Transmission of nerve impulses

?
  • Created by: sierrah
  • Created on: 11-04-14 02:25
View mindmap
  • Transmission of nerve impulses
    • Resting membrane potential
      • There is a difference between the charges on the inside and outside of a neuron
      • The membrane of a neuron at rest is said to be polarised
      • ICF has proteins (neg) and potassium, overall negative charge
      • ECF has sodium and chloride, overall positive charge
      • RMP is -70mV, potential of inside is less than out
    • Maintaining the RMP
      • The membrane of a neuron is selectively permeable - ions can pass in and out of cell
      • Potassium and sodium diffuse across the membrane using channel proteins - limited bc these are gated
      • Sodium-potassium pump works against concentration gradient to keep membrane polarized
        • Uses ATP - 3NA+ leave ICF, 2K+ leave ECF
      • Interior of cell remind negative due to the proteins that cannot leave
    • Generating an action potential
      • The depolarization and repolarisation of a neural membrane is caused by a change in permeability of the membrane to sodium
      • 4 main steps: Stimulus and slight depolarization, rapid depolarization, repolarisationand hyperpolarisation and RMP
      • AP 1 - stimulus and slight depolarisation
        • 3: Sodium spreads along inside of membrane (assisted by proteins)
        • 2: Channel opens
        • 4: Slight depolarization (-70 to -65mV)
          • This slight depolarisation triggers the rapid depolarization
          • Depolarisation only occurs at a certain threshold as this makes the membrane more permeable to sodium
        • 1: stimulus - acetylcholine bonds to a gated channel protein for sodium
      • AP 2 - Rapid depolarisation
        • 3: Sodium floods  the cell
        • 2: Lots of sodium gates open
        • 4: Membrane potential changes (-65 to -35mV)
        • 1: Enough sodium enters the cell to cause rapid depolarization
      • AP 3 - repolarisation
        • 1: Change in membrane potential causes the gates to close
        • 2: Potassium gates open
        • 3: Potassium diffuses from ICF to ECF
        • 4: Repolarisation occurs as the inside becomes more negative and the outside become more positive
      • AP 4 - hyperpolarisation and RMP
        • 1: sodium gates close
        • 2: potassium gates close - this slow response causes hyperpolarization
        • 3: Correct charges across the membrane exist but there is now more potassium outside the cell than in
        • 4: the sodium-potassium pump works to restore this
    • Conduction along an unmyelinated fibre
      • Fibres that don't have a fatty myelin sheath
      • Depolarisation of one area of neural membrane causes a local current in neighbouringareas
      • Process repeats itself along the length of the membrane
      • Action potential moves along the membrane away from point of stimulation (like domino line)
        • If stimulus occurs in middle of fibre impulses travel in both directions away from point of stimulation (impulses usually occur at end of fibre)
      • Nerve impulse prevented from going backwards bc of refractory period
        • Refractory period is time in which another action potential cannot be generated due to imbalance of ions
        • Need ion concentrations to return to normal before another action potential is generated
      • Speed of transmission is 2m/sec
    • Conduction along a myelinated fibre
      • Fibres covered in myelin sheath
      • Nodes of rangier at intervals
      • Myelin sheath insulates fibres from extracellular fluid so no ions can flow between ICF and ECF and an action potential cannot form
      • Action potential 'jumps' from one node of Ranvier to another as myelin is absent from the nodes
      • This jumping is known as saltatory conduction - significantly speeds up impulse transmission
      • Speed of transmission along myelinated fibres is 140m/sec
    • Transmission across a synapse
      • Neuratransmitters diffuse across gap
  • If stimulus occurs in middle of fibre impulses travel in both directions away from point of stimulation (impulses usually occur at end of fibre)

Comments

No comments have yet been made

Similar Human Biology resources:

See all Human Biology resources »See all Transmission of nerve impulses resources »