Test 2, Muscular

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Describe the organization of skeletal muscle fibers into a muscle.
Name the wrappings covering the muscle down to the muscle fiber.
What is an aponeurosis?

Long fibers, striated, nucleus is peripherally located (multiple nuclei’s along the fiber) Muscular Fasica – Surrounds the individual muscles and groups of muscles (red, layer 1) Epimysium – Surrounds muscles (Dark blue, layer 2) Perimysium – Surrounds fasciculi (light blue ring, layer 3) Endomysium – Surrounds muscle fibers (light blue around orange, layer 4) Aponeurosis – Tendons that are broad and sheetlike

A muscle cell is also called a ____________. The plasma membrane of a muscle cell is called a __________.

Muscle Fiber Sarcolemna

What is the role of the sarcoplasmic reticulum? What is stored in the SR?

SR releases calcium ions that will cause troponin/tropomyosin complex to move. Calcium ions stored in the SR

What causes Calcium to be released?

Depolarization of T tubules

Is Ca++ reused or restored in the SR?


Who delivers the stimulus to the muscle cell? What is released?

Motor Neurons Action potential is what causes the muscle fibers to contract.

What is the end of an axon called? What is the space between the axon and the muscle fiber called?

Synapse of the neuromuscular junction Endomysium

Where does ACH bind? What is a ligand gated ion channel?

Binds to the motor end plate (post synaptic membrane) Ligand-gated ion channels open when a ligand binds to a receptor that is part of the ion channel.

Muscle cell membranes are polarized, what does this mean?

A voltage difference, or electrical charge difference, exists across each plasma membrane.

What is the resting membrane potential for muscle cells?

The charge difference across the the plasma membrane of an unstimulated cell. -85 mV is the resting membrane potential

What is depolarization? What is occurring?

Change of the charge difference across the plasma membrane, making the charge inside the cell less negative and the charge outside the plasma membrane less positive.

What channels are open during depolarization?

Voltage Gated Sodium Ion Channels are open.

What is Threshold? What is the charge now?

Value of the membrane potential at which an action potential is produced as a result of depolarization in response to a stimulus. -55 mV is the charge.

What is Repolarization?

Reverse of depolarization, going from positive back to negative (reverse of question 11) The return of the membrane potential to its resting value

What channels are open during repolarization? Which channels are closed?

Voltage gated sodium channels are closed in repolarization Voltage gated potassium channels are open

What pump reestablishes the cells resting membrane potential?

Na – K Pump

What is pumped out during repolarization and what ion is brought back inside the cell.

K is moved out of the cell and Na stops moving in.

An action potential is propagated down a muscle cell, what channels are used?

Voltage gated Ca ion channels and Ligand gated Na ion channels

Is the motor end plate on the axon terminal or the sarcolemma?


How is an action potential sent down the sarcolemma? What does the T tubule have to do with the action potential? What are the receptors on the T tubule? What do they do?

There are 9 steps on page 288

What is the "All or None" principle?

In muscle cells, the cell either contracts to the maximum potential for a given condition or doesn’t contract at all.

What is the functional unit of the muscle?


Describe the arrangement of myofilaments to a myofibril? What are the thick filaments? What are thin filaments?

Myofibril are bundles of protein filaments (contains actin and myosin) Myofilaments are the actin and myosin Actin is thin, myosin is thick.

Which myofilament contains a receptor for ATP? What other receptor is located there?

Myosin myofilament contains a receptor for ATP G actin molecules (active sites, where myosin attaches to the actin)

Actin is composed of what structures? What other protein structures are found on Actin? What role do they play in binding myosin?

2 Strands of fibrous actin, tropomyosin molecules, troponin molecules, g actin molecules. Tropomyosin molecules Tropomyosin wraps around g actin, where the myosin binds to the actin.

What is the head of myosin called? What activity is it involved in?

Myosin heads Muscle Contraction, forming cross-bridges, breaks down ATP

The functional unit of the muscle is __________. Z lines define what structure?

Sacromere Z Disk, disklike structure

What structures are found within a sacromere? Which ones make up an A band? I band?

Z disk, isotropic band (I band), Anisotropic band (A band), H zone, M line, and titin A band is myosin in a sacromere, I band is between the ends of the myosin on each side of the Z disk.

Which zone narrows and may disappear during a contraction?

H zone

Describe the siding filament model of the muscular contraction.

Actin and myosin sliding past one another in muscle contraction, causing sacromeres to shorten.

What is the role of calcium on the actin molecule? Where does is bind?

Binding site for Calcium within the troponin, which regulates interaction between active sites.

Where is the myosin receptor located? Where is the cross bridge?

On the G actin molecules Cross bridge is between the myosin head and actin active site

What are the regulatory proteins? What are they regulating?

Troponin and Tropomyosin Regulates the interaction between active sites on the G Actin and the myosin.

What happens to the Ca++ after the contraction?

Actively transported back into the sarcoplasmic reticulum, relaxing the muscle.

What does ATP bind to? What is the process that splits the terminal phosphate from ATP? The released energy allows for what activity?

Myosin Heads Hydrolysis splits and breaks down the terminal phosphate from ATP. Muscle Relaxation, calcium restoration

When is ATP needed in a muscle contraction?

During Cross-Bridge movement.

What is the power stroke? Do the myofilaments contract? Does the sarcomere?

Movement of the myosin molecule while the cross-bridge is attached. Myofilaments do NOT contract. Sarcomere’s contract.

What 3 structures are involved the Neuromuscular junction? Where is the motor end plate?

Presynaptic terminal, synaptic cleft, and postsynaptic membrane (motor end-plate) Motor end plate is the postsynaptic membrane lining the sarcolemma.

What is AchE?

Acetylcholinesterase – Removes acetylcholine from the synaptic cleft by breaking it down.

What is the immediate source of energy in a muscle contraction?


What is the role of creatine phosphate in producing ATP? How many ATPs can be made for each release of phosphate? How long can you run if using only CP as a source of energy?

Creatine phosphate accumulates in muscle fibers, where it stores energy that can be used to synthesize ATP. 1 Per Creatine Phosphate Up to 10 seconds

What is the anaerobic process for producing ATP? What are the end products of this process? What is the disadvantage of this process? How many ATPs are formed here?

Glycolysis 2 ATP and 2 Lactic Acids Disadvantage is that limited glucose and creatine phosphate equals less ATP 2 ATP’s formed (net).

Where does aerobic respiration take place? What is required for this process? What is produced by the complete breakdown of one glucose molecule? How many ATP units?

In the Mitochondria Requires oxygen and breaks down glucose to produce ATP, carbon dioxide, and water. 36 ATP per 1 glucose

What type of metabolism is used during the resting phase?


What is the function of myoglobin?

Myoglobin enhances the capacity of the muscle fibers to perform aerobic respiration

How does the respiration change during exercise? Why?

Changes from anaerobic to aerobic, ATP production slows so that it can last for a longer period of time, requires oxygen (whereas anaerobic and CP doesn’t)

What factors are involved in fatigue? What makes the pH change during muscle fatigue?

Physchological fatigue – involves the central nervous system Muscular – Low amounts of ATP Synaptic – Depletion of Acetylcholine

What is a muscle twitch? What takes place during the latent period? What is summation? What is Tetanus? What is treppe?

A single, brief contraction and relaxation cycle in a muscle fiber Latent period – Time between the application of the stimulus and the beginning of the contraction Summation – increasing the force of contraction of the muscle fibers within the muscle. Tetanus – Period of sustained contraction Treppe – A muscle fiber, when stimulated in rapid succession, contracts with greater force with each subsequent stimulus.

Distinguish between isotonic and isometric contractions. Which process makes the muscle shorten?

Isometric – length of muscle doesn’t change, but amount of tension increases (spine holding you up when you’re sitting or standing) Isotonic – Constant tension during contraction, but the length of the muscle changes (waving, typing, lifting) Concentric contractions is what makes the muscle shorten.

What is a motor unit?

Consists of a single motor neuron and all the muscle fibers it innervates.

How fast a muscle contract depends on the type of myosin ATPase available. What are oxidative fibers? glycolytic fibers? What would you expect from a fast oxidative fiber in terms of fatigue resistant, mitochondria, myoglobin, capillaries, and myosin ATPase activity?

Oxidative Fibers – enhanced capacity to carry out aerobic respiration (slow twitch). Glycolytic Fibers – Fast Twitch Oxidative Check out table 9.5

Where do you find smooth muscle? Is it voluntary or involuntary? Do they have myofilament arrangements like skeletal muscles?

Smooth muscle found mostly in the GI Tract. Involuntary They do have myofilament arrangements

Smooth muscle lacks troponin, therefore Ca++ levels activate ____________ .

Muscle Contraction

Smooth muscle form large sheets that contract in powerful spiral actions, where would this type of action be useful in the body?

Stomach, GI Tract to move food, absorb nutrients

The speed of smooth muscle contraction is ___________faster/ slower than skeletal muscle.


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