CPR or First Aid Class
in St. Louis?
Register Now!
Use Calendar Below
or Call Us.

Muscle Physiology – outline notes

By at September 21, 2011 | 6:05 am | Print

Muscle tissue – (myo, mys, sarco)
-skeletal – striated, voluntary
-smooth – visceral, nonstriated, involuntary
-cardiac – heart, striations, involuntary

Skeletal Muscle
-cardiac – blood
-smooth – peristalsis
-skeletal – gross movements
-posture  / stabilize joints
-generates heat

As an organ
-blood vessels
-nervous tissue
-skeletal muscle fibers (cells) / (myofibers)
C.T. wrappings – all cont. with each other and tendons
-endomysium – areolar C.T.; wraps each muscle fiber (muscle cell)
-perimysium – collagenic sheath; wraps a bundle of muscle fibers
-epimysium – dense fibrous C.T.

Blood vessels / nerve supply
-arteries – supply oxygen and nutrients
-veins – carry away waste

-each muscle cell has individual innervation

Microanatomy of skeletal muscle cells
-embryonic development
-myoblasts fuse and form large, multinucleated muscle cells
-satellite cells – myoblasts that do not fuse; may fuse after injury

-sarcolemma – cell membrane

-sarcoplasm – cytoplasm
-stored glycogen
-myoglobin – stores oxygen; red pigment
-other normal organelles
-Modified organelles
-sarcoplasmic reticulum

-80% of cell volume; thousands/cell
-rod-like; extend length of cell
-sarcomeres – smallest contractile units; thousands make up myofibril

-Z-line to Z-line
-Z-line – consists of connectin (protein); connects thin
-A-band – DARK band; thin and thick filaments; length of thick filament
-H zone – lighter stripe in A band; only thick filaments
-M line – bisects H zone; darker line; connects thick filaments
-I band – LIGHT band; thin filaments

Thick filaments
-protein – myosin (several hundred myosin molecules / thick filament)
-tails – point toward M line
-head (cross-bridges) – interact with thin filaments
-ATP binding sites and ATPase
-ATP —-ADP and PO43-
-hinge region
-titin – core of filament that continues to Z – line; elastic properties

Thin filaments
proteins – actin, tropomyosin, troponin
-F actin – 2 twisted strands composed of G actin (fibrous)
-G actin – active sites where myosin heads bind (globular)
(2 strings of pearls)
– coils w/ F actin; blocks 7 active sites; relaxed muscle
-troponin – 3 polypeptide subunits
-TnI – binds to G actin; inhibitory
-TnT – binds 1 troponin to 1 tropomyosin
-TnC – binds Calcium
Sarcoplasmic reticulum (SR)
-interconnecting membrane tubule complex; similar to sER
-surrounds each myofibril (loosely crocheted sweater around your arm)
-most run longitudinal w/ myofibril
-some form perpendicular cross channels over A-I junction
– terminal cisternae – occur in pairs
-Control intracellular Calcium; store it and release it on demand
-high [Ca2+] in SR; low [Ca2+] in sarcoplasm

T-tubules (transverse tubules)
-sarcolemma penetrates at each A-I junction
-protrudes b/t each pair of terminal cisternae = triad
-relationship b/t SR and t-tubule(sarcolemma)
-allow for communication deep within the myofiber

Muscle Contraction
-When muscle cells contract, myofilament do not shorten
-Sliding Filament Theory – Huxley 1954
-thin filaments slide centrally passed thick filaments
-Z-lines are pulled closer
-I band and H zone shorten
-width of A band remains constant

Steps of Contraction
Step 1 *Actin Binding Sites Exposed
-muscle cell stimulated; causes SR to release Calcium into cell
-calcium binds to TnC of troponin; troponin changes conformation
and pulls tropomyosin exposing binding sites

Step 2 *Cross Bridge Attachment 
-myosin heads attracted to binding sites and cross bridge
attachment occurs

Step 3 *Power Stroke
-myosin heads configuration changes; heads bend and pull thin
filaments centrally (Power Stroke)
-heads release ADP and PO43- (low energy state)

Step 4  *Cross Bridge Detachment
-ATP binds to myosin head and loosens attachment

Step 5 *Cocking of Myosin Head / Reactivation
-hydrolysis of ATP; returns head to cocked position (high energy
state of myosin head); like a coiled spring
-ADP and Phosphate remain attached until next power stroke

-when calcium is reclaimed by SR –– contraction ceases
-one power stroke shortens muscle ~1%
-Contraction is 30-35% of resting muscle
-Rigor Mortis
-body stops producing ATP
-Calcium invades sarcoplasm —– contraction
-no cross bridge detachment without ATP
-15-25 hours later myofilaments break down

Neuromuscular junction
-axons of motor neurons innervate skeletal muscle
-neuromuscular junction – site where one axon ending innervates one
muscle fiber
-synaptic cleft – space b/t axon ending and muscle cell
-filled with basal lamina – gel like substance
-within axon ending (synaptic terminal)
-synaptic vesicles – membrane sacs that contain
acetylcholine (ACh); neurotransmitter
-motor end plate – highly folded region on sarcolemma that
contains ACh receptors; at neuromuscular junction
-acetylcholinesterase (AChE, or cholinesterase) – found in synaptic
cleft and sarcolemma; breaks down ACh

Neuron stimulation
Step 1  *Release of ACh from synaptic terminal into synaptic cleft
-action potential (electrical impulse) reaches synaptic terminal
-Calcium rushes in; synaptic vesicles release ACh via exocytosis

Step 2  *ACh diffuses across synaptic cleft and binds to ACh receptors
on sarcolemma

Step 3  *Action potential generated on sarcolemma
-electrical impulse spreads across sarcolemma and down t-tubules
at triad
Step 4  *SR releases Calcium

Step 5 Calcium binds to troponin
-Muscle contraction occurs

Excitation-Contraction Coupling – action potential across t-tubules cause SR to release calcium and start muscle contraction

ATP dependent Calcium pumps – immediately pump calcium back into SR
-Calcium levels fall in sarcoplasm
-Calcium detaches from troponin
-tropomyosin covers active sites
-contraction ends

AChE – breaks down ACh to stop signal

Muscle Mechanics

Tension – single muscle fiber
-depends on number of cross bridge interactions (length)
-muscle fiber at any given length (determines overlap of filaments) will
always produce same tension
-muscle fiber is “on” or “off”

**tension produced by a muscle depends on
-number of fibers activated
-frequency of stimulation

Muscle Metabolism
-Muscle contraction requires ATP
-detachment of head
-cross bridge movement
-control of calcium pump in SR
-7300 calories of energy / mole of ATP; stored in high energy bonds

Muscle has ~ 3 sec. of stored ATP

3 pathways to generate ATP during muscle activity

1. Creatine Phosphate (CP)
-stored in muscle
-has high energy phosphate bond
-CP + ADP —– ATP + creatine
-creatine phosphokinase (CPK or CK)
-enzyme catalyzes reaction
-find in high levels in blood when muscle cells are damaged
-muscle at rest replenishes CP
-creatine + ATP —– CP + ADP
-phosphagen energy system
-stored ATP + CP = 8 – 10 seconds of maximal muscle power

2. Glycogen – Lactic Acid system
-Anaerobic, peak muscle activity
-glycogenolysis – store glycogen is split into glucose
-glycolysis – inhibited in the presence of oxygen
–glucose ——– 2 pyruvic acids
-net of 2 ATP production
-with oxygen present
-pyruvic acid ——– 34 ATP in mitochodria
-without oxygen present
-pyruvic acid —– lactic acid
-lactate dehydrogenase
-provides additional 1 ½ minutes of ATP

3. Aerobic System
-at rest, light exercise
-oxygen not limited
-mitochondria metabolizes 2 pyruvic acid to 34 ATP
-also metabolizes fatty acids and amino acids to ATP
-produces much more ATP than Anaerobic system, but works 2 ½  times
more slowly and requires oxygen

Muscle fatigue
-no contraction despite continued neural stimulation
-exhaustion of ATP and CP (short peak levels of activity)
-damage to SR during marathon

Recovery period
-replenish muscle with ATP, glycogen, CP
-Cori cycle
-lactic acid diffuses out of muscle into blood and to liver
-liver converts lactic acid back glucose and release it to blood.
-muscles absorb glucose


Misc Articles Physiology outline notes

Related Posts

Trackbacks For This Post

  1. […] dartos muscle – smooth muscle in superficial fascia 1) wrinkles testes b. cremaster muscles – skeletal muscle that elevates testes 2. Penis a. glans penis – enlarged tip b. prepuce (foreskin) – frequently […]

  2. […] cervix to body exterior b. Layers 1) adventitia – fibroelastic tissue 2) muscularis – smooth muscle 3) muscosa – stratified squamous epithelium a) rugae c. vaginal […]

  3. […] PHARYNX AND ESOPHAGUS A. PHARYNX 1. OROPHARYNX and LARYNGOPHARYNX 2. Muscles of pharynx, oral cavity, and esophagus coordinate to push a bolus of food toward esophagus to […]

  4. […] to muscles and prevents injury -cool down – stretch -beginners start easy -Proper rest of major muscle groups -pectoralis major – chest -biceps, triceps – arms -latissimus dorsi – back […]

  5. […] self explanatory. They include short, abrupt movements that occur repeatedly within a small area of muscle groups. Physical motor tics may include blinking of the eyes, grimacing of the face, shrugging of […]

  6. […] serious condition called post-polio syndrome. PPS is a condition in the nervous system that affects muscles and […]

  7. […] Lets start by breaking down the term necrotizing fasciitis into its simplest form to understand what we are talking about. The literal definition of the word necrotizing is causing the death of a specific area of tissue and fasciitis meaning the inflammation of a fascia. As defined by, a fascia is a flat band of tissue below the skin that covers the underlying tissues and separates different layers of tissue. Necrotizing fasciitis is a rare, systemic toxin- spreading infection of the deep layers of skin, tissue or muscle. […]


Post Your Comments

× Yes, we are your local American Heart Association training site. We offer in-person classes, skills checks, and blended online learning.

*IMPORTANT NOTE: 100% of CPR St. Louis instructors have entirely completed (1) the rigorous and official American Heart Association instructor training and certification process, and (2) the “How to Teach a Stress-Free CPR Class™” classroom and testing training protocol that ensures a superior experience for everyone. In addition, students will receive their AHA Cards the day of class!

[WARNING]: Because of the high quality, stress-free classroom student experience, our classes fill very fast - so register now to ensure your spot. See our course calendar for online registration or contact us directly by phone, live chat or email with questions.