Usmle 1 Neurophysiology: Role of the Brain

• The brain is sensitive to changes in pCO2

• The periphery is sensitive to HYPOXIA (pO2 ↓)

• Control immediate changes in BP

• Baroreceptor that regulates BP

• CO = SV x HR
• BP = CO x TPR

• • SENSES stroke volume (SV)
•   • via response to stretch

• • CN IX & X are always firing
•   • Anything that drops SV (standing for a long time)
•   • Will decrease firing by CN IX and X
•   • Will increase HR (reflex tachycardia) and increase BP
•   • Reflex Tachycardia occurs because sympathetic innervation is no longer opposed and DOMINATES → 
•   • ↑ BP
•   • β1 Blocker will ↓ HR by inhibiting Reflex Tachy.

• Anything that will increase stroke volume

• Will increase firing by CN IX and X

• • Decreased BP, decreased HR 
•   • Reflex Bradycardia
•   • When stand up
•      • BP drops 5-10mm Hg
•      • Pulse ­ 5-10 bpm

• • When standing up the
•   • HR ↑ by  5-10 bpm
•   • BP ↑ by 5 – 10 mmHg

• • If standing, Pulse didn’t ­↑ by AT LEAST 4 bpm
•   • Autonomic Dysfunction
•   • Most common cause
•     • DM
•   • Riley-Day syndrome
•   • Shy-Drager
•   • Sick Sinus Syndrome

• • Newborn
•    • Familial dysautonomia
•    • No autonomic reflex

• Parkinsonian patients that develop autonomic neuropathy

• • Elderly
•    • Calcification of the carotid sinus due to aging
•    • Old lady will pass out when standing up

• • If the BP decreased by > 10 mmHg there is more going on than a reflex problem
•   • Orthostatic Hypotension
•     • patient stands up
•       • HR ↑ by > 20 
•       • BP ↓ below 10 mmHg

• • Carotid massage works by
•   • increasing stroke volume to
•     • increase firing
•      • by CN IX
•      • CN X
•   • cause reflex bradycardia.

• • Vaso-Vagal Syncope
•   • pass out because one induces ↑ reflex bradycardia
•   • Hickee

• • Malignant Htn caused
•   • cutting CN IX
•   • CN IX runs behind the tonsils, so if
•   • accidentally cut 
•    • malignant hypertension.
•    • cause reflex tachycardia.

• • If reflex tachycardia is not enough
•   • NE will come out as 2nd messenger
•   • High affinity for a receptor
•   • Then affinity for b receptor
•     • Increasing HR by a lot
•     • NE & HR ↑ together
•   • TPR goes up every time Stroke volume is low.
•     • Normal BP and High HR
•      • going into early shock
•      • still compensating
•        • Need to hydrate them
•           • Will reverse by firing of CN IX, X
•        • Check HR monitor for adequate hydration

• • Stimulate JG apparatus
•   • by low flow to the kidneys
•   • Renin comes out
•   • Cuts Angiotensinogen
•     • to Angiotensin I
•     • formed in liver
•   • Angiotensin I is converted by ACE 
•     • to Angiotensin II
•     • in lungs
•   
• • Angiotensin II
•   • Very potent vasoconstrictor
•     • ↑TPR
•     • ↑BP
• • Ag II 
•   • also stimulates Aldosterone
•   • To decrease loss of volume
•   • Aldosterone goes to kidney and reabsorbs Na from DCT
•   • Excretes K in the process.
•     • Serum Na will be diluted and decreased. Because Na brings in 3x the Water!!!
•     • Serum Cl will also decrease due to dilution
•     • Serum K will decrease because of secretion
•     • Also excretes H+
•       • Serum pH will go up

• Cerebrospinal fluid

• A filtrate of plasma

• To add cushion for the brain

• Made by the Choroid Plexus in each ventricle

• Requires Vitamin A

• Requires Carbonic Anhydrase

• Less HCO3-

• More CL-

• Lower pH 7.34 (acidic)

• Up to 25 WBCs normal in first month of life normal

• >1 month, only up to 3 WBCs normal

• • Chemotactic Trigger Zone:
•  • located on the floor of the 4th ventricle
•  • Responds to any increase in ICP
•  • Stimulated by dopamine

• • Area Postrema:
•  • located on the blood side of the blood brain barrier (BBB)
•  • Responds to offensive smells or taste
•  • Stimulated by dopamine

• • Non-communicating:
•    • due to an obstruction

• • Communicating:
•   • overproduction of CSF

• • Newborns:
•   • mainly premature newborns
•   • Intraventricular hemorrhage
•    
• • Children:
•   • due to inflammation
•   • Meningitis (posterior fossa)
•     • CN 3
•     • CN 9
•     • CN 10
•     • CN 11
•     • CN 12

• • Adults:
•  • over ingestion of vitamin A
•  • Pseudotumor Cerebri

• • Elderly:
•  • due to brain atrophy
•  • Normal Pressure Hydrocephalus
•  • Ventricles enlarg

• Ventricles expands as the brain atrophies

• Enlarged ventricles then compress the long midline fibers that go to the bladder and legs

• • Triad:
•  • Dementia
•  • Incontinence
•  • Ataxia (degenerative disease of the nervous system)

• Tx: VP shunt

• due to an obstruction

• • In newborns:
•  • MCC: Aqueductal stenosis
•  • 2nd Dandy-Walker cyst

• • In children:
•  • meningitis, especially TB

• • In adults:
•  • cancer

• • In elderly:
•  • cancer

• Benign port wine stain- capillaries



• Opthalmic branch of CN V



• Mental retardation

• Seizure

• Small aneurysmal telangiectasia on the skin and mucus membrane

• 
• 

• Causes GI bleeding

• Pulmonary AV fistula

• AD



• Mental retardation

• Seizure

• Retinal angiomyolipoma

• Cardiac rhabdomyoma

• Pancreatic cyst / Coloboma

• Cerebellar hemangioma



• Retinal hemangioma

• Renal cell carcinoma (increased EPO’s)

• Light must hit the retina by 3 months of age or the child is blind for life

• • You must verify that a child has a RED reflex on eye exam at birth 
•  • retinal arteries
•   • if you can see them
•   • nothing is in the way

• • unequal pupil size
•  
• • MCC: Congenital
•   • AD
•   • check parents
•   • If it occurs in childhood
•    • ICP until proven
•    • otherwise Dx:
•     • CT
•     • LP

• • difference in visual acuity
•  
• • Lazy eye
•  
• • Tx: Patch the eye up to age 5
•  
• • Weak muscles
•   • CN: 3,4,6

• misalignment of the eyes

• • Esotropia
•    • → ←
• • Exotropia
•    • ← →

• Weak muscles of the eye

• Tx. Patch good eye

• corneal defect

• • Straight line card
•   • will see a blip in the line

• Convex or a concave defect in the cornea

• Laser keratotomy

• • near sightedness 
•  • can not see far

• Focus of light is before the retina

• • Tx: Concave lens
•  • disperses light to sides

• far sightedness

• Focus of light is behind the retina

• • Tx: Convex lens
•  • focuses light earlier in middle

• loss of accommodation seen with aging

• Due to muscles weakening with age

• Ability to focus on objects coming close

• • Cataracts
•  • opacification of the lens

• Does not allow light to hit the retina

• Must be removed

• • Increased incidence with
•  • high glucose or
•  • galactose 
•   • sorbitol or
•   • galactitol accumulates

• • Idiopathic: 90%
• • Diabetes or galactosemia
• • Rubella

• • Retinoblastoma 
•   • Rare
•   • Rb gene 
•   • Cancer
•   • High association with Ewing’s sarcoma

• CST (corticospinal tract) motor fibers originates from here

• Unique information:

• • Personality – is stored in the frontal lobe
• • Abstract reasoning
•    • (don’t cry over spilled milk)

• • Atonic seizures- generalized
•  • knock out CST

• • Dementias
•  • Alzheimer's
•  • Pick’s disease

• • Schizophrenia
•  • loss of asymmetry

• Frontal lobotomies

• Hearing

• Balance

• • Hallucinations 
•  • released by serotonin
•  • PCP
•  • LSD

• • Posterior temporal lobe
•  • Wernicke’s area

• • Dominant lobe:
•  • long term memory
•  • all the things you learned since kindergarten
•  • left side is dominant in 90% of right-handed and left-handed people

• • Nondominant lobe
•  • apraxia (motor disorder)   • hemineglect (patients fail to be aware of items to one side of space)
•  • Right side is nondominant in 90% of righthanded and left-handed people

• Middle meningeal artery

• Fracture of temporal bone

• • Lucid interval
•  • temporary improvement in a patient's condition after a traumatic brain injury, after which the condition deteriorates

• Lenticular shape

• Bridging vein

• Venous bleed

• Delayed onset

• Shaken baby

• Elderly

• Crescent shape

• Aneurysm rupture

• Worst headache of their life

• Bloody spinal tap

• The ONLY nucleus with NO known function

• ALL SENSORY information in and out of the brain MUST stop here

• ALL information about the ARMS stay LATERAL

• ALL information about the LEGS stay MEDIAL

• • Controls hunger
•  • Hunger center: lateral
•  • Satiety center: medial
•    • 80% NE and 5HT (+)
•  • You can override via cortex
•    • stimulus “FOOD”

• Controls menstrual cycle

• • Controls temperature 
•  • Anterior: cools
•  • Posterior: warms

• Controls stress response (NE release)

• • Parasympathetic discharge
•  • always first

• • Sympathetic discharge
•  • always second

• • Stress ulcers
• • Curling’s ulcers
• • Cushing’s ulcers 
•  • triad:
•    • bradycardia
•    • HTN
•    • Increased ICP
•     • intracranial pressure
• • IBS

• Final relay station for coordinating fine motor movements

• • Lesion:
•  • Ballismus 
•  • Hemiballismus

• Responsible INITIATING movements

• Uses DOPAMINE for neurotransmitter

• • Receives inhibitory signals from basal ganglia via
•  • ACH or
•  • GABA

• • Loss of DOPAMINE fibers from substantia nigra to striatum (caudate and putamen)
•  • Unable to initiate activities
•  • Mask like facies
•  • Bradykinesia
•  • Shuffling gait
•  • Pill rolling tremor
•  • Autonomic dysfunction:
•    • Shy Dragger syndrome

• • 1st line: L-dopa/ carbidopa
•  
• • 2nd line: Bromocriptine
•   • dopamine agonist
•  
• • Amantadine 
•   • Tx influenza A
•   • increase DA release from nerve terminal
•  
• • Selegiline
•   • MAO-B inhibitor
•   • prevent DA breakdown

• • 90%
• • AD
• • Trinucleotide repeats
• • Caudate nucleus involved
• • Anticipation
• • Decreased GABA fibers
• • Treat with DA blockers 
•  • they have too much DA

• • < 10%
• • AR
• • Ceruloplasmin def
• • Copper excess
• • Lenticular nucleus involved
• • Kayser-Fleischer rings
• • Liver involvement
• • Treat with penicillamine

• ALL MOTOR fibers going in and out of the brain goes through here

• • Blood supply comes from the lenticulostriate arteries
•  • smallest arteries in the brain

• • Lacunar hemorrhages
•   • due to HTN
•   • Causes significant MOTOR deficits

• ADD or ADHD (Not focus).

• RAS not working

• Poor Poor attention and focus attention and focus

• Restlessness

• Unable to sit long enough to complete a task

• Reticular Activating System

• complex network of neurons located in the brainstem

• • acts as the filter between
•  • your senses and
•  • conscious awareness

• is naturally dysregulated 

• • it under-produces
•   • dopamine and
•   • norepinephrine

• • struggles to filter out
•  • background noise or
•  • prioritize important
•  • mundane tasks

• makes standard focus feel impossible

• Central nervous system stimulants

• • methylphenidate 
•  • 1st in children
•  
• • Pemoline
• • Dexedrine
• • Adderall

• important functions in motor movement,

• • particularly movements of the
•  • eye
•  • auditory processing
•  • visual processing

• CST

• Responsible for fine motor activity

• Has to inhibit extension so that smooth flexion can occur

• Fibers originate from the frontal lobes, the precentral gyri

• Fibers descend through the internal capsule and CROSS at the medullary pyramids

• • Spasticity
•  • can not flex

• • Babinski 
•  • extension of toes

• Hyperreflexia

• Clonus

• • Atonic seizures
•  • depolarization across the frontal cortex

• B-12 deficiency

• ALS

• • First sign
•  • papilledema 
•    • optic nerve swelling

• • Second sign
•  • esotropia 
•    • one or both eyes turn inward
•    • cross-eyed
•    • CN VI paralysis
•    • abducens nerve

• • Third sign
•  • Sluggish pupils

• • First symptom
•  • headache

• • Second symptom
•  • diplopia 
•   • blurred double vision

• • Second sign of herniation
•  • DECORTICATE posturing
•   • involuntary
•   • rigid body posture
•   • indicating severe brain injury

• • Compression has occurred
•  • below CN III
•  • but above the red nucleus

• Red nucleus still makes the upper extremities flex while the legs extend

• Herniation goes beyond the red nucleus

• CST and Corticorubral and rubrospinal tracts are all lost

• All extremities will extend by default

• Medulla is pushed through the foramen magnum.

• DECEREBRATE posturing

• 
• 

• • Gracilis
•  • carries leg fibers
•  • located MEDIALLY
•  • superficial muscle
•    • long
•    • slender
•  • S = sacral
•  • L = lumbar
•  • T = thoracic

• • Cuneatus:
•  • carries arm fibers
•  • located LATTERLY
•  • C = cervical 

• Vibratory sensation

• Two-point discrimination

• • Position sense
•  • toe movement

• • Conscious proprioception
•  • eyes closed knowing what he is doing

• The only sensory pathway with four synapses

• • FIRST SYNAPSE
•  • dorsal root ganglion
•  • Fasciculus gracilis
•    • lower extremities
•  • Fasciculus cuneatus
•    • upper extremities

• • SECOND SYNAPSE
•  • MEDULLA

• • THIRD SYNAPSE
•  • THALAMUS

• • FOURTH SYNAPSE
•  • parietal lobes
•  • postcentral gyri
•    • ALL SENSORY

• • Syphilis
• • Vitamin B-12 Def
• • Brown-Sequard

• • Pain and Temperature
•  • opposite all other lesions

• The only pathway that CROSSES in the spinal cord (only one)

• • Fibers
•  • enter the spinal cord
•  • ascend two levels, then
•  • cross to opposite side
•   • via anterior white commissure

• • FIRST SYNAPSE
•  • dorsal root ganglion

• • SECOND SYNAPSE
•  • thalamus

• •THIRD SYNAPSE
•  • parietal lobes
•  • postcentral gyri)- Sensory

• • The only pathway in the spinal cord that crosses twice
•  • equivalent to ipsilateral

• Responsible for depth perception

• • Signs of damage:
•  • INTENTION TREMOR 
•    • during reach
•  • DYSMETRIA 
•    • heal to shin) or
•    • PRONATOR DRIFT
•  • DYSDIODOKINESIS
•    • rapid movement
•  • ROMBERG SIGN
•    • loss of unconscious proprioception

• This pathway does NOT reach the cortex

• • Unconscious proprioception
•  • don’t have to think about it

• • FIRST SYNAPSE:
•  • dorsal root ganglion

• • SECOND SYNAPSE:
•  • thalamus

• • THIRD SYNAPSE:
•  • cerebellum

• • Alcohol attacks the vermis (midline) of the cerebellum
•  • other diseases attack the hemispheres

• Friedreich's ataxia

• Ataxia Telangiectasia

• Adrenoleukodystrophy

• progressive damage to the nervous system

• • retinitis pigmentosa
•  
• • onset between 10 and 15 years
•  
• • Initial symptoms may include
•   • unsteady posture
•   • frequent falling
•   • progressive difficulty in walking due to impaired ability to coordinate voluntary movements

• • spider vein all over your body
•  
• • AR
•  
• • Louis–Bar syndrome

• • defective long chain FA
•   • Fanconi anemia
•   • FA: decreased production of all types of blood cells

• X-linked

• Responsible for responding to the environment

• • PNEUMOTACTIC
•  • prevents pneumothorax
•  • makes you breath out
•  • superior
•  • inhibitory to the APNEUSTIC
• • APNEUSTIC 
•  • makes you breath in
•  • bottom
•  • responds to
•   • pO2 decrease
•   • pCO2 increase

• CNS area most sensitive to osmotic shifts

• Locked-in Syndrome

• Central Pontine Demyelinolysis

• Controls ALL basic functions

• Respiration of 8-10 ipm