Myology of the Leg & Foot: Anatomy & Physiology Study Notes

Introduction

Overview of Myology: Leg & Foot

This study guide summarizes the anatomical basis of human myology, focusing on the muscles of the leg and foot. It is designed for college-level Anatomy & Physiology students and covers key terminology, muscle compartments, origins and insertions, and functional groups relevant to movement and support of the lower limb.

Etymology: Useful Word Roots for Key Terms

Muscle and Structure Terminology

• Digit (L = finger/toe)

• Halluc/hallux (L = the great toe)

• Poplit (L = back of knee)

• Sur (L = calf of leg, e.g., triceps surae)

• Gastrocnemius (G gastro = belly; cneme = leg)

• Sole (L = a sandal, type of fish)

• Plantar (L = sole/underside of foot)

• Dorso-dorsal (L = back of body or body part)

• Lumbric (L = wormlike)

• Peron (G = fibula, brooch; note 'peroneus' is classical name for fibular muscles)

• Interosseous (from inter- (L) between, os- (L) bone)

• Retinaculum (L) holdfast, clamp or strap to 'retain' something in place

Additional info: Understanding etymology aids in memorizing muscle names and their functions.

Learning Objectives

Key Concepts to Master

• Extrinsic vs Intrinsic Foot Muscles: Extrinsic muscles originate outside the foot and control gross movements; intrinsic muscles originate within the foot and control fine movements and arch support.

• Muscle Compartments in Leg: The leg is divided into anterior, lateral, and posterior compartments, each with distinct muscle groups and actions at the ankle/foot.

• Retinacula & Malleoli: These structures hold tendons of extrinsic foot muscles in place as they cross the ankle.

• Interosseous Membrane & Intermuscular Septa: These connective tissues separate muscle compartments and provide attachment surfaces.

• Intrinsic Foot Muscles: Four layers on the plantar side (similar to the hand) and dorsal extensors (unlike the hand).

• Foot Osteology & Arthrology: Review bone and joint structure for context.

Additional info: Students must know origins and insertions for muscles of thigh & leg; details for intrinsic foot muscles are less emphasized.

Regions & Compartments of the Lower Limb

Major Anatomical Divisions

• Hip Region: Gluteal muscles (posterior), hip flexors (anterior, deep)

• Thigh Compartments:

  • Anterior thigh (quadriceps group)

  • Posterior thigh (hamstrings group)

  • Medial thigh (hip adductors)

• Leg Compartments:

  • Anterior leg

  • Posterior leg (superficial and deep layers)

  • Lateral leg

• Foot Groups:

  • Plantar intrinsic foot muscles (4 layers)

  • Dorsal intrinsic foot muscles (2 extensors)

Muscle Compartments of the Leg

Functional Groups and Naming Logic

• Anterior Compartment: Dorsiflexion of ankle, extension of toes

  • Tibialis anterior

  • Extensor digitorum longus

  • Extensor hallucis longus

  • Fibularis tertius

• Lateral Compartment: Eversion of foot

  • Fibularis longus

  • Fibularis brevis

• Posterior Compartment (Superficial): Plantarflexion of ankle

  • Gastrocnemius

  • Soleus

  • Plantaris

• Posterior Compartment (Deep): Flexion of toes, inversion of foot

  • Popliteus

  • Flexor digitorum longus

  • Flexor hallucis longus

  • Tibialis posterior

Origins, Insertions, and Functions of Key Leg Muscles

Anterior Compartment

• Tibialis Anterior:

  • Origin: Lateral condyle and proximal shaft of tibia

  • Insertion: Medial cuneiform and base of first metatarsal (medial, dorsal foot)

  • Function: Dorsiflexion and inversion of foot

• Extensor Digitorum Longus:

  • Origin: Lateral condyle of tibia, anterior surface of fibula

  • Insertion: Superior surfaces of phalanges (digits II-V)

  • Function: Extension of toes II-V, dorsiflexion of foot

• Extensor Hallucis Longus:

  • Origin: Anterior surface of fibula

  • Insertion: Superior surface of distal phalanx of great toe (digit I)

  • Function: Extension of great toe, dorsiflexion of foot

• Fibularis Tertius:

  • Origin: Distal anterior surface of fibula

  • Insertion: Dorsum of fifth metatarsal (dorsal, lateral foot)

  • Function: Dorsiflexion and eversion of foot

Lateral Compartment

• Fibularis Longus:

  • Origin: Head and proximal shaft of fibula

  • Insertion: Base of first metatarsal (crosses plantar foot to insert medially)

  • Function: Eversion and plantarflexion of foot

• Fibularis Brevis:

  • Origin: Lateral, distal fibula

  • Insertion: Base of fifth metatarsal

  • Function: Eversion of foot

Posterior Compartment

Superficial Layer

• Gastrocnemius:

  • Origin: Femoral condyles

  • Insertion: Calcaneus via calcaneal (Achilles) tendon

  • Function: Plantarflexion of foot, flexion of knee

• Soleus:

  • Origin: Head of fibula, proximal tibia

  • Insertion: Calcaneus via calcaneal tendon

  • Function: Plantarflexion of foot

• Plantaris:

  • Origin: Lateral supracondylar ridge of femur

  • Insertion: Calcaneus (sometimes plantar aponeurosis)

  • Function: Weak plantarflexion of foot and flexion of knee

Deep Layer

• Popliteus:

  • Origin: Lateral condyle of femur

  • Insertion: Posterior surface of tibia

  • Function: Unlocks knee by medially rotating tibia

• Flexor Digitorum Longus:

  • Origin: Posteromedial surface of tibia

  • Insertion: Distal phalanges of digits II-V

  • Function: Flexion of toes II-V, plantarflexion of foot

• Flexor Hallucis Longus:

  • Origin: Posterior surface of fibula

  • Insertion: Distal phalanx of great toe (digit I)

  • Function: Flexion of great toe, plantarflexion of foot

• Tibialis Posterior:

  • Origin: Interosseous membrane and adjacent shafts of tibia and fibula

  • Insertion: All medial tarsals

  • Function: Inversion and plantarflexion of foot

Review: Tendons Passing the Ankle

Key Structures and Pathways

• Flexor Retinaculum & Flexor Tunnel: Medial ankle, holds tendons of deep posterior compartment muscles

• Extensor Retinaculum: Anterior ankle, holds tendons of anterior compartment muscles

• Superior & Inferior Fibular Retinacula: Lateral ankle, holds tendons of lateral compartment muscles

• Malleoli: Medial and lateral bony prominences at the ankle, serve as pulleys for tendons

Summary Table: Tendons Passing the Ankle

Compartment	Tendons	Pathway
Anterior	Tibialis anterior, Extensor digitorum longus, Extensor hallucis longus, Fibularis tertius	Pass anterior to ankle joint
Lateral	Fibularis longus, Fibularis brevis	Pass posterior to lateral malleolus
Posterior (Superficial)	Gastrocnemius, Soleus, Plantaris	Insert via calcaneal tendon to heel
Posterior (Deep)	Tibialis posterior, Flexor digitorum longus, Flexor hallucis longus	Pass posterior to medial malleolus

Intrinsic Muscles of the Foot

Plantar and Dorsal Groups

• Plantar Intrinsic Muscles: Four layers, covered by plantar aponeurosis, support arches and control fine movements

• Dorsal Intrinsic Muscles: Extensor hallucis brevis, extensor digitorum brevis (unlike the hand, which lacks dorsal muscles)

Function: Assist in maintaining and adjusting the shape of the foot and digits

Review: Movements of the Ankle & Foot

Major Actions and Muscle Groups

• Dorsiflexion: Lifting the foot upwards (anterior compartment)

• Plantarflexion: Pointing the foot downwards (posterior compartment)

• Inversion: Turning sole medially (tibialis anterior and posterior)

• Eversion: Turning sole laterally (lateral compartment muscles)

Example: Walking involves alternating dorsiflexion and plantarflexion, with inversion and eversion stabilizing the foot on uneven surfaces.

Summary Table: Functional Groups of Leg Muscles

Group	Common Action	Example Muscle
Anterior Compartment	Dorsiflexion of ankle	Tibialis anterior
Lateral Compartment	Eversion of foot	Fibularis longus
Posterior Compartment (Superficial)	Plantarflexion of ankle	Gastrocnemius
Posterior Compartment (Deep)	Flexion of toes, inversion of foot	Flexor digitorum longus

Key Equations and Concepts

• Muscle Force Equation:

$F = m \cdot a$

• Torque at the Joint:

$\tau = F \cdot r$

Additional info: These equations are relevant for understanding how muscle contractions produce movement at joints.