JD - Auditory System Flashcards
What are the two characteristics that characterize sound?
Sound is characterised by its:
- PITCH (tone)
- INTENSITY (loudness)
Where are specialised hair cells located?
Inner ear
What occurs in the outer ear and middle ear?
OUTER EAR:
- Amplifies sound pressure for frequencies 2-5KhZ
- Localization of a sound source (elevation)
MIDDLE EAR:
- Important for amplifying the sound wave
- Conduct movement in the tympanic membrane
What is the requirement for amplification and how does the inner ear achieve this
The sound wave moves from air, which has a low impedance (low resistance) to an aqueous environment in the inner ear which has a high impedance (high resistance)
- Focuses the force of large tympanic membrane down onto the much smaller oval window
- Lever action of the malleus and incus
What are the structural features of the inner ear? (6)
Organ of Corti
- Inner hair cells
- Outer hair cells
- Tectorial membrane
- Basilar membrane
- Endolymph
Describe the structure of the basilar membrane
Tapered structure – narrow at one end and gets progressively wider along its length
Varied frequencies will cause undulations in different regions of the basilar membrane
What is the structure of a hair cell? (4)
Stereocilia
- Rigid structures made of actin filaments
- Increase in length in a step-wise fashion
Basolateral surface
- Involved in exocytosis of neurotransmitters
Outer Hair Cells
- Have efferent inputs (receive signals from the CNS)
Inner Hair Cells
- Have afferent inputs (send signals back to the CNS)
What are TIP LINKS?
Tip links are extracellular filaments that
connect stereocilia to the kinocilium
in the hair cells of the inner ear
- Site of mechanotransduction
What is the ionic basis of hair cell activity?
- Endocochlear potential: Stereo cilia are bathed in endolymph (high K+); the base is bathed in perilymph (low K+)
Both depolarisation and hyperpolarisation K+ dependent = Biphasic response
- This organisation means that the movement of the stereocilia of the hair cells will create a graded response (= generator potential)
Describe the role of hair cells in the auditory system.
Hair cells, specifically stereocilia, transduce vibrational energy in the basilar membrane into an electrical signal
What is labeled line coding in the auditory system? (2)
- The tonotopic organisation of the basilar membrane is an example of labelled line coding
- A single neurone/nerve fibre responds maximally to a particular stimulus
What are the inner and outer hair cells assoicated with and what are cochlear amplifiers?
Inner = sensory receptors (transduction)
Outer = contract and expand in response to electrical currents (active process)
Cochlear amplifiers: enhances amplitude and sharpness
Outer hair cells (oHC): Mechanism of signal amplification (4)
- Sound wave arrives as acoustic energy
- Basilar membrane displacement
- Modulation of current through OHCs
- Mechanical transduction by OHCs
Or 3. AP generated by IHCs
What are 3 key features of the auditory system?
- Auditory nerve cells are bipolar
- Cell bodies of auditory nerves are in the spiral ganglion
- Information of each ear reaches both sides of the system at the superior olive
What is Lloyd Jeffress’s concept of coincidence detection in auditory pathways?
That neural circuits could encode short time intervals by acting as coincidence detectors
i.e. they only respond when two or more signals occur simultaneously – or coincidentally
- If the sound is to the right, the sound arrives at the right ear first, so a longer neural pathway is introduced to the right so that the signal arrives at the coincidence detector simultaneously with the signal from the left side
