Muscular Tissue - Chapter 10

What proteins are found in a thin filament?

Actin.

What is the sarcoplasmic reticulum, structurally?

1.) A fluid-filled system of membranous sacs which encircles each myofibril.

Describe the sequence of events that lead to an increase in the level of Ca2+ in the sarcoplasm (cytosol).

1.) Action potentials from the T-tubules causes Ca2+ to be released from the SR into the muscle cell. 2.) Ca2+ moves tropomyosin away from the myosin-binding sites on actin allowing cross-bridges to form. 3.) The SR membrane contains Ca+2 active transport pumps to return Ca+2 back to the SR quickly --> THUS resulting in a decrease in the calcium ion levels in the sarcoplasm 4.) As the Ca2+ level in the cell drops, myosin-binding sites are covered and the muscle relaxes.

What causes the decrease of the level of Ca2+ ions at the time of muscle relaxation?

1.) After the last action potential has propogated throughout the T tubules, the CA2+ release channels close. 2.) As the pumps Ca2+ back into the SR, the concentration of calcium ions in the sarcoplasm quickly decreases. 3.) the concentration of Ca2+ is 10,000 times higher in the SR than in the cytosol of a relaxed muscle fiber. As the Ca2+ level in the cytosol drops, tropomyosin covers the myosin-binding sites, and the muscle fiber relaxes.

Describe the features of a myosin protein.

1.) Function as motor protein which can achieve motion 2.) Convert ATP to energy of motion 3.) Projections of each myosin molecule protrude outward (myosin head)

Describe what the sarcoplamic reticulum does when the muscle is relaxed and when it contracts.

1.) In a relaxed muscle, the sarcoplasmic reticulum STORES calcium ions (CA2+). 2.) Release of CA2+ from the terminal cisterns of the sarcoplasmic reticulum TRIGGERS muscle contraction. Note: muscle contraction does NOT cause the SR to release CA2+, but the release of CA2+ causes muscle contraction.

Describe the series of events that occur when a nerve impulse (action potential) elicits a muscle action potential.

1.) Release of ACh - Nerve impulse arrives at the synaptic end bulbs stimulates voltage-gated Ca2+ channels to open. Ca2+ then flows inward and stimulates synaptic vesicles to release ACh into the synaptic cleft. 2.) Activation of ACh receptors - Binding of ACh to the receptor on the motor end plate opens an ion channel. Allows flow of Na+ to the inside of the muscle cell. 3.) Production of muscle action potential - the inflow of Na+ makes the inside of the muscle fiber more positively charged triggering a muscle action potential to be generated. The muscle action potential then propogates to the SARCOPLASM RETICULUM to release its stored Ca+2. 4.) Termination of ACh activity - ACh effects last only briefly because it is rapidly broken down by AChE.

Describe the structural components of SKELETAL muscle tissue.

1.) Skeletal muscle is striated 2.) Skeletal muscle tissue IS attached to bones - skeletal muscles move bones 3.)Skeletal muscle tissue works mainly in a VOLUNTARY manner. It can be consciously controlled. Most skeletal muscles also are controlled subconsciously to some extent (the diaphragm alternately contracts and relaxes).

Describe the structural components of SMOOTH muscle tissue.

1.) Smooth muscle tissue does NOT have striations like skeletal and cardiac muscle tissue 2.) Smooth muscle tissue is located in the walls of hollow internal structures (Blood vessels, airways, and many organs. I.E. ureters connected to kidneys, peristalsis in intestinal tract, & arteries and veins) 3.)Mostly / usually involuntary

What is the sarcolemma, structurally, and what role does it play when a muscle is stimulated to contract?

1.) The sarcolemma is the plasma membrane of a muscle fiber's and/or muscle cell's plasma membrane. 2.) Transverse t-tubules are invaginations of the sarcolemma. Transverse t-tubules tunnel in from the plasma membrane (sarcolemma). Muscle action potentials travel ALONG the SARCOLEMMA and thru the T tubules, quickly spreading through the muscle fiber. This arrangement of t-tubules on the sarcolemma ensures that ALL parts of the sarcolemma are excited at the same instant.

Describe the concepts of wave summation, unfused (incomplete) tetanus, and fused (complete) tetanus.

1.) Wave summation = the phenomenon, in which stimuli arriving at different times cause larger contractions. 2.) Unfused (incomplete) tetanus = the state in which a skeletal muscle fiber is experiencing sustained by wavering contraction. 3.) Fused (complete) tetanus = the state of sustained contraction (no relaxation at all).

Describe the series of events that causes the exposure of the myosin-binding sites on actin.

1.) When Ca2+ release channels open due to an action potential , Ca2+ flows out of the SR into the the sarcoplasm around the thick & thin filaments. 2.) Ca2+ conc. rises tenfold in the sarcoplasm. 3.) Released calcium ions combine with troponin, causing it to change shape. 4.) This conformational change moves tropomyosin away from the myosin-binding sites on actin. 5.) Once these binding sites are free, myosin heads bind to them to form cross-bridges, and the contraction cycle begins.

Describe the structural components of CARDIAC muscle tissue.

1.) Yes, cardiac muscle is striated like skeletal muscle. 2.) cardiac muscle is located in the walls of the heart 3.) Action of cardiac muscle tissue is involuntary (contraction and relaxation of the heart is not consciously controlled)

Define tendon.

A cord that attaches a muscle to a bone.

Define motor unit.

A motor unit consists of a somatic motor neuron plus all of the skeletal muscle fibers it stimulates.

Which ion is responsible for starting muscle contraction? Is it an increase or a decrease in the level of ions in the sarcoplasm (cytosol) that starts muscle contraction?

An increase in Ca2+ in the sarcoplasm starts muscle contraction, and a decrease stops it.

What are the terminal cisterns and triads?

Dilated end sacs of the sarcoplasmic reticulum called TERMINAL CISTERNS (there is a release of calcium ions from the terminal cisterns) butt against the T tubules (invaginations of the sarcolemma) from both sides. A transverse tubule and the two terminal cisterns on either side of it form a TRIAD.

A muscle cell is also known as a muscle...

FIBER. Muscle cell = muscle fiber

What is the purpose of splitting ATP on the myosin head?

Hydrolysis of ATP reorients and energizes the myosin head. In other words, the splitting of ATP puts the myosin head in a "cocked" high-energy state. Study figure 10.6.

What are the names of the two contractile proteins?

MYOSIN and ACTIN

Indicate the protein that makes up a thick filament.

Myosin is the main component of thick filaments.

Describe the concept of motor unit recruitment.

The process in which the number of active motor units increases. Motor units are recruited in order from the SMALLEST to the LARGEST.

What is myoglobin, structurally, and what is its purpose?

The sarcoplasm contains a red-colored protein called myoglobin. This protein, found only in muscle, binds oxygen molecules that diffuse into muscle fibers from interstitial fluid. Myoglobin releases oxygen when it is needed by the mitochondria for ATP production.

What is glycogen, structurally, and what is its purpose?

The sarcoplasm includes a substantial amount of glycogen, which is a large molecule composed of many glucose molecules. Glycogen cam be used for synthesis of ATP within the muscle fiber.

What is the effect of the size of a motor unit on its strength of contraction (assuming that each muscle fiber can generate about the same amount of tension)?

The total strength of a contraction depends on the size of the motor units and the # that are activated. For example, muscles in the arm and leg have 2000-3000 muscle fibers per motor unit.

What are myofibrils?

Thread-like structures which have a contractile function.

List and describe each of the four functions of muscular tissue.

Thru contraction and relaxation, muscular tissue performs 4 important functions: 1.) Producing body movements 2.) Stabilizing body positions 3.) Moving substances within the body and regulating organ volume 4.) Producing heat

What are the names of the two regulatory proteins (help to switch contractile process on & off) found in thin filaments, and describe their purposes?

Tropomyosin and troponin are both part of the thin filament. During relaxation - myosin is blocked from binding to actin in relaxed muscle. Strands of tropomyosin cover the myosin-binding sites. During contraction - there is a high concentration of calcium ions in the sarcoplasmic reticulum. Calcium ions binding to troponin moves tropomyosin away from myosin-binding sites. Allows muscle contraction to begin as myosin binds to actin.

What are the two kinds of filaments?

THICK (composed of protein myosin) and THIN filaments (composed mostly of the protein actin).

What is the relationship between myofibrils and filaments?

Within myofibrils are smaller protein structures called FILAMENTS or myofilaments.

What is the sarcoplasm?

Within the sarcolemma is the sarcoplasm, the cytoplasm of a muscle fiber.

Does actin have myosin binding sites?

YES. Actin molecules provide a site where myosin heads can attach.

What is the name of the part of the sarcomere that separates one sarcomere from the other?

Z DISCS!!! Thus, a sarcomere extends from one Z disc to the next. (See Above Photo)

What is a sarcomere?

The filaments inside a myofibril do not extend the entire length of a muscle fiber. Instead, they are arranged into compartments called SARCOMERES, which are the basic functional units of a myofibril.

What is the name of the structure at the end of an axon terminal?

axon terminal

What is the name of the location where a neuron communicates with skeletal muscle fiber?

neuromuscular junction

What is the name of the type of neurons that stimulate skeletal muscles to contract.

somatic motor neurons

What is the name of the space between a motor neuron and a skeletal muscle fiber?

synapse

What is the purpose of mitochondria?

Mitochondria lie in rows throughout the muscle fiber, strategically close to the contractile muscle proteins that use ATP during contraction so that ATP can be produced quickly as needed. Basically, mitochondria PROVIDE ATP for contractile muscle proteins.

What is the name of the part of the sarcolemma at the location of the neuromuscular junction?

Motor end plates (the muscle fiber part of the NMJ) and contain ACh receptors - region of sarcolemma opposite the synaptic end bulbs.

Define fascicles.

Muscle fibers are found in bundles called fascicles.

Describe how the lowering of the level of Ca2+ ions in the sarcoplasm allows muscle relaxation (absence of contraction) to occur.

See above notecard.

What are transverse (T) tubules, structurally, and what role does it play when a muscle is stimulated to contract?

See above notecard. Thousands of tiny invaginations of the sarcolemma, called transverse tubules, tunnel in from the surface toward the center of each muscle fiber. B/c t-tubules are are open to the outside of the fiber, they are filled with interstitial fluid.

Describe the structural differences between the three types of muscular tissue.

See following notecards.

Read Neuromuscular junction section.

See next notecard.

What is the name of the small sacs found in the cytosol in the synaptic end bulb? What is found inside of these sacs?

Suspended in the cytosol within each synaptic end bulb are hundreds of membrane-enclosed sacs called SYNAPTIC VESICLES. In each synaptic vesicle are thousands of molecules of acetylcholine (ACh), the neurotransmitter released at the NMJ.