BSCI201 Exam 3

Glycemic control

muscles help absorb, store, and use glucose

Efficiency of muscle

40% of muscle energy is used as work, 60% is released as heat

Factors that increase body heat

solar radiation, reflected radiation, and muscle heat production

Factors that decrease body heat

body radiation, conduction, and evaporation of sweat

Convection

heat transfer influenced by air temperature, humidity, and water

Contractility

ability of muscle cells to shorten and generate force

Excitability

ability to respond to a stimulus by changing from a chemical signal to an electrical signal

Extensibility

ability to be stretched or extended

Elasticity

ability to return to original shape after being stretched

Muscle organ

made of muscle tissue plus connective tissue

Vascularized and innervated

muscles have blood vessels and nerves

Hypertrophy

increase in muscle cell size; adult skeletal muscle grows mainly this way

Epimysium

connective tissue layer that wraps the whole muscle organ

Perimysium

connective tissue layer that wraps a fascicle

Fascicle

a bundle of muscle fibers

Myofiber

one muscle cell; a multinucleated muscle cell formed by fusion of many cells

Myofibril

protein complex inside a muscle fiber made of repeating sarcomeres

Satellite cells

muscle stem cells involved in repair and replacing nuclei in muscle cells; contribute to hyperplasia/repair

Myofilaments

thin and thick protein filaments in muscle

Thin filament

in skeletal and cardiac muscle, made of actin, tropomyosin, and troponin

Thick filament

made mainly of myosin

Sarcomere

functional contractile unit of muscle between two Z discs

Z disc

boundary of a sarcomere; anchors thin filaments

M line

Middle of the sarcomere; helps anchor thick filaments

A band

dark band containing the full length of thick filaments

Structural proteins

maintain sarcomere structure

Contractile proteins

perform the shortening activity of the sarcomere

Regulatory proteins

control sarcomere activity and contraction

Myosin

main protein of thick filaments; has a head and tail region

Myosin head

region that binds actin and ATP

Actin-binding site

site where myosin attaches to actin

ATP-binding site

site where ATP binds to power contraction cycle

Actin

protein with myosin-binding sites used for cross-bridge formation

Myosin-binding site

site where myosin heads attach; blocked by tropomyosin when relaxed

Tropomyosin

regulatory protein that covers myosin-binding sites on actin in relaxed muscle

Troponin

regulatory protein that binds calcium, tropomyosin, and actin

Tropomyosin binding sites

sites allowing interaction with actin and troponin

Troponin binding targets

calcium, tropomyosin, and actin

Contraction sequence

Ca²⁺ binds troponin, troponin changes shape, tropomyosin shifts, myosin-binding sites on actin are exposed, and myosin binds actin to form cross-bridges.

Sliding filament theory

The process of muscle contraction where thin filaments slide past thick filaments, shortening the sarcomere.

First step of sliding filament theory

Myosin heads hydrolyze ATP, which cocks or tilts the heads.

Cross bridge formation

Myosin heads bind to actin.

Power stroke

Myosin heads release ADP and Pi, causing the heads to pivot and pull the thin filament.

Detachment step in contraction

A new ATP binds to myosin, causing myosin to release actin.

ATP use in skeletal muscle contraction

ATP is required for myosin activation, cross bridge detachment, and pumping calcium back into the sarcoplasmic reticulum.

ATP role: myosin activation

ATP hydrolysis energizes the myosin head so it can bind to actin.

ATP role: cross bridge detachment

ATP binding causes myosin to detach from actin.

ATP role: calcium reuptake

ATP powers active transport that moves calcium ions back into the sarcoplasmic reticulum for storage.

Stored ATP

The small amount of ATP already present in muscle fibers, used first during exercise.

How long stored ATP lasts

A few seconds, usually less than 5 seconds.

Creatine phosphate (CP)

A high energy molecule used to quickly regenerate ATP during short intense activity.

How long creatine phosphate lasts

A few seconds, usually less than 15 seconds.

Creatine kinase

The enzyme that transfers a phosphate from creatine phosphate to ADP to form ATP.

Creatine phosphate reaction

CP + ADP → ATP + Creatine

Direct phosphorylation

A rapid way to make ATP by transferring a phosphate directly from creatine phosphate to ADP.

Anaerobic fermentation

ATP production without oxygen using glycolysis and lactic acid formation.

Anaerobic pathway products

Lactic acid and ATP.

How long anaerobic fermentation supports activity

About 1 minute.

Aerobic respiration

ATP production with oxygen using glycolysis and the Krebs cycle.

Aerobic respiration duration

Can support activity for hours.

Main benefit of aerobic respiration

Produces the most ATP.

Waste products of aerobic respiration

Water and carbon dioxide.

Lactic acid formation

Occurs when pyruvic acid is converted to lactic acid during anaerobic conditions.

Calcium storage in muscle

Calcium is stored in the sarcoplasmic reticulum

Excitation-contraction coupling

Process that links the muscle action potential to muscle contraction

Resting membrane potential

About -70 mV

Voltage-gated ion channels

Channels that open or close in response to changes in membrane potential

Depolarization

Membrane potential becomes less negative

Repolarization

Membrane potential returns toward resting level after depolarization

Hyperpolarization

Membrane potential becomes more negative than resting potential

Motor unit

One motor neuron and all of the skeletal muscle fibers it innervates

Motor unit size

One motor neuron can innervate many muscle fibers, creating small, medium, or large motor units

Muscle fiber innervation

Each muscle fiber is innervated by only one motor neuron

Small motor units

Used for fine movements; example: fingers and extraocular eye muscles; about 5 muscle fibers per neuron

Large motor units

Used for large weight-bearing muscles and gross movements; examples: thighs and back; about 1000 muscle fibers per neuron

Slow oxidative fibers (SO)

Slow and fatigue-resistant muscle fibers; associated with marathon runners

Fast oxidative-glycolytic fibers (FOG)

Intermediate fibers with moderate fatigue resistance; associated with sprinters

Fast glycolytic fibers (FG)

Fast fibers that fatigue quickly; associated with basketball players and hockey players

Aerobic endurance exercise

Primarily affects slow oxidative fibers and causes increases in muscle capillaries, number of mitochondria, and myoglobin synthesis

Effect of aerobic exercise on glycolytic fibers

May convert fast glycolytic fibers into fast oxidative fibers

Resistance exercise

Typically anaerobic and primarily affects fast glycolytic fibers

Effects of resistance exercise

Causes muscle hypertrophy, increases glycogen stores, and produces fibers that fatigue more easily

Tone

Tension exerted by a contracting muscle

Load

Resistance placed on a muscle by the weight of an object being moved

Shortening contraction

Shortening occurs when tension generated by cross bridges on thin filaments exceeds the load

Isometric contraction

Same length during contraction; example: plank

Isotonic concentric contraction

Muscle shortens during contraction; example: lifting a dumbbell in a bicep curl

Isotonic eccentric contraction

Muscle lengthens during contraction; example: lowering a dumbbell in a bicep curl

Structural difference between smooth and skeletal muscle

Myofilaments in smooth muscle are arranged diagonally to the cell

Smooth muscle thick filaments

Thick filaments have heads along their entire length and heads project outward

Smooth muscle dense bodies

Dense bodies and intermediate filaments anchor thin filaments and help transmit force to connective tissue

Regulation of smooth muscle contraction

No troponin complex; calmodulin on thick filaments binds Ca2+

Tropomyosin in smooth muscle

Present in thin filaments but does not block myosin-binding sites on actin

Smooth muscle caveolae

Small pockets in the sarcolemma that contain extracellular fluid rich in calcium

Smooth muscle SR

Sarcoplasmic reticulum is underdeveloped

Smooth muscle connective tissue

Endomysium only

Contraction of smooth muscle

Slow and sustained

Latch phenomenon

Sustained contraction with low ATP consumption

Single-unit smooth muscle (SU)

Electrically coupled cells connected by gap junctions that function as a syncytium

Pacemaker cells in single-unit smooth muscle

Self-exciting cells that change electrical potential without external stimuli; myogenic