---
title: "Flexor Carpi Ulnaris | Anatomy and Physiology I"
description: "Flexor carpi ulnaris is a forearm muscle that flexes and adducts the wrist, with origins on the humerus and ulna and insertion on the pisiform."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/flexor-carpi-ulnaris"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 11"
---

# Flexor Carpi Ulnaris | Anatomy and Physiology I

## Definition

Flexor carpi ulnaris is a forearm muscle in Anatomy and Physiology I that flexes and adducts the wrist. It helps stabilize the wrist during hand movement and is innervated by the ulnar nerve.

## What It Is

Flexor carpi ulnaris is a muscle in the anterior forearm that moves the wrist. Its main actions are flexion, which bends the hand toward the forearm, and adduction, which pulls the hand toward the ulna side of the wrist, the pinky side.

It starts from two places: the medial epicondyle of the humerus and the posterior border of the ulna. That dual origin matters because it links the muscle to both the upper arm and the forearm. The tendon then travels to the wrist and inserts on the pisiform bone and the base of the fifth metacarpal.

Because it crosses both the elbow region and the wrist, flexor carpi ulnaris is classified as a long muscle. In Anatomy and Physiology I, that classification is based on shape and arrangement, not just on whether the muscle is physically huge. Long muscles are built for movement over a joint, and this one is a good example of how muscle structure supports function.

The ulnar nerve supplies the muscle. If you are tracing nerve function in a lab or lecture diagram, this is the nerve to connect with the muscle’s motor action. That connection helps explain why ulnar nerve problems can affect grip stability and wrist motion on the pinky side of the hand.

Flexor carpi ulnaris also helps stabilize the wrist. When you grip a pencil, hold a weight, or push against a desk, the wrist needs to stay steady while the fingers and forearm muscles do their jobs. This muscle contributes to that stability so the hand does not wobble during forceful movements.

A common way to think about it is by motion plus location. If a question shows a forearm muscle on the ulnar side and asks about bending the wrist toward the little finger, flexor carpi ulnaris is the match.

## Why It Matters

Flexor carpi ulnaris shows how A&P connects anatomy, movement, and nerve supply in one structure. It is not just a name to memorize. It gives you a concrete example of how a muscle’s origin, insertion, and line of pull determine what movement it can produce at a joint.

This term also helps you read muscle diagrams and lab models more accurately. If you can identify the ulnar side of the forearm, the pisiform bone, and the wrist joint, you can trace why this muscle flexes and adducts the hand. That kind of tracing is a big part of muscle-system questions.

It matters for understanding stabilizers too. A lot of wrist muscles do not just create motion, they keep the joint steady while the hand applies force. Flexor carpi ulnaris is a good example of a muscle that contributes to positioning and control, not only movement.

The nerve connection matters in clinical-style thinking as well. When the ulnar nerve is involved, you can connect nerve anatomy to changes in hand function instead of treating each system separately. That is exactly the kind of systems-based thinking Anatomy and Physiology I is built around.

## Connections

### Flexion

Flexor carpi ulnaris produces flexion at the wrist, so this movement term is one of the first things to connect to the muscle. In lab or quiz questions, flexion means decreasing the angle between the palm and the forearm. If the prompt asks which muscle bends the wrist forward, this is the action you look for.

### Adduction

Adduction at the wrist means moving the hand toward the ulnar side, or pinky side, of the forearm. Flexor carpi ulnaris is one of the main muscles associated with that motion. If you remember the direction of pull, you can separate it from wrist extensors and from muscles that act more toward the thumb side.

### Wrist Joint

The wrist joint is where flexor carpi ulnaris does its main job, even though the muscle starts farther up the forearm. Its line of pull crosses the joint, which is why its contraction can bend and shift the hand. This is a useful example of how a muscle can influence a joint without sitting directly on top of it.

### [Periosteum](/anatomy-physiology/key-terms/periosteum)

The periosteum is the connective tissue covering bones, and many muscles attach to bones through tendons anchored near it. Flexor carpi ulnaris begins on bony landmarks of the humerus and ulna, which are sites where muscle attachment is organized through the skeletal framework. That connection helps explain how muscle force gets transmitted to bone.

## On the AP Exam

A quiz label question might show a forearm diagram and ask you to name the muscle that flexes and adducts the wrist, or to identify the ulnar-sided muscle attached to the pisiform. In a lab practical, you may need to point to the origin, insertion, or nerve supply on a model or cadaver image. If the question asks about movement, trace the action back to the joint and then match the line of pull to the muscle name. If it asks about classification, remember that flexor carpi ulnaris is a long muscle because it crosses joints and creates movement across a distance. When you see wrist stabilization in a clinical case or movement analysis, this muscle is a good one to mention.

## flexor carpi ulnaris vs Flexor Hallucis Brevis

These muscles sound similar because both are flexors, but they act on different body regions. Flexor carpi ulnaris moves the wrist in the forearm, while flexor hallucis brevis acts on the big toe in the foot. If the question is about hand or wrist motion, choose flexor carpi ulnaris. If it is about toe flexion, it is the foot muscle instead.

## Key Takeaways

- Flexor carpi ulnaris is a forearm muscle that flexes and adducts the wrist.
- Its origin on the medial epicondyle of the humerus and posterior ulna helps explain its pull across the wrist.
- The muscle inserts on the pisiform and base of the fifth metacarpal, which places it on the ulnar side of the hand.
- It is innervated by the ulnar nerve, so nerve and muscle questions often go together.
- In Anatomy and Physiology I, this muscle is a strong example of how structure, movement, and joint stabilization connect.

## FAQs

### What is flexor carpi ulnaris in Anatomy and Physiology I?

Flexor carpi ulnaris is a forearm muscle that flexes and adducts the wrist. It runs along the ulnar side of the forearm and attaches near the wrist at the pisiform and fifth metacarpal. In A&P, it is often used to show how muscle attachments create specific joint movements.

### Where does flexor carpi ulnaris attach?

It originates from the medial epicondyle of the humerus and the posterior border of the ulna. It inserts on the pisiform bone and the base of the fifth metacarpal. Those attachment points explain why it can pull the wrist toward the pinky side while also bending it.

### What movement does flexor carpi ulnaris perform?

Its main movements are wrist flexion and wrist adduction. Flexion brings the hand toward the forearm, and adduction moves the hand toward the ulna side. If a question asks about the muscle that helps stabilize the wrist during gripping, this is a strong match too.

### Is flexor carpi ulnaris a long muscle?

Yes. In Anatomy and Physiology, it is classified as a long muscle because it crosses joints and creates movement over a distance, not because it is especially large. That makes it a good example of how muscle shape relates to function.

## Related Study Guides

- [11.5 Muscles of the Pectoral Girdle and Upper Limbs ](/anatomy-physiology/unit-11/5-muscles-pectoral-girdle-upper-limbs/study-guide/vmMeyxnPvtI7ludS)

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