Muscles and Anatomy

Skeletal Muscle Structure

• Epimysium: Surrounds the entire muscle.

• Perimysium: Surrounds fascicles, each containing 10-100 fibers.

• Endomysium: Surrounds individual muscle fibers.

• Components include:

  • Epimysium

  • Tendon

  • Perimysium

  • Fascicle

  • Blood vessel

  • Endomysium

  • Muscle fiber

Microscopic Anatomy of Skeletal Muscle Cell

• Muscle fibers (myofibers) are long, cylindrical cells ranging from 10 to 100 micrometers in length (10-100 \mu m).

• Myofibers form through the fusion of multiple cells during embryogenesis, resulting in multiple nuclei per fiber.

• Nuclei are located peripherally within the cell, pushed aside by myofibrils.

• Myofibrils are longitudinally arranged organelles filling the sarcoplasm (cytoplasm of muscle fiber).

• Sarcolemma: The plasma membrane of a muscle fiber.

Electron Microscopy of Skeletal Muscle Fiber

• Myofibrils consist of thread-like myofilaments.

• Myofilaments are composed of:

  1. Actin (thin filament)

  2. Myosin (thick filament)

• Sarcomere: The contractile unit of a muscle fiber, extending from one Z band (middle of I band) to the next.

• Sarcomere cross-section:

  • Each thick filament (myosin) is surrounded by six thin filaments (actin).

  • Each thin filament (actin) is surrounded by three thick filaments (myosin).

• Alternating light (I) and dark (A) bands create the striated appearance of muscle fibers.

T Tubules and Sarcoplasmic Reticulum

• T Tubules: Infoldings of the sarcolemma at the A and I band junction, penetrating deep into the muscle fiber.

• Sarcoplasmic Reticulum (SR): Smooth endoplasmic reticulum of muscle cells, with terminal cisterns (cross channels).

• Triad: The structure formed by a T tubule flanked by terminal cisterns of the SR on both sides.

Muscle Components

• Key components:

  • Tendon

  • Bone

  • Muscle

  • Bundle

  • Z line

  • Actin

  • Myosin

  • Sarcomere

  • Myofibril

Muscle Types

• Three types of muscle tissue:

  • Skeletal Muscle

  • Smooth Muscle

  • Cardiac Muscle

Neuromuscular Junction

• Motor Neuron: Contains axon terminals.

• Synaptic Vesicles: Located within axon terminals, containing acetylcholine.

• Sarcolemma: Muscle cell membrane.

• Motor End Plate: Specialized area of the sarcolemma that contains receptors for acetylcholine.

• T Tubule: Transverse tubule.

• Terminal Cisternae: Part of the sarcoplasmic reticulum.

Fascicle Arrangement in Muscles

• Circular: Fascicles arranged in concentric rings (e.g., orbicularis oris).

• Convergent: Fascicles converge toward a single insertion tendon (e.g., pectoralis major).

• Fusiform: Spindle-shaped muscles with parallel fascicles (e.g., biceps brachii).

• Parallel: Fascicles run parallel to the long axis of the muscle (e.g., sartorius).

• Multipennate: Multiple rows of fascicles attaching obliquely to a central tendon (e.g., deltoid).

• Bipennate: Fascicles insert obliquely on both sides of a central tendon (e.g., rectus femoris).

• Unipennate: Fascicles insert into only one side of the tendon (e.g., extensor digitorum longus).

Muscle Architecture

• Key terms:

  • Origin: Attachment site of the muscle that remains relatively fixed during contraction.

  • Insertion: Attachment site of the muscle that moves during contraction.

  • Belly: The main body of the muscle.

• Examples:

  • Biceps brachii: Parallel-fusiform.

  • Rectus femoris: Bipennate.

  • Sartorius: Parallel (non-fusiform).

  • Extensor digitorum (posterior view): Unipennate.

  • Convergent

Mechanical Action of Muscles

• Lever Systems: Skeletal muscles use lever action to produce movement.

• Components:

  • Fulcrum: The joint.

  • Lever: The bone.

  • Effort: Muscle contraction creating force at the insertion point.

• Mechanical Advantage:

  • Power Lever: Load is close to the fulcrum, and effort is applied far from the fulcrum.

    • Requires less effort but produces shorter movements.

  • Mechanical Disadvantage (Speed Lever): Load is far from the fulcrum, and effort is applied close to the fulcrum.

    • Requires more effort but produces longer-distance movements.

Types of Muscle Action

• Abductor: Contracts the joint (flexion), although typically abduction means movement away from the midline.

• Extensor: Extends the joint.

• Prime Movers (Agonists): Muscles primarily responsible for causing a particular movement.

• Antagonists: Muscles that oppose or reverse a specific movement; they relax when the prime mover is active but can act as prime movers themselves (example: biceps and triceps).

• Synergists: Muscles that aid the action of the agonist by assisting the same movement or by stabilizing joints to prevent undesirable movements.

• Fixators: Specialized synergists that immobilize the origin of the prime mover, ensuring all tension is exerted at the insertion point (example: muscles of posture).

Naming Skeletal Muscles

• Direction of Muscle Fibers:

  • Rectus: Straight (e.g., rectus abdominis).

  • Oblique: Angled.

  • Transverse: Horizontal (e.g., transversus abdominis).

• Muscle Size:

  • Maximus: Largest (e.g., gluteus maximus).

  • Minimus: Smallest (e.g., gluteus minimus).

  • Longus: Long (e.g., adductor longus).

  • Brevis: Short (e.g., adductor brevis).

• Muscle Location:

  • Named after the bone to which it is associated (e.g., temporalis-temporal bone).

  • Examples: carpi ulnaris, biceps femoris.

• Number of Origins:

  • Biceps (two origins), triceps (three origins), quadriceps (four origins).

• Attachment Location:

  • Sternocleidomastoid (attaches to sternum, clavicle, and mastoid process), temporalis.

• Muscle Shape:

  • Deltoid (triangular), trapezius (trapezoid).

• Muscle Action:

  • Abductor, extensor.

Key Superficial Muscles

• Facial:

  • Temporalis

  • Masseter

  • Epicranius, frontal belly

  • Occipital belly

  • Orbicularis oculi

  • Zygomaticus

  • Orbicularis oris

  • Platysma

• Neck:

  • Sternohyoid

  • Sternocleidomastoid

  • Trapezius

• Shoulder:

  • Trapezius

  • Deltoid

• Thorax:

  • Pectoralis minor

  • Pectoralis major

  • Serratus anterior

  • Intercostals

• Arm:

  • Triceps brachii

  • Biceps brachii

  • Brachialis

• Forearm:

  • Pronator teres

  • Brachioradialis

  • Flexor carpi radialis

  • Palmaris longus

  • Flexor carpi ulnaris

  • Extensor carpi radialis longus

  • Extensor carpi ulnaris

  • Extensor digitorum

• Abdomen:

  • Rectus abdominis

  • External oblique

  • Internal oblique

  • Transversus abdominis

• Pelvis/thigh:

  • Iliopsoas

  • Pectineus

  • Tensor fasciae latae

  • Sartorius

• Thigh:

  • Rectus femoris

  • Vastus lateralis

  • Vastus medialis
    *Adductor longus
    *Gracilis
    *Adductor Magnus
    *Hamstrings: Biceps Femoris, Semitendinosus, Semimembranosus

• Leg:

  • Fibularis longus

  • Extensor digitorum longus

  • Tibialis anterior

  • Gastrocnemius

  • Soleus

• Hip:

  • Gluteus medius

  • Gluteus maximus
    Gastrocnemius
    Soleus
    Fibularis longus
    Calcaneal (Achilles) tendon

Deep Muscles

• Head/Neck:

  • Epicranius, occipital belly

  • Sternocleidomastoid

  • Trapezius

• Shoulder:

  • Deltoid

  • Infraspinatus

  • Teres major

  • Rhomboid major

  • Triangle of auscultation

  • Latissimus dorsi

Muscles of the Body

• Muscles of Axial Skeleton

  • Head (face, scalp) and Neck

  • Muscles of Trunk (neck and shoulder, Vertebral Column, Thorax (including breathing) abdomen and Pelvic Girdle

• Muscles of Appendicular skeleton:

  • Arm, Forearm, wrist, palm and digits

  • Thigh, leg, and foot

Facial Expression Muscles

• Epicranius:

  • Includes the frontal belly and occipital belly, connected by the galea aponeurotica.

• Orbicularis oculi: Encircles the eye.

• Levator labii superioris.

• Zygomaticus muscles

• Buccinator.

• Risorius.

• Orbicularis oris: Encircles the mouth.

• Mentalis: Located on the chin.

• Depressor labii inferioris.

• Depressor anguli oris.

• Platysma: Covers the anterior neck.

• Muscles of Mastication:
  *Temporalis
  *Masseter

Head and Neck Muscles

• Lateral View:

  • Frontalis.
    *Temporalis
    *Occipitalis

  • Orbicularis oculi.

  • Zygomatic arch.
    *Masseter

  • Parotid gland.

  • Orbicularis oris.

  • Buccinator.

  • Splenius capitis.

  • Levator scapulae.

  • Sternocleidomastoid.

Muscles of Mastication

*Temporalis
*Masseter:
*Deep part
*Superficial.
*Medial pterygoid
*Lateral pterygoid

Anterior Neck Muscles

• Digastric:

  • Anterior belly.

  • Posterior belly.
    *Sternocleidomastoid

• Thyrohyoid.

• Sternothyroid.

• Mylohyoid
  *Sternohyoid

Muscles of Neck and Vertebral Column

• Neck Extensor Muscles:

  • Semispinalis capitis and cervicis.

  • Rectus capitis posterior minor and major.

  • Obliquus capitis superior and inferior.

  • Splenius capitis and cervicis.

Deep Back Muscles

• Erector spinae group:

  • 3 columns muscles

  • From sacrum to the ribs

  • Extends vertebral column

  • Consists

    • Iliocostalis (lateral)

    • Longissimus (intermediate)

    • Spinalis (medial)

Deep Muscles of Thorax

• Muscles of Respiration:

  • External Intercostals.

  • Internal intercostals.
    *Diaphragm

Diaphragm

• Structures passing through diaphragm:

  • Inferior vena cava
    *Esophagus
    *Aorta

Anterolateral Abdominal Wall Muscles

*Skin
*External oblique
*Internal Oblique
*Transversus Abdominis
Tendinous intersection
Rectus Abdominis
Aponeurosis
Inguinal ligament
Linea alba
Serratus Anterior
Pectoralis major

Muscles of the Pelvic Floor

• Levator ani:

  • Pubococcygeus.

  • Iliococcygeus.
    *Coccygeus
    Piriformis
    Obturator internus
    Pelvic diaphragm

Pelvic Floor

*Urogenital diaphragm
*Vagina.
*Anal canal
*Coccyx
*Levator Ani
*Symphysis pubis

Muscles of the Perineum

*Urogenital diaphragm formed from :
* Sphincter urethrae and the deep transverse perineus
Male
Pubic ramus
External urethral sphincter
Deep transverse perineal muscle
Central tendon
Anus
External anal sphincter
Female
Urethral opening
Vaginal opening

Muscles of the Perineum

*Clitoris
*Urethral opening
*Vaginal opening
Ischiocavernosus
Bulbospongiosus
Superficial transverse perineal muscle
Levator ani
Gluteus maximus
Anus

Muscles of The Shoulder and Chest

*Anterior View
Deltopectoral triangle
Acromion
Deltoid branch of thoracoacromial artery
Trapezius muscle
Omohyoid muscle and cervical (investing) fascia
Stemocleidomastoid muscle
Deltoid muscle
Cephalic vein
Long head of biceps brachii muscle
Short head of biceps brachii muscle
Triceps brachii muscle (lateral head)
Latissimus dorsi muscle
Serratus anterior muscle
External oblique muscle
6th costal cartilage
Clavicle
Clavicular head of pectoralis major muscle
Stemocostal head of pectoralis major muscle
Stemum
Abdominal head of pectoralis major muscle
Anterior layer of rectus sheath

Superficial Muscles of Anterior Thorax

Sternocleidomastoid
Deltoid
Pectoralis major
Sternum
Biceps brachii
Subclavius
Clavicle
Subscapularis
Pectoralis minor
Coracobrachialis
Serratus anterior
Humerus

Muscles of Shoulder

*Posterior View
Acromion
Latissimus dorsi muscle
Spinous process of T12
Spine of scapula
Teres minor muscle
Infraspinatus muscle
Teres major muscle
Long head of triceps brachii muscle
Lateral head of triceps brachii muscle

Superficial Muscles of the Posterior Thorax

Trapezius
Deltoid
Rhomboid minor
Rhomboid major
Levator scapulae
Supraspinatus
Clavicle
Infraspinatus
Teres minor
Teres major
Humerus
Latissimus dorsi

Muscles Crossing the Elbow Joint

Deltoid
Sternum
Pectoralis major
Coracobrachialis
Triceps brachii:
Lateral head
Long head
Medial head
Biceps brachii
Brachialis
Brachio-radialis

Posterior muscles of the upper arm

supraspinatus muscle
acromion
greater tubercle of humerus
infraspinatus muscle
teres minor muscle
long head of tricep brachii muscle
teres major muscle
posterior cutaneous nerve
deltoid muscle (cut and faded)
lateral head of triceps brachii muscle
tendon of triceps brachii muscle
medial intermuscular septum
ulnar nerve
brachioradialis muscle
extensor carpi radialis longus muscle
anconeus muscle
flexor carpi ulnaris muscle.
extensor carpi ulnaris muscle
extensor carpi radialis brevis muscle
extensor digitorum muscle

Muscles of Forearm

Tial
Aecondyle
lateral
Medial epicondyle
lateral
Medial epicondyle.
lateral epicondyle.
Common flexor
tendon
Coronoid process.
Interosseous
Interosseous membrane,
Suirialis
Radius
Ulna
Radius
Ulna
Medial epicondyle
lateral epicondyle
Palmar ap
Radius
Radius
Ulna
Flexor digitorum superficialis
Ulna
Flexor digitorum profundus.
Flexor pollicis longus
Flexor digitorum superficialis
tendons (cut away).
Right forearm:
anterior (palmar) views

Deep Anterior Muscles of the Forearm

Tendon of flexor digitorum superficialis
Tendon of brachioradialis (cut)
Tendon of flexor carpi ulnaris (cut)
Tendon of flexor carpi ulnaris (cut)
Pronator quadratus
Flexor pollicis longus
Tendon of flexor carpi radialis (cut)
Flexor digitorum superficialis
Extensor carpi radialis longus
Supinator
Tendon of biceps brachii (cut)
Supinator
Tendon of flexor digitorum profundus
Tendon of flexor digitorum superficialis (cut)
Lumbricals
Tendon of flexor pollicis longus
Thenar muscles of thumb
Pronator quadratus
Flexor pollicis longus
Flexor digitorum profundus

Deep Posterior Muscles of the Forearm

Supinator
Abductor pollicis longus
Extensor pollicis brevis and longus
Extensor indicus
Extensor indicis
Extensor pollicis brevis
Extensor pollicis longus
Abductor pollicis longus
Supinator
Anconeus
Olecranon process of ulna
Interossei

Superficial Posterior Muscles of the Forearm

Brachioradialis - flexes
forearm
Extensor carpi radialis longus
Extensor carpi radialis brevis
Extensor digitorum
Extensor carpi ulnaris
Extensor
expansion
Tendons of extensor digitorum
Extensor pollicis longus
Extensor pollicis brevis
Abductor
pollicis longus
Extensor digitorum
Extensor carpi radialis brevis
Extensor carpi radialis longus
Tendons of extensor carpi radialis brevis and longus -Extensor indicis
Extensor digiti minimi
Extensor carpi ulnaris
Flexor carpi ulnaris
Anconeus
Insertion of triceps brachii
Brachioradialis
GLUTEUS
MEDIUS
ILIAC
CREST
ASIS
TENSOR
FASCIAE
LATAE
SARTORIUS
RECTUS
FEMORIS
VASTUS
MEDIALIS
Gluteus Maximus
Greater Trochanter
Iliotibial Tract
Biceps Femoris
Patella
Gastrocnemius
PATELLA
GRACILIS
TIBIALIS
ANTERIOR
VASTUS
LATERALIS
PES ANSERINUS
(GOOSEFOOT)
TIBIALIS
ANTERIOR
GASTROCNEMIUS
Soleus
ACHILLES
TENDON
MEDIAL MALLEOLUS
(INNER ANKLE BONE)
SOLEUS
EXTENSOR
DIGITORUM
LONGUS
PERONEUS
LONGUS
PERONEUS
BREVIS
ACHILLES
TENDON
Muscles of
Thigh and Leg
Muscles of the Anterior Compartment of the Thigh
12th thoracic vertebra
12th rib
Quadratus lumborum
Psoas minor
Iliac crest
Iliopsoas Psoas major
Iliacus
Anterior superior iliac spine
5th lumbar vertebra
Tensor fasciae latae
Pectineus
Sartorius
Quadriceps femoris:
Rectus femoris
Adductor longus
Gracilis
-Adductor magnus
Vastus lateralis
Vastus medialis
Tendon of quadriceps femoris
Patella
Patellar ligament

Muscles of the Lateral Compartment

Fibularis (peroneus) longus
Fibularis (peroneus) brevis
Flexor hallucis longus
Patella
Head of fibula
Gastrocnemius
Soleus
Fibularis longus
Extensor digitorum longus
Tibialis anterior
Extensor hallucis longus
Fibularis tertius
Fibularis brevis
Extensor hallucis longus
Flexor hallucis longus
Fibular retinaculum
Lateral malleolus
Fibularis tertius
Superior and inferior extensor retinacula
Extensor hallucis brevis
-Extensor digitorum brevis
5th metatarsal

Muscles of the Anterior Compartment

Tibialis anterior
Extensor digitorum longus
Fibularis (peroneus) tertius
Extensor hallucis longus
Fibularis longus
Gastrocnemius
Tibia
Tibialis anterior
Extensor digitorum longus
Soleus
Extensor hallucis longus
Fibularis tertius
Superior and inferior extensor retinacula
Extensor hallucis brevis
-Extensor digitorum brevis

Muscles of the Posterior Compartment

Plantaris
Gastrocnemius
Medial head
Lateral head
Tendon of gastrocnemius
Calcaneal tendon
Medial malleolus
Lateral head (cut).
Gastrocnemius
Medial head (cut)
Soleus
Tendon of plantaris
Lateral malleolus
Tendon of tibialis posterior
Calcaneus

Muscles of the Posterior Compartment

Deep muscles
Plantaris (cut)
Gastrocnemius lateral head (cut)
Popliteus