Bone Wizardry
Neuro exam localizer
Mechanoreceptors
A tuning fork is not a Merkel question. Vibration with a deep, rapidly adapting receptor is Pacinian until proven otherwise.
Before you scroll: A 27-year-old woman is tested with a vibrating tuning fork placed over the distal interphalangeal joint. She detects vibration normally. The receptor responsible is deep in the skin, joints, and ligaments and adapts rapidly. Which receptor is being tested?
Free nerve ending
Meissner corpuscle
Merkel disc
Pacinian corpuscle
The tuning fork is the tell. Pacinian corpuscles sit deep and respond to vibration and deep pressure; they adapt rapidly, so they fire when the pressure changes. Meissner also adapts rapidly, but it sits superficial in hairless skin and senses light moving touch. Merkel is the slow one for sustained pressure and shape. Deep + vibration + rapidly adapting = Pacinian corpuscle.
Sensory receptor split
Depth, Stimulus, Adaptation
Three variables solve nearly every receptor stem: where it sits, what it senses, and whether it fades fast.
Pacinian Meissner Merkel Free ending
Pacinian corpuscle Deep buzz detector
Location Deep dermis, subcutaneous tissue, joints, ligaments
Stimulus Vibration and deep pressure
Adaptation Rapidly adapting
Image hook Onion-ring lamellae around the nerve ending
Meissner corpuscle Shallow flutter detector
Location Superficial dermal papillae of glabrous skin
Stimulus Light touch and low-frequency flutter
Adaptation Rapidly adapting
Trap Fast adaptation alone is not enough. Use depth and stimulus.
Merkel disc Slow edge detector
Location Basal epidermis
Stimulus Sustained pressure, shape, edges, texture
Adaptation Slowly adapting
Trap It holds the signal. It does not handle rapid vibration.
Free nerve ending Bare alarm wire
Location Unencapsulated nerve endings
Stimulus Pain, temperature, itch, crude touch
Capsule None
Trap If the stem says lamellated or corpuscle, it is not free.
Board trap: Rapidly adapting does not automatically mean Meissner. Pacinian is also rapidly adapting. Depth and stimulus decide.
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Receptor switchboard
Name the Receptor
Pick the stimulus and let depth plus adaptation force the answer.
Which receptor owns this clue?
Tuning fork over a joint
Feather across fingertip
Braille dot held still
Pinprick or burn
Onion-ring lamellae
Pick a clue. Fast adaptation splits into Meissner and Pacinian. Depth and stimulus make the final call.
Board trap: Merkel is not vibration. Merkel is the slow pressure pad that keeps reading a held stimulus.
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Two-gate discriminator
Decision Tree
First ask whether the stimulus changes quickly. Then ask whether the receptor is deep or superficial.
1
Is the stem testing pain or temperature instead of mechanical shape, touch, or vibration?
Yes. Pain, heat, cold, or itch.
No. It is mechanical touch, pressure, shape, or vibration.
2
Is the mechanical stimulus rapid vibration or deep pressure from a tuning fork or joint capsule?
Yes. Deep buzz, rapid adaptation.
No. It is superficial light touch or sustained shape.
3
Does the receptor hold firing during a sustained press?
Yes. It reads shape and edges.
No. It fades quickly with a light moving stroke.
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Make it stick
Hooks and Images
Make the receptor a physical object: shallow feather, deep onion, slow pressure pad, bare alarm wire.
DEEP
Pacinian is the basement
Pacinian lives deep and feels the building shake. Tuning fork, vibration, deep pressure, onion rings.
tap to reveal
LIGHT
Meissner is the fingertip feather
Meissner is superficial and quick. A light moving touch on glabrous skin is its lane.
tap to reveal
HOLD
Merkel holds the note
Merkel keeps firing while pressure stays. It reads edges, shape, texture, and sustained pressure.
tap to reveal
Pacinian corpuscle · tap to expand
Meissner corpuscle · tap to expand
Sensory pathway · tap to expand
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Board walkthrough
Prove It
One vignette at a time. Choices shuffle. The bank does not repeat until it is exhausted.
Vignette 1 Never-repeat tracking ready
Exam tools: right-click or long-press to cross out a choice. Double-click or double-tap to highlight one. Tools switch off after you answer.
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