Section 6 Flashcards
Describe the contractile filaments in smooth muscle and explain how it is different from skeletal muscle.
Explain smooth muscle excitation contraction coupling.
Explain the differences between neurogenic and myogenic smooth muscle.
Explain if cardiac muscle is more similar to skeletal or smooth muscle and why.
Similar to Skeletal Muscle:
- Striated appearance.
- Multinucleation (in some cases).
- Involuntary contractions influenced by neural input.
Differences from Smooth Muscle:
- Presence of striations.
- Involuntary, but control mechanisms more akin to skeletal muscle.
-Intercalated discs with gap junctions for rapid communication.
In essence, cardiac muscle exhibits characteristics resembling both skeletal and smooth muscle, but its striated appearance and involvement of neural control align it more closely with skeletal muscle.
Where are smooth muscle cells and cardiac muscle cells typically found in the human body?
Smooth muscle cells are primarily found in the walls of hollow organs and tubes like the digestive system and blood vessels. In contrast, cardiac muscle cells are exclusively located in the heart.
How does the structure of smooth muscle cells differ from skeletal muscle cells?
Smooth muscle cells lack sarcomeres.
They have three types of filaments:
- Thick myosin filaments (longer than skeletal muscle).
- Thin actin filaments containing tropomyosin (but not troponin).
- Intermediate filaments for the cytoskeletal framework.
Instead of Z-lines, they have dense bodies serving as anchor points for both the intermediate and contractile filaments.
The thick and thin filaments are not oriented along the cell’s length but form a diamond-like pattern within the cell.
What is the key difference between the presence of troponin in skeletal muscle and smooth muscle regarding cross-bridge formation?
In skeletal muscle, troponin blocks cross-bridge formation until Ca2+ is present, but smooth muscle lacks troponin.
In smooth muscle, what protein is associated with the myosin head and plays a significant role in cross-bridge formation?
Myosin light chain is associated with the myosin head in both skeletal and smooth muscle, with a more substantial role in smooth muscle.
What are the steps for myosin cross-bridge activation in smooth muscle?
- Ca2+ enters the smooth muscle cell and binds to calmodulin.
- The Ca2+-calmodulin complex activates myosin light chain kinase.
- Activated kinase phosphorylates myosin light chain, allowing the myosin cross-bridge to bind to actin.
What is the role of calmodulin in smooth muscle contraction?
Calmodulin is a calcium-binding messenger protein that activates myosin light chain kinase during excitation, leading to myosin cross-bridge activation.
How do the size and shape of smooth muscle cells compare to skeletal muscle cells?
Smooth muscle cells are smaller, spindle-shaped, and have a single nucleus.
In smooth muscle, do cells extend the length of the muscle or form sheets?
Smooth muscle cells form sheets of muscle.
What protein found in smooth muscle is crucial for cross-bridge cycling, even though it lacks troponin?
Myosin light chain is imperative for cross-bridge cycling in smooth muscle.
How do smooth muscle cells differ from skeletal muscle cells regarding T-tubules and the sarcoplasmic reticulum (SR)?
Smooth muscle cells have no T-tubules and very little SR compared to skeletal muscle cells.
What is the primary function of voltage-gated dihydropyridine receptors in smooth muscle cells?
In smooth muscle cells, voltage-gated dihydropyridine receptors serve as calcium channels to allow calcium entry from the extracellular fluid (ECF).
How is calcium released from the SR in smooth muscle cells, and what is this process called?
Calcium is released from the SR in smooth muscle cells through a process called calcium-induced calcium release (CICR).
How is the equilibrium of calcium levels in the blood maintained in the body, and what processes are involved?
The equilibrium of calcium levels in the blood is maintained through an interplay of calcium absorption from the intestines, movement of calcium into and out of the bones, and the kidney’s reclamation and excretion of calcium into the urine.
What is the key difference between single unit smooth muscle and multiunit smooth muscle in terms of their excitation?
Single unit smooth muscle fibers are electrically connected via gap junctions, which allow them to become excited and contract as a single unit. In contrast, multiunit smooth muscle consists of distinct groups or units of smooth muscle cells that are innervated by autonomic nervous system nerves, leading to neurogenic stimulation.
Where is single unit smooth muscle primarily found in the body?
Single unit smooth muscle is predominantly found in the walls of hollow organs such as the digestive system, reproductive system, urinary tracts, and small blood vessels.
Where is multiunit smooth muscle found in the body?
Multiunit smooth muscle is found in the walls of large blood vessels, small airways to the lungs, the base of hair follicles of the skin, and in the eye to adjust the lens shape and iris.
What is the key difference between single unit and multiunit smooth muscle in terms of excitation?
Single unit smooth muscle is myogenic, meaning it can self-generate action potentials and does not require nerve stimulation, whereas multiunit smooth muscle is neurogenic and requires autonomic nervous system nerves for stimulation.
What is a characteristic of myogenic single unit smooth muscle?
Single unit smooth muscle consists of clusters of specialized smooth muscle cells that are automatic or spontaneously depolarize to generate action potentials that can spread throughout the muscle.
What are the two types of spontaneous depolarization in single unit smooth muscle?
The two types of spontaneous depolarization in single unit smooth muscle are pacemaker potentials and slow-wave potentials.
How do pacemaker potentials work in single unit smooth muscle?
Pacemaker potentials involve a gradual membrane depolarization until it reaches threshold, at which point it fires an action potential. These potentials are generated by If channels that are permeable to Na+ and K+ ions and open to depolarize the cell. When the membrane potential becomes more positive, If channels close, and Ca2+ channels open to continue depolarizing the cell.
