Ch 9 - Muscles & Muscle Tissue Flashcards
Functions of Muscle Tissue
1) Movement
2) Body posture & body position
3) Joint stability
4) Maintaining body temperature
Muscle Characteristics
1) Excitability - Generate action potentials in response to stimulus
2) Contractility - Muscle cells shorten when they contract
3) Exensibility - Muscles cells can lengthen/stretch
4) Elasticity - Healthy muscle cells return to their original shape
Types of Muscle Tissue
1) Skeletal muscle tissue
2) Smooth muscle tissue
3) Cardiac muscle tissue
Muscle tissue identification
Voluntary muscle tissue, striated
Skeletal muscle tissue
Creates most force, but needs most rest, adaptable
Muscle tissue identification
Involuntary muscle tissue, not striated
Smooth muscle tissue
moves fluid through body
uninucleate
Muscle tissue identification
Involuntary muscle tissue, striated
Cardiac muscle tissue
moves blood through the body (rate set by pacemaker cells)
uninucleate
Innervation & Vascularization of Skeletal Muscle
Innervation: each muscle fiber synapses with 1 motor nerve, can be served by multiple motor neurons
Vascularizaton: each muscle recieves 1 artery, 1+ vein (bring in nutrients, remove waste)
Connective Tissue Sheaths of Muscle Tissue
1) Endomysium: innermost layer (ind. muscle fibers; called myocytes)
2) Perimysium: middle layer (grouped muscle fibers - form fascicles)
3) Epimysium: outermost layer (entire muscle)
Individual muscle fiber/cell is called
myocyte
Groups of muscle fibers joined by perimysium
fascicles
Skeletal Muscle Attachment Types
Direct: epimysium of muscle fuses directly to bone/cartilage
Indirect: involves tendons
Skeletal Muscle Attachment Points
1) Origin: where the muscle attaches to a less movable bone (always proximal)
2) Insertion: where the muscle attaches to a movable bone (always distal)
Plasma membrane of muscle fiber
Sarcolemma
Cytoplasm of muscle fiber
Sarcoplasm
Contains high numbers of
A) Glycosomes (glycogen organelle)
B) Myoglobin (oxygen organelle)
Protein filaments in muscle tissue (& types)
Myofilaments
1) Myosin - thick filament
2) Actin - thin filament
Thick filament of muscle tissue
Myosin
has 2 heavy chains, with myosin head found at end of each chain
Myosin head used to link two types of myofilaments during contraction
Binding sites of myosin
2 total;
1 for ATP
1 for actin
Myosin head used to link two types of myofilaments during contraction
Thin filament of muscle tissue
Actin
Chains of G actin proteins with myosin binding sites
Myosin head binds to myosin binding site of actin during muscle contraction
Actin regulatory proteins
1) Tropomyosin: arranged along length; blocks myosin binding sites when muscle is relaxed
2) Troponin: globular protein; binds tropomyosin to position it on the actin filament
Rod-like organelles inside muscle cells that create striations
Myofibrils
Made up of bands of actin & myosin
Myofibril bands
1) A band: region of myofibril where actin and myosin filaments overlap
2) I band: region of myofibril with only actin filaments (z disc at center holds actin filaments in place)
Region of myofibril where actin and myosin filaments overlap
A band
Region of myofibril with only actin filaments
I band
Center of I band, which holds the actin filaments in place
Z disc
Region of a myofibril found between neighboring Z discs
Sarcomere - the smallest contractile unit of skeletal muscle tissue
Extensions of the sarcolemma that wrap around deeper myofibrils
T-Tubules - increase surface area of sarcolemma
importance: changes in membrane potentia can reach myofibrils that are not in direct contact with sarcolemma
Organelle that wraps around myofibrils
Sarcoplasmic reticulum - stores and releases Ca2+ for muscle contraction & relaxation
: : Form terminal cisterns around T-tubules; action potentials travel down T-tubules to stimulate release of Ca2+
Site of synapse between a somatic motor neuron and a muscle fiber
Neuromuscular Junction
ACh released
Steps for muscle fiber stimulation to occur
1) Neuromuscular junction ACh release
2) Generation of EPP & action potential across sacrolemma- ACh opens ion channels to generate an End Plate Potential (graded potential) - depolarizing
3) Excitation-Contraction Coupling - occurs when action potential spreads from sarcolemma to T-tubules
4) Cross Bridge Formation & Muscle Contraction - attachment of myosin to actin
Process of Cross Bridge Formation
a) Ca2+ binds troponin - troponin changes shape
b) Change in troponin shape - tropomysin rolls to the side
c) When tropomyosin is moved - myosin binding site on actin is exposed
d) Myosin head splits APT into ADP + P (allows myosin head to bind to actin)
e) ADP + P is released from myosin head, causing the myosin head to change shape & bend (pulls actin fillament toward center of sarcomere - called power stroke)
f) Myosin head binds to another ATP - myosin head detaches from actin binding site
Need to write out!!
How does the cross-bridge formation end
- Motor impulses no longer sent to muscle fiber
- Ca2+ is returned to sarcoplasmic reticulum
- When Ca2+ levels in sarcoplasm drop, it can no longer bind to troponin
- Troponin returns to original shape; tropomyosin covers actin binding sites again
How does the sliding filament model of contraction work?
Myosin heads “slide” thin filaments toward the center of the sarcomere, shortening the sarcomere without changing length of filaments
Definition
Motor unit
A single motor neuron and all the muscle fibers it innervates
Rules of a motor unit
1) when the motor unit fires, all fibers it innervates will contract (can be spread out in muscle)
2) number of muscle fibers a motor neuron innervates influences movement
Muscle contraction that is modified by the nervous system to produce varying amounts of force
Graded Muscle Contractions:
1) Temporal summation - increasing frequency of stimulation
2) Motor unit summation - increasing the number of motor units used
Types of temporal summation:
1) Unfused (incomplete) tetanus - muscle fiber has very little time to relax before next stimulus
2) Fused (complete) tetanus - no relaxation occurs in the muscle fiber (contractions from individual stimuli fuse into one contraction)
Increasing muscle force by increasing the number of motor units used during contraction
Motor unit summation
Motor units recruited asynchronously, with a size principal - motor units w/ smallest muscle fibers recruited first, increases incrementally
Muscle tone
Relaxed muscles are always slightly contracted - called muscle tone
Does not produce movememt, keeps tissue healthy and responsive, stabilizes joints, maintains posture
Types of Muscle Contraction
1) Isotonic Contraction: muscle tension develops to overcome the load & muscle shortening occurs
2) Isometric Contraction: tension develops in a muscle, but the length of the muscle does not change
Types of Isotonic Contraction
1) Concentric contraction: muscle shortens and does work
2) Eccentric contraction: muscle lengthens while under tension
How does Isometric Contraction work?
Cross bridge formation still occurs, but the sarcomeres do not shorten
How is ATP used/generated in Muscle Contraction
Attaches to Myosin to allow binding, will only produce the amount of ATP as needed
Pathways for ATP Regeneration
1) Direct phosphorylation
2) Anaerobic pathways
3) Aerobic pathways
Direct Phosphorylation Reaction
Creates ATP using creatine phosphate (CP) via criatine kinase - 1 ATP per CP molecule
Whole process supplies ~15s worth of ATP
Does not require oxygen
Anaerobic Pathway: Glycolysis
Glucose broken down to form 2 ATP & pyruvic acid and converted to lactic acid
Creatine phosphate and glycolysis provide ~1 minute of ATP
Benefits and Drawbacks of Anaerobic Pathway
Benefits: does not require oxygen, produces ATP quickly
Drawbacks: low ATP yeild (2 ATP per glucose) lactic acid build-up MIGHT cause muscle fatige or soreness
Aerobic Pathway:
Cellular Respiration
Produces 30-32 ATP per glucose, ~95% of ATP used by muscle during rest and light-to-moderate long-term exercise
Benefits and Drawbacks of
Cellular Respiration
Benefits: produces 30-32 ATP
Drawbacks: slow, requires mitochondria, constant O2 and glucose
When muscle is physiologically incapable of contracting
Muscle Fatigue - rate & duration depends on activity
High intensity = quicker rate, lower duration, vice versa
Factors that affect speed of contraction
1) How fast ATP is split - how fast cross bridges can form & break
2) Electrical activity of motor neurons - fast neurons = fast connections
3) Pathway of ATP production
Types of Muscle Fibers (velocity and duration)
1) Fast glycolytic fibers - contract quickly, use anaerobic pathways (high glycogen, low myoglobin/mitochondria/blood)
2) Fast oxidative fibers - contract quickly, use aerobic pathways (some glycogen, lots of myoglobin/mitochondria/blood)
3) Slow oxidative fibers - contract slowly, use aerobic pathways (low glycogen, high myoglobin, lots of mitochondria/blood)
Gross anatomy of smooth muscle tissue
2 layers of smooth muscle that never contract simultaneously:
1) Longitudinal layer along the length of the organ (widening)
2) Circular layer muscle fiber runs the circumference of the organ (narrowing)
