The difficulty is that 'nerves' has more than one meaning. In the physical sense (electrical channels in body tissue) it is meaningless in collocation with 'shattered'; 'The nerves connecting the legs to the brain run down the spine' - they can be damaged in various ways (severed/atrophied/bruised/pinched between the lumbar vertebrae ...) but not shattered.
'Nerves' can also mean nervous reactions to [often social] stimuli: 'Mrs Bennet suffers dreadfully with her nerves'. Nerves like these can be shattered. To have 'shattered nerves' is to be nervous and react with inappropriate quickness and violence.
In the singular, there is yet another set of meanings - one of which works with 'shattered': 'He hasn't ridden since the accident - his nerve's shattered.'
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