First Palmar Interosseous (Hand)

Origin, Insertion, Action & Nerve

Attachments explained

The First Palmar Interosseous (Hand) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.

Action & function

When the First Palmar Interosseous (Hand) contracts, it produces the following movements: Adducts the index finger toward the axial line of the hand (PAD); flexes MCP and extends IP joints.

As part of the Hand group of the Upper Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.

Nerve supply & clinical relevance

The First Palmar Interosseous (Hand) receives its nerve supply from the Deep branch of ulnar nerve (C8, T1). This nerve carries fibres from spinal segment(s) C8, T1.

Because a muscle can only contract when its nerve is intact, injury to the Deep branch of ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the First Palmar Interosseous (Hand), impairing the movements it normally produces (adducts the index finger toward the axial line of the hand (PAD)). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the First Palmar Interosseous (Hand) (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the First Palmar Interosseous (Hand), work through them in order: picture its origin, trace the muscle to its insertion, reason out the action that shortening between those two points must create, then add the nerve that drives it.

Most students remember the First Palmar Interosseous (Hand) fastest by linking its action back to its attachments rather than memorising each fact in isolation. Once the origin and insertion make sense, the action usually follows logically.

First Palmar Interosseous (Hand) quick facts

Region

Upper Limb

Group

Hand

Origin

Palmar surface of the 2nd metacarpal (unipennate)

Insertion

Extensor expansion and base of proximal phalanx of the index finger

Action

Adducts the index finger toward the axial line of the hand (PAD); flexes MCP and extends IP joints

Nerve

Deep branch of ulnar nerve (C8, T1)

Spinal roots

C8, T1

Frequently asked questions

Related muscles