Skin sensors Flashcards
Which type of mechanoreceptors are classified as slow-adapting receptors in the hand?
Merkel cell neurite complexes and Ruffini end organs. These receptors maintain firing during sustained pressure, detecting static touch rather than dynamic stimuli.
What type of stimuli do Merkel cell neurite complexes primarily respond to?
Static touch/sustained pressure. They potentiate slowly adapting type I (SAI) firing, enhancing perception of continuous stimuli like shapes on fingertips.
Which hand mechanoreceptors are classified as rapidly adapting receptors?
Meissner and Pacinian corpuscles. These adapt quickly, specializing in dynamic touch and vibration due to fast channel inactivation.
What frequencies of vibration are Pacinian corpuscles primarily responsive to?
High frequencies (e.g., 200-300 Hz). Their structure and rapid adaptation make them ideal for detecting transient, high-frequency vibrations.
How do Meissner corpuscles differ from Pacinian corpuscles in terms of frequency sensitivity?
Meissner corpuscles detect lower frequencies (e.g., 20-50 Hz), while Pacinian corpuscles detect higher frequencies (e.g., 200-300 Hz), both being rapidly adapting.
What is the relationship between tactile discrimination and the number of innervated sensory receptors?
Tactile discrimination improves with higher receptor density (e.g., fingertips), as more innervated receptors enhance spatial resolution for fine touch tasks.
Which specific mechanoreceptor is most important for precise spatial discrimination in the hand?
Merkel cell neurite complexes. Their sustained firing during static pressure supports fine spatial discrimination, critical for delicate hand tasks.
What happens to tactile discrimination when receptor density or function is diminished?
It decreases, as seen in neuropathies, due to fewer functional receptors reducing the ability to distinguish fine spatial details.
Why are vibration and cutaneous pressure threshold tests valuable in evaluating chronic nerve compression?
They detect early sensory changes (vibration for high-frequency loss, pressure for static touch), aiding diagnosis of conditions like carpal tunnel syndrome before major damage.
What range of frequencies can modern vibrometers (like Bruel and Kjaer) measure for clinical evaluation of hand sensory function?
8 to 500 Hz. This broad range assesses both low- and high-frequency mechanoreceptor function for comprehensive sensory evaluation.
What does cutaneous pressure threshold testing specifically evaluate in hand sensory assessment?
Function of slowly adapting receptors, especially Merkel cell neurite complexes, measuring static touch perception thresholds.
Can a nerve conduction study show normal latency despite significant nerve pathology?
Yes, if some fast-conducting fibers remain intact, latency appears normal despite reduced amplitude from fiber loss, common in early neuropathies.
What is ‘temporal dispersion’ in the context of nerve conduction studies?
Spreading of the compound action potential over time due to varying conduction velocities, potentially masking pathology in nerve compression.
What phenomenon contributes to potentially misleading lower amplitude measurements in sensory nerve action potentials (SNAPs)?
Phase cancellation. Velocity-dependent dispersion and short SNAP durations reduce amplitude, complicating interpretation of nerve damage.
How do sensory threshold tests aid in early diagnosis of nerve compression?
They detect subtle changes in vibration and pressure perception before major damage, targeting different mechanoreceptors for timely intervention.
In what order are vibration frequencies typically affected in progressive nerve compression?
Higher frequencies (e.g., 200-300 Hz) are affected first, followed by lower frequencies as compression worsens, reflecting early large-fiber involvement.
What is the primary functional difference between rapidly adapting and slowly adapting mechanoreceptors?
Rapidly adapting (Meissner, Pacinian) respond to dynamic touch and stop firing during sustained stimuli; slowly adapting (Merkel, Ruffini) detect static touch with sustained firing.
How do Merkel cells enhance mechanosensory responses in the hand?
They boost Aβ low-threshold mechanoreceptor excitability during static pressure, enabling sustained firing for detailed static touch detection.
Why do Meissner and Pacinian corpuscles not respond to static touch?
Their rapid adaptation limits firing to dynamic stimuli (e.g., vibration), ceasing during sustained pressure unlike slow-adapting receptors.
Why is distinguishing between static and dynamic touch important in hand surgery?
It informs sensory deficit assessment and surgical planning (e.g., nerve repair), as different receptors handle each type of touch.
How do vibration threshold tests complement nerve conduction studies?
They offer early, non-invasive sensory change detection, while NCS assesses nerve function directly, together providing a complete diagnostic view.
What does a normal nerve latency with reduced amplitude suggest?
Intact fast fibers but significant fiber loss, indicating early neuropathy requiring further evaluation beyond latency alone.
Why might Pacinian corpuscles initially respond to static pressure?
They fire briefly before adapting rapidly, reflecting their design for dynamic stimuli rather than sustained static touch.
What is the significance of receptor density in tactile discrimination tests?
Higher density (e.g., fingertips) allows finer resolution in tests like two-point discrimination, essential for assessing sensory recovery post-surgery.
