Muscles: Gross Microanatomy

General Principles of Skeletal Muscle Anatomy

Muscle Terminology

Origin/head - muscle end attached to more stationary of two bones: Does not move

Insertion - muscle end attached to bone with greatest movement : moving part

Belly - Largest portion of the muscle between origin and insertion

Tendons - Attach muscles to bones

Aponeurosis - a very broad tendon

Agonist - muscle that, when it contracts, causes an action

Antagonist - a muscle working in opposition to Agonist

Synergists - muscles that work together to cause a movement

Prime mover - plays major role in accomplishing movement

Fixators - stabilize joint(s) crossed by the prime mover: prevent movement of the origin of the prime mover

Muscles of Facial Expression

Cutaneous - origin and insertion in the superficial fascia

Confined primarily to head and neck: move skin, Act as sphincters.

  • ex: orbicularis oris, orbicularis occuli, platysma

Muscles of Mastication and Hyoid

Mastication - chewing: elevation and depression of the mandible and excursion to grind the teeth together

Act with the muscles of hyped in movement of the mandible

Muscles of the cheek and tongue aid mastication by pushing the food under the teeth

  • Masseter, Temporalis, Pterygoids, digastricus

Head and Neck Muscles

Flexion - muscles deep within the neck along the anterior margins of the vertebral bodies

Extension - posterior neck muscles attached to occipital bone

Rotation and Abduction - lateral and posterior groups

  • sternocleidomastoid, trapezius, splenius muscles

Thoracic Muscles

Involved in breathing: four groups associated with riy cage

  • Scalene - Elevate first two ribs during inspiration

  • External Intercostals - Elevate ribs

  • Internal Intercostals - depress ribs during expiration

  • Transverse Thoracis - depresses ribs during expiration

  • Diaphragm - major movement of inspiration: flattens during contraction and increases the volume of the thoracic Cavity

Abdominal Wall

Flex and rotate vertebral column, decrease volume of abdominal and thoracic cavities

Aid in forced expiration, vomiting, defecation, urination, Child birth

Crossing Patterns of muscles adds strength to abdominal wall to support organs.

Upper Limb Muscles

Scapular Movements

  • Muscles that attach the upper limb to the body and move or stabilize the scapula and clavicle

  • Originate on the axial Skeleton

  • Trapezius, Levator Scapulae, Rhomboideus, serratus anterior, pectoralis Minor

Arm Movements

Muscles that attach arm to thorax-pectoralis Major, latissimus dorsi

Deltoid and Pectoralis major both acts as flexors and extensors of the shoulder

Deltoid abducts and medially and laterally rotates arm

Rotator Cuff

Primary muscles holding humerus in the glenoid cavity

Form a cuff or cap over the proximal humerus

Involved in flexion, Extension, abduction, adduction, rotation, circumduction

Infraspinatus, subscapularis, supraspinatus, teres minor

Forearm Movements

Movements at the elbow

Extension - triceps brachii and anconeus

Flexion - biceps brachii, brachioradialis, brachialis

Supination and Pronation

Supination - supinator and biceps bronchi

Pronation - Pronator quadratus and Pronator teres

Wrist, Hand, and Finger Movements

muscles on anterior surface of forearm - flexion, abduction, and Adduction of the wrist

Muscles on posterior surface of forearm - extension and abduction

Retinacula - bands of deep fascia, hold tendons of muscles of forearm, blood vessels, and nerves to close wrist

  • Flexor retinaculum - on the flexor surface

  • Extensor retinaculum - on extensor surface

Lower Limb Muscles

Thigh Movements

originate on coxal bone; insert onto femur

Anterior, posterolateral, deep

  • Anterior - flex hip. Illiacus and psoas major often reffered to as iliopsoas since they share a tendon of insertion

  • posterolateral - gluteaus and tensor fascine lktae extension of thigh

  • Deep - thigh rotators

Leg Movements

Quadriceps Femoris - Anterior Surface of thigh

  • Extension of the leg at the knee

  • rectus femoris also flexes the hip

  • Insert by common tendon(patellar tendon) on and around patella

  • Patellar tendon extends from patella to bibial tuberosity

Sartorius - flexes hip and knee, laterally rotates thigh

medial thigh muscles - adduction

posterior thigh muscles - hamstrings; flexion and rotation of the knee

Ankle, Foot, and Toe movements

Extrinsic foot muscles

Three leg compartments

Anterior compartment - extensors involved in dorsiflexion

and eversion/inversion of foot, Extend toes

lateral compartment - plantar flexion and eversion

posterior compartment

  • superficial muscles - have common tendon of insertion called Calcaneal (Achilles) tendon

    • Gastrocnemius, Plantaris

  • Deep muscles - plantar flex and invert fool -