Pollical Palmar Interosseus (of the Thumb)

Origin, Insertion, Action & Nerve

Attachments explained

The Pollical Palmar Interosseus (of the Thumb) 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 Pollical Palmar Interosseus (of the Thumb) contracts, it produces the following movement: Adducts the thumb toward the palm.

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 Pollical Palmar Interosseus (of the Thumb) receives its nerve supply from the Deep branch of the 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 the ulnar nerve or to its spinal roots (C8, T1) can weaken or paralyse the Pollical Palmar Interosseus (of the Thumb), impairing the movements it normally produces (adducts the thumb toward the palm). This is why knowing the innervation is central to localising nerve lesions in clinical practice.

How to study the Pollical Palmar Interosseus (of the Thumb) (the OIANS method)

OIANS stands for Origin, Insertion, Action and Nerve, the four facts that uniquely define every skeletal muscle. To learn the Pollical Palmar Interosseus (of the Thumb), 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 Pollical Palmar Interosseus (of the Thumb) 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.

Pollical Palmar Interosseus (of the Thumb) quick facts

Region

Upper Limb

Group

Hand

Origin

Ulnar (palmar) surface of the first metacarpal

Insertion

Ulnar side of the base of the proximal phalanx of the thumb

Action

Adducts the thumb toward the palm

Nerve

Deep branch of the ulnar nerve (C8–T1)

Spinal roots

C8, T1

Frequently asked questions

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