Brain: Structure & Function (Edexcel A (SNAB) A Level Biology)

• The brain, alongside the spinal cord, is part of the central nervous system (CNS)
• The brain is made of billions of interconnected neurones 
• Within the brain are different regions that carry out different functions

Different regions of the brain carry out different functions

• You need to know the functions of the following brain regions

The cerebrum

• The cerebrum is the largest part of the brain in humans, accounting for about 80% of the total mass of the brain
• It carries out a large variety of functions involved with conscious activities, including:
  • Vision
  • Hearing
  • Speech
  • Thinking
  • Memory
• The cerebrum is divided into two halves known as the cerebral hemispheres
  • The hemispheres are joined together by a band of nerve fibres known as the corpus callosum
  • The right hemisphere controls the left side of the body and the left one controls the right side
• The cerebrum has 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 neurone connections 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
• Beneath the cerebral cortex or grey matter layer is the 'white matter'
  • The white matter consists of the myelinated axons of neurones

The cerebrum consists of two hemispheres joined by the corpus callosum

The hypothalamus

• The hypothalamus monitors the blood as it flows through the brain and, in response, releases hormones or stimulates the neighbouring pituitary gland to release hormones
  • The hypothalamus plays an important role in some homeostatic mechanisms
• Hypothalamus functions include
  • Regulating body temperature
    • The hypothalamus monitors blood temperature and initiates a homeostatic response if this temperature gets too high or too low
  • Osmoregulation
    • Cells in the hypothalamus monitor the water balance of the blood and releases the hormone ADH if the blood becomes too concentrated
      • ADH increases absorption of water in the kidneys
  • Regulating digestive activity
    • The hypothalamus regulates the hormones that control appetite as well as the secretion of digestive enzymes
  • Controlling endocrine functions
    • The hypothalamus causes the pituitary gland to release hormones that control a variety of processes e.g. metabolism, growth and development, puberty, sexual functions, sleep, and mood

The cerebellum

• The cerebellum coordinates movement
  • This includes balance; a highly complex function that requires coordination between multiple parts, including the eyes, semicircular canals in the ears, and many muscles

The medulla oblongata

• Also known as the medulla
• The medulla contains co-ordination centres that control different functions e.g.
  • The cardiac centre controls heart rate
  • The respiratory centre controls breathing rate