5.1.3

• All neurones contain:


  Cell body

  Dendrons

  Axons
• Myelinated neurones contain


  Schwann cells that wrap around the axon forming a myelin sheath
• What is the purpose of a myelin sheath?

  Are made of lipid so insulate the axon causing the action potential to jump increasing its rate of transmission.
• Saltatory conduction

  The action potential jumps between the nodes of ranvier making it travel faster
• Neurone structure

  A) dendrites

  B) nucleus

  C) axon

  D) cell body

  E) myelin sheath

  F) Schwann cell

  G) node of ranvier

  H) axon terminal

  
• Sensory neurone diagram

  A) receptor cells

  B) dendron

  C) myelin sheath

  D) axon

  E) axon terminal

  F) peripheral

  G) central

  
• sensory neurones look like


  a snail
• Features of a sensory neurone


  Long dendron

  carry impulse to relay neurone from receptor cell
• Relay neurone diagram

  A) cell body

  B) dendrite

  C) nucleus

  D) axon

  E) axon terminal

  
• What does a relay neurone look like?


  A really squished spider
• Features of a relay neurone


  Many short dendrites

  One long axon

  Connects sensory and motor neurones
• Motor neurone diagram

  A) cell body

  B) Schwann cell

  C) myelin sheath

  D) axon

  E) dendrites

  F) axon terminal

  G) terminal button

  
• Motor neurones look like a


  millipede
• Features of a motor neurone

  Long axon

  short dendrites

  Carry impulse from relay or sensory neurones to effector
• what do sensory receptor cells do

  detect a stimulus
• What are sensory receptor cells also known as


  transducers
• transducers


  convert stimuli energy into another form of energy
• what do photo receptors do


  detect light using rods and cones
• what do thermo receptors do

  detect heat using end bulb of krause
• What is the Pacinian corpuscle


  pressure receptor
• Pacinian corpuscle diagram

  A) lamellae rings

  B) capsule

  C) sensory neurone ending

  D) axon

  E) capillary

  F) gel

  
• what occurs when pressure is applied to the Pacinian corpuscle


  the Na+ channels are opened as the cell deforms allowing Na+ into the cell creating a generator potential
• Resting potential


  When a neurone is not conducting an impulse so is more positive on the outside of the membrane making the inside comparatively negative
• Resting potential mV


  -70 mV
• How is resting potential established


  There are sodium and potassium pumps in the plasma membrane. For every 2K+ in 3Na+ out creating an electrochemical gradient
• To create an electrochemical gradient what is required


  ATP for active transport to move Na+ out the cell to an area already high in Na+ concentration
• Why don't Na+ move into the cell at resting potential


  The membrane is more permeable to K+ as the K+ channels are always open ( the Na+ channel are not permanently open ) and there are more K+ channels overall.
• Action potential


  When a neurones voltage increases beyond a set point from the resting potential generating a nervous impulse.
• Depolarisation


  An increase in internal neurone voltage
• Action potential graph

  A) stimulus

  B) -70

  C) Na+ channels open

  D) -55

  E) threshold

  F) depolarisation

  G) Na+ channels shut

  H) action potential

  I) K+ channels open

  J) repolarisation

  K) K+ channels shut

  L) refractory period

  M) resting state

  N) +40

  O) voltage mV

  P) time ms

  
• Stages of an action potential:

  1. Stimulus - Transducers turn stimulus into energy causing Na+ voltage gated channels to open
  2. Threshold - Once this voltage has been passed an action potential will occur
  3. Depolarisation - More Na+ channels open increasing the positive charge inside the cell
  4. Action potential - A nervous impulse is generated shutting Na+ channels
  5. Repolarisation - K+ moves out of the cell reducing the internal voltage
  6. Hyperpolarisation - Internal voltage becomes too low shutting K+ channels
  7. Refractory period - another action potential cannot be stimulated
• What happens before and after an action potential 


  Resting potential when the outside of the cell is positive and the inside is negative for every 2K+ in there is 3 Na+ out
• What is the reason for having a threshold


  means there is only a response to large stimuli, the all or nothing principle states that there will either be a response or there wont be one at all so it is easier on the brain to only respond to large stimuli and not all stimuli in the environment
• The changes in charge to form an action potential are an example of


  positive feedback as when ion channels open that triggers even more ion channels to open
• How to ions enter the cell during depolarisation and repolarisation


  diffusion using a protein channel
• What does an action potential trigger


  The Na+ voltage gated channels to open on the next node of Ranvier causing saltatory conduction
• What voltage are all action potentials


  + 40 mV
• What voltage is the threshold for an action potential


  -55 mV
• What controls the strength of the feeling from an action potential?


  The frequency of the action potentials
• Why have a refractory period?


  Ensures impulses are separate and can be responded to separately

  Ensures action potentials travel in 1 direction so are fully responded to

  Limits the number of impulse transmissions preventing over reaction to a stimuli