Muscular System

Functions:

•Movement•Posture•Stabilize Joints•Generate Heat

Types:

• Skeletal- voluntary, striated, movement• Cardiac- involuntary, striated,

heart• Smooth- involuntary, not

striated, visceral

Anatomy of Skeletal Muscle

• Muscle fiber (cell) is wrapped by endomysium• Several wrapped fibers are bundled and

wrapped by perimysium• Each bundle is called a fascicle• Many fascicles are wrapped by tough

epimysium• Epimysium ends in a cord like tendon or a

sheet like aponeuroses

Muscle Fiber (Cell)

•Made of many myofibrils covered by a plasma membrane called the sarcolema• Each myofibril has contractile

units called a sarcomere

mm

Sarcomere

• Alternating dark (A) bands and light (I) bands• Z disc- midway in (I) band• H zone midway in (A) band•M line- center of H zone

Sarcomere

• 2 types of protein filaments:–Thick filaments= myosin–Thin filaments= actin

• Cross bridges on myosin filaments connect the two

Sliding Filaments

• Thin fibers are pulled to center of the sarcomere by myosin head cross bridge

• Triggered by rise in Ca ++ which attaches to myosin head to pull it back

• ATP releases the head and it springs forward and pushes the thin filaments over the thick filaments = Muscle Shortens

Skeletal muscle must be stimulated by a nerve

• Motor Unit = one neuron and all the muscle cells it stimulates• More fibers stimulated by one

neuron, the greater the force• Less fibers stimulated by one neuron

than the finer the movement

Glucose is necessary to provide ATP

•Muscle can store glucose as glycogen•Muscle contains myoglobin

which will bind oxygen

3 pathways to ATP production

• 1. Creatine phosphate (CP) good for minutes• 2. Aerobic respiration= C6H12O6 + O2 CO2 + H2O + ATP 95% of all ATP produced (38 ATP / glucose)• 3. Anaerobic glycolysis= without oxygen, glucose is broken into 2 pyruvate acid,

releases 2 ATP and a by product lactic acid, causes muscle soreness

Types of muscle contraction

• Isotonic – contraction occurs and results in movement

• Isometric- the myosin filaments try to contract but the muscle is against something immovable

• Muscle tone- even when the muscle is relaxed, few of the muscle fibers continue to contract and make the muscle firm

Exercise effect

• Aerobic- endurance– does NOT increase size– DOES resist fatigue– more blood hemoglobin, more mitochondria,

more glycogen

• more myoglobin- holds oxygen

Exercise effect continued

• Isometric- resistance– Does increase size and strength– more myofilaments– more connective tissue

• larger cells

5 Golden Rules

• 1. muscles cross at least one joint• 2. the bulk of the muscle lies proximal to the

joint• 3. all muscles have at least two attachments:

---origin and insertion• 4. muscles can only pull; never push• 5. during contraction, the insertion moves

towards the origin

Naming Muscles

• 1. Directions of fibers: Rectus, Oblique• 2. Relative size: Maximus, Minimus• 3. Location over bone: Frontalis, Temporalis• 4. Number of origins: Biceps,Triceps

• 5. Location of origin and insertion: sternocleidomastoid•6. Shape: Deltoid•7. Action: adductor, flexor

• Prime Mover- major responsibility for move• Antagonist- when prime mover is

contracted, it is relaxed• Synergist- helper to prime mover• Fixator- special synergists that hold a

muscle stable

Shapes of Muscles

• Circular- sphincters• Convergent- fan shaped• Parallel- strap like• Fusiform- special parallel with big

body• Pennate- feather like

Muscles of the Head

• Frontalis- raises eyebrows• Orbicularis oculi- blinking, squinting• Zygomaticus- smile• Depressor anguli oris- frown,

(antagonists= smile / frown)• Lavator labii superioris- disgust• Depressor labii- pout

Chewing (Mastication)

• Masseter- prime mover (from zygomatic to ramus of mandible)• Temporalis- synergist• Buccinator- holds food between

teeth/ sucking• Platysma- tenses skin of neck during

shaving

Swallowing

• Digastric- open mouth- depress mandible• Mylohyoid- forces bolus into

pharynx• Pharyngeal constrictors- propels

bolus to esophagus

Neck

• Sternocleidomastoid- head flexion, neck flex, rotate head towards opposite shoulder• Scalenes- flex and rotate neck

Shoulder Joint

• Trapezius- depress shoulder/ adducts scapula• Pectoralis major- prime mover

of arm flexion, adducts arm, rotates medial

Shoulder continued

• Latissimus dorsi- prime mover of arm extension, arm adductor brings arm down in hammering, swimming, rowing• Deltoid- antagonist of pectoralis major,

and latissimus dorsi, prime mover of arm abduction, swinging arm movement while walking

Shoulder (rotator cuff)• Supraspinatus- prevents downward

dislocation, assists in abduction• Infraspinatus- rotates humerus laterally• Teres major- medial rotation of humerus,

extends• Also: Coracobrachialis- • coracoid – humerus, flexion and

adduction of humerus

Elbow Joint• Triceps brachii- antagonist to forearm

flexors, strong forearm extensor, stabilizes shoulder• Biceps brachii- flexes elbow,

supinates forearm, lifts radius• Brachialis- forearm flexor, lifts ulna• Brachioradialis- synergist to forearm

flexion

Back Trunk

• Erector Spinae- prime mover of back extension- made of 3 muscles: Iliocostalis, Longissimus, and Spinalis

• Bending forward at the waist touching fingers to the floor they are relaxed ( held together by ligaments!) that is why lifting can be problem

Thorax (breathing)

• External intercostals- synergist to diaphragm in inspiration, elevates rib cage• Diaphragm- prime mover of

inspiration• Internal intercostals- aid in

expiration, depress the rib cage

Thorax continued

• Serratus anterior- “boxer’s muscle” raises the point of the shoulder, abduction and raising the arm, pushing, punching

Abdominal Girdle

• Rectus Abdominus- pubic crest to xiphoid process, flex and rotate lumbar vertebrae

• External oblique- diagonal fibers, “sit-up” flex abdomen

• Internal oblique- under external oblique• Transverse abdominus- runs across under

obliques

Hip and Knee

• Iliopsoas- prime mover of hip flexion• Sartorius- strap like, superficial, flexes and

laterally rotates thigh, flexes knee, “cross leg position”

• Adductor magnus:• Adductor longus: adducts thigh• Adductor brevis:• Gracilis- adducts thigh, medial rotation when

walking

Quadriceps group (ant. Thigh)

• All extend knee:

• Rectus Femoris: also flexes hip on thigh• Vastus lateralis• Vastus intermedius• Vastus medialis

Hip and Thigh posterior

• Gluteus Maximus- major, powerful, extensor of the thigh, (rising from chair, stairs, running)• Gluteus medius- injection site• Gluteus minimus- adducts thigh

Hamstring group

• Posterior thigh, sciatic nerve runs through, powerful knee flexors, extends thigh:

• Biceps Femoris- extends thigh, flexes knee, lateral rotation of leg when knee is flexed

• Semitendinosus• Semimembranosus

Lower Leg

• Gastrocnemius- prominent belly forms proximal curve of the calf, plantar flexion, large Achilles Tendon (Calcaneal)• Soleus- lies under gastrocnemius,

also plantar flexor