Muscle Tissue Flashcards
What are the three types of muscle tissues?
Skeletal
Cardiac
Smooth
Alternating light and dark bands seen under the microscope and which muscles are these?
Striated
Skeletal
Cardiac
Are skeletal muscles voluntary or involuntary?
Voluntary
- Under conscious control (although many are also controlled subconsciously)
Are cardiac muscles voluntary or involuntary?
Involuntary
- not under conscious control
Where are smooth muscles located?
Blood vessels
Airways
Abdominopelvic organs
Does not exhibit alternating light and dark bands when viewed under the microscope and which muscle has this?
Non- striated
Smooth
Are smooth muscles voluntary or involuntary?
Involuntary
What are the muscle tissue functions?
- Producing body movements
- Stabilizing body positions
- Storing and moving substances within the body
- Generating heat (thermogenesis)
Properties of muscle tissue
- Electrical excitability (carry and respond to APs)
- Contractility (stimulated by AP)
- Extensibility (stretch w/o being damaged)
- Elasticity (return to original shape)
What is a single cell muscle?
Fiber (myofiber)
Bundle of muscle fibers (cells)
Fascicle
An organelle in a muscle fiber composed of filaments
Myofibril
Fibrous protein molecules within myofibrils (the thick and think filaments that are the contractile proteins)
Filaments
What surrounds a fiber?
Endomysium
What surrounds a fascicle?
Perimysium
What surrounds the entire muscle?
Epimysium
What is a broad flat tendon and what blends together to make them?
Aponeurosis
Endomysium
Perimysium
Epimysium
Which nerve cell supplies a group of muscle fibers?
Somatic Motor Neuron
How many neurons supply each muscle fiber?
Only one
Where does the neuron contact the muscle fiber?
Neuromuscular junction
What are skeletal muscles well supplied with and what accompanies it?
Nerves and Blood vessels
An artery and one or two veins usually accompany each nerve
Each muscle fiber is in close contact with one or more capillaries. What do these do?
- Provide nutrients and oxygen
- Remove heat and waste products of muscle metabolism
What happens to form one skeletal muscle fiber during embryonic development?
Myoblasts fuse
- this is why skeletal muscle fibers are multinucleate
The plasma membrane of a muscle fiber and enclosed the sarcoplasm and myofibrils
Sarcolemma
Just inside the sarcolemma (numerous)
Nuclei
The cytoplasm of a muscle fiber
Sarcoplasm
Bundles of filaments that are the contractile elements of the cell (striated appearance)
Myofibrils
Opening from the outside of the fiber toward the interior of the fiber
T-tubules (transverse tubules)
- propagate APs
- filled with interstitial fluid
Stores calcium ions and releases them when the muscle fiber is stimulated
Sarcoplasmic reticulum
Dilated regions that flank T-tubules
Terminal cisterns
What are two terminal cisterns flanking one T- tubule
Triad
Myofibrils are made of smaller structures called filaments. What are the two types and what proteins do they have?
Thin
- Actin: contractile proteins
- Troponin: regulatory protein
- Tropomyosin: regulatory protein
Thick
- Myosin: contractile protein
How many thin filaments to thick filaments are there?
Two think filaments for every thick filament
Filaments inside the myofibrils are arranged in carport nets called?
Sarcomeres
What is a long chain of sarcomeres?
Myofibril
Thick and think filaments overlap to a varying degree depending on what?
The contraction state of the muscle
In the sarcomeres thin and thick filaments overlap to a degree causing….
Z discs A band I band H zone M line
Where adjacent sarcomeres abut; center of an I band
Z discs
Darker zone, which comprises the length of the thick filaments and a varying overlap of thin filaments
A band
Only thin filaments
I band
Center of an A band; only thick filaments
H zone
Midline of a sarcomere
M line
The heads (cross bridges) of the myosin molecules do what?
- Bind and hydrolyze ATP (myosin ATPhase); also bind products of ATP hydrolysis (ADP and phosphate)
- Change shape ( move toward or away from M line)
- Bind reversibly
In the thin filament each individual actin molecule has?
A myosin- binding site
What happens at rest of the thin filament?
Regulatory proteins troponin and tropomyosin form complex that covers these sites
In the thin filaments what allows contraction to begin and what is movement triggered by?
Movement is triggered by calcium binding to troponin
Movement of troponin-tropomyosin complex allows contraction
What three categories comprise muscle fiber proteins?
Contractile proteins
- myosin
- actin
Regulatory proteins
- troponin
- tropomyosin
Structural proteins
- titin
- myomesin
- dystrophin
- sarcolemmal proteins
Each molecule spans half a sarcomere, from a Z disc to an M line, and attaches thick filaments to Z discs and M lines and what does it do?
Titin
- very elastic and helps sarcomere return to its resting length
Binds to titin and holds thick filaments in position from side to side, and form the M line
Myomesin
Links the thin filaments of sarcomeres to integral membrane proteins in the sarcolemma and what does it do?
Dystrophin
-thereby transmitting the tension generated by the sarcomeres through the connective tissues of the muscle to tendons
What is the most common muscular dystrophy?
Duchenne muscular dystrophy
What happens in DMD?
The gene that codes for the protein is mutated, resulting in little or no dystrophin in the sarcolemma
What happens to the sarcolemma when it is absent of dystrophin in DMD?
Sarcolemma tears easily during muscle contraction, causing muscle fibers to rupture and die
Is the synapse between a somatic motor neuron and skeletal muscle fiber
Neuromuscular junction
Synaptic end bulbs at the tips of axon terminals contain what and are filled with what?
Synaptic vesicles
Acetylcholine (ACh)
- which carries the impulse across the synaptic cleft
What is the region of the sarcolemma opposite the synaptic end bulb?
The motor end plate
What binds to the ACh in the sarcolemma?
Acetylcholine receptors
- millions of these proteins are in deep grooves in motor end plate called junctional folds
What happens when the two molecules of ACh?
Opens an ion channel in the ACh receptor allowing cations most importantly Na+, to flow across the membrane
What happens when there is an inflow of Na+?
Inside of the muscle fiber more positively charged, triggering an AP
What blocks exocytosis of synaptic vesicles at the NMJ?
Clostridium botulinum produces botulinum toxin
How does Botox work?
Causes muscle paralysis by binding to and blocking ACh receptors, preventing ion channels from opening
What show the enzymatic activity of acetylcholinesterase allowing ACh to linger longer in synaptic cleft
Anticholinesterase agents
What happens during the contraction cycle?
- Myosin heads hydrolyze ATP and become reoriented and energized
- Myosin heads bind to actin, forming cross bridges
- Myosin cross bridges rotate toward center of the sarcomere (power stroke)
- As myosin heads bind ATP, the cross bridges detach from actin
What are two important point of the contraction cycle?
- Myosin cross bridges detach only when ATP binds to the myosin heads
- Contraction cycle continues as long as ATP is available and the CA2+ concentration in the sarcoplasm is high
What are the changes in length during contraction?
H zone and I band decrease
A band width remains the same
Sarcomere length decreases
Thick and thin filaments do NOT change length (they slide)
The length of individual fibers remain ________, although the overall length _______ with ________ and _________. The _____ band width is constant, but the ____ and ____ bands are not.
Constant Changes Contraction Relaxation A H I
Characteristics of rigor mortis
- starts 3-4 house after death
- cell membranes no maintained and leak Ca++
- Ca++ still binds to troponin-tropomyosin complex, allows one power stroke
- cells no longer produce APT, cross bridges cannot detach from actin, procuring rigidity
- disappear 24 hours after death, proteolytic enzymes form lysosomes digest the cross bridges
What is the increase in diameter of muscle fibers?
Muscular hypertrophy
Increase in size of tissues and organ due to an increase in the number of cells
Hyperplasia
- Smooth muscle of the airway, vascular system, and urogenital tract
Decrease in the size of a cell, tissue, organ, or entire body; accompanied by diminished function
Atrophy
Binds oxygen in muscle cells and releases it when needed by the mitochondria during high levels of aerobic respiration
Myoglobin
- red-colored protein
- found only in muscle
- similar to hemoglobin
What are the uses for ATP in muscle contraction?
- Na+ -K+ pumps
- Calcium ion pumping
- Energize the myosin head in prep for the power stroke
Active transport; necessary to terminate contraction
Calcium ion pumping
Active transport; maintain concentration gradients across the sarcolemma; necessary for producing AP
Na+ -K+ pump
ATP production is via
- Creatine phosphate
- Glycolysis
- Aerobic respiration
Two significant points about ATP in muscle fibers
- Cells don’t store ATP in significant amounts
- ATP must be made at the same rate that is it used
How long does the ATP from glycolysis
30-40 minutes
What can ATP present inside muscle fibers do?
Power contractions
What can provide maximum contraction?
Creatine phosphate plus pre-existing ATP
How long does ATP production from aerobic cellular respiration
Lasts indefinitely
Where is the usual sources of Creatine in the body and where is it derived from foods?
Synthesis in liver, kidneys, pancreas
Milk, red meat, some fish
How much Creatine do adults need per day and what happens if they ingest extra?
2 grams
Investing extra will decrease the body’s own synthesis of Creatine
What does one nerve impulse in a motor neuron cause?
One AP in neurons and muscles fibers of that motor unit
Record of a muscle contraction
Myogram
Begins upon stimulation and commonly lasts into the early part of the contraction period, duration varies
Refractory periods
The muscle action potential sweeps over the sarcolemma, and Ca++ are released from the sarcoplasmic reticulum
Latent period
Ca++ binds to troponin resulting in exposure of myosin binding sites on actin, cross bridges form; peak tension develops in the muscle fiber
Contraction period
Activity transported back into the sarcoplasmic reticulum, myosin binding site are covered by tropomyosin, myosin heads detach from actin; tension in the muscle fiber decreases
Relaxation period
What happens if second stimulus is applied after refractory period
Skeletal muscle will respond to both stimuli
What happens if the second stimulus occurs after the refractory period but before the muscle fiber has relaxed
The seconds will be stronger than the first
More what will be released from the sarcoplasmic reticulum during wave stimulation
More Ca++ = more Contraction
Muscle fibers vary in?
- their content of myoglobin
- speed of contraction/ relaxation
- metabolic reaction used to generate ATP
- how quick they fatigue
(These factors are all interrelated)
What is the difference between red and white fibers
Red muscle fibers
- abundant myoglobin
- have mitochondria (generate ATP)
- well-supplies by blood capillaries
White muscle fibers
- less of each of these above
Slow oxidative (SO) fibers capacity for generating ATP and functions
High capacity, by aerobic (oxygen- requiring) cellular respiration
Functions:
-maintaining posture and aerobic endurance activities
Fast oxidative-glycolytic (FOG) fibers capacity for generating ATP and functions
Intermediate capacity, by both aerobic (oxygen-requiring) cellular respiration and anaerobic (not require oxygen) cellular respiration (glycolysis)
Functions:
- Walking
- Sprinting
Fast glycolytic (FG) fibers capacity for generating ATP and functions
Low capacity; by anaerobic cellular respiration (glycolysis)
Functions:
- Rapid
- Intense movements of short duration
Why does cardiac muscle remain contracted longer than skeletal muscle
Prolonged delivery of Ca++ ions into the sarcoplasm
What muscle fibers are branched
Cardiac muscle fibers
Muscle fibers of cardiac muscle exhibit what?
Autorhythmicity
- interconnectedness of fibers result in synchronous contraction
- altered by autonomic nervous system and endocrine system
What does cardiac muscle have more of than skeletal muscle?
Mitochondria (larger/more numerous)
- has greater dependence on aerobic respiration to generate ATP
What does the sarcoplasm contain in smooth muscle tissue?
Both thick and thin filaments
But filaments are not arranged in orderly sarcomeres so no striations
What do the intermediate filaments do in the smooth muscle tissues?
Attach to dense bodies, which are functionally similar to Z discs found in striated muscle are found in the sarcoplasm and the sarcolemma
What are the two types of smooth muscle?
Single- unit smooth muscle tissue (AKA visceral smooth muscle tissue) (most common)
- Multiunit smooth muscle tissue
Lack gap junctions and contract independently
Multiunit smooth muscle fibers
Connect to one another by gap junction and contract as single unit
Visceral (single-unit) smooth muscle fibers
Where are single unit smooth muscle tissue found?
Wraparound sheets forming part of walls of
- small arteries
- veins
- hollow organs
- stomach
- small intestines
Where are multiunit smooth muscle tissue found?
Walls of
- large arteries
- lung airways
- arrectores pilorum
- intrinsic muscles of eye
Feelings of tiredness and desire to cease activity (protection to stop before getting hurt)
Central fatigue
What are some things that can lead to muscle fatigue?
- Inadequate release of Ca++ ions
- depletion of Creatine phosphate
- insufficient oxygen
- deletion of glycogen
- build up of lactic acid
- failed AP in motor neuron to release enough acetylcholine
Keeps skeletal muscles firm but foes not cause movement
Muscle tone
Neuromuscular disease: disease or damage of the components of a motor unit (problems at these sites)
- Somatic motor neuron
- Neuromuscular junctions
- Muscle Fibers
Autoimmune disease that causes chronic, progressive damage of neuromuscular junction by producing antibodies that bind to and black acetylcholine receptors
Myasthenia gravis
