Auditory Anatomy and Physiology Exam 2: Hair Cell Transduction

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Questions and Answers

What type of information do low frequencies provide to the brainstem and cortex?

Amplitude information

Timing information (correct)

Phase information

Frequency information

Where are afferent nerve fibers connected to in the ear?

Tectorial membrane

Basilar membrane

Inner hair cells (correct)

Outer hair cells

What is the characteristic of nerve fibers located at the base of the basilar membrane?

Low characteristic frequency

Rapid adaptation

High characteristic frequency (correct)

Slow adaptation

What does the post-stimulus time histogram measure?

Adaptation of firing in nerve fibers Signup and view all the answers

What is the characteristic of nerve fibers located at the apex of the basilar membrane?

Low characteristic frequency Signup and view all the answers

What is the phenomenon seen at low frequencies where the nerve fires on a particular phase of the stimulus?

Phase locking Signup and view all the answers

What is the main job of hair cells in the auditory system?

Convert energy into electrical signals Signup and view all the answers

Which component is responsible for the lateral movement that causes displacement of stereocilia in hair cells?

Actin Signup and view all the answers

What causes the inside of a hair cell to become hyperpolarized?

Potassium gates opening Signup and view all the answers

What is the main function of outer hair cells (OHCs) in the auditory system?

Amplify stereocilia vibration Signup and view all the answers

What is the primary role of prestin in outer hair cells (OHCs)?

Control cell membrane movement Signup and view all the answers

What role do inner hair cells (IHCs) play in the cochlear amplifier?

Cause synaptic vesicle release Signup and view all the answers

What is the primary function of the synaptic ribbon in relation to the auditory nerve?

Interact with vesicles containing neurotransmitters Signup and view all the answers

How are action potentials created in the 8th nerve fiber related to auditory function?

Link sensory input to electrical signals in the brain Signup and view all the answers

What distinguishes high spontaneous rate auditory nerve fibers from low spontaneous rate fibers in terms of firing rate?

High spontaneous rate fibers create more action potentials per second Signup and view all the answers

How are responses from the auditory nerve quantified and studied?

Recording firing rates of nerve fibers attached to hair cells Signup and view all the answers

Study Notes

Hair Cell Transduction

Hair cells convert energy into electrical signals
Basilar membrane movement transfers energy through stereocilia bending
Stereocilia are made up of actin monomers and myosin protein

Movement of Stereocilia

Lateral movement causes displacement of stereocilia, pulling sodium channels open
Positively charged ions flow into the endolymphatic space, causing depolarization
Pivot points are the spiral limbus on the tectorial membrane and the spiral lamina on the basilar membrane

Ion Channels and Gradients

Voltage gradient: mutual repulsion of like-charged particles
Concentration gradient: particles distribute homogeneously in a medium
Endolymphatic potential: +80 mV, measured by putting an electrode in the endolymph and grounding anywhere on the body
Inner hair cell potential: -45 mV, measured by putting an electrode in the inner hair cell and grounding anywhere on the body
Total voltage potential: 125 mV (+80 + -45 mV)

Transduction in the Cochlea

Basilar membrane movement:
- Down (condensation): stereocilia deflect towards the modiolus, potassium gates are closed, and the inside of the hair cell becomes hyperpolarized
- Up (rarefaction): stereocilia deflect up towards the stria, potassium ions flow through channels into the hair cells, and depolarization occurs
Calcium channels open, and calcium enters the cell, releasing neurotransmitters

Potassium Recycling

Recycled through hair cells, fibrocytes in the spiral ligament, cells of stria, and back to the endolymph

Key Concepts

Hair cell transduction is non-linear and has asymmetry in compressive non-linearity
Membrane voltage is always negative
Hair cell receptor potentials are measured in both OHCs and IHCs

OHCs and Mechanical Transduction

OHCs contribute to mechanical transduction through motility
OHCs shorten when depolarized and lengthen when hyperpolarized
Prestin is embedded in the cell membrane of OHCs

OHC vs IHC

OHCs provide mechanical feedback to BM motion
IHCs cause synaptic vesicle release
Cochlear amplifier: added mechanical feedback produced by OHCs in concert with the tectorial membrane

Auditory Nerve

Synaptic ribbon anchors near the presynaptic membrane and interacts with vesicles containing neurotransmitters
Neurotransmitter is glutamate
Action potentials are created in the 8th nerve fiber
Firing of nerve fibers occurs once the threshold of excitation has been met
High spontaneous rates (>50 spikes per second) attach on the pillar side of the hair cell
Low spontaneous rate (<10 spikes per second) attach on the modiolar side

Responses from the Auditory Nerve

Histograms, post-stimulus time period, input-output functions, and tuning curves are used to quantify and study responses
Nerve fibers have a characteristic frequency
Afferent nerve fibers are connected to inner hair cells and are located in the basilar membrane

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Description

Test your knowledge on hair cell transduction in auditory anatomy and physiology. Learn about the process of converting energy and messages into another form, how hair cells function as sensory cells, and how basilar membrane movement transfers energy.