Topic 2

• Nervous system


  Detects and responds to changes in your surroundings
• Components of the nervous system

  • Brain
  • Spinal cord
  • Neurones (nerve cells)
  • Receptors
• Central nervous system (CNS)


  Brain and spinal cord
• Receptors


  • Nose - chemical receptors detect smells
  • Tongue - chemical receptors detect tastes
  • Eye - light receptors detect light
  • Skin - contain pain, pressure and temperature receptors
  • Ear - sound and balance receptors
• Receptor cells


  Detect stimuli
• Stages of a nervous response

  1. Receptor cells detect a stimulus and sends an electrical impulse along a sensory neurone to the brain and spinal cord

  2. The brain coordinates the sensory information and sends an electrical impulse along a motor neurone to the effector (usually muscles)

  3. The muscle contracts causing a response
• Sensory neurones


  • Have long dendrons and short axons
  • Carry electrical impulses from receptors to the CNS (brain and spinal cord)
• Relay neurones


  • Many short dendrons and axons
  • Carry electrical impulses from sensory neurones to motor neurones
• Motor neurones


  • Many short dendrons and one long axon
  • Carry electrical impulses from the CNS to the effectors
• Neurone adaptations


  • Myelin sheath - insulates the cell (axon) and increases the speed of transmission of impulses
  • Lots of side branches - transmit impulses to many cells
• Stages of a reflex response

  1. Receptor cells detect a stimulus and sends an electrical impulse along a sensory neurone to the spinal cord

  2. The electrical impulse goes along the relay neurone in the spinal cord

  3. The electrical impulse then goes along a motor neurone to the effector causing a response
• Reflex arc


  The pathway the impulse goes along in a reflex response
• Reflex action


  A fast, automatic response that helps protect you from harm
• Impulses can not jump across the gap between neurones

  A chemical called a neurotransmitter is released which goes across the gap and causes a new electrical impulse to be made in the second neurone
• How an electrical impulse travels across a synapse

  1. An electrical impulse travels along a neurone and stimulates the release of a neurotransmitter at the synapse (gap between neurones)

  2. The neurotransmitter diffuses across the synapse and binds to the receiving (second) neurone, stimulating a new electrical impulse to be made in the second neurone