Flashcards in 15CHAPTER 11: MUSCLE TISSUES Deck (102)
What are contractile proteins and what do they do?
Actin and myosin, shortens muscle fibers
What are regulatory proteins and what do they do?
Troponin and tropomyosin, acts like a switch
What is dystrophin?
A protein that links actin to cell membrane = endomysium
What happens what there is a lack of dystrophin?
Muscular dystrophy (genetic disorder)
What are the different kinds of striations?
A-band (dark), I-band (light), H-band, Z-disc, and sarcomeres.
What are A-bands composed of?
Entire thick filament + portion of thin filament
What are I-bands composed of?
Portion of thin filament, adjacent to Z disc
What are H-bands composed of?
Thick filament only (middle of A-band)
What are sarcomeres composed of?
Distance from one Z disc to the next; contractile unit of a muscle fiber
What are Z-bands composed of?
Anchorage for thin filaments and elastic filaments
What is a motor unit and # fibers innervated by 1 motor neuron depends?
One nerve fiber + all the muscle fibers it innervates, depends on function of muscle
What is a neuromuscular junction?
Functional connection between a nerve fiber and a muscle cell
What happens at the synaptic knob in the neuromuscular junction?
–neurotransmitter (Ach) is released travels across synaptic cleft
–Ach receptors on sarcolemma accepts neurotransmitter
–after a sequence of events, muscle contracts
What does it mean when cells are electrically excitable?
Plasma membranes exhibit voltage changes in response to stimulation
What is membrane potential (MP)?
The electrical charge in a cell relative to outside the cell
What kind of MP does most cells have?
Inside: proteins-, nucleic acids-, K+
Outside: Na+, Cl-
What is resting membrane potential (RMP) and what maintains it?
Difference in charge across the membrane, maintained by Na/K pump
What opens ion gates in plasma membrane?
When do voltage-gated ion channels open?
Open when the MP reaches a critical level (threshold)
When do ligand-gated ion channels open?
Open when a chemical messenger binds; e.g. acetylcholine
What happens during depolarization?
Na+ ion gates open, Na+ rushes into cell causing a positive MP
What happens during repolarization?
K+ ion gates open, K+ rushes into cell causing a negative MP
What is an action potential (AP)?
Quick up-and-down voltage shifts
What are the steps of Excitation of muscle by nerve (steps 1-5)?
1. Arrival of nerve signal
2. Acetylcholine is released
3. Binding of Ach to receptor
4. Opening of ligand-gated ion channel
5. Opening of voltage-gated ion channel
What are the 4 actions involved with behavior of skeletal muscle fibers?
1) Excitation = nerve action potentials lead to action potentials in muscle fiber
2) Excitation-contraction coupling = action potentials on the sarcolemma activate myofilaments
3) Contraction = shortening of muscle fiber
4) Relaxation = return to resting length
What are the steps of Excitation-contraction coupling (steps 6-9)?
6. Action potentials propagated
7. Calcium released from terminal cisternae
8. Binding of calcium to troponin
9. Shifting of tropomyosin; exposure of active sties on actin
What are the steps of Contraction (steps 10-13)?
10. Hydrolysis of ATP; activation and cocking of myosin head
11 Formation of myosin-actin cross-bridge
12. Power stroke; sliding of thin filament over thick filament
13. Binding of new ATP; breaking of cross-bridge
What are the steps of Relaxation (steps 14-18)?
14. Cessation of nervous stimulation and ACh release
15. ACh breakdown by AChE
16. Reabsorption of calcium ions by sarcoplasmic reticulum, ATP needed
17. Loss of calcium ions from troponin
18. Return of tropomyosin to position blocking active sites of actin
When do muscles return to resting length?
- When CT components stretch it out to resting length
- When contraction of antagonist lengthens it
How fast does rigor mortis occur after death?
What is length-tension relationship?
Amount of tension generated by a muscle (the force of its contraction) depends on how stretched (or contracted) the muscle was before stimulation.
What happens when the muscle is overly stretched?
Little overlap exists between actin and myosin
What happens when the muscle is overly contracted?
Little room to build more tension
Strength of a twitch can vary depending on what?
1. Stimulus frequency
2. Amount of calcium in sarcoplasmic reticulum
3. Degree of stretch of muscle before stimulation = L/T relationship
4. Temperature of muscle:
5. pH of muscle:
6. State of hydration of muscle:
If the stimuli arriving close together, the twitches will be _______.
Why do warmed muscle contracts more strongly?
Enzymes in myosin heads work more quickly
Twitches with low frequency (up to __ stimuli/sec) have stimuli that each produce what?
10, produces an identical twitch response, muscle relaxes completely between stimuli
What is Treppe?
moderate frequency of twitches (between 10-20 stimuli/sec)
What happens to a twitch is treppe?
each twitch has time to recover but develops more tension than the one before à stronger twitches (staircase phenomenon)
What causes the enzymes work better during twitches?
Increase calcium in sarcoplasm and increase temperature
What is incomplete Tetanus?
Higher frequency stimulation of twitches (20-40 stimuli/second)
What happens during incomplete tetanus?
Generates gradually more strength of contraction
What is sustained fluttering contractions?
each stimuli arrives before last one recovers, muscle doesn’t relax completely
What is complete Tetanus?
Maximum frequency stimulation of twitches (40-50 stimuli/second)
What happens during complete tetanus?
-muscle has no time to relax at all
-twitches fuse into smooth, prolonged contraction called complete tetanus
- rarely occurs in the body
What is an isometric muscle contraction?
Contraction where tension changes, length does not
-important in postural muscle function
What is an isotonic muscle contraction?
Contraction where length changes, tension does not
What is it called when there is tension while shortening?
What is it called when there is tension while lengthening?
What are the isometric and isotonic phases of lifting?
-tension rises but length remains the same (object is not moved)
-tension levels off, muscle begins to shorten (object is moved)
How much ATP does a human make daily?
100 s of ATP daily.
In the presence of O2, fatty acids and glucose are degraded in aerobic respiration to produce what?
36 TP for muscle cells
In the absence of O2, glucose is degraded in anaerobic fermentation to produce what?
2 ATP + lactic acid
What are the modes of ATP Synthesis?
Myokinase and creatine kinase
What happens during myokinase?
2 ADP to 1 ATP + 1 AMP (transfer of one Pi)
What happens during Creatine kinase?
Pi is transferred from creatine phosphate to ADP to ATP
Limits to endurance are set by what factors?
Depletion of glycogen and blood glucose, loss of fluid, and electrolytes “sports drinks”
What is Fatigue?
Progressive weakness from use
What are the causes of fatigue?
-decrease ATP synthesis as glycogen is consumed
-decrease pH due to increased lactic acid à enzymes don’t work well
-decrease activity of Na/K pump – can’t maintain RMP and excitability of muscle fibers
-decrease ACh in motor nerve fibers depleted and less capable of stimulating muscle fibers
-CNS system fatigue, less signal output to skeletal muscles
What is endurance?
Ability to maintain high-intensity exercise for >5 minutes
What is endurance determined by?
Determined by maximum oxygen uptake
Determined by nutrient availability
Well-conditioned muscles will have what?
– More blood vessels à more O2 delivery
– More mitochondria (for endurance activities)
– More enzymes for the phosphagen system (for burst type activity)
What is oxygen debt?
Fast breathing after exercise
What is the purposes for extra oxygen:
– Replace O2 reserves (myoglobin, blood hemoglobin, in air in the lungs and dissolved in plasma)
– Replenish phosphagen system
– Oxidize lactic acid to glucose (in the liver)
– Serve elevated metabolic rate
What is a slow twitch?
Respond slowly but resistant to fatigue
What is a fast twitch?
Respond quickly but fatigue quickly
What is resistance training?
(weight lifting) Builds muscle size by stimulating cell enlargement due to synthesis of more myofilaments
What is endurance training?
(aerobic exercise) Improves fatigue resistance by producing an increase in mitochondria, glycogen, and density of capillaries rbc,
What is positively changed by endurance training?
better function of cardio system = better aerobic respiration
In multiunit smooth muscle, terminal branches of nerve fibers synapse with what? And what is the ratio?
Synapse with individual myocytes to form a motor unit (like a skeletal muscle motor unit)
What are the different types of smooth muscle?
Multiunit smooth muscle and Single-unit smooth muscle
What is the most common type of smooth muscle?
Single-unit smooth muscle
What do Single-unit smooth muscle form?
Forms circular and longitudinal muscle layers
Autonomic nerve fibers have beadlike swellings called what?
varicosities which release neurotransmitters
What connects muscle fibers in Single-unit smooth muscle?
Stimulation of Smooth Muscle is due to what?
• Chemical stimuli: CO2, hormones, pH
• Autonomic nervous system:
• Presence of pacemaker cells
How does calcium enter smooth muscle and what does it bind to?
-Comes from extracellular fluid through Ca2+ channels, not SR like in skeletal muscle
-Binds to calmodulin
Actin myofilaments are anchored to dense bodies on what?
the sarcoplasm and on the sarcolemma
What causes muscle response to stretch?
Stretch opens mechanically-gated calcium channels in sarcolemma
What is Stress Relaxation Response?
Smooth muscle contracts and then reflexively relaxes in response to stretch
What are the Characteristics of Muscles?
What is conductivity?
Stimulation of one muscle cell= contraction of whole muscle
What is contractility?
Unique to muscle, shortens and pulls on bone= movement
What is the extensibility of muscles?
Can stretch 3x contracted length
What is elasticity?
Stretch and recoil
What is skeletal muscle attached to?
Bone or skin
Are skeletal muscles voluntary or involuntary?
What causes striations in skeletal muscle?
due to overlap of contractile proteins actin and myosin
What is skeletal muscle composed of?
Muscle tissue and CT
What does endomysium surround?
Muscle fiber (cell)
What does perimysium surround?
Bundles muscle fibers into muscle fascicle
What does epimysium surround?
Encloses entire muscle
Muscle fibers are composed of long protein bundles called ____.
each myofibril is a bundle of protein microfilaments called________.
What are the 3 types of myofilaments?
1. Thick filaments
2. Thin filaments
3. Elastic filaments
What are thick filaments?
Myosin (hundreds of myosin molecules)
What are thin filaments?
Actin (beads) with activesites for myosin
What does tropomyosin do?
blocks myosin binding site on actin beads (muscle is relaxed)
What does tropomyosin do?
blocks myosin binding site on actin beads (muscle is relaxed)
What does troponin do?
binds tropomyosin and Ca2+ (shifts tropomyosin off binding sites)
What is elastic filament made of?
What is the function of elastic filament?
-anchor thick filament to the Z disc (stay tuned for more!)
-stabilizes thick filament, centers it between the thin filaments, prevents overstretching