Chapter 10: Muscle Tissue

NMJ

At the ________, the axon terminal releases a chemical messenger, or neurotransmitter, called acetylcholine (ACh)

Slow oxidative

________ (SO) fibers contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP.

mesodermal cells

Paraxial ________ adjacent to the neural tube form blocks of cells called somites.

**excitability**

All three muscle tissues have some properties in common; they all exhibit a quality called

**elasticity**

A muscle can return to its original length when relaxed due to a quality of muscle tissue called

**Contractility**

allows muscle tissue to pull on its attachment points and shorten with force.

**Skeletal muscle**

fibers are multinucleated structures that compose the skeletal muscle.

Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue

skeletal muscle, cardiac muscle, and smooth muscle

Although the term excitation-contraction coupling confuses or scares some students, it comes down to this

for a skeletal muscle fiber to contract, its membrane must first be "excited"-in other words, it must be stimulated to fire an action potential

**Cardiac muscle**

fibers each have one to two nuclei and are physically and electrically connected to each other so that the entire heart contracts as one unit (called a syncytium).

**fascicle**

Inside each skeletal muscle, muscle fibers are organized into individual bundles, each called a

**perimysium**

by a middle layer of connective tissue called the

**endomysium**

Inside each fascicle, each muscle fiber is encased in a thin connective tissue layer of collagen and reticular fibers called the

**aponeurosis**

In other places, the mysia may fuse with a broad, tendon-like sheet called an

**sarcolemma**

The plasma membrane of muscle fibers is called the

**sarcoplasm**

the cytoplasm is referred to as

s**arcoplasmic reticulum (SR)**

the specializedsmooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions (Ca++) is called the

**sarcomere**

Each packet of these microfilaments and their regulatory proteins, **troponin** and **tropomyosin** (along with other proteins) is called a

**neuromuscular junction (NMJ)**

Another specialization of the skeletal muscle is the site where a motor neuron’s terminal meets the muscle fiber—called the

**acetylcholine (ACh)**

At the NMJ, the axon terminal releases a chemical messenger, or neurotransmitter, called

**voltage-gated sodium channels**

As the membrane depolarizes, another set of ion channels called ___ are triggered to open.

**T-tubules**

For the action potential to reach the membrane of the SR, there are periodic invaginations in the sarcolemma, called **_** (“T” stands for “transverse”).

**triad**

The arrangement of a T-tubule with the membranes of SR on either side is called a

**myofibril**

The triad surrounds the cylindrical structure called a

**Creatine phosphate**

is a molecule that can store energy in its phosphate bonds.

**Glycolysis**

is an anaerobic (non-oxygen-dependent) process that breaks down glucose (sugar) to produce ATP; however, glycolysis cannot generate ATP as quickly as creatine phosphate.

**Aerobic respiration**

is the breakdown of glucose or other nutrients in the presence of oxygen (O2) to produce carbon dioxide, water, and ATP.

**isotonic contractions**

where the tension in the muscle stays constant, a load is moved as the length of the muscle changes (shortens).

**concentric contraction**

involves the muscle shortening to move a load.

**eccentric contraction**

occurs as the muscle tension diminishes and the muscle lengthens.

**isometric contraction**

occurs as the muscle produces tension without changing the angle of a skeletal joint.

**motor unit**

The actual group of muscle fibers in a muscle innervated by a single motor neuron is called a

**recruitment**

This increasing activation of motor units produces an increase in muscle contraction known as

**Twitch**

A single action potential from a motor neuron will produce a single contraction in the muscle fibers of its motor unit.

**myogram**

an instrument that measures the amount of tension produced over time.

**latent period**

during which the action potential is being propagated along the sarcolemma and Ca++ ions are released from the SR.

**relaxation phase**

when tension decreases as contraction stops.

**graded muscle response**

Normal muscle contraction is more sustained, and it can be modified by input from the nervous system to produce varying amounts of force; this is called a

 **wave summation**

If the fibers are stimulated while a previous twitch is still occurring, the second twitch will be stronger.

**tetanus**

If the stimulus frequency is so high that the relaxation phase disappears completely, contractions become continuous in a process called complete

**treppe**

The muscle tension increases in a graded manner that to some looks like a set of stairs.

**hypotonia**

The absence of the low-level contractions that lead to muscle tone is referred to as

**Slow oxidative (SO)**

fibers contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP.

**Fast oxidative (FO)**

fibers have fast contractions and primarily use aerobic respiration, but because they may switch to anaerobic respiration (glycolysis), can fatigue more quickly than SO fibers.

**Fast glycolytic (FG)**

fibers have fast contractions and primarily use anaerobic glycolysis.

**hypertrophy**

structural proteins are added to muscle fibers in a process called

**atrophy**

The reverse, when structural proteins are lost and muscle mass decreases, is called

**sarcopenia**

Age-related muscle atrophy is called

**angiogenesis**

The training can trigger the formation of more extensive capillary networks around the fiber, a process called

**intercalated disc**

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

**desmosome**

is a cell structure that anchors the ends of cardiac muscle fibers together so the cells do not pull apart during the stress of individual fibers contracting.

**autorhythmicity**

This group of cells is self-excitable and able to depolarize to threshold and fire action potentials on their own, a feature called

**dense body**

is analogous to the Z-discs of skeletal and cardiac muscle fibers and is fastened to the sarcolemma.

**latch-bridges**

This can happen as a subset of cross-bridges between myosin heads and actin, called

**varicosity**

releases neurotransmitters into the synaptic cleft.

**pacesetter cell**

can spontaneously trigger action potentials and contractions in the muscle.

**visceral muscle**

This type of smooth muscle is found in the walls of all visceral organs except the heart (which has cardiac muscle in its walls), and so it is commonly called

**somites**

Paraxial mesodermal cells adjacent to the neural tube form blocks of cells called

**myoblast**

is a muscle-forming stem cell that migrates to different regions in the body and then fuse(s) to form a syncytium, or **myotube.**

**satellite cell**

is similar to a myoblast because it is a type of stem cell; however, satellite cells are incorporated into muscle cells and facilitate the protein synthesis required for repair and growth

**fibrosis**

If a cell is damaged to a greater extent than can be repaired by satellite cells, the muscle fibers are replaced by scar tissue in a process called

**pericyte**

which is found in some small blood vessels.