2.12B Explain some of the limitations in treating damage and disease in…

The idea

Treating nervous-system damage is hard because neurones are specialised and largely unable to regenerate after injury. In the brain and spinal cord, damaged nerve tissue is not readily replaced, so lost function may be permanent. The skull and vertebrae protect these structures but also make them difficult to access for surgery, and operating risks further damage. Brain tumours are hard to treat because the brain is enclosed, surgery may be impossible in delicate areas, and drugs must cross the blood–brain barrier, which limits which medicines reach the tissue. Spinal injuries can sever or crush neurones carrying impulses, and because these fibres do not regrow well, messages below the injury may not pass. These limitations explain why recovery is often limited.

What earns the marks

• Nervous tissue has limited ability to repair or regenerate, so damage may cause permanent loss of function.
• The brain and spinal cord are enclosed by the skull and vertebrae, making access for surgery difficult and risky.
• The blood–brain barrier restricts which drugs can reach brain tissue, limiting treatment of tumours and disease.
• Spinal injuries can damage neurones that carry impulses, and these fibres do not regrow effectively, so signals may not pass.
• Brain tumours are difficult to remove surgically without damaging surrounding nervous tissue.

Common mistakes and how to put them right

• Assuming the brain and spinal cord heal as easily as skin.

  Put it right: Neurones have very limited regeneration, so damage is often permanent.

• Thinking any drug can reach the brain freely.

  Put it right: The blood–brain barrier limits which substances enter brain tissue.

• Believing spinal injury only affects the bone.

  Put it right: It can damage neurones carrying impulses, disrupting signalling below the injury.

Exam tips

• Link each limitation to a specific structure, such as the blood–brain barrier or the spinal cord, rather than saying 'it is hard'.
• Use the words 'regenerate' and 'blood–brain barrier' accurately when explaining why treatment is limited.
• When a question names spinal injury or brain tumour, give a reason specific to that case as well as a general reason.