Smooth Muscle Lecture Notes

These flashcards cover key vocabulary and concepts related to smooth muscle structure and function, aimed at aiding study and revision.

Smooth Muscle

Non-striated involuntary muscle found in the walls of most hollow organs.

Unitary Smooth Muscle

Type of smooth muscle that exhibits spontaneous action potentials and is electrically coupled by gap junctions.

Multiunit Smooth Muscle

Smooth muscle consisting of independent fibers that form motor units and is innervated by autonomic neurons.

Innervation

The supply of nerves to a particular body part, important for muscle contraction.

Autonomic Nervous System (ANS)

Part of the peripheral nervous system that controls involuntary functions and innervates smooth muscle.

Contraction of Smooth Muscle

Occurs via diagonal arrangement of thick and thin filaments, leading to a corkscrew shortening.

Ca2+ (Calcium ions)

Essential for smooth muscle contraction; enters from extracellular fluid and triggers contraction mechanisms.

Excitation-Contraction Coupling

Process by which an electrical signal leads to muscle contraction.

Myogenic Activity

Ability of smooth muscle to contract without nerve stimulation, linked to pacemaker cells.

Calmodulin

A protein that binds calcium ions and activates myosin light chain kinase in smooth muscle.

Thick and Thin Filaments Ratio

In smooth muscle, the ratio is 1:13, less than in skeletal muscle, which is 1:2.

Caveolae

Small invaginations in the plasma membrane that store calcium channels in smooth muscle.

Dense Bodies

Cytoplasmic proteins in smooth muscle that anchor thin and intermediate filaments.

Relaxation of Smooth Muscle

Occurs via calcium dissociation from calmodulin and other processes leading to reduced cross-bridge formation.

Neuromuscular Junction

A synapse between a motor neuron and a muscle fiber; unique in smooth muscle.

Skeletal Muscle vs. Smooth Muscle

Smooth muscle lacks striations and is involuntary, while skeletal muscle is striated and voluntary.

Pacemaker Potentials

Spontaneous depolarizations in unitary smooth muscle that lead to rhythmic contractions.

Slow-wave Potentials

Cyclical changes in membrane potential that can initiate contractions in smooth muscle.

Stress-Relaxation Response

A process where muscle adjusts to a new length after sustained stretch.

Muscle Tone

Sustained contractions exhibited by smooth muscle that maintains tension without fatigue.

Subtypes of Smooth Muscle

Unitary and multiunit smooth muscle, distinguished by their neuromuscular connections and contraction behavior.

Regulation of Muscle Contraction

Influenced by neurotransmitters, hormones, and stretch; determines contraction strength.

Electrically Coupled

A characteristic of unitary smooth muscle allowing contractile coordination through gap junctions.

Rhythmic Contractions

Regular, repeating contractions characteristic of certain types of smooth muscle.

Contractile Strength

The force produced by muscle contractions, which can vary depending on initial muscle stretch.

Calcium-Induced Calcium Release (CICR)

Mechanism by which calcium entry triggers additional calcium release from the sarcoplasmic reticulum.

Endomysium

The connective tissue that surrounds individual muscle fibers in smooth muscle.

Mechanism of Crossbridge Cycling

In smooth muscle, involves myosin heads binding to actin filaments, but regulated differently than in skeletal muscle.