Anatomy Quiz: Vertebral Column & Brachial Plexus

Study Notes

Vertebral Column

Composed of 33 vertebrae
5 vertebrae fuse to form the sacrum, considered a single bone
4 vertebrae fuse to form the coccyx, considered a single bone
Total of 26 individual bones

Brachial Plexus

Network of nerves in the shoulder
Carries movement and sensory signals from the spinal cord to the arms and hands
Injuries can cause pain, weakness, and numbness in the arm and hand
Formed by the lower four cervical (C5-C8) and first thoracic (T1) spinal nerves
Travels through the neck, axilla, and into the arm
Supplies nerves to the shoulder, chest, and arms

Formation of the Brachial Plexus

Roots: Formed by the anterior rami of the spinal nerves (C5-T1).
Trunks: Formed by the union of roots:
- Upper trunk: C5 and C6 roots
- Middle trunk: C7 root
- Lower trunk: C8 and T1 roots
Divisions: Each trunk divides into anterior and posterior divisions.
Cords: Formed by the merging of divisions:
- Lateral cord: Formed by the anterior divisions of the upper and middle trunks.
- Medial cord: Formed by the anterior division of the lower trunk.
- Posterior cord: Formed by the posterior divisions of all three trunks.

Brachial Plexus Branches

Roots:
- Dorsal scapular nerve (C5): Innervates levator scapulae, rhomboid major, and rhomboid minor muscles.
- Long thoracic nerve (C5, C6, C7): Innervates the serratus anterior muscle.
Upper Trunk:
- Subclavius nerve (C5, C6): Supplies the subclavius muscle.
- Suprascapular nerve (C5, C6): Supplies the supraspinatus and infraspinatus muscles.
Cords:
- Lateral Cord
  - Musculocutaneous nerve (C5, C6, C7): Innervates the biceps brachii, brachialis, and coracobrachialis muscles.
  - Lateral root of median nerve (C6, C7, C8): Contributes to the median nerve, which controls forearm and hand movements.
  - Lateral pectoral nerve (C5, C6, C7): Innervates the pectoralis major muscle.
- Medial Cord
  - Ulnar nerve (C8, T1): Supplies the flexor carpi ulnaris, flexor digitorum profundus (medial half), and intrinsic hand muscles.
  - Medial root of median nerve (C8, T1): Contributes to the median nerve.
  - Medial pectoral nerve (C8, T1): Innervates the pectoralis major muscle.
  - Medial cutaneous nerve of the arm (T1): Provides sensory innervation to the medial aspect of the arm.
  - Medial cutaneous nerve of the forearm (T1): Provides sensory innervation to the medial aspect of the forearm.
- Posterior Cord
  - Upper subscapular nerve (C5, C6): Supplies the subscapularis muscle.
  - Lower subscapular nerve (C5, C6): Supplies the teres major muscle.
  - Middle subscapular nerve (C5, C6): Also known as the nerve to latissimus dorsi, supplies the latissimus dorsi muscle.
  - Axillary nerve (C5, C6): Innervates the deltoid and teres minor muscles, and provides sensory innervation to the shoulder.
  - Radial nerve (C5, C6, C7, C8, T1): Innervates the extensor muscles of the arm and forearm, as well as the supinator muscle. It also provides sensory innervation to the posterior aspect of the arm, forearm, and hand.