Physiology (Skeletal Muscle Physiology)

Base only on ppt

• Movement

-Movement of the body and movement of internal materials

• Posture maintenance

• Stabilization of joints

• Protection of internal organs

• Temperature regulation

Functions of Muscle Tissue

Excitability

Responds to changes in electrical potentials across cell membrane

Involuntary

unconsciously controlled

(Smooth and cardiac muscle)

Voluntary

consciously controlled

(skeletal muscle)

Extensibility

can stretch or extend

Elasticity

can stretch and return to original shape

Contractility

can pull on attachment site and shorten

Skeletal muscle

• Long, multinucleated cells

• Cylindrical shape

• Striated

Smooth muscle

• One nucleus

• Spindle-shaped (appearance

like a football)

• Non-striated

Cardiac muscle

• One or two nuclei

• Shorter, branching cells

• Striated

Skeletal Muscle

Smooth Muscle

Cardiac Muscle

Muscle Tissues

Epimysium

surrounds entire muscle

Fascia

additional layer of connective tissue (CT) external to epimysium

Perimysium

surrounds fascicles

Fascicles

bundles of muscle cells

Endomysium

surrounds individual muscle cells

Epimysium

Perimysium

Endomysium

Connective Tissue (CT) Coverings of Skeletal Muscle

(Superificial to deep)

Sarcolemma

cell membrane

Sarcoplasm

cytoplasm

Transverse tubules (T-tubules)

extensions of sarcolemma

Myofibrils

cylinders of contractile proteins

Sarcoplasmic reticulum (SR)

endoplasmic reticulum that stores

calcium

Sarcomere

• Contractile unit of skeletal muscle

• Made of contractile proteins

Myosin

Thick filament

Actin

Thin filament

A band

region spanning the length of the thick filament

I band

region containing only thin filament

M line

horizontal line in center of sarcomere

H zone

space where only thick

filament can be found; extends

laterally from M line

Neuromascular Junction

• Point of contact between skeletal muscle and motor neuron that controls it

Motor neuron

Skeletal muscles must be

stimulated by a ___________

(nerve cell) to contract

Motor unit

one motor neuron

and all the skeletal muscle cells

stimulated by that neuron

-90 mV

Resting membrane potential is

depolarization

Membrane potential becomes +30 mV

repolarization

When slow potassium channels open,

potassium diffuses out of cell and

membrane potential becomes more

negative

Sodium

What ions enter skeletal muscle, causing it to depolarize?

• Creatine phosphate

• Glycolysis

• Lactic acid

• Aerobic respiration

SOURCES OF ATP

Creatine Phosphate

• Resting muscle builds up stores of creatine phosphate

• Donates phosphate to ADP

• Quickly regenerates ATP

• Short-lived source of ATP

• Only lasts about 15 seconds

Glycolysis

• Breaks down glucose to yield ATP and pyruvate

• Energy from bonds in glucose used to bind phosphate to ADP

• Generates ATP slower than creatine phosphate

• If oxygen is available, pyruvate used for aerobic respiration

• If oxygen not available, pyruvate converted to lactic acid

• Lactic acid can be broken down by liver

• Produces ATP for approximately 1 minute of muscle activity

Aerobic Respiration

• Occurs in mitochondria and produces large quantities of ATP

• Requires oxygen

• Myoglobin stores oxygen in muscle cells for use by mitochondria

• Glucose is also stored by muscle cells as glycogen for use by mitochondria

• Pyruvate is broken down to generate approximately 36 ATP

• Supplies the majority of ATP used by muscle cells

Muscle Fatigue

Occurs when muscle can no longer contract

1. Depletion of ATP

2. Lactic acid and ADP buildup

3. Impaired ion movement

4. Inadequate release of calcium from sarcoplasmic reticulum

Multiple causes of Muscle Fatigue

1. Slow oxidative (SO)

2. Fast glycolytic (FG)

3. Fast oxidative (FO)

Muscles are a blend of three different types of muscle fibers

1. Fast glycolytic (FG)

2. Fast oxidative (FO)

3. Slow oxidative (SO)

STRONGEST TO WEAKEST MUSCLE FIBERS

Slow Oxidative (SO) Muscle

Fibers

• Contract slowly

• Weakest strength of contraction of the three types of muscle fibers

• Produce ATP via aerobic respiration

• Red due to presence of myoglobin

• Fatigue slowly

• Maintain posture and stabilize joints

Fast Glycolytic (FG) Muscle Fibers

• Fast contractions

• Produce strongest contractions

• Produce ATP via glycolysis

• Store glycogen in higher amounts

• Fatigue quickly

• Used for fast, powerful movements

Fast Oxidative (FO) Muscle Fibers

• Also known as intermediate fibers

• Possess characteristics of both SO and FG fibers

• Contract quickly

• Produce ATP via glycolysis and aerobic respiration

• More fatigue-resistant than FG fibers

• Used for movements like walking

Muscle Tension

Force generated by contraction of muscle

Tension

can be used to move an object (load)

Isometric contraction

muscle contracts, but does not move a load

Isotonic contraction

moves a load

Concentric contraction

muscle shortens to move load

Eccentric contraction

muscle lengthens to move load

• Concentric isotonic contraction

• Eccentric isotonic contraction

• Isometric contraction

Types of Muscle Contractions

Concentric isotonic contraction

Muscle shortens and moves a load

(Types of Muscle Contractions)

Eccentric isotonic contraction

Muscle lengthens and moves a load

(Types of Muscle Contractions)

Isometric contraction

Muscle contracts but does not move load

(Types of Muscle Contractions)

Twitch

singular contraction of a muscle cell

Myogram

displays the amount of tension produced by a twitch over a period of time

Summation

a series of action potentials that sustain muscle contraction

Tetanus

occurs when action potentials

occur quickly and lead to sustained

maximal contraction

Muscle Tone

Skeletal muscles are rarely fully relaxed (flaccid)

Motor units

consists of a motor neuron and

all the skeletal muscle fibers it controls