oral physio script 2
TRANSCRIPT
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Last lecture, we stopped at pain neuron. As we know, neuron is one cell. It is a cell with modified
function (to transmit or conduct impulses from one neuron to another). So in other for the neuron to
perform its function, it should have a cell body (information integration), dendritic processes
(responsible in receiving information from another neuron) and the axon (contain nerve terminal at the
end of axon that will form synapse with the adjacent neuron). Synapse is the site where information /
impulse are passed from a neuron to another.
Nerves conducting pain consists of primary neuron, secondary neuron and tertiary neuron. There are
three levels for the pain signal to reach the brain. The three levels are the primary neuron (cell bodies of
primary neuron exist in the posterior root ganglia of the spinal cord / the ganglia of cranial nerve),
secondary neuron and tertiary neuron.
Trigeminal nerve is the primary nerve responsible for the conduction of pain in the head region. So
trigeminal nerve (CN V) is the one responsible for carrying pain information from pain receptor located
in the skin, teeth or epithelium to the brain. So the cell bodies of the primary neuron exist in the ganglia
of the trigeminal nerve (trigeminal ganglion). In the cranial area, all primary neurons conduct pain signal
from the pain receptor (nociceptor) to the final nucleus of trigeminal nerve which is a specialized
nucleus present in medulla oblongata.
(le doctor showed a picture) As you see here, the information is passed from the source of pain through
the primary neuron until the spinal nucleus of trigeminal nerve. This is where primary neuron ends and
the second neuron starts. So at this nucleus we have synapse between the primary and secondary
neurons,
Secondary neuron starts from the spinal nucleus of trigeminal nerve until the signal reaches the
thalamus. Some of these nerves may cross the midline. The tertiary neuron starts from the thalamus
and ends in the cerebral cortex. There is no crossing in the midline here.
Q: Crossing of the midline in conduction of pain happens during this stage:
A: One of the following:
1. Nerve terminal spinal nucleus of trigeminal nerve2. Spinal nucleus of trigeminal nerve thalamus3. Thalamus Cerebral cortex
So if we have pain the right side of our cheek, this will be interpreted in our left brain as thesignal has crossed the midline during the secondary neuron.
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Q: What are the stations for the pain started in the head region?
A: The stations are spinal nucleus of trigeminal nerve (end of primary neuron and beginning of second
neuron), thalamus (end of secondary neuron and beginning of tertiary neuron) and cerebral cortex (final
destination)
The trigeminal nerve is the main nerve that will receive sensory information from the full face,mouth and nose. So pain signal from these areas will go to those three stations via the primary
neuron, secondary neuron and tertiary neuron.
The Gate Control Theory
We discussed that this theory actually explained the acupuncture treatment. In general, if we stimulate
other sensory receptor such as the chemical, thermal or mechanical receptor at the same time as the
propagation of pain signal, we can prevent the perception of pain. This is because the gate only allows
one kind of sensation to pass through.
[The self-reading slide is not required. You can read it if you want, but it wont be included in the exam]
Now well go to the factors affecting the pain threshold. Pain threshold is the level of stimulus that is
enough to cause pain.
As an example, when you walk and step on a very small stone, you wont be able to sense the pain
because the stimulus is not enough to reach the pain threshold. If the stimulus is able to reach the pain
threshold (stepping on large stone) then you will feel the pain.
Threshold is an all-or-none response. In regard of pain threshold, some factors may lower the pain
threshold. So when we lower the pain threshold, even a small amount of stimulus can make you feel
pain.
Factor that can lower the pain threshold is psychological factor such as stress, worry, frightened or
anxiety.
So, usually during examination when all of you are in stress, you can feel pain more easily.
Some factors can elevate the pain threshold. So when you elevate the pain threshold, you need a larger
amount of stimulus to cause you pain. One of these factors is excitement or relaxation. Listening to
soothing music can also elevate your pain threshold. For this particular reason, classical music is present
in many dental clinics (no Kpop in the clinics, right? :P)
Now well go to nerve physiology. (The doctor assumed that we all already know about the nerve
physiology, so he just went through the slide)
The conduction of nerve impulse Nerve cell axon Intracellular fluid (inside the neurons)
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Intercellular fluid (outside the neurons) Na and K ions with their respective channels Difference in polarity of exterior and interior of axon
These are important in conduction of nerve impulses.
Now we go to resting membrane potential. So when the nerve is at rest, the nerve axon is not
conducting pain (not conducting signal). The resting membrane potential results from the relative
distribution of Na and K ions across the axon membrane. Intracellularly, the concentration potassium,
[K] is high and concentration sodium, [Na] is low. Extracellularly, [Na] is high and [K] is low. At the state
of rest, the interior of axon is negative in relative to the exterior. Due to that, we have potential
difference of 60 to 90 mV. The natural tendency of Na influx is prevented by Na pump which needs
energy (Na is high extracellularly so it will passively diffuse into inside). By that we can maintain the
potential difference. So in order to be able to prevent Na from getting inside, you need energy. So at
rest, you need energy.
Now we go to depolarization.
By depolarization, we will create action potential that represents the passage of nerve impulse.
We have rapid fall in membrane potential from -70 to 20/30 mV.
Nerve impulse (action potential) propagates along the axon and when it reaches the resting segment of
the axon it creates an electrical stimulus which increases the permeability of the diffusion barrier to Na
and K ions by opening voltage gated ion channels.
So in this case, we dont have the Na pump that prevents the passage of Na. but what should we have
for the depolarization to occur? We should have increased permeability of the diffusion barrier to Naand K. Therefore Na will get inside and K will get outside. This actually will be responsible for changing
the membrane potential from -70 to 20/30 mV.
Now repolarization, will start to propagate and when it affect the resting membrane segment or
segment in resting membrane potential, it leads to depolarization of that segment. So Na ions move
into cell and K ions move outside along the concentration gradient. So this segment of depolarization
doesnt need energy. Resting membrane potential need energy. Therefore, intracellular charge is +ve
relative to extracellular.
This segment of the axon has undergone depolarization and is in a state of action potential. As
depolarization progress along the axon, the action potential is propagated and the nerve stimulus
continues down the length of the axon. And after depolarization, you want to repolarize.
The axon returns to its original state with initial concentrations of Na and K ions restored and the
interior once againve relative to the exterior. This is achieved by Na and K channels. The axon is ready
to undergo depolarization again to propagate a nerve impulse. This process needs energy because it is
an active process.
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Which is when you want to return the axon from depolarization to the normal state, you NEED energy.
If you want to maintain the resting membrane potential, you NEED energy.
If you want to depolarize, you DONTNEED energy. Remember this for I may ask you in the exam.
What is the mechanism of action oflocal anesthesia?
What is the main action of local anesthesia that is used in dentistry?
It blocks the Na ions pump in the cell membrane wall. This result in the inability for the Na to get inside.
Na go outside very great. In order to depolarize that segment you need these ions to come inside but
the influx of Na is already prevented. Therefore the action potential cannot propagate through the
segment and block the passage of pain. This result in the inability of Na ions influx when the action
potential arrives at a given segment of the nerve that encountered anesthesia. No effect on resting
membrane potential.
So, local anesthesia does not affect resting membrane potential. It only prevents depolarization.
One segment of this nerve is under local anesthesia, so pain will start until it reach that area then it will
stop, do not pass and continue. This is the main idea about local anesthesia in dentistry.
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So now we have finished the pain lecture and will begin a new one.
The Pulpal and Dentinal or Dental Pain.
Dental pulp is a specialized connective tissue. And you know what it means by that?
Connective tissue is composed of cells, ground substance and fibers. So, the cell in the pulp, cells are
fibroblast also we have other type of cells. The fibers are collagen fibers and other fibers as well. And the
ground substance we have like glycogen and glycoprotein and different material.
Anyways, why do we call it specialized connective tissue?
It is considered a specialized connective tissue bcz it is contain within the tooth.
Let say this is the tooth. Inside the tooth we have a space, this space is filled with CT. This connective
tissue is called dental pulp. It is enclosed by dentin.This is the only CT that is surrounded by a rigid wall
and this is important. Why? Because in inflammation, one of the classical sign is swelling. Any
inflammation needs swelling. Let say that you have infection on your skin. This infection need swelling.
So no problem, this part of your skin can swell. Swelling is important *by* using the amount of pressure
on nerve. So the pressure on the nerve remain minimal. _______. But the swelling cannot expand
because it is limited by the rigid wall of the pulp. Instead, therell be increased pressure on the *nerve
on the pulp*. Thats why dental pulp pain is very-very strong. Dental pulp is also specialized because it is
connective with periodontal ligament_____ outside the tooth. So let say this is the tooth. Inside the
tooth we have dental pulp, at the apex of the tooth or at the tip of the root we have an opening where
the dental pulp is continous with the dental tissue surrounding the tooth or the periodontal ligament. So
this is important. Why? Because when we have infection in the tooth, inside the dental pulp or
inflammation, this inflammation is not treated, some infection can pass from the dental pulp to the
surrounding tissues or the periodontal tissues. So this is also a significant issue. Thats why usually
results in periapical *pertititis*.
The apical foramen is the way of communication between dental pulp and the periodontal ligament.
Apical foramen is narrow so it only allows the pathway of neurovascular bundle. The pulp has a very
small volume. The total volume of a pulp is
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When you remove the dental pulp, and you dig into your tooth, youll not feel anything. Or the patient
wont feel anything.
Dental pulp is important in the growth of the tooth. What happen if a child who has not completed the
root of one of the teeth, if this child actually fell over and hits one of his teeth, this will leads to pulp
necrosis. If this tooth is chronic growing , the growth of the tooth will stop. This means that the pulp isvery important in continuation of the growth of the tooth also maintain the viability of the dentine and
the last point is the pair of dentin in injury. If this caries proceed without any fighting or any resistance,
this will lead to pulp necrosis. But what happen to dental pulp?? usually that the dentine prevents this
caries from getting in the pulp by building in new bridge of dentin. Any lost of the dentine outside is
replaced by the addition of new dentine or repaired dentin from inside. By this, dental pulp remains all
the time away from the caries. What happen when we have inflammation? The process of destruction is
faster than the process of repair. Also, sometimes, the level of destruction is really very fast, that it
seems that they kill us suddenly. By this pulp is dead. But sometimes, what happen, the destruction is
fast but not to the extends that its faster, they can destroying faster but they can only have small
opening.
Pulp nerve, what do we have in dental pulp? we have sensory nerve (pain nerve) and plexus of
Raschkow. Lets talk about A delta and C fibers, these are the two type of pain fibers that are present in
dental pulp. In addition we have the plexus of Raschkow which is plexus that is present under the
odontoblast. Odontoblast, these are the cells that form dentine And they are many in the dental pulp
that just at periphery of dental pulp. Just underneath these cells we have the network of the nerve
called plexus of Raschkows. Individual axons divide into many branches in the plexus,so this plexus is
really very rich. Pulp nerve during the tooth formation, this also, you might not understand this fully
until we discuss the process of formation of tooth. At the beginning, fibers are located at the base of
dental papilla. Dental papilla is the tissue that will become dental pulp later on.
During the Cap stage, one of the stage of tooth development, fibers form a plexus.. okay? And this
plexus go to dental follicle and dental papilla. Dental follicle is the tissue deriving from tooth and dental
papilla is the tissue located inside the forming tooth and that will become the dental pulp.
At the bell stage of development, all the fibers are unmyelinated. At eruption, the number & their
average size increase, why?? Because we have a transition towards myelination. This means that
myelination of nerve fibers takes place during eruption of the tooth, not before that. But not all nerves
are myelinated because you still have C fibers which are the group of nerves which are not
myelinated.This continues to increase for a few years after eruption which means the amount of nerves
continue to increase for a few years after eruption. While dentin is laid down. (dont understand)
because of that the nerve plexus decrease in size(dont understand) and this leads to aging of the
pulp.We have decrease in the number of axons entering the pulp, reduction in myelinated fibre size and
also Plexus of Raschkows shows little change.
Pulp nerves in primary teeth.The number of axons is less than the number of axons in permanent
teeth.For example, 1mm3 of dental pulp in deciduous tooth and 1mm3 of dental pulp in permanent
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tooth and youll find that the number of axons is much less in deciduous dental pulp. This is true for all
teeth except the primary canine.In primary canine.. okay..the number of axons in primary canine is
same as the number of axons in permanent canine. The number of axons decrease with resorption until
the root is shed.For deciduous tooth, for example, this is the root of deciduous tooth,and here we have
the permanent tooth that is erupting and resorbing the roots.So this resorptionokay..leads to also the
decrease in the amount of axons until the deciduous tooth is loss.
Neurotrophic substances, inside the nerve we have what we called nerve growth factor.This are
important for the growth of the nerve.In this slide, we dont need to remember all this details.. ok? But
we need to know that we have nerve growth fibers. This are important for the growth and development
of the nervous system inside the dental pulp.
Functions of A fibers. This is similar to what we discuss last time about the A fibers and also the
C fibers, the same..
Neurotransmitter in dental pulp. Neurotransmitters are transmitters that are secreted at nerve
terminals into the synapse and then they convey information from one neurons to another. What are
the neurotransmitter that are present in the dental pulp?? We have what we called Calcitonin gene
related peptide, Subtance P and Neurokinin A.Do we have autonomic nervous system in the pulp or do
we have autonomic nerves??? Do we have sympathetic and parasympathetic nerves?? YES.. we do have
it in dental pulp. What is the function of sympathetic?? Why do we need sympathetic nerve inside
dental pulp?? What do we have in dental pulp??we have blood vessels.We need to maintain the pulp
pressure or the blood pressure inside the dental pulp.In order to maintain that, we need the
sympathetic nerve that contract the smooth muscles inside the artery.So thats why we have
sympathetic fibers inside the pulp.
The majority of autonomic fibers are sympathetic.The amount of parasympathetic component ofthe autonomic system in the dental pulp is very small .Some of these sympathetic are cholinergic, they
have acetylcholine as neurotransmitter, NOT noradrenalin. How could we know?? Because they found
that removal of the superior cervical ganglion, cervical ganglion in the ear, it provides the sympathetic
system to all upper and lower teeth. They found some decrease in cholinesterase staining in the pulp.
Cholinesterase staining is a stain that takes acetylcholine in the dental pulp . In the mouse, 2 of
sympathetic nerve in pulp horn, in pulp chamber and the rest in root canal. What are the functions of
sympathetic nerves inside the pulp ?? They control pulp blood flow, its very important. They regulate
odontogenesis. Odontogenesis is the process of tooth formation . Afferent transmission of impulses
associated with pain sensation, they have rolls in pain sensation.
Evidence of functions . Anatomically, usually we see these fibers close to the blood vessel. Why do
we need nerves fibers beside blood vessels?? Because these are the sympathetic nerve fibers that
control the diameter of blood vessels. Thats why this is a very big evidence that they are presence. Also,
sympathectomy (google: procedure during which at least one sympathetic ganglion is removed) results
in vasodilatation in pulp and also they found some changes in dentin apposition .This means that the
http://en.wikipedia.org/wiki/Sympathetic_ganglionhttp://en.wikipedia.org/wiki/Sympathetic_ganglion -
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sympathetic system is very important for the formation of the tooth and the formation of different sizes
of the tooth.
We also have parasympathetic system in the dental pulp. The majority are cholinergic .The
resection of inferior alveolar nerve which are the main sensory nerve that supply the teeth abolish
cholinesterase stain . Also when we remove the parasympathetic supply in the dental pulp.. whathappen is the increase rate of tooth eruption because the intra-pulpal pressure increase.
~~THANK YOU~~
(p/s : sorry for any mistakes)