**Core Concept**
The muscles involved in a tight grip of the hand are primarily responsible for flexion and adduction of the fingers. This action is essential for activities such as grasping and manipulating objects. The muscles involved are part of the thenar and hypothenar eminences.

**Why the Correct Answer is Right**
The thenar muscles, specifically the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, play a crucial role in gripping the hand. These muscles work together with the hypothenar muscles, including the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi, to achieve a tight grip. The intrinsic muscles of the hand, particularly the lumbricals and interossei, also contribute to finger flexion and adduction.

**Why Each Wrong Option is Incorrect**
**Option A:** The palmaris longus muscle is primarily involved in wrist flexion, not hand gripping.
**Option B:** The flexor carpi radialis muscle is responsible for wrist flexion and radial deviation, not hand gripping.
**Option C:** The extensor pollicis longus muscle is involved in thumb extension, not gripping.

**Clinical Pearl / High-Yield Fact**
The thenar and hypothenar muscles are innervated by the median and ulnar nerves, respectively. Damage to these nerves can result in weakness or paralysis of the hand, affecting the ability to perform activities such as grasping and manipulating objects.

**Correct Answer:** C.