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Electrophysiology Exam 1
Notes
38
Physiology
Graduate
02/29/2008

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Term
Voltage Potentials that are read by AERs come from...
Definition
Transmembrane ionic current flow
Term
3 ways we look at transmembrane ionic current flow
Definition

1. Rest state - negative

2. Excited state - positive

3. Return to rest state - negative

Term
Potential Field
Definition
Distribution of current flow in extracellular space.  This creates an action potential (positive activity)
Term
Transmembrane current flow
Definition
action potential- travels along the axon of the neuron
Term
Synapse
Definition
current flow between two or more neurons
Term
Dipole
Definition
negative polarity at one end and positive polarity at the other end.  The positve end forms the transmission.  This is how current travels
Term
factors effecting surface recorded AERs
Definition

Location of recording electrodes in relation to electrical field/dipole

 

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

Term
Near field response
Definition

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)

Term
Far Field Response
Definition

non-invasive

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

Term
Open potential fields vs. Closed potential fields
Definition

Open- where axons are parallel, enhance volume conduction

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

Term
Volume conduction increases for...
Definition

neurons with a wider area of neuron

 and

extended duration voltage changes (longer transient voltage potential)

Term
How many types of neuron make up the VIII craniel nerve and auditory brainstem response?
Definition

5

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

Term
Evoked responses are a product of _____ transmembrane electrical activity for thousands of CNS neurons
Definition
summated
Term

Greater number of neurons =

Definition
= larger amplitude of AER
Term
Afferent Auditory System =
Definition
sensory
Term
Efferent Auditory System =
Definition
motor
Term
Electrocochleography (EcochG) - generated by? gives info. about?
Definition

- generated by Compound VIII Craniel nerve AP

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

Term

3 cochlear potentials evoked by sound:

Definition

1. Cochlear microphonics (CM)

2. Summating potential (SP)

and Action Potential (AP)

Term
Cochlear microphonics comes from...
Definition

- 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

 

Term

Where is CM measured from invasivley and noninvasivley?

How is it best elicited by?

What happens when there are alternating stimulus polarity?

 

Definition

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.

Term
Condensation
Definition
movement in positve direction (positive polarity)
Term
Rarefaction
Definition

Pressure wave in a negative direction (negative polarity)

 

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

Term

Summating Potential (SP) is a direct current potential.

How is it recorded?

Origin?

Most prominent?

Definition

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

Term

Action Potential (AP)

aka?

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

Largest for what type of stimuli?

Definition

- 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

Term
What happens when you increase the intensity (for an ABR)??
Definition
- the latency is decreased. i.e. you will see your wave earlier.  High intensity stimuli produces mostly basal cochlear activity
Term

N2

 

derives from...

what happens when you increase amplitude?

Definition

- 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

Term
Wave I comes from?
Definition
distal portion of the VIII nerve (afferent activity of the VIII neve fibers as they leave the cochlea and enter the iternal auditory canal)
Term
Wave II comes from...
Definition

- 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

Term
Wave III comes from...
Definition

- second order neuron, beyone the VIII nerve

- possibly in or near the cochlear nucleus

- negative trough generated from the trapezoid body

Term
Wave IV - leading shoulder to wave V - comes from...
Definition

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

- referred to as Wave IV-V complex

Term
Wave V comes from...
Definition
- generated from end o the LL fibers entering the inferior colliculus (contra to stimulated ear)
Term
Waves VI and VIII come from...
Definition
Unknown!
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