The key difference between multiunit and visceral smooth muscle is that the multiunit smooth muscle is a neurogenic smooth muscle, which is composed of cells that work as multi-units and function independently. But, the visceral smooth muscle is a myogenic smooth muscle, which is composed of cells that work as a single entity and function together.
Smooth muscles are composed of spindle-shaped cells that are non-striated. Their distribution is mostly seen in the internal system surrounding the internal organs. Therefore, they are involuntary in their action.
CONTENTS
1. Overview and Key Difference
2. What is Multiunit Smooth Muscle
3. What is Visceral Smooth Muscle
4. Similarities Between Multiunit and Visceral Smooth Muscle
5. Side by Side Comparison – Multiunit vs Visceral Smooth Muscle in Tabular Form
6. Summary
What is Multiunit Smooth Muscle?
Multiunit smooth muscles contain muscle cells that act independently in their muscular movements. The main two types of movements these cells undergo are relaxations and contractions. Thus, the movement of each smooth muscle cell is independent of each other. Smooth muscles are the types of muscles that form the internal organs of an organism.
Figure 01: Vascular Smooth Muscle
As individual cells function on it, there is no requirement for transmission of energy from the gap junctions between the cells. Therefore, the generation of an action potential does not take place in multiunit smooth muscles. Hence, the action of the multiunit smooth muscle cell is neurogenic and not myogenic. The cells do not rely on the neighbouring cells for their function. The best example of a multiunit smooth muscle cell is the vascular smooth muscle cell, forming the vascular muscle; they often undergo more contractions than relaxations.
What is Visceral Smooth Muscle?
Visceral smooth muscle is also called the single-unit smooth muscle. These muscles are composed of units or cells that function together. Each visceral muscle cell depends on each other and functions as a bundle that undergoes the same type of movement. Therefore, the action potential transits through each cell between the gap junctions in order to activate all cells simultaneously. And, this is why it is essential to have proper transmission of energy between the cells for the functioning of the visceral smooth muscle.
The visceral muscle cell is myogenic and is regulated via the input of the motor neuron. Each cell undergoes a coordinated movement in the visceral muscle. Their movements show rhythmic patterns. The visceral smooth muscles are mainly found in the internal viscera of the body, which includes the uterus, gastrointestinal tract and the bladder.
What are the Similarities Between Multiunit and Visceral Smooth Muscle?
- Multiunit and visceral smooth muscles are two types of smooth muscles
- These muscles are involuntary in nature.
- They are distributed in the internal organs.
- Moreover, they are both made up of non-striated, spindle-shaped cells.
- There are gap junctions between the multiunit and visceral smooth muscle cells.
What is the Difference Between Multiunit and Visceral Smooth Muscle?
The key difference between multiunit and visceral smooth muscle lies in the way in which its individual cells function. In multiunit smooth muscle, the individual cells function independently, while in visceral smooth muscle, cells are dependent on each other for their function. Thus, the passing of the action potential is important for visceral muscle cells while it’s not a requirement for the activity of the multiunit smooth muscle cell. Hence, this is another difference between multiunit and visceral smooth muscle. Most importantly, multiunit smooth muscle is neurogenic while visceral smooth muscle is myogenic.
The below infographic summarizes the difference between multiunit and visceral smooth muscle.
Summary – Multiunit vs Visceral Smooth Muscle
Multiunit and visceral smooth muscles are two types of smooth muscles. The difference between multiunit and visceral smooth muscle depends on how individual cells form the muscle act. In multiunit muscles, the individual muscle cells act independently as separate entities. They undergo varied movements. Visceral smooth muscles are composed of cells that work together. Therefore, they undergo coordinated movements. Although both types of cells are involuntary in nature, multiunit muscles are neurogenic while visceral muscles are myogenic.
Reference:
1. Hafen, Brant B. “Physiology, Smooth Muscle.” StatPearls [Internet]., U.S. National Library of Medicine, 17 Dec. 2018, Available here.
Image Courtesy:
2. “Endotelijalna ćelija” By DRosenbach at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia