
- P on the resp centre in the medulla causes impaired function & a decline in RR or cheyne-stokes respiration
- increased sensitivity to PCO2
- accelerated systemic circulation
what are cheynes-stokes respiration
- periods of apnea
- followed by a period of rapid breathing with an increasing then decreased tidal volume
how can increased ICP cause herniation
- by causing displacement on the brain within the cranium
what are 4 types of brain herniations
- cingulate
- central
- uncal
- cerebellar
what does the dura mater form? give 2 examples
- the meningeal folds
1. falx cerebri
2. tentorium
what is the falx cerebri
- fold that goes down into the longitudinal fissure
- separates the two hemispheres of the brain
what is the tentorium
- fold that separates the cerebrum from the cerebellum
what is the foramen magnum
-opening at the base of the skull thru which the spinal cord exits
what is an uncal herniation
- when the temporal lobe is pushed under the tentorium cerebelli
what does an uncal herniation result in?
- compresses the oculomotor nerve (in the brainstem) and posterior artery
= ipsilateral pupil dilation & ischemia
what does ipsilateral mean
- occuring on the same side
what is the posterior cerebral artery
- one of a pair of arteries that supplies blood to the occipital lobe
what is a central herniation
- parts of both temporal lobes herniate thru the tenotiral notch
what does a central herniation cause
- downward pressure on the brainstem & brainstem dysfunction
what is a cingulate herniation
- when the innermost part of the frontal lobe (cigulate gyrus) gets squeezed under the falx cerebri to the opposite hemisphere
what does a cingulate herniation often result in
- coma / unconscious
what is the cingulate gyrus responsible for
- processing emotions & behavior regulation
what is a cerebellar herniation
- part of the cerebellum pushes thru the foramen magnum
what does a cerebellar herniation often result in
- impairment of brainstem function
as pressure increases on the brain stem due to herniation, what occurs
- motor strength & coordination becomes impaired
what symptoms occur later due to increased P on the brainstem r/t herniation (5)
- posturing
- flaccidity
- fixed & dilated pupils
- unconciousness
- resp arrest
