The Neuromuscular Junction: Function, Structure & Physiology

Your next lesson will play in 10 seconds
  • 0:07 Synaptic Transmission
  • 1:24 Anatomy of a Synapse
  • 2:18 Physiology of a Synapse
  • 4:47 Neuromuscular Disease
  • 5:38 Lesson Summary
Create An Account
To Start This Course Today
Used by over 10 million students worldwide
Create An Account
Try it free for 5 days
Lesson Transcript
Instructor: John Simmons

John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology.

A neuromuscular junction is a synapse between a motor neuron and skeletal muscle. This lesson describes the events of synaptic transmission leading to contraction of skeletal muscle. Myasthenia gravis is described as a neuromuscular disease.

Synaptic Transmission

In order for skeletal muscle to contract, it must first be stimulated by a motor neuron. The space between the motor neuron and the skeletal muscle cell is simply referred to as a synapse. More specifically, the synapse between a motor neuron and a skeletal muscle cell is referred to as a myoneural or neuromuscular junction. If you break down these terms, the names will make better sense. 'Myo'- means muscle, and 'neuro'- refers to nerves. Regardless of the name, the synapse is a real space across which the excitatory impulse must travel before the muscle contracts.

A neuromuscular junction between a motor neuron and skeletal muscle cell
Neuromuscular Junction Diagram

Synaptic transmission includes all the events within the synapse leading to excitation of the muscle. Let me make a quick note that other synapses occurs between other cells - for example, nerve to nerve and nerve to gland. For example, the adult human brain is thought to contain 100-500 trillion synaptic connections, and those are in between neurons. In this lesson, we will describe the anatomy of a neuromuscular junction and then discuss the events of synaptic transmission.

Anatomy of a Synapse

The image you see on the screen illustrates a synapse between a neuron and a muscle cell. The neuron is sending the transmission and is thus referred to as the pre-synaptic cell, while the muscle is receiving the transmission and is referred to as the post-synaptic cell. Neurotransmitters are molecules stored in the pre-synaptic cell that are secreted into the synapse. Neurotransmitters, in turn, bind to receptors on the post-synaptic cell membrane, and these receptors are specific for that neurotransmitter.

Think of the neurotransmitter-receptor relationship as a lock and a key, where only one key will fit that lock. The synaptic cleft refers to the space between the two cells and is only about 20 nanometers wide. That's pretty thin!

A diagram of a synapse between a muscle cell and neuron
Synapse Muscle Cell Diagram

Physiology of a Synapse

Now that we know what makes up a synapse, we're ready to describe the function of the neuromuscular junction. It's important to keep the big picture in mind. So what is that big picture? Synaptic transmission carries the excitatory signal from the neuron to the muscle cell, much like a bridge could connect two land masses.

Let's start with the motor neuron. Calcium enters the excited neuron, and the calcium stimulates exocytosis of the neurotransmitter. Where does the neurotransmitter go but into the synaptic cleft. The neurotransmitter secreted by the somatic motor neurons is acetylcholine.

So the acetylcholine diffuses across the cleft and binds to acetylcholine receptors within the muscle cell membrane. Like a key unlocking a door, acetylcholine opens ion channels, and sodium ions diffuse into the muscle cell. It's important to note that acetylcholine does not remain in the synaptic cleft forever, but rather an enzyme called acetylcholinesterase catalyzes the breakdown of acetylcholine, and where is it located - in the synaptic cleft. This enzyme breaks down acetylcholine and therefore prevents overcontraction, or prevents contraction for lasting longer than necessary.

Since sodium is a positive ion, it depolarizes and thus excites the skeletal muscle cell membrane as it enters. Now the excitatory impulse has transferred from the motor neuron to the muscle cell, much like a car would cross a bridge from one land mass to the next.

Calcium is released into the cell interior, causing contraction.
Calcium Triggers Muscle Contractions

To unlock this lesson you must be a Member.
Create your account

Unlock Your Education

See for yourself why 10 million people use

Become a member and start learning now.
Become a Member

Already a member? Log In

Earning College Credit

Did you know… We have over 49 college courses that prepare you to earn credit by exam that is accepted by over 2,000 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Click "next lesson" whenever you finish a lesson and quiz. Got It
You now have full access to our lessons and courses. Watch the lesson now or keep exploring. Got It
You're 25% of the way through this course! Keep going at this rate,and you'll be done before you know it.
The first step is always the hardest! Congrats on finishing your first lesson.
Way to go! If you watch at least 30 minutes of lessons each day you'll master your goals before you know it.
Congratulations on earning a badge for watching 10 videos but you've only scratched the surface. Keep it up!
You've just watched 20 videos and earned a badge for your accomplishment!
You've just earned a badge for watching 50 different lessons. Keep it up, you're making great progress!
You just watched your 100th video lesson. You have earned a badge for this achievement!
Congratulations! You just finished watching your 200th lesson and earned a badge!
Congratulations! You just finished watching your 300th lesson and earned a badge!
You are a superstar! You have earned the prestigious 500 video lessons watched badge.
Incredible. You have just entered the exclusive club and earned the 1000 videos watched badge.
You have earned a badge for watching 20 minutes of lessons.
You have earned a badge for watching 50 minutes of lessons.
You have earned a badge for watching 100 minutes of lessons.
You have earned a badge for watching 250 minutes of lessons.
You have earned a badge for watching 500 minutes of lessons.
You have earned a badge for watching 1000 minutes of lessons.