Arm and Elbow Flashcards
What are the 5 big terminal branches of the brachial plexus?
Musculocutaneous Axillary Median Radial Ulnar
What is function of brachial plexus?
Gives motor and sensory innervation to upper limb
What is the brachial plexus composed of?
The ventral rami of the spinal nerves from the spinal cord segments C5 (C5, C6, C7, C8) to T1
When spinal nerves exist the spinal canal, how do they leave?
Via intervertebral foramen
What are dermatomes?
Areas of skin that are innervated by a single spinal nerve
What do spinal nerves contain?
Mixed - motor and sensory information
What do anterior rootlets of a spinal nerve contain?
Motor information
What do posterior/dorsal rootlets contain?
Sensory information
What do the anterior/ventral rootlets come together to form?
What do the posterior/dorsal rootlets come together to form?
An anterior root
A posterior root
What do the ventral and dorsal roots join to form?
Mixed spinal nerve –> this then exits canal via intervertebral foramen
What happens once spinal nerve leaves intervertebral foramen?
It splits into an ventral ramus and a posterior ramus that head to the respective sides of the body (these contain both motor and sensory info)
Is the ventral or dorsal ramus larger?
Anterior
What rami form the brachial plexus?
Anterior rami of C5, C6, C7, C8 and T1
The anterior rami of C5-T1 form the roots of the brachial plexus. Some of these roots come together to form common nerves. Which roots come together?
C5 and C6 join to form a common nerve
C7 continues on its on
C8 and T1 join to form a common nerve
What is the common spinal nerve of C5 and C6, of C8 and T1, and C7 on its own collectively known as?
The trunks of the brachial plexus
Superior trunk: C5 and C6
Middle trunk: C7
Inferior trunk: C8 and T1
What do the superior, middle and inferior trunks then divide into?
Each trunk divides into an anterior segment and a posterior segment
- The anterior segments of the superior and middle trunks come together
- The anterior trunk of the inferior trunk continues alone
- The posterior segments of all 3 trunks come together
These are called the divisions
What do the divsions then turn into?
Cords
What are the cords of the brachial plexus called? How are they formed?
- Lateral –> formed from anterior divsions of superior and middle trunks
- Posterior –> formed from posterior divisions of all 3 trunks
- Medial –> formed from continuation of anterior division of inferior trunk
How are the cords named?
According to their location to the axillary artery (lateral, posterior, medial)
What do the cords then turn into?
The 5 terminal branches (formed by the 3 cords)
What does the posterior cord give rise to?
Posterior cord gives rise to 2 out of 5 terminal branches:
- Axillary nerve –> a smaller branch given off the posterior cord
- The rest of the cord continues as the radial nerve
Where does the axillary nerve carry nerve fibres from?
C5-C6
What does the axillary nerve innervate?
Travels posteriorly, behind surgical neck of humerus (where it is vulnerable to fracture), emerge in the posterior pectoral region through the quadrilateral space, innervates deltoid and teres minor
Deltoid and teres minor
Skin on upper lateral arm
Where does the radial nerve carry fibres from?
C5-T1
What does the radial nerve innervate?
Goes into posterior portion of arm to supply:
- Posterior arm (triceps) and forearm muscles
- Skin of the arm and hand
What happens to the lateral cord?
Divides into 2 branches
What happens to the medial cord?
Divides into 2 branches
What forms the terminal median nerve?
One of the divsions from the lateral cord and one of the divisions from the medial cord come together to form the terminal median nerve
Where does the median nerve carry fibres from?
C5-T1
What does the median nerve innervate?
Most atnerior forearm muscles, small muscles of the thumb, skin of the hand
Passes through arm but doesn’t innervate any muscles until it reaches the forearm
What does the 2nd division of the lateral cord form?
The terminal musculocutenous nerve
Where does the musculocutaneous nerve carry fibres from?
C5-C7
What does the musculocutaenous nerve innervate?
Travels anteriorly –> Muscles of the anterior arm, skin of the arm
What happens to the 2nd division of the medial nerve?
Continues down the arm as the terminal ulnar nerve
Where does the ulnar nerve carry fibres from?
C8-T1
What does the ulnar nerve innervate?
2 anterior forearm muscles, most small muscles of the hand, skin of the hand
What is an important nerve landmark of the brachial plexus?
M shape –> lies anterior to axillary artery
3 legs of M: musculocutenous, median and ulner nerve
What are the forearm bones?
The ulna and radius
What forms the elbow joint?
The distal humerus articulates with the ulna and radius to form the elbow joint
Right humerus, anterior surface image
Right humerus, posterior surface image
What is this groove? It separates the greater and lesser tubercle
Intertubercular sulcus OR bicipital groove
What runs in the intertubercular sulcus?
One of the tendons of the bicep muscle
What is the deltoid tuberosity?
Roughened slightly raised area on midpart of anterior humerus where deltoid muscle inserts
Name this landmark
Medial epicondyle (positioned on side closest to body)
Name this landmark
Lateral epicondyle
Name these 2 regions
Lateral and medial supracondylar ridge (lateral on the left, medial on the right as closest to the body)
Name this region. What is its importance?
Trochlea - important for articulation of the humerus at the elbow joint
Name the 3 highlighted landmarks
Blue - coronoid fossa
Left yellow - capitulum
Middle yellow - trochlea
Full labelled diagram of right humerus anterior surface
Where is the radial groove?
A shallow depression that runs diagonally down the posterior surface of the humerus, parallel to the deltoid tuberosity.
Name the 2 dotted landmarks
- Anatomical neck
- Radial groove
Clinical importance of radial groove?
Where the radial nerve runs
Name the highlighted landmark. Note this is now the posterior surface of the humerus
Olecranon fossa
Full labelled diagram of posterior surface of humerus
What 3 bones are involved in the elbow joint?
- Humerus
- Ulna
- Radius
What 2 articulations are involved in the elbow joint?
- Humero-ulnar
- Humero-radial
Describe the humero-ulnar articulation
Between the trochlea on the humerus and the trochlear notch on the ulnar
Where is the trochlea found? Where is the trochlear notch found?
Trochlea - found on the distal end of humerus
Trochlear notch - found on ulna
Describe the humero-radial articulation
Between the capitulum and radial head (orange highlight)
Where is the capitulum found? Where is the radial head found?
Capitulum - found on the distal end of the humerus
Radial head - found at the top of the radius bone
Is the elbow joint stable?
Yes due to good congruity
What does the coronoid fossa articulate with?
Coronoid fossa (found on distal end of humerus) receives coronoid process (found on the ulna) but only during flexion
Highlighted in blue