Question

1) Describe the creation of the action potential from start to finish, make sure you discuss the flow of ions across the membrane. What is the function of myelin and what happens if a baby is placed on a no fat diet?

2) Describe the pathway of sound from the ear to the cochlea. Describe two types of deafness that can occur and how are they treated. How do we localize the source of a sound?

Answer 1

Ans1)

During the resting state,before an action potential occurs,all of the gated sodium and potassium channels are closed. Voltage-gated sodium have two gates (gate m and gate h), while the potassium channel only has one (gate n).

• Gate m (the activation gate) is normally closed, and opens when the cell starts to get more positive.
• Gate h (the deactivation gate) is normally open, and swings shut when the cells gets too positive.
• Gate n is normally closed, but slowly opens when the cell is depolarized (very positive).

Voltage-gated sodium channels exist in one of three states:

1. Deactivated (closed) - at rest, channels are deactivated. The m gate is closed, and does not let sodium ions through.
2. Activated (open) - when a current passes through and changes the voltage difference across a membrane, the channel will activate and the m gate will open.
3. Inactivated (closed) - as the neuron depolarizes, the h gate swings shut and blocks sodium ions from entering the cell.

Voltage-gated potassium channels are either open or closed.

As soon as signal reaches the neuron depolarisation of neuron occurs.

Depolarization - makes the cell less polar (membrane potential gets smaller as ions quickly begin to equalize the concentration gradients) . Voltage-gated sodium channels at the part of the axon closest to the cell body activate. This lets positively charged sodium ions flow into the negatively charged axon, and depolarize the surrounding axon.

Repolarization - brings the cell back to resting potential. The inactivation gates of the sodium channels close, stopping the inward rush of positive ions. At the same time, the potassium channels open. There is much more potassium inside the cell than out, so when these channels open, more potassium exits than comes in. This means the cell loses positively charged ions, and returns back toward its resting state.

Hyperpolarization - It makes the cell more negative than its typical resting membrane potential. As the action potential passes through, potassium channels stay open a little bit longer, and continue to let positive ions exit the neuron. This means that the cell temporarily hyperpolarizes, or gets even more negative than its resting state. As the potassium channels close, the sodium-potassium pump works to reestablish the resting state.

This is then transmitted to the next neuron and via this process conduction of action potential occurs.

Myelin sheath helps in faster conduction by allowing saltatory conduction of potential.

If a baby is placed on no fat diet then there will be no formation of myelin resulting in slower comduction which may then lead to neurological defects.

Ans2)

1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
3. The bones in the middle ear amplify, or increase, the sound vibrations and send them to the cochlea, a snail-shaped structure filled with fluid, in the inner ear. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
4. These vibrations then cause the fluid inside the cochlea to ripple.

There are two types of hearing loss-Sensorineural and conductive

Sensorineural-Sensorineural hearing loss (SNHL) is the most common type of hearing loss and occurs when the inner ear nerves (and hair cells) are damaged and do not properly transmit auditory signals to the brain. This permanent type of hearing loss can be treated with hearing aids.

Conductive: Conductive hearing loss is typically the result of obstructions in the outer or middle ear. Sound does not properly conduct through the outer ear to the middle ear. Possible treatment options include surgery, medicine and hearing aids.

Sound waves are signaled by the difference in arrival times between the ears, by the relative amplitude of high-frequency sounds , and by the asymmetrical spectral reflections from various parts of our bodies, including torso, shoulders, and pinnae.

The distance cues are the loss of amplitude, the loss of high frequencies, and the ratio of the direct signal to the reverberated signal.

Depending on where the source is located, our head acts as a barrier to change the timbre, intensity, and spectral qualities of the sound, helping the brain orient where the sound emanated from.