Neuronal communication

• What is the general pathway from stimulus to response?

  Stimulus → receptor --(sensory neurone)--> Co-ordinator (brain or spinal cord) --(motor neurone)--> Effector (muscles or glands)--> Response

  
• When is the brain used as the co-ordinator?

  For conscious activities
• When is the spinal cord used as the co-ordinator?

  For unconscious activities, like reflexes and goes through the relay neurone
• Transducers

  Convert one type of energy into another form
• For these receptors, what is their energy change detected and what energy is it converted to:

  
  

  a) Rods - eyes

  b) Cones - eyes

  c) Olfactory cells -nose

  d) Taste buds - nose

  e) Sterocilia - ears

  f) Pacinian corpuscles -skin

  g) Proprioreceptors - muscle fibres

  All and every receptors convert their energy into electrical energy

  
  

  a) Detect light intensity

  b) Detect wavelength of light

  c) Detect volatile chemicals

  d) Soluble chemicals

  e) Vibrations

  f) Pressure

  g) Length of muscle fibres
• How are nerve cells polarised?

  There is more positive charge outside the cells due to the higher accumulation sodium ions than inside, creating a potential difference
• How is a generator potential produced?

  When stimulated, receptors cause gated sodium ion channels to open, so sodium diffuses into the cell.
• How is an action potential generated?

  The bigger the stimulus, the more gated channels open and if big enough, the generator turns into an action potential.
• Why is synapse useful?

  Even though it slows down the message, it sends messages to multiple places.

  
  

  Like when you touch a hot pan, you send a message to the hand to take it off and to the brain to acknowledge it.
• What is a nerve?

  Many neurones parallel together
• Reflex arc

  Fast - not elongate the distance

  Automatic

  Innate

  Bypasses the conscious parts of the brain

  For protective reasons

  Free from complex thought

  
  

  
  

  Fro eyes, it's an unconscious part of the brain, as it's closer.

  
• Sensory neurone

  Carry action potential from receptors to CNS

  Cell body is just before the CNS

  Long dendron and short axon

  
• Motor neurone

  Carry action potentials from CNS to effectors

  Cell body is in the CNS

  Short dendrites, long axon and no dendron

  
• Relay neurone

  Connect sensory and motor neurones

  Cell is located within the CNS
• Components of a sensory neurone

  Axon - after the cell body

  Cell body

  Dendron

  Schwann cell

  Node of Ranvier

  Myelin Sheath

  Dendrite
• Components of a motor neurone

  Axon - after the cell body

  Cell body

  Schwann cell

  Node of Ranvier

  Myelin Sheath

  Dendrite
• Components of a relay neurone

  Axon - after the cell body

  Cell body

  Synaptic endings

  Dendrites
• Cell body

  Mitchondria, ribosomes, nucleus

  No mitotic apparatus - no centrioles/spindle

  Can't be replaced, sometimes can be regenerated
• Dendrites/ dendrons


  Nerve impulses carried towards the body

  Large surface area - receive information

  Have loads of chemically gated ion channels
• Axon


  Nerve impulses carried away the cell body to the synaptic endings
• Myelin sheath

  Electrically insulating, high phospholipid substance that surround axons, secreted by Schwann cells

  Saltatory impulse conduction - an electrical impulse skips from node to node down the full length of an axon,
• Nodes of Ranvier

  Electric signal jumps across on these; gaps between myelin; speeds it up

  No myelin

  Saltatory conduction
• Schwann cell


  Encircles the axon

  When two of these cells are together, overlapping happens, which pushes the nucleus and cytoplasm to the outside layer.
• Neurilemma

  Name given to the surrounding Schwann cell coverings. Every PNS (NOT CNS) nerve fiber has such a covering-doesn't mean every fiber is myelinated.

  Plays a part in regeneration
• Synaptic end bulb or synaptic button

  Important in conduction

  Synaptic vesicles storing neurotransmitters prior to release and diffusion to the post-synaptic membrane.
• What is the resting potential of a neurone?

  About -70mV, meaning that the inside of the axon is negatively charged compared to the outside.
• How is the resting potential bough about?

  Sodium potassium pump actively pumps three sodium ions out of the cell and two potassium ions into the cell.

  
  

  Protein channels are always opened, allowing for diffusion, but about hundred times more potassium ions leak out than sodium ions leak in, as it's more permeable to potassium ions than sodium ions.
• How does an action potential occur?

  As well as the sodium potassium pump and channel protein, when the generator potential is at -50mV or above it, the voltage gated sodium and potassium ion channels open.

  
  

  Sodium ion channels open and sodium ions move through the channels into the neurone - -70mV<x<-50mV - generator potential. (Depolarisation)

  
  

  Above -50mV - voltage gated sodium ion channels open and sodium ions diffuse into the neurone along the electrochemical gradient, reaching until +40mV more positive in the axon than outside.
• What happens after depolarisation?

  At +40V, the voltage gated sodium ion channels close and the voltage gated potassium channels open.

  
  

  Potassium ions diffuse out of the axon along an electrochemical gradient.

  
  

  Hyperpolarisation - potassium channels open for a few more milliseconds about -90mV

  
  

  Repolarises back to -70mV

  
  

  Cycle repeats again with sodium potassium pump again
• Refractory period

  The time needed for the action potential to return to resting potential from hyperpolarisation, can't respond to another stimulus.
• What does the graph look like of time against potential difference of a neurone during an action potential?

  
• What is the passage of an action potential along an unmyelinated neurone?

  The sodium ions diffuse along the neurone causong the next region of the membrane to depolarise.

  
  

  Bringing a further inflow of sodium ions

  
  

  Stimulating the next region to undergo an action potential

  
  

  Nerve passes all the way along the neurone
• What is the passage of an action potential along a myelinated neurone?

  More quicker than unmyelinated ones, as action potentials only occur at the nodes of Ranvier.

  
  

  Saltatory conduction - local current set up which sodium ions move from one node to another - is longer - more efficient and less energy for sodium potassium pump
• All or nothing principle

  A stimulus has to be the threshold potential to be an action potential, so they're all the same size
• How do you distinguish whether it's a weak or strong stimulus?

  Frequency of the action potentials not the size of the action potential. A stronger stimulus will result in a more frequent action potential being produced in a neurone.
• Synapse


  Junction between 2 neurons where electrical signals pass (dendrite and terminal endings)
• Label a synapse diagram

  
• At a synapse a ---- neurone comunicates with a ---- neurone.

  
  

  At the end of the ----- neurone there are -------- ----

  presynaptic, postsynaptic

  
  

  presynaptic, synaptic knobs.
• What happens at the synaptic knobs?

  Come close to the dentrites of the postsynaptic membrane.
• Synaptic cleft

  Narrow gap separating the presynaptic neuron from the postsynaptic cell