Muscles and Motion in Human Anatomy

Full Extension and Trapezius Regions

• Full extension occurs when the arm reaches back, but the head remains stable.

• Discusses the upper, middle, and lower trapezius regions.

Arm Motion and Brachiation

• Humans are apes designed for brachiation (arm-swinging) movement.

• Arm motion primarily involves pulling upwards (brachial motion), unlike most other mammals (dogs, cats).

Rotator Cuff Anatomy

• The rotator cuff consists of the following muscles, often remembered by the mnemonic "SITS":

  • Supraspinatus: Positioned above the scapula, involved in shoulder abduction.

  • Infraspinatus: Located in the middle, assists in external rotation of the arm.

  • Teres Minor: Aids in external rotation, originating from the scapula and inserting on the humerus.

  • Subscapularis: A deep muscle responsible for internal arm rotation, attaching to the lesser tubercle of the humerus.

• All rotator cuff muscles insert into the top part of the humerus, contributing to shoulder mobility.

Pectoral and Deltoid Muscles

• Deltoid Muscle:

  • Originates from clavicle and scapula, and attaches to the humerus (deltoid tuberosity).

  • Functions to flex, extend, and abduct the arm.

• Pectoralis Major:

  • Originates from the clavicle, sternum, and ribs, inserts at the intertubercular groove.

  • Primarily responsible for adduction and internal rotation of the arm.

Deep Muscles of the Trunk and Shoulder

• Subscapularis and Pectoralis Minor:

  • Pectoralis Minor aids in respiration and scapula movement.

  • Important in elevating the rib cage during inhalation.

Arm Movement Mechanics

• Discusses movements like protraction of the shoulder and the role of intercostals in respiration:

  • External Intercostals: Elevate ribs during inhalation.

  • Internal Intercostals: Depress the ribs during exhalation.

• Diaphragm: Key muscle for respiration, flattens to aid inhalation, arches during exhalation.

Posterior Trunk and Shoulder Muscles

• Trapezius: Covers upper back, involved in shoulder movement.

• Latissimus Dorsi: Broad muscle connecting lower back to the humerus, functions in arm adduction and extension.

• Rhomboids: Stabilize and retract the scapula.

Abdominal Muscles

• Composed of three layers: external oblique, internal oblique, and transversus abdominis.

• Rectus Abdominis: Known as the "six-pack," flexes the trunk.

• Their arrangement allows for various movements: flexion, rotation, and lateral bending.

Muscles of the Arm

• Biceps Brachii: Flexor of the elbow, consists of two heads.

• Brachialis: Prime mover for elbow flexion.

• Triceps Brachii: Extensor of the elbow, with three heads for stabilization.

• Brachioradialis: Assists in elbow flexion, especially in neutral positions.

Forearm Muscle Functions

• Pronator Teres: Pronates the forearm; important for activities like dribbling a basketball.

• Supinator: Helps in supinating the hand to hold objects.

• Flexors and Extensors:

  • Flexors: Located on the anterior side, control wrist flexion and finger movement.

  • Extensors: Located on the posterior side, responsible for extending the wrist and fingers.

Muscles of the Leg

• Iliopsoas Group: Consists of psoas major and iliacus, responsible for hip flexion.

• Tensor Fascia Latae: Works with the iliotibial band to stabilize the leg during motion.

• Sartorius: Longest muscle in the human body; assists in hip flexion and outward leg movements.

• Adductor Muscles: Bring the leg towards midline; includes adductor longus and magnus.

• Quadriceps Femoris: Major knee extensor, has four muscle heads including rectus femoris and vastus muscles.

• Hamstrings: Consist of biceps femoris, semitendinosus, and semimembranosus; crucial for knee flexion.

Calf Muscles and Ankle Movement

• Gastrocnemius and Soleus: Major plantar flexors; essential in walking and running, together known as triceps surae.

• Tibialis Anterior: Critical for controlling movements of the foot, particularly in dorsiflexion.

• Fibularis Muscles: Aid in foot eversion and stabilization during ankle movements.

Foot Muscles and Distal Extensions

• Flexor Digitorum Longus: Flexes toes.

• Extensor Digitorum Longus: Assists in extending the toes.

Summary of Muscle Actions

• Muscle actions are interconnected and contribute to complex movements like walking, running, and arm swinging. Understanding each muscle's origin, insertion, and function is crucial for comprehending human anatomy and motion dynamics.