BSCI 2101 Exam 2 Review (Muscles, Elderly Hip Fractures, Muscle Contraction, ACL Tears Sex Differences)

What are glycosomes?

Granules of stored glycogen that provide glucose during muscle cell cavity for ATP production

Describe how cardiac muscle contractions are regulated

Usually contracts at a fairly steady rate set by the heart's pacemaker But, - neural controls allow the heart to speed up for brief periods

What is the physiological definition of contraction? When does contraction end?

What is contraction: - the activation of myosin's cross bridges, which are the force-generating sites When does shortening only occur: - if the cross bridges generate enough tension on the thin filaments to exceed the forces that oppose shortening When does contraction end: - ends when cross bridges become inactive, the tension declines, and the muscle fiber relaxes

What is the sarcoplasmic reticulum (SR)? What does it do?

What it is: - an elaborate smooth endoplasmic reticulum in muscle fibers What it does: - regulates intracellular levels of Ca++ - stores Ca2++ and releases it on demand when muscle fiber is stimulated to contract

What is an action potential?

large change in membrane potential that spreads rapidly over long distances within a cell AKA nerve impulse

What ultimately controls muscle contraction?

nerve-initiated electrical impulses that travel along the sarcolemma

What are the 3 types of muscle tissue?

skeletal, cardiac, smooth

What is anaerobic threshold?

the point at which muscle metabolism converts to anaerobic glycolysis

Why does skeletal muscle have a rich blood supply?

- Contracting muscle fibers use huge amounts of energy and require almost continuous delivery of oxygen and nutrients via the arteries - Muscle cells also give off large amounts of metabolic wastes that must be removed through veins if the contraction is to remain efficient

Describe the sequence of events at the NMJ leading to muscle contraction (including the aftermath)

- a motor neuron fires an AP down its axon - AP arrives at the motor neuron's axon terminal - voltage-gated Ca++ channels open and Ca++ enters the axon terminal, moving down its electrochemical gradients - Ca++ entry causes ACh to be released into the synaptic cleft by exocytosis - ACh diffuses across the synaptic cleft and binds to ACh receptors on the junctional folds of the sarcolemma - ACh binding opens chemically-gated ion channels that allow the simultaneous passage of Na+ into and K+ out of muscle fiber - more Na+ ions enter than K+ exit, producing a local depolarization (EPP) Aftermath: - ACh effects are terminated when it diffuses away from the junction and is degraded by acetylcholinesterase in the synaptic cleft

What do terminal cisterns form? What do they contain? How do they always occur?

- larger, perpendicular cross channels at the A band-I band junctions - contains Ca++ - they always occur in pairs

What is an isometric contraction?

- muscle is attached to a weight that exceeds the muscle's peak tension-developing capabilities - when stimulated, the tension increase to the muscle's peak tension-developing capabilities, but the muscle does not shorten If muscle tension develops but the move is not moded - this is an isometric contraction

What 2 sets of intracellular tubules do skeletal fibers contain? What do they do?

- sarcoplasmic reticulum and T tubules - help regulate muscle contraction

How many myofibrils are in each muscle fiber?

100s-1000s that run parallel to its length - so densely packed in the fiber that mitochondria and other organelles appear to be squeezed between them

In general, ___ nerve, ____ artery, and ____ or more veins serve each muscle -- (how many of each)

1; 1; 1

How is energy used during short-duration, high-intensity exercise at 6 seconds, 10 seconds, and 30-40 seconds to the end of the exercise?

6 seconds: - ATP stored in muscles is used first 10 seconds: - ATP is formed from creatine phosphate and ADP (direct phosphorylation) 30-40 seconds to the end of exercise: - glycogen stored in muscles is broken down to glucose, which is oxidized to generate ATP using the anaerobic pathway

What are striations? In an intact muscle fiber, how are the different types of bands aligned?

A repeating series of dark A bands and light I bands - along the length of each myofibril In an intact muscle fiber: - dark A and light I bands are nearly perfectly aligned

What is multi-unit muscle? Where is it?

A type of smooth muscle Located: - smooth muscles in large airways to the lungs -in large arteries - the arrectior pili musccles attached to hair follicles - the internal eye muscles that adjust pupil size and allow the eye to focus

What NT do motor neurons release for skeletal muscle contraction?

ACh - acetylcholine

In all skeletal muscle fibers, what generates the initial change in membrane potential? What does this trigger?

ACh receptor -- chemically-gated ion channel Triggers voltage-gated ion channels to create an AP

What is an isotonic contraction?

AKA concentric contraction: - on stimulation, muscle develops enough tension (force) to lift the load (weight) - once the resistance is overcome, the muscle shortens, and the tension remains constant for the rest of the contraction If the muscle tension developed overcomes the load and muscle shortening occurs - this was an isotonic contraction

What is a neruomuscular junction (NMJ)? What do they consist of?

AKA end plate region where: - the motor neuron contacts the skeletal muscle consists of: - multiple axon terminals (which contain synaptic vesicles with ACh) - the underlying junctional folds of the sarcolemma (which contain 1000s of ACh receptors)

What is unitary muscle? Where is is located?

AKA visceral muscle Atype of smooth muscle: - located in the walls of all hollow organs except the heart - most common type

Where do nerves, arteries, and veins interact with muscle?

All enter or exit near the central part of the muscle and branch profusely through its connective tissue sheaths

What do T tubules do with respect to the nerve-initiated electrical impulses of muscle contraction? What do they ensure about muscle contraction?

Because they are continuations of the sarcolemma: - they conduct impulses to the deepest regions of the muscle cell and every sarcomere Thus: - these impulses trigger the release of Ca++ from the adjacent terminal cisterns T tubules are like a rapid communication system that ensures that every myofibril in the muscle fiber contracts at virtually the same time

Describe the body location and cell shape/appearance of skeletal muscle

Body location: - attached to bones - attached to skin for some facial muscles Cell shape/appearance: - single, very long, cylindrical, multinucleate cells - elongated - has obvious striations

Describe the body location and cell shape/appearance of cardiac muscle

Body location: - bulk of heart's walls Cell shape/appearance: - branching chains of cells - uni- or binucleate - has striations - not elongated

Describe the body location and cell shape/appearance of smooth muscle

Body location: - unitary muscle in walls of hollow visceral organs (like stomach, urinary bladder, respiratory passages) - multi-unit muscle in intrinsic eye muscles, airways, large arteries Cell shape/appearance: - single, spindle-shaped, uninucleate - elongated - no striations

Which muscle(s) can contract without the need for nerve stimulation?

Cells of cardiac and smooth muscle tissues

What differs about the sarcoplasm from the cytoplasm of other cells?

Contains unusually large amounts of glycosomes and myoglobin

What factors increase the force of skeletal muscle contraction?

Contractile force increases (more cross bridges attached) with these factors: 1. High frequency of stimulation: - when a muscle is stimulated more frequently, contractions are summed due to temporal summation and tetanus 2. Large # of muscle fibers recruited - the more motor units recruited, the greater the force 3. Large muscle fibers - the bulkier the muscle and the greater the cross-sectional area, the more tension it can develop - larger fibers produce greater tension 4. Muscle and sarcomere stretched to slightly over 100% of resting length - length-tension relationship

What are the characteristics of smooth muscle contractions? What is the role of smooth muscle?

Contractions: - slow and sustained Role: - force fluids and other substances through internal body channels - forms valves to regulate the passage of substances through internal body openings - dilates and constricts the pupils of your eyes - forms the arrector pili muscles attached to hair follicles

Describe the sequence of events of cross bridge cycling when a muscle contraction is being initiated and sustained

Cross bridge formation: - energized myosin head attaches to actin thin filament active site, forming a cross bridge Working (power) stroke: - ADP and Pi are released from myosin head - then, myosin head pivots, returning to its low-energy state - results in pulling of thin filament toward M line Cross bridge detachment: - ATP attaches to myosin head, causing cross bridge to detach Cocking of myosin head: - energy from ATP hydrolysis "cocks" myosin head into prestroke high-energy state - this energy is used for the power stroke in the next cross bridge cycle This process is repeated - cycle continues as long as ATP is available and Ca++ is bound to troponin - if ATP is not available, the cycle stops between the power stroke and cross bridge detachment steps

Describe the muscle fiber and its connective tissue wrappings - what is it - what is beneath its sarcolemma - how does it appear - how is it formed

Description: - a long cylindrical, elongated, multinucleate cell - multiple oval nuclei just beneath its sarcolemma - has a striated/banded appearance - formed by fusing of 100s of embryonic cells Connective tissue wrappings: - surrounded by endomysium

Describe the fascicle and its connective tissue wrappings - what is it - what is it made of

Description: - a portion of the muscle - discrete bundle of muscle cells, segregated from the rest of the muscle by a connective tissue sheath Connective tissue wrappings: - surrounded by perimysium

Describe the myofibril and its connective tissue wrappings - what is it - what is it made of - how do they appear - how are their bands aligned

Description: - complex organelle composed of bundles of myofilaments - rodlike contractile elements that occupy most of the muscle cell volume - composed of sarcomeres arranged end to end - they appear banded - bands of adjacent myofibrils are aligned Connective tissue wrappings: - N/A

Describe the muscle and its connective tissue wrappings - what is it - what is it made of

Description: - organ - consists of 100s to 1000s of muscle cells along with: connective tissue wrappings, blood vessels, and nerve fibers Connective tissue wrappings: - covered externally by epimysium

What is myasthenia gravis? What is it characterized by? What does it involve? What does this suggest?

Disease Characterized by: - drooping upper eyelids - difficulty swallowing and talking - generalized muscle weakness Involves: - shortage of ACh receptors bc a person's ACh receptors are attacked by their own antibodies Suggests: - this is an autoimmune disease

What does the sliding filament model of contraction state? What never changes length during contraction?

During contraction: - the thin filaments slide past the thick ones - so that the actin and myosin filaments overlap to a greater degree Neither thick nor thin filaments change length during contraction

Describe the events of muscle fiber excitation leading to a muscle contraction (including the aftermath)

EPP triggers an AP that travels/sweeps across the entire surface of the sarcolemma EPP is generated at NMJ, which causes a wave of depolarization that spreads to the adjacent sarcolemma: - depolarization of the sarcolemma opens voltage-gated Na+ channels, so Na+ enters the cell following its electrochemical gradient - at a certain membrane potential, an AP is generated - this causes AP to spread to adjacent areas of the sarcolemma and opens voltage-gated Na+ channels there, propagating the AP in all directions Aftermath: - repolarization wave (restores sarcolemma to initial polarized state -- negative in, positive out) occurs - caused by the closing of voltage-gated Na+ channels close and opening voltage-gated K+ channels - [K+] is much higher inside cell than in the ECF, so K+ diffuses out of the muscle fiber - repolarization restores electrical conditions of resting state & ATP-dependent Na+/K+ pump restores ionic conditions of resting state

What is the endomysium? What does it consist of?

Endomysium = "within the muscle": - a wispy sheath of connective tissue that surrounds each individual muscle fiber - located between individual muscle fibers - consists of fine areolar connective tissue

What is the epimysium? What is sometimes blend with?

Epimysium = "outside the muscle" An "overcoat" of dense irregular connective tissue that surrounds the whole muscle Sometimes it blends with: - the deep fascia that lies between neighboring muscles - or the superficial fascia deep to the skin

What are the overall sequence of events leading to muscle contraction?

Events at the NMJ Muscle fiber excitation Excitation-contraction coupling - myosin heads bind actin Cross bridge cycle: - contraction occurs via cross bridge cycling - repeating cycle of steps that cause myofilaments to slide relative to each toher

What controls the activity of every skeletal muscle fiber?

Every skeletal muscle fiber is supplied with a nerve ending that controls its activity

What is a fascicle? What is the perimysium?

Fascicles = "bundles": - groupings of muscle fibers within each skeletal muscle that resembles bundles of sticks Perimysium = "around the muscle" - layer of dense, irregular connective tissue that surrounds each fascicle

For fast glycolytic fibers, what are the following structural characteristics: fiber diameter, mitochondria, capillaries, color?

Fiber diameter: - intermediate Mitochondria: - few Capillaries: - few Color: - white (pale)

For fast oxidative fibers, what are the following structural characteristics: fiber diameter, mitochondria, capillaries, color?

Fiber diameter: - largest Mitochondria: - many Capillaries: - many Color: - red to pink

For slow oxidative fibers, what are the following structural characteristics: fiber diameter, mitochondria, capillaries, color?

Fiber diameter: - small Mitochondria: - many Capillaries: - many Color: - red

How is energy used during prolonged-duration exercise during the hours?

Hours: - ATP is generated by breakdown of several nutrient energy fuels by aerobic pathway

What occurs at the microscopic level as a muscle cell shortens?

I bands shorten Distance between successive Z discs shortens: - as the thin filaments slide centrally, the Z discs are pulled toward the M line The H zones disappear Neighboring A bands move closer together - their length does not change

What does tropomyosin do in a relaxed muscle fiber?

In a relaxed muscle fiber: - TM blocks myosin-binding sites on actin - so that myosin heads on thick filaments cannot bind to the thin filaments

Describe the paths and characteristics of capillaries in muscle. What happens to them when the muscle stretches and contracts?

Long, winding path through muscle Have numerous cross-links, features that accommodate changes in muscle length - Straighten when the muscle stretches - Contort when the muscle contracts

From the macro to micro, break down the structural/organization levels of skeletal muscle

Macro to micro: - muscle (organ) - fascicle (portion of muscle) - muscle fiber (cell) - myofibril (complex organelle composed of bundles of myofilaments) - sarcomere (a segment of a myofibril) - myofilament/filament (extended macromolecular structure)

What is the excitation-coupling of muscle contraction? Describe this sequence of events (including the aftermath)

Sequence of events by which AP transmission along sarcolemma leads to sliding fo myofilaments: - AP propagates along sarcolemma and travels down T tubules - AP transmission along T tubules of triads causes voltage-sensitive tubule proteins to change shape, which opens Ca++ release channels in the terminal cisterns of SR - Ca++ flows into the cytosol and binds to troponin subunit, causing conformational changes in troponin that lead to shift of tropomyosin to uncover actin's myosin-binding sites (on thin filaments) - Myosin binding to actin forms cross bridges and contraction (cross bridge cycling) begins and E-C coupling is over Aftermath: - when muscle AP ceases, the voltage-sensitive tubule proteins return to original shape - this closes the Ca++ release channels on the terminal cisterns of the SR - Ca++ levels in the sarcoplasm fall as Ca++ is pumped back into the SR by active transport

What is cross bridge cycling? What happens when cross bridge cycling is initiated?

Series of events during which myosin heads pull thin filaments toward the center of the sarcomere Causes sarcomere shortening and muscle contraction

What are triads?

Sites of close contract of terminal cistern pair and T tubule - along its length, each T tubule runs between the paired terminal cisterns of the SR, forming triads - successive groupings of the three membranous structures (terminal cistern, T tubule, and terminal cistern)

For fast oxidative fibers, what are the following metabolic characteristics: speed of contraction, myosin ATPase activity, primary pathway for ATP synthesis, myoglobin content, glycogen stores, recruitment order, rate of fatigue?

Speed of contraction: - fast Myosin ATPase activity: - fast Primary pathway for ATP synthesis: - aerobic (some anaerobic glycolysis) Myoglobin content: - high Glycogen stores: - intermediate Recruitment order; - 2nd Rate of fatigue: - intermediate (moderately fatigue-resistant)

For fast glycolytic fibers, what are the following metabolic characteristics: speed of contraction, myosin ATPase activity, primary pathway for ATP synthesis, myoglobin content, glycogen stores, recruitment order, rate of fatigue?

Speed of contraction: - fast Myosin ATPase activity: - fast Primary pathway for ATP synthesis: - anaerobic glycolysis Myoglobin content: - low Glycogen stores: - high Recruitment order; - 3rd Rate of fatigue: - fast (fatigable)

For slow oxidative fibers, what are the following metabolic characteristics: speed of contraction, myosin ATPase activity, primary pathway for ATP synthesis, myoglobin content, glycogen stores, recruitment order, rate of fatigue?

Speed of contraction: - slow Myosin ATPase activity: - slow Primary pathway for ATP synthesis: - aerobic Myoglobin content: - high Glycogen stores: - low Recruitment order; - 1st Rate of fatigue: - slow (fatigue-resistant)

In an intact muscle, there are several different connective tissue sheaths. What do these connective tissue sheaths do together?

Support each cell Reinforce and hold together the muscle - this prevents the bulging muscles from bursting during exceptionally strong contractions

What is a T tubule? Where are they located?

T (transverse) tubule: - an elongated tube formed by a deep protrusion/invagination of the sarcolemma into the cell interior - located at each A band-I band junction - run deep into the cell between the termianl cisterns

As they pass from one myofibril to the next, the ___ _________ also encircle each ___________

T tubules; sarcomere

What is the length-tension relationship? Describe the tension %max at different percents of resting sarcomere length (RSL)

The amount of tension a muscle can generate during an isometric contraction at various lengths 80-120% RSL: - optimal sarcomere operating length - tension % is 100% at 100-120% RSL

What are eccentric contractions?

The muscle generates force as it lengthens -- type of isotonic contraction - Muscle neither shortens nor lengthens bc the load is greater than the tension (force) the muscle can develop

Describe tropomyosin - what is it - what is its function in thin filaments - how are they arranged - what do they do in a relaxed muscle fiber

Tropomyosin (TM): - a rod-shaped regulatory protein in thin filaments

What are the steps of the sliding filament model of contraction?

When the nervous system stimulates muscle fibers, the myosin heads on the thick filaments latch onto myosin-binding sites on actin in the thin filaments forming cross bridges - the sliding begins These cross bridge attachments form and break several times during a contraction - act like tiny ratchets to generate tension and propel the thin filaments toward the center of the sarcomere As this event occurs simultaneously in sarcomeres throughout the cell, the muscle cell shortens

What makes up myofibrils from end to end?

a chain of sarcomeres linked end to end

What is an ACh receptor? What does it create?

a single protein in the plasma membrane that is both a receptor and an ion channel - creates small local depolarization (decrease) in the membrane potential

All of these connective tissue sheaths are ____________ with one another as well as with the tendons that join muscles to bones

continuous

Skeletal muscle can ___________ rapidly, but it ________ easily and must rest after short periods of activity

contract; tires

What is the sarcoplasm?

cytoplasm of a muscle cell

What are slow and fast muscle fibers?

determined on the basis of speed of fiber shortening

What are terminal cisterns?

dilated, end-sacs of SR formed by SR tubules that fused

What do voltage-gated channels respond to?

direct change in the membrane potential

Generally, APs ______ spread from cell to cell. What does this lead to?

don't The signal has to be converted to a chemical signal: - NT that diffuses across the small gap between excitable cells to the start the signal again

When is the sequence of E-C coupling repeated?

each time an AP arrives at the NMJ

What activities are slow oxidative fibers best suited for? Give examples

endurance-type activities ex: - running a marathon - maintaining posture (antigravity muscles)

Neurons and muscles are both ____________ cells

excitable

What is the lumen of the T tubule continuous with? What does this result in?

extracellular space results in the T tubules greatly increasing the muscle fiber's surface area - this allows changes in the membrane potential to rapidly penetrate deep into the muscle fiber

What surrounds each myofibril?

interconnecting tubules of SR - the way the sleeve of a loosely knitted sweater surrounds your arm

What is an end plate potential (EPP)?

local depolarization of sarcolemma caused by ACh binding to ACh receptor

Skeletal muscle fibers are the __________ muscle cells and have obvious stripes called ___________. Is it voluntary or involuntary?

longest; striations voluntary muscle because it is the only type subject to conscious control

What direction do most SR tubules run? Where do they communicate with each other?

longitudinally along the myofibril at the H zone

What interferes with the events at the NMJ involving muscle contraction?

many toxins, drugs, and diseases

The contraction of a skeletal muscle ultimately comes down to activating a few _______ neurons in the spinal cord. They are how the nervous system ______ with skeletal muscles and "tells" them to contract

motor; connects

What are skeletal and smooth muscle cells also known as?

muscle fibers

What 3 specialized structures does a muscle cell contain?

myofibrils sarcoplasmic reticulum T tubules

How many NMJ's does each muscle fiber have?

one --- located midway along its length

Where to thin and thick filaments overlap in a relaxed muscle fiber?

only at the ends of the A band

Each skeletal muscle is a discrete ________, made up of several kinds of tissues. Skeletal muscle ________ predominate, but blood vessels, nerve fibers, and substantial amounts of connective tissue are also present.

organ fibers

What is the sarcolemma?

plasma membrane of a muscle cell

What does Ca++ signal for?

provides the final "go" signal for muscle contraction

What state is the muscle fiber in during repolarization?

refractory period - bc cell cannot be stimulated again until repolarization is complete

What activities are fast glycolytic fibers best suited for? Give an example

short-term intense/powerful movements ex: hitting a baseball

What does Ca++ do for muscle contraction?

the internal messenger that links the AP to contraction

How can skeletal muscle cells be classified?

slow oxidative fibers fast oxidative fibers fast glycolytic fibers

Why does the axon of each motor neuron branch profusely as it enters the muscle?

so that it can innervate multiple muscle fibers

What activities are fast oxidative fibers best suited for?

sprinting walking

What are glycolytic muscle fibers?

the cells that rely more on anaerobic glycolysis and creatine phosphate

What are oxidative muscle fibers?

the cells that rely mostly on the oxygen-using aerobic pathways of ATP generation