WBR0598

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Physiology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 45 year old male patient presents to the physician's office for his annual check-up. He currently has no complaints. The patient's past medical history is significant only for hypertension and hyperlipidemia. On physical examination, the physician uses a 128 Hz tuning fork and places it on the patient's knee. When asked, the patient confirms the sensation of vibration of the tuning fork. The physician then explains that his peripheral sensation travels to the central nervous system with the help of neurons and synpases. Which of the following structures is first able to detect the sensation of vibration from the skin?]]
Answer A	AnswerA::Merkel complex
Answer A Explanation	[[AnswerAExp::Merkel complex is a group of unencapsulated specialized type of epithelial cells that is found in hairy and non-hairy skin. It senses touch signaling the location and the magnitude of the pressure with slow adaptation by distorting the complex when forces are applied to the overlying skin.]]
Answer B	AnswerB::Ruffini corpuscle
Answer B Explanation	[[AnswerBExp::Ruffini corpuscle is a cirgar-shaped encapsulated collagenous group of fibers with longitudinal strands that contain primary afferent fiber branches sensitive to skin stretch singaling the direction and force of the stretch. They are also characterized by slow adaptation.]]
Answer C	AnswerC::Pacinian corpuscle
Answer C Explanation	AnswerCExp::Pacinian corpuscle is responsible for relaying the sensation of vibration from the skin.
Answer D	AnswerD::Meissner corpuscle
Answer D Explanation	[[AnswerDExp::Meissner corpuscle is located in hairless skin, also called glabrous skin in the dermal layer. It is made of encapsulated flat epithelial laminar cells. The afferent terminal fibers are found between the cells. It senses the fluttering touch and fine movement and signifies the velocity and duration of the signal with rapid adaptation.]]
Answer E	AnswerE::Golgi tendon organ
Answer E Explanation	[[AnswerEExp::Golgi tendon organs (GTO) are encapsulated collagen-containing groups of cells located near the muscular-tendon junction of extrafusal muscles and is continuous with them. It signals muscle contraction and muscle tension, not muscle length (which is signaled by the muscle spindle). The terminals of GTO are compressed upon muscle contraction. Sustained muscle contraction causes a sustained afferent response. Adaptation to the twisting force is slow.]]
Right Answer	RightAnswer::C
Explanation	[[Explanation::Pacinian corpuscles are encapsulated specialized cells located beneath the dermis that have an onion-shaped appearance with concentric layers that contain fluids and responds to the sensation of vibration. In the center of its concentricity, the corpuscle contains one primary afferent terminal fiber. The fluid inside the concentric layers will be displaced upon the application of force on the pacinian corpuscle that will migrate towards the axonal terminal in the center. The Pacinian corpuscle is characterized by rapid adaptation because despite sustained force, the axonal terminal will only receive a transient force. Educational Objective: Pacinian corpuscles located in the dermal layer of the skin are the first relay sensory vibration forces from the environment. Reference: Purves D, Augustine GJ, Fitzpatrick D, et al. Mechanoreceptors specialized to receive tactile information. in Neuroscience. 2nd ed. Sunderland (MA): Sinauer Associates; 2001. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::pacinian, WBRKeyword::corpuscle, WBRKeyword::corpuscles, WBRKeyword::complex, WBRKeyword::merkel, WBRKeyword::merkel's, WBRKeyword::ruffini, WBRKeyword::golgi, WBRKeyword::tendon, WBRKeyword::organ, WBRKeyword::adaptation, WBRKeyword::meissner
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::