ANSWERS
(a) Required to write about cranial nerve.
Cranial Nerves
The cranial nerves are a set of 12 paired nerves in the back of your brain,
cranial nerves emerge directly from the brain, including brain stem. Cranial nerve
occurs in pair and each pair splits to two and serve the 2 sides of the body.
-Cranial nerves relay information between the brain and parts of the body, primarily
to and from regions of the head and neck, including the special senses of vision,
taste, smell, and hearing.
-Cranial nerves send electrical signals between your brain, face, neck and torso, help
us to taste, smell, hear and feel sensations. They also help you make facial
expressions, blink your eyes and move your tongue.
Diagram showing cranial nerves.
Origin of cranial nerves.
Two of your cranial nerve pairs originate in your cerebrum. The cerebrum is the largest portion
of your brain that sits above your brainstem.
Types and functions of cranial nerves.
Cranial nerves are categorized based on number and functions as follows:
(1) Olfactory nerve: Is the first cranial nerve (CN I) that Sense of smell.
(2) Optic nerve: a bundle of more than 1 million nerve fibers/cranial nerve (CN II). It
transmits sensory information for vision in the form of electrical impulses from
the eye to the brain.
(3) Oculomotor nerve (CN III): Enables eye movements, such as focusing on an
object that's in motion,also makes it possible to move your eyes up, down and
side to side. Ability to move and blink your eyes.
(4) Trochlear nerve (CN IV) : It enables movement in the eye's superior oblique
muscle. This makes it possible to look down. The nerve also enables you to move
your eyes toward your nose or away from it Ability to move your eyes up and
down or back and forth.
(5) Trigeminal nerve (CN V): responsible for sending pain, touch and temperature
sensations from your face to your brain. It's a large, three-part nerve in your
head that provides sensation. One section called the mandibular nerve involves
motor function to help you chew and swallow, aids Sensations in your face and
cheeks, taste and jaw movements.
(6) Abducens nerve (CN VI) controls the movement of the lateral rectus muscle, one
of the extraocular muscles responsible for outward gaze. It is a somatic efferent
nerve.
(7) Facial nerve (CN VII): emerges from the pons of the brainstem, controls the
muscles of facial expression, and functions in the conveyance of taste sensations
from the anterior two-thirds of the tongue. Facial expressions and sense of taste.
(8) Auditory/vestibular nerve(CNVIII) control Sense of hearing and balance.
(9) Glossopharyngeal nerve (CNIX) It provides motor, parasympathetic and sensory
information to your mouth and throat. Among its many functions, the nerve
helps raise part of your throat, enabling swallowing control ability to taste and
swallow.
(10)
Vagus nerve (CNX):Digestion and heart rate. it is the largest cranial nerve
having both motor and sensory functions running
many parts of your body, including your tongue, throat, heart and digestive
system.
(11)
Accessory nerve (or spinal accessory nerve (CNXI) supplies the
sternocleidomastoid and trapezius control Shoulder and neck muscle movement.
(12)
Hypoglossal nerve ( CNXII): It travels down your neck and branches out,
ending at the base and underside of your tongue control ability to move your
tongue.
What conditions and disorders affect the cranial nerves?
Conditions and disorders of the cranial nerves can affect processes that
involve vision, smell, hearing, speaking, and balance. They can also change the way
you perceive sensation on the face and prevent or alter the movement of the head,
eyes, neck, shoulders, throat, and tongue.
Cranial nerve palsy affects a motor nerve — one that controls movement.
If a sensory nerve is affected, it can cause pain or reduced sensation.
Conditions and disorders that affect the cranial nerves and their effects include:
Third nerve palsy, This disorder can cause a closed or partially closed eyelid,
an enlarged pupil, and the movement of the eye outward and downward.
Trigeminal neuralgia, is a disorder of the fifth cranial nerve and typically
causes pain on one side of the face.
Fourth nerve palsy or superior oblique palsy, This disorder can cause
misalignment of the eyes and can affect one or both eyes.
Sixth nerve palsy or abducens palsy This type of palsy can cause the eye to
cross inward toward the nose.
Bell’s palsy, a disorder of the seventh cranial nerve, can cause temporary
weakness or paralysis in one side of the face.
Hemifacial spasm, A hemifacial spasm happens when blood vessels constrict
the seventh cranial nerve and cause a facial spasm or tic.
Glossopharyngeal neuralgia, this condition affects the ninth cranial nerve
and can cause pain at the base of the tongue that may travel to the ear and neck.
Cranial base tumors,These are tumors that can form in the skull and affect
different cranial nerves.
Injury, trauma, and whiplash can also cause damage to cranial nerves.
symptoms of cranial nerve damage
 pain in the face, tongue, head, or neck
 inability to focus the eye
 an eye that drifts to one side or downward
 weakness or paralysis in the face
 slurred speech
 vision or hearing loss
 changes in vision
Treatments for cranial nerve damage
Medication
The first line of treatment for cranial never disorders, is to help relieve the pain
of trigeminal neuralgia is usually medication therapy. The drugs most commonly
used for treating trigeminal neuralgia are anti-convulsants, which are
medications that were originally developed for the treatment of epilepsy. This
class of medications has also been found to be quite effective in treating nerve
pain, including trigeminal neuralgia when taken on an on-going basis.
Microvascular Decompression (MVD).
Also known as the Jannetta procedure, microvascular decompression is a
surgical procedure to relieve the symptoms of trigeminal neuralgia. In this
procedure, the neurosurgeon surgically opens the skull, (a craniectomy),
exposing the nerve at the base of the brainstem to insert a tiny sponge between
the compressing vessel and the trigeminal nerve. This sponge isolates the nerve
from the pressure and pulsating of the blood vessel. By alleviating and removing
the neurovascular compression, the trigeminal nerve recovers and painful
symptoms are relieved. The process does not damage or destroy the nerve.
Gamma Knife® Perfexion™ Radiosurgery
Gamma Knife Perfexion Radiosurgery is one of the most precise, powerful, and
proven treatments for brain disorders, including cranial nerve disorders. It is
also a preferred treatment for dysfunctions, such as trigeminal neuralgia.
The Gamma Knife Perfexion is a highly advanced machine that delivers a
powerful dose of radiation to a precise target in the brain. The Gamma Knife
Perfexion delivers 201 beams of extremely focused radiation to a precise target
in the brain. Individually, the beams are too weak to damage healthy tissue.
Together, they converge to deliver powerful treatment to a single point. Patients
experience little or no discomfort during the procedure, usually go home the
same day, and are generally able to resume normal activities.
Supra Orbital and Infra Orbital Peripheral Nerve Stimulation
Supra Orbital and Infra Orbital Peripheral Nerve Stimulation is a new modulatory
technique that has value in patients with neuralgias that are not consistent with
trigeminal neuralgia.
Percutaneous Glycerol Rhizotomy.
Percutaneous Glycerol Rhizotomy is a minimally-invasive procedure that is usually
performed as an outpatient procedure. The procedure usually takes approximately
one hour and is performed under local anesthesia. This procedure is also an ablative
procedure that disrupts the pain pathway of the trigeminal nerve, thus relieving the
pain.
A needle is inserted in the skin beside the mouth, and directed through an opening
at the base of the skull. A harmless dye may be injected to confirm the needle is in
the precise location, as seen on an x-ray. The chemical glycerol is then injected into
the space surrounding the Gasserian ganglion. This glycerol produces a relatively
mild injury to the nerve with minimal risk of permanent facial numbness. The entire
nerve is not destroyed. The majority of patients achieve early relief of trigeminal
neuralgia pain with this technique. The long-term benefit of the procedure is similar
to that of the Gamma Knife radiosurgical procedure.
(b)
ANSWER
Required to write about auditory and vestibular system.
Auditory system is the sensory system for the sense of hearing,the following are components
of auditory system.
The auditory system includes the outer, middle, and inner ears, as well as the central
auditory nervous system.
The outer ear includes the pinna and the external auditory meatus (ear canal). The
tympanic membrane (eardrum) is the boundary between the outer and middle ear.
The middle ear is housed in the mastoid portion of the temporal bone and is a
completely enclosed cavity that is connected to the nasopharynx by the Eustachian tube. The
middle ear houses the three smallest bones in the body, the malleus, incus, and stapes, also
known as the ossicular chain.
The inner ear is called the cochlea, which contains the sensory hair cells and
auditory nerve fiber endings that convert mechanical energy from the middle ear into electrical
energy. The VIII cranial nerve, vestibulocochlear nerve, brings the auditory information to the
central auditory nervous system which consists of the brainstem...
Functions of components of auditory system
OUTER EAR
PINNA :- Collects sound waves from environment and directs towards ear canal.
EXTERNAL AUDITORY MEATUS:-funnels sound waves toward the ear drum or tympanic
membrane (TM), causing it to displace and move the ossicular chain of bones in the air-filled
middle.
Have hair like structures that trap dusts and germs and secrete waxy material for
trapping dusts and germs.
MIDDLE EAR
OSSICLES ( INCUS,STAPES,MALEUS ):-Three small bones that are connected and transmit the
sound waves to the inner ear.
EUSTACHIAN TUBE :-A canal that links the middle ear with the back of the nose. The eustachian
tube helps to equalize the pressure in the middle ear.
INNER AIR
COCHLEA:- The cochlea is the auditory area of the inner ear that changes sound waves into
nerve signals.
AUDITORY NERVE:- Runs from the cochlea to a station in the brainstem (known as nucleus).
From that station, neural impulses travel to the brain – specifically the temporal lobe where
sound is attached meaning and we HEAR.
SEMI CIRCULAR CANAL:- The semicircular canals sense balance and posture to assist in
equilibrium.
VESTIBULE:-This is the area of the inner ear cavity that lies between the cochlea and
semicircular canals, also assisting in equilibrium.
mechanism of hearing.
Hearing starts with the outer ear., When a sound is made outside the outer ear, the sound
waves or vibration are collected by pinna , traveled down the external auditory canal and strike
and cause vibrations to the eardrum (tympanic membrane).
The eardrum vibrates, The vibrations are then passed to 3 tiny bones in the middle ear called
the ear ossicles. The ear ossicles tends to amplify the sound. They send the sound waves to the
inner ear and into the fluid-filled hearing organ (cochlea).
Once the sound waves reach the inner ear cochlear which is fluid filled. As the fluid moves,
25,000 nerve endings are set into motion. These nerve endings transform the vibrations into
electrical impulses that then travel along the eighth cranial nerve (auditory nerve) to the brain.,
they are converted into electrical impulses. The auditory nerve sends these impulses to the
brain. The brain then translates these electrical impulses as sound
HEARING LOSS
Hearing loss can be defined as an increase in the threshold of sound perception.Hearing loss is
of
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CONDUCTIVE HEARING LOSS.
CENTRAL HEARING LOSS.
SENSORINEURAL HEARING LOSS.
Conductive hearing loss.
Conductive hearing loss is caused by impairment in air transmission of sound waves to
the inner ear. The impairment of function is due to pathology at the level of the external
auditory canal, the tympanic membrane, or the ossicular chain, resulting in inefficient
conversion of sound waves from air to the fluid medium of the endolymph in the
membranous labyrinth.
causes of conductive hearing loss
 External Auditory Canal Stenosis or Absence.
 External Auditory Canal Tumors.
 Cholesteatoma.
 Cerumen Impaction.
central hearing loss.
Central hearing loss is caused by a lesion in the central auditory pathway or in the
auditory cortex. The auditory cortex processes and interprets the sounds amplified and
received by the ossicles and cochlear hair cells. The auditory cortex is located on the
transverse temporal gyri of Heschl.
Sensorineural hearing loss.
Sensorineural hearing loss is caused by damage to the cochlear sensory epithelium or,
less commonly, the peripheral auditory neurons. The type of hearing loss a patient has
can be quite different depending on whether the cochlea or the auditory nerve fibers
are involved.
VESTIBULAR SYSTEM.
is a sensory system that is responsible for providing our brain with information about
motion, head position, and spatial orientation; is located within the inner ear. Laterally,
it is bordered by the middle ear and medially, lies adjacent to the temporal bone.
components and functions of vestibular system
The components of the system can be divided into three parts:
-Peripheral apparatus
-Central processors
-Motor output
 Bony Labyrinth,forms 3 semicircular canals, the cochlea, and an ovaluar chamber
called the vestibule. This bony shell is filled with perilymphatic fluid that suspends a
membranous labyrinth within it.
 Membranous Labyrinth, contains 5 sensory organs: 3 semicircular ducts and 2
otolith organs known as the saccule and utricle. All are filled with endolymph, a
liquid whose composition is similar to intracellular fluid.
 Otolith Organs,The otolith organs are located in the vestibule.They take the form of
two sacs that detect linear acceleration of the head. The utricle is responsible for
sensing horizontal movement (i.e. forward-backwards and left-right movement),
while the saccule serves to detect movement in the sagittal plane (i.e. up-down
movement).
 Semicircular Ducts,The semicircular ducts are three, orthogonal rings encased within
the semicircular canals. They are responsible for detecting head rotation.
 Vestibular Sensory Epithelium and Hair Receptor Cells,convert information about
head acceleration into neurologic signals that are later processed by the central
vestibular system.
mechanism of vestibular system action(body balance)
mechanism for posture
control
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DISORDERS OF VESTIBULAR SYSTEM
Common vestibular system disorders
Benign paroxysmal positional vertigo (BPPV)
Vestibular migraine.
Labyrinthitis or vestibular neuritis.
Ménière's disease.
Age-related dizziness & imbalance.
Vestibular damage due to head injury.
Secondary endolymphatic hydrops.
Perilymph fistula.
ANSWER( c)
Required to write about visual system.
The visual system is the part of the central nervous system that is required for
visual perception – receiving, processing and interpreting visual information to build a
representation of the visual environment.
collective working of the sensory organ or the eye along with sections of the
central nervous system (i.e. the retina containing photoreceptor cells, the optic tract,
the optic nerve, and the visual cortex) and will contribute together to allow organisms
the sense of vision, that is the capability of detection and processing visible light. These
components are also responsible for enabling the generation of various non-image
photo response functions and will permit the detection and interpretation of info from
the optical spectrum perceptible to that specie for “forming a representation” of the
surrounding..
components and functions of each component of visual system
EYE:- The eye is the main part of the visual system. Lightray falls on the cornea (gets
refracted on the aqueous humor) and enters the eye via the pupil (controlled by the iris).
After entering the eye the light rays suffer a series of refractions through the eye lens
and vitreous humor. These series of refractions form an inverted image on the retinal
surface.
RETINA:-The refracted light rays fall on the retina that contains a number of
photoreceptor cells. The retina comprises two types of protein molecules contributing
to conscious vision, namely rod opsins, and cone opsins. an opsin absorbs a refracted
photon and directs the signal to the cell, hyper-polarizing the photoreceptor. Rod opsins
are present near the boundary of the retina and help in visualizing at low light levels.
Cone opsins are present near the center of the retina and help in visualizing color at
normal light levels. We can found 3 categories of cone opsins for human eye namely
short or blue, middle or green, and long or red respectively.
OPTIC NERVE:-The information signal processed in the retinal cells is transmitted to the
brain cells by the optic nerve. Around 89% of the nerve fibers send the information
signal to the lateral geniculate nucleus present in the thalamus. Here, parallel processing
is undergone to perceive vision.
OPTIC CHIASM.The optic fibers from the retina of both the eyes meet and cross at the
optic chiasm, here, the simultaneous information signals from both the eyes are
combined first and then separated based on the FOV (left FOV of both eyes and right
field of views of both eyes). The right and left half of the corresponding FOV are sent to
the left and right half of the brain, respectively for further analysis and central portion of
the FOV is analyzed by both the parts of the brain. (FOV – field of views)
LATERAL GENTICULATE NUCLEUS:-This is present in the thalamus of the brain and this is
basically a system of sensory relay nucleus that relays the image information to the
visual cortex.
VISUAL CORTEX:-Visual cortex is the main visual processing unit of the brain. It lies
above the cerebellum at the rear part of the brain. Information about vision-related
reflexes, color, and motion are processed in the visual cortex.
..
MECHANISM OF IMAGE FORMATION.
Light enters through the lens then when the lens functions with the cornea to focus light
aptly on the retina. When light passes the retina, special cells referred to as
photoreceptors convert light into electrical signals. These signals pass from the retina to
the brain through the optic nerve. The brain then turns signals into images which we see.
.NEURO-VISUAL DISORDER
Neuro-visual disorders comprise a range of problems affecting the nerves in and around
the eye.
Optic Nerve Disorders
Optic Neuropathies, Damage to the optic nerves can cause pain and vision problems,
most commonly in just one eye. A person may notice vision loss in only the center of
their field of vision (scotoma) or pain when they move the affected eye.
Optic Neuritis, result from infections (such as chickenpox or influenza) or immune
system disorders such as lupus, symptoms of optic neuritis are pain and vision
disturbances.corticosteroids or other medications to address an overactive immune
system if that is what is causing the nerve inflammation.
Giant Cell (Temporal) Arteritis;Giant cell arteritis (also called temporal arteritis) is an
inflammation of medium-sized and large arteries that extend from the neck up into the
head. The condition can affect a person’s vision in one eye. Other symptoms include a
dry cough, fever, headache, jaw pain and problems with blood circulation in the arms.
People with giant cell arteritis may be at risk for developing aneurysms.
Chiasm Disorders; Problems with blood vessels in the brain, including bleeding, are the
most common cause of problems in the optic chiasm, but tumors and trauma can also
result in chiasm disorders.
The symptoms can be disabling, affecting the person’s ability to read and visually scan
and navigate the world around them. They may not notice approaching vehicles or
people, and this may result in a loss of the ability to drive.
Treatment involves addressing the underlying cause of a chiasm disorder.
REFERENCES:
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Atlas of Human anatomy
https://www.cdc.gov/visionhealth/basics/ced/index.html
https://www.nature.com/subjects/visual-system
https://www.physiopedia.com/File:Inner_ear%27s_cupula_transmitting_indication_of_acceleration.jpg
https://en.wikipedia.org/wiki/Vestibular_system
https://clinicalgate.com/auditory-system-disorders/
https://www.healthline.com/health/inner-ear#takeaway
https://nba.uth.tmc.edu/neuroscience/m/s2/chapter12.html
https://www.hopkinsmedicine.org/health/conditions-and-diseases/neurovisual