The axilla and brachial plexus Flashcards
What is the lateral wall of the axilla made up from?
The humerus
Importance of the axilla?
An important place for things which serve the upper limb to enter and leave such as vessels and nerves
Which muscles are found medially, posteriorly and anteriorly to the axilla?
Medial: serratus anterior
Posterior: subscapular muscles
Anterior: pectoral muscles
The apex of the axilla forms a triangle between…
- What is the relevance of this triangle?
The 1st rib, the superior margin of the scapula and the clavicle
- It is over the first rib that major vessels and nerves pass, through this triangle area, to enter the axilla and serve the upper limb
What are the contents of the axilla?
Axillary vessels - Axillary vein and artery
Axillary lymphatics
Brachial plexus
Where does the axillary vein pass under the clavicle? Why is this clinically relevant
At the junction of the medial third and middle third
- Clinically important as you can put a needle into this vein and insert a line, which is an access point/line to the heart and venous system
What are the 5 named lymph node groups through which lymphatic vessels drain the breast and upper limb and enter the axillary lymphatic system?
- Lateral
- Subscapular
- Pectoral
- Central
- Apical
What is the brachial plexus?
A network of nerves that forms between the emergence of spinal nerves that are supplying the upper limb from the lateral aspect of the vertebral column through the vertebral foramen
- Supply motor and sensation to the upper limb
From which vertebral level does the brachial plexus originate?
C5-T1
The roots of the brachial plexus are formed from?
Ventral primary rami
The brachial plexus branches go from roots –>….
Roots –> Trunks –> Divisions –> Cords
How many trunks does the brachial plexus have? How do the cervical vertebrae C5-T1 contribute to this?
3 - superior, middle and inferior
- C5 & C6 merge to give the superior trunk
- C7 forms the middle trunk
- C8/T1 have merged to give the inferior trunk
How do each of the trunks of the brachial plexus divide?
Each trunk divides into a posterior and anterior division
Which of the brachial plexus cords do the superior and middle trunk contribute to?
The lateral and posterior cords
Superior anterior –> lateral cord
Superior posterior –> posterior cord
Middle anterior –> lateral cord
Middle posterior –> posterior cord
Which of the brachial plexus cords does the inferior trunk contribute to?
The posterior and medial cords of the brachial plexus
Inferior posterior –> posterior cord
Inferior anterior –> medial cord
What happens to the lateral, posterior and medial cords of the brachial plexus?
They branch to form peripheral nerves that supply the skin with sensation and motor to muscles of the UPPER LIMB
What is the principal nerve which originates from the lateral cord of the brachial plexus?
The musculocutaneous nerve
- This is formed by the anterior division of the brachial plexus
Where does the musculocutaneous nerve supply?
The uppermost part of the upper limb
- Coracobrachialis
- Biceps brachii
- Brachialis
- FLEXORS
The anterior divisions of nerve plexuses give rise to nerves that supply which muscle types?
Flexors and adductors
The posterior cord of the brachial plexus has two main branches, what are they?
Axillary nerve
Radial nerve
Where does the radial nerve supply?
It supplies motor to extensor muscles of the upper arm, then travels through the radial groove into the forearm where it supplies many of the extensor muscles here.
- It also has a long sensory branch which supplies the dorsum of the hand
The anterior division of the medial and lateral cords of the brachial plexus come together to form which nerve?
The median nerve
Where does the median nerve supply?
It passes through the arm without giving off any branches BUT it supplies the FLEXOR muscles of the forearm and a few muscles in the hand, more so the radial aspects where the thumb is
The anterior division of the medial cord gives rise to which nerve?
The ulnar nerve
Where does the ulnar nerve supply?
It passes, like the median nerve, all the way through the arm to supply just a few muscles in the forearm and many small muscles in the hand
The sensory fibres carried by the median nerve supply…
The thumb, the index finger and half of the ring finger
The sensory fibres carried by the ulnar nerve supply…
The other half of the ring finger and the little finger
The sensory fibres carried by the radial nerve supply…
The dorsum of the hand
- Exclusively to the webbing of the thumb and index
- As does the ulnar nerve’s dorsal branch
Where does the median nerve EXCLUSIVELY supply sensation?
Tip of the index and middle fingers
Where does the ulnar nerve EXCLUSIVELY supply sensation?
At the tip of the little finger
Where does the radial nerve EXCLUSIVELY supply sensation?
At the webbing between the thumb and index
What is the innervation type supplied by the brachial plexus?
Segmental
What is meant by a segmental pattern of innervation?
The muscles are innervated by particular spinal nerves from particular segments
- Segmental innervation refers to the distribution (innervation) of nerves within an organ or muscle. These nerves are attached to a segment of the spine. Segmental innervation can be mapped through stimulation of the nerve at the spinal segment.
The muscles of the upper arm, particularly the shoulder, are innervated by which vertebral segments?
C5 and C6
The lower segments of the arm, including the fingers and thumbs are innervated by which vertebral segments?
C6, C7 and C8
The hand is innervated by which vertebral segment? Clinical importance?
Th1
- V IMPORTANT as any injury to Th1 will paralyse the intrinsic muscles of the hand, we wont be able to perform fine movements (adduction/abduction of digits)
What is Erb’s palsy? Clinical manifestation?
An injury to the upper roots of the brachial plexus - C5 and C6
- Affects upper myotomes and dermatomes
- Results in paralysis to muscles around shoulder and arm hangs limply by the side
What is Klumpke’s paresis? Causes?
Injury to the lower roots of the brachial plexus, particularly Th1
- Th1 supplies sensation over medial side of forearm and supplies motor sensation to small muscles of the hand (adduction/abduction of digits) - so this is lost
- Through birth injuries or stabs & gunshot wounds
