Anatomy Course Module 5 Sample

Module Five Course Index

Lesson 1:

The Arm: Anterior compartment

Lesson 2:

The Arm: Posterior compartment

Quiz

Lesson 3:

The Arm: Anterior forearm

Quiz

Lesson 4:

The Arm: Posterior region of the forearm

Quiz

Module Five Lesson One & Two

The Arm

The Arm is the first segment of the free upper limb (more mobile part of the upper limb independent of the trunk) and the longest segment of the limb. It extends between and connects the shoulder and the elbow and consists of anterior and posterior regions of the arm, centred around the humerus.

• The arm extends from the shoulder to the elbow.

• Two types of movement occur between the arm and the forearm at the elbow joint: flexionextension and pronation – supination.

TIP: to views muscles in motion search by muscle name and then search motions.

• The muscles performing these movements are clearly divided into anterior (flexors) and posterior groups (extensors), separated by the humerus and medial and lateral intermuscular septae (Images 1 & 2 below).

• The chief action of both groups is at the elbow joint, but some muscles also act at the glenohumeral joint.

• The superior part of the humerus provides attachments for tendons of the shoulder muscles IMAGE 1

Image 1. Cross section of left arm

Lesson One The anterior flexor compartment App: Click or copy this link to view a 4 min video on the anterior compartment of the arm.

Note, the brachioradialis is a muscle of the extensor compartment of the forearm.

Biceps brachii • As the term biceps brachii indicates, the proximal attachment of this fusiform muscle usually has two heads (bi, two + L. caput, head).

• The two heads of the biceps arise proximally by tendinous attachments to processes of the scapula, their fleshy bellies uniting just distal to the middle of the arm images below.

• Approximately 10% of people have a third head to the biceps.

• When present, the third head extends from the superomedial part of the brachialis (with which it is blended), usually lying posterior to the brachial artery.

• In either case, a single biceps tendon forms distally and attaches primarily to the radius.

Image below • Although the biceps is located in the anterior compartment of the arm, it has no attachment to the humerus.

IMAGE 4

Image 4.

Biceps brachii •

As the term biceps brachii indicates, the proximal attachment of this fusiform muscle usually has two heads

IMAGE 5

Image 5.

Bicipital aponeurosis

Lesson Two

The posterior compartment

App: Click or copy the link to view a 4 min. video on the posterior compartmenthttps://3d4medic.al/t57gPmsF

Triceps brachii • The triceps brachii is a large fusiform muscle in the posterior compartment of the arm (Images 8-10 below).

• As indicated by its name, the triceps has three heads: long, lateral, and medial.

• The triceps is the main extensor of the forearm.

• Because its long head crosses the glenohumeral joint, the triceps helps stabilize the adducted glenohumeral joint by serving as a shunt muscle, resisting inferior displacement of the head of the humerus.

• The long head also aids in extension and adduction of the arm • The medial head is the workhorse of forearm extension, active at all speeds and in the presence or absence of resistance.

• The lateral head is strongest but is recruited into activity primarily against resistance (Hamill and Knutzen, 2003).

• Pronation and supination of the forearm do not affect triceps operation.

• Just proximal to the distal attachment of the triceps is a friction-reducing sub-tendinous olecranon bursa, between the triceps tendon and the olecranon.

IMAGE 8

Image 8. Triceps brachii

IMAGE 3

Image 3. The left forearm, looking down toward the hand with the forearm facing up, or “supinated.” Extensor muscles are at the bottom of the image and the flexor muscles are in the top of the image in the anterior compartment.

• F or the distal forearm, wrist, and hand to have minimal bulk to maximize their functionality, they are operated by “remote control” by extrinsic muscles having their bulky, fleshy, contractile parts located proximally in the forearm distant from the site of action. Their long, slender tendons extend distally to the operative site, like long ropes reaching to distant pulleys.

• Because the structures on which the muscles and tendons act (wrist and fingers) have an extensive range of motion, a long range of contraction is needed, requiring that the muscles have long contractile parts as well a long tendon(s).

• The forearm proper is not, in fact, long enough to provide the required length and sufficient area for attachment proximally, so the proximal attachments (origins) of the muscles must occur proximal to the elbow – in the arm – provided by the humerus. See Image 4.

IMAGE 4

Image 4. Showing some of the attachment points of the extensor muscles of the forearm.

There are multiple muscle attachments at the lateral condyle, indicted by the number of red dots. Each red dot represents the attachment point of an extensor muscle.

• Generally, flexors lie anteriorly and extensors posteriorly; however, the anterior and posterior aspects of the distal humerus are occupied by the chief flexors and extensors of the elbow (see Module “Arm”). To provide the required attachment sites of the flexors and extensors of the wrist and fingers, medial and lateral extensions (epicondyles and supra-epicondylar ridges) have developed from the distal humerus. Image 5 below.

• The medial epicondyle and supra-epicondylar ridge provide attachment for the forearm flexors. Image 6.

IMAGE 5

Image 5.

Anterior surface of right humerus. The purple region displays the medial and lateral condyles. The region above is called the supra-epicondylar ridges. At the proximal end of the humerus the greater and lesser tubercles are highlighted in green.

IMAGE 6

Image 6. (Right arm) forearm flexors attach to the medial surface of the distal humerus

IMAGE 6

Coracobrachialis • The coracobrachialis is an elongated muscle in the superomedial part of the arm.

See image above and Image 6.

• The coracobrachialis helps flex and adduct the arm and stabilize the glenohumeral joint.

• With the deltoid and long head of the triceps, it serves as a shunt muscle, resisting downward dislocation of the head of the humerus, as when carrying a heavy suitcase.

Image 6. The coracobrachialis IMAGE 7

Brachialis • A flattened fusiform muscles lying posterior/deep to the biceps (see Image 7).

• Distal attachment covers the anterior part of the elbow joint • Main flexor of the forearm • Flexes the forearm in all position, regardless of the degree of pronation or supination • Regarded as the workhorse of the elbow flexor.

Image 7. Brachialis

IMAGE 9

Image 9.

Triceps brachii

IMAGE 10

Image 10.

Anterior perspective of trips highlighting the medial head, almost totally obscured by the lateral aand long heads when looking from the posterior perspective

Compartments of Forearm • As in the arm, the muscles of similar purpose and innervation are grouped within the same fascial compartments in the forearm.

• The flexors and pronators of the forearm are in the anterior compartment • The extensors and supinators of the forearm are in the posterior compartment and are all served by the radial nerve • See Images 2 & 3.

• Although the proximal boundary of the forearm per se is defined by the joint plane of the elbow, functionally the forearm includes the distal humerus.

IMAGE 2

Image 2.

A cross section of the forearm, cut at roughly this angle, is below in image 3

2. An intermediate layer, consisting of one muscle (flexor digitorum superficialis).

Image 11.

• Near the wrist, the Flexor digitorum superficialis (FDS) gives rise to four tendons, which pass deep to the flexor retinaculum through the carpal tunnel to the fingers.

See image 11 below.

• The four tendons are enclosed (along with the four tendons of the flexor digitorum profundus) in a synovial common flexor sheath.

• The FDS flexes the middle phalanges of the medial four fingers at the proximal interphalangeal joints.

• In continued action, the FDS also flexes the proximal phalanges at the metacarpophalangeal joints and the wrist joint. The FDS is capable of flexing each finger it serves independently.

IMAGE 11

Image 11. FDS of anterior right forearm.