Muscular System

I. Muscle Types

• A. Smooth– 1. S: muscle which LACKS STRIATIONS (stripes) and

is located in stomach, intestines, bladder, uterus, and blood vessels• Arranged in layers

– 2. It is INVOLUNTARY MUSCLE• Unconsciously contracts

– 3. F: move food through digestive tract, constrict blood vessels, contract uterus, empty bladder

• B. Cardiac– 1. S: muscle which IS STRIATED located in the

heart and contains INTERCALATED DISKS• Def of ID: junctions of cardiac muscle cells which

transmit impulses easily and allow the heart to beat as one• Cells look as though they are in figure 8 patterns

– 2. it is INVOLUNTARY muscle– 3. F: to pump blood into heart chambers and

certain blood vessels

• C. Skeletal – 1. S: muscle found connected to bones which IS

STRIATED• Contain much connective tissue to attach to bones

– 2. they are VOLUNTARY• Can consciously control contractions

– 3. F: to move head, neck, trunk, limbs, facial expressions, and many actions like writing, chewing, talking etc

• ** throughout this unit we will focus on structure and function of SKELETAL muscle

II. Muscle Structure

• A. Connective Tissue Coverings– 1. Fascia

• Fibrous tissue covering of individual muscle

– 2. Tendon• Extension of tissue connecting muscle to bone• Ex: Tendonitis – swelling of tendon at connection

– 3. Epimysium• Under fascia

– 4. Perimysium• Separate muscle into bundles

– 5. Endomysium• Surrounds individual muscle fiber/cell

• B. Skeletal Muscle Fibers– 1. 1 fiber = 1 cell– 2. sarcolemma – cell membrane– 3. sarcoplasm – cytoplasm in cell– 4. myofibrils – parallel fibers in sarcoplasm

• a. myosin– T H I C K , D A R K protein filament

• b. actin– Thin, light protein filament

• ** actin and myosin make striations in muscle – light/dark

– 5. A-bands • Dark portion of muscle myofibril

– 6. I-bands• Light portion of muscle myofibril

– 7. Z-lines• Place where actin myobifrils meet

– 8. Sarcoplasmic reticulum• Channels running parellel on outside of fiber

– 9. Transverse Tubules – T Tubules• Channels running opposite SR between SR on outside of fiber

– ** SR and T Tubules communicate signal to whole muscle when stimulated

• C. Skeletal Muscle Contraction– 1. Neuromuscular Junction• Def – connection between nerve fiber and muscle• ** Each muscle is connected to a nerve called a motor

neuron

– 2. Role of myosin and actin• Myosin cross bridges connect to actin and pull

– 3. Process of Contraction• a. motor neuron releases ACETYLCHOLINE

– Chemical needed for a muscle contraction

• b. actetylcholine stimulates impulses through the SR and T Tubules• c. impulses cause Ca+ to move through the muscle• d. Myosin cross bridges connect to actin myofibrils

because of presence of Ca+• e. bridges slide actin along myosin = CONTRACTION• f. Ca+ leave muscle• g. Myosin releases bridges = MUSCLE RELAXES

• D. O2 Debt, Fatigue, and Heat Production– 1. O2 Debt

• a. if muscles are exercised strenuously, O2 cannot be supplied fast enough

• b. Lactic Acid builds up• c. ATP energy (body’s energy) decreases• d. CO2 increases• e.O2 must be replenished before more exercise can be

done – may take hours– ** the O2 needed to replenish is O2 debt

• f. to replenish O2 you automatically breath deep and fast

– 2. Muscle fatigue• a. def – MF occurs when a muscle loses its ability to

contract• b. causes:

– Blood supply is cut off (no O2)– Acetylcholine supply runs out in motor neuron– Build up in lactic acid

• c. cramping results– Muscle keeps contracting and can’t relax

– 3 . Heat Production– Muscle contractions release heat– Keeps body at 98.6

• E. Muscle responses– 1. Threshold Stimulus

• a. def – the minimum stimulus strength needed to cause a muscle contraction

• ** electric stim on muscles uses this on isolated muscles to help strengthen them

– 2. ALL or NONE response• a. there are NO partial contractions in muscle FIBERS• b.Once stimulus is reached, muscle fiber contracts to full

extent• C.Not all muscle fibers are stimulated – weaker contraction

– 3. Contraction types• a. twitch – a single contraction that lasts only a fraction

of a second• b. tetany – a sustained forceful contraction which lacks

relaxation– Ex: holding a heavy box still out on front of your body

• c. tonus – a small sustained contraction in a muscle which seems to be at rest– Due to the muscle being contracted rapidly for varying lengths

of time– Ex: when walking and leg is back– Ex: maintaining posture

• F. Muscle Interactions– 1. origin• Def: immovable place where muscle is attached

– 2. insertion• Def: moveable place where muscle is attached

• ** insertion always moves towards origin– Ex: Bicep Brachii• Origin: coracoid process and scapula• Insertion: radius

– 3. Muscles ALWAYS act in groups• a. prime mover

– The muscle responsible for the most movement– Ex: lift arm = deltoid

• b. synergists– Muscles the contract and ASSIST prime mover– Helpers

• c. antagonist– Muscle that acts against the prime mover– Ex: flex arm

» PM – bicep brachii - contracts» Ant – tricep - extends

– 4. muscle fiber types• a. fast twitch

– Muscles which contract quickly and tire quickly– Ex: sprinters

• b. slow twitch– Muscles which contract slow and are more resistant to fatigue– Ex: marathon runners, weight lifters

III. Major Skeletal Muscles

• A. Muscles of Facial Expression– 1. frontalis• Lies over frontal bone

– 2. occipitalis• Lies over occipital bone

– 3. orbicularis oculi• Around the eye orbit

– 4. orbicularis oris• Around mouth orbit

– 5. buccinator• Fish face

– 6. zygomaticus• Smiling

– 7. platysma

• B. Muscles of chewing – mastication– 1. masseter• Main muscle of chewing

– 2. temporalis• Lies over temporal bone

• C. Muscles that move the head– 1. sternocleidomastoid• Head flexion

– 2. splenis capitis– 2. semispinalis capitis

• D. Muscles of the pectoral girdle– 1. trapezius• O:

– Occipital bone– Spinous process of cervical and thoracic vertebrae

• I:– Clavicle– Scapula

• A: – Move scapula– Raise arm

– 2. Rhomboideus Major– 3. serratus anterior– 4. pectoralis minor• O:

– Sternal ends of upper ribs

• I:– Coracoid process

• A: – Pull scapula down– Pull scapula forward– Raise ribs

• E. Muscles that move the Upper Arm– 1. Pectoralis Major

• O:– clavicle– Sternum– Costal cartilage

• I:– Humerous

• A:– Adduct arm– Rotate humerus– Pull arm forward

– 2. Teres Major– 3. Latissimus Dorsi• O:

– Spinous process of vertebrae– Iliac crest– Lower ribs

• I:– Humerous

• A:– Adducts arm– Pulls shoulder down and back

– 4. supraspinatus– 5. deltoid• O:

– Acromion process– Scapula spine– Clavicle

• I:– Humerous

• A:– Abducts arm – main muscle to abduct

– 6. subscapularis• On anterior side of scapula

– 7. infraspinatus– 8. teres minor

• F. Muscles that move the forearm– 1. biceps brachii• O:

– Coracoid process– Scapula

• I:– Radius

• A:– Flex arm at elbow– Rotate hand laterally

– 2. Brachialis– 3. brachioradialis– 4. triceps brachii• O:

– Lateral and medial surfaces of humerous

• I:– Proximal ulna

• A:– Extend arm at elbow

– 5. supinator• In charge of supination

– 6. pronator teres– 7. pronator quadratus

• G. Muscle that move the wrist, hand, and fingers– 1. flexor carpi radialis– 2. flexor carpi ulnaris– 3. extensor carpi radialis longus– 4. extensor carpi radialis brevis– 5. extensor carpi ulnaris– 6. extensor digitorum

• H. Muscles of the abdomen– 1. LINEA ALBA

• CONNECTIVE TISSUE which abdominal muscles connect to

– 2. external oblique• O:

– Outer surface of lower rib

• I:– Linea alba, iliac crest

• A:– Compress abdomen

– 3. internal oblique• O:

– Iliac crest

• I:– Rib cartilage, linea alba, pubis

• A:– Compress abdomen

– 4. Transverse abdominus

– 5. Rectus abdominus• O:

– Pubis

• I:– Xyphoid process, costal cartilage

• A:– Compress abdomen, flex vertebral column

• I. Muscles that move the Thigh– 1. tensor fascia latae– 2. gluteus maximus• O:

– Sacrum, coccyx, ilium

• I:– Posterior femur

• A:– Extend leg at hip

– 3. gluteus medius• Top of maximus over hip

– 4. adductor longus– 5. adductor magnus– 6. gracilis– 7. fascia: sheet of connective tissue which muscle

may connect to

• J. Muscles that move the lower leg– ** the next 3 muscles make up the HAMSTRING– 1. biceps femoris• O:

– Ischium and posterior surface of femur

• I:– Fibula, tibia

• A:– Flex/rotate leg, extend thigh

– 2. semitendinosous– 3. semimembranous

– 4. sartorius• Longest muscle in body• Crosses 2 joints

– 5. quadraceps femoris• Rectus femoris• Vastus lateralis• Vastus medialis• Vastus intermedius

• K. Muscles that move ankle, foot, and toes– 1. tibialis anterior• O:

– Lateral surface of tibia

• I:– Tarsals, 1st metatarsal

• A:– Dorsal flexion and inversion of foot

– 2. extensor digitorum longus• Extends toes -digits

– 3. gastrochnemius• O:

– Lateral/medial condyles of femur

• I:– Posterior surface of calcaneous

• A:– Plantar flexion of foot and flexion of leg at knee

– 4. soleus– 5. flexor digitorum longus– 6. peroneous longus