Chapter 10 Muscle Tissue Flashcards
What are six muscle functions?
1– movement of bones are fluids. 2– maintaining posture and body position. 3– stabilizing joints. 4-heat generation 5-protect internal organs 6-regulate body openings
What are the three connective tissue sheaths of skeletal muscle? And what do they surround?
Epimysium-dense regular connective tissue surrounding entire muscle (outer).
Perimysium- fibrous connective tissue surrounding fascicles groups of muscle (fibers).
Endomysium-fine areoleor connective tissue surrounding each muscle fiber
What are the two ways muscles can attach?
Directly –epimysium of muscle is fused to the periosteum of bone or perichondrium of cartilage.
Indirectly – connective tissue wrappings extend beyond the muscle as a (rope like) tendon or (sheet like) aponeurosis.
What is a sarcomere?
Smallest contractile unit of a muscle fiber.
Region of a myofibril between 2 Z disks.
Composed of thick and thin myofilaments made of contractile proteins.
What are the features of a sarcomere?
Thick filaments myosin -run the entire length of the A band.
Thin filament Actin- run link of I band and partway into a band.
Z disc – sheet of proteins that anchors the thin filaments and connects myofibrils to each other.
H zone – lighter mid region where filaments do not overlap.
M line-line of protein myomesin that hold adjacent thick filaments together.
What are the 4 special characteristics of muscle tissue?
Excitability – ability to receive and respond to stimuli.
Contractility– ability to shorten when stimulated.
Extensibility – ability to be stretched. Elasticity – ability to recoil to resting length.
What and where is sarcoplasmic reticulum?
Network of smooth ER surrounding each myofibril.
Pairs of terminal cisternae at the end of the sarcomere are perpendicular to form cross channels.
Regulates intracellular calcium levels
What and where are T tubules?
Continuous with sarcolemma. Penetrate the cells interior at the A band I band junction.
Pairs with terminal cisternae to form triads in circles eat sarcomere.
In a contraction, what shortens?
H band shortens
I band shortenes
sarcomere shortens
length between Z disks shortens
A BAND does not change
What are the two requirements for a skeletal muscle contraction?
Activation: neural stimulation at the neural muscular junction (release of ACH)
Excitation – contraction coupling:
Generation and propagation of action potential along sarcolemma. Final trigger is brief rise in intracellular calcium levels.
Briefly Explain where and what is happening at the neuromuscular junction.
Each axon of motor neurons travel from CNS via nerves to skeletal muscle.
Axons form several branches, each ending forms neuromuscular junction with single muscle fiber Midway along muscle fiber.
Fiber and terminal separated by synaptic cleft. Synaptic vesicles of axon terminal contain ACH. Junctional folds of sarcolemma contain ACH receptors.
Nerve impulse arrives in axon terminal, ACH is releasing vines with receptors. How much accordantly to generation of action potential.
What terminates acetylcholine, contraction?
Enzyme acetylcholinesterase
Stop letting sodium in and potassium out, ends stimulation
What is myasthenia gravis?
Drooping eyelids, difficulty swallowing, less of weakness,.
Involves shortage of ACH receptors maybe auto immune disease.
What are the four events in the generation of an action potential?
1-local depolarization (end plate potential)
2-generation and propagation of action potential (wave of depolarization).
3-Repolarization (wave of rep)
4-Refractory period.
Explain local depolarization.
ACH binding opens chemically gated ion channels.
Simultaneous diffusion of sodium inward and potassium out.
More sodium diffuses so the interior of the sarcolemm becomes less negative.
*Local depolarization = endplate potential.
Explain generation and propagation of an action potential.
End plate potential spreads to adjacent membrane areas.
Voltage gated sodium channels open. Sodium influx decreases the membrane voltage toward the critical threshold.
If the threshold is reached, an action potential is generated.
Explain the repolarization.
Sodium channels close and voltage gated potassium channels open. Potassium efflux rapidly restores the resting polarity.
Fiber cannot be stimulated and is in a refractory period until repolarization is complete.
Explain refractory period.
Muscle fiber cannot be stimulated again, until Repolarization is complete.
Ionic conditions of the resting state are restored by the sodium potassium pump.
What is hyperpolarization?
Sodium potassium pump resetting resting state.
What is excitation contraction coupling?
Sequence of events by which transmission of an action potential along the sarcolemma leads to sliding of the myofilaments.
What is the latent period?
Time when excitation contraction coupling events occur.
Time between action potential initiation and the beginning of a contraction.
What happens in the events of excitation contraction coupling?
Action potential is propagated along the sarcomere to the T tubules.
Voltage sensitive proteis stimulate calcium release from sarcoplasmic reticulum.
What is the role of calcium concentration in a contraction?
High calcium – calcium binds to troponin changing its shape moving tropomyosin away from active sites. Crossbridge cycle occurs.
When nerve ceases, calcium is pumped back into the SR and contraction ends.
Low calcium-tropomyosin blocks active sites on Actin.
Myosin heads cannot attach to Actin. Muscle fiber relaxes.
What is rigor mortis?
Stiffness of death.
Mitochondria not making ATP.
Cross bridges do not detach and calci not pumped back into cisternae. Muscles begin to stiffen within 3 to 4 hours and peek at 12.
What are the two types of contractions?
Isometric contraction – no shortening. Muscle tension increases but does not exceed the load.
Isotonic contraction – muscle shortens because muscle tension exceeds the load.
What is a motor unit?
A motor neuron and all muscle fibers that it supplies.
What two types of motor units are there and what do they control?
Small motor unit – control fine movements (eye, fingers).
Large motor units – large weight-bearing muscles (thighs, hips).
Why do motor units contract asynchronously?
To prevent fatigue.
They are spread throughout the muscle so that a single motor unit causes weak contraction of entire muscle.
What is a muscle twitch?
Response of a muscle to a single brief threshold stimulus.
(Brief release of ACH).
What are the three phases of a twitch?
Latent – Excitation contraction coupling
Period of contraction – Crossbridge formation, tension increases
Period of relaxation – calcium reentry to the SR, tension declines to zero.
What are two ways muscle response is graded?
1 – changing the frequency of a simulation.
2 – changing the strength of the stimulus.
Define simple twitch, unfused tetanus, and fused Tetany.
ST-Single stimuluss making single contractile response. ^\_____
UT-increased frequency of stimulus (no relax completion). Calcium release stimulates further contraction Temporal (wave) summation. _^^^^^_
FT-quickly given stimuli _———_
Define threshold stimulus and recruitment.
TS-stimulus strength at which the first observable muscle contraction occurs.
R-Controls contraction force. Brings more and more muscle fibers into action.
Explain size principle.
Motor units with larger and larger fibers are recruited as stimulus intensity increases.
What is muscle tone?
Constant slightly contracted state of all muscles.
When stored in ATP is depleted how is it regenerated during contraction?
And direct phosphorylase and of ATP by creatine phosphate.
Anaerobic pathway (glycolysis).
Aerobic respiration.
How does anaerobic pathway begin in muscle contraction, and what happens?
70% of maximum contractile activity makes bulging muscles compress blood vessels. 02 delivery is impaired pyruvic acid is converted to lactic acid.
Lactic acid diffuses into bloodstream, used as fuel by the liver kidneys and heart. Converted back into pyruvic acid by the liver.
*Partially responsible for muscle soreness.
What is the use of aerobic pathway, and what fuels that?
Produces 95% of ATP during rest and light moderate exercise.
Field by stored glycogen, blood-borne glucose, Pyruvic acid from glycolysis and free fatty acids.
What are some explanations for muscle fatigue?
Physiological inability to contact.
Ionic inbalances (k, p, ca) interfere with EC coupling. Prolonged exercise damages SR interfering with CA regulation and release.
Total lack of ATP causes contractures (continuous contraction)
Why is oxygen needed after exercise?
Replenish oxygen reserves, glycogen stores, ATP And CP reserves.
Conversion of lactic acid to Pyruvic acid, glucose, and glycogen.
The force of muscle contraction is affected by what 4 reasons?
Number of muscle fiber simulated (recruitment)(intensity).
Relative size of the fibers. Hypertrophy of cells increases strength. (Bigger)
Frequency of stimulation (faster).
Length – tension relationship
Velocity induration of a contraction is influenced by what three things?
Muscle fiber type, load, recruitment
What two characteristics classify muscle fiber types?
Speed of contraction – slow or fast according to:speed at which myosin ATPases split ATP. Or pattern of electrical activity of the motor neuron.
Metabolic pathways for ATP synthesis-oxidative fibers (aerobic pathway). Glycolic fibers (anaerobic glycolysis).
What are the three muscle fiber types, and what are they used for?
Slow oxidative fibers – fatigue resistance lots of mitochondria, marathon running.
This oxidative fibers – moderate fatigue resistant, fewer mitochondria, sprinting.
Fast glycolic fibers – fatigues quickly, few mitochondria, weightlifting.
What is hyper trophy?
Increase in the size of cells in a tissue.
Aerobic exercise leads to?
Increased: Muscle capillaries, mitochondria, myoglobin synthesis.
Greater endurance, strength and resistance to fatigue. May convert fast glycolytic fibers into fast oxidative fibers.
What are the effects of resistance exercise?
Muscle hypertrophy. Increased mitochondria, myofilaments, glycogen stores, and connective tissue.
What is peristalsis of smooth muscle?
Alternating contractions and relaxation of smooth muscle that mix and squeeze substances through the lumen of hollow organs.
Longitudinal layer contracts Organ dilates and shortens.
Circular layer contracts Organ constricts and elongates.
What is the microscopic structure of smooth muscle?
Spindle-shaped fibers thin and short compared to skeletal.
Endomysium connective tissue only. SR is less developed.
Pouchlike infoldings of sarcolemma sequester calcium.
No sarcomeres, myofibrils, or t tubules.
Explain innervation of smooth muscle.
Autonomic nerve fibers innervate smooth muscle at defuse junction.
Varicosities of nerve fibers store and release neurotransmitters.
What is caveolae?
Pouch like in foldings of sarcolemma in smooth muscle.
How are Myofilaments in smooth muscle?
Thick to thin filaments is much higher 1:13. Thick filaments have heads along their entire length. No troponin complex instead protein Calmodulin binds calcium.
Myofilaments are spirally arranged causing muscle to contract as a corkscrew.
What are dense bodies?
proteins that anchor noncontractile intermediate filaments to sarcolemma at regular intervals.
What is the role of calcium ions in smooth muscle?
Calcium binds to and activates Calmodulin enzyme.
Activated Calmodulin activates myosin Kinase.
Activated kinase phosphorylates and activates myosin.
Cross bridges interact with actin.
What does relaxation require for smooth muscle contraction?
Calcium detachment from calmodulin.
Active transport of calcium into SR and ECF.
Dephosphorylation of myosin to reduce myosin ATPase activity.
What is hyperplasia?
Smooth muscle cells can divide and increase their numbers.
What are the two types of smooth muscle?
Single unit muscle (on or off)
and
multiunit muscle (variations)
Explain single unit smooth muscle.
Around hollow visceral organs.
Sheets contract rhythmically as a unit (gap junction).
Spontaneous action potentials. Arranged in opposing sheets and exhibit stress relaxation response.
Explain multi unit smooth muscle.
Located in large airways, arteries arrector Pilli and Iris of eye.
Rare for gap junction.
Arranged in motor units.
Graded contractions occur in response to neural stimuli.
All muscle tissues develop from embryonic _______ cells called _________.
Mesoderm
Myoblasts
Multi nucleated skeletal muscle cells form by _________.
Fusion
Growth factor Agrim stimulates clustering ____________ of neuromuscular junction.
ACH receptors
Cardiac and smooth muscle myoblast develop __________.
Gap junctions
Muscle development occurs ______ to _______ and ________ to _________.
Head to toe
Proximal to distal
What is Sarcopenia?
Loss of muscle mass.
Begins by age 30.
What is claudication?
Periodic interruption in blood flow
What is Duchenne muscular dystrophy?
Inherited, sex linked, carried by females in express in males as lack of dystrophin.
Muscles atrophy while fat and scar tissue buildup.
What is a hernia?
Protrusion of an organ through the body cavity wall.
What is tetanus?
Sustained contraction of a muscle caused by bacterium Clostridium tetani.
