31 Introduction to MSK
Muscle cells:
Simply walking through an apple orchard would not be possible without the careful coordination of millions of muscle cells. Not only do these cells facilitate movement, but they also play crucial roles in digestion, respiration, and several other facets. A muscle cell or a myocyte is a specialized cell designed to contract and relax – an essential contractile unit – which has 3 variations:
Table 35 Muscle cells
| Type of Muscle Cells | Description |
| Smooth muscle | An involuntary contractile unit throughout the reproductive, digestive, urinary, vascular and respiratory systems. |
| Cardiac muscle | A striated and involuntary contractile unit present in the heart. |
| Skeletal muscle | A striated and voluntary contractile unit which maintains posture and movement. |
This chapter will primarily describe the role and anatomy of skeletal muscle throughout the body and how it facilitates basic anatomical movements. Each skeletal myocyte contains thousands of sarcomeres, the essential protein unit which contracts and relaxes to facilitate movement of muscles.
The neuromuscular junction:
To consciously move our muscles, the nervous system is required to coordinate our movements. The neuromuscular junction is the place where nerve cells communicate with myocytes to make them move, acting as the bridge between the nervous system and the muscular system. When you want to move part of your body, it sends an electrical signal down a nerve to the neuromuscular junction. There, the nerve releases special chemicals called neurotransmitters, which cross over to the muscle and trigger it to contract or relax. This process allows us to do everything from blinking to running – it’s what connects our thoughts to our actions! The nervous system, as it relates to coordinating movement as well as its many other functions, will be explored further in Chapter 5.
Figure 71 Neuromuscular junction
Antagonistic muscle pairs:
Let’s go back to the apple that you picked from the apple orchard, it is time to taste the fruits of your labour! Imagine holding the apple and slowly bending your elbow, bringing your hand closer to your mouth. This movement, known as flexion at the elbow, allows your forearm to move upward, bringing the apple towards your shoulder. Within this movement a muscle must contract and another muscle must simultaneously relax. In the case above, the biceps brachii muscle will contract and the triceps brachii muscle will relax. This contraction and relaxation is known as antagonistic muscle pairs and is present in every movement described above.
As we progress into this chapter, note how every muscle will have a synergist and antagonist partner. Kicking a soccer ball requires extension of the knee, which simultaneously requires contraction of the synergist group – the quadriceps muscle – and concurrent relaxation of the antagonist group – the hamstring group.
