Muscle Physiology Quiz

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Questions and Answers

What is the duration of contraction in fast-twitch fibers?

100 msec

7.5 msec (correct)

50 msec

20 msec

Which muscle fiber type is considered fatigable?

Oxidative fibers

Glycolytic fibers (correct)

Slow-oxidative fibers

Fast-oxidative fibers

What characteristic is associated with oxidative fibers?

Large stores of glycogen

Fast myosin ATPase enzyme

High levels of myoglobin depletion

Extensive capillary network (correct)

Which of the following fibers has a slower contraction time?

Slow-oxidative fibers Signup and view all the answers

What determines the speed at which contraction initiates in muscle fibers?

The type of myosin ATPase present Signup and view all the answers

Which fiber type primarily relies on aerobic cellular respiration for ATP production?

Oxidative fibers Signup and view all the answers

Which characteristic does not belong to glycolytic fibers?

High levels of myoglobin Signup and view all the answers

What is a key feature of fast-twitch fibers?

Shortened contraction duration Signup and view all the answers

What is the primary energy source for fast-glycolytic (FG) fibers during contraction?

Glycolysis Signup and view all the answers

Which type of muscle fiber is characterized by a high degree of endurance and a central body?

Parallel muscles Signup and view all the answers

What is the appearance of fast-glycolytic (FG) fibers primarily due to?

Lack of myoglobin and mitochondria Signup and view all the answers

Which term is used to refer to the less movable attachment of a muscle?

Origin Signup and view all the answers

Which muscle fiber type is known for providing both power and speed?

Fast-glycolytic fibers Signup and view all the answers

What happens to the diameter of a circular muscle when it contracts?

It decreases Signup and view all the answers

In the context of muscle fiber types, what is the least extensive characteristic of fast oxidative (FO) fibers compared to slow oxidative (SO) fibers?

Vascular supply Signup and view all the answers

Which of the following best describes the function of tendons?

Connect muscle to bone or other muscles Signup and view all the answers

What occurs during cross bridge formation?

The energized myosin head attaches to an actin myofilament. Signup and view all the answers

What is the correct description of isometric contraction?

Muscle tension develops but the load does not move. Signup and view all the answers

Which statement about wave summation is true?

It arises from the rapid succession of identical stimuli. Signup and view all the answers

What happens during the power stroke?

ADP and P are released, and the myosin head pivots. Signup and view all the answers

How does the strength of muscle contractions change?

By varying the strength of stimulation and changing the frequency of stimulus. Signup and view all the answers

During cross bridge detachment, what is the role of ATP?

It weakens the link between actin and myosin. Signup and view all the answers

What triggers the release of more calcium ions during wave summation?

There is an increase in the firing rate of motor neurons. Signup and view all the answers

What is meant by 'graded muscle responses'?

Variations in muscle strength based on different demands placed on them. Signup and view all the answers

What results in a sustained muscle contraction known as Tetanus?

Maximal contraction of motor units Signup and view all the answers

Which energy source is primarily used for high-intensity exercise before cellular respiration kicks in?

Creatine phosphate Signup and view all the answers

What is the correct sequence of stages in a muscle twitch?

Latent period, Contraction period, Relaxation period Signup and view all the answers

What characterizes fast twitch muscle fibers?

Quicker fatigue with anaerobic energy dependence Signup and view all the answers

Which of the following best describes muscular endurance?

Resistance to muscle fatigue Signup and view all the answers

What is a primary effect of eccentric muscle contractions?

They improve strength and reduce inflammation Signup and view all the answers

Which metabolic pathway begins by breaking down glycogen to glucose?

Anaerobic glycolysis Signup and view all the answers

Muscle tone is described as:

Some motor units are always contracted Signup and view all the answers

Which of the following statements about slow twitch fibers is true?

They have more mitochondria and myoglobin Signup and view all the answers

What causes lactate formation in muscles?

Fermentation of glucose Signup and view all the answers

What is a primary cause of Delayed Onset Muscle Soreness (DOMS)?

Microtears in muscle fibers Signup and view all the answers

Which neurotransmitter's release is inhibited by the toxin from Clostridium botulinum?

Acetylcholine Signup and view all the answers

What process occurs when nerve signals terminate, leading to muscle relaxation?

Decreased calcium channel activity Signup and view all the answers

Which energy source is primarily used during maximum exertion for an additional 20-25 seconds?

Creatine phosphate Signup and view all the answers

What is the main advantage of glycolysis compared to aerobic cellular respiration?

No oxygen needed Signup and view all the answers

What role does estrogen play in muscle recovery?

Increases repair of muscle fibers Signup and view all the answers

What is the consequence of insufficient ATP availability in muscle cells post-mortem?

Muscles remain contracted (rigor mortis) Signup and view all the answers

What type of contractions are associated with more muscle fiber tears, contributing to DOMS?

Eccentric contractions Signup and view all the answers

Which of the following is a primary method for skeletal muscle metabolism during rest?

ATP and creatine phosphate replenishment Signup and view all the answers

Which enzyme is involved in the transfer of phosphate from ADP to ATP?

Myokinase Signup and view all the answers

Study Notes

Muscle Twitch

Muscle twitch occurs when a motor unit is stimulated by infrequent electrical impulses.
This results in a single contraction lasting a fraction of a second.
During a muscle twitch, calcium ions are released from the sarcoplasmic reticulum (SR) for contraction and return to the SR for muscle relaxation.
Three stages of muscle twitch: latent period, contraction period, and relaxation period.
Nerve fibers can deliver rapid series of stimuli to the motor unit, which can lead to increased muscle contraction.

Tetanus

If maximal contraction occurs, a sustained contraction called tetanus is achieved.
Tetanus continues until fatigue sets in and the muscle relaxes even when stimulated.
Tetanus doesn't usually happen because some motor units are contracting maximally while others are resting, allowing for sustained contractions.
Muscle tone represents a state where some motor units are always contracted but not enough to cause movement.

Energy Sources for Muscle Contraction

Muscle cells have limited amounts of ATP stored and need to acquire more energy for contraction.
Energy sources stored in muscle: glycogen and fat (triglycerides).
Energy sources derived from blood: blood glucose and plasma fatty acids.
ATP production for muscle contraction can occur through three pathways:
- Anaerobic: Creatine PO4 Pathways (no need for O2) and Fermentation (no need for O2)
- Aerobic: Cellular respiration

Aerobic vs Anaerobic

Creatine PO4 Pathway: Fastest and simplest way for muscles to produce ATP.
CP is formed during muscle cell resting and storage is limited.
CP is used for high-intensity exercise before cellular respiration takes over.
Fermentation: produces ATP by breaking down glucose and producing lactate.
Lactate formation causes muscle aches and fatigue, but with rest and O2 intake, lactate is converted back to glucose.
Cellular respiration: more likely to supply energy when exercise is sub-maximal in intensity.

Fast Twitch vs Slow Twitch

Muscle cells contain myoglobin, which combines with and stores O2.
Fast twitch fibers differ from slow twitch fibers in color, myoglobin content, and blood vessel density
Fast twitch: Develops maximum tension quickly and to a greater degree.
Fast twitch fibers fatigue quickly and build up lactate rapidly.
Slow twitch: Darker in color (more mitochondria), lots of myoglobin, and dense capillary beds for O2 intake.
Slow twitch fibers have better endurance and are resistant to fatigue.

Types of Contractions

Concentric: muscles shorten during contraction.
Eccentric: muscles lengthen during contraction.
Eccentric contraction benefits include:
- Improves strength.
- Reduces inflammation
- May help prevent Type 2 diabetes.
- Strengthens knee muscles.
- Treats tennis elbow.
- Lower strength losses during reduced training periods.
- Improved performance
- Prevents injuries.
- Lengthens careers.

Five Rules of Skeletal Muscles

These rules describe the characteristics of fast twitch fibers and their ability to produce a strong, quick contraction:
- Fast rate of action potential propagation along the sarcolemma.
- Quick Ca^++^ release and re-uptake by the SR.
- Stronger contraction.
- Initiate contraction quicker.
- Produce a contraction of shorter duration.

Muscle Fiber Sub-Types

Three types of muscle fibers:
- Slow-oxidative (SO) fibers (Type I)
- Fast-oxidative (FO) fibers (Type II)
- Fast-glycolytic (FG) fibers (Type IIb)

Skeletal Muscle Composition/Action

Tendons: attach muscle to bone, muscle to skin, or muscle to muscle.
The less movable attachment is called the origin, and the more movable attachment is called the insertion.
- Superior/inferior attachments (axial muscles)
- Proximal/distal attachments (appendicular muscles)

Skeletal Muscle Organizational Patterns

Fascicles lie parallel to each other in the following patterns:
- Circular muscles (sphincters): concentrically arranged around openings.
- Parallel muscles: have a central body (belly).
  - High endurance but not strong.
- Convergent muscles: widespread muscle fascicles converging on a common site.
  - Can be a single tendon, a tendinous sheet, or both.
- Pennate muscles: fibers attach obliquely to a tendon.
  - Increased muscle power.

Muscular Paralysis

Tetanus (Clostridium tetani): toxin blocks release of glycine, the inhibitory neurotransmitter in the spinal cord leading to overstimulation of motor neurons and excessive muscle contraction.
Botulism (Clostridium botulinum): toxin prevents release of ACh at synaptic terminals, causing muscular paralysis.
- Botulism A can be used to reduce wrinkles and treat spasticity.

Skeletal Muscle Relaxation

Termination of rapid nerve signal: nerve signal stops, ACh release stops, ACh receptors close on the sarcolemma, Ca^++^ channels decrease Ca^++^ and return it to storage.
ATP is required for both contraction and relaxation of muscles.
In death, ATP is not available, muscles remain contracted (rigor mortis).

Skeletal Muscle Metabolism

Most ATP produced for muscle cells is used to re-set the myosin heads for contraction.
ATP is also required for Ca^++^ pumps within the sarcoplasmic reticulum to store Ca^++^.
Muscle fibers store limited ATP, and additional ATP can be obtained from myokinase which transfers P from ADP to ATP, providing energy for 5-6 seconds of maximum exercise.
Creatine PO4 stores can provide an additional 20-25 seconds of maximum exertion.

Rest

During rest, ATP and Creatine PO4 stores are replenished through cellular respiration and creatine kinase activity.

Glycolysis

Glucose from glycogen stores or blood provides energy for glycolysis, which is advantageous because it doesn't need O2 and produces ATP rapidly.

Aerobic Cellular Respiration

Cellular respiration occurs within the mitochondria, requires O2, and can utilize a variety of nutrients

### Cross Bridge Formation

Includes four steps:
- Energized myosin head attaches to an actin myofilament.
- The power stroke, where ADP and P are released and the myosin head pivots, pulling the actin filament.
- Cross-bridge detachment, where ATP attaches to myosin, weakening the link between myosin and actin.
- Cocking of the myosin head, where ATP is hydrolyzed to ADP and P, returning the myosin head to its pre-stroke position.

Wave Summation and Recruitment

Muscle tension is the force exerted by a contracting muscle.
Load is the opposite force on the muscle.
Isometric contraction develops tension but the load doesn't move.
Isotonic contraction develops tension, overcomes the load, and shortens the muscle.
Muscle contractions can be graded in two ways:
- By changing frequency of stimulation
- By changing the strength of stimulation

Muscle Contraction Changes/Stimulus Frequency

The nervous system increases the firing rate of motor neurons to generate greater muscular force.
Wave or temporal summation occurs when two identical stimuli are delivered in rapid succession, resulting in a stronger second twitch.
The second contraction happens before complete relaxation, leading to more shortening than the first contraction. This summation applies as long as the second stimulus arrives before the muscle is completely repolarized.

### DOMS

Delayed Onset Muscle Soreness (DOMS) usually occurs 24-48 hours after exercise.
Microtears in muscle fibers are often the cause.
Estrogen increases repair.
Active recovery is best for DOMS.

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Description

Test your knowledge on muscle twitches and tetanus with this quiz. Understand the stages of muscle contraction, the role of calcium ions, and how motor units work together. This quiz will also cover the concept of muscle tone and sustained contractions.