The dictionary definition of 'negligence' is 'lack of proper care or attention', which is clearly applicable in this case.
Although circumstances vary, an accusation of 'negligence', against a nurse, is likely to be far more serious than one of 'misconduct'.
e.g. a nurse kissing a patient would probably be seen as misconduct but it's not going to kill anyone. (As long as he/she otherwise carried out her duties properly, she couldn't be accused of negligence).
However, 'negligence' (i.e. neglecting one's duties) could be far more serious for the patients and for the nurse.
'Misconduct' is normally dealt with by internal disciplinary procedures (unless, of course, it involves a criminal offence, such as stealing from patients).
'Negligence', as well as triggering internal disciplinary procedures, can lead to court action. This could be through the civil courts, with the nurse being sued for compensation for injury to the patient or for the loss of a loved one. In extreme cases, it could result in a criminal prosecution for manslaughter.
Chris