• Question: if you had an artificial body part would it be more flexible than a normal body part

    Asked by chuen to Andrew, Lizzie, Nick, Sonia on 14 Jun 2015.
    • Photo: Elizabeth Kapasa

      Elizabeth Kapasa answered on 14 Jun 2015:

      I guess it depends which body part it was. Some body parts you want to be flexible and some you don’t. For example you wouldn’t want flexible bones – reminds me of the poem about elastic jones!

      Which body part were you thinking of?

      https://books.google.co.uk/books?id=kSDraefPHKQC&pg=PA56&lpg=PA56&dq=elastic+jones+had+rubber+bones&source=bl&ots=2c1–Okigx&sig=JujBhQTutz9YnWh5Qcn1hR3Ic6M&hl=en&sa=X&ved=0CB8Q6AEwAWoVChMIteGEgLKPxgIVA1sUCh0o0QDX#v=onepage&q=elastic%20jones%20had%20rubber%20bones&f=false

    • Photo: Andrew Phillips

      Andrew Phillips answered on 14 Jun 2015:

      At the moment most artificial body parts, limb and joint replacements for example, are much stiffer than the normal body part. It depend what material they are made out of and what their structure is. Having joint replacements stiffer than the bone they are replacing can cause problems, as they don’t transfer the forces in the same way as the natural skeleton. Bone responds to the loads its placed under, and so something you get bone resorping (https://en.wikipedia.org/?title=Bone_resorption) away from the artificial joint – which is bad news! Some of our working is looking at making the implant the same stiffness as the bone around it.

    • Photo: anon

      anon answered on 14 Jun 2015:

      I can only comment on the bits I have any knowledge of. As far as hearing is concerned the cochlear implant (CI) is far inferior to its natural counter part – the cochlear.

      The range of input volume of a CI is 40-60dB compared with 0-120dB (3 dB increase is a doubling in power). CI range 70Hz – 8kHz, cochlear 20 Hz – 20kHz. Until the patient get used to the ‘sound’ when the implant is first switch on many report speech sounds like a dalek or donald duck, so the implant is not reproducing the sound naturally.

      And of course the implant has an electrode 30mm long with up to 22 electrical contacts, the electronics package is around 25mm x 12mm x 4mm, the receiver coil is around 2mm in diameter, plus there is the external ‘hearing aid part’. The cochlear itself is 10-12 mm in diameter, 4.5 mm thick comprising of 2.5 urns, there are 15,000-20,000 nerve cells.

      So the human cochlear is far superior to the artificial replacement. Also the human cochlear is design to work as a pair. There are areas in the brainstem (the part of the brain which controls the autonomic systems) which detect whether sound is reaching one ear quicker than the other, and the volume at which the sound is reaching both ears. Our brain uses this information to determine which direction the sound is coming from.

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