final exam study guide - hair cells

describe how moving your head gets translated into a signal by hair cells in the vestibular system

movement of the head cause fluid to move in the semicircular canals, which bends the hair cells. This bending opens ion channels, leading to changes in neurotransmitter release and generating signals sent to the brain about head position and movement.

describe the difference between endolymph and perilymph and why that matters

• Endolymph – high K+ concentration and low Na+ concentration

• Perilymph – High Na+ concentration and Low K+ concentration

• • The top of the cells is exposed to endolymph, but their bodies are exposed to perilymph. This means that channels in the tops of the stereocilia are driven by different ion concentration than the cell body.

describe the flow of K+ through hair cells, and each step in that process

1. Stereocilia Bending: Sound waves cause the basilar membrane to vibrate, bending hair cell stereocilia.

2. Opening of Ion Channels: Bending opens mechanically gated ion channels via 'tip links' between stereocilia.

3. K+ Influx: Opened channels allow K+ ions from endolymph to flow into hair cells.

4. Depolarization: K+ influx depolarizes the hair cell membrane, crucial for signaling.

5. Neurotransmitter Release: Depolarization opens voltage-gated Ca2+ channels, triggering neurotransmitter release.

6. Signal Propagation: Neurotransmitters diffuse to afferent neurons, generating action potentials for auditory information.

describe the importance of the reticular lamina

the reticular lamina keeps endolymph and perilymph separated

Movement of Outer Hair Cells

Outer hair cells respond to sound vibrations through their stereocilia, which bend to open ion channels. This allows K+ ions to enter, depolarizing the cells and triggering the prestin protein to change shape, leading to elongation or contraction of the hair cells. This movement amplifies sound vibrations, improving sensitivity and frequency selectivity, and enhances inner hair cell stimulation, which is crucial for auditory perception.

describe the two ways that outer hair cells modulate what you hear

1. Cochlear Amplification:Outer hair cells amplify sound via shape changes from K+ influx, enhancing basilar membrane movement, allowing for detection of softer sounds.

2. Frequency Tuning: Outer hair cells contract and elongate, adjusting cochlear stiffness to improve frequency discrimination and selectivity in complex sound environments.

describe how outer hair cells affect inner hair cells

Outer hair cells amplify sound by changing shape upon depolarization, enhancing basilar membrane vibration and increasing stimuli to inner hair cells for better auditory transduction. They also improve frequency selectivity, allowing inner hair cells to better differentiate sounds.

describe the differences in the connections for the inner and outer hair cells

Type of Neuron Connections:

• Inner Hair Cells: Synapse with multiple afferent neurons, transmitting auditory information to the brain.

• Outer Hair Cells: Primarily have efferent connections, modulating sensitivity rather than sending sensory information directly.

Signal Direction:

• Inner Hair Cells: Act as primary sensory transducers, sending signals from cochlea to auditory pathways in the brain.

• Outer Hair Cells: Regulate and amplify signals from inner hair cells, reflecting feedback for adjusting auditory sensitivity.