Food for Thought: an example interview question
‘What are the similarities and differences between the upper limb and lower limb in humans? How does this relate to their different functions?’
This might seem like a bizarre question that you have never thought about before - don’t worry, that would almost certainly be expected! This is an anatomy-related topic, which is a subject nobody studies at school, and so is designed purely to get you thinking.
Let’s think about the difference between an arm and a leg! Throughout this example approach I will drop in some of the fancy anatomical terms (in bold) for everyday concepts, but remember that you are not expected to know any of this - it’s purely for interest and to get you thinking!
Anatomy likes to be annoyingly precise with its language, so let’s start by defining our terms. Upper limb is the term for all of the arm, forearm and hand.
Lower limb is the term for all of the thigh, leg and foot.
The upper limb is good at picking things up, holding onto things and doing complicated fine movements. The fancy term for this is prehension. Consider how tricky it would be to eat your dinner, write an essay or play tennis with your feet (a clip from one of my favourite shows to illustrate this!).
The lower limb is good for standing, walking and running. Scientifically we might call this weight-bearing and locomotion. We don’t tend to do very long hand-stands or walk about on our hands (another clip from another great show demonstrates this!).
Let’s now think about the structure of each limb and see if it relates to these functions. Remember you are not expected to know any names of bones or muscles!
The arm has a single bone (humerus), the forearm has two bones (radius and ulna) and then the hand has many bones (wrist, palm, fingers = carpals, metacarpals and phalanges).
The thigh has a single bone (femur), the leg has two bones (tibia and fibula) and the foot has many bones (ankle, main foot, toes = tarsals, metatarsals and phalanges). The upper and lower limb therefore seem very similar in their basic structure!
The main muscles of the arm are biceps (which bend it at the elbow, i.e. flexion) and the triceps (which straighten out the elbow, i.e. extension). In the leg we have the hamstrings (bend the knee, i.e. flexion) and quadriceps (straighten the knee, i.e. extension). We won’t go into details or mention other muscles, but again this seems similar in both limbs.
How do they differ then? Let’s start with size. Usually the upper limb is smaller and shorter than the lower limb. The femur in the lower limb (longest bone in body) is bigger and thicker than its upper limb counterpart, the humerus. The quadriceps and hamstrings are bigger, stronger muscles than the biceps and triceps. This all makes some sense - to support our body weight and walk about, we want bigger bones and stronger muscles in the lower limb. To do fancy movements such as play the piano or solve a Rubik’s cube, we don’t need as big structures and can keep the upper limb lighter.
How about how the limbs attach to the body? The upper limb attaches at the shoulder (glenohumeral joint) and the lower at the hip (acetabulofemoral joint). We won’t go into the details of their structures, but the shoulder is a much more flexible joint than the hip. Think about swinging your arm around in a circle - you can do this pretty easily and in all directions but would struggle to get the same range of movement with a leg! Again this makes sense - your arm needs to be able to move into all sorts of positions for various complicated manoeuvres, whereas your legs mainly need to keep you standing up and move forwards and backwards for walking. You could say that the upper limb has prioritised mobility whereas the lower limb has prioritised stability - this is at least partly due to the joints involved. This is also why dislocated shoulders are more common than dislocated hips!
We could go into lots more detail on this - including how thumbs differ from big toes, where the different muscle groups are placed in the limbs, and how evolution ties into all of this. I will leave that up to you if you are interested (an article on it is available here but again remember you are not expected to understand this!). Hopefully this short summary has given you an idea of how to approach a question you might never have considered before!
Remember, you aren't expected to know everything - the interviewer is much more interested in whether you can think.
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