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Physiology of facial nerve

CONTENTS INTRODUCTION TERMINOLOGIES NEURON NERVE FIBER AND FACIAL NERVE FIBERS NERVE CONDUCTION PROCESS SYNAPSE NEURO TRANSMITTER NEUROMUSCULAR JUNCTION AUTONOMIC NERVOUS SYSTEM REGENERATION POTENTIAL

INTRODUCTION

Nervous system controls all the activity of the body.

It is quicker than other control system in the body which is endocrine system.

Primarily, the nervous system is divided into the

two parts Central nervous system Peripheral nervous system

NERVOUS SYSTEM

Central nervous system-brain and spinal cord (Integrating/command centre)

Peripheral nervous system-Nerves from brain and spinal cord

Brain tissue is made up of the large number of the neurons which can be called as functional unit i.e. one neuron can function itself

Neuron consist of three part Cell body Axon Dendrite Collection of cytons together forms

gray matter Collection of peripherial process

together forms white matter

TERMINOLOGIES

NeuronCell Body ( cytons )Axon Dendrite

Myelin sheathProtein‐lipid filled cytoplasm of Schwann

cells– Neurilemma– Myelin sheath• Protects/insulates AXON

TERMINOLOGIES NUCLEUS: Collection of cytons in side CNS is

known as nucleus. GANGLION: Collection of cytons out side the

CNS is known as ganglion. TRACT: Collection of axon in side CNS is know as

tract. NERVE: Collection of axon outside CNS is known

as nerve. cranial nerve spinal nerve Facial nerve is seventh cranial nerve arising

from second branchial arch.

CENTRAL NERVOUS SYSTEM:brain and spinal cord

PERIPHERAL NERVOUS SYSTEM sensory division motor division

Sympathetic division parasympathetic division

Visceral sensory division

Visceral motor division

Somatic motor division

somatic sensory division

DIVISION OF THE NERVOUS SYSTEM

TYPES OF CELLS FOUND IN THE NERVOUS SYSTEM

• Neurons : excitable cells motor neuron sensory neuron• Neuroglia: supporting cells (glial cells) non excitable cellsGLIAL CELLS IN PNS Satellite cells -regulate o2 ,co2,neutrients

and neurotransmitter

around ganglia Schwann cells-myelin sheaths formation

GLIAL CELLS IN CNS Astrocyte-most abundant, blood brain

barrier Microglia-removes the debris

(phagocytosis) Ependymal cells-produce CSF Oligodendrocytes-myelin sheath

formation

NERVE FIBRES Depending upon structure - myelinated nerve fibre -non myelinated nerve fibre Depending upon distribution - somatic nerve fibre -visceral or autonomic nerve fibre Depending upon source -cranial nerve -spinal nerve

Depending upon function -motor nerve fibre -sensory nerve fibre Depending upon chemical neurotransmitter -adrenergic nerve fibre(nor-adrenalin) -cholinergic nerve fibre(acetylcholine)

Depending upon the thickness thickness = conduction velocity

type 1 -A alpha fibre (12 to 24 micron) type 2 -A beta fibre (6 to 12 micron) type 3 -A delta fibre (2 to 5 micron) type 4 - C fibre (1.5 micron)

FACIAL NERVE FIBER Special Visceral Efferent (Branchial Motor

fiber)

General Visceral Efferent (Parasympathetic fibers)

Special Visceral Afferent (Taste)

General Sensory

Special Visceral Afferent(branchial Motor)

motor cortex bilateral facial motor nuclei (pons)

facial muscles supply the facial muscles and

stapedius muscle

General Visceral Efferent (Parasympathetic ) Superior salivatory nucleus(pons) nervus intermedius greater/superficial petrosal nerve spheno /pterygopalatine ganglion postganglionic parasympathetic fibers lacrimal gland & seromucinous glands of nasal and oral cavity

Superior salivatory nucleus nervus intermedius chorda tympani joins lingual nerve submandibular ganglion – postganglionic parasympathetic fibers submandibular and sublingual glands

Special visceral afferent

nucleus solitaries –> tractus solitarius –>

nervus intermedius –>

geniculate ganglion –>

chorda tympani

joins lingual nerve anterior 2/3 tongue, soft and hard palate

General Sensory Afferent These fibers innervate a part of the skin

and ear. Its fibre communicate with the vegus nerve fibre.

NERVE CONDUCTION

• Function– Sensory (afferent neurons) – Motor (efferent neurons) – Interneurons (association neurons) Facial nerve is mixed nerve mainly

motor and partly sensory

Nerve impulse is transmitted through a nerve fibre (axon) electrochemically.

it is not a flow of electrons as in electric current but it travel as wave of depolarization.

EXCITABILITY: excitability is defined as the physiochemical changes in a tissue when stimulus is applied

Stimulus two type of response accure

Action potential(nerve impulse)

Electronic potential(local response)

(firing level below15mv)

ACTION POTENTIAL: Strength of the stimulus must be

adequate to produce the action potential

this is known as threshold or minimal stimulus

Resting potential=-70MVFiring level=-55MVDepolarization end at =+35MV

Resiting membrane potential in nerve fibre is -70MV. When stimulus is applied to nerve

membrane this potential increase this is known as depolarization.

In normal (resting) condition nerve is in polarized state

This is maintained by,1. Na+ - K+ pump (three Na+ pumped out for

every K+ inside)2. more permeability to K+ than Na+.3. Immobile (-) vely charged protein ions occur

inside.

NERVE CONDUCTION

When an axon receives stimulus A wave of depolarization passes through it. It reverses the membrane potential with inner surface

becoming positive and outer surface electronegative due to

1. membrane becoming 10 times more permeable to Na+ (than K+) and

Na+ from extra cellular fluid the neuron interior .2. stoppage of Na+ - K+ pump

Repetition of this process produces a wave of stimulation along the axon

Conduction by Action Potential Action potential transmitted through the nerve

fiber as nerve impulse. Depolarization accure at first spot cause the

depolarization of neighbour area. This depolarization travel through nerve fiber. Conduction from myelinated nerve fiber is 50

time more faster then non myelinated nerve fiber

Because meyelin seath forms an effective insulator and action potential jump from

one node of renvier to another so conduction is faster.

Role of Synapse The Junction between the two neuron is

called synapse. It is physiologic continuation.

As there is a gap between the junctions we have

to explain how the nerve impulse generated in one nerve is passed to the other nerve through this synaptic junction.

1. Cholinergic transmission i.e. those nerves which on stimulation secrete

acetylcholine at the nerve ending. They are

a. Parasympathetic nerves of autonomic nervous

systemb. Somatic nerves i.e. nerves supplying the

skeletal muscles.

2. Adrenergic transmission that means those nerves which will be

secreting adrenaline at the nerve ending when stimulated.

The fiber of this category is only one i.e. sympathetic fiber of A.N.S.

1.A.P Arrival of the stimulus at the synaptic junction.

2. This stimulus will release Ca.

3. This Ca will break the vesicle releasing acetylcholine.

4. This acetylcholine can easily pass through the synaptic junction.

5. This acetylcholine will depolarize the membrane thereby forming the nerve impulse again.

6. This nerve impulse passes to the next node.

Neurotransmitter Chemical mediator substances

responsible for the transmission of impulse through synapse.

Small molecules -acetylcholine - nor adrenalin,

dopamine serotonin,

histamine(amines) -Amino acid-

GABA, glycine

glutamate Large molecules- substance p

Synthesized in presynaptic neuron. Stored in synaptic vesicle.

Some neurotransmitters causes excitation of post synaptic neuron other causes inhibition.

EXCITATORY- Acetylcholine, Nor adrenalin

INHIBITORY-GABA, Dopamine

Neuromuscular junction

Nerve impulse stimulates the release of a neurotransmitter (acetylcholine)

from synaptic vesicles into synaptic cleft Stimulates muscle impulse (MAP) Impulse spreads across sarcolemma and

into fiber along the T-tubules . This impulse causes an increase in the

cisternae's permeability to calcium ions.

The sarcoplasmic reticulum has a high conc. of Ca++.

Calcium ions diffuse into the sarcoplasm ' the Ca++ causes the formation of "cross bridges" between the actin and myosin filaments ' the filaments slide between each other.

This shortens the myofibrils which in turn shorten the muscle fibers, which shortens the muscles

PHYSIOLOGY OF PAIN PAIN :- It is defined as unpleasant sensations and

emotional experience with or without actual tissue damage.

GATE CONTROL THEORY:- Nerve fibers with smaller diameter carry the pain

stimuli through the gate mechanism present in spinal cord

Nerve fiber with large diameter carry the other stimuli like touch and pressure passes through the same gate.

Large nerve inhibits transmission of the pain signals by smaller nerves through gate.

FUNCTION OF AUTONOMIC NERVOUS SYSTEM Autonomic nervous system concern with

regulation of function, which are beyond voluntary control. By controlling various vegetative functions.

It helps in maintenance of constant internal environment (homeostasis)

All visceral components are supplied by the sympathetic or parasympathetic division of ANS

Two division produce and antagonistic effect on each organ.

When fibers from one devision supplying organ is sectioned or affected by lesion, the effect from fibers from other division on the organ become more prominent.

Regeneration Potential Degenerated nerve may be regenerated.

Regeneration mainly accure in PNS due to presence of myelin sheath.

It accur only in favorable condition.

Following criteria are necessary Gap between the cut should less than 3 mm. Neurilemma should be present. As it is

absent in CNS regeneration does not accur in CNS.

Nucleus must be intact. Two cut end should be in same line.

Cells of Schwann from proximal and distal cut end grow in all direction and form pseudopodia like fibrils

Fibril from one end join with fibril of another end.

Filling the gap lead to development of continuity of Neurilemmal tube.

myelin seath is formed by Schwann cell myelination is completed in one year.

Nissl granules appear followed by Golgi apparatus.

Functional recovery accur after long period.