Question

1. Describe the anatomy and physiology of hearing.

2. Describe the anatomy and physiology of taste and smell.

Answer 1

1. Anatomy of hearing:

# Outer ear:

* Sound is collected by the outer ear which is also known as the pinnae.

* It travels down the ear canal and vibrates the eardrum.

* This turns an invisible energy ( the acoustic signal) into visible movement of the eardrum ( mechanical force)

# Middle ear:

* The eardrum movement causes movement of the middle earbones.

* This bone movement provides an increase in the force of the energy as it moves from air filled middle ear space to a fluid filled cochlea.

# Inner ear:

* The cochlea is snail shaped and is filled with tens of thousands of hair cells.

* The air cells are embedded in structures that move in response to the waves created by the incoming sound.

* The movement of these hair cells result in a small electrical charge.

* This charge is send by auditory nerve upto the brain for interpretation as sound.

* The cochlea is arranged tonotopically like a piano keyboard.

* High frequencies are processed at the base of the cochlea, low frequencies are processed at the apex of the cochlea.

@ Physiology of heraing:

* Hearing is the process by which the ear transforms sound vibrations in the external environment into nerve impulses that are conveyed to the brain, where they are interpreted as sounds.

* Sounds are produced when vibrating objects, such as the plucked string of a guitar, produce pressure pulses of vibrating air molecules, better known as sound waves.

* The ear can distinguish different subjective aspect s of a sound, such as its loudness and pitch, by detecting and analyzing different physical characteristics of the waves.

* Pitch is the perception of the frequency of sound waves - I.e, the number of wavelengths that pass a fixed point in a unit of time.

* Frequency is usually measured in cycles per second or hertz.

* The human ear is most sensitive to and most easily detects frequencies of 1,000 to 4,000 hertz, but atleast for normal young ears the entire audible range of sounds extends from about 20 to 20,000 hertz.

* Sound waves of still higher frequency are referred to as ultrasonic, although they can be heard by other mammals.

* In order for a sound to be transmitted to the central nervous system, the energy of the sound undergoes three transformations.

* First, the air vibrations are converted into vibrations of the tympanic membrane and ossicles of the middle ear.

* These in turn become vibrations in the fluid within the cochlea.

* Finally, the fluid vibrations set up travelling waves along the basilar membrane that stimulate the hair cells of the organ of corti.

* These cells convert the sound vibrations to nerve impulses in the fibres of the cochlear nerve, which transmits them to the brainstem, from which they are relayed, after extensive processing, to the primary auditory area of the cerebral cortex, the ultimate centre of the brain for hearing.

* Only when the nerve impulses reach this area does the listener become aware of the sound.

This is about physiology of hearing.

2) Anatomy of taste and smell:

* Taste ( gustation) and smell ( olfaction) are both chemical senses, the stimuli for these chemicals are senses.

* The more complex sense is olfaction.

* Olfactory receptors are source of complex receptors called G- protein coupled receptors( GPCRs).

* These structured are proteins that weave back and forth across the membranes of olfactory cells seven times, forming structures outside the cell that sense deodorant molecules and structures inside the cell that activate the neural message ultimately conveyed to the brain by olfactory neurons.

* The structures that sense odorants can be thought of as tiny binding pockets with sites that respond to active parts of molecules.

* There are about 350 function olfactory genes in humans, each gene is expresses a particular kind of olfactory receptor.

* All olfactory receptors of a given kind project to structures called glomeruli( paired clusters of cells found on the both sides of the brain).

* The olfactory system creates an image for the mixture and stores it in memory as it just as for the odour of a single molecule.

* Taste is simpler than olfaction. Bitter and sweet utilize GPCRs, just as olfaction does, but the number of different receptors is much smaller.

* Sweet is even simpler. The primary sweet receptor is composed of two different G protein coupled receptors.

@ Physiology of taste and smell:

* The senses of smell and taste combine at the back of the throat.

* When you taste something before you smell it, the smell lingers internally upto the nose causing you to smell.

* Both smell and taste use chemoreceptors, which essentially means they are both sensing the chemical environment.

* Olfactory receptor, the axons of the olfactory receptor neurons pierce the cribiform plate of the ethmoid bone and enter the olfactory bulbs.

* The olfactory mucus membrane is constantly covered by mucus produced by Bowman's gland which is also located in the basal lamina of the olfactory epithelium.

* Olfactory bulbs, the axons of the receptors contact the primary dendrites of the mitral cells and tufted cells to form the complex globular synapses called olfactory glomeruli.

* Physiology of taste includes taste receptor cells, taste buds and taste nerves.

* The sense of taste is mediated by taste receptor cells which are bundled in clusters called taste buds.

* Taste receptor cells sample oral concentration of a large number of small molecules and report a sensation of taste to centers in the brainstem.

* Taste buds are most prevalent on small pegs of epithelium on the tongue called papillae.

* Taste buds are composed of group of between 50 and 150 columnar taste receptor cells bundled together like a cluster of bananas.