The Neuromuscular Junction and Muscle Contraction

Vocabulary flashcards covering the anatomical structures, chemical signals, and physiological steps of transmission at the neuromuscular junction and the sliding filament model of muscle contraction.

Action potential

An electrical impulse initiated in the primary motor cortex that stimulates muscle tissue to contract or shorten in length.

Primary motor cortex

The area in the brain where the action potential is initiated before traveling down the spinal cord.

Motor neuron

A nerve cell that sends action potentials to muscle fibers.

Innervate

To connect to and stimulate.

Motor unit

A motor neuron and all of the muscle fibers that it innervates (connects to and stimulates).

Neuromuscular junction

The synapse between a motor neuron and a muscle fiber.

Axon terminal

The end of a motor neuron where synaptic vesicles and voltage gated calcium ion channels are located.

Presynaptic membrane

The membrane of the axon terminal.

Synaptic vesicles

Structures at the axon terminal that are filled with neurotransmitter.

Neurotransmitter

A chemical messenger contained within synaptic vesicles that diffuses across the synaptic cleft.

Voltage gated calcium ion channels

Ion channels that open in response to a voltage or an action potential, allowing calcium ions to diffuse.

Synaptic cleft

The open space between the motor neuron and the motor end plate across which neurotransmitter diffuses.

Sarcolemma

The cell membrane of the muscle fiber.

Motor end plate

The region of the sarcolemma (postsynaptic membrane) with which the motor neuron synapses.

Chemical gated sodium ion channels

Channels located on the sarcolemma that open in the presence of a neurotransmitter binding to their receptor, allowing sodium ions to diffuse into the muscle fiber.

T tubule

A structure down which the action potential travels from the sarcolemma into the terminal cisternae.

Terminal cisternae

Structures that receive the action potential from the T tubule and release calcium ions through voltage gated calcium ion channels into the sarcomere.

Sarcoplasmic reticulum

An organelle that stores calcium and releases or replenishes calcium ions into the terminal cisternae.

Troponin

A component of the actin myofilament that binds calcium ions, changes configuration, and pulls on tropomyosin.

Tropomyosin

A protein pulled by troponin when calcium binds, which exposes the active binding site of G actin.

Crossbridge

The binding of the myosin head to the exposed active binding site of G actin.

Working stroke

The step where ADP and phosphate are released from the myosin head, changing its configuration from upright to bent and pulling the actin myofilament.

Detachment

The step where ATP binds to the myosin head, causing it to detach from the active binding site of G actin.

ATP hydrolysis

The process of breaking down ATP into ADP and phosphate to reconfigure the myosin head from a bent position back to an upright position.

Reconfiguration

The step in which the myosin head changes configuration from bent back to upright via ATP hydrolysis so another crossbridge can occur.

Sliding filament model

The mechanism of muscle contraction involving the sliding of actin and myosin past each other through the steps of crossbridge, working stroke, detachment, and reconfiguration.