 Sound enter pinna  Ear canal acts as resonator for 3000Hz frequency  Vibrates tympanic membrane  Set ossicles into vibration: Sound amplifiers  Transfer vibrations to oval window by piston action of stapes  Perilymph of scala vestibuli  Organ of corti: Basilar and tectorial membrane vibrates bending hairs of hair cells  Fluid of Scala tympani and finally round window

The deflection of the hair-cell stereocilia opens mechanically gated ion channels that allow any small, positively charged ions (primarily potassium and calcium) to enter the cell. Unlike many other electrically active cells, the hair cell itself does not fire an action potential. Instead, the influx of positive ions from the endolymph in Scala media depolarizes the cell, resulting in a receptor potential. This receptor potential opens voltage gated calcium channels, calcium ions then enter the cell and trigger the release of neurotransmitters at the basal end of the cell.

 The neurotransmitters diffuse across the narrow space between the hair cell and a nerve terminal, where they then bind to receptors and thus trigger action potentials in the nerve.  In this way, the mechanical sound signal is converted into an electrical nerve signal. The repolarization in the hair cell is done in a special manner. The Perilymph in Scala tympani has a very low concentration of positive ions. The electrochemical gradient makes the positive ions flow through channels to the Perilymph.

 The louder the sound is, the greater height or amplitude of the vibrations in the sound waves, the more movement of hairs/stereocilia of hair cells and thus more action potentials  Greater the frequency of action potentials, louder the sound is  If you could hear someone talking, that means the voice is loud enough to generate action potentials in the sensory neurons of your ear.

 If they raise their voice, that causes an increase in the APs to your brain. If they lower their voice into a whisper, the frequency decreases.  If they lower their voice to the point where you can’t hear them, then that means you’re not even generating ONE action potential. So if you can’t hear a sound, it doesn’t mean there’s no sound in the room, it means the sound is too soft for you to hear.

 Hearing loss is typically described as being conductive, sensorineural, or mixed.  Conductive hearing loss refers to an impairment of one's ability to conduct airborne sound through the middle ear to the inner ear. Scar tissue or otosclerosis, the abnormal growth of bone within the middle ear, can lead to restricted movement of the ossicles.ossicles  Sensorineural hearing loss refers to impairment of the sensory unit consisting of the auditory nerve and the hair cells that excite it.auditory nerve

 Sometimes the distinction between these two types of hearing loss can be made with a simple tuning fork test. If the tuning fork cannot be heard when sounded in air, then the base of the tuning fork is placed against the hard bone behind the ear.  If the person can now hear it by conduction through the bone, then conductive hearing loss is indicated. If it cannot be heard by either air or bone conduction, then sensorineural loss is indicated.

 Sometimes a satisfactory level of hearing can be restored by a hearing aid - a combination of a microphone to sense ambient sound, an amplifier, and a tiny speaker that projects the amplified sound into the ear canal. 1.Sound goes in the Microphone. 2.Sound gets amplified. 3.Sound comes out the Speaker into your Ear

 Body  Behind The Ear (BTE)  In The Ear (ITE)  In The Canal (ITC)  Completely In the Canal (CIC)

 Stimuli: All changes in the environment both internal and external are known as stimuli  Receptors: Organs of the body that detect these changes or stimuli are called “receptors” or “sense organs”. Sensory receptors are specialized to respond to only certain stimuli, which will activate the receptor with weak or moderate levels of intensity. Sensory receptors transduce the stimuli into a graded potential caused by opening of membrane channels

The sensitivity range of a sensory organ is much broader than the range of a single receptor cell This is because individual afferent (sensory) fibers of the sensory system cover different parts of the sensitivity spectrum  Sensory neurons: If the receptor potential is strong enough to reach threshold, sensory neurons fire (generate action potentials  Sensation: Sensation arise when signals are detected by sensory receptor cells and transmitted through the nervous system to the designated parts of the brain

 Stimulation  Transduction  Conduction: The impulse must be conducted along a neural pathway from the receptors to the brain  Translation: A region of the brain designated for the specific stimulus or spinal cord must translate the impulse into a sensation

 Touch: includes contact, pressure, heat, cold etc  Taste: for certain substances in solution  Smell: for volatile chemicals and gases in air  Hearing: for vibrations in air, water or solid  Sight: for light waves

 Olfaction: The sense of smell  Gustation: The sense of taste

 Three cell types  Supporting cells: Provides metabolic and physical support for the olfactory sensory neurons  Basal cells: Precursor cells to olfactory sensory neurons  Olfactory sensory neurons (OSNs): The main cell type in the olfactory epithelium » OSNs are small neurons located beneath a watery mucous layer in the epithelium

 Cilia: Hairlike protrusions on OSN dendrites - Have receptor sites for odorant molecules. - structures for olfactory signal transduction - Takes seven or eight odor molecules binding to a receptor to initiate an action potential - Very sensitive to stimuli however they quickly become fatigued. This explains the reason why odours seem to go away after being easily noticable

 Detects sweet, sour, salty, bitter, & amino acids (umami)

 Taste receptor cells are modified epithelial cells  are in each taste bud  Each bud can respond to all categories of tastants

 Salty & sour do not have receptors; act by passing through channels 10-29

 Sweet & bitter have receptors; act thru G-proteins 10-30