Biology Chapter 6: The Muscular System

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Questions and Answers

Which of the following factors is NOT associated with muscle fatigue?

Ion imbalances (Ca2+, K+)

Oxygen deficit and lactic acid accumulation

Decrease in energy (ATP) supply

Increase in ATP supply (correct)

What characterizes isotonic contractions?

Muscles contract against an immovable object

Muscle filaments slide past each other (correct)

Tension decreases during the contraction

Muscle length does not change

Which type of exercise leads to increased muscle size and strength?

Resistance exercise (correct)

Isometric exercise

Aerobic exercise

Flexibility exercise

Muscle tone is primarily described as:

State of continuous partial contractions Signup and view all the answers

After strenuous exercise, how is the oxygen deficit repaid?

Through rapid, deep breathing Signup and view all the answers

What is the primary function of muscles in the body?

To facilitate all types of body movement Signup and view all the answers

Which of the following muscle types is known for being under conscious control?

Skeletal muscle Signup and view all the answers

Which term best describes muscle cells?

Myofibers Signup and view all the answers

What characteristic differentiates skeletal muscle fibers from others?

Striations and multinucleation Signup and view all the answers

Which connective tissue layer covers the entire skeletal muscle?

Epimysium Signup and view all the answers

What type of connective tissue attachment is described as cordlike structures and primarily made of collagen fibers?

Tendons Signup and view all the answers

Which prefix is commonly used to refer to muscle?

Myo- Signup and view all the answers

Which characteristic is unique to smooth muscle compared to other muscle types?

Unconscious control Signup and view all the answers

What is the term for the connective tissue that encloses a single muscle fiber?

Endomysium Signup and view all the answers

What is the primary role of skeletal muscle in addition to producing movement?

Generate heat Signup and view all the answers

Which muscle type is characterized as involuntary and found in internal organs?

Smooth muscle Signup and view all the answers

What structure is responsible for the striated appearance of skeletal muscle?

Sarcomeres Signup and view all the answers

In cardiac muscle, what structures connect branching cells together?

Intercalated discs Signup and view all the answers

Which muscle type is found only in the walls of the heart?

Cardiac muscle Signup and view all the answers

What is the appearance of smooth muscle fibers?

Non-striated and spindle-shaped Signup and view all the answers

What does the 'A band' in a skeletal muscle fiber contain?

Both thick and thin filaments Signup and view all the answers

What must stimulate skeletal muscles for contraction?

Motor neuron Signup and view all the answers

What is the neurotransmitter that stimulates skeletal muscle?

Acetylcholine (ACh) Signup and view all the answers

Which area serves as the association site between the nerve and muscle?

Neuromuscular junction Signup and view all the answers

What happens when a nerve impulse reaches the axon terminal?

Calcium channels open Signup and view all the answers

What is established when enough ACh is released?

Depolarization Signup and view all the answers

What fills the synaptic cleft between the nerve and muscle?

Interstital fluid Signup and view all the answers

What occurs to sodium ions during the muscle stimulation process?

They enter the cell more than potassium exits Signup and view all the answers

What triggers the release of acetylcholine in the axon terminal?

Calcium ion entry Signup and view all the answers

What initiates the action potential in a nerve cell?

Opening of sodium channels Signup and view all the answers

Which enzyme is responsible for breaking down acetylcholine after its release?

Acetylcholinesterase Signup and view all the answers

How does a contraction occur according to the sliding filament theory?

Calcium ions allow myosin-binding sites to be exposed Signup and view all the answers

What is the result when potassium ions leave the nerve cell during repolarization?

The cell returns to its resting state Signup and view all the answers

What are the two ways graded responses can be produced in skeletal muscle?

By changing the duration of muscle stimulation and the number of muscle cells being stimulated Signup and view all the answers

What does the sodium-potassium pump accomplish after an action potential?

It restores sodium and potassium ions to their original concentrations Signup and view all the answers

What characterizes a single, brief contraction of a muscle?

It is known as a twitch contraction. Signup and view all the answers

What occurs when nerve impulses are delivered at a rapid rate to a muscle?

Contractions are summed together. Signup and view all the answers

What is meant by 'graded responses' in muscle fiber contraction?

Different levels of stimulation can affect contraction strength Signup and view all the answers

What role does ATP play in muscle contraction?

It facilitates the detachment of myosin heads from actin Signup and view all the answers

What happens to muscle contractions as stimulations become more frequent?

Muscle contractions become smoother and more effective. Signup and view all the answers

Which statement is true about acetylcholine's function in muscle contraction?

It stimulates muscle contraction when released at the neuromuscular junction Signup and view all the answers

What is fused (complete) tetanus?

A state where contractions appear smooth and sustained without relaxation. Signup and view all the answers

How does muscle force depend on the stimuli applied?

It is dependent on the number of fibers stimulated. Signup and view all the answers

What is a result of activating all motor units in a muscle?

The muscle contraction achieves maximum strength. Signup and view all the answers

What is unfused tetanus characterized by?

Muscle contractions are steady but interspersed with relaxation. Signup and view all the answers

Study Notes

Chapter 6: The Muscular System

Muscles are responsible for all types of body movement
Three basic muscle types are found in the body: skeletal, smooth, and cardiac
Skeletal and smooth muscle cells are elongated (muscle cell = muscle fiber)
Muscle contractions are due to the movement of microfilaments
All muscles share terminology, including prefixes like "mys-" referring to muscle and "prefix" referring "flesh".
Most skeletal muscle fibers are attached to bones.
Skeletal muscle cells are multinucleated and cigar-shaped.
Skeletal muscle is also known as striated muscle because of its obvious stripes
Skeletal muscle is also known as voluntary muscle because it's the only muscle tissue subject to conscious control
Connective tissue surrounds and bundles skeletal muscle cells.
The epimysium encloses a single muscle fiber.
The perimysium wraps around a fascicle (bundle) of muscle fibers.
The epimysium covers the entire skeletal muscle.
The epimysium is on the outside of the epimysium.
The epimysium blends into connective tissue attachments, forming cordlike structures (tendons) or sheetlike structures (aponeuroses).
Tendons and Aponeuroses attach muscles to bones, cartilages, or connective tissue coverings.
Smooth muscle has no striations and is not under conscious control.
Smooth muscle is commonly found in the walls of hollow organs (such as the stomach, urinary bladder, and respiratory passages).
Smooth muscle fibers are spindle-shaped.
Smooth muscle contractions are sustained.
Cardiac muscle has striations and is found only in the walls of the heart.
Cardiac muscle cells are uninucleate (one nucleus) and branching.
Cardiac muscle cells are joined by intercalated discs.
Cardiac muscle contracts at a rate set by the pacemaker.
Skeletal muscle has three important roles: maintaining posture and body position, stabilizing joints, generating heat.

Microscopic Anatomy of Skeletal Muscle

Myofibrils, specialized plasma membranes, and organelles are inside muscle cells
Light and dark bands give skeletal muscle its striated appearance
I band = light band (contains only thin filaments); Z disc is a midline interruption
A band = dark band (contains the entire length of thick filaments); H zone is a lighter central area; M line is in the center of H zone
Sarcomere is the contractile unit of muscle fibers; it’s the structural and functional unit of skeletal muscle
Myofilaments produce banding (striped) patterns; thick filaments are myosin filaments; thin filaments are actin filaments
Thick filaments consist of the protein myosin; contain ATPase enzymes which split ATP to release energy for muscle contractions
Myosin heads act as cross bridges when they link thick and thin filaments during contraction
Thin filaments consist of the contractile protein actin; actin is anchored to the Z disc; at rest, the H zone within the A band lacks actin filaments
Sarcoplasmic reticulum (SR) is a specialized smooth endoplasmic reticulum which surrounds myofibrils and stores and releases calcium

Stimulation and Contraction of Skeletal Muscle Cells

Functional properties of skeletal muscle include responsiveness, conductivity, contractility, and elasticity.
Responsiveness (also called irritability) is the ability to receive and respond to a stimulus.
Conductivity is the ability to propagate an electrical signal over the muscle cell membrane.
Contractility is the ability to forcibly shorten.
Elasticity is the ability to recoil to resting length after shortening or stretching.

The Nerve Stimulus and Action Potential

Skeletal muscles must be stimulated by a neuron to contract.
The association site of the axon terminal of the motor neuron and the sarcolemma of a muscle is known as the neuromuscular junction.
ACh (acetylcholine) is a chemical released by nerve impulse upon arrival at the axon terminal, stimulating skeletal muscle.
The synaptic cleft is the space between the nerve and muscle.
When a nerve impulse reaches the axon terminal of the motor neuron, calcium channels open and calcium enters the terminal.
Calcium ions causes synaptic vesicles to release acetylcholine (ACh).
ACh diffuses across the synaptic cleft and attaches to the sarcolemma of the muscle cell.
If enough ACh is released, the sarcolemma becomes temporarily more permeable to sodium ions (Na+).
More Na+ ions enter than K+ ions leave, establishing an electrical gradient (depolarization), opening more Na+ channels.
An action potential is created.
The action potential is conducted along the sarcolemma from one end of the cell to the other.
Acetylcholinesterase (AChE) breaks down ACh into acetic acid and choline, ending muscle contraction
A single nerve impulse produces only one contraction.
Cell returns to resting state when potassium (K+) ions exit the cell; sodium-potassium pump moves sodium (Na+) and potassium (K+) ions back to their original positions.

Mechanism of Muscle Contraction: The Sliding Filament Theory

Calcium (Ca2+) binds regulatory proteins on thin filaments, exposing myosin-binding sites.
Myosin heads attach to thin filaments, causing them to slide toward the center of the sarcomere.
Contraction occurs as the cell shortens.
A cross-bridge attaches and detaches several times during a contraction.
ATP provides energy for the sliding process, continuing as long as calcium is present.

Contraction of Skeletal Muscle as a Whole

Graded responses are different degrees of skeletal muscle shortening produced by changing the frequency of stimulation or the number of muscle cells being stimulated.
Muscle fibers contract to their maximum when adequately stimulated.
Within a whole skeletal muscle, not all fibers may be stimulated during the same interval.
Different of muscle fiber contractions may give differing responses.
Graded responses produce different degrees of skeletal muscle shortening.
Muscle response to increasingly rapid muscle stimulation results in muscle contractions becoming “summed,” where one contraction is immediately followed by another.
When stimulations become more frequent, contractions get stronger and smoother.
Muscle now exhibits unfused tetanus.
Fused (complete) tetanus is achieved when the muscle is stimulated so rapidly that there is no evidence of muscle relaxation, resulting in smooth and sustained contractions.
Muscle force depends on the number of fibers stimulated.
Contraction of more fibers results in greater muscle tension.
When all motor units are active, the muscle contraction is as strong as it can get.

Providing Energy for Muscle Contraction

ATP is the only energy source that powers muscle contraction directly.
Muscle fibers store a small amount of ATP, which is quickly used up.
Other pathways must produce ATP after the initial ATP is depleted.
Three pathways to regenerate ATP include direct phosphorylation of ADP by creatine phosphate, aerobic pathway, and anaerobic glycolysis and lactic acid formation.

Types of Muscle Contractions

Isotonic contractions: myofilaments slide past each other during contractions; the muscle shortens and movement occurs (e.g., bending the knee, lifting weights, smiling).
Isometric contractions: muscle filaments try to slide, but the muscle is pitted against an immovable object; tension increases, but muscles do not shorten (e.g., pushing palms together).

Muscle Tone

Muscle tone is the state of continuous partial contractions of muscles.
It results from different motor units being stimulated systematically.
Muscle tone maintains firmness and readiness for action.

Effect of Exercise on Muscles

Aerobic exercise increases muscle size, strength, and endurance, making the body's metabolism more efficient and improving digestion and coordination. Resistance exercise increases muscle size and strength through individual muscle fibers enlarging.
Muscle fatigue and oxygen deficit occur when muscle activity is strenuous and prolonged; ion imbalances, oxygen deficit, and lactic acid accumulation contribute to muscle fatigue.

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Description

Explore the intricacies of the muscular system in this quiz focused on Chapter 6 of biology. Learn about the three types of muscle: skeletal, smooth, and cardiac, along with their distinctive features and functions. Test your knowledge on concepts such as muscle contractions, terminology, and connective tissue roles.