Module 8: Smooth Muscle

Smooth Muscle

A type of muscle tissue that is not striated and is controlled involuntarily, found in the walls of hollow organs.

Autonomic nerve fibers

Nerves that innervate smooth muscle at diffuse junctions, unlike the neuromuscular junction in skeletal muscle.

Single unit smooth muscle

Muscle cells that are electrically coupled by gap junctions and contract together, found in hollow organs.

Multi-unit smooth muscle

Muscle cells that operate independently and are found in structures such as the iris and large airways.

Contraction mechanism of smooth muscle

Involves the sliding filament mechanism where actin and myosin interact, initiated by an increase in intracellular calcium.

Phasic smooth muscles

Undergo periodic contraction and relaxation cycles

Tonic smooth muscles

Continuously contracted

Calmodulin

A calcium-binding protein that activates myosin light chain kinase (MLCK) in smooth muscle contraction.

Dense bodies

Proteins that anchor non-contractile filaments to the plasma membrane in smooth muscle, similar to Z discs in skeletal muscle.

Stress-relaxation response

The ability of smooth muscle to adapt to stretch and maintain tension, allowing organs to temporarily store contents.

Hyperplasia in smooth muscle

The process of smooth muscle cells dividing and increasing in number, particularly influenced by hormones like estrogen.

Myosin light chain kinase (MLCK)

An enzyme activated by calcium-bound calmodulin that phosphorylates myosin light chains, facilitating contraction.

Latch state

A sustained contraction state of smooth muscle that does not require continuous stimulation and is maintained by a balance of MLCK and MLCP activity.

Cardiac Muscle

A type of striated muscle found only in the heart, which exhibits characteristics of both skeletal and smooth muscle.

Pacemaker potentials

Spontaneous depolarizations in certain muscle cells that can initiate contraction, found in cardiac and some smooth muscles.

Varicosities (bulbous swellings) of nerve fibers ____

Store and release neurotransmitters into diffuse junctions

Myogenic Contraction

Contraction of smooth muscle in response to stretching, influenced by voltage-gated and ligand-gated channels. (Intrinsic)