Question

need to know a, b, and c

A. compare the structures and physiology of the sense of hearing and balance with thise of the sense of vision. maks sure to describe ALL the vital structures of each system.

B. explain in detail the physiological process of hearing and balance.

C explain the process of vision.

Answer 1

a.

Physiology of hearing and balancing and vision have some similarities and differences.
Similarities are:

• In both hearing and vision there is conversion of energy from one form to neural impulses.
• Both of the physiology occurs through a cascade of steps involving the different levels of processing.
• Both the pathway ultimately reaches to the cerebral cortex
• Both the physiological output is dependent on intensity of the the input. Whenever there is a high intensity sound or light there will be a higher perception.

Differences:

• The structures involved in hearing are pinna, external auditory meatus, middle ear and ossicles, tympanic membrane, oval window, perilymph, basilar membrane hair cells, tectorial membrane and cochlear nerve. In case of balancing vestibular apparatus including semicircular canal, utricle and sacule and otolith organs .
• In case of vision the structures involved are retina, photoreceptor cells, bipolar cells, ganglion cells and optic nerve.
• In hearing sound energy is converted into to a nerve impulse, whereas in vision the light energy is converted into nerve impulse
• Both in hearing and balancing there are mechanical structures and processes involved. In vision chemical changes are mainly occurring.
• Hearing occurs through a macro macro level of transmission of sound wave. In vision, Daya minute microscopic levels of conduction of light energy as impulse.
• Hearing and balance are controlled by cochlear nerve whereas vision is controlled by optic nerve.
• Hearing and vision is referred with the temporal lobe of primary auditory cortex whereas in case of vision it is situated in occipital lobe as primary visual cortex.

The involved structures are detailed below in the description:

b. Ear is the organ of hearing and balance.

Ear is classified into:

1. External ear
2. Middle ear and
3. Internal ear

External ear is comprised of a pinna located outside. It is composed of cartilaginous tissue. Its function is to collect the sound waves and concentrate it to the tube like structure called external auditory canal/meatus. It is 2.5 cm in length and consist of seruminous glands which secrete serumin; a sticky substance to which the microbes or dust particles attach. It functions as a part of immunity. The external acoustic meatuds leads to the tympanic membrane which is also known as the ear drum. Its function is to transmit the sound waves from the external ear to the middle ear. The middle ear is an air-filled cavity comprising three ear ossicles.

1. Malleus
2. Incus
3. Stapes.

The sound waves travel in the form of vibrating particles through the external acoustic meatus to reach the tympanic membrane. It vibrates and pass on this vibrations to the malleus which conduct the vibration and passes it to the stapes. Basically these three ear ossicles act as a lever system to transmit the sound wave to one another. The sound waves will be amplified Up to 18 times from the tympanic membrane to the foot end of the stapes. This is due to the difference in the surface area of the tympanic membrane and stapes as it keeps decreasing progressively. The foot end of the stapes is in close contact with the window of the inner ear known as 'Oval window'.Internal ear is a spiral organ having 4 parts:

1. Cochlea -Main organ for hearing.
2. Saccule - Saccule and utricle collectively known as vestibule.
3. Utricle
4. Semicircular canal- Vestibule and semicircular canal are collectively known as vestibular apparatus which helps in ear balancing.

Cochlea is a tortuous organ, to make it more understand, let's imagine it in a stretched form like 'A test tube within a test tube' manner. This structure creates 2 windows with the middle ear.

1. Oval window
2. Round window

There are three compartments inside the cochlea:

1. Scala vestibuli
2. Scala media
3. Scala tympani.

Scala vestibuli is associated with the oval window. Scala tympani is associated with the round window. The internal ear is a fluid filled cavity. The fluid is scala vestibuli and Scala tympani is known as perilymph. The fluid in the scala media is known as endolymph. The test tube within the test tube structure create two membranes:

1. Reissner's membrane :Present between the scala vestibuli and scala media
2. Basilar membrane : Between the Scala media and scala tympani.

The cochlea in the internal ear plays the major role in converting the mechanical energy of the sound waves into neuronal impulses. This is achieved by the help of an organ known as 'Organ of corti'- It is a spiral organ located inside the scala media. The organ of corti is comprised of hair cells which are outer hair cells located outside throughout the scala media and cochlea & Inner hair cells which are located a bit inside and also throughout the cochlea. Both hair cells are excitatory in function. There are some other supporting cells too. Those are Pillar cells, Henson cells and Deiter cells . Besides these cells of organ of corti, there is one another structure  present inside the scala media known as the tectorial membrane. All these structures actually comprises the organ of corti.

The actual physiology of the hearing is the receiving of the sound waves by the pinna, then it concentrates and conducts through the external auditory meatus to the middle ear via the tympanic membrane. The tympanic membrane is the connectivity between the external ear and the middle ear. Middle ear is an air filled Activity containing three ear ossicles - malleus. incus and stapes which are interconnected to each other. The handle of malleus is in close contact with the ear drum. So the sound waves pass on the energy to the ear drum which further passes it on to malleus. Now the malleus is in close contact with the ear drum and it transfer the energy into stapes. The stapes passes it to the oval window of scala vestibuli with which it is in close contact.The oval window transfer the energy into the scala vestibuli and perilymph. Perilymph starts vibrating and passes on the energy to the membrane - Reissner's membrane which compresses and passes the vibrations to the Scala media and endolymph. The endolymph starts vibrating and passes the energy on to the Basilar membrane,. The Basilar membrane compresses and renounces again. On rebounding, the outer hair cells and the inner hair cells gets irritated by coming into contact with the acellular membrane .Thus creating the action potential. This is where the sound waves are converted to impulses via mechanical interface. From there, Various neurons arise and form the cochlear nerve which further continues as the VIII th cranial nerve to the temporal lobe of the cerebral cortex, where the sound is perceived.

BALANCING PHYSIOLOGY

The balancing organ is vestibular apparatus. The vestibular apparatus comprises of utricle, Saccule and semicircular canals. There are three semicircular canals

1. Anterior
2. Posterior
3. Lateral

There are right angles to each other in the three dimension. Each of these canals are filled with the fluid known as endolymph. The sensations of fluid movement inside the Semicircular canals are detected. The speed of the endolymph and its movement gives te idea of the rotation of the body. The otolith organ is another part of the balancing organ that detect the balance and orientation. Otolith organ consists of utricle and Saccule. There are crystal of calcium carbonate attached to the hair cells in a viscous Gell substance. When we go for lying down, form the standing posture, these crystals move in the surrounding viscous substance. Once they move, it physically pulls the hair cells that are attached to them. This triggers an action potential that carry information to the brain.

C.

Physiology of vision includes three steps:
1. Initiation of vision that is phototransduction
2. Processing and transmission of visual sensation
3. Visual perception
Eye has three layers:
1. Outer sclera
2. Middle choroid
3. Inner retina

Initiation of vision:
The retina layer is further divided into outer layer, middle layer and inner layer. The outer layer consists of retinal pigment epithelium and photoreceptors. The photoreceptors are are rods and cones. The retinal pigment epithelium plays a crucial role in vision as it stores and process vitamin A. The photoreceptor cells rods and cones are responsible for a lot of photochemical reactions that occurs within them. This information then released to the bipolar layer cells in the middle layer and transmitted to ganglion cells. The axons of the ganglion cells forms the optic nerve.
Cones are having higher threshold receptors for photopic vision and color vision.
Rods are having low threshold receptors for night vision or scotopic vision.
Rhodopsin or visual purple is the visual pigment present in rods. Rhodopsin is composed of opsin and retinin(11-cis-retinal or vitamin A aldehyde)
The outer segment of water receptors contain photo chemicals. And the inner segment contains nucleus synaptic body and other organelles. Photo chemicals are light sensitive chemicals that decompose on exposure to light and excite nerve fibres leading from eye to central nervous system. Rhodopsin is present in rods - scotopsin and 11-cis-tetinal composes it. Iodopsin is the photochemical pigment of cones which consist of photopsin and 11-cis-tetinal.

The photo transaction is the phenomenon of conversion of light energy into nerve impulse. Light falls on retina that causes photochemical changes and trigger cascade of biochemical reactions ultimately generating electrical impulses. The photochemical changes occurring in rods are rhodopsin bleaching and rhodopsin regeneration.
In the retina light sensitive rod cells contain stacks of membranes called as discs in which the light sensitive pigment rhodopsin is present. Each rhodopsin is a molecule of retinal which is present in 11-cis-tetinal form.11-cis-retinal absorbs the photon energy from the light and convert into All-trans retinal.
The rhodopsin activation occurs by conversion of 11-cis-tetinal to All-trans-retinal. In the next step opsin activates transducin and transducin activates phosphodiesterase. This phosphodiesterase convert the cyclic GMP to GMP. Since the cyclic GMP levels are decreased the sodium channel closes. After the closure of sodium channels the membrane gets hyperpolarized. Therefore whatever the inhibitory neurotransmitters were released from rods does not release now.This causes the bipolar cells to be excited and the information to be transferred to the ganglion cells and the action potential is initiated. this action potential is transmitted to the brain to vision to occur
The rhodopsin is regenerated later by 11-cis-retinal is regenerated from all trans-retinal and vitamin A from blood. The regeneration process is independent of the light.

Processing and transmission of visual sensation:
The information received by ganglion cells are transferred to neurons of lateral geniculate body then to the primary visual cortex. This occurs by the retina relays the information to the optic nerve, optic chiasm, optic tract and the lateral geniculate body from there to the optic radiations and finally to the primary visual cortex.

Visual perception:
it is a complex integration of light sense, form sense sense of contrast and color sense that occurs in the brain.

Malleus Tympanic membrane Pinna Seruminous glands Incus Oval window Stapes Reisnner's membrane Inner and outer hair cells Supproting cells Perilymph External auditory meatus Endolymph Middle ear LOTTIR Cochlha Round window Basillar membrane Cochlear nerve

Anteriror semicircular canal Utricle Sacule Lateral Posterior Cochlea

Malleus Tympanic membrane Pinna Seruminous glands Incus Oval window Stapes Reisnner's membrane Inner and outer hair cells Supproting cells Perilymph External auditory meatus Endolymph Middle ear LOTTIR Cochlha Round window Basillar membrane Cochlear nerve

Anteriror semicircular canal Utricle Sacule Lateral Posterior Cochlea

Axons of ganglion cells forming optic Ganglion cell layer nerve Ganglion cell Amacrine cell Innaer plexiform layer Muller cell Inner nuclear layer Bipolar cell Outer plexiform layer Horizontal cell External limiting membrane Outer nuclear layer SINI Layer of photoreceptor outer segments Photoreceptor cell Pigmented epithelium