What is a motor unit - how muscles contract

What is a motor unit? How a muscle contracts

What is a motor unit?

In short… it’s how a muscle contracts!

Let’s make this module super easy and jump into today’s video:

What we’re really talking about here is, module 8 of the Level 2 Anatomy and Physiology exam: The Nervous System. You can expect 4 to 6 exam questions around this module in your final exam so it’s key you understand the “Ins & Outs” to ensure you pass.


and take notes as you go through the 3-minute video making this complex topic, super simple!

A motor unit is made up of a single neuron [nerve cell]  that innervates a group of skeletal muscles.

The neurons receive signals from the brain and stimulate all the muscle fibres in that particular motor unit.

There are two components that make up a motor unit and you need to know both of these ready for your level 2 anatomy exam.

  1. A motor neuron 
  2. The muscle fibres that are innervated by the motor neuron.

What is a Motor Unit? Component 1: Motor Neuron

When we need to move a muscle, our Central Nervous System (brain and spinal cord) is responsible for deciding what muscles need to be activated and when. So, whether you want to do a squat or just lift a pencil, your central nervous system is “deciding” what muscles need to contract in order for this to happen.

Once the Central Nervous System has “decided” what muscle needs to contract, the information needs to get to the muscle. This is the job of the motor neurone.

A motor neuron carries information from the central nervous system to the muscles. The information that is carried, determines whether the muscle will contract or not. This is a simple “ON or OFF” option sent down the motor neuron. Each motor neuron is attached to a group of muscle fibres and it sends an electrical impulse that stimulates all of these fibres to contract at once.

The second component of the motor unit is the muscle fibre.

What is a Motor Unit?  Component 2: Muscle Fibre

There are a couple of differences between a muscle fibre, myofilament and a muscle belly. You’ll need to know these for your level 2 anatomy exam.

To help with these differences, watch this video as well. In this video you’ll learn everything about the muscle structure and anatomy.

WATCH NOW >> https://youtu.be/VLhgN5DxnkU

Muscle fibres can only switch on or off, there are no half measures. And for that reason, it’s called the, “all or none law,” when we’re talking about muscle contraction. As a result, there is only one variable that will change the intensity of muscle contraction. We need to engage and recruit more motor units, not more muscle fibres.

So, if you imagine or remember back to a time when you had to lift up a heavy box but you thought it was quite light. So, you think it’s a light box, you go up to it, you go to pick it up and you can’t lift it, it doesn’t move.

The reason for this is that you’ve recruited enough motor units to be able to lift what you deemed as a light box. When you try again, you can actually lift it because at that point, you’ve recruited enough motor units.

To recap, the motor unit is the motor neuron and all the muscle fibres that it innervates.

Together, the motor unit causes a muscle contraction.

Now you know everything there is to know about motor units ready for your level 2 anatomy exam.

If you want more mock questions like this, then you can download your Revision Pass Pack which includes 88 Level 2 Anatomy and Physiology mock questions: DOWNLOAD NOW

The fastest way to accelerate your learning and revision is to check out the L2 Anatomy and Physiology revision Mastery Series. Here all 8 modules are covered in 8x full HD video tutorials, with accompanying cheat sheet to make revision even easier again and test your knowledge as you go! I’ve also packed in 5 BONUSES for you as well, click the link below:

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