Smooth Muscle Basics
This type of muscle is found in the walls of most hollow organs, except the heart.
What is smooth muscle?
Smooth muscle is innervated by this branch of the nervous system.
What is the autonomic nervous system?
Smooth muscle gets most of its intracellular Ca²⁺ from this source.
What is the extracellular fluid (ECF)?
Smooth muscle shortens in this distinctive pattern due to diagonal filament arrangement.
What is a corkscrew contraction
Smooth muscle maintains moderate, constant tension without fatigue, a property known as this.
What is smooth muscle tone
Smooth muscle fibres are shaped like this, making them thinner and shorter than skeletal muscle cells.
What is spindle-shaped
These swellings on autonomic axons release neurotransmitters into diffuse junctions.
What are varicosities?
Smooth muscle uses these plasma membrane indentations (instead of T-tubules) to bring in Ca²⁺.
What are caveolae
These protein structures anchor thin and intermediate filaments and transmit force.
What are dense bodies?
This response causes smooth muscle to contract when stretched, even without neural input.
What is the smooth muscle stretch reflex
Smooth muscle contains this connective tissue layer but lacks epimysium and perimysium.
What is the endomysium
Smooth muscle found in hollow organs that contracts as a syncytium due to gap junctions is known as this type.
What is unitary (visceral) smooth muscle?
In smooth muscle, Ca²⁺ binds to this protein instead of troponin.
What is calmodulin (CaM)?
The smooth muscle thick-to-thin filament ratio is 1:13, compared to this ratio in skeletal muscle.
What is 1:2?
This special response lets organs like the stomach stretch then adjust tension to hold contents.
What is the stress–relaxation response
Unlike skeletal muscle, smooth muscle is controlled under this type of nervous system control.
What is involuntary control (autonomic nervous system)?
This type of smooth muscle behaves more like skeletal muscle because its fibres are independent and form motor units.
What is multiunit smooth muscle
Calmodulin activates this enzyme, which phosphorylates and activates myosin heads.
What is myosin light chain kinase (MLCK
This process describes Ca²⁺ entering from the membrane triggering more Ca²⁺ release from the SR.
What is calcium-induced calcium release (CICR)
Chemicals like histamine, high CO₂, low O₂, and low pH can modify contraction by influencing this ion’s entry
What is Ca²⁺ (calcium)?
Smooth muscle lacks these structural units found in skeletal muscle, even though thick and thin filaments still overlap.
What are striations / sarcomeres
In unitary smooth muscle, spontaneous rhythmic activity is due to these special self-excitable cells.
What are pacemaker cells?
Smooth muscle contraction ends when Ca²⁺ is pumped out and myosin undergoes this process.
What is dephosphorylation
Because myosin heads line the entire filament and latch longer, smooth muscle requires less of this during contraction.
What is energy (ATP)
Norepinephrine causes bronchioles to do this, but blood vessels to do the opposite.
What is bronchiole dilation and blood vessel constriction