KCC Bio- Muscle Tissues

Excitable

muscle cell membranes can generate electricity

Contraction (muscle shortening)

Actin and myosin protein filaments slide across each other

What is required to initiate contraction?

Ca2+

What is required to power contraction?

ATP

Elasticity

ability to recoil back to original length due to elastin fibers

Extensibility

ability to stretch/extend

Contractility

ability to pull on attachment points, and shorten with force

What do skeletal muscles cause?

Cause movement

What do skeletal muscles resist and why?

Resist gravity to maintain posture

What do skeletal muscles maintain?

Maintain balance

What does skeletal muscles prevent?

Prevent excess movement at joints, keeping them stable and undamaged

Where do skeletal muscles act and why?

Act internally to allow for voluntary control over swallowing, urination, and defecation

What do skeletal muscles protect?

Protect and support internal organs (ex. Abdominal muscles)

Do skeletal muscles generate heat?

Yes, though ATP usage

What are skeletal muscles?

Is an organ, containing muscle fibers, blood vessels, nerve fibers, and connective tissue

How are skeletal muscles structured?

Muscle fibers (cells) are bundled together into fascicles, which are bundled together into whole muscle.

Epimysium

Dense, irregular connective tissue around whole muscle

What does epimysium separate?

Separates muscle from other tissues and organs in the area

What does epimysium maintain and through what?

Maintains structural integrity during powerful contractions

Perimysium

surrounds and separates individual muscle fascicles, in order to allow for finer motor control

Endomysium is made of?

Collagen and reticular fibers

What does endomysium surround? 

Surrounds individual muscle fibers

What does endomysium contain?

ECF/nutrients supplied by the blood to support the muscle fibers.

Tendons are continuous with?

the connective tissue layers (mysia) on the muscle side

Periosteum are continuous with?

The connective tissues on the bone side, giving an extremely strong connection when paired with tendons 

Muscle cells are also?

muscle fiber

Multinucleated

from fusion of many embryonic myoblasts

Sarcolemma

plasma membrane

Sarcoplasm

cytoplasm

Sarcoplasmic reticulum

specialized smooth endoplasmic reticulum

Sarcomere

functional unit of skeletal muscle that stretches from one Z-disc (Z-line) to the next.

How are sarcomere organized?

Highly organized arrangement of the contractile proteins actin (thin filament) and myosin (thick filament) (along with associated troponin and tropomyosin)

What does sarcomere connect to form?

Connect end to end to form long myofibrils

Neuromuscular Junction (NMJ)

Where a motor neuron’s terminal meets the muscle fiber, and the muscle fiber first responds to signaling by the motor neuron

Excitation signals from the neuron

the only way to functionally activate the fiber to contract

Excitation-contraction coupling

Excitation occurs when the motor neuron triggers an action potential in the muscle fiber

What is Excitation-contraction coupling “coupled” to and through what?

the contraction through the release of calcium ions (Ca2+) from the SR which causes tropomyosin to stop blocking the active sites of actin, and allows contraction to occur.

Excitation-contraction coupling begins?

when action potential from a motor neuron makes it to the NMJ.

The motor neuron releases? the neurotransmitter acetylcholine (ACh)

The ACh molecules diffuse and bind to? across the synaptic cleft and bind to ACh receptors located on the motor end-plate of the sarcolemma.

What do Na+ channels in the ACh receptors do?

open and allow an influx of Na+ which depolarizes (flips the electric charge) that part of the membrane

This depolarization triggers?

nearby voltage-gated Na+ channels to open, setting off a chain reaction that spreads an action potential (electricity) down the rest of the entire membrane.

What happens immediately following depolarization?

the cell membrane at the NMJ is repolarized by the rapid outflux of K+ ions

ACh in the synaptic cleft is?

degraded by the enzyme acetylcholinesterase (AChE) to prevent constant re-stimulation of muscle contraction

The initial action potential is still going though?

It travels down T-tubules (transverse tubules), which are invaginations of the sarcolemma that are bordered by sarcoplasmic reticulum on either side (forming a “triad”). These triads wrap around the myofibrils at regular intervals.

Depolarization of the T-tubules triggers?

the opening of Ca2+ channels in the membranes of the adjacent SR, causing Ca2+ to diffuse out of the SR and into the sarcoplasm, which initiates contraction.

Creatine phosphate During rest-

phosphate from extra ATP gets transferred to creatine.

Creatine phosphate During the first 15 seconds

the phosphate from this creatine is transferred to ADP to form ATP.

Glycolysis

Anaerobic (no oxygen)

Muscle glycogen and blood glucose are used to produce?

2 ATP and pyruvate

If O2 is available?

pyruvate moves to aerobic respiration. 

If O2 is not available?

pyruvate is converted to lactic acid and may contribute to muscle fatigue.

Aerobic respiration-

Requires O2, which is provided by myoglobin in the muscle and hemoglobin in the blood

Where does aerobic respiration take place?

Takes place in mitochondria

95% of the energy- 

for muscle contraction

What does aerobic respiration use?

Can use blood glucose, pyruvic acid, or fatty acids

Muscle fatigue-

Muscle can longer contract

Possibly of muscle fatigue-

-Lack of ATP

-Lactic acid buildup affecting pH, and thus enzyme activity

-Na+ and K+ imbalances from repeated depolarization/repolarization

-SR and/or sarcolemma damage affecting Ca2+ regulation

Muscle tension-

the force generated by a muscle

Isotonic contraction –

tension stays constant as muscle length changes

Concentric contraction –

muscle shortens under constant tension (ex. flexing at the elbow to lift a weight)

Eccentric contraction –

muscle lengthens under constant tension (ex. extending at the elbow to put the weight back down).

-Contributes more to muscle soreness and hypertrophy

-Important in movement and balance

sometric contraction –

muscle produces tension without moving (ex. holding a weight straight out against gravity)

-Important in maintaining posture

Each muscle fiber is innervated by?

only one motor neuron, but one motor neuron innervates multiple muscle fibers.

Motor Unit -

group of muscle fibers in a muscle innervated by a single motor neuron

Small motor units (very few fibers per neuron) provide?

very fine motor control (ex. extrinsic eye muscles, fingers)

Large motor units (many fibers per neuron) provide?

strong, gross movements (ex. calf, thigh, back muscles)

Recruitment –

activating more and more motor units in a muscle to reach the required amount of strength for a given task (ex. picking up a feather vs picking up a brick)

The optimal length of a sarcomere maximizes?

the overlap of actin-binding sites and myosin heads, providing the greatest amount of tension during a contraction.

If too stretched-

thick and thin filaments do not overlap enough, which results in weaker contractions.

If stretched to where thick and thin no longer overlap at all? 

no cross-bridges could be formed, and no tension would be produced (this is prevented by titin (connectin) protein that anchors thick filaments to z-discs).

If too contracted?

thick filaments hit z-discs, and cannot slide, resulting in weaker contractions.

Muscle tone –

the constant state of partial contraction maintained in muscles by the CNS.

Hypotonia –

flaccid muscles, weak reflexes

Hypertonia –

hyperreflexia, muscle rigidity, spasticity.

Slow oxidative (SO)

-Aerobic respiration

-Slow, weaker contractions (small diameter)

-High endurance (marathons, posture, joint stabilization)

-More mitochondria, blood vessels, and myoglobin

Fast oxidative (FO) (Intermediate Fibers)

-Aerobic, but can switch to anaerobic.

-Provide more tension than SO, but fatigue more easily, though not as easily as FG.

-Used for movements like walking.

Fast glycolytic (FG)

-Anaerobic respiration (glycolysis)

-Fast, strong contractions (large diameter)

-Fast ATP hydrolysis

-Fatigue quickly

-Burst activities (sprinting

When muscles grow do new cells form? 

New cells are not formed 

Hypertrophy –

cell diameter increases as structural proteins are added to muscle fibers

Atrophy –

structural proteins are lost and muscle mass decreases

Sarcopenia –

Age-related muscle atrophy

Endurance Exercise-

-More SO fibers present in endurance muscles

-Cells produce more mitochondria for more aerobic ATP production

-Increases the amount of myoglobin in a cell

Angiogenesis –

new blood vessels form to supply additional oxygen and remove additional metabolic waste

Angiogenesis can result in overuse injuries –

stress fractures; joint and tendon inflammation

Resistance (Strength) Exercise-

More FG fibers in muscles used for power

Muscle fiber thickness increases due to?

increase in sarcomeres and myofibrils

Can lead to overuse injuries of muscle, tendon, or bone if:

-Load is too heavy

-Muscles are not given enough time between workouts to recover

-Joints are not aligned properly during exercise.

Damage to sarcolemma and myofibrils causes?

soreness, but muscles gain mass as damage is repaired, and extra structural proteins are added to replace the damaged ones.

Anabolic steroids –

a form of testosterone to boost muscle mass and increase power output.

Erythropoietin (EPO) –

hormone normally produced in the kidneys that triggers red blood cell production, and thus increases the oxygen carrying capacity of the blood

Human growth hormone (hGH) –

increases muscle mass and the healing of muscle and other tissues after strenuous exercise

Creatine –

to try to increase short term ATP availability for burst activities

Some risks of performance enhancing substances:

infertility, aggressive behavior, cardiovascular disease, brain cancer, kidney disease, body acne, muscle/tendon/bone injury, and others.

Cardiac Muscle Tissue-

Only found in the heart

-Striated and organized into sarcomeres

-Longer contractions than skeletal muscle due to sustained depolarization from external Ca2+ entering the cell

-Many mitochondria and myoglobin

-Highly fatigue resistant

-Extensively branched

Intercalated discs that allow?

the cardiac muscle cells to contract in a wave-like pattern so that the heart can work as a pump

Gap junctions –

electrically connect cardiac muscle cells to create a functional unit of contraction called a syncytium

Desmosomes –

prevent cells from pulling apart

Autorhythmic-

pacemaker cells in the SA node of the heart initiate the heart

beat

Though the heart beats on its own, the heart rate is adjusted by?

the autonomic nervous system and hormones to meet the varying demands of the body at different levels of activity.

Smooth Muscle-

Present in walls of hollow organs like urinary bladder, uterus, stomach, intestines, and in walls of passageways, like arteries, veins, airways, and urinary and reproductive tracts. Also intrinsic eye muscles, and hair follicles.