Upper Extremity

Brachial Plexus

The brachial plexus supplies nerve innervation to most of the upper limb.  The roots of the brachial plexus start at C5 and runs through T1.  They pass through the anterior and middle scalene muscles with the subclavian artery.  There are three trunks within the brachial plexus: superior, middle and inferior.  Each trunk emerges into an anterior and posterior division.  All the posterior divisions merge to form the posterior cord.  The anterior divisions of the superior trunk and the middle trunk meet to form the lateral cord and the anterior division of the inferior trunk merge to make the medial cord.  The figure below shows the organization of the brachial plexus from the roots to the cords. 

A neuronal disease associated with the brachial plexus is "acute brachial plexus neuritis".  This disease has no known cause.  Symptoms of brachial plexus neuropathy(BPN) include severe pain around the shoulder that start at night.  This condition typically is followed by weakness in the muscles and sometimes muscle atrophy.  BPN often follows some type of event like upper respiratory infection, vaccination, or non specific trauma.

Axillary Artery

The borders of the axillary artery are the lateral bordero of the first rib and the inferior border of the teres major.  As it passes the pectoralis minor it becomes the brachial artery.  The axillary artery is divided into three parts.  The first part of the axillary artery only has one branch and that is the superior thoracic artery.  The borders of the first part of the artery are the lateral border of the first rib and the medial border of the pectoralis minor.  The second part of the artery has two branches, and those are the thoracoacromial trunk and the Lateral thoracic artery.  The third part of the axillary artery consists of three branches which are the Subscapular artery, Anterior humeral circumflex artery, and the Posterior humeral circumflex artery.  The subscapular artery has two artery branching off of it, and they are the circumflex scapular artery and the thoracodorsal artery. The figure below is a representation of the axillary artery transcending into the brachial artery as it passes the pectoralis minor.


The axillary artery can be palpated on the most inferior part of the axilla. The third part of the axillary artery can be compressed against the humerus as a necessary result of some type of trauma.  If compression is required that is more proximal, the origin can be compressed as the subclavian artery crosses the first rib.  The first part of the axillary artery can enlarge and can result in an axillary artery aneurysm.  An axillary artery aneurysm will compress the trunks of the brachial plexus, and this will cause pain and loss of sensation on certain areas of the skin that the nerves of the brachial plexus innervate.  Aneurysms occur frequently in baseball pitchers because of the rapid movement of the arm.

The acromioclavicular joint is a plane type of synovial joint.  This joint allows the acromion of the scapula to articulate with the acromion of the clavicle.  The joint capsule contains a fibrous layer that is lined with a synovial membrane.  The ligaments of the acromioclavicular joint consist of the acromioclavicular ligament, coracoclavicular ligament (as shown in figure below), conoid ligament and the trapezoid ligament.  Movements of the acromioclavicular joint consists of rotation of the acromion of the scapula on the acromion of the clavicle.  Blood is supplied to the AC joint by the thoracoacromial arteries and innervation sources are the lateral pectoral and axillary nerves.  Shown below are some of the attributes of the acromioclavicular joint. 


The acromioclavicular joint is a joint that can be easily injured if exposed to some type direct trauma.  Oftentimes, the cause of these forceful blows are sports like football, soccer, hockey  or even martial arts.  Dislocation of the acromioclavicular joint is very common due to a hard fall on the shoulder or outstretched upper limb.  A dislocation of the acromioclavicular joint is considered severe when the acromioclavicular ligament and the coracoclavicular ligament are torn . This is due to the separation of the shoulder from the clavicle and the weight of the upper limb falls. 

Advanced Human Anatomy Post #1

Characteristics of the Cervical Vertebrae
There are seven cervical vertebrae in the average human vertebral column.  These vertebrae are found below the cranium and above the thoracic vertebrae.  Cervical vertebrae are smaller than any of the other vertebrae, because they do not bear as much weight as other vertebrae. They have the greatest range of motion.  Vertebra C1(atlas) is the most superior vetebra of the cervical vertebrae. The lateral masses of  the atlas articulate with the cranium at the occipital condyles of the cranium.  C1 is unique in that it has no spinous process or body.  The atlas rotates on the superior articular facets of C2 (axis) .  The axis is the strongest of the cervical vertebrae, and contains a tooth like projection called the dens. The head rotates about the dens. 

Injuries to the axis are the most common of the cervical vertebrae.  A fracture at the pars interarticularis is called traumatic spondylolysis.  Traumatic spondylolysis is usually the result of "hyperextension of the head on the neck".  This should not be confused with whiplash injury, which is hyperextension of the head and neck.  Hyperextension of the head on the neck is the premise behind the execution of criminals by hanging. 

Curvatures of the Vertebral Column
The human adult vertebral column has four curvatures.  There are two kyphoses in the thoracic and the sacral region, and there are two lordoses in the cervical and lumbar region.  The sacral and thoracic kyphoses are considered the primary curvatures of the human adult vertebral column.   These curvatures develop during the fetal period of human development. These curvatures are kept throughout the lifetime of human. The secondary curvatures are the cervical and lumbar lordoses.  The secondary curvatures start to develop during the late fetal period, but they do not become apparent until infancy. 



Abnormal curvatures in the human vertebral column must be observed in anatomical position.  Excessive thoracic kyphosis is commonly known as hunchback or humpback. It is more commonly called Dowager's hump in older women as a result of osteoporosis, but it is also found in older men as well. The vertebrae erode and collapse causing a hump in the thoracic region and a loss in height.   Excessive throracic kyphosis is characterized by an excessive posterior curve in the thoracic region. 



Intervertebral disks are the cushions between the vertebral bodies.  They are classified as symphyses joints and allow movement between individual vertebrae.  IV discs act as shock absorbers for the vertebral column.  IV discs contain an anulus fibrosus and a nucleus pulposus.  The anulus fibrosus runs the outside of the IV disc and consists of fibrocartilage. The nucleus pulposus is considered the core of the IV disc. It contains mostly water and is held mostly accountable for the flexible nature of the IV disc.  It is avascular, meaning, that it receives nutrients by diffusion from the anulus fibrosus and the verterbral body. 

When there is a protrusion of the nucleus pulposus, it is often recognized as a hernia in the lower back.  Herniation of the nucleus pulposus causes pain in the lower back as well as in the lower limbs.  Although there are many causes of lower back pain, herniation of the nucleus pulposus is usually an asymptomatic finding.  Most nucleus pulposus herniations occur in the lumbar and lumbosacracal region.  This is due to the IV discs being the largest in this region and have the greatest amount of movement.