Week 1 assumed knowledge

Questions and Answers

What is the primary function of the sarcoplasmic reticulum in muscle contraction?

Facilitates the sliding of myofilaments

Synthesizes ATP for energy

Transmits the action potential to the myofibrils

Stores and releases calcium ions (correct)

Which components of the muscle fiber are responsible for the process of excitation-contraction coupling?

Motor neurons and vesicles

ACh and junctional folds

Thick filaments and Z lines

Transverse tubules and sarcoplasmic reticulum (correct)

What occurs at the neuromuscular junction when an action potential arrives?

Acetylcholine is released into the synaptic cleft (correct)

Calcium ions are released from the thick filaments

Sodium ions exit the motor end plate

Myofibrils contract immediately

Which area of the sarcomere does NOT change length during contraction?

A band Signup and view all the answers

What role does acetylcholinesterase (AChE) play at the neuromuscular junction?

It breaks down acetylcholine Signup and view all the answers

Which unit represents the fundamental functional unit of skeletal muscle?

Sarcomere Signup and view all the answers

What is the role of thick and thin filaments within a sarcomere during muscle contraction?

Thick filaments pull thin filaments toward the M line Signup and view all the answers

What defines the 'zone of overlap' in a sarcomere?

The overlap of thick and thin filaments Signup and view all the answers

What happens to tension production when the thick filaments are jammed against the Z lines?

Tension production falls to zero. Signup and view all the answers

What role do titin filaments play in muscle tension production?

They prevent excessive stretching of muscle fibers. Signup and view all the answers

At which sarcomere length is tension production typically greatest?

At the optimal resting length. Signup and view all the answers

How does increased sarcomere length affect tension production?

Tension production declines. Signup and view all the answers

What structure prevents excessive compression of muscle fibers?

Connective tissues and joints. Signup and view all the answers

What effect does extreme stretching of a muscle fiber have on contraction?

Contraction becomes ineffective. Signup and view all the answers

Which factor directly influences the number of cross-bridge interactions?

Sarcomere length relative to optimal length. Signup and view all the answers

What becomes impossible when the zone of overlap between filaments is reduced to zero?

Cross-bridge formation. Signup and view all the answers

Which physiological factor is associated with the fast-to-slow transition in muscle types?

Endurance training Signup and view all the answers

Which physiological factor would most likely lead to muscle unloading?

Microgravity exposure Signup and view all the answers

What effect does hyperthyroidism have on muscle type transitions?

Promotes slow-to-fast transitions Signup and view all the answers

Which experiment would likely demonstrate the effects of electrical stimulation on muscle types?

Cross-reinnervation Signup and view all the answers

How does muscle overload influence muscle type transitions?

Supports slow-to-fast transitions Signup and view all the answers

Which of the following combinations correctly correlates physiological factors with their effects on muscle type transitions?

Hypothyroidism - fast-to-slow transitions Signup and view all the answers

What does SDS-PAGE stand for?

Sodium Dodecyl Sulfate-PolyAcrylamide Gel Electrophoresis Signup and view all the answers

Which process is specifically associated with the physiological effects in rodents as per the nearest-neighbour principle?

Muscle unloading Signup and view all the answers

What type of electrical stimulation mimics fast-type motor neurons in muscle transitions?

High-frequency electrical stimulation Signup and view all the answers

Which protein chains are analyzed using single fiber protein gel electrophoresis according to the content?

Myosin Heavy Chains and Myosin Light Chains Signup and view all the answers

What characteristic is reflected in the protein electrophoresis patterns during fiber staining?

Variability across proteins such as MHC and MLC Signup and view all the answers

What is a common feature of Myosin Heavy Chains (MHC) as mentioned in the content?

MHC show variability across many different proteins Signup and view all the answers

What is the primary technique mentioned for protein analysis in muscle fibers?

Single Fiber Protein Gel Electrophoresis Signup and view all the answers

What type of analysis is emphasized in Larsson's research related to muscle protein?

Protein gel electrophoresis focusing on myosin chains Signup and view all the answers

In the context of single fiber analysis, what do MHC and MLC refer to?

Myosin Heavy Chains and Myosin Light Chains Signup and view all the answers

What is the implied significance of variability across myosin proteins as discussed?

It alters the contractile properties of muscle fibers Signup and view all the answers

What is the main structural role of titin in a sarcomere?

It allows for the elasticity and stabilization of myofilaments. Signup and view all the answers

How many individual G-actin molecules typically form a strand of F-actin?

300–400 Signup and view all the answers

Which protein is primarily associated with holding the F-actin strand together?

Nebulin Signup and view all the answers

What characterizes the arrangement of myosin heads in a thick filament?

They face towards the surrounding thin filaments. Signup and view all the answers

In a longitudinal section of a sarcomere, where are thin filaments attached?

To the Z line at either end Signup and view all the answers

Which component is NOT part of the thin filament structure?

M line Signup and view all the answers

What allows the pivoting motion of the myosin head during muscle contraction?

Hinge-like connection Signup and view all the answers

What structure contains around 300 myosin molecules twisted around one another?

Thick filament Signup and view all the answers

Study Notes

Muscle Contraction Overview

Muscle contraction is primarily explained through the sliding filament and cross-bridge theory.
Myofibrils consist of repeating functional units called sarcomeres, which contain thick and thin myofilaments.

Structure of a Muscle Fiber

Myofibrils: Composed of myofilaments, surrounded by sarcoplasm.
Sarcoplasmic Reticulum (SR): Stores calcium ions, crucial for contraction.
Transverse Tubules (T Tubules): Invaginate into muscle fibers, facilitating action potential transmission.

Sarcomeres

The basic unit of striated muscle tissue, characterized by the area between two Z lines.
A Band: Dark band containing thick filaments.
I Band: Light band containing thin filaments.
M Line and Z Line: Structural components within the sarcomere.

Thin and Thick Filaments

Thin Filaments: Composed of G-actin, F-actin, troponin, and tropomyosin.
- Active Site: Where myosin heads attach during contraction.
Thick Filaments: Comprised of myosin molecules.
- Myosin heads facilitate cross-bridge formation during contraction.

Neuromuscular Junction (NMJ)

Site where motor neuron communicates with muscle fibers.
Acetylcholine (ACh) is released from synaptic vesicles into the synaptic cleft, binding to receptors at the motor end plate.
This triggers an action potential in the muscle fiber, leading to contraction.

Excitation-Contraction Coupling

Action potentials propagate along the sarcolemma and down T tubules.
Trigger the SR to release calcium ions (Ca2+) into the cytoplasm, initiating muscle contraction.

Muscle Fiber and Sarcomere Length

Muscle tension production is optimized at specific sarcomere lengths.
Extreme stretching or compression decreases tension due to reduced overlap of thick and thin filaments.

Protein Composition Influence

Variability in myosin heavy chains (MHC) and light chains (MLC) affects muscle fiber type and performance.
Different activities (training, hormonal changes) can prompt slow-to-fast and fast-to-slow muscle fiber transitions.

Single Fiber Protein Analysis

Electrophoresis can identify and quantify different proteins within muscle fibers, indicating fiber types and possible adaptations.

Factors Affecting Muscle Plasticity

Factors such as electrical stimulation patterns and mechanical loading can influence the transition between muscle fiber types.
Muscle unloading (e.g., during suspension) can lead to fast-to-slow transitions, while overload can induce slow-to-fast changes.

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Description

This quiz covers the first lecture of NEUR3101, focusing on muscle contraction, the sliding filament theory, and cross-bridge theory. It is based on key concepts from the chapters in Kenney et al. and Martini et al. regarding muscle structure and function. Test your understanding of the physiological aspects of muscle performance!