What are the 4 basic characteristics of muscle tissue?
1.Excitability - respond to stimuli
2.Contractility - shorten and exert a pull
3.Extensibility - can be stretched & still contract
4.Elasticity - return to its original length
What are the 5 functions of the skeletal muscle?
1.Produce movement - bones
2.Maintain posture/body position
3.Support soft tissues
4.Guard entrances & exits
5.Maintain body temperature
How is skeletal muscle attached to bone?
-attached by extensions of fascia.
-Collagen fibers of all 3 layers of muscle fascia come together to form the tendon.
-tendons are continuous with periosteum.
What is Epimysium and what does it do?
-a type of fascia that envelopes the entire muscle.
-separates muscle from surrounding tissue & organs.
-made of collagen fibers.
What is Perimysium and what does it do?
-a type of fascia that separates muscle fibers into bundles (fascicles).
-it contains blood vessels and nerves that supply the fascicles.
- it is made of collagen and elastic fibers
What is Endomysium and what does it do?
-a type of fascia that envelopes cell membrane of each fiber.
-attaches adjacent fibers together.
-stem cells are scattered among the fibers to help repair damaged muscle tissue.
What are satellite cells?
-formed from myoblasts
-aid in repair of damaged muscle tissue
-found between muscle fibers
What is the approximate diameter and length of a muscle fiber?
Diameter: 10-100 microns
Length: 10-16 inches (in a thigh muscle)
What are the components of a muscle fiber?
Transverse tubules:openings scattered across the surface of the sarcolemma.
-filled with extracellular fluid.
-plays a major role in coordination of muscle contraction.
How does an electrical impulse of a muscle contraction reach the inside of a muscle fiber?
The electrical impulse travels along the T-tubules (which extend deep into the sarcoplasm).
What are the myofibrils attached to?
Myofibrils are attached to the sarcolemma at each end of the cell.
What provides the myofibrils the ATP needed for muscular contraction?
The breakdown of glucose and the activity of mitochondria which are scattered among the myofibrils.
What is the sarcoplasmic reticulum (SR)?
A specialized form of smooth endoplasmic reticulum which is bonded to the T-tubule in the muscle cell.
What does a terminal cisternae have to do to begin a muscle contraction?
Release the calcium ions it is storing.
What are sarcomeres?
-The smallest functional unit of the muscle fiber.
-consists of repeating units of thin and thick myofilaments.
What are the interconnecting proteins that make up the boundaries of each sarcomere and cross the center of each I band?
What protein structure connects the central portions of each thick filament to its neighbor?
What are the thin filaments made of?
A twisted strand of actin molecules with an active site capable of interacting with myosin.
In a resting muscle, what are the active sites in the thin filaments covered by?
strands of the protein tropomyosin.
What holds the tropomyosin in position on the active sites of the thin filaments?
molecules of troponin
How are the Myosin molecules oriented?
They are oriented away from the center of the sacomere, with the heads projecting outward.
What has to change position for a myosin head to attach to the active site on a strand of actin?
The troponin has to change position
What is the key that unlocks the active sites and starts a muscle contraction?
Calcium (ions bind to the troponin causing it to change shape and swing the tropomyosin away from the active sites)
What is the source of the calcium that triggers a muscle contraction?
terminal cisternae of the sarcoplasmic reticulum
What is the sliding filament theory?
when sarcomeres contract the thin filaments slide toward the center along side the thick filaments.
what are cross-bridges?
The myosin heads of the thick filaments when they are connected to thin filaments.
Where does communication between the nervous system and skeletal muscle fiber occur?
NMJ (neuromuscular junction)- A specialized intercellular connection.
What is the synaptic cleft?
a narrow space that separates the synaptic terminal from the sarcolemma.
What enzyme breaks down ACh?
Acetylcholinesterase (AChE or cholinesterase) contained in the synaptic cleft and the motor end plate.
What triggers the massive release of Calcium ions by the terminal cisternae before a muscle contraction?
the passage of an action potential along the t tubules
When do the cross-bridges detach from the actin during a contraction cycle?
When the myosin head binds to another molecule of ATP
What has to happen before the myosin can repeat the contraction cycle?
It must split the ATP and capture the released energy.
When is a contraction cycle broken?
When calcium ion concentrations return to normal resting levels by active transport into the sarcoplasmic reticulum.
What is tension?
When muscle cells contract, pulling on collagen fibers, it produces an active force called tension.
What direction does tension generaly pull?
Tension applied to an object tends to pull the object toward the source of the tension.
What determines the amount of tension produced by an individual muscle fiber?
The number of cross-bridges it contains
What is summation?
when a second stimulus arrives before the relaxation phase has ended (in a twitch)
What is complete tetanus?
when the rate of stimulation in a muscle is increased until the relaxation phase is eliminated all together.
What is recruitment?
The activation of more and more motor units resulting in smooth steady increase in muscle tension.
What is an isotonic muscle contraction?
Tension rises and the skeletal muscle's length changes. Tension in the muscle remains at a constant level until relaxation occurs.
What is isometric muscle contraction?
Tension never exceeds the resistance and the muscle as a whole doesn't change length.
What 3 things will help return a muscle to its original length after a contraction?
It is a combination of elastic forces, movements of opposing muscles and gravity.
When a muscle is at rest, what does ATP transfer energy into for storage?
creatine phosphate molecules and glycogen.
During muscle contraction what happens to the energy being stored in creatine phosphate?
The energy stored in creatine phosphate is transferred back to ATP.
How does the body feel fatigue from repeated muscle contractions?
From the lactic acid diffusing from the cell into the blood, which lowers the pH of the blood.
What is the Krebs cycle?
Organic substrates that are broken down by a series of chemical reactions during aerobic metabolism.
A common carbohydrate substrate that is broken down in Krebs cycle, producing 17 ATP molecules.
What molecule is the limiting factor for ATP production by the mitochondria?
Oxygen (bottom of pg 209)
What can continue to provide ATP when the availability of oxygen limits the rate of mitochondrial ATP production?
What happens when the muscle fiber begins to run short of ATP and CP during muscle contraction?
Enzymes break the glycogen molecules apart to release glucose that can be used to generate more ATP.
About how much ATP does mitochondrial activity provide during periods of peak muscle activity?
During periods of peak muscle activity what is the primary source of ATP?
The anaerobic process of glycolysis.
What is lactic acid?
An organic acid that dissociates into a hydrogen ion and lactate ion in body fluids, lowering the pH levels.
How many ATP molecules are generated from the 2 pyruvic acids under anaerobic (glycolysis) conditions versus aerobic (mitochondrial) conditions?
2 ATP molecules under anaerobic conditions vs 34 molecules under aerobic conditions.
What type of muscle fatigue is the result of reserves of glycogen, lipids, and amino acids being depleted? ATP is used at or below the maximum rate of mitochondrial ATP generation. (the muscle fiber is functioning aerobically)
fatigue after long endurance activities.
What type of fatigue happens when the ATP is provided by glycolysis and lactic acid levels lower pH levels?
when a muscle produces a sudden, intense burst of activity.
During the recovery period of a muscle what is the muscle's metabolic activity focused on?
The removal of lactic acid and the replacement of intracellular energy reserves.
What is oxygen debt?
The additional oxygen required during the recovery period to restore the normal preexertion levels.
describe slow fibers
red muscles, contract slowly, contain myoglobin (serving as a source of O2), has more extensive blood vessels, slower to fatigue
What is Anaerobic conditioning?
the length of time muscle contractions can be supported by glycolysis and existing energy reserves of ATP and CP.
What is Aerobic endurance?
The length of time a muscle can continue to contract while being supported by mitochondrail activities.
For each pyruvic acid molecule broken down in the TCA cycle (or Krebs cycle, or citric acid cycle), the cell gains how many ATP molecules?
__________ is the length of time muscle contractions can be supported by glycolysis and existing energy reserves of ATP and creatine phosphate (CP).
What concept is defined as the maximum amount of tension produced by a particular muscle or muscle group?
Aerobic endurance is determined by the availability of substrates for aerobic metabolism from the breakdown of which of the following substances?
amino acids, lipids, carbohydrates.
Cardiac muscle tissue contracts without neural stimulation, a property called____________.
What is the source of most of the calcium ions that enter smooth muscle cells to trigger contractions?
the extracellular fluid
In the digestive and urinary systems, rings of smooth muscles called ________ regulate movement along internal passageways
About how much longer does a cardiac muscle contraction last compared to a skeletal muscle?
About 10 times longer.
What does the cardiac sarcoplasm contain to store oxygen?
large numbers of mitochondria and abundant reserves of myoglobin.
What are the intercalated discs of the cardiac muscles?
The cellular connections that contain gap junctions which allow for the rapid movement of ions and small molecules and the rapid passage of action potentials from cell to cell, resulting in simultaneous contraction.
What is the most obvious structural difference between cardiac and skeletal muscle fibers?
Cardiac muscle fibers are branched and each cardiac cell contacts several others at intercalated discs.
What is muscle tension dependent on?
the frequency of stimulation and the number of muscle fibers being stimulated.
What happens in the latent phase of the twitch sequence?
The impulse penetrates the muscle fiber and Ca ions are released (about 2msec)
What happens during the contraction phase in the twitch sequence?
tension rises to a peak. The cross bridges are interacting with the active sites on the actin filaments. (max tension is reached ~15msec after stimulation)
What happens during the relaxation phase in the twitch sequence?
muscle tension falls to resting levels as calcium levels drop, active sites are being covered and cross bridges are declining. (lasts ~25msec)
How does the internal organization of a smooth muscle cell differ from skeletal and cardiac muscle cells?
smooth muscle cells have NO myofibrils, sarcomeres, or striations, myofiliments are scattered throughout sarcoplasm.
What is the muscle insertion point?
The point that moves (usually the distal end), contraction of muscle moves insertion toward origin
What is an Antagonist muscle?
it's the muscle that provides resistance to the Prime mover and allows for controlled movement
What is a synergist muscle?
It's a muscle that assists the Prime Mover by providing additional pull or stabilizes the point of origin.