Muscle Physiology

Tropomyosin molecules

As rest, active sites on actin are blocked by:

Troponin molecules

At rest, the tropomyosin molecule is held in place by:

Tendon

At the end of each muscle, the collagen fibers of the epimysium, and each perimysium and endomysium, come together to form a:

The interaction of the thin filaments sliding past thick filaments generates tension throughout the sarcomere during muscle contraction. This is known as the sliding filament mechanism. Myosin heads of the thick filament grab active sites on the thin filaments and pull the thin filaments towards the M line as the myosin heads rotate. The pulling action brings the Z disks closer together and shortens the sarcomere. Neither the thin nor the thick filaments actually shorten; instead the thin filaments are pulled and slide towards the M line.

Briefly discuss the role of the myosin heads in the sliding filament mechanism of muscle contraction.

Larger than normal cells, multinucleate, filled with cylindrical structures containing contractile proteins, capable of rapid shortening against a load

Compared to a "typical" body cell, skeletal muscle cells are:

I bands and A bands create the dark and light areas known as striations on a skeletal muscle fiber. I bands, or light bands, contain only thin filaments. A bands, or dark bands, contain thick filaments. The thick filaments block more light that thin filaments.

Describe the bands that create the light and dark areas of skeletal muscle fibers known as striations.

Calcium binds troponin upon its release from the sarcoplasmic reticulum when the skeletal muscle fiber is excited. As a result of the binding, tropomyosin shifts and moves revealing the active sites on actin. As the muscle relaxes, calcium ions are pumped back into the sarcoplasmic reticulum. Without calcium, troponin and tropomyosin return to their positions blocking the active sites on actin. Myosin heads are prevented from binding and muscle contraction is inhibited.

Describe the role of calcium in the regulation of the troponin-tropomyosin complex.

Contractile proteins produce tension while regulatory proteins control when the muscle can contract.

Describe the roles of contractile and regulatory proteins in the myofibril.

The synaptic cleft is a narrow gap of space between the axon terminal and the muscle fiber into which acetylcholine is released.

Describe the synaptic cleft.

Hundreds to thousands

Each skeletal muscle contains ______ myofibrils:

Neuromuscular junction

Each skeletal muscle fiber is controlled by a motor neuron at a single:

Two protein strands coiled helically around eachother

Each thin filament consists of:

Acetylcholine is a neurotransmitter responsible for triggering muscle cells. When released by axon terminals into the synaptic cleft, acetylcholine binds to ligand-gated channels in the motor end plate of the skeletal muscle. Upon binding the receptors, sodium ion channels open and sodium ions enter the muscle fiber to produce a local depolarization in the skeletal muscle leading to the muscle cell's action potential.

Explain the role of acetylcholine in the excitation phase of excitation- contraction coupling.

Positively charged sodium ions make the membrane potential become less negative during depolarization. Sodium ions rush into a muscle cell with their concentration gradient when a voltage-gates sodium ion channel opens. The membrane potential reaches a peak of +30mV.

Explain the roles sodium ions play in the depolarization stage of the action potential.

A membrane is considered polarized in its resting state when opposite charges are located on either side or the membrane. At rest, the concentration of sodium ions is greater in the extracellular fluid and lower in the cytosol due to the actions of the Na+/K+ ATPase pump. Potassium ion concentration is higher in the cytosol and lower in the extracellular fluid at rest.

Explain where sodium and potassium ions are relative to a muscle cell during resting membrane potential.

M line

In a sarcomere, thick filaments are linked laterally by the proteins of the:

Endomysium

Individual muscle cells are surrounded by:

Muscle contraction

Interactions between actin and myosin filaments of the sarcomere are responsible for:

A thin filament composed of actin, tropomyosin, and troponin. Actin is a contractile protein. Actin has an area known as an active site that can bind a myosin head. Strings of actin molecules form the largest part of the thin filament. Tropomyosin is a regulatory protein that spirals around the actin strands and covers the active sites. Troponin is a second regulatory protein that holds tropomyosin in place and binds a calcium ion.

List and describe the types of contractile proteins found in a thin filament.

Have many nuclei

Muscle fibers differ from "typical cells" in that muscle fibers:

Conduction, contraction, peristalsis, cushioning

Muscle tissue, one for the four basic tissue groups, consists chiefly of cells that are highly specialized for:

Endomysium

Nerves and blood vessels that service the muscle fibers are located in the connective tissues of:

Motor end plate

Receptors for acetylcholine are located on the:

Synaptic cleft

The narrow space between the synaptic terminal and the muscle fiber is the:

Sarcolemma

The plasma membrane of skeletal muscle is called the:

H band

The region of the sarcomere containing the thick filaments is the:

I band

The region of the sarcomere that always contains thin filaments is the:

Sarcomere

The repeating unit of skeletal muscle fiber is the:

A transverse tubule and two terminal cisternae

The skeletal muscle complex known as the triad consists of:

Actin

The thin filaments of striated muscle are made of which protein(s)?

Striated muscle

The types of muscle tissue include all of the following, except:

Inward extensions of the sarcolemma are known as transverse tubules (t-tubules). During excitation-contraction coupling, the action potential is carried down the t-tubules into the depths of the muscle fiber to stimulate the release of calcium ions from the terminal cisternae.

What are fhe inward extensions of the sarcolemma into the muscle cell called? What funcion do these extensions serve?

The sarcoplasmic reticulum (SR) stores and releases capsicum ions.

What is the function of the sarcoplasmic reticulum?

The Z lines get closer together

When a skeletal muscle fiber contacts:

Storage and release site for calcium ions

Which of the following best describes the sarcoplasmic reticulum?

Repeating unit of striated myofibrils

Which of the following best describes the term Z line?

Repeating unit of striated myofibrils

Which of the following best describes the term sarcomere?

Where thin filaments are anchored

Which of the following best describes the term titin?

Produce movement, maintain posture, maintain body temperature, guard body entrances and exits

Which of the following is a recognized function of skeletal muscle?

Skeletal muscles are responsible for the pumping action of the heart.

Which of the following statements is incorrect?

Tubular extensions of the sarcolemma penetrate the fiber transversely, cross striations result from the lateral alignment of thick and thin filaments, each fiber has many nuclei, muscle fibers are continuous from tendon to tendon

Which statement about the microscopic anatomy of skeletal muscle fibers is true?

Myosin molecules

Cross-bridges are a potion of:

Transverse tubules

The action potential is conducted into a skeletal muscle fiber by:

The ability to produce large amounts of the muscle proteins needed for muscle contraction.

The advantage of having many nuclei in a skeletal muscle fiber is:

H band

The area of the center of the A band that contains no thin filaments is the:

Tendon

The bundle of collagen fibers at the end of a skeletal muscle that attaches muscle to bone is called a(n):

Endomysium

The delicate connective tissue that surrounds the skeletal muscle fibers and ties adjacent muscle fibers together is the:

Epimysium

The dense layer of connective tissue that surrounds an entire skeletal muscle is the:

Shortens

Since each myofibril is attached at either end of the muscle fiber, when sarcomere s shorten, the muscle fiber:

Myoblasts

Skeletal muscle fibers are formed from embryonic (immature) cells called:

During the crossbridge cycle, a myosin head binds to an active sire on actin that leads to the sliding of myofilamemts. ATP hydrolysis cocks the myosin head into its high energy position. ADP and a phosphate remain attached to the myosin head. The myosin head binds to an active site on active. When ADP and phosphate detach from the myosin head, the power stroke occurs in which myosin pulls actin toward the center of the sarcomere. ATP is needed for the release of the myosin head from the actin so that this crossbridge cycle can repeat again.

Summarize the steps in the crossbridge cycle.