Chapter 10: Muscular System

Prime movers/Agonists

A muscle that provides the major force for producing a specific movement.

Functional Groups of Muscles

Prime movers/agonists, synergists, antagonists, and fixators

Antagonists

Muscles that oppose or reverse a particular movement.

Synergists

Muscles that help prime movers by adding extra force to the movement or reducing undesirable or unnecessary movements.

Fixators

Function as synergists that immobilize a bone or a muscle's origin.

Naming Skeletal Muscles

Location, Shape, Size, Direction of Fibers, Number of Origins, Location of Attachments, and Action

Location

Some muscles indicate bone or body region, such as Intercostal and temporalis.

Shape of the muscle

Muscles are named after the shape they resemble, such as Deltoid (triangle) and Trapezium (Trapezoid).

Relative Size

Some muscles are named based on their size, such as maximus (largest), minimus (smallest), longus (long), or brevis (short).

Direction of muscle fibers

Some muscle names reveal the direction of the muscle fibers relative to the mid-line of the body or longitudinal axis of the bone, such as Rectus (straight), Transversus (run at right angles), and Oblique (form oblique angles).

Number of origins

Occasionally incorporated is the number of origins, such as biceps, triceps, or quadriceps.

Location of attachment

Some muscles are named by where they attach, with points of origin and insertion, whereby the origin is named first, such as Sternocleidomastoid (Sternum and Clavicle).

Action

Muscles are often named by their action and incorporate action words such as flexor, extensor, adductor, abductor, supinator, and pronator.

Extensor carpi radialis longus

An example of a muscle name that uses several criteria for naming.

Arrangement of Fascicles

circular, convergent, parallel, fusiform, pennate

Circular

The fascicles are arranged in concentric rings (orbicularis oris)

Convergent

When the muscle has a broad origin but converges toward a single tendon (Pectoralis Major)

Parallel

The long axis of the fascicles run down the long axis of the muscle (Sartorius)

Fusiform

Muscles that run parallel but have an expanded midsection (Biceps brachii)

Pennate

The fascicles are short and attach obliquely to a central tendon that runs the length of the muscle, giving a feather-like appearance (pennate - feather)

Unipennate

Extensor digitorum longus

Bipennate

Rectus femoris

Multipennate

Deltoid

Lever

A small rigid bar that moves on a fixed point (bones)

Fulcrum

The fixed point in which a lever moves on (joints)

Effort

The applied force used to move a resistance (muscle contractions)

Load

The resistance being moved (the bone intended to be moved with all attached tissue)

Types of Levers

power lever and speed lever

Power lever

When the load is close to the fulcrum allowing a given effort to move a heavier load (mechanical advantage)

Speed lever

When the load is far from the fulcrum, the force exerted must be greater to move a smaller load (mechanical disadvantage)

Class of Levers

first class, second class, third class

First Class Lever

The fulcrum sits in between the effort and the load

Second Class Lever

The load sits in between the fulcrum and the effort

Third Class Lever

The effort is applied in between the load and the fulcrum

Frontalis (A)

(A) Raises Eyebrows

Occipitalis (O)

(O) Occipital and Temporal bones

(A) Pulls Scalp posteriorly

Zygomaticus (O, I, A)

(O) Zygomatic Bone

(I) Corners of the mouth

(A) Smiling

Orbicularis Oculi (O, A)

(O) Frontal bone and Maxilla

(A) Closes the eyelids and moves eyebrows inward

Orbicularis Oris (A)

(A) Closes the lips, Puckers lips for kissing and whistling

Masseter (O, I, A)

(O) Zygomatic Arch

(I) Angle and Ramus of Mandible

(A) Prime mover of jaw closure; elevates mandible

Temporalis (O, A)

(O) Temporal Fossa

(A) Closes jaw; elevates and retracts mandible

Genioglossus (I, A)

(I) Hyoid and Tongue;

(A) Primarily protrudes tongue

Hyoglossus (O)

(O) Hyoid bone

Styloglossus (O)

(O) Styloid Process

(A) Retracts tongue

Digastric (I)

(I) Hyoid

Stylohyoid (O, I)

(O) styloid process of temporal bone

(I) hyoid bone

Mylohyoid (O, I)

(O) mandible

(I) hyoid

Geniohyoid (O, I)

(O) inferior mental spine of mandible

(I) hyoid

Sternothyroid (O, I)

(O) sternum

(I) thyroid

Thyrohyoid (O, I)

(O) thyroid

(I) hyoid

Sternocleiodomastoid (O, I, A)

(O) sternum

(I) mastoid

(A) Flexes the head and rotates neck towards shoulder

Splenius (O, I, A)

(O) Spinous process of vertebrae C7 - T6

(I) Mastoid Process and transverse process of C2 - C4

(A) Extends Head and Neck and rotates Neck and head laterally

External Intercostals (A)

(A) Aides in inspiration

Internal Intercostals (A)

(A) Aides in Expiration

Diaphram (I, A)

(I) Central Tendon

(A) Prime mover for inspiration

Rectus Abdominis (O, I, A)

(O) Pubic Crest and Symphysis

(I) Xiphoid Process

(A) Flex and rotate lumbar region

Obliques (I, A)

(I) Linea Alba

(A) Flexes vertebrae, rotates trunks, and lateral flexion

Transverse Abdominis (A)

(A) compresses abdominal content

Pectoralis Major (I, A)

(I) Intertubercular groove

(A) Adducts arm

Pectoralis Minor (I, A)

(I) Coracoid process

(A) Draws scapula down and forward and rib cage superiorly

Levator Scapulae (A)

(A) Elevates/adducts scapula

Rhomboids (I)

(I) Medial border of scapula

Trapezius (O, I)

(O) occipital bone, spines of C7 and thoracic vertebrae

(I) acromion and spine of scapula and clavicle

Latissimus Dorsi (A)

(A) Brings arm down

Deltoid (I, A)

(I) Deltoid tuberosity

(A) Abduction of Arm

Triceps brachii (I, A)

(I) Olecranon Process

(A) Forearm Extensor

Biceps brachii (I, A)

(I) radial tuberosity

(A) flexes elbow joint

Brachialis (O, I, A)

(O) Humerus

(I) Coronoid process

(A) Forearm Flexor

Brachioradialis (O, I, A)

(O) Humerus

(I) Styloid process of radius

(A) Stabilizes elbow

Pronator teres (A)

(A) pronates forearm

Flexor carpi radialis (A)

(A) flexes wrist

Palmaris longus (O, A)

(O) medial epicondyle of humerus

(A) Tenses skin and facia of palm

Flexor Carpi Ulnaris (A)

(A) Flexes wrist

Pronator quadratus (A)

(A) Holds radius and Ulna together

Extensor Carpi Radialis Longus (I, A)

(I) Second metacarpal

(A) Extends and abducts wrist

Extensor Carpi Radialis Brevis (I, A)

(I) Third metacarpal

(A) Extends and abducts wrist

Extensor digitorum (A)

(A) Extends wrist and fingers

Extensor carpi ulnaris (I, A)

(I) Fifth metacarpal

(A) Extends wrist

Abductor pollicus longus (I, A)

(I) Base of first metacarpal and trapezium

(A) Abducts and extends thumb

Sartorius (O)

(O) Anterior Superior Iliac Spine

Gracilis (O, I, A)

(O, I) Ischial and pubic ramus and body of Pubis

(A) Adducts thigh

Quadriceps Femoris (I, A)

(I) Patella

(A) Knee Extensor

Rectus Femoris (O, I, A)

(O) Anterior Inferior Iliac Spine

(I) Patella and Tibial Tuberosity

(A) Extends Knee and Flexes thigh

Vastus Lateralis and Medialis (O, A)

(O) Greater trochanter, Intertrochanteric line, and Linea Aspera

(A) Extends the knee

Gluteal maximus (O, I, A)

(O) Dorsal Ilium, Sacrum, and Coccyx

(I) Gluteal Tuberosity

(A) Extensor of thigh

Gluteal medius (I, A)

(I) Hamstrings

(A) Greater Trochanter

Muscles that make up the Hamstrings

biceps femoris, semitendinosus, semimembranosus

Biceps Femoris, Semitendinosus, and Semimembranosus (O, A)

(O) Ischial Tuberosity

(A) Extends thigh and flexes knee

Tibialis anterior (O, I, A)

(O) Lateral condyle and upper 2/3 Tibial shaft

(I) 1st Cuneiform and metatarsal

(A) Dorsiflexion

Gastrocnemius (O,I,A)

(O) Medial lateral Condyles of Femur

(I) Calcaneus

(A) Plantar Flexion of foot

Soleus (O, I, A)

(O) Upper Tibia and Fibula

(I) Calcaneus

(A) Plantar Flexion of Foot and postural muscle during walking, running, and dancing