Motoneuron Types

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From the course by The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

670 ratings

The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

670 ratings

Learn how the nervous system produces behavior, how we use our brain every day, and how neuroscience can explain the common problems afflicting people today. We will study functional human neuroanatomy and neuronal communication, and then use this information to understand how we perceive the outside world, move our bodies voluntarily, stay alive, and play well with others.

From the lesson

Voluntary Movements

"Voluntary movements are how we interact with the world. The organization of the motor system has implications for how we move, and the types of movements we can make. This module we'll start to explore the organization of the motor system, from neurons to muscles. This module contains a lot of material, so be sure to start early so that you have time to finish!"

Fast and Slow Fibers5:12

Motoneuron Types4:11

Orderly Recruitment7:40

Exercise and Muscle Mass2:48

Meet the Instructors

Peggy Mason
Professor
Neurobiology

[MUSIC]

As you know, skeletal muscles cannot move on their own, they need motor neurons

and now we've just looked at the

fact that muscle fibers, skeletal muscle fibers differ.

Some are dependent on oxygen, some are dependent on glycogen.

Some can stay contracted for a long time and some for a very short time.

Well, those different types of muscle fibers, the slow, the fast that are

dependent on oxygen, I'm sorry, on

glycogen alone, are innervated by different types

of motor neurons and there's an intermediate type of muscle fiber that is

dependent on oxygen, until the oxygen runs out and then it's dependent on glycogen.

And whereas, the slow muscle fibers can last for hours and

hours and hours and the fast glycogen dependent ones can last for,

say, three to five minutes, the fast glycogen, oxygen and glycogen muscle

fibers, can last for on the order of 30 minutes or so.

Okay, so each type of muscle fiber is innervated by a different type of

motor neuron and the motor neurons get the names of slow, innervating

is slow, fast fatigue resistant, innervating

these muscle fibers that can use either

oxygen or glycogen, and fast fatigable, that

can innervate these, that innervate only these

fast muscle fibers that are dependent on glycogen.

So every muscle fiber only gets input from one motor neuron

and every motor neuron innervates some number of muscle

fibers and, in general, the number of muscle fibers

innervated by a motor neuron is low for the slow fibers,

slow motor neurons, higher for the fast fatigue resistant

motor neurons and highest for the fast fatigables.

So when you're standing all day, you're using these.

When you go and you lift weights, you're using these.

In a disease such as polio, what you're

losing is you're losing a motor neuron and

all of the muscle fibers that it innervates.

So in the case of, the name of this motor neuron, plus all the

muscle fibers that it innervates is called the motor unit and as

a motor neuron dies, which is what happens in polio, the motor

neuron dies and now all of these muscle fibers are not innervated.

They, they're offline and so there's fewer motor neurons

to do the same amount of work and this is actually, one of the

reasons why people think that there's a post polio syndrome.

When people that have survived polio get to

be 50 or 60, their motor neurons start to

give out and the thought is that perhaps, now

they've got say, 30% of the motor neurons that

they've started with are doing the job of 100%

and at age 60 or 70, they're tired and

now they're going on the fritz and so these

people are starting to have problems with the same

muscles that they originally lost motor neurons in.

What we're going to look at in the next segment is how we are going to make a

smooth movement recruiting these different types of motor neurons.

[MUSIC]

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