Muscles

Briefly describe the length-tension relationship.

A muscle generates different amounts of tension depending upon its length at the time of stimulation. A muscle fiber stimulated at its resting state exerts the most tension, because there is optimal overlap of thick and thin filaments. A muscle that is either already contracted or overly stretched produces a weaker contraction when stimulated, because thick and thin filaments are not optimally aligned and thus are limited in their movement.

What is a motor unit? List the components of a typical motor unit.

A motor unit is a single motor neuron and the muscle fibers it controls. A typical motor unit contains the axon, the muscle, the neuromuscular junction, the synaptic knob (the expanded tip of the ion), the axonal terminal, the synaptic cleft, the motor end plate, synaptic vesicles and the acetylcholine that the vesicles transport.

Describe the physical state of a muscle fiber in rigor mortis and the conditions that produce this state.

A muscle fiber in rigor mortis is constantly contracted. When a person dies, myosin heads bind to receptors on the actin fibers, but there is no longer any ATP being produced in the mitochondria to allow the heads to release. Thus, the muscles stay contracted.

Why is cardiac muscle tissue that has been damaged by injury or disease incapable of regeneration?

Cardiac muscle does not contain stem cells, so it is not able to regenerate when it's been damaged.

What effect does increasing the frequency of action potentials in a skeletal-muscle fiber have upon the force of contraction? Explain the mechanism responsible for this effect.

Increasing the frequency of action potentials in a skeletal muscle fiber increases the force of contraction. The higher the frequency of action potentials, the greater the amount of calcium is released by the sarcoplasmic reticulum, opening up more troponins to bind with myosin heads on the actin and myosin filaments.

2. What are the major functions of skeletal muscles

The major functions of the skeletal muscles are body movement, maintenance of posture, protection/support, regulating the elimination of materials and heat production through shivering.

6. What prevents cross bridges from attaching to sites on the thin filaments in a resting skeletal muscle?

Tropomyosin blocks binding sites so they don't contract. Calcium comes along, removes the tropomyosin, and binds to troponin to allow the actin lines to come together and the muscle to contract.

What is treppe?

Treppe is when the tension of muscle contractions increases over time in response to repeated stimuli of consistent strength. The tension increases because of increased availability of calcium ions as the muscle receives more and more stimuli.

Compare and contrast skeletal, cardiac and smooth muscle tissues in terms of calcium and energy source.

- Skeletal muscles require calcium to bind with troponin so that the tropomyosin can change conformation, giving access for the myosin heads to connect to the troponin. They obtain their calcium from the sarcoplasmic reticulum. ATP is required to remove the myosin head from the troponin site, allowing it to move to the next site so the muscle can contract. - Cardiac muscles require calcium to bind to troponin, similar to the process in skeletal muscles. However, cardiac muscles obtain calcium from outside the cell, rather than from the sarcoplasmic reticulum. Cardiac muscles almost exclusively use ATP produced by aerobic respiration needed for their constant contractions. - Smooth muscles' thin fibers don't contain troponin for calcium to bind to, as it is in skeletal muscles. Instead, calmodulin, a protein, binds to calcium to form the calcium-calmodulin complex and myosin light-chain kinase (MLCK), and enzyme that is activated to phosphorylate the myosin head. Smooth muscles also use ATP, which is used in the detachment of the myosin head, similar to how it happens in skeletal muscle.

Briefly describe ATP generation through aerobic metabolism and glycolysis.

Aerobic metabolism and glycolysis produce long-term supply of ATP. Aerobic respiration requires oxygen. The process picks up where anaerobic metabolism left off, using pyruvate that has been created from glucose. Pyruvate enters the mitochondrion, where it is oxidized to CO2 via the citric acid cycle and the electron transport chain. The citric acid cycle releases NADH and FADH2, which enter the electron transport chain and lead to the creation of ATP. The entire process of aerobic metabolism has the potential to create 34 ATPs from each glucose molecule.

In a short paragraph describe Bell's Palsy.

Bell's Palsy is the temporary paralysis of the muscles on one half of the face. The cause of Bell's Palsy is unknown, but risk factors include diabetes and a recent URI. It occurs due to the malfunction or damage of the facial nerve which controls the muscles of the face.

What is carpal tunnel syndrome and what nerve is involved?

Carpal tunnel syndrome is numbness and tingling in the hand caused by the compression of the median nerve.

What is creatine kinase and what is its significance?

Creatine kinase plays a role in creating an immediate supply of ATP in skeletal muscles. Creatine kinase is the enzyme that allows Pi to be transferred from creatine phosphate to ADP, creating ATP and creatine.

What is the function of creatine phosphate in skeletal-muscle contraction

Creatine phosphate can be used to generate ATP in muscle tissue. ATP is generated when the enzyme creatine kinase transfers Pi from creatine phosphate to ADP, yielding creatine and ATP.

4. Draw and describe the microstructure of a muscle fiber. Include the following terms in your description: nuclei, sarcolemma, sarcoplasm, myofibril, T-tubules, sarcoplasmic reticulum, thin filaments and thick filament.

Draw & Label

5. Describe the following: F actin, G actin, tropomyosin, troponin. Briefly describe how they relate to each other.

F actin and G actin are motor proteins that combine to make the fibrous strand of actin that makes up the thin filaments in myofibrils. G actin is a small globular molecule that combines with other G actin to form a fibrous strand of F actin. Troponin and tropomyosin are regulatory proteins that are on the surface of the F actin and regulate the attachment and detachment of myosin heads on the actin protein, allowing muscles to contract. Tropomyosin blocks troponin binding sites when muscles are at rest. When muscles receive a stimulus to contract, calcium removes the tropomyosin so that myosin heads can bind to and move along the actin filament, causing the muscle to contract.

. You are asked to develop a two-step scheme that can be used to identify the three types of muscle tissue. What would the two steps be?

First, I would develop a way to determine whether the muscle contracts using the troponin-tropomyosin complex or the calmodulin complex. This would differentiate smooth muscle (calmodulin) from skeletal and cardiac muscles (troponin). Then, I would look to see if the muscle is innervated by motor neurons which originate from the somatic nervous system (as it is in skeletal muscles) or whether the innervation of the muscle was spread by gap junctions, as it is in the involuntary cardiac muscle. This would differentiate skeletal and cardiac muscle fibers from each other. I could also look at tissue samples under a microscope

Describe hypertrophy and atrophy.

Hypertrophy is the increase in muscle fibers caused by exercise that repeatedly stimulates a given muscle. Atrophy, by contrast, is the decrease of muscle size, tone and power due to lack of exercise.

Define the following terms: origin, insertion, primary mover, agonist, antagonist, and synergist muscles

In a skeletal muscle, the less moveable attachment of a muscle to bone is called the origin; the more moveable attachment is the insertion. An agonist, or primary mover, is a muscle that contracts to produce a particular movement. Antagonist muscles' actions oppose the movements of the agonist. For example, if an agonist produces extension, the antagonist produces flexion. A synergist muscle is one that assists the agonist in performing its action.

Describe the differences between single-unit and multiunit smooth muscle

Multiunit smooth muscle is found within the eye, in the skin, the wall of larger airways in the respiratory system and the walls of larger arteries. Muscle cells are organized into motor units and are able to achieve varying levels of tension, depending upon how many of the units are stimulated. Most smooth muscle is single-unit. Smooth muscle cells form two to three sheets which are connected by gap junctions. Single-unit smooth muscle is found in the lining of the intestines, urinary and reproductive tracts. Neurons pass in close proximity to single-unit smooth muscle. Neurotransmitters released from varicosities stimulate numerous smooth muscle cells simultaneously. The stimulation is then spread through gap junctions from one cell to another. Thus, all of the smooth muscle cells contract as one unit.

What are the several different fascicle arrangements of skeletal muscle? Give an example of each.

Muscles can be circular (i.e. orbicularis oris, around the mouth), parallel (rectus abdominis), convergent (pectoralis major) or pennate (deltoid).

List the methods used in naming muscles.

Muscles can be named based upon many factors, and usually a muscle's name gives clues to its structure and/or function. They are named based upon the following criteria: muscle action, specific body regions, muscle attachments, orientation of muscle fibers, muscle shape, muscle size and muscle heads/tendons of origin.

Compare and contrast slow oxidative, fast oxidative and fast glycolytic fibers in terms of fatigue, blood supply, diameter, energy source and myoglobin

Slow oxidative fibers provide slow, weak contractions, but don't fatigue very easily because they don't use much ATP. They are roughly half the diameter of other muscle fibers and contain slow ATPase. They produce ATP aerobically. They are highly vascularized, and contain a large amount of myoglobin. Fast oxidative fibers produce a fast powerful contraction with ATP provided mostly through aerobic respiration. However, the vascular supply is lower than in SO fibers, and they don't have as much myoglobin. They fatigue relatively quickly. Their diameter is intermediate, between SO and FG fibers. Fast glycolytic fibers are very strong and powerful. They have the largest diameter, and they fatigue quickly. They are not very vascularized, and have low levels of myoglobin. They use ATP produced anaerobically.

9. Describe the neuromuscular junction. Use axonal terminal, synaptic cleft, motor end plate, synaptic vesicles and acetylcholine in your description.

The neuromuscular junction is where motor neuron axons align with motor end plates on muscle fibers and allow for excitation of the muscle fiber due to reception of an impulse from the axon. The axonal terminal is the very end of the axon, which branches out of a nerve cell. It's the part on the axon that is closest to the motor end plate. There is a small space between the axonal terminal and the motor end plate called the synaptic cleft. Synaptic vesicles are small small membrane sacs created by the nerve cell and sent through the axon to deliver acetylcholine (ACh), a neurotransmitter that enters muscle cells through specific chemically-gated transport proteins embedded in the sarcolemma.

During increases in the force of skeletal-muscle contraction, what is the order of recruitment of the different types of motor units?

The order of recruitment goes type I, type IIa, then type IIb. Type I, or slow oxidative fibers, are first. Their contractions are slow and not very powerful, and thus they don't use much ATP. Type IIa, or fast oxidative fibers, are recruited next. If the force continues, Type IIb, or fast glycolytic fibers, are used. They are strong and powerful, and create ATP via anaerobic respiration.

List the factors responsible for skeletal-muscle fatigue.

The primary cause of muscle fatigue during exercise is a decrease in glycogen stores. It can also be caused by insufficient calcium ions at the neuromuscular junction, or a decreased number of synaptic vesicles to release a neurotransmitter. It can also be due to a change in ion concentration that interferes with the ability of the muscle fiber to conduct an action potential along the sarcolemma, which then interferes with the amount of calcium that can be released by the sarcoplasmic reticulum. At the crossbridge cycling level, excess phosphate groups in the sarcoplasm can interfere with the Pi release from the myosin head when the head needs to detach from the actin filament, causing reduced contraction within the myofibril.

7. What is the contractile unit of a muscle fiber called?

The sarcomere.

8. Briefly describe the mechanism of the sliding filament theory in your own words. Include in your answer all the components.

The sliding filament theory describes the process of muscle contraction. It's a process by which the thick and thin filaments bind and move along each other, causing the sarcomere to contract and generate tension in the muscle. Calcium binds to tropomyosin, which changes its conformation and allows myosin heads to bind to troponin on actin filaments. This attachment is called the crossbridge formation. The myosin head swivels toward the center of the sarcomere, releasing an ADP and a Pi. After the head has swiveled, one ATP binds to a binding site on the myosin head, causing another conformational change, which causes the head to release from the troponin on the actin strand. Then, the ATP is split into ADP and Pi by an enzyme, providing the energy for the myosin head to go back to its original position, where it will bind to the next open troponin on the actin filament. As the muscle receives repeated impulses, more calcium continues to bind, causing the process to continue, and causing the muscle to continue to contract.

1. What are the three different muscle tissue types? Describe where in the body each type of muscle is located, and state whether they exhibit voluntary or involuntary contractions.

The three muscle types are skeletal, cardiac and smooth. Skeletal muscles are attached to bones and allow for movement. They are voluntary. Cardiac muscle is in the heart, and it's involuntary. Smooth muscle is located in some internal organs, such as the intestines, and it's involuntary.

3. Describe the 3 layers of connective tissues that cover muscles.

The three types of CT that cover muscles are epimysium, perimysium and endomysium. The epimysium is a layer of dense irregular CT that wraps the whole muscle. The perimysium is also dense irregular CT, and it wraps each fascicle. The endomysium is areolar CT that wraps each individual muscle fiber.

Describe wave summation.

Wave summation is when muscles receive multiple repeated impulses to contract, so the tension continues to increase in a wave formation. When maximum tension is reached, the muscles have reached fatigue and the tension drops quickly when contraction stops.

What happens to skeletal-muscle fibers when the motor neuron to the muscle is destroyed?

When motor neurons are destroyed, denervation atrophy occurs. This causes the muscle fiber to atrophy and eventually die. If the muscle is reinnervated, then the atrophy will stop.

Briefly describe oxygen debt.

When someone exercises vigorously, the demand for oxygen can exceed the amount of oxygen available within the body. Oxygen debt is the amount of oxygen overuse that then has to be made up following exercise to return to pre-exercise conditions.