Lecture 9: Muscle Histology and Physiology Flashcards
Types of Muscle
Skeletal,
Cardiac,
Smooth
Skeletal Muscle Brief Definition
Moves skin on face and joints,
Voluntary
Cardiac Muscle Brief Definition
Allows heart to contract,
Involuntary
Smooth Muscle Brief Definition
All over,
Lines body,
Blood pressure, move waste through intestines, etc
Involuntary
Functions of Skeletal Muscles
Produce Joint Movement, Maintain Posture, Support Soft Tissue (hold in organs), Guard Entrances and Exits (eyes/mouth/etc), Maintain Body Temperature, Store Nutrient Reserves
Types of Connective Tissue in Skeletal Muscles
Epimysium,
Perimysium,
Endomysium
Epimysium Connective Tissue of Skeletal Muscles
Covers outside of the muscle,
Separates muscle from muscle,
Most outer layer,
Surrounds each muscle
Perimysium Connective Tissue of Skeletal Muscles
Covers muscle fascicles,
Inside of Epimysium,
Separates fascicle from fascicle
Endomysium Connective Tissue of Skeletal Muscles
Covers and separates individual muscle cells (fibers) in the muscle fascicle
Where Are Skeletal Muscle Fibers In Cell?
Innermost ‘layer’,
Covered with Endomysium
Tendons
All three connective tissue layers come together at the end of a muscle to form a tendon,
Dense regular CT proper,
Anchor muscle belly to a bone
Skeletal Muscle Fibers (Cells)
Are very long,
Develop through fusion of mesodermal cells,
Become very large,
Contain hundreds of nuclei,
Individual muscle cell inside a fascicle,
Contain microfibrils
How Long Can A Skeletal Muscle Fiber Be?
They can run the length of the muscle
Myoblasts
Fuse together to create muscle fibers
Sarcolema
Cell membrane that surrounds the whole muscle
Sarcoplasmic Reticulum
Like smooth reticulum,
Stores calcium
Thick and Thin Filaments
Protein filaments (actin and myosin)
Myofibrils
Inside skeletal muscle fibers,
Made up of sarcomeres,
Smallest functional units of a skeletal muscle
Sarcoplasm
Cytoplasm of a muscle fiber
Sarcomeres
Made of protein filaments,
Make up myofibrils,
Connect end to end in myofibrils,
Composed of myosin and actin
Myosin Filament
Thick filament with a globular head at one end
Actin Filament
Composed of actin, tropomyosin, and troponin,
Attached to a Z disk
Tropomyosin
Covers actin active sites to stop myosin from connecting to it
Troponin
Calcium binds to it to remove the tropomyosin from the actin filament
Cross-Bridge
Actin and myosin bond with one another when actin active sites are exposed
T Tubules
Transverse Tubules,
Allow action potentials to quickly spread into cell via tunnels of sarcolemma that network through the sarcoplasm
Action Potentials
Happens in excitable cells (nerves/neurons and muscles)
When Do Action Potentials Occur?
When a signal causes sodium channels to open in the plasma membrane and a rush of sodium to depolarize the cell membrane
What Are Action Potentials Like?
A wave across the surface of a cell,
Quickly and then the cell repolarizes
What Neurotransmitter Is Released at the Synapse?
Acetylcholine (ACh)
Neuromuscular Junction (NMJ)
Synapse where ACh is released
Motor End Plate
Where the ACh binds to receptors on the sarcolemma and triggers an action potential
As The Action Potential Spreads, It Triggers The Release Of…
Calcium
Power Stroke
Tilt of the myosin head and drag of the actin filaments in the opposite directions
Contraction
The pulling of the actin filaments past the myosin filaments results in sarcomere shortening and generation of muscle force
Excitation-Contraction
The steps that occur to depolarize the muscle cell and cause contractions together
Triads
One T-Tubercle and two terminal cisternae,
Where excitation-contraction coupling occurs
What Happens After The Power Stroke?
Myosin heads release actin and ‘recock’ so they can attach to actin again
Recocking of Myosin Head
Requires of ATP to detach the head,
ADP is used to recock,
1 ATP per 1 myosin head
Acetyl-Cholinesterase Molecules
Breaks down ACh, prevents a prolonged contraction within 1 muscle myofibril
Skeletal Muscle Fiber Shortening
As many sarcomeres shorten, muscle pulls together (shortens), producing tension
Contraction Duration Depends On… (3)
Duration of neural stimulus,
Number of free calcium ions in sarcoplasm,
Availability of ATP
Relaxation Of Skeletal Muscles
Calcium concentrations fall,
Calcium detaches from troponin,
Active sites are re-covered by tropomyosin,
Sarcomeres remain contracted and other forces lengthen them again
Rigor Mortis
A fixed muscular contraction after death (starts usually 3 hours after death)
Causes of Rigor Mortis (3)
Ion pumps cease to function (no more ATP made),
Calcium builds up in the sarcoplasm,
Ends in about 3 days (depends on external factors)
Lack Of ATP Production In Rigor Mortis Causes..
Myosin to never detach,
Cross-bridges do not break,
No shortening,
No lengthening
How Many Myosin Filaments Per Muscle Fiber?
Millions to billions
1 Second Skeletal Muscle Contraction
Each myosin filament can breakdown 2500 ATP molecules per second,
Muscles contain only enough ATP to start contraction, then they have to make more
ATP + Creatine = ?
ADP + Creatine Phosphate (CP)
Creatine Phosphate
Stores energy in the cell for long-term
ADP + Creatine Phosphate = ?
ATP + Creatine
Creatine Phosphokinase (CPK)
Enzyme that makes ATP Resynthesis happen
15 Second Skeletal Muscle Contraction
ATP + Creatine = ADP + Creatine Phosphate
ADP + Creatine Phosphate = ATP + Creatine
CP is used up in 15 seconds
Anaerobic Glycolysis
Without Oxygen,
Occurs in Sarcoplasm,
Glucose to Lactic Acid and ATP
Aerobic Metabolism
With Oxygen, More ATP made than anaerobic glycolysis, Kreb's Cycle/Citric Acid Cycle, Pyruvate to ATP (glucose, fat, protein) ATP + H2O + CO2
Skeletal Muscle Fatigue
When muscles can no longer perform a required activity
Causes of Skeletal Muscle Fatigue (4)
Depletion of metabolic reserves,
Damage to sarcolemma and sarcoplasmic reticulum,
Low pH (lactic acid),
Muscle damage/exhaustion and pain
Skeletal Muscle Recovery Period
Time required after exertion for muscles to return to normal (like after exercising),
Oxygen becomes available,
Mitochondrial activity resumes,
Protein fibers heal and may become more numerous
Slow-Twitch (ST) Skeletal Muscle Fibers
Plenty of oxygen,
High aerobic capacity and fatigue resistance,
Low anaerobic capacity and motor unit strength,
Slow contractile speed (110 ms) and myosin ATPase (slowing ATP splitting),
Low sarcoplasmic reticulum development,
Good at endurance,
More mitochondria = more ATP
Example of Slow-Twitch Skeletal Muscle Fibers
Core muscles,
Spine muscles,
Eyes,
Fingers
Fast-Twitch (Fta) Skeletal Muscle Fibers
Faster,
More tension,
Contract for less periods of time,
Moderate aerobic capacity and fatigue resistance,
High anaerobic capacity and motor unit strength,
Fast contractile speed (50 ms),
High sarcoplasmic reticulum development
Fast-Twitch (Ftb) Skeletal Muscle Fibers
Fastest muscle fiber, Fatigue quickly, Low aerobic capacity, Fast contractile speed (50 ms), High sarcoplasmic reticulum
Resistance and Speed of Skeletal Muscle Contraction
Heavier the load (resistance) on a muscle the longer it takes for shortening to begin and the less the muscle will shorten
Skeletal Muscle Relaxation
After a contraction, a muscle fiber returns to resting length by elastic forces, opposing muscle contractions, and gravity
Skeletal Muscle Hypertrophy
Muscle growth from heavy training,
Increase diameter of muscle fibers too allow for more sarcomeres, no size,
Increases number of myofibrils (actin and myosin),
Increases mitochondria, glycogen reserves
Skeletal Muscle Atrophy
Lack of muscle activity,
Reduces muscle size, tone, and power
Tone
Action potential that makes muscle ready/prepared for movement
Anaerobic Activities
Physical Conditioning,
Use fast fibers to produce more ATP,
Fatigue quickly with strenuous activity,
50 m dash, weight lifting, etc
How Is Physical Conditioning Improved With Anaerobic Activities?
Frequent, brief, intensive workouts, strength training,
Hypertrophy
Aerobic Activities
Physical Conditioning, Supported by mitochondria, Require oxygen and nutrients, Prolonged activity (long distance runs), Rely more on slow-twitch muscle fibers to keep up with physical demands, Able to provide enough oxygen and blood
How Is Physical Conditioning Improved With Aerobic Activities?
Repetitive training (neural responses), Cardiovascular training/endurance training
What Couple Replace Muscle Fibers During Prolonged Inactivity?
Fibrous Tissue (scar tissue)
Motor Unit
One motor neuron and muscle fiber it innervates,
Uses fine control with slow-twitch muscle fibers,
Strength control
Length-Tension Relationship
Tension generated depends on length of muscle
Tension Production
Three phases:
Latent period,
Contraction phase,
Relaxation phase
Latent Period Before A Skeletal Muscle Contraction
Action potential moves through a sarcolemma that causes calcium release,
Action potential spreads over the muscle and t tubules
Contraction Phase Of A Skeletal Muscle Twitch
Calcium ions bind,
Tension begins to peak,
Interaction of actin and myosin
Relaxation Phase Of A Skeletal Muscle Twitch
Calcium levels fall after the optimum number of interactions occur,
Active sites are covered,
Tension falls to resting levels,
Higher Stimulus Frequency = ?
An increase in tension production
Treppe Skeletal Muscle Stimulation
Low frequency (up to 10/sec), Stimulating right after a twitch makes it stronger because less of a latent period and calcium is already available, Stronger each time until constant twitch strength
Wave Summation Skeletal Muscle Stimulation
Stimulus before the end of relaxation phase,
Results in incomplete Tetanus Stimulation
Complete Tetanus Skeletal Muscle Stimulation
Stimulating before relaxation phase even starts,
Allows for smooth body movements
Structure of Cardiac Muscle Tissue
Striated, Found only in heart, Sarcomeres, Smaller than skeletal muscles, Single nuclei
Cardiac Muscle Cells Are Called
Cardiocytes
Characteristics of Cardiocytes (7)
Small, Single nucleus, Short, wide T tubules, No triads, SR with no terminal cisternae, Aerobic (high myoglobin and mitochondria), Intercalated discs
Intercalated Discs of Cardiac Muscles
Specialized contact points between cardiocytes,
Join cell membranes of adjacent cardiocytes with gap junctions and desmosomes,
Able to depolarize
Allow ions to spread from 1 cardiac muscle cell to another
Functions of Intercalated Discs of Cardiac Muscles
Maintain structure of cardiac muscles,
Enhance molecular and electrical connections,
Conduct action potentials
Automaticity of Cardiac Muscles
Self depolarizing,
Contraction without neural stimulation,
Controlled by pacemaker cells (leakiest cells)
Extended Contraction Time of Cardiac Muscles
To be able to push blood along/through arteries thoroughly,
10 times as long as skeletal muscle
Prevention of Wave Summation in Cardiac Muscles
Long refractory period,
Want long contraction/long relaxation because there is no need for seizing or long term contraction of cardiac muscles
Smooth Muscle Tissue in Body Systems
Forms around other tissues, Blood vessels, Reproductive and Glandular systems, Digestive and Urinary systems, Integumentary system
Smooth Muscle Tissue Function in Blood Vessels
Regulates blood pressure and flow
Smooth Muscle Tissue Function in Reproductive and Glandular Systems
Produces movement
Smooth Muscle Tissue Function in Digestive and Urinary Systems
Forms sphincters,
Produces contractions
Smooth Muscle Tissue Function in Integumentary System
Arrector pili muscles cause goose bumps
Structure of Smooth Muscle Tissue
Nonstriated tissue (no sarcomeres),
Scattered actin and myosin filaments,
Whole cell shrinks during a contraction
Characteristics of Smooth Muscle Tissue (4)
Long, slender, spindle shaped,
Single, central nucleus,
No T tubules, myofibrils, or sarcomeres,
No tendons
Smooth Muscle Tissue Contractions Are Caused By…
Neurons, hormones, or other local chemical factors
