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Neurophysiology of LA

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Definition of LA:-
A loss of sensation in a
circumscribed area of the body caused by a
depression of excitation in nerve endings or an
inhibition of the conduction process in peripheral
nerves.

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PROPERTIES OF LA:-
1.It should not be irritating to the tissue.
2.It should not cause any permanent alteration to the tissues.
3.Its systemic toxicity should be low.
4.It should be effective regardless of whether it is injected into
the tissues or applied locally to mucous membrane.
5.The time of onset of LA should be as short as possible.
6.The duration of action must be long enough to complete
procedure yet not so long as to require an extended recovery.
7.It should have potency sufficient to give complete anesthesia
without the use of harmful concentrated solutions.
8.It should be relatively free from producing allergic reactions.
9.It should be stable in solution & readily undergo
biotransformation in the body.
10.It should be sterile or capable of being sterilized by heat
without deterioration.

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Neuron:
• It is the structural unit of the nervous system.
• It is able to transmit message between the
nervous system & all parts of the body.
2 TYPES:
-SENSORY NEURON
-MOTOR NEURON

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PARTS OF NEURON:
1.Dendritic zone-It respond to stimulation produced
in the tissues in which they lie provoking an
impulse that is transmitted centrally along the
axon.
2.Axon- It is a thin cable like structure transmits
impulses.
3.Cell Body- Provides the vital metabolic support for
the entire neuron.

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TYPES OF NERVE
FIBERS:
• Myelinated nerve fiber
• Unmyelinated nerve fiber
The insulting properties of
the myelin sheath enable a
myelinated nerve to conduct impulses
at a much faster rate than can an
unmyelinated nerve of equal size.

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Electrophysiology of
nerve conduction:
• Step 1- A stimulus excites the nerve leading to
the following sequence of events;
A.Initial phase of slow depolarization.
B.Firing threshold-When the falling eletrical
potential reaches a critical level.
C.Rapid repolarization – The interior of the nerve
is now eletrically positive in relation to the
exterior.
Step 2-After these steps of depolarization
occurs .The electrical potential gradually becomes
more negative inside the nerve cell relatively to
outside until the resting potential of -70mV is
again achieved.

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Theories of LA:
1.Acetylcholine theory
2.Membrane expansion theory
3.Specific receptor theory

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Mechanism of action of
LA :
1.Displacement of Ca ions from the Na channel
receptor site which permits..
2.Binding of LA molecule to this receptor site which
thus produces…
3.Blockade of the Na channel & a
4.Decrease in the Na conductance which leads to
5.Depression of the rate of electrical depolarization
& a
6.Failure to achieve the threshold potential level
along with a
7.Lack of development of propagated action
potentials,which is called
8.Conduction blockade.

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Maxillary nerve:-
• Maxillary nerve is one of the three divisions of the trigeminal
nerve.
• It is entirely sensory in function.
Course:- -Maxillary nerve originates at the middle of the
semilunar ganglion & continues forward in the lower part of
caverous sinus.
-Then passes to the foramen rotundum through which it leaves
cranial fossa.
-Then enters the inferior orbital fissure to pass into the orbital
cavity,here it turns laterally in a groove on the orbital
surface of maxilla, called infraorbital groove.
-Continuing forward the second division emerges on the anterior
surface of the maxilla through the infraorbital foramen
where it divides.

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Branches of maxillary
nerve:
1. Branch within the cranium:-
Middle meningeal nerve
Supply- sensory innervation to the dura
mater.
2. Branch within the pterygopalatine fossa:-
Branches of the pterygopalatine nerves
include those that supply 4 areas:
Orbital branches-
supply- periosteum of the orbit
Nasal branches-
supply-mucous membrane of of
superior & middle conchae,lining of the
posterior ethmoidal sinuses,posterior portion of
nasal septum.

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Palatine branches:
-Greater palatine n
-lesser palatine n
Pharyngeal branches:
supply- mucous membrane of the nasal
part of the pharynx
-posterior to auditory tube.

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3. Branches in the infraorbital canal:
-Middle superior alveolar N:
Provides sensory innervation to:
-2 maxillary premolars
-mesiobuccal root of first molar &
periodontal tissue
-Buccal soft tissue
-Bone in the premolar region
-Anterior superior alveolar N:
descends within the anterior wall of the
maxillary sinus
supply- -pulpal innervation to the central &
lateral incisors & canine
-sensory innervation to the periodontal
tissues, buccal bone, mucous membrane of these
teeth.

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4. Branches on the face:
• Infraorbital N emerges through the
infraorbital foramen onto the face to divide into
terminal branches:
-Inferior palpebral branch-
supply- Skin of the lower eyelid with
sensory innervation.
-External nasal branches-
supply- Sensory innervation to the skin
on the lateral aspect of the nose.
-Superior labial branches-
supply-sensory innervation to the skin &
mucous membrane of the upper lip.

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Mandibular Nerve:-
It is one of the largest divisions of the
trigeminal nerve.
It is formed by the union of the large
sensory bundle of fibers & a small motor
bundle of fibers.

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Branches of mandibular
n:
1.Branches from the undivided n:
Nervous spinosus-Arises out side the skull & then
passes into the middle cranial fossa to supply the
dura mater & mastoid cells.
N to internal pterygoid muscle-A branch of the
motor root passes to innervate the internal
pterygoid muscle. This branch passes without
interruption to innervate the tensor veli palatini &
tensor tympani muscles.
2.Branches from the divided N:
Below the level of the undivided part of the
mandibular division the trunk separates into 2
parts.
Anterior division
posterior division

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A) Anterior Division:
The anterior division is smaller than the posterior division.It
receives sensory & motor fibers that supply the – muscles
of mastication
- skin & mucous membrane of the
cheek
-Buccal gingiva & lower molars
It passes downwards & forwards where it divides-
1.Pterygoid N- Enters the medial side of the external
pterygoid muscle to provide its motor n supply
2.Masseter N-Masseter N passes above the external
pterygoid to traverse the mandibular notch & enter the
deep side of masseter muscle.

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3.N to temporal muscle:-
Anterior deep temporal N
Posterior deep temporal N
4.Buccal N:-
It provides sensory innervation to
buccinator muscle

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B) Posterior division:
• The largest posterior division is sensory but also
carries some motor components.
This division extends downwards & medially & then
branches into the –auriculotemporal n
- lingual n
-inferior alveolar n
1)Auriculotemporal N:supply
-Tragus of pinna of external ear
-To scalp
-As for upward as the vertex of the skull

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2) Lingual nerve:
It is the smaller of the two terminal branches of the
posterior division of the mandibular nerve.
It contributes many sensory fibers to the mucous membrane of the
the floor of the mouth & gingiva on the lingual surface of the mandible.
It occasionally supplies sensory fibers to the bicuspids & first molar
teeth.
3) Inferior alveolar nerve:
It is the largest of the branches of the posterior
division of the posterior division of the mandibular n.
On the medial side of the ramus in the pterygomandibular space,it
enters the mandibular foraen.
Within the mandible the inferior alveolar n descends in the inferior
alveolar canal & distributed throughout the body of the mandible.
I inferior alveolar canal - It gives of branches to the mandibular teeth
to supply the dental pulps. Someof the fibers
are distributed to the periodontal membrane
of the various lower teeth.

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-At region of mental foramen – Gives mental nerve.
Supply- skin of the chin & lower lip & to
the mucous membrane lining the lower lip.
-At the region of incisive foramen- Gives incisive nerve.
Supply- cuspid tooth & incisor teeth
4)Mylohyoid nerve – Before the inferior alveolar nerve enters the
mandibular foramen it gives off a branch the
mylohyoid nerve.
Supply – Motor fibers – to the anterior belly of
digastric muscle.
Sensory fibers- Enter the mandible in the
area of the chin to aid in the
sensory nerve supply to the
mandibular incisors.

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