Session 5: The Brachial Plexus Flashcards
What are the 5 segments of the brachial plexus called?
Proximal to distal:
- roots
- trunks
- divisions
- cords
- terminal branches (peripheral nerves)
What are the names of the trunks of the brachial plexus? How many are there?
- 3
- superior, middle and inferior
Which nerve roots go into the brachial plexus?
- C5 (superior trunk)
- C6 (superior trunk)
- C7 (middle trunk)
- C8 (inferior trunk)
- T1 (inferior trunk)
Long thoracic nerve
- C5,6,7
- supplies serratus anterior
- Emerges from the root of the neck and runs over the surface of the serratus anterior muscle which it supplies.
supraclavicular and infraclavicular branches
x
Dorsal scapular nerve
- C5
- innervates rhomboids
Divisions
- anterior and posterior
- no terminal branches coming off diviisons
Trunks
- divisions recombine to form trunks
- upper 2 anterior divisions form lateral trunk
- all posterior fibers form the posterior trunk
- anterior trunk of inferior root forms median trunk
Summary of the motor nerves of the Upper limb (spinal levels)
- C3-7 supply shoulder girdle muscles
- C5-C6 supply shoulder joint muscles and elbow flexors
- C7-C8 supply elbow joint extensors
- C6-C8 supply wrist and coarse hand muscles
- C8-T1 supply small muscles of the hand (fine movements)
=> opposing movements are generally supplied by adjacent nerves -> see slide 13)
Dermatome vs. cutaneous nerve patterns
Because of all the fibre recombination that takes place in a plexus, the pattern of cutaneous nerve distribution is very different from the dermatome pattern.
Axillary nerve
- comes of the posterior branch of the brachial plexus
- passes posteriorly and then becomes lateral
- passes under the shoulder joint
- vulnerable to shoulder dislocation
- surgical neck of the humerus damage can also damage axillary nerve
- innervates deltoid muscle
What happens in axillary nerve damage?
- deltoid muscle wasting
- teres minor also supplied by that nerve
- superior lateral cutaneous nerve of arm -> loss of sensation in that area if that nerve is damaged
What does the axillary nerve innervate?
M:
- deltoid
- teres minor
S:
- name of the area
Radial nerve injury
- posterior muscle wasting if higher up
- wrist drop
- loss of power grip (you have to extend the wrist to get an efficient power grip)
=> depends on the level of the injury (where along the course of the nerve the damage occurs)
What is a plexus?
- nerve roots from different spinal levels merge together and produce peripheral nerves.
- these nerves usually have fibres from more than one spinal level
What are the names of the cords of the brachial plexus?
- lateral (anterior divisions of superior and middle trunk -> C5,6,7)
- posterior (made of all posterior divisions -> C5,6,7,8,T1)
- medial ( anterior division of inferior trunk -> C8,T1)
What are the names of the divisions of the brachial plexus?
- there are anterior and posterior divisions of each trunk (superior, middle, inferior)
What are the terminal branches of the brachial plexus called?
- musculocutanoues
What does the thoracodorsal nerve innervate?
Latissimus dorsi
What are the cords of the brachial plexus named in relation to?
- The cords of the brachial plexus are named according to their relationship to the axillary artery.
- The posterior cord is posterior to the artery etc.
Why are the dermatomes of the upper limb not as nice as the stripes on the torso? What are the dermatomes arranged like?
- If you lean forward and put your hands to the ground you can see the normal alignment.
- the dermatomes go around the upper limb in a circle (see slide 14)
What is the difference between dermatomes and the pattern of sensory nerve distribution?
- different than dermatomes due to nerve merging
- i.e. there are multiple nerves formed from a certain spinal level so the area that is innervated by a spinal nerve can be made up of several nerves that the spinal root formed.
- dermatome vs. cutaneous pattern: Because of all the fibre recombination that takes place in a plexus, the pattern of cutaneous nerve distribution is very different from the dermatome pattern.
- see slide 15 and 16
Where is the axillary nerve derived from?
- posterior cord
What does the axillary nerve supply?
- deltoid muscle
- teres minor muscle