Neuronal communication

• What is a neurotransmitter?

  Chemical messenger
• What are the types of neurones?

  Sensory, motor, and relay
• Characteristics of a sensory neurone:

  • big dendron
  • small axon
  • cell body in between dendron or axon
• Motor neuron:

  • Cell body at the end of the neuron
  • Long axon
• Relay Neurone:

  • no mylein sheat
  • cell body at the end of the cell
• Stages of nervous transmission:

  Stimulus, depolarisation, repolarisation, hyperpolarisation, resting potential
• Resting Potential = The potential difference across the membrane of a neuron when it is not active.

  • the outside has a positive charge and the inside has a negative charge
• What is a nerve impulse?

  Wave of depolarisation moving down the neuron
• What happens at an action potential?

  • Sodium channels open which allows sodium to move inside membrane = depolarises membrane
  • This happens due to changes in membrane permeability
  • Inside of the cell becomes a positive
• When enough sodium enters to depolarise the membrane an action potential arises which generates an impulse = threshold of excitation
• After an action potential is generated the membrane enters a refractory period where it cannot be stimulated = sodium channles close
• Repolarisation Stage:

  Potassium channels open and moves outside the membrane so the membrane becomes more negative on inside
• Hyperpolarisation:

  • More potassium on outside than sodium on the inside
  • Potassium gates close
  • Membrane potential drops slightly lower than resting potential so there is a greater potential difference on the outside of the membrane
  • This causes the inside of the membrane to become polarised
• Key features on Neurones:

  • long = transmitt signal over big distance
• Outside of the axon it has a positive charge as three sodium ions are pumped out compared to two potassium ions pumped in
• In resting potential:

  • Most gated sodium ion channels stay closed
  • Most gated potassium channels are open = they diffuse in and out of the axon
• [13. 1] - 1) State one internal factor which causes a response in (2 marks)

  a. a plant

  b. an animal

  1a. Water potential in cells

  1b. Blood pH
• [13.1] - 2) Describe how cells are able to communicate with one another (2 marks)

  Cell releases a chemical (1), which has an effect on a target cell (1)
• [13.1] - 3) Use examples, explain how and why coordination is required in a multi-cellular organism (6 marks)

  - Organism needs to respond to internal/external environments changes for survival (1)

  - Occurs by electrical impulses/nervous system in animals (1)

  - Chemicals/hormonal system in plants/animals (1)

  - Different cells rely on others for materials/removal of waste such as glucose/oxygen (2)

  - Different organs work together to ensure homeostasis (1)

  - Cells communicate through cell signalling (1)
• [13.2] - 1) State the difference between the function of a motor and sensory neurone (1 mark)

  Sensory neruones transmit impulses to the CNS from the receptor/ motor neurones transmit impulses away from the CNS to an effector
• [13.2] - 2) Draw and annotate a diagram of a motor neurone (4 marks)

  - Dendrites; drawn as short multiple protrusions from cell body (1)

  - Cell body containing a nucleus (1)

  - Long single Axon (1)

  - myelin sheath with nodes of Ranvier (1)
• [13.2] - 3) Describe the difference in structure between a myelinated and a non-myelinated neurone and how this affects the speed a nerve impulse is transmitted (4 marks)

  - Axon of a myelinated neurone is covered in myelin (1)

  - Myelin is an electrical insulator (1); formed by Schwann cells growing several times around it

  - nodes of Ranvier: gaps in myelin sheath (1)

  - electrical impulses 'jumps' from one node to another a.k.a. Saltatory conduction (1)

  - impulses transmitted much faster than along an unmyelinated axon (1)
• [13.3] - 1) Describe the role of a sensory receptor in the body (2 marks)

  - Detect stimuli (1)

  - Convert energy into a nervous impulse
• [13.3] - 2) State the transformation that takes place in a cone cell (1 mark)

  light energy is converted into a nervous impulse/action potential
• [13.3] - 3) Explain how your body detects that your finger has touched a pin (6 marks)

  - when you touch a pin, it exerts mechanical pressure on your skin (1)

  - Pacinian corpuscle found within skin detects pressure (1)

  - pressure changed shape of pacinian corpuscle (1)

  - stretched-mediated sodium channels in neuronal membrane stretches (1)

  - channels widen (1)

  - Sodium ions diffuse into membrane (1)

  - membrane is depolarised (1)

  - action potential is created (1) and transmitted along neurones to CNS
• [13.4] - 1) state how the body detects the difference between a small and large stimulus (1 mark)

  the larger the stimulus the more frequent the nerve impulses/action potential
• [13.4] - 2) state the difference between depolarisation, repolarisation and hyperpolarisation (2 marks)

  -depolarisation: potential difference becomes more positive

  -repolarisation: potential difference becomes more negative

  -hyperpolarisation: when potential difference is lower than resting potential
• [13.4] - 3) describe what would happen is a refractory period did not exist (2 marks)


  - Axon could be immediately depolarised after an action potential

  - therefore action potential could travel backwards/both directions/not reach target cells
• [13.4] - 4) Describe how the movement of ions establishes the resting potential in an axon (4 marks)

  - Na+/K+ pump actively transport Na+ and K+ ions

  - 3 Na+ ions out for every 2 K+ ions in

  - K+ ions can diffuse out via K+ ion channel

  - Na+ ions cannot diffuse out as Na+ channel is closed

  - more positive ions outside than inside the axon/ positively charged outside

  - axon membrane is polarised
• [13.4] - 5) explain how temperature receptors in the hand generate an action potential in the sensory neruone (6 marks)

  - heat energy acts a stimulus

  - stimulus causes (voltage-gated) Na+ channels to open

  - Na+ ions diffuse into axon

  - down electrochemical gradient

  - inside axon becomes less negative/more positive

  - action potential is triggered along a sensory neurone to CNS