12 microscopic anatomy

Skeletal Muscle

The type of muscle tissue that attaches to the skeleton and allows for voluntary movement.

Smooth Muscle

Muscle tissue that forms the walls of hollow organs and moves materials within the body.

Cardiac Muscle

Muscle tissue that forms the walls of the heart and pumps blood.

Muscle Fiber

Large, long cylindrical cells that make up skeletal muscle.

Sarcolemma

The plasma membrane of skeletal muscle fibers.

Myofibrils

Long rod-shaped organelles in muscle fibers, made up of myofilaments.

Myofilaments

Threadlike structures within myofibrils composed of contractile proteins actin and myosin.

Sarcomeres

The contractile units of muscle, extending from one I band to the next.

T Tubule

Transverse tubules that run deep into muscle fibers and are involved in muscle contraction.

Neuromuscular Junction

The junction between a motor neuron and a muscle fiber, essential for muscle contraction.

Motor Unit

A motor neuron and all the muscle fibers it stimulates.

Synaptic Cleft

The small fluid-filled gap between the axon terminal of a neuron and the muscle fiber.

Acetylcholine (ACh)

A neurotransmitter released at the neuromuscular junction that stimulates muscle contraction.

Endomysium

Delicate connective tissue sheath surrounding each muscle fiber.

Perimysium

Collagenic membrane surrounding a bundle of muscle fibers, known as a fascicle.

Epimysium

Dense irregular connective tissue sheath that surrounds the entire muscle.

Tendon

Cord-like structure that attaches a muscle to a bone.

Aponeurosis

Sheet-like structure that serves a similar function as a tendon.

Z disc

The boundary of a sarcomere where thin filaments attach.

A Band

Region of a sarcomere that contains thick filaments and overlaps with thin filaments.

I Band

Region of a sarcomere that contains only thin filaments.

H Zone

The central region of the A band where there are only thick filaments.

M Line

The line that appears in the center of the A band, anchoring thick filaments.

Triad

Structure formed by a T tubule and two terminal cisterns of the sarcoplasmic reticulum.

Origin (Muscle Attachment)

The fixed or immovable attachment point of a muscle.

Insertion (Muscle Attachment)

The more movable attachment point of a muscle.