Basic Neurosciences - exam-focused guide
Basic Neurosciences underpins every clinical decision in neurosurgery. The Iraqi Board expects applied anatomy, physiology, pathology and pharmacology rather than isolated facts.
Core rules
- Resting membrane potential near −70 mV is set mainly by K+ permeability and the Na+/K+-ATPase; the action potential depends on voltage-gated Na+ influx and K+ efflux.
- Excitatory transmission is largely glutamate acting on AMPA/NMDA receptors; GABA-A receptor chloride currents mediate fast inhibition. Status epilepticus involves failure of GABAergic inhibition and NMDA-mediated excitotoxicity.
- Cerebral blood flow is about 50 mL/100 g/min; autoregulation holds flow stable between MAP 50–150 mmHg but is impaired after trauma and ischemia. CPP = MAP − ICP.
- The Monro–Kellie doctrine: brain, blood and CSF share a rigid container; once compensation is exhausted, small volume increases raise ICP steeply.
- Cytotoxic edema follows ATP failure and intracellular swelling; vasogenic edema follows blood–brain barrier disruption and leaks into white matter.
Worked example: A head-injured patient has MAP 70 mmHg and ICP 25 mmHg. CPP = 70 − 25 = 45 mmHg. Because autoregulation is impaired, raising MAP to 85–90 mmHg with fluids/pressors can improve CPP, provided the cause of raised ICP-hematoma, hydrocephalus, edema-is treated. Mannitol 0.25–1 g/kg or hypertonic saline lowers ICP by osmotic and rheologic effects; it is not a substitute for decompression.
Traps: do not calculate CPP as MAP + ICP; do not assume autoregulation is intact in injured brain; do not use steroids for cytotoxic edema outside tumour; remember that mannitol causes initial volume expansion and can worsen hypovolemia.