Skeletal and smooth muscle cells show a number of similarities however they also display many differences. These similarities and differences can be seen through observing the structure and appearance of these cells, their control mechanisms and the ways in which they contract.
When observing both cell types under a microscope several differences are obvious. Firstly, skeletal muscles are larger than smooth muscle cells (one muscle cell can be up to 100µm in length). They are also multinucleated whilst smooth muscle cells are uninucleate (Alberts et al, 2002: 961). Additionally, skeletal muscle cells appear to be striated, whereas smooth muscle cells do not show this banding pattern; but are instead smooth and tapered. The absence of this patterning in smooth muscle cells suggests that they consist of a less organised collection of contractile fibres (Silverthorn, 2007: 397). This banding pattern in skeletal muscles is known as the sarcomere.
The sarcomere is found in structures called myofibrils which make up skeletal muscle fibres. Within the sarcomere there are various different proteins. One of the most significant, myosin is found in the thick filaments of the sarcomere. Although both cells contain myosin, it is important to highlight that smooth muscle cells contain a much lower percentage of myosin compared to skeletal muscle cells. Despite this, myosin filaments in smooth muscle cells bind to actin filaments in a manner similar to that in skeletal muscle cells; although there are some differences. For instance, myosin filaments in smooth muscle cells are saturated with myosin heads so that myosin can glide over bound actin filaments over longer distances, enabling smooth muscle cells to stretch further, whilst in skeletal muscle cells myosin heads are only located at the ends of these fibres (Silverthorn, 2007: 424). This is advantageous when one considers the location, the interior walls of blood vessels and organs, and therefore the functions that smooth muscle cells are able to execute- such as peristalsis (Tamarkin, 2011). This spontaneous and rhythmic movement displays how smooth muscle cells bring about involuntary movements through contraction, whilst skeletal muscle cell contractions are voluntary.
Smooth muscle cells are able to communicate with adjacent cells locally via gap junctions. However, only single unit smooth muscle cells are able to carry out such interactions (Bárány et al, 1997). They are also able to respond to paracrine signalling. An example of this is the relaxation of smooth muscle cells when Nitric Oxide acts as a neurotransmitter and binds to guanylyl cyclase to produce cGMP. Furthermore, smooth muscle cells react in the presence of hormones such as epinephrine. This particular hormone is able to induce behavioural changes in the cell through a signal cascade. The ability to communicate in these ways is significant as it enables smooth muscle cells to interact without firing action potentials. Although...