UPPER LIMB Neuroanatomy

Human beings for better or for worse have developed into the dominant species on this planet beyond our incredible capacity for imagination cooperation and thought is our ability to make and to do we are the only species that combines a powerful brain with an upper limb that can be used as a tool the anatomy of the upper limb enables us to position our hand in space so that we can interact with our environment large movements at my shoulder joint and elbow position my hand and small movements in the hand are used for grasping.

Anatomy of the upper limb 

Anatomical features of the upper limb provide us 

with strength flexibility and precision, we'll start close to the body core at the shoulder and move towards the hand the closer we are to the body core the larger and more powerful our muscles are as we move towards the hand we trade strength for precision now we're the only species that doesn't use the upper limb consistently for walking this has allowed us to specialize in humans the shoulder blade or scapula has moved to the back and is not anchored to the vertebral column allows for great.

Mobility and allows us to extend the reach 

into our environment, the scapula can rotate move up and down and forward and backward this mobility allows us to point our shoulder joint in multiple directions for a wide range of movement of our upper limb

These are the bones of the shoulder joint the scapula and the humerus now you can see here that the head of the humerus is really large and it has to articulate with this tiny articular facet of the scapula now you can see right away that's not stable it's never gonna hold together so how are we gonna stabilize it well if we were to stabilize it with ligaments or bones we would lose all mobility so along with the joint capsule.

We stabilize it with muscles that will 

allow the head of the humerus to be anchored but now it can also move freely here are some of the muscles of the posterior scapular region three of the rotator cuff muscles can be seen in this position this is the supraspinatus infraspinatus and teres minor for the last member of the rotator cuff we need to look at the scapula from the front. prosection

All of these muscles attach around the head of the humerus they cuff the joint and provide rotation while the shoulder joint provides large positioning movements of the entire upper limb the elbow takes on a different function it's the elbow that allows you to move your hand towards or away from your head, you can now pick up an object and examine it more closely and you can eat it the elbow allows for flexion and extension movements as well as these movements that rotate the hand pronation and supination the elbow is the articulation between three bones the humerus the radius and the ulna flexion and extension occur between the bones of the forearm and the humerus.

Flexion and extension of the elbow is 

provided by large muscles in the arm the anterior compartment provides flexion mainly with brachialis here and biceps here the posterior compartment provides extension with triceps here pronation occurs when the radius rotates on the humerus and flips the hand over supination brings the hand back into position these important movements of supination and pronation are provided by only four muscles pronation is mediated by pronator teres here and pronator quadratus pronator.

Pronator quadratus is deep to all of these muscles and wraps around  two bones allowing for this 

movement supination is a powerful movement and the most important supinator is the biceps here in the arm another supinator is located deep in the forearm and simply called supinator as we move further towards the hand our movements become smaller and more precise the wrist is a very stable joint with limited mobility if our wrist was floppy the precise movements of our hand would be shakey movements of the wrist modify and stabilize the position of the hand itself particularly obvious when grasping and unscrewing.

The rest of the wrist joint is the articulation between the radius of the forearm and the carpal bones of the hand side to side movements of the wrist are done by two flexor muscles in the anterior compartment of the forearm and three extensor muscles in the posterior compartment flexor carpi ulnaris and extensor carpi ulnaris are here on the ulnar or medial side and they can pull the hand inward or a ducted flexor carpi radialis and extensor carpi radialis long us and Brevis are on the radial or lateral side and in an opposing function abduct 

The wrist outward together they allow you to 

rotate your hand everything we've talked about so far was for one purpose to position our hand it is the first point of connection and tool for exploring and creating the world around us we get a grasp on the world with our hand when we grasp objects we can do this with power or with precision

Power requires big muscles but our hands 

are way too small for that so our hands outsource the power of large muscles to the forearm it's only their tendons that extend into the hand in this dissection of the forearm and hand large flexor muscles are located in the anterior compartment of the forearm and their tendons extend into the hand and attach to the bones of the fingers and thumb, in the same way, large extensor muscles in the posterior compartment also have tendons that project into the hand and attach to the posterior aspect of the fingers and thumb however the use of our hand is not just about the power we can perform remarkably delicate and precise movements as well these movements are done by small muscles that are actually within the hand itself these small muscles can modify movements generated.

By the large muscles of the forearm and 

make them more precise this muscle here a lumbrical muscle is one of the coolest hand muscles it does something really unique it allows us to do this movement a combination of extension and flexion we can do this because the muscle originates from a flexor tendon and extends around the finger to attach to an extensor tendon other muscles such as these in Taurasi can abduct and adduct the fingers these remarkable movements of the thumb are generated by a specialized set of muscles here these allow us to oppose the thumb to the other fingers rotated abduct and a ducted you know we own nearly everything we make do and hold with our hands to the muscles of our opposable thumbs we may take it for granted but this dexterity and opposed ability remains one of the main reasons for our dominance on this planet even with our intelligence our imagination and creativity we may never have realized our potential as a species without it.