Skeletal Muscle Anatomy and Functions

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Questions and Answers

What is the role of a motor neuron in muscle contraction?

It stores energy needed for muscle movement.

It increases the blood flow to the muscle.

It transmits an impulse to a muscle to cause contraction. (correct)

It protects the muscle fibers from damage.

What is meant by a threshold stimulus?

The minimal level of stimulation required for a muscle fiber to contract. (correct)

The point at which muscle fibers begin to fatigue.

A stimulus that weakens muscle contractions.

The maximum level of stimulation a muscle can receive.

What does the term 'all or none' refer to in muscle physiology?

A muscle fiber always contracts fully once a threshold stimulus is met. (correct)

Muscle fibers can only relax fully or not at all.

A muscle will respond based on the strength of the stimulus.

Muscles can only contract partially in response to weak stimuli.

How does muscle tone contribute to the body?

It stabilizes the position of bones and joints and maintains posture. Signup and view all the answers

What is a motor unit?

The combination of a motor neuron and the muscle fibers it controls. Signup and view all the answers

What is the primary functional role of skeletal muscles?

To produce movement Signup and view all the answers

Which connective tissue covers the entire skeletal muscle?

Epimysium Signup and view all the answers

How many skeletal muscles are included in the muscular system?

Approximately 700 Signup and view all the answers

What characteristic gives skeletal muscle fibers their striped appearance?

The repeating pattern of sarcomeres Signup and view all the answers

What is the role of the endomysium in skeletal muscle?

To cover each muscle fiber and tie them together Signup and view all the answers

What type of muscle tissue is skeletal muscle classified as?

Striated muscle Signup and view all the answers

Which of the following is NOT a function of skeletal muscles?

Producing hormones Signup and view all the answers

What is a unique feature of skeletal muscle fibers?

They are multinucleate and can be very long Signup and view all the answers

What is the primary energy source for muscle contraction?

ATP Signup and view all the answers

What percentage of a resting muscle cell's ATP needs is provided by aerobic metabolism?

95 percent Signup and view all the answers

During muscle contraction, ATP is generated at what rate in comparison to its usage?

At the same rate as it is used Signup and view all the answers

What process primarily occurs in muscle fibers to generate ATP during rest?

Aerobic fatty acid metabolism Signup and view all the answers

What are the end products of aerobic metabolism?

ATP, water, and carbon dioxide Signup and view all the answers

What type of muscle movement is plantar flexion associated with?

Pointing the toes downwards Signup and view all the answers

Inversion movement of the ankle primarily involves which direction?

Turning the sole of the foot inward Signup and view all the answers

Which component is primarily involved in aerobic metabolism within muscle cells?

Mitochondria Signup and view all the answers

What role do tropomyosin strands play in muscle contraction?

They cover the active sites on actin when the muscle is at rest. Signup and view all the answers

Which component is directly responsible for uncovering active sites on thin filaments?

Troponin binding with calcium ions. Signup and view all the answers

What occurs to the I bands during muscular contraction?

They decrease in size. Signup and view all the answers

What describes the position of myosin heads in thick filaments?

Heads project outward, tails point inward. Signup and view all the answers

What must occur for myosin heads to attach to actin during contraction?

Calcium must unlock active sites on actin. Signup and view all the answers

Which statement about the sliding filament theory is correct?

Thick filaments remain stationary while thin filaments slide toward the center. Signup and view all the answers

What is the main function of the neuromuscular junction?

To transmit signals from motor neurons to muscle fibers. Signup and view all the answers

What causes myosin heads to detach from actin during the contraction cycle?

The binding of a new molecule of ATP. Signup and view all the answers

What is the primary end product of glycolysis?

Pyruvate Signup and view all the answers

Which process occurs if pyruvate is produced faster than it can be used by mitochondria?

It is converted to lactic acid Signup and view all the answers

What is the primary cause of muscle fatigue in endurance athletes?

Depletion of energy reserves and pH decline Signup and view all the answers

What is NOT a part of the recovery period for muscles?

Increasing exercise intensity Signup and view all the answers

What determines muscle performance in terms of endurance?

Time a specific activity can be sustained Signup and view all the answers

Which type of skeletal muscle makes up about 60 percent of skeletal muscles and is involved in posture?

Axial muscles Signup and view all the answers

Which factor does NOT influence muscle performance?

Dietary intake of carbohydrates Signup and view all the answers

What happens during glycolysis in terms of ATP production?

It produces 4 ATP per glucose but nets 2 ATP Signup and view all the answers

Study Notes

Introduction

Muscle tissue is one of four primary tissue types.
It is comprised of elongated cells specialized for contraction.
Three main types of muscle tissue are skeletal, cardiac, and smooth.

Skeletal Muscles

Composed of skeletal muscle tissue.
Contain other tissues, including connective, nervous, and vascular.
Attach to bones directly or indirectly.
The muscular system contains around 700 skeletal muscles.

Skeletal Muscle Functions

Producing movement.
Maintaining posture and body position.
Providing soft tissue support.
Guarding entrances and exits.
Maintaining body temperature.
Storing nutrients.

Organization of Skeletal Muscle Tissue

Composed of skeletal muscle tissue, connective tissue, blood vessels, and nerves.
Each skeletal muscle cell is called a muscle fiber.

Connective Tissue Organization

Epimysium covers the entire muscle.
Perimysium divides the muscle into fascicles (bundles of muscle fibers).
Endomysium covers each muscle fiber and ties them together.

Features of Skeletal Muscle Fibers

Can grow up to 60 centimeters in length.
Each fiber contains hundreds of nuclei.
Have a repeating pattern that creates a striated appearance.

Thin Filaments

Thin, twisted strands composed primarily of the protein actin.
Active sites are covered by tropomyosin strands at rest.
Tropomyosin strands are held in place by troponin.
Contain active sites where thick filaments can bind.

Thick Filaments

Composed of the protein myosin.
Myosin molecules have a tail and globular head.
Tails point inward while heads project outward.
Heads interact with active sites on actin to initiate contraction.

Sliding Filament Theory

Explains sarcomere contraction.
Observed changes during contraction include:
- I bands becoming smaller.
- Z lines moving closer together.
- H bands decreasing.
- Zones of overlap getting larger.
- A bands remaining the same length.
Theory concludes that thin filaments slide toward the center of the sarcomere, while thick filaments stay in place.

Mechanism for Sliding Filaments

Myosin heads of thick filaments bind to active sites on thin filaments, forming cross-bridges.
Cross-bridges pivot towards the sarcomere center, pulling the thin filaments.
Cross-bridges detach after ATP binding, returning to their original position during ATP hydrolysis (splitting into ADP and P).
This cycle repeats throughout contraction.

The Neuromuscular Junction

Specialized connection between a motor neuron and a skeletal muscle fiber.
Contains an axon terminal of a motor neuron and a motor end plate of a muscle fiber.

Motor Unit

Stimulation of a muscle by a nerve impulse is required for contraction.
Motor neuron transmits an impulse to the muscle, causing the contraction.
Neuromuscular junction (NMJ) is where the nerve ending meets the muscle fiber.
Motor unit refers to the combination of a motor neuron and the muscle fibers it controls.

Muscle Stimulus

A minimum level of stimulus intensity, called the threshold stimulus is required for a muscle fiber to contract.
Once stimulated, the muscle fiber contracts completely, demonstrating an "all or none" response.

Muscle Tone

Resting tension in skeletal muscle.
Some motor units in each muscle are active at all times, even during relaxation.
Helps to stabilize bones and joints, maintain posture, and body position.

Movements Produced by Skeletal Muscle Contractions

Dorsiflexion and plantar flexion: Upward and downward ankle movements.
Inversion and eversion: Sideward ankle movements.
Flexion: Decreasing the angle between bones.
Extension: Increasing the angle between bones.
Abduction: Moving a limb away from the midline.
Adduction: Moving a limb towards the midline.
Rotation: Moving a bone around its longitudinal axis.

ATP as the Energy Source for Muscle Contraction

Large amounts of ATP are required for muscle contraction.
Resting muscle fibers have enough energy reserves to sustain contraction until new ATP is produced.
During contraction, ATP is generated at the same rate it is used.

Aerobic Metabolism

Requires oxygen.
Provides approximately 95% of ATP for resting muscle cells.
Occurs in the mitochondria.
Involves breaking down organic substrates through a series of chemical reactions.
Produces ATP, water, and carbon dioxide.
Resting muscle fibers predominantly rely on aerobic fatty acid metabolism for ATP production.

Glycolysis

Breaks down glucose into pyruvate.
Occurs in the cytoplasm of the cell.
Does not require oxygen (anaerobic).
Produces only 2 ATP per glucose molecule.
If pyruvate accumulates faster than it can be used, it is converted to lactic acid.
Lactic acid accumulation can lead to pH problems within cells.

Muscle Fatigue

Occurs when a muscle can no longer perform at the required level, even with stimulation.
Caused by the depletion of energy reserves or a decline in pH due to lactic acid production.
Affects endurance athletes after they exhaust their glycogen and lipid stores.
Sprinters experience fatigue more quickly because they rapidly build up lactic acid, lowering tissue pH.

The Recovery Period

The time it takes for a muscle to return to its pre-exertion state, involving:
- Restoring oxygen levels.
- Removing lactic acid.
- Replacing intracellular energy reserves.
- Releasing heat produced during contraction.

Muscle Performance

Measured by force, the maximum tension produced by a muscle or muscle group.
Measured by endurance, the duration of a particular activity.
Two key factors affect muscle performance:
- Muscle fiber types (fast-twitch and slow-twitch).
- Physical conditioning or training.

Divisions of Skeletal Muscles

Axial muscles:
- Arise from the axial skeleton.
- Represent about 60% of skeletal muscles.
- Position the head, spinal cord, and move the rib cage.
Appendicular muscles:
- Stabilize or move the appendicular skeleton.

Major Skeletal Muscles, Anterior View

Includes a general overview of the major skeletal muscles on the anterior (front) of the body.

Major Skeletal Muscles, Posterior View

Includes a general overview of the major skeletal muscles on the posterior (back) of the body.

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Description

Explore the structure and functions of skeletal muscle tissue in this quiz. Learn about the organization of skeletal muscles, their roles in the muscular system, and the connective tissues associated with them. Test your knowledge on muscle types and their specific functions.