Muscle Anatomy and Functions

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Questions and Answers

What is one of the main functions of muscle tissue?

Generate heat as they contract (correct)

Serve as the body's main source of fat storage

Regulate blood pressure

Protect internal organs

Which type of muscle is characterized by being striated and under voluntary control?

Involuntary muscle

Smooth muscle

Skeletal muscle (correct)

Cardiac muscle

Which characteristic is NOT shared by all types of muscle tissue?

Response to nervous impulses

Presence of myofibrils

Striated appearance (correct)

Ability to contract

What primarily plays a role in regulating cardiac muscle contraction?

Pacemaker cells Signup and view all the answers

Which statement about smooth muscle is correct?

It is located in hollow organs. Signup and view all the answers

What defines a skeletal muscle fiber?

They are multinucleate and can contract rapidly. Signup and view all the answers

Which characteristic of muscle tissue contributes to movement?

Ability to generate force Signup and view all the answers

What is a common feature of cardiac muscle cells?

They are striated but shorter than skeletal muscle fibers. Signup and view all the answers

What is the primary function of contractility in muscle fibers?

Ability to shorten forcibly when stimulated Signup and view all the answers

Which structure in muscle fibers increases the surface area for electrical nerve transmission?

T tubules Signup and view all the answers

Which functional group of muscles is responsible for opposing or reversing a movement?

Antagonist Signup and view all the answers

What is the composition of a sarcomere within a myofibril?

Both actin and myosin filaments Signup and view all the answers

What role do tropomyosin and troponin play in muscle contraction?

Block and unblock myosin binding sites Signup and view all the answers

Which muscle attachment type refers to the point connected to movable bones?

Insertion Signup and view all the answers

What causes the striated appearance of skeletal muscle fibers?

The arrangement of actin and myosin filaments Signup and view all the answers

What is the role of synergist muscles during contraction?

Enhance the effectiveness of the prime mover Signup and view all the answers

Which of the following is NOT a function of muscle tissues?

Indefinite extension Signup and view all the answers

What type of muscle tissue is primarily responsible for voluntary movement?

Skeletal muscle Signup and view all the answers

What role does calcium play in muscle contraction?

Ca2+ binds to troponin, which then moves tropomyosin. Signup and view all the answers

What occurs at low intracellular Ca2+ concentrations?

Muscle fibers remain relaxed. Signup and view all the answers

What is the first step in the cross bridge cycle?

Myosin head binds to actin. Signup and view all the answers

Which process produces the most ATP in muscle fibers?

Aerobic respiration Signup and view all the answers

How does ATP contribute to muscle function?

ATP allows myosin to detach from actin. Signup and view all the answers

During the cross bridge cycle, what happens after the myosin head undergoes a power stroke?

The myosin head binds to a new ATP molecule. Signup and view all the answers

Where is Ca2+ reabsorbed after muscle contraction?

Through the sarcoplasmic reticulum. Signup and view all the answers

What effect does ATP hydrolysis have on the myosin head during contraction?

It provides energy for the power stroke. Signup and view all the answers

What is the opening voltage for voltage-gated sodium channels?

-70 mV Signup and view all the answers

Which of the following correctly describes the role of calcium channels in cardiac muscle contraction?

Open during early depolarization at -40 mV and close towards the plateau phase at +10 mV to 0 mV Signup and view all the answers

What event triggers the contraction of the ventricles in the heart?

Atria contraction through the AV node Signup and view all the answers

What role do slow potassium channels play in the cardiac cycle?

Open at0 mV and close at -90 mV, returning the membrane potential to resting state Signup and view all the answers

What does the QRS complex in an electrocardiogram represent?

Ventricular depolarization Signup and view all the answers

Which of the following phases occurs during diastole of the cardiac cycle?

Blood is filling the heart as the muscle relaxes Signup and view all the answers

What percentage of cardiomyocytes are pacemaker cells responsible for initiating heart contractions?

1% Signup and view all the answers

What is the purpose of the plateau phase in cardiac muscle contraction?

To prevent sustained contractions and allow relaxation Signup and view all the answers

What is the primary function of arteries within the circulatory system?

To carry blood away from the heart Signup and view all the answers

Which layer of blood vessel walls is consistent across all types of blood vessels?

Endothelium Signup and view all the answers

What does a systolic blood pressure reading of 120 mmHg represent?

Blood pressure 120 mmHg above atmospheric pressure Signup and view all the answers

What is the role of venous valves in the circulatory system?

To prevent the backflow of blood Signup and view all the answers

Which factor is NOT indicated to affect blood pressure efficiency?

Capacity of veins Signup and view all the answers

What is primarily measured to determine blood pressure?

Pressure in arteries near the heart Signup and view all the answers

What occurs during the baroreceptor reflex in response to high blood pressure?

Heart rate decreases Signup and view all the answers

Which statement about capillaries is accurate?

They connect arterioles and venules Signup and view all the answers

Study Notes

Muscle Function

Muscle is an organ composed of muscle tissue, blood vessels, nerves, fat, and connective tissue
Muscle makes up nearly 50% of the body's mass
Muscle tissue is responsible for movement, maintaining posture, stabilizing joints, and generating heat

Muscle Types

There are three types of muscle tissue: skeletal, cardiac, and smooth
Skeletal muscles are the longest type
Skeletal muscles are voluntary and striated, while cardiac muscle is involuntary and striated
Smooth muscle is found in the walls of hollow organs and other areas, it is involuntary and lacks striations

Muscle Characteristics

All muscle tissues share four characteristics: excitability, contractility, extensibility, and elasticity

Skeletal Muscle Structure

Skeletal muscle is organized in a hierarchy: muscle, fascicle, muscle fiber
Muscle fibers are multinucleated, cylindrical cells that are the functional units of skeletal muscle
Muscle fibers contain numerous mitochondria and are surrounded by the sarcolemma and sarcoplasm

Muscle Attachments

Muscles span joints and attach to bones
The origin is the attachment to the stationary bone, while the insertion attaches to the movable bone

Muscle Actions

Muscles work in groups to produce movement
Prime movers (agonists) produce a specific movement, antagonists oppose or reverse that movement, and synergists assist prime movers

Microscopic Anatomy

Myofibrils are the contractile units within muscle fibers
Sarcomeres are the repeating units within myofibrils, composed of actin and myosin filaments
The A band contains both actin and myosin filaments, while the I band only contains actin
Titin and nebulin are proteins that stabilize and regulate the structure of the sarcomere

Actin and Myosin

Myosin filaments are thick and composed of myosin protein dimers, with heads that bind to ATP
Actin filaments are thin and composed of two actin chains twisted into a helix
Tropomyosin blocks the binding sites on actin, while troponin is a calcium-binding protein that regulates tropomyosin's position

Muscle Contraction

Calcium binds to troponin, causing a conformational change that shifts tropomyosin and exposes myosin binding sites on actin
The cross-bridge cycle is initiated when ADP-bound myosin heads bind to actin
The "power stroke" of the cross-bridge cycle is powered by the release of ADP and the stored energy from ATP hydrolysis
ATP binding to myosin heads causes their detachment from actin, and ATP hydrolysis resets the myosin head for another power stroke.

Sources of ATP

Muscle fibers store oxygen (myoglobin) and glucose (glycogen)
Glycolysis is a rapid, anaerobic process that produces a small amount of ATP
Aerobic respiration, which requires oxygen, produces a larger amount of ATP

Cardiac Muscle

Cardiac muscle cells are shorter than skeletal muscle fibers and possess a less pronounced striation pattern
Cardiac muscle is regulated by pacemaker cells, the autonomic nervous system, and epinephrine

Pacemaker Cells

Pacemaker cells spontaneously depolarize and initiate the heart's rhythmic contractions
The sinoatrial (SA) node depolarizes the atria, causing atrial contraction
The impulse travels to the ventricles through the atrioventricular (AV) node and AV bundle, leading to ventricular contraction

Electrocardiography

An electrocardiogram (ECG) records the electrical signals in the heart
The P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization

Cardiac Cycle

The cardiac cycle describes the blood flow through the heart during one heartbeat
Systole is the period of ventricular contraction, during which blood is ejected to the pulmonary trunk and aorta
Diastole is the period of ventricular relaxation, during which the ventricles fill with blood

Blood Vessels

Arteries carry oxygenated blood away from the heart, except in the pulmonary circulation and umbilical vessels
Veins carry deoxygenated blood toward the heart, except in the pulmonary circulation and umbilical vessels
Capillaries are tiny vessels that connect arteries to veins and facilitate the exchange of nutrients, gases, and waste products with tissue cells

Blood Pressure

Blood pressure is the force of blood exerted on the walls of blood vessels
It is measured in millimeters of mercury (mmHg) and is typically measured in arteries near the heart
Systolic pressure is the peak pressure during ventricular contraction, while diastolic pressure is the pressure during ventricular relaxation
Healthy blood pressure is typically below 120/80 mmHg, readings above this can indicate problems with the heart or blood vessel elasticity

Blood Pressure Distribution

Arteries have the highest blood pressure, followed by arterioles, capillaries, venules, and veins
The low blood pressure in veins is assisted by the muscular pump and venous valves to ensure blood return to the heart

The Baroreceptor Reflex

Baroreceptors are specialized sensory receptors located in the walls of blood vessels that detect changes in blood pressure
When blood pressure decreases, baroreceptors send signals to the brain, which triggers an increase in heart rate and vasoconstriction to increase blood pressure
When blood pressure increases, baroreceptors send signals to the brain, which triggers a decrease in heart rate and vasodilation to decrease blood pressure

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Description

Explore the fascinating world of muscle anatomy and functions in this quiz. Learn about the different types of muscle tissue, their characteristics, and the structural organization of skeletal muscle. Test your knowledge on how muscles contribute to movement and overall body functions.