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Audition (Perception of Sound waves (Detecting pitch (Basilar membrane…
Audition
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Vestibular system
It plays a role imposture and balance, located in the inner ear. There are two components: vestibular sacs and semicircular canals
Vestibular Sacs
Also called the otolith structures. There are two sacs - saccule (little sack) and utricle (little pouch). Each contain hair cells, gell like mass which informs the cilia in the direction which relays information on direction.
Semicircular canals
Respond to angular acceleration (changes in the rotation of the head). Made out of three ring like structures, orientated to the three mager planes in the head (horizontal, transverse and sagittal). Receptors in each canal respond to angular acceleration in one plane. Comprised of soft canal floating in a bony one filled with fluid with hair cells in gletatinous. The movement of the fluid relative to angular acceleration on the cilia are disrupted which sends signals.
Pathway to the brain
Vestibular and cochlear nerves are the two branches of the auditory nerve. Most axons in vestibular nerve terminate in vestibulor nuclei of medulla, some travel directly to cerebellum. Vestibular nuclei neutrons send information to cerebellum, spinal cord, medulla, pons and temporal lobe
Anatomy of the ear
Outer Ear
Sound is funnelled by the external ear (pinna) through the ear canal to the tympanic membrane (eardrum). Sound causes the eardrum to vibrate
Middle Ear
Contains three bones called ossicles. Malleus, incus and stapes. They transmit vibration to oval window of the cochlea (membrane covered opening that is on the outside of the cochlea). Magnify sound so that it can be processed by the cochlea. Males is connected to the timpani membrane.
Ossicles
Malleus, Incus and Stapes
Inner Ear
Contains the cochlea and is filled with fluid. Organ of corti is also there which allows the detection of sound.
Cochlea
Changes the sound vibration into receptor potential via bending of hairs. There are three main structures: hair cells; basilar membrane; sectoral membrane. Hair cells are anchored to flexible basilar membrane. Some of the hair cells (at the cilia) also attach to rigid tectoral membrane. Basilar membrane moves relative to the tectorial membrane which bends the cilia of the hair cells producing receptor potential
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Hair Cells
They have rigid cilia 'eyelashes'. Cilia have two functions: one is to transduce sensory information; movement throughout the body. So they detect movement and pass objects/substances through the body. Though the cochlea coils there are two layers of hair cells. Hair cells connect to bipolar cells to transmit information to the brain via choclea nerve. The vibrations may be big enough that they move on their own but if they are too small the fluid in the cochlea which moves the cilia
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Cilia tip links
Tip links (elastic filaments) connect one cilia to the next. They are under a small amount of tension (taught) at rest which allows small amount of movement to be detected. The stretching and relaxing is what creates the messages and in turn causes the chemical messages.
Stretching the tip link
Depolarisation leads to increased receptor potential which allows neurotransmitters to be released to bipolar cells - go towards the biggest
Relaxing the tip link
Hyperpolarisation leads to decrease in receptor potential which allows a decrease of neurotransmitters to bipolar cells - go towards the smallest
Hearing Disorders
Conductive Deafness
Problem conducting sound waves through outer ear, tymbic membrane or middle ear. Cause - infection, tumour, wax, eardrum perforation. Treatments can be surgery, medication, hearing aids to help people with the conduction of sound waves
Sensory/neural deafness
Damage to cochlear, auditory nerve, hair cells (sensory is just hair cells). The cause is either hereditary or due to loud noise. Usually permanent but can treat it with a cochlea implant
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Sound waves
sound is generated by objects vibrating. Air molecules around vibrating objects condense and rarefy producing waves. The waves travel away from the object. Then the waves stimulate the receptors in our ears.
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Auditory Cortex
Arrangement
Core Regions - contains primary auditory cortex, input from medial geniculate nucleus
Belt Region - first level of auditory cortex input from primary auditory cortex, dorsal and medial geniculate nucleus
Parabelt region - highest level of auditory association cortex, in put coming from belt and medial geniculate nucleus
Two streams
Dorsal Stream - Terminates in posterior parietal. Sound localisation, where is it coming from? Runs upwards then back on itself.
Ventral Stream - Terminates in parabelt region (anterior temporal lobe). It analysed complex sounds - properties of sound