Muscular System
Jan 19, 2016
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