Arm Muscles & Attachments
Here are some of the major muscles attached to the arm and their attachments:
- Biceps brachii: The biceps is a two-headed muscle located on the front of the upper arm. Its long head originates from the supraglenoid tubercle of the scapula, and the short head originates from the coracoid process of the scapula. Both heads merge and attach to the radial tuberosity of the radius bone in the forearm.
- Triceps brachii: The triceps is a three-headed muscle on the back of the upper arm. Its long head originates from the infraglenoid tubercle of the scapula, the lateral head from the posterior humerus, and the medial head from the posterior humerus, just below the radial groove. All three heads merge and attach to the olecranon process of the ulna in the forearm.
- Brachialis: The brachialis is a muscle located deep to the biceps on the front of the upper arm. It originates from the anterior surface of the humerus and attaches to the ulnar tuberosity of the ulna in the forearm.
- Brachioradialis: This muscle is located on the lateral side of the forearm. It originates from the lateral supracondylar ridge of the humerus and attaches to the styloid process of the radius.
These muscles play important roles in elbow and Forearm movements, providing strength and stability to the arm. Keep in mind that there are many more muscles in the arm with various attachments, but these are some of the major ones.
Forearm Muscles & Attachments
The forearm contains several muscles responsible for various movements of the wrist, hand, and fingers. Here are some of the key muscles and their attachments:
- Flexor Digitorum Superficialis: This muscle is located on the anterior (front) side of the forearm. It originates from the medial epicondyle of the humerus and the ulna. It attaches to the middle phalanges of the four fingers (index to little finger).
- Flexor Digitorum Profundus: Also found on the anterior side, this muscle originates from the ulna and interosseous membrane. It attaches to the distal phalanges of all four fingers.
- Flexor Carpi Ulnaris: Situated on the medial side of the forearm, it originates from the medial epicondyle of the humerus and the olecranon of the ulna. It attaches to the pisiform bone and the hamate bone in the wrist.
- Flexor Carpi Radialis: Located on the lateral side, it originates from the medial epicondyle of the humerus. It attaches to the base of the second and third metacarpal bones in the wrist.
- Extensor Digitorum: This muscle is situated on the posterior (back) side of the forearm. It originates from the lateral epicondyle of the humerus and the posterior surface of the ulna. It extends to the dorsal surface of the phalanges of all four fingers.
- Extensor Carpi Radialis Longus: Found on the lateral side of the forearm, it originates from the lateral supracondylar ridge of the humerus. It attaches to the base of the second metacarpal bone.
- Extensor Carpi Radialis Brevis: Also located laterally, it originates from the lateral epicondyle of the humerus. It attaches to the base of the third metacarpal bone.
- Extensor Carpi Ulnaris: Situated on the posterior and medial side of the forearm, it originates from the lateral epicondyle of the humerus and the posterior border of the ulna. It attaches to the base of the fifth metacarpal bone.
These muscles work in coordination to enable various movements, including flexion, extension, abduction, and adduction of the wrist, hand, and fingers.
Arm Muscles Classification
The muscles of the arm can be classified into several groups based on their primary functions. Here’s a detailed classification:
- Flexors: These muscles are responsible for bending or flexing the arm at the elbow joint. The main flexors of the arm include the biceps brachii, brachialis, and brachioradialis.
- Extensors: These muscles are responsible for straightening or extending the arm at the elbow joint. The primary extensor of the arm is the triceps brachii.
- Pronators: These muscles rotate the forearm and hand to face downwards in a pronated position. The pronator teres and pronator quadratus are the main pronators of the forearm.
- Supinators: These muscles rotate the forearm and hand to face upwards in a supinated position. The biceps brachii and supinator muscles are the primary supinators.
- Adductors: These muscles bring the arm closer to the body’s midline. The main adductor of the arm is the coracobrachialis.
- Abductors: These muscles move the arm away from the body’s midline. The deltoid muscle is the primary abductor of the arm.
- Rotators: The rotator cuff muscles, including the supraspinatus, infraspinatus, teres minor, and subscapularis, are essential for stabilizing and rotating the shoulder joint.
- Serratus Anterior: This muscle helps in protracting the scapula, allowing the arm to move forward.
Remember that some muscles may have secondary functions or assist in multiple movements. The above classification provides an overview of the primary functions of the major muscles in the arm.
Forearm Muscles Classification
The muscles of the forearm can be classified into two main groups based on their functions:
Anterior (Flexor) Compartment:
1) Flexors: These muscles are responsible for flexing the wrist and fingers, as well as pronating the forearm.
a. Flexor Carpi Radialis: Flexes and abducts the wrist.
b. Palmaris Longus: Weakly flexes the wrist.
c. Flexor Carpi Ulnaris: Flexes and adducts the wrist.
d. Flexor Digitorum Superficialis: Flexes the middle and proximal phalanges of the fingers.
e. Flexor Digitorum Profundus: Flexes the distal phalanges of the fingers.
f. Flexor Pollicis Longus: Flexes the thumb.
2) Posterior (Extensor) Compartment:
Extensors: These muscles are responsible for extending the wrist and fingers, as well as supinating the forearm.
a. Extensor Carpi Radialis Longus and Brevis: Extend and abduct the wrist.
b. Extensor Carpi Ulnaris: Extends and adducts the wrist.
c. Extensor Digitorum: Extends the fingers at the metacarpophalangeal joints.
d. Extensor Digiti Minimi: Extends the little finger.
e. Extensor Pollicis Longus and Brevis: Extend the thumb.
These muscles work in coordination to provide movement and stability to the forearm, wrist, and hand. Keep in mind that there are other muscles in the forearm that play supporting roles, but the ones mentioned above are the primary ones based on function.
Muscle Innervation
Muscles are innervated by nerves, and this innervation allows them to contract and perform movements. The nervous system sends signals through motor neurons to the muscles, causing them to contract or relax as needed for various movements and actions.
Arm Muscle Innervation
The innervation of the muscles in the arm is primarily governed by nerves that originate from the brachial plexus, a complex network of nerves formed by the spinal nerves C5 to T1. The brachial plexus splits into various branches, each supplying different muscles in the arm.
- Musculocutaneous Nerve: This nerve innervates the biceps brachii and the brachialis muscles. It arises from the lateral cord of the brachial plexus and provides sensory innervation to the lateral forearm.
- Axillary Nerve: The axillary nerve innervates the deltoid and teres minor muscles. It branches from the posterior cord of the brachial plexus and is responsible for the motor control and sensation in the shoulder region.
- Radial Nerve: The radial nerve is the largest nerve in the arm and supplies many muscles, including the triceps brachii, anconeus, and the extensor muscles of the forearm. It runs down the arm on the posterior aspect and provides motor control and sensation to the posterior arm, forearm, and hand.
- Median Nerve: The median nerve innervates various muscles in the forearm, including the flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus, and pronator teres. It also supplies sensation to the palm and the palmar side of the thumb, index, middle, and half of the ring finger.
- Ulnar Nerve: The ulnar nerve innervates the flexor carpi ulnaris, flexor digiti minimi, and the intrinsic muscles of the hand. Additionally, it provides sensory innervation to the palmar and dorsal aspects of the little finger and the medial half of the ring finger.
The coordinated action of these nerves ensures proper muscle contraction and movement in the arm, allowing us to perform various activities, from simple tasks to complex movements. Keep in mind that this is a general overview, and there might be additional variations or minor innervation patterns in specific individuals.
Forearm Muscle Innervation
The muscles of the forearm are innervated by the median, ulnar, and radial nerves, which originate from the brachial plexus. Let’s go into more detail about the innervation of specific forearm muscles:
- Median Nerve: The median nerve supplies several muscles in the forearm, including the pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum superficialis, and the lateral half of the flexor digitorum profundus. It also innervates the muscles of the thenar eminence in the hand, responsible for thumb movements.
- Ulnar Nerve: The ulnar nerve innervates the flexor carpi ulnaris, medial half of the flexor digitorum profundus, and the intrinsic muscles of the hand (such as the hypothenar muscles and the interossei) that control finger movements and grip strength.
- Radial Nerve: The radial nerve supplies the muscles on the posterior aspect of the forearm. It innervates the extensor carpi radialis longus and brevis, extensor carpi ulnaris, and the superficial and deep extensors of the fingers. The radial nerve also innervates the brachioradialis and the triceps brachii, which are muscles located above the elbow joint.
The innervation of these muscles allows for various movements of the forearm, including flexion, extension, pronation, and supination. Damage or compression of these nerves can lead to weakness or loss of function in the corresponding muscles, causing issues with hand and forearm movements.
