Chapter 10 - Muscular Fibers: Microanatomy

Skeletal Muscle

A type of muscle tissue that is striated, multinucleated, and under voluntary control.

Highly Vascular

Refers to the presence of many blood vessels in skeletal muscle.

Well Innervated

Indicates that skeletal muscle has many nerves present for stimulation.

Fascia

Connective tissue located beneath the skin that surrounds muscles.

Epimysium

A layer of connective tissue that encases individual muscles, containing blood vessels and nerves.

Sarcolemma

The plasma membrane of muscle fibers.

Sarcoplasmic Reticulum

A structure involved in calcium metabolization within muscle fibers.

Sarcoplasm

The cytoplasm of muscle fibers, filled with myofibrils made of myofilaments.

Myofilaments

The contractile proteins within muscle fibers, consisting of thin (actin) and thick (myosin) filaments.

Sarcomeres

The basic unit of muscle fiber, consisting of highly ordered repeating units of myofilaments.

Z Disk

A protein network that serves as an attachment point for actin filaments in a sarcomere.

I Bands

Regions in a sarcomere that extend from two Z disks to the start of thick filaments.

A Bands

The length of thick filaments within a sarcomere.

H Zone

The area in the A band where actin and myosin do not overlap.

M Line

The middle of the H zone, where delicate filaments hold myosin in place.

Motor Neurons

Nerves that stimulate muscle fibers to contract.

Neuromuscular Junction

The contact point between a motor neuron and a muscle fiber.

Motor End Plate

A specialized area of the neuromuscular junction.

Transverse (T) Tubules

Invaginations of the plasma membrane that help conduct impulses rapidly through muscle fibers.

Smooth Muscle

A type of muscle tissue with smaller, spindle-shaped fibers and a single central nucleus.

Dense Bodies

Structures in smooth muscle that replace Z disks and contain noncontractile intermediate filaments.

Visceral/Unitary Smooth Muscle

Smooth muscle that functions as a unit with numerous gap junctions and is often autorhythmic.

Multiunit Smooth Muscle

Smooth muscle composed of independent cells or groups of cells, such as those in blood vessels.

Cardiac Muscle

A striated muscle found only in the heart, characterized by intercalated disks and autorhythmic cells.

Intercalated Disks

Specialized cell-cell contacts in cardiac muscle that allow for synchronized contraction.

Desmosomes

Structures that hold cardiac muscle cells together.

Gap Junctions

Connections that allow action potentials to move between cardiac muscle cells.

Electrically Functional Unit

Refers to the behavior of cardiac muscle cells in the atria and ventricles acting as a single unit during contraction.