The humerus

Question 1

Bones of the Humerus

Answer 1

1. Proximal End:
   - Head: The rounded top of the humerus that fits into the glenoid cavity of the scapula, forming the shoulder joint (glenohumeral joint).
   - Greater and Lesser Tubercle: Bony prominences that serve as attachment points for muscles.
   - Intertubercular Groove: A groove between the tubercles that houses the tendon of the biceps brachii.
2. Shaft: The long, cylindrical part of the humerus that provides structural support.
3. Distal End:
   - Capitulum: A rounded knob that articulates with the radius at the elbow joint.
   - Trochlea: A spool-shaped structure that articulates with the ulna.
   - Medial and Lateral Epicondyles: Bony projections on either side of the distal humerus for muscle attachment.

Question 2

Joints Involving the Humerus

Answer 2

1. Shoulder Joint (Glenohumeral Joint):
   - Type: Ball-and-socket joint.
   - Movements: Allows a wide range of motion including flexion, extension, abduction, adduction, internal rotation, and external rotation.
2. Elbow Joint:
   - Type: Hinge joint.
   - Movements: Primarily allows flexion and extension of the forearm relative to the upper arm.

Question 3

Muscles Associated with the Humerus

Answer 3

1.Shoulder Muscles:
- Deltoid: Responsible for shoulder abduction, flexion, and extension.
- Rotator Cuff Muscles: Including supraspinatus, infraspinatus, teres minor, and subscapularis, which stabilize the shoulder joint and allow for rotational movements.

2. Arm Muscles:
   - Biceps Brachii: Flexes the elbow and supinates the forearm.
   - Triceps Brachii: Extends the elbow.
   - Brachialis: A primary flexor of the elbow.

Question 4

Ligaments Associated with the Humerus

Answer 4

1. Shoulder Ligaments:
   - Glenohumeral Ligaments: A group of ligaments that stabilize the shoulder joint.
   - Coracoacromial Ligament: Provides support to the shoulder joint and prevents superior displacement of the humerus.
2. Elbow Ligaments:
   - Ulnar Collateral Ligament: Stabilizes the inner side of the elbow joint.
   - Radial Collateral Ligament: Stabilizes the outer side of the elbow joint.
   - Annular Ligament: Encircles the head of the radius and holds it in place against the ulna.

Question 5

Nerves of the Humerus

Answer 5

1. Radial Nerve:
   - Origin: The radial nerve arises from the brachial plexus (C5-T1).
   - Innervation: It innervates the muscles of the posterior compartment of the arm, including the triceps brachii and anconeus, which are responsible for elbow extension. It also provides sensory innervation to the skin of the posterior arm and forearm.
   - Course: The radial nerve travels in the radial groove of the humerus, making it susceptible to injury, particularly in mid-shaft fractures of the humerus.
2. Ulnar Nerve:
   - Origin: The ulnar nerve also arises from the brachial plexus (C8-T1).
   - Innervation: It primarily innervates the flexor muscles in the forearm (except the flexor carpi radialis and part of the flexor digitorum superficialis) and most of the intrinsic muscles of the hand, including the hypothenar muscles and interossei.
   - Course: The ulnar nerve runs posterior to the medial epicondyle of the humerus, which is a common site for nerve entrapment or injury (commonly referred to as “funny bone” sensation).
3. Musculocutaneous Nerve:
   - Origin: This nerve arises from the brachial plexus (C5-C7).
   - Innervation: It innervates the muscles of the anterior compartment of the arm, including the biceps brachii, brachialis, and coracobrachialis, which are primarily responsible for elbow flexion.
   - Course: The musculocutaneous nerve pierces the coracobrachialis muscle and continues down the arm, providing sensory innervation to the skin of the lateral forearm.
4. Axillary Nerve:
   - Origin: The axillary nerve arises from the brachial plexus (C5-C6).
   - Innervation: It innervates the deltoid and teres minor muscles, which are involved in shoulder abduction and external rotation.
   - Course: The axillary nerve wraps around the surgical neck of the humerus, making it vulnerable to injury during shoulder dislocations or fractures of the humeral neck.

These nerves are critical for the motor functions of the upper limb and provide sensory feedback from the skin, contributing to the overall functionality of the arm. Injuries to these nerves can result in significant motor deficits and sensory loss, highlighting their importance in upper limb anatomy and function

Question 6

Blood Vessels of the Humerus

Answer 6

1. Arterial Supply:
   - Brachial Artery: The primary artery supplying the humerus is the brachial artery, which runs along the medial side of the arm. It bifurcates into the radial and ulnar arteries at the elbow.
   - Profunda Brachii Artery: This artery branches off from the brachial artery and travels along the posterior aspect of the humerus. It gives off several perforating branches that supply the muscles and the bone.
   - Nutrient Artery: The humerus also receives a nutrient artery that enters through a foramen on the bone’s shaft, providing essential blood supply to the medullary cavity.
2. Veins:
   - The deep veins of the arm accompany the arteries and include the brachial veins, which typically run alongside the brachial artery. These veins drain into the axillary vein.
   - The profunda brachii vein accompanies the profunda brachii artery and also drains into the brachial veins.