Note outline

Skull
● Bony vault with brain, CSF, & blood
● Cerebrospinal fluid: 10%
● Intravascular blood: 12%
● Brain tissue: 78%
● Posterior pituitary secretes ADH (vasopressin)
○ Responsible for holding water in the body
○ Not enough ADH → Diabetes Insipidus
● Brainstem
○ Midbrain
■ Cranial nerves 3-4 → control movement of eye muscles
■ Relay center for impulses from body going to and from brain
○ Pons
■ Cranial nerves 5-8
■ Cranial nerve 5 → trigeminal
■ Cranial nerve 7 → facial
■ Cranial nerve 8 → auditory
■ Reticular activating system- controls sleep wake cycles
● Important part of circadian rhythm
● Responsible for wakefulness, ability to focus, fight or flight
response, & how the world is perceived
● Patients with head injury are asked if they had any loss of
consciousness to see if the reticular activating system was affected
○ Medulla oblongata
■ Cranial nerves 9-12
■ Control mouth, throat, tongue, swallowing, & neck
■ Contains both motor & sensory pathways that help unite the brainstem,
cerebellum, & cerebrum to coordinate information coming back to the
brain/going to the body
■ Controls heart rate & respiratory rate


Factors Affecting Cerebral Blood Vessel Tone
● CO2

, ○ Hypercapnia (increased CO2) → dilates cerebral vessel → increased cerebral blood
flow
○ Hypocapnia (decreased CO2) → constricts cerebral vessel → decreased cerebral
blood flow
● O2
○ Low O2 → dilates cerebral vessel → increases cerebral blood flow
● H+ Ion
○ Byproduct of low O2 is lactic acid → increased H+ ions → dilates cerebral vessel →
increased cerebral blood flow
○ Can be an issue if the patient has increased ICP
● Temperature
○ High temperature/fever → dilates cerebral vessel → increased cerebral blood flow
○ High temperature also increases metabolic demand, which consumes more O2
○ Shivering uses a lot of O2 stored in the body & produces CO2 as a byproduct →
dilates cerebral vessel → increased cerebral blood flow
● Increased cerebral blood flow increases ICP


Intracranial Pressure (ICP)
● Monroe-Kellie doctrine
○ CSF, blood, & brain must remain at a relatively constant volume within the skull
○ If the volume of any increases, the volume of one or both of the others will
decrease
○ The volume is constant
○ Only applies when the skull is closed
● Normal ICP 5 to 15 mm Hg
○ Elevated if >20 mm Hg sustained
● Cerebral blood flow (CBF)
○ Amount of blood passing through brain tissue in one minute
● Cerebral perfusion pressure (CPP)
○ Pressure needed to ensure blood flow to the brain
○ CPP= MAP - ICP
○ Normal is 60 to 100 mg Hg
○ <50 mg Hg- ischemia & neuronal death
○ When ICP is elevated, it is important to maintain adequate MAP

, Clinical Manifestations
● Change in level of consciousness
○ Impaired cerebral blood flow & decreased oxygenation
● Change in vital signs due to damage to brainstem
○ Cushing’s triad
■ Bradycardia
■ Cheyne-stokes respirations
■ Increased BP
● Change in body temperature
○ Controlled by hypothalamus, which is compromised by increased ICP
● Compression of oculomotor nerve
○ Controls muscles in the eye
○ Eyes may be sluggish, not respond to light, or have ptosis
● Decrease in motor function
○ Hemiparesis
● A
○ Decorticate
○ Internal rotation, adduction of arms, & flexion of elbows
○ May see extension of the legs
○ Due to the interruption of voluntary motor tracks in cerebral cortex
● B
○ Decerebrate
○ Results from injury of motor fibers in midbrain & brainstem
● C
○ Decorticate on right & Decerebrate on the left
○ Part of cerebral cortex & part of brainstem affected
● D
○ Opisthotonic
○ Similar to Decerebrate, except neck & back are arched posteriorly
● HA
● Vomiting
○ Due to increased pressure in the skull