muscle terms to know

Muscle fiber:

A single muscle cell, also known as a myocyte, that contains multiple nuclei and is the basic building block of muscles.

Myofibril

Rod-like structures within muscle fibers composed of repeating units called sarcomeres, which are responsible for muscle contraction.

Myofilament

Protein filaments within myofibrils, mainly composed of actin (thin filament) and myosin (thick filament), that slide past each other to produce muscle contraction.

Actin

A protein that forms the thin filament in muscle cells and interacts with myosin to enable muscle contraction.

Myosin

A protein that forms the thick filament in muscle cells, with heads that attach to actin to generate contraction.

Sarcomere

The functional unit of a muscle fiber, defined by the area between two Z-lines, where actin and myosin filaments interact to produce contraction.

Striated

Describes muscle tissue with a striped appearance due to the regular arrangement of sarcomeres, found in skeletal and cardiac muscles.

Troponin

• A regulatory protein attached to actin filaments that binds to calcium to initiate muscle contraction

Tropomyosin

A regulatory protein that blocks myosin-binding sites on actin, preventing contraction until it is moved by troponin.

Thick filament:

Composed primarily of myosin, it forms part of the sarcomere and interacts with thin filaments to produce contraction.

Thin filament:

Composed primarily of actin, along with tropomyosin and troponin, and interacts with thick filaments for contraction.

Transverse (T) tubule:

Invaginations of the sarcolemma (muscle cell membrane) that allow action potentials to reach deep into the muscle fiber, ensuring coordinated contraction.

Terminal cisternae

Enlarged areas of the sarcoplasmic reticulum that store calcium ions and release them upon stimulation.

Sarcoplasmic reticulum

A specialized type of endoplasmic reticulum in muscle cells that stores and releases calcium ions, essential for muscle contraction.

Triad:

The structure formed by a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum, critical for calcium release and muscle contraction.

Endomysium:

Connective tissue that surrounds individual muscle fibers.

Perimysium

Connective tissue that surrounds groups of muscle fibers, forming bundles called fascicles.

Fascicle

• A bundle of muscle fibers surrounded by perimysium.

Epimysium

Connective tissue that surrounds the entire muscle, helping to form its structure.

Fascia

Connective tissue that surrounds and separates muscles and other internal organs.

Tendon

• A strong, fibrous connective tissue that connects muscle to bone.

Aponeurosis

A flat, broad tendon that attaches muscles to bones or other muscles.

Neuromuscular junction:

The synapse where a motor neuron communicates with a muscle fiber to stimulate contraction.

Motor unit

A single motor neuron and all the muscle fibers it innervates. It functions as a single unit for contraction

Synaptic cleft

The small gap between the motor neuron and muscle fiber at the neuromuscular junction.

Junctional folds

• Folds in the muscle cell membrane (sarcolemma) at the neuromuscular junction that increase the surface area for neurotransmitter reception.

Acetylcholine

A neurotransmitter released by motor neurons that binds to receptors on muscle fibers, initiating contraction.

Axon terminal

The end of a motor neuron that releases neurotransmitters to stimulate muscle fibers.

Muscle twitch

A single, brief contraction of a muscle fiber following a single action potential. It has three phases:

• Latent phase: The time between stimulation and contraction.

• Contraction phase: When the muscle fiber shortens.

• Relaxation phase: When the muscle returns to its resting length.

Excitation-contraction coupling

The sequence of events that link the electrical signal (action potential) to muscle contraction, involving calcium release and binding to troponin.

Motor unit:

A single motor neuron and all the muscle fibers it controls.

Recruitment

The process of activating more motor units to increase muscle force.

Threshold voltage

The minimum electrical stimulus needed to cause a muscle fiber to contract.

Stimulus frequency and muscle contraction:

Increasing the frequency of stimuli can lead to stronger contractions through wave summation (adding twitches) and tetanus (sustained contraction).

Wave summation:

Increased contraction strength due to repeated stimulation before the muscle fully relaxes.

Treppe

The phenomenon where successive contractions become stronger, often called the "staircase effect."

• Unfused tetanus:

• Partial relaxation between contractions.

Length-tension relationship

The optimal sarcomere length for maximal force generation is between too stretched and too contracted states.

Agonist

The primary muscle responsible for a movement.

Antagonist

The muscle that opposes the agonist

Synergist

A muscle that assists the agonist in a movement.

Fixator

A muscle that stabilizes the origin of the agonist.

• Fused tetanus:

• Sustained contraction without relaxation.

• Muscle fatigue:

• The inability to maintain contraction due to resource depletion.