muscular sytem

PREPARED BY:PAUL MARK P. PILAR, RN

FUNCTIONS OF THE MUSCULAR SYSTEM1. Body movement

- contraction of skeletal muscles is responsible for the overall movements of the body

- enables us to respond quickly to changes in the environment

2. Maintenance of posture

- skeletal muscles constantly maintain tone, which keeps us sitting or standing erect

3. Respiration

- muscles of the thorax are responsible for the movements necessary for respiration

4. Production of body heat

- when skeletal muscles contract, heat is given off as by – product

- heat released is critical to the maintenance of body temperature

FUNCTIONS OF THE MUSCULAR SYSTEM5. Communication

- skeletal muscles are involved are involved in all aspects of communication such as speaking, writing, typing, gesturing and facial expression

6. Constriction of organs and vessels- contraction of smooth muscle within the walls of internal

organs and vessels causes constriction of the structures- contraction can help propel and mix food and water in the

digestive tract, propel secretions from organs and regulate blood flow through vessels

7. Heart beat- the contraction of cardiac muscle causes the heart to beat,

propelling blood to all parts of the body

8. Stabilizes the joints- reinforces and stabilizes joints upon movement

CARDIAC MUSCLES

- IS THE MUSCLE OF THE HEART AND IS RESPONSIBLE FOR PUMPING BLOOD

- UNDER INVOLUNTARY CONTROL

STRUCTURE:

- CYLINDRICAL IN SHAPE BUT SHORTER IN LENGTH THAN SKELETAL MUSCLES

- STRIATED AND USUALLY HAVE ONE NUCLEUS PER CELL

- BRANCHED AND CONNECTED TO ONE ANOTHER BY INTERCALATED DISCS

LOCATION:

HEART

SMOOTH MUSCLES

- forms the walls of hollow organs except the heart

- also found in the skin and the eyes

- under involuntary control

Structure:

- tapered at each end, not striated and have a single nuclus

Function:

- regulates the size of organs

- forces fluids through tubes

- controls the amount of light entering the eye

- produces goose flesh in the skin

SKELETAL MUSCLES

- also called “striated muscle”

- constitutes about 40% of a person’s body weight

- attaches to the skeleton and enables movement

- under voluntary control

Structure:

- cells are large, long and cylindrical

- cells are striated

- multiple nuclei located in the periphery

Location:

- attaches to bone or other connective tissue

CHARACTERISTICS OF SKELETAL MUSCLE

1. Contractility- is the ability of the skeletal muscle to shorten with force- when skeletal muscles contract they cause movement of the structures to which they are attached

2. Excitability / Irritability- is the capacity of skeletal muscle to respond to stimulus- skeletal muscle contract as a result of stimulation by nerves

3. Extensibility- means that the skeletal can be stretched

4. Elasticity- ability of skeletal muscles to recoil to their original resting length after they have been stretched

STRUCTURE OF SKELETAL MUSCLE1. Muscle fiber / muscle cell

- single cylindrical cell that contains several nuclei located at the periphery of the muscle fiber- the largest, longest human muscle can reach up to 30 cm long and .15 mm in diameter

2. Endomysium- loose connective tissue sheath that surrounds each muscle fiber

3. Fascicle / muscle fasciculi- bundle of fibers- composed of several endomyseum sheathed muscle fibers

4. Perimysium- loose connective tissue sheath that surrounds each fascicle

5. Epimysium / Fascia- a connective tissue sheath that surrounds the skeletal muscle, which is a group of fascicles

STRUCTURE OF A MUSCLE CELL1. Sarcoplasm

- cytoplasm of the muscle cell

- contains numerous myofibrils

2. Myofibril

- threadlike structure that extends from one end of the muscle fiber to the other

- composed of several sarcomeres

3. Sarcomeres

- basic structural and functional unit of skeletal muscle

- it is the smallest portion of the skeletal muscle capable of contracting

- consist of two major kinds of threadlike protein fibers: actin and myosin myofilaments

STRUCTURE OF A MUSCLE CELL4. Myosin myofilament (thick filament)

- resemble bundles of minute golf clubs

- part of the myosin filaments that resemble minute golf clubs are called Cross bridges because the heads binds to attachment sites of actin filaments

- contains ATPase enzyme which breaks down ATP

5. Actin myofilament (thin filament)

- resembles two minute strands of pearls twisted together

- consist of actin, troponin and tropomyosin

6. Sarcolemma

- cell membrane of the cell fiber

- transverse or T Tubules connect the sarcolemma to the sarcoplasmic reticulum which is a storage site for calcium ions

http://upload.wikimedia.org/wikipedia/commons/c/c0/Skeletal_muscle.jpg

MEMBRANE POTENTIALS

- muscle fibers, like all other cells of the body, have electrical properties

- outside of most cell membranes is positively charged compared with the inside of the cell membrane which is negatively charged

- the charge difference is called the Resting membrane potential

Resting membrane potential develops for two reasons:

1. The concentration of K inside the cell membrane is higher than that outside of the cell membrane

2. The cell membrane is more permeable to K than it is to other ions

- Movement of K from inside of the cell to the outside of the cell causes the outside of the cell membrane to become positively charged

THE NERVE STIMULUS AND ACTION POTENTIAL

MEMBRANE POTENTIALS- when a muscle cell or nerve cell is stimulated, Na channels open quickly and the membrane becomes very permeable to sodium for a brief time

- when Na channels open, diffusion occurs, wherein the Na ions outside of the cell decrease their concentration by entering the cell, causing the inside of the cell membrane to become more positive than the outside of the cell

- This change is called depolarization

- at the end of depolarization or when the stimulus is stopped, Na channels closes and additional K channels open. The tendency for Na to enter the cell is decreased and the tendency of K to leave the cell is increased

- these changes cause the inside of the cell membrane to become more negative than the outside once again and the cell returns to its resting condition

- the change back to the resting membrane potential is called repolarization

MEMBRANE POTENTIALS- the rapid depolarization and repolarization of the cell membrane is called an action potential

- in muscle fiber, an action potential results in muscle contraction

NERVE SUPPLY OF SKELETAL MUSCLE

- nerve muscles does not contract unless they are stimulated by motor neurons

1. Motor unit- consists of one neuron and all the skeletal muscles it stimulates

2. Motor neurons- are nerve cells along which action potentials travel to skeletal muscle fibers- axons of these neurons enter muscles and send out branches to several muscle fibers called axon terminals- each branch forms a junction with a skeletal muscle fiber, called a neuromuscular junction or synapse.

3. Synapse- refers to the cell – to – cell junction between a nerve cell with another nerve cell or an effector cell, such as a muscle or gland cell

NERVE SUPPLY OF SKELETAL MUSCLE

4. Synaptic cleft

- the gap between presynaptic terminal/axon terminal and the muscle fiber

- filled with interstitial fluid

NEUROMUSCULAR JUNCTION- formed by a cluster of enlarged axon terminals resting in indentations of the muscle fiber’s cell membrane

1. Presynaptic terminal- an enlarged axon terminal- contains synaptic vesicles which contain acetylcholine which is a neurotransmitter

• Neurotransmitter – a molecule released by a presynaptic nerve cell that stimulates or inhibits a postcynaptic cell

2. Postcynaptic membrane- the muscle fiber membrane

3. Synaptic cleft- the space between the presynaptic and postcynaptic membrane filled with tissue fluid

MUSCLE TWITCH, SUMMATION, TETANUS AND RECRUITMENT

Muscle twitch- is the contraction of a muscle fiber in response to a stimulus- contraction of all muscle fibers in a motor unit

3 phases: 1. The lag phase

- the time between the application of a stimulus and the beginning of a contraction

2. Contraction phase- is the time of the contraction

3. Relaxation phase - time during which the muscle relaxes


STRENGTH OF MUSCLE CONTRACTIONS

- varies from weak to strong

Force of Contraction is increased in 2 ways:

1. Summation

-involves increasing the force of contraction of the muscle fibers within the muscle by rapidly stimulating them

2. Recruitment

- involves increasing the number of muscle fibers contracting


1. Summation- involves increasing the force of contraction of the muscle fibers within the muscle by rapidly stimulating them

• Stimulus frequency – number of times a motor neuron is stimulated per second

- when stimulus frequency is low there is time for complete muscle relaxation between muscle twitches

- as stimulus frequency increases, there is not enough time between contractions for the muscle fibers to completely relax. Thus one contraction summates or is added to a previous contraction and the overall force of contraction increases.

• Tetanus (convulsive tension)- is a sustained contraction that occurs when the frequency of stimulus is so rapid that there is no relaxation


2. Recruitment- strength of muscle contraction is increased by increasing the number of motor units stimulated.

- when only a few motor units are stimulated, a small force of contraction is produced.

- as the number of motor units stimulated increases, more muscle fibers contract and the force of muscle contraction increases

• Maximum Force of contraction- achieved when all motor units of a muscle is stimulated (recruited)

* Smooth relaxation of muscles occur because some motor units are held in tetanus while other motor units relax

ENERGY REQUIREMENTS FOR MUSCLE CONTRACTION

- muscles require ATP for contraction and relaxation

- ATP is constantly produced by the muscle cells

- muscles have initially a limited supply of energy that can last for 4 – 6 seconds

3 ways of ATP regeneration

1. Direct phospholyration of ADP by CP

- Creatinine is phosphate is stored on muscle fibers as an alternate source of energy when initial ATP supply is exhausted

- ATP is produced when Adenosine Diphosphate (ADP) interacts with Creatinine Phosphate (CP)

Products: 1 ATP per CP, creatinine



2. Aerobic respiration

- glucose is broken down completely to carbon dioxide, water and 36 ATP by the use of oxygen

- occurs in the mitochondria

- provides a rich supply of ATP but ATP production is slow and it requires continuous supply of oxygen and nutrients to fuel the muscle

- more efficient in ATP production than Anaerobic respiration

• Products:

- carbon dioxide, water and 36 ATP



3. Anaerobic respiration- glucose is broken down to produce 2 ATP molecules and lactic acid- occurs in the cytoplasm of the cell- occurs when the CP supply is exhausted and when there insufficient oxygen supply in the muscle- less ATP molecules per molecule of glucose are produced but it is 2 ½ times faster than aerobic respiration- it is very important when O2 availability limits aerobic respiration.- it is limited by the depletion of glucose and a build up of lactic acid within the muscle fiber

• Lactic acid- one of the end products of anaerobic respiration- can irritate muscle fibers, causing short – term pain


PRODUCTION OF ATP IN RESTING AND EXERCISING MUSCLE

1. At rest, ATP is produced by aerobic respiration

2. Small amounts of ATP are used in muscle contractions that maintain muscle tone and posture

3. Excess ATP is used to produced creatinine phosphatase

4. As exercise begins, ATP stores in the cells are first used

5. During moderate exercise, aerobic respiration provides most of the ATP necessary for muscle contraction

6. Energy stored in CP can also be used to produce ATP

7. During times of extreme exercise, anaerobic respiration provides small amounts of ATP that can sustain muscle contraction for brief periods

• Muscle fatigue

- results when ATP is used during muscular contraction faster than it can be produced in the muscle fibers and lactic acid builds up faster than it can be removed

- as a result the muscle cannot contract even if it is still being stimulated

- believed to be a result from the oxygen debt that occurs during prolonged muscle activity

• Oxygen debt

- occurs when the person is not able to take in oxygen fast enough to keep the muscles supplied with oxygen during vigorous muscular contraction, as a result anaerobic respiration occurs and there is build up of lactic acid

- during the recovery period after activity, there is increase in the depth and rate of respiration until all muscles are supplied with adequate oxygen to produce ATP and CP reserves and the accumulated lactic acid is removed from the muscles

TYPES OF MUSCULAR CONTRACTIONS1. Isotonic (equal tension, same tone) contraction

- the amount of tension produced by the muscle is constant during contraction but the length of the muscle decreases

Examples:

1.bending the knee

2. movement of arms and fingers

3. smiling

2. Isometric (equal distance, same length) contraction

- the amount of tension increases during contraction, but the length of the muscle does not change

- responsible for the constant length of the muscles of the back

• Muscle Tone

- refers to the constant tension produced by muscles of the body over long periods of time

- responsible for keeping the backs and legs straight, the head held in an upright position.

- depends on a small percentage of all motor units in a muscle being stimulated at any point in time

EFFECTS OF EXERCISE ON MUSCLES1. Aerobic, or endurance types of exercises produces stronger and more

flexible muscles resistant to fatigue

- exercise increases the blood supply to muscles and formation of more mitochondria and it increases the muscle’s ability to store more oxygen

2. The heart enlarges so that more blood is pump with every beat

3. Resistance or isometric exercises increases muscle cells and the production of more myofilaments

• Bodybuilding

- is the exercise to produce muscle hypertrophy

DISORDERS OF MUSCLE TISSUE1. Cramps

- are painful, spastic contractions of muscle that are usually the result of an irritation within a muscle.- it is a local inflammation from buildup of lactic acid or by connective tissue inflammation that can cause muscle contraction of muscle fibers in the surrounding region

2. Hypertrophy- is an enlargement of a muscle resulting from an increase in the number of myofibrils within muscle fibers- result of increased testosterone levels in the blood

3. Atrophy- decrease in muscle size because of a decrease in myofilaments within muscle fibers.severe atrophy involves the permanent loss of skeletal muscle fibers and the replacement of muscle fibers by connective tissue

DISORDERS OF MUSCLE TISSUE- caused by immobility or by the disuse of muscles- can also be a result when nerve supply to the muscle is severed

in which the muscle becomes flaccid

4. Muscular dystrophy- refers to a group of inherited muscle disorder in which skeletal, cardiac and smooth muscle tissue degenerates- the person experiences progressive weakness and other symptoms including heart problems- characterized by the progressive degeneration of muscle fibers leading to atrophy

Myotonic Muscular dystrophy- characterized by the failure of muscles to relax following a forceful contraction as well as muscular weakness- it is an inheritable disease that occurs in 1 every 20,000 births- the disorder progresses slowly, usually affecting the face and neck muscles and affects the hands most severely

The two points of muscle attachment are:

1. Origin

2. Insertion

1. Origin

- also called the head

- attached to the immovable or less movable bone

2. Insertion

- is the end of the muscle attached to the movable bone

* As contraction occurs, the insertion moves toward the origin

TYPES OF BODY MOVEMENTSFlexion

- moves a part of the body in the anterior or ventral to the coronal plane

- movement, generally in the sagittal plane, that decreases the angle of the joint and brings two bones closer together

Extension

- moves a part in a posterior or dorsal to the coronal plane.

- opposite of flexion, movement that increases the angle or distance between the two bones

Plantar flexion

- movement of the foot toward the plantar surface (sole of the foot), such as standing on toes

Dorsiflexion

- movement of the foot toward the shin, such as when walking on heels

TYPES OF BODY MOVEMENTSAbduction

- to take away

- is a movement away from the median or midsagittal plane

Adduction

- to bring together

- movement toward the median plane

Pronation

- rotation of the forearm so that the palm is down

Supination

- is a rotation of the forearm so that the palm faces up

Rotation

- movement of a bone along its longtitudinal axis

- common movement of ball and socket joints

TYPES OF BODY MOVEMENTSEversion

- turning the foot so that the plantar surface faces laterally

Inversion- is turning the foot so that the plantar surface faces medially

Protraction- movement of the mandible anteriorly

Retraction- the mandible glides posteriorly

Elevation- movement of the mandible in a superior direction

Depression- movement of the mandible in a n inferior direction

TYPES OF BODY MOVEMENTSExcursion

- movement of the mandible from side to side

Opposition

- movement unique to the thumb and the other fingers

- the thumb and one of the fingers are brought toward each other across the palm of the hand

Reposition

- returns the digits to the anatomic position

Circumduction

- occurs at freely movable joints such as the shoulder

- proximal end of the limb is stationary, and its distal end moves in circle

NAMING SKELETAL MUSCLESDirection of the muscle fibers

- muscles are named in reference to the midline of the bodyRectus – means straight, in which in runs parallel to the midlineOblique – muscles run at a slant to the midline

Relative size of the muscleMaximus – largestVastus – largeMinimus – smallestLongus – long

Location of the muscle group- muscles are named for the bone with which they are associated

Number of originsBi – twotri – threeQuad – four

NAMING SKELETAL MUSCLESLocation of the muscle’s origin and insertion

- muscles are named for their attachment sites

Shape of the muscle

Deltoid – triangular

trapezius – diamond or kite shaped

Action of the muscle

Flexor – muscles that flexes a structure

Adductor – muscles that adduct a structure

Abductor – muscles that abduct a structure

MUSCLES OF THE HEAD AND NECK

- Muscles of head and neck include those involved in facial expression, mastication, movement of the tongue, swallowing, voice production, eye movements and movements of the head and neck

MUSCLES OF FACIAL EXPRESSION1. Occipitofrontalis – raises the eyebrows, moves scalp

2. Orbicularis oculi – encircles the eyes, tightly closes the eyelids

- causes “crows feet” wrinkles in the skin at lateral corners of the eyes

3. Orbicularis oris – closes lip

and buccinator – are sometimes called the “kissing muscles” because they pucker the mouth

4. Buccinator – flattens the cheeks as in whistling or blowing a trumpet

- also called the “trumpeter’s muscle”

5. Zygomaticus (major and minor – called the “smiling muscle” because it elevates the upper lip and corner of the mouth

6. Depressor anguli oris – “frowning muscle”

- it depresses the corner of mouth

MUSCLES OF FACIAL EXPRESSION

7. Levator labii superioris and Levator anguli oris - elevates upper lip

MUSCLES OF MASTICATION- some of the strongest muscles in the body

1. Temporalis – fan shaped muscle overlying the temporal bone- acts a synergist of the masseter in closing the jaw

2. Masseter – closes the jaw by elevating the mandible

3. Pterygoid (lateral and medial) – protracts and depresses mandible, involved in excursion

- located deep into the mandible

TONGUE AND SWALLOWING MUSCLES1. Intrinsic muscles – muscles that makes up the tongue

- responsible for the changes in the shape of tongue

2. Extrinsic muscles – located outside the tongue but are attached to and move the tongue

3. Hyoid muscles – elevates or stabilizers hyoid

4. Pharyngeal muscles – elevates and constricts the pharynx

NECK MUSCLES

1. Sternocleidomastoid – a pair of muscle found on each side of the neck

- contraction of one sternocleidomastoid muscle causes rotation of the head

- contraction of both muscles results in flexion or extension of the head

• Torticolis / wry neck / twisted neck – injury of one or both sternocleidomastoid muscle

2. Trapezius – extends head and neck

TRUNK MUSCLES

- include those that move the vertebral column, those of the thorax and abdominal wall, and those of the pelvic floor

MUSCLES MOVING THE VERTEBRAL COLUMN

1. Erector spinae muscles (iliocostalis, Longissimus, Spinalis)

– group of muscles in each side of the back are the muscles primary responsible for keeping the back straight and the body erect

2. Deep back muscles – responsible for several movements of the vertebral column such as extension, lateral flexion and rotation

THORACIC MUSCLES

- are involved almost entirely in the process of breathing

1. External intercostals – elevate the ribs during inspiration

2. Internal intercostals – depresses the ribs during forced expiration

3. Diaphragm – depresses the floor of the thorax during inspiration

4. Scalenes – elevates ribs during inspiration

ABDOMINAL WALL MUSCLES

- anterior abdominal wall muscles flex and rotate the vertebral column, compress the abdominal cavity, and hold in and protect the abdominal organs.

Linea alba – vertical indentation, extending from the sternum through the navel to the pubis

- consists of a white connective tissue rather than muscle

1. Rectus abdominis – found on each side of the linea alba

- flexes vertebral column and compresses abdomen

2. External abdominal oblique / internal abdominal oblique - compresses the abdomen and flexes and rotates the vertebral column

3. Transversus abdominis – compresses the abdomen

PELVIC FLOOR AND ABDOMINAL MUSCLES

Pelvic Floor / pelvic diaphragm

- mostly formed by the levator ani muscle

1. Levator ani – elevates anus, supports pelvic viscera

Perineum – area inferior to the pelvic floor

2. Perineal muscles

a. Bulbospongiosus – constricts urethra and erects penis and clitoris

b. External anal sphincter – keeps orifice of anal canal closed

c. Ischiocavernosus – compresses base of penis or clitoris

UPPER LIMB MUSCLES

- includes muscles that attach the limb and pectoral girdle to the body and those that are in the arm, forearm and hand

MUSCLES ACTING ON THE SCAPULA

- these muscles acts as fixators to hold the scapula firmly in position when the muscles of the arm contract

1. Levator scapulae – elevates, retracts and rotates scapula and laterally flexes neck

2. Pectoralis minor – depresses scapula or elevates ribs

3. Rhomboids major – retracts, rotates and fixes scapula

4. Rhomboids minor – retracts, slightly elevates, rotates and fixes scapula

5. Trapezius – elevates, depresses, retracts, rotates and fixes scapula and extends head and neck

ARM MOVEMENTS1. Pectoralis major – attaches the arm to the thorax

- flexes shoulder. Extends shoulder from flexed position, adducts and medially rotates arm

2. Latisimus dorsi - attaches the arm to the thorax- also called the “swimmer’s muscle”- powerfully extends shoulder, adducts and medially rotates arm

3. Deltoid – forms the rounded mass of the shoulder- common site for administering injections- flexes and extends the shoulder, abducts and medially and laterally rotates arm

4. Rotator cuff muscles – attaches the humerus to the scapula and forms a cuff or cap over the proximal humerus

- stabilizes the shoulder joint by holding the the head of the humerus in the glenoid cavity during arm movements

ARM MUSCLES

1. Triceps brachii – primary extensor of the elbow occupies the posterior portion of the arm

- extends elbow, extends shoulder and adducts arm

2. Biceps brachii– occupies the posterior portion of the arm

- primary flexors of the elbow

- flexes elbow, suppinates forearm, flexes shoulder

3. Brachialis – flexes elbow

FOREARM MUSCLES

Anterior forearm

1. Palmaris Longus – tighten skin of palm

2. Flexor carpi radialis and ulnaris – flexes and abducts wrist

3. Flexor digitorum superficialis– flexes fingers and wrist

4. Pronator teres – pronates forearm

LOWER LIMB MUSCLES

- includes muscles located in the hip, thigh, leg and foot

MUSCLES MOVING THE THIGH

1. Iliopsas – muscles of the loin, found anteriorly

- flexes the hip

2. Gluteal muscles / tensor fascia latae – makes up the posterior and lateral hip muscles

• Tensor fascia latae – stedies femur on the tibia when standing, flexes hip and medially rotates and abducts thigh

3. Gluteus maximus – contributes most of the mass that can be seen as the buttocks

- extends the hip and abducts and laterally rotates thigh

4. Gluteus medius – abducts and medially rotates the thigh

- creates a smaller mass just superior and lateral to the gluteus maximus

- common site for intramuscular injections

MUSCLES MOVING THE LEGAnterior Muscles1. Quadriceps femoris – primary extensors of the knee

- extends knee and flexes hipa. Vastus lateralis – extends knee, used as intramuscular injection site

especially for infantsb. Rectus femoris – extends knee; flexes hipc. And d. Vastus medialis, intermedius – extends knee

2. Sartorius – the longest muscle in the body- also called the “tailor’s muscle”- flexes hip and knee, laterally rotates thigh

• Patellar ligament – is an extension of the patelar tendon onto the tibial tuberosity

- is tapped with a rubber hammer when testing the knee – jerk reflex in physical examination

3. Posterior muscles / hamstring muscles – responsible for flexing the knee and extending the hip

4. Medial thigh muscles / adductor muscles – primary function is to adduct the thigh

POSTERIOR THIGH MUSCLES

MUSCLES OF THE LEG ACTING ON THE LEG, ANKLE AND FOOTAnterior Muscles – involved in dorsiflexion of the foot and extension of the

toesa. Extensor digitorum longus – extends four lateral tous, dorsiflexes and

everts footb. Extensor hallicus longus – extends great toe; dorsiflexes and inverts

footc. Tibialis anterior – dorsiflexes and inverts foot

Superficial Posterior muscles – involved in plantar flexion of the foota. Gastrocnemius – plantar flexes the foot and flexes legb. Soleus – plantar flexes the foot• Gastrocnemius and soleus form the bulge of the calf

Lateral muscles of the leg1. Fibularis muscles – primarily everts and plantar flexes the foot

Intrinsic foot muscles – 20 muscles found in the foot- flex, extend, abduct and adduct the toes

SUPERFICIAL POSTERIOR MUSCLES

EFFECTS OF AGING ON SKELETAL MUSCLES

1. Muscle loss begins at age 25 and by 80 years of age the muscle mass is reduced by 50%

2. Surface area of neuromuscular junction decreases

3. Number of motor neurons decreases

INTERACTIONS OF SKELETAL MUSCLES IN THE BODY

Agonist- a muscle that accomplishes a certain movement such as flexion

Antagonist- a muscle acting in opposition to the agonist- muscles that oppose or reverse movement

Prime mover- the muscle that plays the major role in accomplishing the desired movement

Synergists- muscles that help the prime movers by producing the same movement or by reducing undesirable movements

Fixators- specialized synergists- are muscles that hold one bone in place relative to the body while a usually more distal bone is moved

muscular sytem

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