Special Senses Flashcards
What is sound
Compressive air wave that travels at 343m/s in air
Ear detects sound as vibrations and converts to electrical signals to be processes as sound
What is frequency
Number of wave cycles per second, in Hz
What is volume
Loudness of sound relative to threshold (sound just audible), in decibels
What is cochlea
Part of inner ear responsible for hearing
What are the parts of cochlea
Bony labyrinth
Membranous labyrinth
Organ of Corti
What is bony labyrinth
Bony canal in petrous part of temporal bone, containing perilymph and surrounding membranous labyrinth
In cochlea it forms the cochlear canal
What is membranous labyrinth
Duct suspended in perilymph in bony labyrinth, containing endolymph
In cochlea forms cochlear duct
Describe structure of cochlear duct
Bounded by Reissner’s Membrane, basilar Membrane
Contains endolymph
Contains Organ of Corti
It separates cochlear duct into Scala vestibuli and scala tympani superiorly and inferiorly
Describe structure of Organ of Corti
It is the part of inner ear responsible for detecting sound, composed of epithelial hair cells on basilar membrane and tectorial membrane that hair cells interact with
What do hair cells do
Hair cells are epithelial cells on basilar membrane with sterocilia
Inner hair cells: have sterocilia that move relative to endolymph, detect sound
1 row
Outer hair cells: have sterocilia embedded in tectorial membrane, detect amplitude of sound by relative movement of basilar membrane against tectorial membrane
3 Rows
How is sound wave conducted in inner ear
Vibrations from middle ear pass through oval window to scala vestibuli, scala tympani, out through round window
How are vibrations in inner ear converted to electrical signals
- Vibrations of perilymph cause movement of basilar membrane
- Leads to movement of stererocilia: IHC relative to endolymph, OHC relative to tectorial membrane
- Bending of sterocilia cause influx of K+ into cell
- Depolarisation causes influx of Ca by VOCC
- Increased [Ca2+] triggers neurotransmitter release
- Neurotransmitter triggers AP in spiral ganglion neurones
- AP transmitted down spiral ganglion neurones to CN VIII
What is tonotopy
Point-for- point Representation of specific sound frequencies on specific regions of primary auditory cortex
How are different frequencies detected
Different regions of basilar membrane have different frequencies
Frequency decreases down length of BM
Hair cells at specific regions transmit signals about specific frequencies
Describe the auditory pathway
- Spiral ganglion cells form form cochlear part of CN VIII
- Cn viii travel in internal acoustic meatus and divide into cochlear/vestibular nerve at level of medulla
- SGN synapse with second order neurones in cochlear nucleus in medulla
- SON synapse in: A. Superior olivary complex in medulla and ascend in lateral meniscus
or B. Inferior colliculi in midbrain - From inferior colliculi axons project to medial geniculate nucleus in Thalamus
- From thalamus axons project to auditory cortex in superior temporal gyrus
- TON project to primary auditory cortex in superior temporal gyrus
