Bio 17.1 Types of Muscles and Myocyte Structure

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Questions and Answers

What primary function do myocytes perform in the muscular system?

Store glucose for energy

Facilitate nerve conduction

Produce force through actin and myosin interaction (correct)

Transport oxygen in blood

Which ion's concentration is crucial for myocyte contraction?

Chloride ion (Cl-)

Sodium ion (Na+)

Potassium ion (K+)

Calcium ion (Ca2+) (correct)

Which of the following best describes the sarcolemma?

The site of ATP production in muscles

The cytoplasm of myocytes

The plasma membrane of muscle cells (correct)

The specialized endoplasmic reticulum

What is the role of the sarcoplasmic reticulum in muscle cells?

To regulate calcium ion concentration Signup and view all the answers

How do actin and myosin contribute to muscle contraction?

They interact to produce force Signup and view all the answers

Which structure is NOT typically found in myocytes?

Oligodendrocytes Signup and view all the answers

What distinguishes striated muscle cells from smooth muscle cells?

Striated muscle cells contain actin and myosin in a specific arrangement Signup and view all the answers

Which statement about myocytes is true?

Myocytes have low calcium ion concentration at rest Signup and view all the answers

What are actin filaments commonly referred to as based on their relative thickness?

Thin filaments Signup and view all the answers

Which structure connects the myosin heads to the myosin tails?

Hinges Signup and view all the answers

What is the appearance of muscles that have overlapping actin and myosin filaments when viewed under a microscope?

Striated Signup and view all the answers

What is a key feature that distinguishes smooth muscle cells from striated muscle cells?

They have a spindle shape Signup and view all the answers

What type of muscle lacks striations and appears homogeneous under a microscope?

Smooth muscle Signup and view all the answers

During muscle contraction, what happens to the length of actin and myosin filaments?

They remain unchanged Signup and view all the answers

What optimizes force production in striated muscle cells?

Maximal actin-myosin overlap Signup and view all the answers

Which of the following is NOT a description associated with striated muscles?

They appear homogeneous Signup and view all the answers

Which structure marks the boundary between neighboring sarcomeres?

Z line Signup and view all the answers

What is the primary function of titin within the sarcomere?

To maintain the structural arrangement of filaments Signup and view all the answers

Which band in the sarcomere only consists of myosin filaments?

H band Signup and view all the answers

In which type of muscle are thick filaments arranged with myosin heads along their entire length?

Smooth muscle Signup and view all the answers

How do striated muscle cells primarily differ from smooth muscle cells in terms of contraction speed?

Striated muscles contract more rapidly and intermittently. Signup and view all the answers

What does the A band in the sarcomere represent?

The length of the myosin filaments including overlap with actin Signup and view all the answers

Which region of the sarcomere contains only actin filaments?

I band Signup and view all the answers

What is a key characteristic of the arrangement of thin and thick filaments in smooth muscle cells?

They are oriented in multiple directions. Signup and view all the answers

What characteristic of smooth muscle cells allows for slower and more sustained contractions?

Specialized contractile mechanisms Signup and view all the answers

Which type of muscle exhibits more capillaries and myoglobin for aerobic energy production?

Striated muscle Signup and view all the answers

What role does ATP play in muscle contraction?

Hydrolyzes to reposition myosin heads Signup and view all the answers

How do striated muscles replenish ATP more rapidly during brief contractions?

Through substrate-level phosphorylation Signup and view all the answers

Which process is responsible for moving ions across cellular membranes in muscle cells?

ATP-requiring pumps Signup and view all the answers

What type of muscle contraction is described as energetically more efficient?

Smooth muscle contractions Signup and view all the answers

What is a primary role of myoglobin in muscle fibers?

To stabilize oxygen supply for respiration Signup and view all the answers

Which statement about the energetic costs of muscle contraction is correct?

They arise from actin movement and ionic gradients maintenance. Signup and view all the answers

What is the role of epinephrine in smooth muscle contraction?

It can induce contraction or relaxation depending on the receptor type. Signup and view all the answers

What initiates the contraction of skeletal muscles?

Neuromuscular junction and motor neuron action potentials. Signup and view all the answers

Which of the following statements about voluntary muscles is correct?

They can also be activated involuntarily during reflex responses. Signup and view all the answers

How does acetylcholine (ACh) affect muscle fibers at the neuromuscular junction?

It binds to receptors and opens ligand-gated channels in the sarcolemma. Signup and view all the answers

What is a characteristic feature of a neuromuscular junction (NMJ)?

It converts action potentials from motor neurons into muscle fiber action potentials. Signup and view all the answers

What happens to unbound acetylcholine after it is released into the synaptic cleft?

It either diffuses away or is degraded by acetylcholinesterase. Signup and view all the answers

Which system innervates skeletal muscles?

Somatic nervous system. Signup and view all the answers

What initiates muscle contraction in response to chemical signaling in smooth muscle cells?

Binding of a ligand to a receptor on the cell surface. Signup and view all the answers

Study Notes

Types of Muscles

Muscles are composed of cells specialized to produce force through the interaction of actin and myosin.
Muscle cells are called myocytes.
There are three types of muscles:
- Skeletal muscle - attached to bones, responsible for movement.
- Cardiac muscle - found in the heart, responsible for pumping blood.
- Smooth muscle - found in the walls of internal organs, responsible for involuntary movements.

Myocyte Structure

Myocytes are specialized for force production.
Force production is dependent on the concentration of calcium ions (Ca2+).
Myocytes are nucleated.
The plasma membrane of myocytes is called the sarcolemma.
Myocytes have a specialized type of endoplasmic reticulum called the sarcoplasmic reticulum.
Myocyte cytoplasm is called sarcoplasm.

Actin and Myosin

Actin and myosin interact to produce force.
Actin molecules form thin filaments.
Myosin molecules form thick filaments.
Myosin filaments contain a rod-like central region with heads that extend outwards.
During muscle contraction, myosin heads bind to and pull on actin filaments.
This sliding movement shortens the muscle cell, but the length of the actin and myosin filaments do not change.

Striated Muscle

Striated muscles have actin and myosin filaments arranged parallel to one another, creating visible striations under a microscope.
Striated muscle cells are long cylindrical fibers.
Force production is greatest when actin-myosin overlap is maximal.
Striated muscles have repeated functional units along the length of myofibrils called sarcomeres.
Each sarcomere contains:
- I band: only actin filaments
- H band: only myosin filaments
- A band: includes both actin and myosin filaments
- M line: center of the sarcomere
- Z line: boundary between sarcomeres

Smooth Muscle

Smooth muscles lack sarcomeres.
Thick filaments in smooth muscles have myosin heads along their entire length, allowing optimal actin-myosin interaction over a greater length.
Smooth muscle cells are spindle-shaped.
Smooth muscles are specialized for slower, sustained contractions.

Muscle Contraction and Energy

Muscle contraction requires energy from ATP hydrolysis.
ATP is used to power the movement of myosin heads and to pump ions across cellular membranes.
Striated muscles that are actively used have more capillaries, myoglobin, and mitochondria, indicating a greater reliance on aerobic energy production.
Striated muscles with infrequent use rely on less efficient but faster methods, like glycolysis and creatine phosphate.

Muscle Activation and Regulation

Skeletal muscles are innervated by the somatic nervous system.
The interface between a somatic motor neuron and a skeletal muscle fiber is called a neuromuscular junction (NMJ).
The NMJ converts motor neuron action potentials into muscle fiber action potentials.

Neuromuscular Junction

Action potentials at the axon terminal of a motor neuron trigger the release of acetylcholine (ACh) into the synaptic cleft.
ACh diffuses across the cleft and binds to receptors in the sarcolemma, opening ion channels.
This opens the channels, allowing ions to flow across the membrane and trigger muscle contraction.

Glossary

Contraction: An instance of muscle force production.
Myocyte: Muscle cell.
Sarcolemma: Plasma membrane of a muscle cell.
Sarcoplasmic reticulum: Specialized type of endoplasmic reticulum in muscle cells.
Sarcoplasm: Cytoplasm of a muscle cell.
Actin: Protein that forms thin filaments in muscle.
Myosin: Protein that forms thick filaments in muscle.
Striations: Regularly spaced lighter and darker bands in striated muscle.
Smooth muscle: Muscle lacking striations.
Myofibril: Tiny cylindrical bundles of interacting thick and thin filaments within a myocyte.
Sarcomere: Functional contractile unit of a striated muscle cell.
Titin: Large, elastic protein that helps maintain the ordered arrangement of actin and myosin filaments in a sarcomere.
Neuromuscular junction (NMJ): Specialized synapse between a motor neuron and a skeletal muscle fiber.
Acetylcholine (ACh): Neurotransmitter released at the NMJ.
Acetylcholinesterase: Enzyme that breaks down ACh.

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Description

Explore the fascinating world of muscle types and the structure of muscle cells. This quiz covers skeletal, cardiac, and smooth muscles, as well as the role of actin and myosin in muscle contraction. Test your knowledge on myocyte structure and function.