Chapter 8- Skeletal Muscle Fibers and the Neuromuscular Junction

Muscle fiber

cell that contracts when stimulated/relaxes when stimulation ends

What is in abundance in a muscle fiber?

Many small nuclei/mitochondria

Sarcolemma

the cell membrane surrounding a muscle fiber.

Sarcoplasm

The cytoplasm of a muscle fiber, containing essential substances for muscle contraction.

What are myofibrils responsible for?

Myofibrils are responsible for muscle contraction and are located in the sarcoplasm.

What is within myofibrils?

Protein filaments: actin and myosin.

What do actin and myosin do?

Affect the striations of a skeletal muscle fiber by interacting to produce a muscle contraction.

Sarcomeres

Functional unit of a muscle contraction on a myofibril. Span from Z-line to Z-line.

I-bands

Light, composed of only actin filaments, attach to the Z-lines.

A-bands

Contain both actin and myosin.

H-zone

Within the A-band, composed of only myosin filaments.

Sarcoplasmic Reticulum

A network of membranous channels within the sarcoplasm that surround the myofibrils.

Transverse/ T Tubules

Extend into the fiber and pass all the way through, opening up to the outside. Contains extracellular fluid.

Cisternae

2 enlarged portions of the sarcoplasmic reticulum, where t-tubules lie in between.

Motor neurons

Control muscles

Muscle Contraction

Muscles only contract when stimulated by a motor neuron

ALS/Lou Gehrig’s Disease

Impairs the motor neurons that control skeletal muscle contractions

Where are individual muscle fibers connected (functionally)?

Connects to the axon of a motor neuron through a synapse.

Axon

Projection of a nerve cell that transmits electrical impulses to produce contractions

Synapse

Structures where neurons release neurotransmitters to the correlating cells to communicate

Neuromuscular junction

Where a motor neuron and the muscle fiber connect

Motor end plate

Formed at the neuromuscular junction, where nuclei and mitochondria are abundant and the sarcolemma is extensively folded.

Synaptic cleft

Separates the neuron membrane from the muscle fiber membrane

Cytoplasm of the motor neuron

Contain many synaptic vesicles that store neurotransmitters and mitochondria are abundant