CH 9 - Muscle Tissue & Physiology Flashcards
Intercalated disc
Specialized junctions only found in cardiac muscle
Sphincter
A ring of muscle tissue that encircles an opening
What are the 6 functions of muscle tissue?
Produce body movement
Maintain body posture/position
Support soft tissue
Guard entrances and exits
Maintain body temperature
Store nutrient reserves
Excitability (irritability)
Ability to receive and respond to an internal or external stimulus
Contractility
Ability to shorten forcibly when adequately stimulated
Extensibility
Ability to be stretched or extended
Elasticity
Ability to recoil and resume its resting length after being stretched
What is the epimysium made of? What is its function?
Dense collagenous CT
Separates muscle from surrounding tissues and organs
Connects or blends into the muscle fascia
What is the perimysium made of? What are its functions?
Dense collagenous CT, blood vessels, nerves
Surrounds fascicles
Fascicle
A bundle of muscle fibers bound by a perimysium
What is the endomysium made of? What are its functions?
Elastic and reticular CT, capillary networks, satellite cells, nerve fibers
Surrounds each muscle fiber
Satellite cells
Muscular stem cells made from lingering myoblasts that aid in skeletal muscle replacement
*Skeletal muscle cannot regenerate
How are muscles attached to bones?
The muscle fascia is continuous with the tendon attached to the bone’s periosteum
Muscle fascia
A band (tendon) or sheet (aponeurosis) of CT that extends beyond the muscle for attachment to bone
Origin
Attachment of a muscle on a stationary bone
Insertion
Attachment of a muscle on a bone that moves
Agonist (prime mover)
The primary muscle that enables the movement by shortening
Antagonist
The primary muscle that opposes the movement by lengthening
Synergistic muscle
A muscle that prevents unwanted movements and aids the movement of the agonist
How are skeletal muscles formed?
- Embryonic mesoderm cells called myoblasts undergo cell division
- Several myoblasts fuse to form a myotube
- Myotube matures into a skeletal muscle fiber
Sarcolemma
The plasma membrane of the muscle fiber
Sarcoplasm
The cytoplasm of the muscle fiber
*Contains glycosomes and myoglobin
Transverse (T) tubule
The part of the sarcolemma that penetrates into the sarcoplasm of the muscle fiber to conduct and transmit the muscle action potential
Myofibril
Rodlike structures densely packed into the muscle fiber that are responsible for skeletal muscle contraction
*Contains myofilaments
What is the thick myofilament?
Myosin
What are the thin myofilaments?
Actin
Troponin
Tropomyosin
Nebulin
What is the elastic myofilament?
Titin
Sarcoplasmic reticulum
Smooth endoplasmic reticulum and site of calcium ion storage that encircles each myofibril
Triad
A T tubule and both of the terminal cisternae of the sarcoplasmic reticulum
Terminal cisternae
The portion of the sarcoplasmic reticulum in direct contact with the T tubule
Sarcomere
The smallest contractile unit measured between two Z-discs
A band
The length of the thick myofilaments that remains constant regardless of muscle contraction
I band
The distance between thick myofilaments that shortens during muscle contraction
H zone
The distance between thin myofilaments that shortens during muscle contraction
Myomesin
A structural protein that forms the M line
Also binds to titin and connects adjacent thick myofilaments together
Dystrophin
A structural protein that links thin myofilaments to membrane proteins in the sarcolemma
Helps reinforce the sarcolemma
Helps transmit tension generated by sarcomeres to tendons
a-Actinin
A structural protein of the Z disc that attaches to actin and titin
Filamentous actin (F-actin)
A thin myofilament protein
Two twisted rows of globular actin (G-actin) with each G-actin containing a myosin binding site
Nebulin
A thin myofilament protein
A long, nonelastic protein that holds F-actin together and anchors thin myofilaments to the Z disc
Tropomyosin
A thin myofilament protein
A double stranded protein molecule that spirals around actin core and helps stiffen the F-actin
Covers the myosin binding site on actin
Troponin
A thin myofilament protein
Globular protein composed of three subunits that binds tropomyosin to G-actin
Controlled by calcium ions
What makes up the troponin complex?
TnT - binds to tropomyosin
TnC - binds to calcium
TnI - binds to actin
How does calcium expose the myosin binding site of actin?
Calcium ions bind to TnC, causing a structural change that moves the entire troponin complex aside, exposing the myosin binding site.
*Stays this way until calcium is removed
What are the two binding sites on a myosin head?
ATP binding site
Actin binding site
What is the relaxed form of myosin called? Is it high or low energy?
Cocked
High energy
What is the pivoted form of myosin called? Is it high or low energy?
Power stroke
Low energy
Cross-bridges
Myosin heads interact with myosin binding site on G-actin
Sliding filament mechanism
Thin myofilaments of the sarcomere slide towards the M line
A band width is unchanged
H zone, I band disappear
Z discs move closer together
Neuromuscular junction
A specialized intercellular connection between a somatic motor neuron and and a skeletal muscle fiber
Synaptic knob (synaptic end bulb)
The enlarged bottom of a somatic motor neuron
Voltage gated calcium ion channel
A channel that is gated by calcium and has permeability for calcium ions (Ca2+)
Acetylcholine vesicles
A vesicles that carries acetylcholine
Acetylcholine (ACh)
A neurotransmitter
Synaptic cleft
The space between the axon terminal and the muscle fiber
Motor end plate
The part of a neuromuscular junction that touches the nerve fiber
Junctions folds
Invaginations that increase the surface area of the sarcolemma
Ligand gated sodium ion channel
A channel that is opened and closed by a ligand
Aceytlcholinesterase
An enzyme that hydrolyzes acetylcholine
Graded potential
Temporary changes in the membrane voltage
What does the duration of a muscle contraction depend on?
Duration of nerve action potential
Number of calcium ions in the sarcoplasm
Availability of ATP
During relaxation, a fall in calcium ion concentration allows for what?
Calcium ions to detach from troponin (TnC)
Myosin binding site on actin are re-covered by tropomyosin
What factors contribute to the return to resting length?
Tendons stretch sarcomeres back to resting length
Antagonist or gravity reverse direction of original motion
What is rigor mortis?
A fixed muscular contraction involving all skeletal muscles after death that lasts until lysosomal enzymes are released by autolysis
*Begins 2-7 hours after death, ends in 1-6 days
What causes rigor mortis?
Lack of ATP
Calcium build up in the sarcoplasm
Calcium ion ATPase pumps stop working
SR membrane breaks down
Motor unit
One somatic motor neuron and all the skeletal muscles that it controls
What controls how precise a movement is?
The ratio of number of muscle fibers to one motor neuron
*Fewer muscle fibers per somatic motor neuron indicates a more controlled movement
Length-tension relationship
Resting length at time of stimulation
Determines degree of overlap and number of pivoting cross bridges
Frequency of stimulation
Number of stimuli per unit time
Affects concentration of calcium ions in the sarcoplasm and bound to troponin
Twitch
A single stimulus-contraction-relaxation sequence
- Duration depends upon the type and location of muscle, and internal/external environment conditions
- 7-100 milliseconds
What are the three phases of a twitch?
Latent (lag) period, contraction period, relaxation period
Latent (lag) period
Begins at stimulation and lasts 2 milliseconds
Excitation-contraction coupling (cross-bridges) occurrs
Contraction period
Tension rises to a peak and contraction cycle begins
Lasts 10-100 milliseconds
Myosin power strokes
Relaxation period
Relaxation cycle begins
Lasts 10-100 milliseconds
Myosin cocks
Treppe
A stair-step increase in twitch tension that occurs when skeletal muscle fibers are stimulated a second time immediately after the relaxation phase ends, resulting in a contraction with slightly higher than that of the first
Tension will increase over first 30-50 stimulations but will eventually plateau
Wave summation
Successive stimuli arrive before the relaxation phase has been completed
Duration of a single twitch determines the max time available for wave summation
Incomplete tetanus (unfused tetany)
Stimulus frequency increases further without allowing the muscle to relax completely
Tension rises further and reaches a peak
Complete tetanus (fused tetany)
Stimulus frequency is so high that the relaxation phase is eliminated and tension plateaus at maximum levels
*Full muscle contraction
Multiple motor unit summation (recruitment)
Increasing the strength of the stimulus by increasing the number of stimulated motor units
Subthreshold stimulus
Stimulus strength is too low and no contraction occurs
Threshold stimulus
Stimulus at which the first observable contraction occurs
Submaximal stimuli
Progressive increase in stimulus strength
Maximal stimulus
Strongest stimulus at which all of the muscle’s motor units are recruited
Supramaximal stimuli
No real change from increasing stimulus strength since maximal motor units are already working
Synchronous motor unit summation
Peak tension that occurs when all motor units in the muscle contract in a state of complete tetanus
*Very brief because individual muscle fibers use up all available energy reserves
Asynchronous motor unit summation
Sustained contraction in which motor units are activated on a rotating basis
*Prolongs strong contraction by preventing or delaying fatigue
Muscle tone
Normal tension and firmness of a resting muscle
- Some motor units are always active to keep the muscle firm and healthy, but this does not produce an active movement
- Higher muscle tone accelerates the recruitment process during voluntary contraction
- Stabilizes positions of bones and joints
- Increases metabolic rate
Isotonic contraction
A muscle contraction that maintains constant tension in the muscle as the muscle changes length
Muscle’s max force of contraction > total load on the muscle
*Thin filaments are sliding
Concentric isotonic contraction
Peak muscle tension > load
Muscle shortens and decreases angle at joint and moves the load
Tension remains constant at a value just above the load
*EX. Bicep curl up
Eccentric isotonic contraction
Peak muscle tension < load
Muscle elongates and exerts precise control over the amount of tension and rate of elongation
*EX. Bicep curl down
Isometric contraction
The muscle as a whole does not change length and results in no motion
Occurs when the muscle isn’t strong enough to move the load
Peak muscle tension < load
- Cross-bridges generate force, but do not move thin filaments
- EX. Muscles that maintain upright posture or hold joints stationary
How does myokinase make ATP?
Removes 1 phosphate from ADP and adds it to another ADP, resulting in 1 AMP and 1 ATP
Aerobic endurance
The length of time a muscle can continue to contract using aerobic pathways
Anaerobic threshold
The point at which muscle metabolism converts to anaerobic pathways
Phosphagen system:
Description Energy source Oxygen use Products Duration of energy
Coupled reaction of creatine phosphate and ADP
Creatine phosphate
None
1 ATP, creatine
15 seconds
Creatine phosphate
A high-energy molecule stored in muscles much more abundantly than ATP
*Replenished during rest
Anaerobic pathway:
Description Energy source Oxygen use Products Duration of energy
Glycolysis and lactic acidosis formation
Glucose
None
2 ATP, lactic acid
30-40 seconds
Aerobic pathway:
Description Energy source Oxygen use Products Duration of energy
Aerobic cellular respiration
Glucose, pyruvic acid, fatty acids, amino acids
Required
32 ATP, CO2, H2O
Hours
Force
The maximum amount of tension produced
Endurance
The amount of time an activity can be sustained
What do both force and endurance depend on?
The type of muscle fibers and physical conditioning
Fast glycolytic (FG) fibers
Energy pathways (metabolism) Myoglobin Mitochondria Glycogen Capillaries Fatigue resistance Myosin ATPase activity Color
🚭Anaerobic glycolysis
⬇️Low myoglobin
⬇️Few mitochondria
🔺High glycogen
⬇️Few capillaries
⏩⏩Contract quickly, fatigue quickly
⏩Fast myosin ATPase
🤍Pale muscle fibers
Fast oxidative (FOG) fibers
Energy pathways (metabolism) Myoglobin Mitochondria Glycogen Capillaries Fatigue resistance Myosin ATPase activity Color
🚭🌬Anaerobic glycolysis, aerobic respiration
🔺High myoglobin
🔺Many mitochondria
🔺High glycogen
🔺Many capillaries
⏩⏯Contract quickly, fatigue slower
⏩Fast myosin ATPase
💗❤️Pink-red muscle fibers
Slow oxidative (SO) fibers
Energy pathways (metabolism) Myoglobin Mitochondria Glycogen Capillaries Fatigue resistance Myosin ATPase activity Color
🌬Aerobic respiration
🔺High myoglobin
🔺Many mitochondria
⬇️Low glycogen
🔺Many capillaries
⏸⏸Contract slowly, fatigue slowly
⏸Slow myosin ATPase
♥️Red muscle fibers
Hypertrophy
Muscle growth from heavy training
Atrophy
Muscle shrinkage from lack of activity
Disuse atrophy
Atrophy due to lack of use
Denervation atrophy
Atrophy due to damaged nerves that are unable to send action potentials to activate the muscle
Duchenne muscular dystrophy
A fatal degenerative disease causing muscles to weaken due to inability to produce dystrophin
Myasthenia
General muscular weakness due to a reduction in ACh receptors on the motor end plate
Fibromyalgia
Chronic disorder of widespread pain, fatigue, and tenderness
Central/Psychological fatigue
Exhaustion and pain
Muscle fatigue
Physiologically inability to contract or produce tension
What can muscle fatigue be caused by?
Depletion of metabolic reserves
Damage to sarcolemma or myofibrils
Insufficient oxygen supply
Buildup of lactic acid
Depletion of ACh (nerve AP fails to release it)
Recovery period
Time required after exertion for muscles to return to normal
What happens during the recovery period?
Oxygen becomes available
Mitochondrial activity restores energy reserves
Repairs made to skeletal muscle fibers
Cori cycle
Returning lactate to the liver
Returning glucose back to muscle cells
Oxygen debt
Excess post exercise oxygen consumption, EPOC
Heavy breathing resulting from increased oxygen demand to normalize metabolic rates
