Muscle Tissue and Function Quiz

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Questions and Answers

What initiates the signal for conscious muscle contraction?

Intramuscular calcium ion concentration

Muscle cell electrical impulses

Signals from sensory neurons

The frontal lobe of the cerebral cortex (correct)

What role does Acetylcholine play in muscle contraction?

It stimulates the release of calcium ions

It binds to protein receptors on the muscle cell membrane (correct)

It binds to actin to promote myosin attachment

It provides ATP for energy

What occurs when calcium binds with troponin during muscle contraction?

Myosin heads detach from actin

Troponin moves out of the way, exposing actin binding sites (correct)

Z-lines move further apart

Calcium is released back into the sarcoplasmic reticulum

What happens to myosin heads after they bind to actin?

They release ADP + P and bend, bringing Z-lines closer Signup and view all the answers

What triggers muscle relaxation?

End of nervous stimulation and subsequent calcium recycling Signup and view all the answers

What is the primary energy source used by muscles during initial contraction?

ATP stored in the muscle cells Signup and view all the answers

What causes muscle fatigue?

Accumulation of lactic acid and low ATP supply Signup and view all the answers

During aerobic cellular respiration, what is primarily used to replenish ATP?

Glucose and triglycerides Signup and view all the answers

What is the main function of skeletal muscle?

Produce movement under voluntary control Signup and view all the answers

Which type of muscle is responsible for involuntary movements, such as in the digestive tract?

Smooth muscle Signup and view all the answers

What mechanism describes how muscles contract?

Sliding Filament Mechanism Signup and view all the answers

What are the two types of muscle groups that work together in movement?

Antagonistic and Synergistic Signup and view all the answers

In skeletal muscle cells, what is the structure that serves as the basic contractile unit?

Sarcomere Signup and view all the answers

Where do the actin filaments attach within the sarcomere?

Z lines Signup and view all the answers

How are muscle fibers in skeletal muscle categorized in terms of nuclei?

Multinucleic Signup and view all the answers

What happens during relaxation of muscle contraction?

Filaments slide back into their original positions Signup and view all the answers

Which type of muscle fibers are better suited for endurance activities such as long-distance swimming?

Type I fibers Signup and view all the answers

What is the composition of fast twitch muscle fibers that makes them optimal for short bursts of power?

High glycogen and creatine phosphate stores Signup and view all the answers

What is a motor unit composed of?

One motor neuron and all the muscle cells it stimulates Signup and view all the answers

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

They contain more mitochondria and have better blood supply. Signup and view all the answers

How does strength training affect muscle composition?

Enhances both fast twitch myofibrils and glycogen storage Signup and view all the answers

Which type of activities are slow twitch fibers primarily associated with?

Long duration aerobic exercises Signup and view all the answers

What role does myoglobin play in slow twitch muscles?

It transports oxygen to muscle cells. Signup and view all the answers

What characterizes a fine control motor unit?

Fewer muscle cells per motor neuron Signup and view all the answers

What is a primary benefit of endurance training for muscles?

Improves ATP production for prolonged periods Signup and view all the answers

Which type of muscle is characterized by being involuntary and having a net-like arrangement of actin and myosin?

Smooth muscle Signup and view all the answers

What effect does aging typically have on muscle tissue starting at around age 30?

Leads to some cell loss and myofibril reduction Signup and view all the answers

Which of the following statements about anabolic steroids is true?

They mimic testosterone and assist in muscle growth Signup and view all the answers

What is the primary role of gap junctions in cardiac muscle cells?

To facilitate quick conduction of contraction signals Signup and view all the answers

Which type of muscle is attached to bones for voluntary movement?

Skeletal muscle Signup and view all the answers

What common issue can occur if a muscle is stretched beyond its limit?

Pulled muscles Signup and view all the answers

Which of the following describes slow-twitch muscle fibers?

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

Study Notes

Muscle Tissue

Makes up 40% of a male’s body weight and 32% of a female’s body weight
There are three types of muscle tissue: skeletal, cardiac, and smooth.
Skeletal muscle is responsible for voluntary movement.
Cardiac muscle makes up the heart, its contractions are involuntary.
Smooth muscle is responsible for the involuntary movement of the digestive tract, blood vessels, urinary bladder, uterus.

Muscle Function

Muscles contract and relax to create movement.
When muscles contract, the distance between bones is shortened (for skeletal muscles).
Muscles are attached to bones by tendons.
Muscle groups can work synergistically (muscles working together) or antagonistically (muscles working in opposing directions).
Antagonistic muscle groups do not contract at the same time.

Muscle Structure

A muscle is made up of many muscle cells that share the same insertion and origin.
Fascicles are bundles of muscle cells. Connective tissue surrounds each fascicle and joins to form tendons.
Each muscle cell contains myofibril bundles.
Myofibrils are made up of sarcomeres that are laid out end-to-end.
A sarcomere is the basic contractile unit of a muscle.
Skeletal muscle cells are multinucleated because many cells were fused together during development.

Sliding Filament Mechanism

Myosin makes up thick filaments.
Actin molecules make up thin filaments.
When a muscle contracts, cross-bridges form between myosin and actin filaments.
When a muscle relaxes, the cross-bridges break down, and the filaments passively slide back into place.

Skeletal Muscle Contraction

Actin and myosin are the proteins that allow for muscle contraction.
Z-lines are attachment points for actin.
Muscle contraction shortens many sarcomeres.

Steps of Skeletal Muscle Contraction

The signal for muscle contraction begins in the frontal lobe of the cerebral cortex (for conscious movement).
Motor neurons carry messages from the brain, down the spinal cord, and to the muscles.
Motor neurons release acetylcholine (a neurotransmitter) which binds to receptors on the muscle cell's membrane.
The release of acetylcholine initiates an electrical impulse in the muscle cell.
The electrical impulse causes calcium ions to be released into the cell cytoplasm from the sarcoplasmic reticulum.
Calcium ions bind to troponin, which moves tropomyosin. This exposes the actin-binding sites to myosin.
Energized myosin heads bind to the exposed actin binding sites, forming cross-bridges.
The myosin heads bend, pulling the Z-lines closer together.
ADP + P are released from the myosin head.
ATP binds to the myosin head, causing it to detach from the actin filament.
The myosin head splits ATP into ADP + P, making the head energized.
If the muscle is still being stimulated to contract, the cycle will repeat.

Muscle Relaxation

When nerve stimulation stops, calcium ions are no longer released.
Calcium ions are pumped back into the sarcoplasmic reticulum, removing them from troponin.
The actin-binding sites are then covered by tropomyosin, preventing myosin from attaching.
The sarcomere relaxes.

Energy Required for Muscle Activity

The primary source of energy for muscle activity is ATP.
Muscles first use ATP stored within the cells, but this only lasts for about 10 seconds.
Other ways that ATP is replenished include:
- Creatine phosphate, which transfers phosphate to ADP. This lasts for about 25 seconds.
- Stored glycogen in muscles, which can be broken down aerobically or anaerobically. This lasts for about 5-10 minutes.
- Aerobic cellular respiration using glucose, triglycerides, and proteins.

Muscle Fatigue

Muscle fatigue occurs when muscles can no longer contract, even when stimulated by a nerve signal.
It occurs because of low ATP supply and lactic acid accumulation in muscle cells.
Muscle fatigue can be prevented by taking deep breaths and resting (breaks down lactic acid and allows ATP to be replenished) and by exercising aerobically to ensure sufficient oxygen supply.

Motor Unit

One motor neuron stimulates several muscle cells.
A motor neuron and all the muscle cells it stimulates are called a motor unit.
When a nerve signal arrives, all the muscle cells within a motor unit contract.
Muscles cannot contract without nerve input.
Muscles requiring fine control (like eye muscles) have fewer muscle cells per motor neuron (about 10).
Muscles requiring brute strength (like leg muscles) have many muscle cells per motor neuron (about 1000).

Skeletal Muscle Fiber Types

Slow twitch fibers break down ATP slowly, and the sarcoplasmic reticulum is further away from the myofibrils. They are best for endurance activities. They also have:
- More mitochondria.
- A better supply of blood for oxygen and nutrient delivery.
- Oxygen is stored in myoglobin.
- Low glycogen levels.
- Low creatine phosphate.
Fast twitch fibers break down ATP quickly and have a sarcoplasmic reticulum that is close to the myofibrils. They contract rapidly, and are therefore best for power activities. They also have:
- More glycogen and creatine phosphate.
- Fewer mitochondria.
- Fewer blood vessels.
- No myoglobin.
Muscles contain both slow twitch and fast twitch fibers in varying amounts.

Exercise and Muscles

Strength training builds more fast twitch myofibrils, increases glycogen and creatine phosphate stores, and increases muscle mass.
Endurance training increases blood vessels to muscle cells, increases the number of mitochondria, and increases myoglobin in slow twitch muscle fibers. It also improves an individual's aerobic capacity.

Benefits of Exercise for Muscles

Exercise builds muscle mass (strength training)
Exercise boosts endurance (endurance training)
Exercise slows muscle deterioration caused by aging (starts around 30).
Muscle tissue burns calories (like fat), and more muscle mass makes it easier to control weight.

Comparison of Muscle Types

Location and Function
- Skeletal muscle: attached to bones by tendons for voluntary movement
- Smooth muscle: artery walls, vein walls, digestive system, reproductive system and urinary system. Involuntarily controls blood vessel diameter and hollow organ movements
- Cardiac muscle: Heart, involuntarily pumps blood
Structure
- Skeletal muscle: Long, cylindrical, and multinucleated.
- Cardiac muscle: Short, with blunt ends connected by gap junctions. These junctions allow signals to move rapidly between cardiac muscle cells, resulting in synchronized contractions.
- Smooth muscle: Small spindle cells with gap junctions.

Anabolic Steroid Use

Anabolic steroids mimic testosterone and cause an increase in muscle protein synthesis. This leads to larger, more powerful muscles.
Anabolic steroids have many disadvantages, including:
- Liver tumors/cancer, kidney tumors, severe acne and baldness.
- Men: breast development, rage, shrinking testes, infertility
- Women: facial hair, deepened voice, changes to the menstrual cycle.

Muscle Disorders

Pulled muscle: Some muscle cells are torn apart. This happens when a muscle is stretched too far.
Sore muscles: Result from damaged sarcomeres that are not used regularly. The damage occurs during exercise.

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Description

Test your knowledge on muscle tissue types, structure, and function. This quiz covers the three types of muscle tissue—skeletal, cardiac, and smooth—and their roles in the body. Understand how muscles contract, their attachments, and interactions for movement.