Hearing nerve damage quiz,ear infection nose running panting,constant ringing in ears with dizziness fatigue,earring stuck inside earlobe - Step 1

Author: admin, 16.09.2014
There are two general types of hearing loss: Conductive hearing loss and Sensorineural hearing loss.
Conductive hearing loss is caused by any disruption in the passage of sound from the external ear via the middle ear to the oval window.  Possible causes are impacted wax,  tympanic membrane perforation, otitis media, middle ear effusion, ossicle problems including otosclerosis. Topographic maps of this sort are a big deal - we'll see many examples in the visual system of how information about various aspects of vision gets laid out amongst a collection of neurons in a systematic way.
Two cues for localizing a sound source are: inter-aural intensity difference (IID) and inter-aural timing difference (ITD).
In above figures, the sound arriving at the ear that is furthest from the sound source is delayed (time difference) and lower in amplitude (intensity difference). LSO contains neurons that are selective to intensity differences and MSO contains neurons that are selective for timing differences.
This graph shows the responses (firing rates) of an example LSO neuron that response strongly when the sound arriving at the ipsilateral ear is louder than the sound in the contralateral ear (Recall that there are two superior olives, one on the right and the other on the left, and note that ipsilateral means same side and contralateral means opposite side). This graph shows the responses (firing rates) of an example MSO neuron to different interaural timing differences.
Konishi took a close look at the anatomy of the MSO (also called the nucleus laminaris) and found that the neurons are connected in a way that looks remarkably like the wiring diagram predicted by Jeffries. A sound source is vibration (see the ‘what do I hear’ chapter) which is encoded in the cochlea (the auditory inner ear). These signals (stating whether the sound is loud or soft, high or low, long or short, etc…) are transmitted to the brain via the auditory nerve.Inside the brain, groups of specialised neurones and the auditory cortex decode the message so that the following perception is as precise as possible.
It’s said that the left hemisphere of the brain controls the right half of the body and vice versa.
When it comes to initiating motor actions, does each hemisphere of the brain control the opposite side of the body?
The precentral gyrus is also known as the motor cortex or primary motor area, because its function is the execution of voluntary movements. The postcentral gyrus is also known as the somatosensory cortex, or primary sensory area, because it receives sensory input from the body.
Figure 3: Organization of the sensory and motor cortices, starting with the toes on the inside surface of the hemisphere, wrapping around towards the face, tongue, and throat on the outside surface. The sensory and motor cortices are actually highly organized – each part of it corresponds to a specific part of the body, and the size of the area devoted to each part of the body depends on the complexity of the movements that are carried out, or the sensations processed, by that body part. Figure 4: And if you built a body that according to the proportion of motor or sensory cortex devoted to each part of the body, it would look something like this.
So if you decide you want to move your right arm, or your right leg, the signal would leave the motor cortex of the left hemisphere, travel down towards your brainstem, and then at the level of the medulla, it would decussate, or cross over to the right side of the brainstem, and then continue into your spinal cord.
So broadly, Tyler was correct, the right motor and sensory strips control the left side of the body, and vice versa.
There are also two exceptions to this exception: cranial nerve 12 that controls the muscles that allow you to stick out your tongue, and part of cranial nerve 7 that controls the muscles of your lower face both send and receive signals to the opposite hemisphere, like the rest of the body.
In general, as with the rest of the body, it is true that the primary auditory cortex of each hemisphere processes input from the opposite ear. Figure 6: Visual pathway, from the eye back to the visual cortex, in the occipital lobe, in the back of the brain. If you inspect the image, you’ll notice that each eye sends data from the retina back to both hemispheres, so that the right visual cortex processes data from both the right and left eyes, as does the left visual cortex. Each of your eyes, and thus each of your retinas (which is the part of the eye that receives the visual input), can be split in half: the temporal part, which is on the outside, (the right part of your right retina, and the left part of your left retina), and the nasal part, which is on the inside, near your nose (the left part of your right retina, and the right part of your left retina). Notice that the light coming into your eyes from the left half of the scene interacts with the temporal part of the right retina, and the nasal part of the left retina. When the nerves partially decussate across the optic chiasm, the sensory input from the left half of the visual field combines and continues into the right hemisphere. While I know many of these points, having them given to me in one go helps integrate things enormously.


These synapse on spiking neurons in the spiral ganglia, the axons of which form the auditory (8th cranial) nerve.
Sounds arriving from the right side also arrive at the right ear first because it's closer. Indeed, this amount of time is actually smaller than the amount of time it takes to develop an action potential in the auditory nerve. Konishi (at CalTech) and his colleagues have performed a large number of auditory experiments on barn owls.
Then the firing rates of neurons in the right cochlear nucleus are higher than those in the left cochlear nucleus. It responds most strongly when the sound in the right ear leads that in the left ear by about 50 microseconds. And, the temporal tuning of these nerve cells has precisely the property that Jeffress predicted. Geometrically, the set of locations in the world that are, say, 5 cm closer to one ear than the other is (approximately) a cone with its apex at the center of the head.
However, we also have a certain degree of loudness constancy (sounds appear equally loud as the sound source changes in distance, despite the change in intensity at the ear).
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Does this apply to the processing of audio and visual stimulus of the ears and eyes as well? By being so folded, the surface area of the brain can increase without substantially increasing the overall volume of the brain. The motor cortex controls the more than six hundred muscles involved in voluntary movements, and can be found at the rear of the frontal lobe, just in front of the central sulcus.
The somatosensory cortex can be found at the front of the parietal lobe, just behind the central sulcus.
What that means is that the part of the motor cortex that controls the fingers is way bigger than the part of the motor cortex devoted to the torso, even the your torso is way bigger than your fingers. Likewise if you wanted to move your left arm, the signal would leave your right hemisphere’s motor cortex, decussate at the level of the medulla, and then continue in the left side of your spinal cord. This means that both the left and right members of a pair of cranial nerves are innervated by the motor cortex of both the left and right hemispheres. If you go back and examine figure 5, above, you’ll notice that the signals from the ears are carried by cranial nerve eight, the vestibulocochlear nerve, which controls the inner ear, and cranial nerve ten, the vagus nerve, which controls, among other things, the outer ear. The light coming at your eyes from the right half of the scene stimulates the temporal part of the left retina, and the nasal part of the right retina. The sensory input from the right visual field combines and continues into the left hemisphere.
I am left wondering about cross wiring in the nervous systems of other animals–is it similar to the human configuration? These then lead to the cochlear nucleus, then to the superior olive, then to the inferior colliculus, then to the medial geniculate nucleus, and finally on to auditory cortex. You can, if you wish, attend to the violin part, and then listen specifically to the line played by the cellos.
This cue is especially easy to use with abrupt sounds, as you can compare the onset (beginning) of the sounds in each ear. Remarkably enough, this very precise temporal information is made available to your perceptual experience.
While studying the inputs to the medial superior olive (MSO) and lateral superior olive (LSO), they discovered neural circuits and neurons that appear to be well-suited to representing these two types of information, both timing and intensity differences. This hypothetical LSO neuron computes a difference between the firing rates (right cochlear nucleus firing rate minus left cochlear nucleus firing rate) and it responds strongly. There are other neurons in the MSO that respond best to different interaural timing differences.


The neurons communicating signals from the two ears converge in a very orderly fashion, with increasing delay in the transmission length. Sound sources located at any position in the cone (above-right, in front and to the right, behind and to the right, closer, further) generate exactly the same IID and ITD cues for the listener and thus can not be distinguished using IIDs or ITDs. Thus, there must be other cues to distance (as loudness constancy works, to some extent, even with your eyes closed). Likewise, the area of the sensory cortex that processes sensation from your lips is bigger than the part that processes sensation from your feet, even though your feet are bigger than your lips. So if you severed a nerve bundle below the level of the medulla that you knew to be involved in the execution of motor commands, then the side of your body that would become paralyzed would be ipsilateral – the same side of the body in which the lesion occurred. Since cranial nerves communicate with both the left and right hemispheres, then the primary auditory cortices do receive input from both ears, though most of the input is from the contralateral ear. So the quick answer is that visual information from each of the optic nerves (cranial nerve 2), gets processed by both hemispheres. So each hemisphere doesn’t process visual input from the opposite retina, but from the opposite visual field. But in fact, the physical stimuli (the sound pressure waveforms) from these two groups of string instruments are very similar - entirely overlapping and intertwined with each other. That's what I need to know about to survive and function in the world, whether the event was you clapping your hands or a tiger in the jungle stepping on a twig. For continuous pure tones, this is more difficult as it involves a phase difference between the sound in the two ears. Another LSO neuron does the opposite comparison (left minus right) and it would respond strongly only if the sound in the left ear is stronger than than in the right ear. Some prefer it when the sound in the right ear leads and others prefer it when the sound in the left ear leads. The inputs from the two ears are combined to generate neurons whose preference for inter-aural time differences varies systematically. There are two ways to disambiguate the direction (azimuth and elevation) from which a sound is coming. All sounds arrive at your ear both directly, and as echoes and reverberations involving reflections off the ground and other environmental surfaces.
However, if you had a lesion higher in your brainstem, above the level of the medula, or if you suffered a stroke that affected part of your motor cortex, then the affected part of the body would be contralateral – the opposite side of the body as the lesion. If there was a lesion on only the left side of the brain, both sides of the body areas connected to cranial nerves would continue to receive motor messages from the right hemisphere.
The right visual field, initially split across both of your eyes, combines and gets processed by the left visual cortex. So we don't hear (and most of the time we don't want to hear) a large portion of the physical stimulus (the sound waves) coming to our ears. If there was a lesion affecting only the left auditory cortex, the right ear would not become entirely deaf. Others prefer 50 microseconds, 55 microseconds, 70 microseconds, 100 microseconds, 200 microseconds, etc. However, the timing of these reflections and the number and intensity of them is a cue to the kind of space you are in (hallway, concert hall, living space, outdoors) and to the distance to the sound source. The outer ears (the pinnae) are asymmetrically shaped, and filter sounds differently depending on where the sound sources are located and what frequency the sound has.



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