How do multi-unit smooth muscle fibers, such as those in the iris of the eye, typically contract in response to nerve stimuli?
Explanation
This question explores the specific mechanism of excitation in multi-unit smooth muscle, which differs from unitary smooth muscle by contracting without propagating action potentials.
Other questions
Compared to skeletal muscle fibers, what is the typical size range for the diameter and length of smooth muscle fibers?
Which type of smooth muscle is composed of discrete, separate fibers that operate independently and are controlled mainly by nerve signals?
Which structures in smooth muscle serve a similar role to the Z disks in skeletal muscle?
What percentage of their length can smooth muscle cells contract, and how does this compare to skeletal muscle?
What is the cycling frequency of myosin cross-bridges in smooth muscle compared to skeletal muscle?
How much energy is required to sustain the same tension of contraction in smooth muscle compared to skeletal muscle?
What is the typical total contraction time for a smooth muscle tissue, and how does this compare to an average skeletal muscle fiber?
What is the maximum force of contraction of smooth muscle, and how does it compare to that of skeletal muscle?
What is the 'latch mechanism' in smooth muscle?
What is the name of the regulatory protein in smooth muscle that calcium ions bind with to initiate contraction?
What is the direct action of the activated myosin light chain kinase (MLCK) in smooth muscle?
What is the primary source of the calcium ions that cause contraction in most smooth muscle?
What is the average latent period before contraction begins in smooth muscle, and how does this compare to skeletal muscle?
What is the function of caveolae in smooth muscle cells?
What is the role of myosin phosphatase in smooth muscle function?
How do the neuromuscular junctions in smooth muscle typically differ from those in skeletal muscle?
What determines whether a neurotransmitter like acetylcholine or norepinephrine will be excitatory or inhibitory to a smooth muscle fiber?
What is the normal resting membrane potential in a smooth muscle fiber?
Which ion is mainly responsible for generating the action potential in most smooth muscle?
What is the importance of the action potential plateau in some types of smooth muscle?
What are slow waves in unitary smooth muscle, and what is their primary importance?
What is the approximate threshold for eliciting action potentials in most visceral smooth muscle?
Which of the following local tissue chemical factors causes smooth muscle relaxation and vasodilation?
How can a hormone cause smooth muscle contraction or inhibition without a direct change in the membrane potential?
Which of the following is NOT a characteristic of unitary smooth muscle?
What is the phenomenon called where a hollow organ with smooth muscle, like the urinary bladder, can return to nearly its original force of contraction seconds or minutes after being elongated or shortened?
In the mechanism for smooth muscle contraction, what complex joins with and activates myosin light chain kinase?
What happens when the extracellular fluid calcium ion concentration decreases to about 1/3 to 1/10 of its normal level?
What is the primary action of the calcium pump in causing smooth muscle relaxation?
In the autonomic nerve fiber endings that innervate smooth muscle, what is contained within the vesicles in the varicosities?
What is the duration of a typical spike action potential in unitary smooth muscle?
Why do the calcium channels in smooth muscle largely account for the prolonged plateau action potentials?
How can visceral (unitary) smooth muscle be excited to generate spontaneous action potentials?
Which of the following hormones is NOT listed as affecting smooth muscle contraction?
In unitary smooth muscle, what structure allows force generated in one muscle fiber to be transmitted to the next?
The arrangement of 'side polar' cross-bridges on myosin filaments in smooth muscle allows for what key functional advantage?
What is the primary reason for the slow cycling of myosin cross-bridges in smooth muscle?
In multi-unit smooth muscle, what are the neuromuscular junctions called when the varicosities are separated from the muscle cell membrane by only 20 to 30 nanometers?
Which of the following describes inhibition of smooth muscle contraction by a hormone?
What is the role of norepinephrine in the intestine versus in blood vessels?
In the physical structure of smooth muscle, about how many times more numerous are actin filaments than myosin filaments?
What does a single smooth muscle contraction lasting for seconds rather than hundredths of a second indicate about its calcium pump?
Besides local tissue chemical factors, what is the other major type of non-nervous, non-action potential stimulating factor for smooth muscle contraction?
What is the approximate extracellular calcium ion concentration compared to the intracellular concentration in a smooth muscle cell?
The contractile process in smooth muscle is activated by calcium ions, and what other molecule is degraded to provide energy?
In the walls of most viscera, such as the gastrointestinal tract and uterus, which type of smooth muscle is found?
How is the cessation of smooth muscle contraction primarily determined?
What is the function of the second messengers cAMP or cGMP in inhibiting smooth muscle contraction?
Which of the following are examples of multi-unit smooth muscle?