traveling only certain distances. This means that there is essentially a frequency âmapâ of the cochlea, with the regions at the very start of the cochlea being stimulatedby higher-frequency soundwaves (meaning high-pitched noises, like an excited toddler inhaling helium) whereas the very âendâ of the cochlea is activated by the lowest-frequency soundwaves (very deep noises, like a whale singing Barry White songs). The areas between these extremes of the cochlea respond to the rest of the spectrum of sounds audible to humans (between 20 Hz and 20,000 Hz).
The cochlea is innervated by the eighth cranial nerve, named the vestibulocochlear nerve. This relays specific information via signals from the hair cells in the cochlea to the auditory cortex in the brain, which is responsible for processing sound perception, in the upper region of the temporal lobe. And the specific part of the cochlea the signals come from tells the brain what frequency the sound is, so we end up perceiving it as such, hence the cochlea âmap.â Quite clever really.
The trouble is, a system like this, involving a very delicate and precise sensory mechanism essentially being shaken constantly, is obviously going to be a bit fragile. The eardrum itself is made up of three tiny bones arranged in a specific configuration, and this can often be damaged or disrupted by fluid, ear wax, trauma, you name it. The ageing process also means the tissues in the ear get more rigid, restricting vibrations, and no vibrations means no auditory perception. It would be reasonable to say that the gradual age-related decline of the hearing system has as much to do with physics as biology.
Hearing also has a wide selection of errors and hiccups, such as tinnitus and similar conditions, that cause us to perceive sounds that arenât there. These occurrences are known as endaural phenomena; sounds that have no external source, caused by disorders of the hearing system (for example,wax getting into important areas or excessive hardening of important membranes). These are distinct from auditory hallucinations, which are more the result of activity in the âhigherâ regions of the brain where the information is processed rather than where it originates. Theyâre usually the sensation of âhearing voicesâ (discussed in the later section on psychosis), but other manifestations are musical ear syndrome, where sufferers hear inexplicable music, or the condition where sufferers hear sudden loud bangs or booms, known as exploding head syndrome, which is one from the category âconditions that sound far worse than they actually are.â
Regardless of this, the human brain still does an impressive job of translating vibrations in the air to the rich and complex auditory sensations we experience every day.
So hearing is a mechanical sense that responds to vibration and physical pressure exerted by sound. Touch is the other mechanical sense. If pressure is applied to the skin, we can feel it. We can do this via dedicated mechanoreceptors that are located everywhere in our skin. The signals from the receptors are then conveyed via dedicated nerves to the spinal cord (unless the stimulation is applied to the head, which is dealt with by the cranial nerves), where theyâre then relayed to the brain, arriving at the somatosensory cortex in the parietal lobe which makes sense of where the signals come from and allows us to perceive them accordingly. It seems fairly straightforward, so obviously it isnât.
Firstly, what we call touch has several elements that contribute to the overall sensation. As well as physical pressure, there are vibration and temperature, skin stretch and even pain in some circumstances, all of which have their own dedicated receptors in the skin, muscle, organ or bone. All of this isknown as the somatosensory system (hence somatosensory cortex) and our whole body is innervated by the nerves that serve it.
The cochlea is innervated by the eighth cranial nerve, named the vestibulocochlear nerve. This relays specific information via signals from the hair cells in the cochlea to the auditory cortex in the brain, which is responsible for processing sound perception, in the upper region of the temporal lobe. And the specific part of the cochlea the signals come from tells the brain what frequency the sound is, so we end up perceiving it as such, hence the cochlea âmap.â Quite clever really.
The trouble is, a system like this, involving a very delicate and precise sensory mechanism essentially being shaken constantly, is obviously going to be a bit fragile. The eardrum itself is made up of three tiny bones arranged in a specific configuration, and this can often be damaged or disrupted by fluid, ear wax, trauma, you name it. The ageing process also means the tissues in the ear get more rigid, restricting vibrations, and no vibrations means no auditory perception. It would be reasonable to say that the gradual age-related decline of the hearing system has as much to do with physics as biology.
Hearing also has a wide selection of errors and hiccups, such as tinnitus and similar conditions, that cause us to perceive sounds that arenât there. These occurrences are known as endaural phenomena; sounds that have no external source, caused by disorders of the hearing system (for example,wax getting into important areas or excessive hardening of important membranes). These are distinct from auditory hallucinations, which are more the result of activity in the âhigherâ regions of the brain where the information is processed rather than where it originates. Theyâre usually the sensation of âhearing voicesâ (discussed in the later section on psychosis), but other manifestations are musical ear syndrome, where sufferers hear inexplicable music, or the condition where sufferers hear sudden loud bangs or booms, known as exploding head syndrome, which is one from the category âconditions that sound far worse than they actually are.â
Regardless of this, the human brain still does an impressive job of translating vibrations in the air to the rich and complex auditory sensations we experience every day.
So hearing is a mechanical sense that responds to vibration and physical pressure exerted by sound. Touch is the other mechanical sense. If pressure is applied to the skin, we can feel it. We can do this via dedicated mechanoreceptors that are located everywhere in our skin. The signals from the receptors are then conveyed via dedicated nerves to the spinal cord (unless the stimulation is applied to the head, which is dealt with by the cranial nerves), where theyâre then relayed to the brain, arriving at the somatosensory cortex in the parietal lobe which makes sense of where the signals come from and allows us to perceive them accordingly. It seems fairly straightforward, so obviously it isnât.
Firstly, what we call touch has several elements that contribute to the overall sensation. As well as physical pressure, there are vibration and temperature, skin stretch and even pain in some circumstances, all of which have their own dedicated receptors in the skin, muscle, organ or bone. All of this isknown as the somatosensory system (hence somatosensory cortex) and our whole body is innervated by the nerves that serve it.
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