nervous communication

• what is a nerves resting potential and how is it maintained?

  Nerve resting potential: -70mV Maintained by: Sodium-potassium pump
• explain the generation of an action potential?


  1)stimulus excites the membrane causing sodium channels to open and ions diffuse in

  2)if the membrane reaches threshold it depolarises cause even more sodium channels to open

  3)repolarisation sodium channels close , potassium channels open and reestablish concentration gradient

  4)hyperpolarisation when too many potassium diffuse out causing a larger negative

  5)sodium potassium pump returns nerve to resting state
• how does an action potential travel down a nerve?


  diffusion of sodium ions sideways opening more sodium channels causing more depolarisation
• what is a refractory period and why do we have them?


  temporary hyperpolarisation so that we dont fire again

  it ensures no overlapping action potentials and unidirectional conduction
• what is a myelin sheath and why is it useful?


  Insulating layer around nerve fibers made of wrapped schawnn cells ; speeds up nerve impulses.
• how does a myelin sheath speed up impulses?


  stops diffusion of ions instead uses saltatory conduction causing electrical charge to jump between nodes of ranvier
• why does axon diameter help faster conduction?


  less resistance to flow of ions , can depolarise areas quicker
• why does temperature increase conduction times?


  allows ions to diffuse faster
• nerve impulses across a cholinergic synapse?


  1)action potential arrives at presynaptic knob stimulating calcium channels to open

  2)influx if calcium ions into the knob causes vesicles to move towards the membrane

  3)acetylcholine released into synaptic cleft by exocytosis

  4)diffuses and binds to receptors on postsynaptic membrane causing sodium channels to open

  5)influx of sodium ions causes depolarisation carrying on the action potential
• what do excitory and inhibitory neurotransmitters do?


  Excitatory: Increase the likelihood of a neuron firing, depolarise Inhibitory: Decrease the likelihood of a neuron firing , hyperpolarise
• what is spatial summation?


  Spatial summation is the process by which multiple synaptic inputs are integrated in a neuron to generate an action potential.
• what is temporal summation?


  two or more nerve impulses arrive from the same presynaptic neuron