The Musculoskeletal System

Now for some notes on muscles and bones! Don't worry, I won't attempt to name every single one of them :)

1. Describe the chemical reaction at the neuromuscular junction across the synapse.

Communication at the neuromuscular junction is similar to communication between two neurons- the neuron releases neurotransmitters into the synapse, which bind to receptor sites on the other cell, triggering further reactions in the next cell. In the case of muscle contraction, the neurotransmitter released is most commonly ACh (acetylcholine). ACh binds to receptors on the motor end plate (part of the muscle on the other end of the synapse). This opens channels in the muscle cell membrane, allowing Na+ ions to rush in and create a depolarisation potential, stimulating the muscle to contract (well that's how I understand it, anyway). After ACh has had its effect, it is broken down by an enzyme called acetylcholinesterase.

2. Distinguish between isotonic and isometric contraction.

In isotonic contractions, the length of the muscle changes despite the tone and tension remaining the same. An example of an isotonic contraction exercise would be bicep curls- the load (and therefore the muscle tension) remains the same but the length of the bicep changes as you move the weight up and down.

In isometric contractions, the length of the muscle stays the same, but the force changes. An example of an isometric contraction exercise would be pushing hard against a wall. The length of your biceps would remain the same but more tension would be exerted. Believe it or not, isometric exercises can be good at building strength. However, they are not good at building bulk, so if you want to get bulky you'll probably just have to stick with weightlifting.

3. Describe a first-class lever. What muscle group and bone falls into this category?

A first-class lever is generally what first comes to mind when we think of a lever. In a first-class lever, the fulcrum is in the middle, the load is on one end and the force is being exerted on the other. An example of this in the body is the point where the neck articulates with the skull. At this joint, the neck is the fulcrum, the face and head is the load while the muscles at the back of the neck exert force allowing us to lift our head.

4. Why are third-class levers preferred in nature?

A third-class lever is a lever in which the fulcrum is at one end, the load is at the other and force is exerted from somewhere in the middle. There are plenty of third-class levers in our body. One example is the bicep, where the elbow is the fulcrum, the hand (and whatever we might be holding) is the load and the bicep exerts force upwards.

One important point to note about third-class levers (and about levers in general) is that the amount of force and distance that the force is required to move varies depending on the location of the force relative to the fulcrum and load. In the case of a third-class lever, if the force is being exerted closer to the load, the amount of effort required is reduced but the amount of distance required to move to lift the load is large. The inverse is also true: if the force is being exerted at some point closer to the fulcrum, the amount of effort required is significantly increased but the amount of distance required to move to lift the load is small. Many third-class levers in the body, such as the bicep, have the force located close to the fulcrum, allowing for greater speed in movements as well as a greater range of motion but with decreased mechanical advantage (strength).

5. Name and describe at least four functions of the bones.

Movement- Bones provide a point of attachment for skeletal muscles. In this way, bones also allow us to move around.

Storage- Certain substances, such as calcium salts, can be stored in the bones. (Incidentally, storage of calcium is responsible for the hardness of bones.

Protection- Some bones surround organs that need protection. For example, the ribs surround the heart and lungs while the skull surrounds the brain.

Support- Bones help keep us upright.

6. If the radius and ulnar heads are fractured (Colles' fracture), what joints must be immobilised in a cast to control movement until healing takes place?

In a Colles' fracture, treatment generally consists of first trying to move the bones back to their normal positions if they have been displaced. I would assume that then the wrist bones are immobilised to allow the fracture to heal. I'm not a doctor, and taking medical advice over the Internet isn't exactly the wisest idea anyway, so if you get a fracture and do all that and get worse, don't sue me. *disclaimer over*