Flexion of metacarpophalangeal joint and extension of interphalangeal joints is major action of
First, I need to recall the anatomy of the hand muscles. The MCP joints are the ones between the metacarpals and the proximal phalanges, and the IP joints are the ones between the phalanges. Flexion at the MCP and extension at the IP is a specific movement pattern.
The muscle that comes to mind is the Flexor digitorum superficialis (FDS). Wait, no, the FDS is more involved in flexing the PIP joints. The Flexor digitorum profundus (FDP) flexes the DIP joints. Then there's the Lumbricals. The lumbricals are four muscles that arise from the tendons of the FDS. Their action is to flex the MCP joints and extend the IP joints. That fits the question. So the correct answer should be the lumbricals.
Now, checking the options. The user hasn't provided the options, but assuming the options include lumbricals. Let's say the options are A. Flexor digitorum superficialis, B. Lumbricals, etc. The correct answer would be B.
Why are the other options incorrect? The FDS (Option A) is mainly for PIP flexion. The FDP (Option C) flexes DIP. The interossei (Option D) might flex MCP and extend IP, but they also adduct or abduct fingers. Wait, the lumbricals do flex MCP and extend IP. The interossei have similar actions but are more involved in adduction/abduction. So the main muscle for this specific movement is the lumbricals.
Clinical pearl: Remember that the lumbricals are the only muscles that flex MCP and extend IP. They are crucial in the "claw hand" deformity when damaged, which is a classic exam point. Also, they are innervated by the median nerve for the first two and ulnar for the last two.
So putting it all together, the correct answer is lumbricals.
**Core Concept**
This question tests knowledge of hand muscle anatomy, specifically the actions of intrinsic muscles. The lumbricals are unique in their dual action on MCP and IP joints, critical for grip and finger movement coordination.
**Why the Correct Answer is Right**
The lumbricals (Option B) originate from the tendons of the flexor digitorum superficialis. They flex the metacarpophalangeal (MCP) joints **and** extend the interphalangeal (IP) joints. This action is essential for movements like gripping objects. Their dual action is due to their insertion on the extensor hood mechanism, which allows simultaneous flexion at MCP and extension at IP joints.
**Why Each Wrong Option is Incorrect**
**Option A (Flexor digitorum superficialis):** Primarily flexes the proximal interphalangeal (PIP) joints, not the MCP joints.
**Option C (Flexor digitorum profundus):** Flexes the distal interphalangeal (DIP) joints, not involved in MCP flexion.
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