Anatomy and Physiology for Nursing and Healthcare Students at a Glance. Ian Peate

place in the superior sagittal sinus through structures called arachnoid villi. When the CSF pressure is greater than the venous pressure, CSF will flow into the bloodstream. However, the arachnoid villi act as ‘one‐way valves’: if the CSF pressure is less than the venous pressure, the arachnoid villi will not let blood pass into the ventricular system.

      Clinical practice point

      Due to the brain’s many important roles, damage to any of its lobes from injuries, illnesses or chronic conditions such as brain tumour can cause major losses in brain function. A space‐occupying lesion of the brain is usually due to malignancy but it can be caused by other pathologies such as an abscess or haematoma. The effect of a tumour may be local, due to focal brain damage, and the presentation can provide an indication of the location of the lesion but not its cause. There may be more general symptoms related to raised intracranial pressure or seizures, behavioural changes or false localising signs. While large lesions in some regions, for example the frontal lobe, may be relatively silent, a small lesion in the dominant hemisphere may impact severely on speech, for example.