Intro and Structure

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Del curso dictado por Duke University

Introductory Human Physiology

1619 calificaciones

Duke University

Introductory Human Physiology

1619 calificaciones

In this course, students learn to recognize and to apply the basic concepts that govern integrated body function (as an intact organism) in the body's nine organ systems.

De la lección

The Senses and the Somatic Nervous System

In this module, we consider two types of cells: one that relays information to the central nervous system (brain) for interpretation and a second set, motor neurons which relay information away from the central nervous system to govern voluntary movement. The input pathway to the brain is mediated by specific cells called senses. The senses convert energy (such as light or heat) into an energy form (electrical potentials) recognized by neurons in the brain. The brain, in turn, interprets this information (as vision or pain) and then sends out a motor response via the motor neurons of the somatic nervous system to effector cells in the body. The motor neurons activate skeletal muscle to control breathing and the movement of the limbs. The things to do this week are to watch the 5 videos, to answer the in-video questions, to read the notes, and to complete the problem set. It will be most effective if you follow the sequence of videos. The notes provide a more detailed summary of each topic. We encourage you to find which resource (videos and/or notes) works best for you and to try the problems sets. The problem sets are not graded. Both your understanding and retention will increase with application of the new learned information.

Intro and Structure10:17

Control of Movement26:12

Conoce a los instructores

Jennifer Carbrey
Assistant Research Professor
Department of Cell Biology
Emma Jakoi
Associate Research Professor
Department of Cell Biology

Hello we're going to finish our consideration of the nervous system by

now considering an efferent pathway, the somatic nervous system.

So we talked about the afferent pathways coming into the central nervous system and

now we're gonna kind of combine the two when we after we consider just the ether

pathway the semantic nervous system that activates skeletal muscle.

Then in the next session we are going to talk about reflexes,

which is where we bring in sensory information,

the central nervous system integrates that information, decides what to do,

and then we're gonna consider the efferent pathway through the somatic

nervous system and how that controls things like reflexes and locomotion.

So in this session,

we're gonna talk about general principles of the Somatic Nervous System.

Some aspects,

spinal cord structure and just touch again on the neuromuscular junction

by the fair amount of this will be some review from just the nervous in general.

And then in the next session we're gonna talk more about how the afferent

pathways and efferent pathways come together to control movement.

So you've seen this figure before,

just to place this in the context of the larger nervous system,

where we're gonna have sensory information coming in through afferent pathways.

That's what we've talked about.

Most recently, the CNS is gonna integrate and

then we're gonna be talking about the somatic nervous system which is the part

of the efferent nervous system that controls skeletal muscle.

That's going to be in contrast to the autonomic nervous system

which is gonna be what controls the organs.

And this again is review to remind you that with the autonomic nervous system,

such as the sympathetic portion and the parasympathetic portion, we have

two neurons in series, where the first neurons in the central nervous system.

And the second one is sitting out in the periphery.

But with the somatic nervous system, we have

the single neuron sitting in the central nervous system and

sending it's axon all the way out to the muscle to stimulate it.

So, it's a single neuron system in terms of the e-parent portion.

And also keep in mind that the skill of muscle is gonna perform a variety

of actions, not just voluntary actions.

So, it's gonna be involved in reflexes and

breathing, which are gonna be somewhat involuntary actions.

Let's review our spinal cord structure where we've already talked about how we're

gonna have an afferent neuron coming in.

It's cell body is sitting usually in the dorsal root ganglion for

the body sensory information.

And then there will be neurons sitting in the spinal cord called interneurons

that are going to be part of the system that is going to

interpret the stimuli coming in.

And we'll see in the next session concrete examples of the circuitry.

So we're gonna have interneurons that are collecting information.

And then based on what they decide, we will have firing of

the efferent neuron for the somatic nervous system, that's gonna be sitting

in the ventral what we call the ventral horn of the spinal cord.

So, this is the ventral portion of the spinal cord and

here we're going to have all of our motor, somatic motor neurons with their cell

bodies sending their axon all the way out to the skeletal muscle.

We need to now consider that somatic motor neuron that we're just

looking at in the spinal cord.

What is it synapsing with?

And so that comes to the definition of a motor unit,

where motor unit is a single motor neuron.

And all of the muscle fibers,

which is the same thing as a muscle cell, that it controls.

So that's what a motor unit is, and

we'll be talking about this more when we talk about skeletal muscle as well.

Where a usually a neuron is gonna control anywhere

from 3 to around 1,000 different muscle cells,

skeletal muscle cells or, which is the same thing as skeletal muscle fibers.

All of those fibers are gonna be in the same muscle, but

they're usually gonna be spread out.

So that's what's shown here in this muscle,

where we're saying that these blue muscle cells are the ones that are enervated and

receiving signals from one neuron.

This is this one motor neuron's motor unit.

Keep in mind that one,

a single muscle cell is only going to be intervated by one neuron.

Which means that it is only being controlled or regulated by one neuron,

so our decision making about whether or not a muscle

cell should contract is coming at the level of the somatic motor neuron.

If it sends an action potential down it's axon to the muscle

the muscle is gonna contract and we'll talk about that in just a minute and

that muscle cell is only getting inputs from that one neuron.

So the muscle cell is not having to decide whether or

not it's gonna contract because it's only being controlled by one neuron and

whenever that neuron fires, that muscle is going to contract.

So the decision making is happening with the somatic motor neuron

not with the muscle cell receiving multiple inputs from multiple neurons and

deciding whether or not to contract.

So let's talk about the Neuromuscular Junction,

which is just gonna be a certain type of synapse which we've already talked about.

There's nothing so unusual with it.

We're gonna have the axon from the somatic motor neuron

coming to contact the plasma membrane of the skeletal muscle cell.

So the action potential will travel down that axon and when it does,

just like in a normal snaps, it's going to open voltage-gated

calcium channels that will let calcium into the terminus of the axon.

Which is gonna be the signal to cause vesicles of the neurotransmitter,

and more specifically, acetylcholine, to fuse and

to be released into the synaptic cliff, cleft.

So acetylcholine is gonna be what's released by all somatic motor neurons.

The muscle motor end plate, which is just the portion of the muscle plasma membrane

that is at the synapse, is gonna contain nicotinic acetylcholine receptors.

So these are nicotinic synapses.

And we know that nicotinic acetylcholine receptors

are going to be acetylcholine dated sodium channels.

So that means that if this neuron fires, it's going to open sodium channels.

That's going to cause a greater potential.

However, keep in mind that right next to this synapse on

the skeletal muscle plasma membrane we're going to have voltage,

gated ion channels.

Which is going to be somewhat unique compared to what we saw with neurons.

So that means that basically we are having a synapse to

what would be equivalent to the axon initial segment.

And so that means whenever we have firing of the somatic motor neuron, for

all intents and purposes we're also going to have an action potential that occurs in

the skeletal muscle membrane as well.

And we'll be talking more about that once we cover muscle.

But again, it's this idea that if that neuron fires,

we're gonna have an action potential in the muscle membrane.

And that's gonna cause contraction just because we're having a graded potential

right next to voltage gated channels.

And so it's a pretty much given that one's going to follow the other.

So, we've just had an introduction to the somatic nervous system,

where we're gonna control many different types of movement.

One, because for instance,

the diaphragm that controls our breathing is skeletal muscle.

So things like that, as well as obviously the muscles that are important for

posture, and locomotion and these somatic nervous motor neurons are going to act,

they're sitting in the spinal cord and they're going to act on skeletal muscle.

A motor unit is going to be a somatic motor neuron and

the fibers that it innervates or controls.

And we're gonna have these motor neurons in the grey matter

of the ventral horn of the spinal cord.

And then we mentioned just briefly, but we'll talk more about it.

About this, interneurons in the spinal cord and how they

are gonna be important in coordinating responses and integrating information.

And this is a subject that we're gonna really focus on in the next

section in terms of talking about how we make reflexive movements.

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