Term
| What is a typical resting membrane potential for a CNS neuron? |
|
Definition
|
|
Term
| At rest, where is the concentration of Na+ higher? |
|
Definition
|
|
Term
| T/F: The Golgi tendon organ is encapsulated and parallel with the extrafusal muscle fibers. |
|
Definition
|
|
Term
| T/F: The tendon organ is stretched when muscle is stretched. |
|
Definition
|
|
Term
| T/F: The tendon organ is still stretched when the muscle actively contracts. |
|
Definition
|
|
Term
| T/F: Muscle tone is an abnormal degree of tension maintained in skeletal muscles by voluntary spinal reflexes. |
|
Definition
|
|
Term
|
Definition
Reflex is an involuntary, very fast movement in response to
a stimulus. A reflex action (the movement) is mediated by
a reflex arc. This is the basic pathway from sensory
stimulation to motor response. The overall purpose of this
lecture is for you to become aware of different types of
reflexes and understand some common and basic reflex
arcs. |
|
|
Term
|
Definition
There are many different ways to classify reflexes, e.g.,
• Place: cranial nerve vs. spinal nerve mediated
• Function: postural, flexor-extensor, protective,
blood-pressure regulation
• What: somatic vs. visceral |
|
|
Term
| deep vs superficial relexes |
|
Definition
Clinically, it is convenient to classify reflexes
as deep or superficial.
• Deep: stretch reflexes (mediated by muscle
spindles and Golgi tendon organs); an easy
clinical way to elicit a reflex is by a sharp tap in
the appropriate tendon—this induces stretching
of the muscle followed by a reflexive shortening
of the same muscle
• Superficial reflexes: withdrawal reflexes
induced by noxious or tactile stimuli |
|
|
Term
|
Definition
Now what you have here is the Golgi tendon organ. It's also highly specialized, as I said, also encapsulated. It uses virus type Ib, and it's at the insertion between tendon and muscle. It measures something very different. And this is important for you guys to remember.
While the spindle is in charge of changes in muscle length, the Golgi tendon organ is in charge of muscle tension--force that is applied. It is also-- it's low in tensile adaptation rate. So it's different from the way in which the muscle, the spindle has adaptation. But it's low in tensile activation threshold. |
|
|
Term
|
Definition
• Muscle tension
• In series with
extrafusal muscle
fibers
• Sensory axon: Ib |
|
|
Term
|
Definition
• Muscle length
• In parallel with
extrafusal muscle
fibers
• Sensory axons:
Ab/group Ia
Ab/group II |
|
|
Term
|
Definition
Before we get into all of the details of the muscle, the spindle, and the Golgi tendon, and so on, I want to do a mental exercise. I want us to understand perhaps most basic type of reflex. That is the muscle stretch. And then we will go into the details.
So what you have is an arc, a reflex arc that involves only two cells. Therefore, is monosynaptic, is a monosynaptic arc. You have an efferent fiber. That's the central information which is being collected, is going to collect information about this stretch of the muscle, the lengthening of the muscle fibers.
And it brings that information to a motor neuron that is residing in the grey matter of the spinal cord. That is an alpha motor neuron that immediately goes back to the same muscle to the extrafusal muscle fibers, excites them, and makes them contract. So the sensory part is coiling around that interfusal muscle fibers, detects the stretch, tells the motor neuron that something has happened, the muscle has a stretch
The alpha motor neuron comes back to the extrafusal muscle fibers, excites them, and make them contract. This is a mechanism to protect the muscle so that there is not too much stretching. So you stretch it, and then you contract it. Two cells-- one sensory cell, one motor cell.
The sensory cell is in the dorsal root ganglia. The motor cell is in the grey matter of the spinal cord, does the simplest type of reflex that you can have, and it's extremely fast and extremely efficient. Now, what we are going to do is we're going to start giving you more and more details as to what other things happen.
Now, what you have here is differences between Golgi tendon organ and the muscle spindle. So you have both, and they are both working together. In this diagram, you can see the coiling of the sensory fiber around interfusal muscle fibers. That interfusal muscle fibers are in the belly of the muscle surrounded by extrafusal muscle fibers.
So in the case of the muscle spindle that is going to be in charge of measuring muscle length, the fibers in the sensory apparatus is in parallel with the extrafusal fibers. Sensory axons, again, are type Ia and type II. On the other hand, the Golgi tendon organ is down here after the fibers, the muscle fibers. So it is going to measure muscle tension. And it is not in parallel but series with the extrafusal muscle fibers. And the type of axon which is going to be responsible for collecting sensory information is Ib.
Now, beware. What you are going to see is basically the same information over and over, different flavors. So the idea is that with the repetition, you will get the main ideas in different ways. You don't get it one way, you get it the other way. So what we have now is more details of the same thing. |
|
|
Term
|
Definition
You have a Golgi tendon organ here, muscle spindle, and comparisons between both of them. In the case of the Golgi tendon organ, it's giving you details about the encapsulation and the collagen fibers that are in both. In the case of their muscle spindle, suffice it to say that you have these interfusal muscle fibers inside, of which there are different flavors. The nuclear bag chains are, for instance, one of them. And then the coiling of the central information around them.
Now, you also have gamma motor neurons that come to the ends of those interfusal muscle fibers. That is important to maintain them taut. In other words, they are able to respond whether they are stretched or they are relaxed. Then around, you have the extrafusal muscle fibers. So you have at least a couple of different motor neurons in a couple of [? centrally ?] different fibers. |
|
|
Term
|
Definition
• Encapsulated complex
• In the tendon, at the insertion of
skeletal muscle
• A single Ib sensory axon that
branches and coils around the
collagen strands
• Arranged in series with
extrafusal muscle fibers
• Responds to tension due to
stretch of the muscle, but the
response of the spindle is
stronger (higher AP firing
frequency)
When the extrafusal muscle fibers
are made to contract by the α-MN,
firing increases (while the spindle
becomes silent). |
|
|
Term
|
Definition
| Now, if we move to the next slide, we have still more details on the Golgi tendon organ. Important to keep in mind-- it's encapsulated inside the insertion of the skeletal muscle. That's why it is able to [? measure ?] tension. It's a single Ib sensory axon that branches around in coils inside of this complex. And it's in series with the extrafusal muscle fibers. Again, it responds to tension. |
|
|
Term
|
Definition
Details about muscle spindle. Nothing new, everything that we have already mentioned. In here, you have nuclear bag fibers, again, and you have other types of fibers like the nuclear chain fibers. And then outside, you have the extrafusal muscle fibers. So you have interfusal in the belly and extrafusal outside.
The ones that receive alpha motor neuron excitation and make the muscle contract are the extrafusal muscle fibers. So these are just more and more details. We can make it more and more detailed. Both of them work together. It's important to keep this in mind. The Golgi tendon organ and the muscle spindle are working together. |
|
|
Term
|
Definition
AP firing frequency inc's w stretch and dec's w contraction
However, if both
a and g MNs are
activated, there is
no decrease in
fiber Ia firing
during muscle
shortening.
g MNs regulate
the gain of
muscle spindles
so they can
operate efficiently
at any length. |
|
|
Term
|
Definition
If you have paid attention to somebody, for instance, lifting a heavy weight. They go like that, and they have the muscle working very heavily. OK? And all of that time, something is happening to the Golgi tendon organ. When the Golgi tendon takes over, boom, they let go because now, it's a reversal of the activation.
Again, it's a mechanism to protect the muscle. If you keep on putting tension into the muscle and you don't respond to it, then it will break. OK. Now, both alpha motor neurons and gamma motor neurons are activated. There is no decrease in the fiber Ia by muscle shortening. However, this is important as I already mentioned, because you need to regulate the gain of the spindle so that they can respond under every type of circumstance for what is happening to the fibers.
Here you have it in the picture. Know what is going on in terms of the action potential frequencies. So this is important. Pay attention to this part here. The action potential firing frequency goes up with a stretch-- that is the stretch of the muscle fibers-- and it decreases with contraction. |
|
|
Term
The muscle
spindle and stretch |
|
Definition
Increased stretch
of muscle fibers
opens stretch
sensitive ion
channels in the
nerve, allowing
influx of cations
(+ charge). This
causes increased
receptor potentials
in the nerve. |
|
|
Term
|
Definition
Now, in terms of the mechanism that is at work, it's a very interesting one, and you have some of the details in these diagrams. Now to understand what is going on, let me give you an example. If you have a balloon, and you have little holes in the balloon, and the balloon is not inflated, you may not even see the holes. So the holes are basically closed.
Now, when you inflate the balloon, you stretch all the fibers in the balloon. You make it bigger. You are filling it with air. And then you are able to see those holes, and then air will escape through the holes. It's the same simple idea in terms of the types of ion channels which are in bold.
When the muscle inflates, basically, then they are opening. And then there is exchange of ions. Here, you have the electrophysiology for those events. Let me see if I can't make it bigger right here.
And so what you see, that's where the stretch, the amplitude is increasing. And that's an important characteristic. That's the electrophysiological characteristic of this type of receptors. These receptors are anchored, by the way, via cytoskeleton strands. So it's like a mesh that is holding them together.
And on the lower part of the screen right now, you have responses that are recorded electrophysiologically from single channels. So we are able to record electrophysiology through single channels, and so we know how they work. We move to the next slide. That brings us to the end of this first part of reflexes. |
|
|
Term
|
Definition
|
|
Term
|
Definition
the normal degree of tension maintained in skeletal muscles
by involuntary spinal reflexes; the resistance of skeletal muscle to passive
elongation or stretch |
|
|
Term
|
Definition
This is part two of our short lecture on reflexes. So here, we are going to go back and review the basic reflex arc that I already described. What you have is a muscle spindle right here, and if the muscle is stretched, it's sending that information straight to one alpha motor neuron.
That goes back. You can see one and then the number two. So one is the afferent sensory information. Number two is efferent-- the motor information. That goes back to those [INAUDIBLE] muscle fibers and makes them contract. So you stretch, then you contract.
Now that, as I said, is a monosynaptic reflex-- is the simplest part of everything which is going on with reflexes. However, as I also mentioned earlier, everything is a little bit more complicated.
Now after that part, it's only two cells that are in both now. The truth of the matter is that [INAUDIBLE] interneurons, you need to also communicate to the contralateral muscle, to the muscle opposite the one that is undergoing stretching and contraction, and you need that muscle to relax. The reason for that is that you don't want two sets of muscles that are opposite to each other to be doing the same thing at the same time because then they will work against each other, and they might damage each other.
So we call this reciprocal innervation-- so innervation to the reciprocal set muscle or set of muscles on the other side of the muscle that is undergoing the first stage of contraction. All of these so far-- we are keeping it on one side. It's ipsilateral. It's one side of the body. But like with everything else, things are more complicated, and things can also involve the ipsilateral and contralateral side.
However, before we move into that part, lets do the same thing now, not by stretching normally the muscle, but as you can have it here, by a small tap of the tendon. So you are also-- when you do that, you are also stretching the muscle. And so the reaction is to lift the foot. This is exactly the same thing that we did before, but now you have the involvement of a little bit more stuff, including the Golgi tendon organ that might take place, might start activating. So now we are going to still complicate things a little bit more. Let me move to the next slide. |
|
|
Term
|
Definition
is a reflex contraction of a muscle in response to stretching
of the muscle (will use the muscle spindle) or/and an attached tendon (will
use tendon organ). The stretch reflex is very fast and constantly working as
an anti-gravity response (keeping the limbs extended against the force of
gravity pulling you down). Gravity exerts tension on the extensor muscles
and they contract and keep the limbs straight. |
|
|
Term
|
Definition
monosynaptically excite motor neurons innervating agonistic
muscle (resulting in contraction) and polysynaptically inhibit motor neurons for
antagonistic muscle, resulting in stretching or extension |
|
|
Term
|
Definition
| And now we give an example from the arms. This is still one side of the body. It's exactly the same idea. And you are now going into a different tendon, but all of reflexes are happening the same way.. deep tendon stretch reflex |
|
|
Term
|
Definition
The tendon
pulls the muscle and makes it
stretch.
• The patellar tendon
• The Achilles tendon
• The biceps tendon
Absence of tendon reflex is
usually a sign of disease. |
|
|
Term
|
Definition
is
innervation so that the
contraction of a muscle or set
of muscles is accompanied by
the simultaneous inhibition of
an antagonistic muscle or set
of muscles—This assures that
the agonist and antagonist
muscles do not contract
simultaneously |
|
|
Term
|
Definition
| Now, if I still move to the next one, now we involve still more cells, and other things might be happening. And this is now making sure that you understand the concept of reciprocal innervation. |
|
|
Term
|
Definition
= withdrawal reflex
A protective polysynaptic ipsilateral segmental reflex in which a painful stimulus
triggers the contraction of ipsilateral flexor muscles (and the ipsilateral
extensors are inhibited) which takes the limb away from the source of pain.
These reflexes have slower onset and longer response than the stretch
(extensor) reflexes. |
|
|
Term
|
Definition
flexor/withdrawal reflex
Here is that we have both sides. And this is a lot of reflexes that happen that you do all the time and you don't even think. When we walk, for instance, there is our reflexes, which are at work, that keeps us in balance. So this is one of the reasons why we walk like that.
In one of the reasons, if you pull or you push against a force in one arm, you might have a reaction on the other arm as well. So remember, things might be complicated. The first set of actions involve just the simplest reflex arc, which is two cells, sensory and motor cell. But in reality, you need to also have inputs to the opposite muscles so that the two muscles are not working against each other.
So this innervation has to be there. So now you in both, and interneuron and another set of neurons to go to the other muscle. You may have the case in which you also have to involve the other side of the body. And then not only ipsilateral bodies will be contralateral.
A lot of these details is what is contained in all of this presentation. Unfortunately, we don't have enough time to go into every single detail. But I hope that is well explained, explained to the point that you can read it and understand it. |
|
|
Term
| Golgi tendon organ main points |
|
Definition
• Encapsulated
• In series with extrafusal muscle fibers
• One type of sensory axon: Ib
• Endings: branching and coiling around collagen strands
• Tendon organ is stretched when muscle is stretched
• Tendon organ is still stretched when the muscle actively
contracts |
|
|
Term
| muscle spindle main points |
|
Definition
• Encapsulated
• In parallel with extrafusal muscle fibers
• Two types of intrafusal fibers:
- Nuclear bags: (one or two), 7–8 mm long; 25 µm wide • Each nuclear bag has 1–2 gMN axons and 1–6 motor end
plates
- Nuclear chains: 4–5 mm long, 12 µm wide • Each nuclear chain has gMN axons and irregular trail endings
• Two types of sensory axons: Ab group IA; Ab group II
• Two types of sensory fiber endings: annulo-spiral (coils);
flower-spray
• Spindle is stretched when muscle is stretched
• Spindle is shortened when muscle actively contracts |
|
|
Term
|
Definition
pupillary light-reflex
This is part 3 of our short introduction to reflexes. So now we are going to talk about something a little bit different. We already did things that have to do with the muscles, and so on. This has to do with muscles as well, but for the visual system. And what we will do is describe the pupillary light reflex. Now before we go into the anatomy, which is rather simple and straightforward, I want to show you, in a schematic, what is going on.
What you have is fibers from the optic nerve that are extrageniculate, extrageniculate because they are not going to the lateral geniculate nucleus of the thalamus but rather, to pretectal areas. And then from pretectal areas, they go to the Edinger-Westphal nucleus, which is where you have preganglionic parasympathetic neurons, and then to the ciliary ganglion. This is via cranial nerve 3. So I hope you remember your cranial nerves olfactory optic oculomotor is the number 3.
And from there, constrictor muscle fibers of the iris. Now what happens is that when you shine light, as you know, in one pupil, both of them react. |
|
|
Term
|
Definition
So in the next slide, we are going to look at it from the anatomical point of view. So light comes into one of the eyes. Now remember, this sensory information of the optic chiasm, right here in the middle, is now going both ways, ipsilateral and contralateral.
And if you notice, when it's going to the pretectal nucleus, the little yellow nucleus depicted in the diagram, then it is collecting information and sending it again both ways, ipsilateral and contralateral. So at this point, all the information is already mixed. The sensory information came from one eye, but at this point, it has now split and is on both sides.
Now it doesn't matter anymore that ipsilateral from the Edinger-Westphal to the ciliary ganglion, because it's already on both sides. So is from both Edinger-Westphal to both ciliary ganglions. And they are both affecting the corresponding pupillary constrictor muscles, so both of the muscles are going to contract in reaction to the light. And that's how it works.
Now, of course, all of these things are clinically important. This is one of the reasons why you go to the doctor's office and they put a light into your eye. They are checking for this particular reflex. That's one of the things that they are doing. |
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
lower motor neuron problem—reduced muscle tone,
e.g., skeletal muscles become limp and cannot contract; can be fatal, e.g., if
it affects the respiratory muscles (Causes? Botulism, polio, curare) |
|
|
Term
|
Definition
upper motor neuron problem—hypertonia—excessive
muscle contraction; hence, hyperreflexia: exaggerated deep tendon reflex
(treated with baclofen: GABA agonist) |
|
|
Term
|
Definition
basically loss of muscle function—
damage to either CNS or PNS |
|
|
Term
|
Definition
| cardiovascular accident—ischemia |
|
|
Term
|
Definition
viral
attacks very effectively the interneurons that are present in the grey matter of the spinal cord. And so the poliovirus is effective at disconnecting the command that is coming from the upper motor neuron is unable to reach some of the lower motor neurons, because it will kill interneurons in the pathway. |
|
|
Term
|
Definition
| bacterial (Clostridium botulinum) |
|
|
Term
|
Definition
infants <6 months—honey is the
only known dietary reservoir of C. botulinum spores |
|
|
Term
|
Definition
injury to motor control centers in
developing brain—occurs during pregnancy—
infancy ~<3 years; thought to have genetic
component |
|
|
Term
| Amyotrophic lateral sclerosis (ALS) |
|
Definition
motor neuron disease (both UMN and LMN are affected)—
Lou Gehrig’s disease |
|
|
Term
|
Definition
| developmental congenital disorder— incomplete closing of neural tube |
|
|
Term
|
Definition
| considered inflammatory disease—remove myelin —remove AP transmission |
|
|
Term
|
Definition
| affects PNS—polyneuropathy—triggered by infection?, zika virus |
|
|
Term
|
Definition
remember lecture 1—stop
transmission of APs and you stop the motor
command to the muscle; e.g., use Curare |
|
|
Term
|
Definition
UMn stays in CNS
LMn leaves CNS
UMn to neuron
LMn to efferent
Here LMn in cord;
but could be in
brainstem (for
motor CNS)
-Here you have again, the concept of upper motor neuron, in the central nervous system, lower motor neurons, and the different levels and what you can find them. One of the reasons I put this in here is to remind people that the whole idea is you have first, a command, a motor command, but that motor command that is going down to communicate to a lower motor neuron in the ventral horn of the grey matter of the spinal cord is the lower motor neuron, the one that goes to the muscle. So again, anything that may happen at any level in this pathway will affect movement. |
|
|
Term
|
Definition
Finally, Babinski sign is useful for diagnosis also. In adults, the idea is that in response to stimulation of the sole of the foot, they think that there is a toe down flexion. If they say a problem, then there is extensor plantar response. Very good for diagnosis in adults.
Be aware that in children, what seems to be wrong here is completely OK up to about 18 months of age, because the pathways that are for walking and so on are not completely developed yet. So in small children, in infants, that are not walking yet, the Babinski sign that corresponds to pos in an adult is normal for a baby |
|
|
Term
| Intersegmental reflex arc |
|
Definition
a polysynaptic neuron pathway
which involves sensory impulses being received in one
segment of the spinal cord and then stimulating interneurons
which route the sensory information to motor neurons in both
the superior and inferior segments of the spinal cord in order
to permit innervation of a variety of muscles in the reflex
action |
|
|
Term
|
Definition
a polysynaptic contralateral
segmental reflex that is usually associated with the same
painful stimulus which triggered a flexor/withdrawal reflex; in
the crossed extensor reflex, the contralateral extensors
contract (and the ipsilateral flexors are inhibited) which tends
to adjust for any shift in the center of gravity so that balance is
maintained and body weight is properly supported |
|
|
Term
| Patellar (knee jerk) reflex |
|
Definition
a monosynaptic ipsilateral
segmental stretch reflex, resulting from a sharp tap on
the patellar tendon, in which proprioceptive sensory
information from muscle spindles in the quadriceps
muscles of the thigh are routed to the appropriate spinal
segments, where motor impulses to the quadriceps
muscle of the thigh cause a reflex extension of the leg |
|
|
