1. Rest state - negative

2. Excited state - positive

3. Return to rest state - negative

Location of recording electrodes in relation to electrical field/dipole

i.e. Near field response v. far field response

invasive

1. intracraniel (pretty close to the potential field)

2. intraoperative monitoring (electrode directly on area that you are monitoring)

3. transtympanic membrane EcochG (needle thru TM ends near prominatory to measure at the cochlea)

non-invasive

scalp recorded AER - reduces amplitude and special resolution (combo of several differfent waves)

Open- where axons are parallel, enhance volume conduction

Closed- where axons are orientated in different directions, may cancel electrical fields (++ or --)

neurons with a wider area of neuron

 and

extended duration voltage changes (longer transient voltage potential)

5

Each have its own characteristics, but not sure which are evoked in AER.

Greater number of neurons =

- generated by Compound VIII Craniel nerve AP

- gives info about OHC and really where evoked responses are generated

3 cochlear potentials evoked by sound:

1. Cochlear microphonics (CM)

2. Summating potential (SP)

and Action Potential (AP)

- an alternating current (AC) potential that mimics the waveform of the stimulus (i.e. pure tone stimulus produces a sine wave of the same frequency)

- CM has no latency (begins with the stimulus)

- Arises from the OHCs and reflects activity from the basal portion of the basilar membrane

Where is CM measured from invasivley and noninvasivley?

How is it best elicited by?

What happens when there are alternating stimulus polarity?

1. promontory of the middle ear (invasive)

2. The external ear (tiptrode) (non-invasive)

3. it cancels the CM out! So you must use a single polairty.

Pressure wave in a negative direction (negative polarity)

f.y.i. alternating polarity switches between condensation and rarefaction polarities.

Summating Potential (SP) is a direct current potential.

How is it recorded?

Origin?

Most prominent?

1. from a continuous tone or transient acoustic stimulus (click or tone burst)

2. unknown, but may be linked to innr and outer hair cell activity

3. prominent with high frequency tone burst stimuli

Action Potential (AP)

aka?

represents the compound AP (synchronous firings of many fibers) of the...____ due to_____

Largest for what type of stimuli?

- also referred to as N1 (i.e. wave 1 for ABR)

...VIII nerve due to...activity in the basal portion (first turn/high frequency portion of cochlea)

- transient stimuli with increased intensity

N2

derives from...

what happens when you increase amplitude?

- VIII nerve firing from the apical (second turn/lower frequency) regions of the cochlea.

- equivalent to Wave II of ABR when click is presented at high intensity

- amplitude increases with decreased intensity

- proximal portion of the VIII nerve as it enters the brainstem (first order neurons)

f.y.i.

-non consistently rcorded in small children due to shorter VIII nerve length

-reflects activity of the VIII nerve itself, not BS

-reliable wave II can still be recorded in brain dead, this supports VIII nerve origin

- second order neuron, beyone the VIII nerve

- possibly in or near the cochlear nucleus

- negative trough generated from the trapezoid body

third order neurons located in the Superior Olivary Complex with help from the CN and LL.

- referred to as Wave IV-V complex