Skeletal Muscle Physiology

what is the most outer layer of muscle

epimysium

what is the fiber that surrounds the individual bundles of muscle fibers

perimysium

what are the bundles of muscle fibers called

fasicles

what is the innermost layer of the muscle fiber

endomysium

what is the correct order of muscle fibers from smallest to largest

epimysium, perimysium / fascicles, and endomysium

what is important about the sarcoplasmic reticulum (SR)

storage site for calcium (Ca2+)

what is important about transverse tubules (T-tubules)

extend from sarcolemma, deep into muscle fiber and all the way through

what is the functional contractile element of the muscle

Myofibrils

what are the two primary functional units of muscle cell structure

Myosin (thick filament)

actin (thin filament)

what is the complex process of events involving multiple cellular proteins and energy production systems called?

sliding filament theory

how does the sliding filament theory work

muscle fibers contract by actin sliding over the myosin (thin moves over thick) and reduces the sarcomere length by pulling the z-disks together

what is the path that an action potential takes while inside of the neuromuscular junction (NMJ)

axon → synapse → sarcolemma

what are the 6 steps of muscle contraction or excitation coupling

1. calcium is released and binds to troponin on the tropomyosin, and exposes the myosin-binding sites on the actin filament

2. myosin heads bind to actin, release of Pi initiates power stroke

3. during the power stroke, the myosin heads changes conformation, forced to slide past each other

4. ADP and Pi are released binding to myosin, causing a release of actin

5. Myosin ATPase is released and the myosin head returns to its original configuration

6. when excitation stops Ca2+ is returned to the SR using Ca ATPase and the muscle relaxes

what is type I fiber

slow twitch

slow contraction, force production is low but resilient to fatigue

what is type IIa fiber

fast twitch

fast contraction, force production is high but not fatigue-resistant

what is type IIx fiber

fastest contraction, used in short force activities, and has very low fatigue resistance

what are some functional characteristics of type I fibers

high in mitochondria, lower specific force, but more efficient

what are some functional characteristics of type IIx fibers

small number of mitochondria, highest power output, less efficient that all other fibers

what are some functional characteristics of type Ila fibers

contains characteristics of both fibers

blended type I and type IIx fibers

how are muscle fibers recruited

smallest units are recruited first

midsize next (type IIa)

largest (type IIx)

what is fatigue

the inability to maintain required force production

what are the two mechanisms of fatigue

central or peripheral

what causes peripheral fatigue

1. inadequate energy delivery or metabolism

2. accumulation of metabolic by-products, like H+

3. failure of muscle contractile mechanisms

what causes central neural control

altered neural control of muscle contraction

accumulation of metabolic by-products of H+

decrease in muscle pH (acidosis)

An increase in H+ can negatively impact Ca2+ release and binding within the muscle fiber

what are the two buffers that help minimize drop in pH

bicarbonate and carnosine