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Muscle Anatomy

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Description

Name

  • Muscle Anatomy
  • Skeletal Muscle

General

  • This page summarizes all the skeletal muscles of the human body

Head and Neck

Muscles of Facial Expression (Anterior View)[1]
Illustration of the anterior, middle and posterior scalen[2]

Muscles of the Head

  • Muscles of Facial Expression
    • Scalp/Forehead: Frontalis, Occipitalis
    • Eyes/Eyelids: Orbicularis oculi, Corrugator supercilii, Levator palpebrae superioris
    • Nose: Nasalis, Procerus, Depressor Septi Nasi
    • Mouth/Lips: Orbicularis oris, Buccinator, Risorius, Zygomaticus major, Zygomaticus minor, Levator labii superioris, Levator anguli oris, Depressor anguli oris, Depressor labii inferioris, Mentalis
    • Neck: Platysma
  • Muscles of Mastication
    • Masseter
    • Temporalis
    • Medial Pterygoid
    • Lateral Pterygoid
  • Muscles of the Tongue
    • Intrinsic: superior longitudinal, inferior longitudinal, transverse and vertical muscles of the tongue
    • Extrinsic: Genioglossus, Hyoglossus, Styloglossus, Palatoglossus
  • Extra Ocular Muscles
    • Rectus: Superior rectus, Inferior rectus, Medial rectus, Lateral rectus
    • Accessory Muscle: Levator palpebrae superioris

Superficial Neck Muscles

Suboccipital Muscles

Deep Neck Flexors Muscles

Suprahyoid Muscles

Infrahyoid Muscles

Scalene Muscles

Thorax

Muscles of respiration[3]
Deep spinal muscles including semispinalis, multifidus, spinalis, longissimus, iliocostalis[4]

Primary Muscles of Respiration

Accessory Muscles of Respiration

Intrinsic Muscles of the Chest Wall

Deep Back Muscles Related to Thorax

Abdomen and Pelvis

Illustration of the diaphragm muscle[5]

Anterolateral Abdominal Wall Muscles

Posterior Abdominal Wall Muscles

Pelvic Diaphragm (Floor)

Urogenital Diaphragm (Deep Perineal Pouch)

  • Deep transverse perineal muscle
  • External urethral sphincter
  • Compressor urethrae (in females)
  • Sphincter urethrovaginalis (in females)

Superficial Perineal Muscles

  • Ischiocavernosus
  • Bulbospongiosus
  • Superficial transverse perineal muscle

Other Associate Muscles

Back

Superficial Posterior

Intermediate Posterior

Deep Posterior

Shoulder and Upper Arm

Anatomy of the rotator cuff muscles and tendons[6]
The extrinsic muscles of the shoulder[7]

Shoulder Region

Anterior Region

Posterior Region

Extrinsic Muscles of the Shoulder

Intrinsic Muscles of the Shoulder

Upper Arm

Forearm, Hand and Wrist

Superficial dorsal compartment[8]
Deep anterior compartment of the forearm.jpg[9]
Intrinsic muscles of the hand[10]

Posterior Compartment of the Forearm

Anterior Compartment of the Forearm

Intrinsic Muscles of the Hand

Hip and Thigh

Hip flexor muscles[11]
Cross-sectional anatomy of the thigh, demonstrating the anterior (quadriceps), posterior (hamstrings), and medial (adductor) compartments. Note the relatiosnship between the intermuscular septa and the neurovascular structures of each compartment.[12]

Hip Flexor Muscles

Gluteal/External Rotators

Anterior Compartment of the Thigh

Posterior Compartment of the Thigh

Medial Compartment of the Thigh

Leg and Foot

Cross-section of the lower leg depicting the 4 compartments and select key structures[13]
Intrinsic muscles of the foot. Plantar intrinsics: Layer 1: 1 = abductor hallucis, 2 = flexor digitorum brevis, 3 = abductor digiti minimi; Layer 2: 4 = quadratus plantae, 5 = lumbricals 1-4; Layer 3: 6 = flexor digiti minimi, 7a = adductor hallucis oblique head, 7b = adductor hallucis transverse head, 8 = flexor hallucis brevis; Layer 4: Dorsal Interossei. Dorsal Intrinsics: 10 = dorsal interossei, 11 = extensor digitorum brevis[14]

Anterior Compartment of the Leg

Lateral Compartment of the Leg

Superficial Posterior Compartment of the Leg

Deep Posterior Compartment of the Leg

Intrinsic Muscles of the Foot

Skeletal Muscle Anatomy

Skeletal muscle anatomy[15]

Muscle Cell

  • Also called Muscle Fiber, myocyte
  • The basic unit of a muscle is a muscle fiber, which is a single, elongated cell
  • Muscle fibers are multinucleated and contain many mitochondria for energy

Myofibrils

  • Each muscle fiber contains many myofibrils, which are rod-like structures that run the length of the cell.
  • Myofibrils are composed of repeating units called sarcomeres.

Sarcomeres

  • The sarcomere is the functional contractile unit of a muscle.
  • It contains actin (thin filaments) and myosin (thick filaments) arranged in a precise pattern

Sliding Filament Theory

  • During contraction, myosin heads bind to actin and pull the actin filaments inward, shortening the sarcomere
  • This process is powered by ATP and regulated by calcium ions and proteins like troponin and tropomyosin

Neuromuscular Junction

  • A motor neuron releases acetylcholine (ACh) at the neuromuscular junction, triggering an electrical impulse in the muscle fiber.

Excitation-Contraction Coupling

  • The electrical impulse (action potential) travels down the T-tubules and triggers the sarcoplasmic reticulum to release calcium ions
  • Calcium binds to troponin, which moves tropomyosin, exposing binding sites on actin for myosin to attach.

Muscle Fiber Contraction

  • Multiple sarcomeres contracting in a muscle fiber cause the whole fiber to shorten

Fascicles

  • Muscle fibers are grouped into bundles called fascicles, wrapped in a connective tissue sheath called perimysium.

Whole Muscle

  • Multiple fascicles are bundled together to form a whole muscle, surrounded by epimysium
  • Tendons connect the muscle to bones, allowing movement when the muscle contracts

See Also

References

  1. ↑ Buettner, Ricardo. "Robust user identification based on facial action units unaffected by users' emotions." (2018).
  2. ↑ Image courtesy of teachmeanatomy.info
  3. ↑ Jolley, C. J., and J. Moxham. "Respiratory muscles, chest wall, diaphragm, and other: Clinical implications." Encyclopedia of Respiratory Medicine, Four-Volume Set. Elsevier Inc., 2006. 632-643.
  4. ↑ Galbusera, F., and H. J. Wilke. "Biomechanics of the Spine: Basic Concepts." Spinal Disorders and Treatments. 1st ed: Academic Press, 2018. 456 p (2018).
  5. ↑ Image courtesy of sciencephoto.com
  6. ↑ Rajalekshmi, Resmi, and Devendra K. Agrawal. "Understanding Fibrous Tissue in the Effective Healing of Rotator Cuff Injury." Journal of surgery and research 7.2 (2024): 215.
  7. ↑ Image courtesy of geekymedics.com
  8. ↑ Image courtesy of teachmeanatomy.info
  9. ↑ Image courtesy of teachmeanatomy.info
  10. ↑ image courtesy of /meddists.com/
  11. ↑ Image courtesy of kenhub.com
  12. ↑ Burghardt, Rolf D., et al. "Compartment syndrome of the thigh. A case report with delayed onset after stable pelvic ring fracture and chronic anticoagulation therapie." BMC geriatrics 10 (2010): 1-5.
  13. ↑ Pechar, Joanne, and M. Melanie Lyons. "Acute compartment syndrome of the lower leg: a review." The Journal for Nurse Practitioners 12.4 (2016): 265-270.
  14. ↑ Fraser, John J., Mark A. Feger, and Jay Hertel. "Midfoot and forefoot involvement in lateral ankle sprains and chronic ankle instability. Part 1: anatomy and biomechanics." International journal of sports physical therapy 11.6 (2016): 992.
  15. ↑ Image courtesy of courses.lumenlearning.com
Created by:
John Kiel on 17 April 2025 20:50:17
Authors:
Last edited:
16 August 2025 22:34:55
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