Muscle Tissue Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the primary function of muscle cells?

To store and release oxygen

To transport nutrients

To convert chemical energy into mechanical energy (correct)

To synthesize proteins

Which type of muscle tissue is responsible for the pumping action of the heart?

Smooth muscle

Visceral muscle

Skeletal muscle

Cardiac muscle (correct)

Which of the following properties of muscle tissue allows it to shorten with force?

Excitability

Extensibility

Contractility (correct)

Elasticity

Which type of muscle tissue is found in the walls of hollow organs like the stomach and intestines?

Smooth muscle (D) Signup and view all the answers

What is the primary characteristic that distinguishes skeletal muscle from smooth muscle?

The presence of striations (B) Signup and view all the answers

Which of the following statements is TRUE regarding cardiac muscle?

It is found only in the heart (D) Signup and view all the answers

How does smooth muscle contribute to the movement of food through the digestive system?

By creating wave-like contractions called peristalsis (A) Signup and view all the answers

What is the role of intercalated discs in cardiac muscle?

They allow for the rapid transmission of electrical impulses between muscle cells (A) Signup and view all the answers

What is the role of troponin in muscle contraction?

It binds Ca ions and regulates muscle contraction. (C) Signup and view all the answers

Which component of the sarcomere is responsible for the dark regions visible under a microscope?

Myosin filaments (B) Signup and view all the answers

What is a sarcomere?

The distance between two Z membranes. (D) Signup and view all the answers

Which protein connects the cytoskeleton of a muscle fiber to the extracellular matrix?

Dystrophin (A) Signup and view all the answers

What is the primary function of transverse tubules (T tubules) in muscle cells?

They provide rapid transmission of action potential into the muscle cell. (C) Signup and view all the answers

Which of the following statements about actin and myosin is correct?

Myosin filaments demonstrate anisotropic properties. (B) Signup and view all the answers

What is the significance of the M line in the sarcomere structure?

It connects myosin tails together. (C) Signup and view all the answers

What could result from a deficiency of dystrophin in muscle fibers?

Impaired muscle contraction. (C) Signup and view all the answers

What is the primary function of the connective tissue layers (endomysium, perimysium, epimysium) in muscle tissue?

They provide support, strength, flexibility, and electrical isolation. (C) Signup and view all the answers

Which connective tissue surrounds each individual muscle fiber?

Endomysium (D) Signup and view all the answers

What is the major structural component of thick filaments in skeletal muscle?

Myosin (C) Signup and view all the answers

Which statement accurately describes the role of tropomyosin in muscle fibers?

It blocks the active sites on actin in a relaxed muscle fiber. (C) Signup and view all the answers

What do myofibrils mainly consist of?

Myofilaments (C) Signup and view all the answers

What is the function of the ATP binding site found on myosin?

It hydrolyzes ATP for energy release. (A) Signup and view all the answers

What composes the sarcoplasm of a muscle fiber?

Glycogen granules and myoglobin (D) Signup and view all the answers

What is the main characteristic of the epimysium in skeletal muscle?

It is a dense regular connective tissue surrounding the entire muscle. (D) Signup and view all the answers

What is the primary function of the sarcoplasmic reticulum (SR) in skeletal muscle?

Uptake, storage, and release of calcium ions (C) Signup and view all the answers

Which structure forms a system of hollow sheets and tubes within the sarcomere?

Longitudinal elements (B) Signup and view all the answers

What key event must occur to trigger skeletal muscle contraction?

A rise in intracellular Ca2+ levels (B) Signup and view all the answers

Which protein in the terminal cisternae weakly binds calcium ions?

Calsequestrin (B) Signup and view all the answers

How does the resting membrane potential (RMP) of skeletal muscle compare to that of nerve cells?

Skeletal muscle RMP is approximately -90 mV (D) Signup and view all the answers

What is the conduction speed of action potentials along the skeletal muscle membrane?

5 m/s (B) Signup and view all the answers

Which part of the skeletal muscle is responsible for impulse transmission from nerve to muscle?

Neuromuscular junction (C) Signup and view all the answers

What is the approximate duration of the absolute refractory period in skeletal muscle?

1-3 ms (A) Signup and view all the answers

What happens when acetylcholine binds to nicotinic receptors on the postsynaptic membrane?

The receptors undergo a change allowing sodium and potassium ions to pass. (B) Signup and view all the answers

What is the role of acetylcholinesterase in the neuromuscular junction?

To catalyze the breakdown of acetylcholine in the synaptic cleft. (D) Signup and view all the answers

What triggers the release of acetylcholine from the vesicles at the neuromuscular junction?

The binding of calcium ions after the opening of calcium channels. (D) Signup and view all the answers

What is the synaptic cleft?

The narrow gap between the presynaptic neuron and the postsynaptic muscle cell. (D) Signup and view all the answers

What initiates the depolarization of the postsynaptic membrane at the neuromuscular junction?

The binding of acetylcholine to its receptors. (C) Signup and view all the answers

What type of channels open in response to the wave of depolarization in the axon terminal?

Calcium channels. (C) Signup and view all the answers

What is the endplate potential?

A local depolarization of the postsynaptic membrane. (C) Signup and view all the answers

What is the main consequence of curare binding to ACh receptors?

Inhibition of ion channel opening (B) Signup and view all the answers

Which structures are responsible for releasing acetylcholine at the neuromuscular junction?

Presynaptic vesicles. (A) Signup and view all the answers

Which step initiates the cross-bridge cycle?

Binding of energized myosin to actin (A) Signup and view all the answers

What is released from myosin during the power stroke of the cross-bridge cycle?

ADP and Pi (B) Signup and view all the answers

What is the function of ATP in the cross-bridge cycle?

Energizes the myosin cross-bridge (C) Signup and view all the answers

How does the binding of ATP affect myosin's affinity for actin?

Decreases affinity for actin (C) Signup and view all the answers

What type of paralysis results from the action of curare?

Complete muscle paralysis (D) Signup and view all the answers

Which of the following best describes the sliding filament model of contraction?

Activation of cross-bridges generates muscle force (D) Signup and view all the answers

What happens to myosin right after it releases ADP and Pi during the power stroke?

It must be re-energized to continue cycling (B) Signup and view all the answers

Study Notes

Muscle Physiology

Muscle tissue constitutes 50% of the body weight.
Muscle cells are the primary cells in muscle tissue.
Specialized muscle cells convert chemical energy into mechanical energy using ATP.
Diverse muscle types exist, specialized for functions like locomotion, blood pumping, and food movement.

Muscular System Functions

Muscle movement enables body motion.
Muscles maintain posture.
Breathing relies on muscle action.
Muscles produce body heat.
Muscle contractions are crucial for communication and transmitting signals.
Control over internal organs and blood vessel constriction involves muscle action.
Muscle action is vital for heart function.

Properties of Muscle

Contractility: Ability of a muscle to shorten with force.
Excitability: Capacity of a muscle to respond to a stimulus.
Extensibility: Ability of muscle to stretch.
Elasticity: Ability of a muscle to recoil to its original resting length after stretching.

Muscle Tissue Types

Skeletal Muscle: Attached to bones, striated, voluntary (conscious control), multinucleated.
- Attached to bones.
- Nuclei are multiple and peripherally located.
- Striated.
- Voluntary and involuntary (reflexes).
Cardiac Muscle: Found in the heart; striated, involuntary, single nucleus, intercalated discs.
- Found in the heart.
- Single nucleus centrally located.
- Striations.
- Involuntary, intercalated disks.
Smooth Muscle: Found in walls of hollow organs, blood vessels, eye, and glands. Not striated, involuntary, single nucleus, gap junctions.
- Walls of hollow organs, blood vessels, eye, glands, and skin
- Single nucleus centrally located.
- Not striated.
- Involuntary; gap junctions in visceral smooth muscle.

Skeletal Muscle (Striated)

Attaches to the skeleton.
Microscopically, has stripes called striations.
Voluntary muscle, controlled consciously.
Multinucleated.

Cardiac Muscle

Occurs only in the heart.
Striated, branching pattern; intercalated disks.
Involuntary & automatic.
Usually one nucleus but may have more.
Neural controls; adjusts heart rate.

Smooth Muscle

Found within most organs, arteries, and veins.
Helps move substances through internal body channels via peristalsis.
Not striated; involuntary.
Single nucleus.

Structure of the Muscle Cell

A single skeletal muscle cell is called a muscle fiber.
Adult skeletal muscle fibers have diameters between 10 and 100 µm and lengths that may extend up to 25 cm.

Embryologic Origin

Muscle fibers form during development via the fusion of undifferentiated, mononucleated cells called myoblasts.
This fusion creates a multinucleated cell.
Skeletal muscle differentiation is complete around birth.

Skeletal Muscle Fiber Repair

Skeletal muscle fibers cannot be replaced by division of existing muscle fibers after birth.
New fibers can form from undifferentiated cells, called satellite cells, located adjacent to the muscle fibers.
Satellite cells differentiate similarly to embryonic myoblasts.

Skeletal Muscle Compensation for Loss

The capacity for forming skeletal muscle fibers is considerable, but doesn't fully repair severe damage.
Muscle tissue loss compensation often occurs through increase in the size of existing muscle fiber (hypertrophy).

Skeletal Muscle: Nerve and Blood Supply

Each muscle receives a nerve, artery, and one or more veins.
These enter near the muscle's center and branch throughout it.
Skeletal muscle fibers (cells) receive nerve endings to control contraction.
Continuous delivery of oxygen and nutrients through arteries is crucial for muscle contraction.
Muscle cell waste removal occurs via veins.

Skeletal Muscle- CT Sheaths

The muscle is surrounded by connective tissue sheaths.
Endomysium: Delicate CT sheath surrounding each muscle fiber (cell).
Perimysium: CT surrounding groups of muscle fibers (fascicles.)
Epimysium: Dense regular CT surrounding the entire muscle.

Skeletal Muscle- CT Sheaths (at each end)

Collagen fibers of the endomysium, perimysium, and epimysium merge to form tendons or aponeuroses.
This provides support, strength, flexibility, and electrical isolation for muscles.

Microscopic Anatomy- Skeletal Muscle Fiber/Cell

Sarcoplasm: Cytoplasm of the muscle fiber.
Sarcolemma: Cell membrane of the muscle fiber.
Myofibrils, sarcoplasmic reticulum, and T tubules are unique to muscle fibers.
Sarcoplasm contains glycosomes (glycogen granules) and myoglobin (oxygen-binding protein).

Myofibrils - Striations

Myofibrils (contractile elements) comprise ~80% of muscle volume.
Made of myofilaments: thick (myosin) and thin (actin).

Ultrastructure of Myofilaments: Thick Filaments

Composed of Myosin protein.
Myosin found in striated muscle is class II myosin.
Myosin has a head and tail.

Ultrastructure of Myofilaments: Thick Filaments (Further Detail)

Each globular head has actin- and ATP-binding sites.
The actin-binding site forms acto-myosin bridges.
The ATP-binding site is an ATPase, hydrolyzing ATP.
Myosin tail regions form the thick filament.

Thin Filaments (with regulatory proteins)

Composed of actin, tropomyosin, and troponin proteins.
Actin: Main component, with myosin-binding sites.
Tropomyosin: Long filaments; blocks active sites in relaxed muscle.
Troponin: Regulatory protein complex.

Troponin

Attaches to thin filaments, tropomyosin, and actin.
Binds calcium ions to trigger muscle contraction.
Consist of three subunits:
- TnT (attaches to tropomyosin)
- TnI (attaches to actin)
- TnC (binds calcium)

Structure of Actin and Myosin

Myofilaments are structured into sarcomeres.
Sarcomeres comprise the contractile units of a myofibril.
Actin and myosin myofilaments are arranged in repeating patterns within the sarcomeres.
Important proteins like titin, nebulin, and dystrophin are also present.

Myofibrils - Striations- Banding

Dark bands (A bands) contain (primarily) myosin.
Lighter bands (I bands) contain primarily actin.
The Z disc is the midline of an I band.
The H zone is a region in the center of the A band where actin and myosin filaments do not overlap.
The M line is the middle of the sarcomere and the attachment point for myosin.

Sarcomere

The smallest functional unit of contraction within a myofibril.
The distance between neighboring Z discs.
Z discs connect the thin filaments.
Shortening of sarcomeres results in muscle contraction.

Myofilaments: Banding Pattern

A transverse dark line (M line) appears in the center of the H zone.
M line represents the protein connections for myosin tails.

Other Proteins

Titin, Nebulin, Actinin, and Dystrophin are proteins involved in muscle structure and function.

Dystrophin

Dystrophin is a cytoplasmic protein.
Integral component of a protein complex associating muscle fibers' cytoskeleton with the extracellular matrix.
Located between the sarcolemma and outermost myofilaments in muscle fibers.

Various Myopathies

Myopathies occur as a result of defects in myofilament proteins.

Transverse Tubules (T-tubules) and Sarcoplasmic Reticulum (SR)

T tubules are invaginations of the muscle cell membrane extending into the sarcoplasm.
Important for rapid action potential transmission.
The SR is specialized endoplasmic reticulum.
Stores, releases calcium ions crucial for controlling contraction and relaxation.
Two structures within each sarcomere: Longitudinal elements, and Terminal cisternae.

The SR (further detail)

Longitudinal elements form a system of hollow sheets and tubes around myofibrils.
Terminal cisternae (lateral sacs) contain calsequestrin, a calcium-binding protein.

Skeletal Muscle Contraction

For contraction, skeletal muscle: gets stimulated by nerve endings, propagates electrical current along its sarcolemma, and has a rise in intracellular Ca2+ levels.

Electrical Characteristics (Skeletal Muscle)

Electrical events in skeletal muscle resemble nerve cells, but there are timing and magnitude differences.
RMP is about -90 mV, compared to -70 mV of nerve cells.
Action potential lasts 2-4 ms vs 0.5-1 ms in nerve cells.
Conduction speed in skeletal muscles is slower (≈5 m/s) than axons (≈100 m/s).

Neuromuscular Junction (NMJ)

Nerve-muscle signal transfer occurs at the NMJ (myoneural junction).
Presynaptic portion: Axon axon terminals.
Postsynaptic portion: Muscle cell membrane.

Neuromuscular Junction (NMJ, Further Detail)

The axon, at the NMJ, branches numerous times.
These numerous branches form the presynaptic terminal portion of the NMJ.
The postsynaptic portion of the NMJ is the muscle cell membrane.
Nicotinic acetylcholine receptors are specifically clustered at postjunctional folds.

Neuromuscular Junction (NMJ, Still More Detail)

Within nerve axon terminals lie membrane enclosed vesicles.
Vesicles contain acetylcholine (ACh).
Mitochondria are plentiful, associated with the terminal metabolic needs.

Neuromuscular Junction (NMJ, Final Detail)

The postsynaptic membrane area presents folds.
These folds locate many nicotinic acetylcholine receptors.

Neuromuscular Junction (NMJ, Ion Considerations).

Chemically gated ion channels increase the permeability of the postsynaptic membrane to ACh.
The synaptic cleft is the narrow space between the nerve and muscle.
ACh must diffuse across the cleft to reach receptors.

Neuromuscular junction

Acetylcholinesterase (AChE), an enzyme, is present in the synaptic cleft.
AChE breaks down ACh, stopping the signal.

Electrical Events at the Neuromuscular Junction

Action potential reaches axon terminal, depolarizing.
Depolarization causes calcium channels to open, calcium enters.
Calcium triggers vesicle fusion, releasing ACh.
ACh diffuses across the cleft, binds to ACh receptors.
Receptor binding triggers channel opening (sodium and potassium ions through).
Voltage change (endplate potential) occurs.

Electrical Events at the NMJ (Continued)

Depolarization spreads to adjacent membrane, activating sodium channels.
An action potential subsequently occurs in the muscle membrane.
Propagated along all muscle cell membrane.

Propagation of Action Potential at Muscle Membrane

When an action potential encounters T-tubules, it's propagated down the T-tubule membrane.
This propagation also results in numerous action potentials going towards the central part of the fiber.

T tubules

T-tubules communicate with the outside of the muscle fiber cell membrane.
Run deep into the muscle fiber.

DHP and Ryanodine Receptors

Action potential in T tubules initiates DHP receptors.
These receptors open ryanodine receptors, calcium channels.
The opening of the calcium channels releases calcium from the terminal cisternae of the sarcoplasmic reticulum.
Calcium increase within the cell triggers muscle contraction.
Excitation-contraction coupling refers to these events.

Neuromuscular Transmission (with Toxins)

Presynaptic blockade: Botulinum toxin blocks the release of ACh.
This toxin is from Clostridium botulinum bacteria.
Low doses of botulinum toxin (Botox) are therapeutically used for conditions like facial wrinkles.
Curare-tubocurarine blocks postsynaptic ACh receptors.
It's a South American arrow poison.

Sliding Filament Model of Muscle Contraction

The process involving sequential interactions between myosin and actin.
Results in the shortening of sarcomeres.
Four Steps of a Cross Bridge cycle:
- Attachment
- Movement
- Detachment
- Energizing.

Sliding Filament Model in detail

Contraction in muscles involves the activation of myosin crossbridges, structures generating the force.
In a resting state, actin and myosin filaments do not fully overlap.
Muscle stimulation causes myosin heads to bind to actin.
Thin filaments are pulled past thick filaments, increasing their overlap.
This is the basic mechanism underlying muscular contraction.

Sarcomere Shortening

When muscles contract, sarcomeres shorten, and the H zones and I bands become narrower.
The Z disks move closer together.

Calcium and the Contraction Mechanism

Low intracellular calcium concentrations: tropomyosin blocks myosin binding sites on actin.
High intracellular calcium concentrations:
- Calcium binds to TnC (troponin C).
- Troponin changes shape, shifting tropomyosin.
- Myosin binding sites on actin are exposed.
- Muscle contraction begins as myosin crossbridges cycle.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge about different types of muscle tissue and their functions in the human body. This quiz covers skeletal, smooth, and cardiac muscle, along with their unique characteristics and roles. Perfect for students studying biology or anatomy.