Neurology - Anatomy and Physiology (4)

Question 1

Cranial nerve nuclei

• Located…
• Nuclei
  
  • Midbrain
  • Pons
  • Medulla
  • Spinal cord
• Lateral vs. medial nuclei

Answer 1

• Located in tegmentum portion of brain stem (between dorsal and ventral portions)
• Nuclei
  
  • ƒƒMidbrain—nuclei of CN III, IV
  • Pons—nuclei of CN V, VI, VII, VIII
  • ƒƒMedulla—nuclei of CN IX, X, XII
  • Spinal cord—nucleus of CN XI
• Lateral vs. medial nuclei
  
  • Lateral nuclei = sensory (aLar plate).
  • —Sulcus limitans—
  • Medial nuclei = Motor (basal plate).

Question 2

Cranial nerve reflexes

• For each
  
  • Afferent
  • Efferent
• Corneal
• Lacrimation
• Jaw jerk
• Pupillary
• Gag

Answer 2

• Corneal
  
  • Afferent: V1 ophthalmic (nasociliary branch)
  • Efferent: VII (temporal branch: orbicularis oculi)
• Lacrimation
  
  • Afferent: V1 (loss of reflex does not preclude emotional tears)
  • Efferent: VII
• Jaw jerk
  
  • Afferent: V3 (sensory—muscle spindle from masseter)
  • Efferent: V3 (motor—masseter)
• Pupillary
  
  • Afferent: II
  • Efferent: III
• Gag
  
  • Afferent: IX
  • Efferent: X

Question 3

Vagal nuclei

• For each
  
  • Function
  • Nerves
• Nucleus Solitarius
• Nucleus Ambiguus
• Dorsal motor nucleus

Answer 3

• Nucleus Solitarius
  
  • Function: Visceral Sensory information (e.g., taste, baroreceptors, gut distention).
  • Nerves: VII, IX, X.
• Nucleus aMbiguus
  
  • Function: Motor innervation of pharynx, larynx, and upper esophagus (e.g., swallowing, palate elevation).
  • Nerves: IX, X, XI (cranial portion)
• Dorsal motor nucleus
  
  • Function: Sends autonomic (parasympathetic) fibers to heart, lungs, and upper GI.
  • Nerves: X.

Question 4

Cranial nerve and vessel pathways

• Cribriform plate
• Middle cranial fossa
• Posterior cranial fossa

Answer 4

• Cribriform plate (CN I).
• Middle cranial fossa (CN II–VI)—through sphenoid bone:
  
  • ƒƒOptic canal (CN II, ophthalmic artery, central retinal vein)
  • Superior orbital fissure (CN III, IV, V1, VI, ophthalmic vein, sympathetic fibers)
  • Foramen Rotundum (CN V2)
  • Foramen Ovale (CN V3)
  • Foramen spinosum (middle meningeal artery)
  • Divisions of CN V exit owing to Standing Room Only.
• Posterior cranial fossa (CN VII–XII)—through temporal or occipital bone:
  
  • Internal auditory meatus (CN VII, VIII)
  • Jugular foramen (CN IX, X, XI, jugular vein)
  • ƒƒHypoglossal canal (CN XII)
  • Foramen magnum (spinal roots of CN XI, brain stem, vertebral arteries)

Question 5

Cavernous sinus

• Definition
• What pass through
• Cavernous sinus syndrome

Answer 5

• Definition
  
  • A collection of venous sinuses on either side of the pituitary.
  • Blood from eye and superficial cortex Ž–> cavernous sinus –>Ž internal jugular vein.
• What pass through
  
  • CN III, IV, V1, V2, and VI and postganglionic sympathetic fibers en route to the orbit all pass through the cavernous sinus.
  • Cavernous portion of internal carotid artery is also here.
  • The nerves that control extraocular muscles (plus V1 and V2) pass through the cavernous sinus.
• Cavernous sinus syndrome
  
  • e.g., due to mass effect, fistula, thrombosis
  • Ophthalmoplegia and decreased corneal and maxillary sensation with normal visual acuity.
  • CN VI commonly affected.

Question 6

Common cranial nerve lesions

• CN V motor lesion
• CN X lesion
• CN XI lesion
• CN XII lesion (LMN)

Answer 6

• CN V motor lesion
  
  • Jaw deviates toward side of lesion due to unopposed force from the opposite pterygoid muscle.
• CN X lesion
  
  • Uvula deviates away from side of lesion.
  • Weak side collapses and uvula points away.
• CN XI lesion
  
  • Weakness turning head to contralateral side of lesion (SCM).
  • Shoulder droop on side of lesion (trapezius).
  • The left SCM contracts to help turn the head to the right.
• CN XII lesion (LMN)
  
  • Tongue deviates toward side of lesion (“lick your wounds”) due to weakened tongue muscles on the affected side.

Question 7

Auditory physiology

• For each
  
  • Definition
  • Function
• Outer ear
• Middle ear
• Inner ear

Answer 7

• Outer ear
  
  • Definition: Visible portion of ear (pinna), includes auditory canal and eardrum.
  • Function: Transfers sound waves via vibration of eardrum.
• Middle ear
  
  • Definition: Air-filled space with three bones called the ossicles (malleus, incus, stapes).
  • Function: Ossicles conduct and amplify sound from eardrum to inner ear.
• Inner ear
  
  • Definition:
    
    • Snail-shaped, fluid-filled cochlea.
    • Contains basilar membrane that vibrates 2° to sound waves.
  • Function:
    
    • Vibration transduced via specialized hair cells –>Ž auditory nerve signaling –>Ž brainstem.
    • Each frequency leads to vibration at specific location on the basilar membrane (tonotopy):
      
      • Low frequency heard at apex near helicotrema (wide and flexible).
      • ƒƒHigh frequency heard best at base of cochlea (thin and rigid).

Question 8

Hearing loss

• Noise-induced
• For each
  
  • Rinne test
  • Weber test
• Conductive
• Sensorineural

Answer 8

• Noise-induced
  
  • Damage to stereocilliated cells in organ of Corti
  • Loss of high-frequency hearing 1st
  • Sudden extremely loud noises can produce hearing loss due to tympanic membrane rupture.
• Conductive
  
  • Rinne test: Abnormal (bone > air)
  • Weber test: Localizes to affected ear
• Sensorineural
  
  • Rinne test: Normal (air > bone)
  • Weber test: Localizes to unaffected ear

Question 9

Facial lesions

• UMN lesion
• LMN lesion
• Facial nerve palsy
  
  • Definition
  • Findings
  • Associated with…
  • Treatment

Answer 9

• UMN lesion
  
  • Lesion of motor cortex or connection between cortex and facial nucleus.
  • Contralateral paralysis of lower face
    
    • Forehead spared due to bilateral UMN innervation.
• LMN lesion
  
  • Ipsilateral paralysis of upper and lower face.
• Facial nerve palsy
  
  • Definition
    
    • Complete destruction of the facial nucleus itself or its branchial efferent fibers (facial nerve proper).
    • Can occur idiopathically (called Bell palsy [A])
      
      • Gradual recovery in most cases
  • Peripheral ipsilateral facial paralysis (drooping smile [A]) with inability to close eye on involved side.
  • Associated with Lyme disease, herpes simplex and (less common) herpes zoster, sarcoidosis, tumors, and diabetes.
  • Treatment includes corticosteroids.

Question 10

Mastication muscles

• Innervation
• Muscles that close jaw
• Muscles that open jaw

Answer 10

• All are innervated by the trigeminal nerve (V3)
• 3 muscles close jaw:
  
  • Masseter, teMporalis, Medial pterygoid.
  • M’s Munch
• 1 muscle opens jaw:
  
  • Lateral pterygoid.
  • Lateral Lowers (when speaking of pterygoids with respect to jaw motion).
• “It takes more muscle to keep your mouth shut.”

Question 11

Eye and retina

Answer 11

Question 12

Common eye conditions:
Refractive errors

• Definition
• Hyperopia
• Myopia
• Astigmatism
• Presbyopia

Answer 12

• Definition
  
  • Impaired vision that improves with glasses.
• Hyperopia
  
  • Eye too short for refractive power of cornea and lens Ž–> light focused behind retina.
• Myopia
  
  • Eye too long for refractive power of cornea and lens –>Ž light focused in front of retina.
• Astigmatism
  
  • Abnormal curvature of cornea resulting in different refractive power at different axes.
• Presbyopia
  
  • Decrease in focusing ability during accommodation due to sclerosis and decreased elasticity.

Question 13

Common eye conditions

• Uveitis
• Retinitis
• Central retinal artery occlusion

Answer 13

• Uveitis
  
  • Inflammation of anterior uvea and iris, with hypopyon (sterile pus), accompanied by conjunctival redness [A]).
  • Often associated with systemic inflammatory disorders (e.g., sarcoid, rheumatoid arthritis, juvenile idiopathic arthritis, TB, HLA-B27–associated conditions).
• Retinitis
  
  • Retinal edema and necrosis leading to scar [B].
  • Often viral (CMV, HSV, HZV).
  • Associated with immunosuppression.
• Central retinal artery occlusion
  
  • Acute, painless monocular vision loss.
  • Retina cloudy with attenuated vessels and “cherry-red” spot at the fovea [C]

Question 14

Common eye conditions

• Retinal vein occlusion
• Diabetic retinopathy
  
  • Definition
  • Two types
    
    • Non-proliferative
    • Proliferative

Answer 14

• Retinal vein occlusion
  
  • Blockage of central or branch retinal vein due to compression from nearby arterial atherosclerosis.
  • Retinal hemorrhage and edema in affected area.
• Diabetic retinopathy
  
  • Definition
    
    • Retinal damage due to chronic hyperglycemia.
  • Two types
    
    • Non-proliferative
      
      • Damaged capillaries leak blood –>Ž lipids and fluid seep into retina –>Ž hemorrhages and macular edema.
      • Treatment: blood sugar control, macular laser.
    • Proliferative
      
      • Chronic hypoxia results in new blood vessel formation with resultant traction on retina.
      • Treatment: peripheral retinal photocoagulation, anti-VEGF injections.

Question 15

Aqueous humor pathway

Answer 15

Question 16

Glaucoma

• Definition
• Open angle
  
  • Associated with…
  • Primary
  • Secondary
• Closed/narrow angle
  
  • Primary
  • Secondary
  • Chronic closure
  • Acute closure

Answer 16

• Definition
  
  • Optic disc atrophy with characteristic cupping, usually with increased intraocular pressure (IOP) and progressive peripheral visual field loss.
• Open angle
  
  • Associated with increased age, African-American race, family history.
    
    • Painless, more common in U.S.
  • Primary
    
    • Cause unclear.
  • Secondary
    
    • Blocked trabecular meshwork from WBCs (e.g., uveitis), RBCs (e.g., vitreous hemorrhage), retinal elements (e.g., retinal detachment).
• Closed/narrow angle
  
  • Primary
    
    • Enlargement or forward movement of lens against central iris (pupil margin) leads to obstruction of normal aqueous flow through pupil
    • –> fluid builds up behind iris, pushing peripheral iris against cornea and impeding flow through trabecular meshwork.
  • Secondary
    
    • Hypoxia from retinal disease (e.g., diabetes, vein occlusion) induces vasoproliferation in iris that contracts angle.
  • Chronic closure
    
    • Often asymptomatic with damage to optic nerve and peripheral vision.
  • Acute closure
    
    • True ophthalmic emergency.
    • Increased IOP pushes iris forward Ž–> angle closes abruptly.
    • Very painful, sudden vision loss, halos around lights, rock-hard eye, frontal headache.
    • Do not give epinephrine because of its mydriatic effect.

Question 17

Cataract

• Definition
• Risk factors

Answer 17

• Definition
  
  • Painless, often bilateral, opacification of lens [A] –>Ž decreased in vision.
• Risk factors
  
  • Increased age, smoking, EtOH, excessive sunlight, prolonged corticosteroid use, classic galactosemia, galactokinase deficiency, diabetes (sorbitol), trauma, infection.

Question 18

Papilledema

Answer 18

• Optic disc swelling (usually bilateral) due to increased intracranial pressure (e.g., 2° to mass effect).
• Enlarged blind spot and elevated optic disc with blurred margins seen on fundoscopic exam [A].

Question 19

Extraocular muscles and nerves

• CN III damage
• CN IV damage
• CN VI damage
• ​​The superior oblique

Answer 19

• The “chemical formula” LR6SO4AR3.
• CN III damage
  
  • Eye looks down and out
  • Ptosis, pupillary dilation, loss of accommodation.
  • CN III innervates All the Rest.
• CN IV damage
  
  • Eye moves upward, particularly with contralateral gaze and head tilt toward the side of the lesion
  • Problems going down stairs, may present with compensatory head tilt in the opposite direction
  • CN IV innervates the Superior Oblique.
  • The superior oblique abducts, intorts, and depresses while adducted.
• CN VI damage
  
  • Medially directed eye that cannot abduct.
  • CN VI innervates the Lateral Rectus.

Question 20

Testing extraocular muscles

Answer 20

• To test the function of each muscle, have the patient look in the following directions (image)
  
  • e.g., to test SO, have patient depress eye from adducted position
• IOU: to test Inferior Oblique, have patient look Up.
• Obliques move the eye in the Opposite direction.

Question 21

Pupillary control

• Miosis
  
  • 1st neuron
  • 2nd neuron
• Mydriasis
  
  • 1st neuron
  • 2nd neuron
  • 3rd neuron

Answer 21

• Miosis (constriction, parasympathetic)
  
  • 1st neuron: Edinger-Westphal nucleus to ciliary ganglion via CN III
  • 2nd neuron: short ciliary nerves to pupillary sphincter muscles
• Mydriasis (dilation, sympathetic)
  
  • 1st neuron: hypothalamus to ciliospinal center of Budge (C8–T2)
  • 2nd neuron: exit at T1 to superior cervical ganglion (travels along cervical sympathetic chain near lung apex, subclavian vessels)
  • 3rd neuron: plexus along internal carotid, through cavernous sinus; enters orbit as long ciliary nerve to pupillary dilator muscles

Question 22

Pupillary light reflex

• Definition
• Marcus Gunn pupil

Answer 22

• Definition
  
  • Light in either retina sends a signal via CN II to pretectal nuclei (dashed lines) in midbrain that activates bilateral Edinger-Westphal nuclei
  • Pupils contract bilaterally (consensual reflex).
  • Result: illumination of 1 eye results in bilateral pupillary constriction.
• Marcus Gunn pupil (afferent pupillary defect)
  
  • Due to optic nerve damage or severe retinal injury.
  • Decreased bilateral pupillary constriction when light is shone in affected eye relative to unaffected eye.
  • Tested with the “swinging flashlight test.”

Question 23

Cranial nerve III

• Motor (central) output to ocular muscles
  
  • Affected by…
  • Signs
• Parasympathetic (peripheral) output
  
  • Affected by…
  • Signs

Answer 23

• Motor (central) output to ocular muscles
  
  • Affected primarily by vascular disease (e.g., diabetes: glucose Ž–> sorbitol) due to decreased diffusion of oxygen and nutrients to the interior fibers from compromised vasculature that resides on outside of nerve.
  • Signs: ptosis, “down and out” gaze.
• Parasympathetic (peripheral) output
  
  • Fibers on the periphery are 1st affected by compression (e.g., posterior communicating artery aneurysm, uncal herniation).
  • Signs: diminished or absent pupillary light reflex, “blown pupil” often with “down-and-out” gaze.

Question 24

Retinal detachment

Answer 24

• Separation of neurosensory layer of retina (photoreceptor layer with rods and cones) from outermost pigmented epithelium (normally shields excess light, supports retina) Ž–> degeneration of photoreceptors –>Ž vision loss.
  
  • May be 2° to retinal breaks, diabetic traction, inflammatory effusions.
• Breaks more common in patients with high myopia and are often preceded by posterior vitreous detachment (flashes and floaters) and eventual monocular loss of vision like a “curtain drawn down.”
  
  • Surgical emergency.

Question 25

Age-related macular degeneration

• Definition
• Causes…
• Dry
• Wet

Answer 25

• Definition
  
  • Degeneration of macula (central area of retina).
• Causes…
  
  • Distortion (metamorphopsia) and eventual loss of central vision (scotomas).
• ƒƒDry (nonexudative, > 80%)
  
  • Deposition of yellowish extracellular material in and beneath Bruch membrane and retinal pigment epithelium (“drusen”) [A] with gradual decreases in vision.
  • Prevent progression with multivitamin and antioxidant supplements.
• ƒƒWet (exudative, 10–15%)
  
  • Rapid loss of vision due to bleeding 2° to choroidal neovascularization.
  • Treat with anti-vascular endothelial growth factor injections (anti-VEGF) or laser.

Question 26

Visual field defects

• Image
• Meyer loop
• Dorsal optic radiation
• When an image hits 1° visual cortex…

Answer 26

• Image
  
  1. Right anopia
  2. Bitemporal hemianopia (pituitary lesion, chiasm)
  3. Left homonymous hemianopia
  4. Left upper quadrantic anopia (right temporal lesion, MCA)
  5. Left lower quadrantic anopia (right parietal lesion, MCA)
  6. Left hemianopia with macular sparing (PCA infarct), macula –>Ž bilateral projection to occiput
  7. Central scotoma (macular degeneration)
• Meyer loop
  
  • Inferior retina
  • Loops around inferior horn of lateral ventricle.
• Dorsal optic radiation
  
  • Superior retina
  • Takes shortest path via internal capsule.
• When an image hits 1° visual cortex…
  
  • It is upside down and left-right reversed.

Question 27

Internuclear ophthalmoplegia (INO)

• Medial longitudinal fasciculus (MLF)
• INO
• When looking left…
• Directional term (e.g., right INO, left INO)

Answer 27

• Medial longitudinal fasciculus (MLF)
  
  • Pair of tracts that allows for crosstalk between CN VI and CN III nuclei.
  • Coordinates both eyes to move in same horizontal direction.
  • Highly myelinated (must communicate quickly so eyes move at same time).
• Lesion in MLF = INO
  
  • Lack of communication such that when CN VI nucleus activates ipsilateral lateral rectus, contralateral CN III nucleus does not stimulate medial rectus to fire.
  • Abducting eye gets nystagmus (CN VI overfires to stimulate CN III).
  • Convergence normal.
  • Lesions seen in patients with demyelination (e.g., multiple sclerosis).
    
    • MLF in MS.
• When looking left…
  
  • The left nucleus of CN VI fires, which contracts the left lateral rectus and stimulates the contralateral (right) nucleus of CN III via the right MLF to contract the right medial rectus.
• Directional term (e.g., right INO, left INO)
  
  • Refers to which eye is paralyzed.