5.1.3

• 
  

  1. Sensory neurone transmits El from receptors to CNS

  2. Relay neurone transmits El from sensory neurone to motor neurone

  3. Motor neurone transmits El from CNS to effector (muscle or gland) to carry out response
• Action potential

  • If generator potential reaches threshold (-55mV), then action potential (nerve impulse) is generat
• Non-myelinated axons


  • No Schwan cells
  • Slower conduction as a whole
  • Axon must depolarise for El to be transmitted
  • No Nodes of Ranvier
• Stretch-mediated sodium channels

  • On the membrane of sensory neurone
  • When stimulus (pressure) is detected, SMSC open and Na+ enters cell causing depolarisation
• Generator potential

  • Stimulus detected → Na+ diffuses into cell → causes depolarisation (less negative charge)
  • Change in potential difference because of stimulus
• Pacinian corpuscle is a mechanoreceptor that detects mechanical pressure
• Myelinated axons

  • Have Schwan cells that provide insulation and speed up conduction (saltatory conduction)
  • No Na+ channels except in Nodes of Ranvier
• Transducer


  Converts one type of energy into another
• Factors that increase conduction speed

  • Myelinated neurones: Electrical jumps
  • Increased temperature: Ions have more kinetic energy, leading to faster diffusion
• Resting potential

  ● Sodium-potassium pump actively pumps 3Na+ out for every 2K+ that goes in. Less positive inside cell than .

  ● K+ diffuses out (down electrochemical gradient) through potassium ion channels. Axon membrane permeable to K+ not Na+

  
• Increased temperature 🌡 will do what to conduction speed?

  Ions have more KE, faster diffusion