Smooth Muscle Flashcards
Smooth muscle properties
- Shorter and thinner
–They have a single, centrally-located nucleus
–No striations
–No T-tubules
–A poorly developed sarcoplasmic reticulum
Why do smooth muscle fibres lack striation?
Although they contain actin and myosin, the filaments are thin and randomly arranged so that it lacks striations.
Similarities between smooth and skeletal muscle striations
- Both contractile mechanisms depend on the action of actin and myosin;
- Both are triggered by membrane impulses and the release of calcium ions; and
- Both require ATP
Differences between smooth and skeletal muscle striations
- Actin has no troponin
- Ccalcium required for contraction comes into the cell by diffusion from the extracellular fluid.
- More resistant to fatigue, slower, longer lasting contraction
- More energy efficient in that it can maintain a more forceful contraction for a longer period of time with the same amount of ATP.
What is calmodulin and where is it found?
It is a calcium binding protein called calmodulin. This protein activates the actin and myosin crossbridge formation.
Smooth muscle is under autonomous nervous system control. True or false?
True
Nuerotransmitters of smooth muscle
- Acetylcholine (as in skeletal muscle)
* Norepinephrine.
Difference between neurotransmitters of skeletal and smooth muscle
For smooth muscle, they can be either excitatory (causing muscle contraction), or inhibitory (prevent muscle contraction) depending on the receptor on the smooth muscle cell membrane, whereas, the neurotransmitter for skeletal muscle is always excitatory.
Smooth muscle can be stimulated by certain hormones. True or false?
True
Example of hormones stimulating smooth muscle
Oxytocin, which stimulates smooth muscle contraction in the walls of the uterus during childbirth.
Types of smooth muscle fibres
Multiunit smooth muscle
Single unit smooth muscle
Properties of multi unit smooth muscle
- Fibers are not very well organized
- Occur as separate fibers scattered throughout the sarcoplasm rather than in sheets.
- Requires stimulation by a motor nerve impulse from the autonomic nervous system.
Multiunit smooth muscle fibres are found in…
…the irises of the eyes, arrector pili muscles, blood vessels, and large airways of the lung
What type of smooth muscle is found in the walls of the hollow visceral organs such as the stomach, intestines, urinary bladder and uterus?
Single Unit or Visceral Smooth Muscle
Which is the more common of the two types of smooth muscle?
Single Unit or Visceral Smooth Muscle
Properties of single unit smooth muscle fibres
The muscle fibers are organized into sheets of cells held in close contact by gap junctions.
Single unit smooth muscle fibres are organized into ___ layers
Two layers:
•Longitudinal layer
•Circular layer
Describe the longitudinal layer of single unit smooth muscle
Outer layer directed longitudinally along the length of the structure. Contraction of this layer causes the structure to dilate and shorten
Describe the circular layer of single unit smooth muscle
The inner layer arranged circularly around the structure. Contraction of this layer causes the structure to constrict and elongate.
Intrinsic control of smooth muscle contraction is by…
Myogenic Response
Describe the myogenic response of smooth muscle
Smooth muscle is stimulated to contract when it is stretched. It is able to distend, or stretch, without great increases in tension or tightness, allowing hollow organs to be filled. When smooth muscle reaches its stretching capacity, it will contract and force the contents out, e.g. intestines or urinary bladder.
