Combined

What is a muscle fascicle?

A bundle of multiple muscle fibers grouped together within a muscle

What are muscle fibers within a fascicle?

Individual muscle cells aligned in parallel inside each fascicle

What is the endomysium?

A thin connective tissue sheath that surrounds and wraps each individual muscle fiber

What is the sarcolemma?

The specialized plasma membrane of the muscle fiber located directly beneath the endomysium

What cellular components can be found along the sarcolemma?

Multiple nuclei and mitochondria positioned near the membrane

Why do muscle fibers have multiple nuclei?

Because muscle fibers are multinucleated cells that require many nuclei to support their large size and protein production

What structures are found inside a muscle fiber?

Hundreds to thousands of myofibrils and mitochondria distributed throughout the cytoplasm

What are myofibrils?

Long cylindrical contractile structures that run the entire length of the muscle fiber and produce force

What becomes visible when the endomysium and sarcolemma are removed?

Hundreds to thousands of myofibrils inside the muscle fiber

What are sarcomeres?

Repeating functional units of contraction found within myofibrils

What is the functional unit of muscle contraction?

The sarcomere

What are Z-discs?

Structures that form the boundaries of each sarcomere

What happens to Z-discs during contraction?

They move closer together

What two main filaments are found in a sarcomere?

Thick filaments made of myosin and thin filaments made of actin

What happens during cross bridge formation?

Myosin heads bind to specific sites on actin forming a cross bridge

What is the power stroke?

The pivoting movement of the myosin head that pulls actin toward the center of the sarcomere

What happens during sarcomere shortening?

Actin is pulled inward causing the sarcomere Z-discs myofibril and muscle fiber to shorten

What are T tubules?

Transverse tubules that surround the myofibrils and conduct electrical signals deep into the muscle fiber to initiate contractio

Where does voluntary movement begin?

All voluntary movement begins in the brain where sensory information from the body is received, integrated, and processed

What do upper motor neurons do?

carry the command signal from the brain down through the central nervous system

What happens when the signal leaves the CNS?

The signal enters the peripheral nervous system and synapses with a lower motor neuron usually an alpha motor neuron

How is the signal from the brain carried to the alpha motor neuron?

It travels as electrical signals called action potentials

What happens when the action potential reaches the end of the alpha motor neuron?

Synaptic vesicles release the neurotransmitter acetylcholine

What happens to acetylcholine at the neuromuscular junction?

Acetylcholine diffuses across the synaptic cleft and binds to nicotinic acetylcholine receptors on the sarcolemma of the muscle fiber

What happens when acetylcholine binds to its receptors?

Ion movement across the sarcolemma generates a new electrical signal in the muscle fiber

What type of signal conversions occur during excitation contraction coupling?

Electrical signal in the neuron chemical signal across the synapse and electrical signal again in the muscle fiber

What is excitation contraction coupling?

The process where a signal from the nervous system triggers contraction in a muscle fiber

What analogy can describe signal conversion between nerve and muscle?

It is like a currency exchange where the signal changes form from electrical to chemical and back to electrical

What happens when the action potential reaches the alpha motor neuron terminal?

The electrical signal travels down the neuron to the axon terminal at the end of the motor neuron

What is the axon terminal also called?

The synaptic terminal or terminal bulb

What happens to voltage gated calcium channels when the electrical signal reaches the axon terminal?

They open because they respond to changes in membrane voltage

What happens when calcium channels open in the axon terminal?

Calcium ions enter the axon terminal from the extracellular space

What role does calcium play in neurotransmitter release?

Calcium activates synaptic vesicles that contain acetylcholine

What happens to synaptic vesicles after calcium enters the axon terminal?

They move toward and fuse with the presynaptic membrane

What occurs when synaptic vesicles fuse with the membrane?

Acetylcholine is released into the synaptic cleft

Why is calcium entry important at the neuromuscular junction?

It converts the electrical signal in the neuron into a chemical signal

What happens when acetylcholine binds to nicotinic acetylcholine receptors on the sarcolemma?

The receptor channel opens

What ions move across the sarcolemma when the receptor opens?

Sodium enters the muscle fiber and potassium exits the muscle fiber

What causes depolarization of the sarcolemma?

The influx of sodium into the muscle fiber

What is produced when the sarcolemma depolarizes?

A muscle action potential

How does the muscle action potential spread?

It spreads across the entire sarcolemma like an electrical wave

How does acetylcholine convert the signal in the muscle fiber?

It converts the chemical signal back into an electrical signal in the muscle fiber

What happens when the electrical signal reaches the alpha motor neuron terminal during excitation contraction coupling?

Voltage gated calcium channels open allowing calcium to enter the axon terminal

What causes acetylcholine to be released into the synaptic cleft?

Calcium activates synaptic vesicles which fuse with the presynaptic membrane

Where are nicotinic acetylcholine receptors located?

On the sarcolemma of the muscle fiber at the motor end plate

What type of channels are nicotinic acetylcholine receptors?

Ligand gated ion channels

What happens when acetylcholine binds to these receptors?

Sodium enters the muscle fiber and potassium exits

What does this ion movement cause?

Depolarization of the sarcolemma and generation of a muscle action potential

How does the electrical signal travel deeper into the muscle fiber?

It spreads through the T tubules

What happens when the signal reaches the sarcoplasmic reticulum?

The sarcoplasmic reticulum opens calcium release channels

What happens when calcium is released into the sarcoplasm?

Calcium levels increase inside the muscle fiber

Why is calcium release important for muscle contraction?

Calcium interacts with regulatory proteins allowing actin and myosin to interact and produce force

What is the main concept of excitation contraction coupling?

It converts a neural electrical signal into calcium release inside the muscle fiber which allows muscle contractio