Brachial Plexus Anatomy
The brachial plexus is a network of nerves that is responsible for innervation of the shoulder and arm region. Read on to know all about brachial plexus anatomy...
The brachial plexus is a particular arrangement of nerve fibers that run from the spine and are formed by the ventral rami of the lower four cervical and the first thoracic nerve roots. This network of nerves proceeds through the neck, the axilla (armpit) region and into the arm. The brachial plexus is a very important structure that is responsible for cutaneous and muscular intervention of the entire upper limb, except for the trapezius muscle (which is neurally innervated by the spinal accessory nerve) and the skin near the axilla, which is innervated by the intercostobrachial nerve. Given below is a detailed explanation of the brachial plexus anatomy, which will help you understand the structure and innervation of this neural plexus better.
Anatomy of Brachial Plexus
The anatomy of the brachial plexus will be better understood with the help of the brachial plexus anatomy diagram on the right. As is visible from the diagram, the brachial plexus is divided into roots, trunks, divisions, cords and branches.
The rami (divisions) of the spinal nerves from C5 to T1 are referred to as the roots of brachial plexus. These are five roots that come from C5, C6, C7, C8 and T1. These five roots merge together in a certain order to form three trunks. C5 and C6 roots merge to form the superior or the upper trunk. C7 travels alone and continues as the middle trunk. C8 and T1 roots join to form the inferior or lower trunk.
Each of these trunks then split into two, to form a total of six divisions. These are the anterior divisions of the upper, middle and lower trunks and the posterior divisions of the upper, middle and lower trunks. These six divisions then once again merge to form three cords. These cords are named in accordance with their relative position with respect to the axillary artery.
The posterior cord is formed by the three posterior divisions of the trunks C5 and T1. The posterior cord gives rise to the upper subscapular nerve, lower subscapular nerve, thoracodorsal nerve, axillary nerve and the radial nerve. The axillary nerve gives sensation to the shoulder region, while the radial nerve innervates the upper and lower arm.
The lateral cord is the anterior division from the upper and middle trunk, that is, from C5 and C7. The lateral cord gives rise to the lateral pectoral nerve which innervates the pectoralis major muscle. The mucocutaneous nerve is the second nerve, which innervates the biceps. The last nerve that branches out from the lateral cord is the median nerve. This partly arises from the medial cord as well.
The medial cord is the last cord which gives rise to various nerves. It is a continuation of the anterior division of the lower trunk (C8 - T1). The median pectoral nerve innervates the pectoralis muscle. The medial brachial cutaneous nerve and the medial antebrachial cutaneous nerve arise from T1, and C8 and T1 respectively. The median nerve partly arises from the medial cord and partly from the lateral cord. The ulnar nerve is the last nerve, which originates in nerve roots C7, C8 and T1. It provides sensation to the ring finger and the pinky finger.
This was a brief look at the brachial plexus anatomy. Brachial plexus injuries or lesions can occur as a result of shoulder trauma, or due to inflammations and tumors in the region. By studying the brachial plexus anatomy on MRI, one can locate the exact point of trauma. Furthermore, the signs and symptoms will also help to indicate which section of the plexus has been injured. However, all of this can only be done if the anatomy is something that one is thorough with!
Anatomy of Brachial Plexus
The anatomy of the brachial plexus will be better understood with the help of the brachial plexus anatomy diagram on the right. As is visible from the diagram, the brachial plexus is divided into roots, trunks, divisions, cords and branches.
The rami (divisions) of the spinal nerves from C5 to T1 are referred to as the roots of brachial plexus. These are five roots that come from C5, C6, C7, C8 and T1. These five roots merge together in a certain order to form three trunks. C5 and C6 roots merge to form the superior or the upper trunk. C7 travels alone and continues as the middle trunk. C8 and T1 roots join to form the inferior or lower trunk.
Each of these trunks then split into two, to form a total of six divisions. These are the anterior divisions of the upper, middle and lower trunks and the posterior divisions of the upper, middle and lower trunks. These six divisions then once again merge to form three cords. These cords are named in accordance with their relative position with respect to the axillary artery.
The posterior cord is formed by the three posterior divisions of the trunks C5 and T1. The posterior cord gives rise to the upper subscapular nerve, lower subscapular nerve, thoracodorsal nerve, axillary nerve and the radial nerve. The axillary nerve gives sensation to the shoulder region, while the radial nerve innervates the upper and lower arm.
The lateral cord is the anterior division from the upper and middle trunk, that is, from C5 and C7. The lateral cord gives rise to the lateral pectoral nerve which innervates the pectoralis major muscle. The mucocutaneous nerve is the second nerve, which innervates the biceps. The last nerve that branches out from the lateral cord is the median nerve. This partly arises from the medial cord as well.
The medial cord is the last cord which gives rise to various nerves. It is a continuation of the anterior division of the lower trunk (C8 - T1). The median pectoral nerve innervates the pectoralis muscle. The medial brachial cutaneous nerve and the medial antebrachial cutaneous nerve arise from T1, and C8 and T1 respectively. The median nerve partly arises from the medial cord and partly from the lateral cord. The ulnar nerve is the last nerve, which originates in nerve roots C7, C8 and T1. It provides sensation to the ring finger and the pinky finger.
This was a brief look at the brachial plexus anatomy. Brachial plexus injuries or lesions can occur as a result of shoulder trauma, or due to inflammations and tumors in the region. By studying the brachial plexus anatomy on MRI, one can locate the exact point of trauma. Furthermore, the signs and symptoms will also help to indicate which section of the plexus has been injured. However, all of this can only be done if the anatomy is something that one is thorough with!
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