Bio D170 Lecture 10: Muscles II

Lever

A rigid bar that moves on a fixed point

Fulcrum

The fixed point on which the rigid bar of a lever moves

Effort

The applied force used to move a resistance (load) on a lever

Load

The resistance that is moved by the effort on a lever

Prime mover

AKA agonist

Muscle that has the major responsibility for producing a specific movement

Agonist

AKA prime mover

Muscle that has the major responsibility for producing a specific movement

"leader"

Antagonist

Muscles that oppose or reverse a particular movement

Synergist

Help PM by adding extra force to the movement being carried out or by reducing undesirable extra movements that the PM may produce

Fixator

A synergist that holds a bone firmly in place so that a PM has a stable base on which to move a body part (e.g. muscles that fix scapula when arm moves)

Masseter

Powerful muscle that covers the lateral aspect of the ramus of mandible

*Closes jaw

Temporalis

Fan-shaped muscle that covers parts of the temporal, frontal, and parietal bones

*Closes jaw

Buccinator

Thin, horizontal cheek muscle

Principle muscle of cheek; deep to masseter

*Compresses cheek

Medial pterygoid

Deep two-headed muscle that runs along internal surface of mandible; largely concealed by mandible

*Acts w/ lateral pterygoid to protract mandible and produce grinding (side-to-side) movements

Lateral pterygoid

Deep two-headed muscle; lies superior to medial pterygoid muscle

*Protracts mandible and produces grinding (side-to-side) movements of lower teeth

Digastric

Consists of two bellies united by an intermediate tendon, forming a V shape under the chin

*Opens mouth and depresses mandible

Pectoralis minor

Flat, thin muscle deep to the pectoralis major

*With ribs fixed, protracts and rotates scapula downward

Serratus anterior

Fan-shaped muscle deep to scapula

Forms medial wall of axilla

*Rotates scapula upward

Subclavius

Small cylindrical muscle extending from rib 1 to clavicle

*Helps stabilize and depress pectoral girdle

Trapezius

Most superficial muscle of posterior thorax

Flat and triangular

*Stabilizes, elevates, retracts, and rotates scapula

Levator scapulae

Located at back and side of neck, deep to trapezius;

Thick, straplike

*Elevates and adducts scapula

Rhomboids

Two rectangular muscles deep to trapezius and inferior to levator scapulae

Minor rhomboid is more superior

*Stabilize scapula

Pectoralis major

Large, fan-shaped muscle covering upper portion of chest

Divided into sternal and clavicular parts

*PM of arm flexion; rotates arm medially; adducts arm

Deltoid

Thick, multipennate muscle forming rounded shoulder muscle mass; used for IM injection

*PM of arm abduction when all its fibers contract simultaneously

Latissimus dorsi

Broad, flat, triangular muscle of lumbar region

*PM of arm extension; adductionn and medial rotation of arm

Teres major

Thick, rounded muscle located inferior to teres minor

*Extends, medially rotates, and adducts the arm

Subscapularis

Rotator cuff muscle; Forms part of posterior wall of axilla; tendon of insertion passes in front of shoulder joint

*Medially rotates arm

Supraspinatus

Rotator cuff muscle; named for its location of posterior aspect of scapula; deep to trapezius

*Initiates abduction of arm

Infraspinatus

Rotator cuff muscle; partially covered by deltoid and trapezius; named for its scapular location

*Laterally rotates arm

Teres minor

Rotator cuff muscle; small, elongated; inferior to infraspinatus

*Laterally rotates arm

Coracobrachialis

Small, cylindrical muscle; located in anterior compartment of arm

*Flexion and adduction of arm

Biceps brachii

Two-headed fusiform muscle

Bellies unite as insertion point is approached

*Flexes and supinates forearm

Triceps brachii

Large, fleshy muscle

Only muscle in posterior compartment of arm

Three-headed origin

*Powerful forearm extensor

Anconeus

Short, triangular muscle

Closely associated with distal end of triceps on posterior humerus

*Abducts ulna during forearm pronation

*Synergist in elbow extension

Brachialis

Strong muscle immediately deep to biceps brachii

*Flexes forearm

Brachioradialis

Superficial muscle of lateral forearm

*Synergist in forearm flexion

Sartorius

Straplike superificial muscle running obliquely across anterior surface of thigh to knee

*Flexes, abducts, and laterally rotates thigh; flexes leg

Quadriceps femoris

Four separate heads that form the flesh of the front and sides of thigh:

Rectus femoris, lateral, medial, and intermediate vastus muscles

*All extend the leg

Rectus femoris

Superficial muscle of anterior thigh; runs straight down thigh

Longest head and only muscle of group to cross hip joint

*Extends leg and flexes thigh

Vastus lateralis

Largest head of group, forms lateral aspect of thigh; common IM site

*Extends leg and stabilizes knee

Vastus medialis

Forms inferomedial aspect of thigh

*Extends leg

Vastus intermedius

Obscured by rectus femoris; lies between vastus lateralis and vastus medialis on anterior thigh

*Extends leg

Hamstrings

Fleshy muscles of posterior thigh:

Biceps femoris, semitendinosus, semimembranosus

*All extend the thigh and flex the leg

Biceps femoris

Most lateral of hamstrings; Arises from two heads

*Extends thigh and flexes leg, laterally rotates leg

Semitendinosus

Medial to biceps femoris; Has a long, slender tendon that begins about two-thirds of the way down the thigh

*Extends thigh and flexes leg, medially rotates leg

Semimembranosus

Deep to semitendinosus

*Extends thigh and flexes leg, medially rotates leg

Popliteus

Thin, triangular muscle of posterior knee; passes downward and medially to tibial surface

*Flexes and rotates leg medially to unlock knee from full extension when flexion begins

External oblique

Large and superficial, part of anterior and lateral wall of abdomen

*Flexes vertebral column and compresses abdominal wall

Internal oblique

Fibers run superiorly and medially, part of anterior and lateral wall of abdomen

*Flexes vertebral column and compresses abdominal wall

Transverse abdominus

Deepest muscle, fibers run horizontally, part of anterior and lateral wall of abdomen

*Compresses abdominal contents

Rectus abdominus

Medial muscle pair of anterior and lateral abdominal wall

Extend from pubis to ribcage

*Flexes and rotates lumbar region of vertebral column

Psoas major

Long, thick, medial muscle of iliopsoas

*PM in thigh flexion and flexion of trunk

*Causes lateral flexion of vertebral column