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Muscle cells in resting state just before stimulation; contraction mechanism in a skeletal muscle cell.

There is a greater concentration of ______ outside the cell.

Na+ or Sodium

There is a greater concentration of ______ inside the cell.

K+ or potassium

When the stimulus is delivered, the permeability of the membrane at that point is changed; and ______, initiating the depolarization of the membrane.

Na+ diffuses into the cell

Almost as soon as the depolarization wave has begun, a repolarization wave follows it across the membrane. This occurs as _________.

K+ diffuses out of the cell

Repolarization restores the ________ of the resting cell membrane.

electrical conditions

The relative ionic concentrations are reestablished by ______.

Activatiion of the sodium-potassium pump, which moves K+ into the cell and Na+ out of the cell.

Describe in order the contraction mechanism in a skeletal muscle cell.

-Depolarization occurs; and the action potential is generated
-The action potential, carried deep into the cell by the T Tubules, triggers the release of calcium ions from the sarcoplasmic reticulum.
-Calcium Ion concentrations at myofilaments increase; myofilaments slide past one another, and the cell shortens
-The concentration of the calcium ions at the myofilaments decreases as they are actively transported into the sarcoplasmic reticulum
-Muscle cell relaxes and lengthens

Name the 3 layers of connective tissue that are part of each muscle.

Epimysium, Perimysium, and Endomysium

dense collagen fibers that separate the muscle from surrounding tissues and organs


surrounds fasicles and contains blood vessels and nerves that maintain blood flow and innervate the muscle fibers within the fasicles


Within a fascicle, surrounds individual skeletal muscle cells, or muscle fibers, and loosely interconnects adjacent muscle fibers.


Skeletal Muscles are comprised of:

Skeletal muscle tissue, connective tissue, nerves, and blood vessels.

Name the six functions of skeletal muscle

Produce skeletal movement
Maintain posture and body position
Support Soft Tissues
Guard entrances and exits
Maintain body temperature
Store Nutrient Reserves

A bundle of muscle fibers


The 3 types of muscle tissue are:


At each end of the muscle collagen fibers of the epimysium, perimysium, and endomysium come together to form either a bundle known as a ______ or a broad sheet called an _________.


Attach skeletal muscle to bones

Tendons and aponeuroses

Large, multinucleate group of cells

Skeletal muscle fibers

Plasma membrane of a muscle fiber


Specialized cytoplasm of a muscle fiber with varying calcium concentration


1st step in muscle contraction

A sudden change in the transmembrane potential

Narrow tubes that are continuous with the sarcolemma and extend into the sarcoplasm at right angles to the cell surface, filled with extracellular fluid, distribute contraction signals quickly throughout the interior of the cell.

T-Tubules (Transverse Tubules)

The triggers for muscle fiber contraction

Action Potentials

Cylindrical structures encircled by transverse tubules consisting of bundles of protein filaments (myofilaments) and titin.


Composed primarily of Actin

Thin filaments

Composed primarily of myosin

Thick Filaments

Cell membrane of muscle cell


Stores calcium and forms a tubular network around each individual myofibril

Sarcoplasmic Reticulum

Combination of a pair of terminal cisternae, and a transverse tubule


A muscle contraction begins when:

Stored calcium ions are released into the sarcoplasm, then diffusing into individual contractile units called sarcomeres

Dark staining proteins that help stabilize the positions of the thick filaments

M Line

Contains thick filaments but no thin filaments

H Band

Region where each thin filament is surrounded by 3 thick filaments and each thick filament is surrounded by six thin filaments

Zone of overlap

Contains thin filaments but not thick filaments and extends from the A band of one sarcomere to the A band of the next sarcomere

The I band

Mark the boundary between adjacent sarcomeres consisting of the protein actinin, which interconnect thin filaments of adjacent sarcomeres

Z lines

Strands of the elastic protein _______extend from thick filaments to attachment sites at the Z line and aids in thick and thin filament alignment, restoring resting sarcomere length, and resistance of extreme muscle fiber stretching.


Triads are located at:

The zone of overlap

Encircle each sarcomere

2 T tubules

A single __________ contains 4 proteins: F-actin, nebulin, tropomyosin, and troponin.

Thin Filament

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