Neurones in the Brain (HL) (HL IB Biology)

• Pain receptors (nociceptors) are sensory receptors
• These receptors have free nerve endings which are unencapsulated nerve endings
• The exposed dendrites on these nerves have transient receptor potential (TRP) channels which open in response to stimuli which indicate a risk of damaged tissue
• Stimuli might include:
  • High temperature
  • Acid
  • Chemicals e.g. capsaicin in chilli peppers
• Entry of positively charged ions causes the threshold potential to be reached
• An action potential is generated, it moves along the axon of the sensory neurone to the central nervous system
• Nerve impulses then pass through the neurones to the cerebral cortex in the brain, where pain is perceived and a protective response results
• The sensitivity of an organism to these stimuli provides a survival and reproductive advantage

Pain Receptors Diagram

Pain receptors in the skin can respond to a number of different stimuli as the nerve endings are exposed

The cerebrum

• The cerebrum is the largest part of the brain in humans (accounts for about 80% of the total mass of the brain)
• The cerebrum carries out a large variety of functions involved with conscious activities, including:
  • Vision
  • Hearing
  • Speech
  • Thinking
  • Memory
• The cerebrum is divided into two hemispheres, each of which have a thin outer layer known as the cerebral cortex or 'grey matter'
  • The cerebral cortex consists of the cell bodies of neurones
  • It is highly folded, which increases its surface area and allows it to contain a greater number of neurones
  • With more neurones in the brain, more connections between neurones can be made
  • This is important, as the more connections between neurones in the brain, the greater the ability of the brain to carry out more complex behaviours
    • These behaviours that result from a combination of complex pathways, are called emergent properties 
  • It is in this part of the brain where interactions between neurones lead to consciousness
  • This idea of consciousness incorporates qualitative perception of feelings associated with colour, temperature, sound as well as communication which results in a complex awareness of the environment
• The structure and function of the brain as an organ is covered in more detail here