The Nervous System

HideShow resource information
View mindmap
  • The Nervous System
    • The Resting Potential
      • Initially, the inside of the neurone is negatively charged (-65mV)
        • At rest, the voltage gated channels are closed.
          • The sodium-potassium pump actively transports 3Na+ out of the axon for every 2K+ that are pumped into the axon
            • This sets up a concentration gradient and causes Na+ to diffuse into the axon and K+ to diffuse out of the axon by their respective channels
              • K+ diffuses 50x faster than Na+ because there are 50x more K+ channels
                • The outside of the axon is now positive with respect to the inside
                  • The membrane is said to be polarised
                    • The Resting Potential
                      • Initially, the inside of the neurone is negatively charged (-65mV)
                        • At rest, the voltage gated channels are closed.
                          • The sodium-potassium pump actively transports 3Na+ out of the axon for every 2K+ that are pumped into the axon
                            • This sets up a concentration gradient and causes Na+ to diffuse into the axon and K+ to diffuse out of the axon by their respective channels
                              • K+ diffuses 50x faster than Na+ because there are 50x more K+ channels
                                • The outside of the axon is now positive with respect to the inside
                                  • The membrane is said to be polarised
      • Action Potential
        • The depolarisation of the cell membrane- inside more positive than outside- potential diff. of +40mV
          • Transmitted along the axon/ dendron plasma membrane
        • Resting neurone= negatively charged- Active neurone= positively charged
          • Neurones' charge increases to +40mV= Action potential
            • A stimulus causes the Na+ channels to open and an Na+ diffusion into the neurone
              • If the stimulus is strong enough, a threshold is reached and the Na+ voltage gated channel opens= Na+ diffusion into neurone
                • The inside of the neurone becomes more positive
                  • Known as Depolarisation
                    • Action Potential
                      • The depolarisation of the cell membrane- inside more positive than outside- potential diff. of +40mV
                        • Transmitted along the axon/ dendron plasma membrane
                      • Resting neurone= negatively charged- Active neurone= positively charged
                        • Neurones' charge increases to +40mV= Action potential
                          • A stimulus causes the Na+ channels to open and an Na+ diffusion into the neurone
                            • If the stimulus is strong enough, a threshold is reached and the Na+ voltage gated channel opens= Na+ diffusion into neurone
                              • The inside of the neurone becomes more positive
                                • Known as Depolarisation
                                • Voltage gated channels allow passage of ions and respond to changes in potential difference across the membrane
                                • Threshold potential across membrane is -50mV, if this is not achieved the depolarisation doesn't occur
                  • Voltage gated channels allow passage of ions and respond to changes in potential difference across the membrane
                  • Threshold potential across membrane is -50mV, if this is not achieved the depolarisation doesn't occur
        • Repolarisation
          • Na+ channels close and K+ channels open
            • K+ begins to diffuse out of the membrane and the inside of the neurone becomes more negative
              • The Na+/K+ pump restores the resting potential
                • Repolarisation
                  • Na+ channels close and K+ channels open
                    • K+ begins to diffuse out of the membrane and the inside of the neurone becomes more negative
                      • The Na+/K+ pump restores the resting potential
          • Hyperpolarisation
            • The potential diff. dips below -60mV for a short time as the K+ channels close
              • The resting potential of -40mV is then restored
                • Hyperpolarisation
                  • The potential diff. dips below -60mV for a short time as the K+ channels close
                    • The resting potential of -40mV is then restored
            • Local Currents
              • Action potentials are self-perpetuating- continues down neurone
                • Na+ ions diffuses onto neurone when the Na+ channels open
                  • A localised increase in conc. of Na+ ions inside neurone= Action Potential
                    • Na+ diffuses down its concentration gradient along the length of the neurone= local current
                      • As Na+ diffuse, voltage gates channels open and allow Na+ influx
                        • Na+ influx sets up action potential
                          • Local Currents
                            • Action potentials are self-perpetuating- continues down neurone
                              • Na+ ions diffuses onto neurone when the Na+ channels open
                                • A localised increase in conc. of Na+ ions inside neurone= Action Potential
                                  • Na+ diffuses down its concentration gradient along the length of the neurone= local current
                                    • As Na+ diffuse, voltage gates channels open and allow Na+ influx
                                      • Na+ influx sets up action potential
              • Saltatory Conduction in Myelinated Neurones
                • For quicker conduction of action potentials
                  • Myelin Sheath is Schwann cells- electrically insulating
                    • Action potential can only be set up at nodes of Ranvier
                      • Action Potential skips over large sections of neurone= faster conduction 120m s-1
                        • Saltatory Conduction in Myelinated Neurones
                          • For quicker conduction of action potentials
                            • Myelin Sheath is Schwann cells- electrically insulating
                              • Action potential can only be set up at nodes of Ranvier
                                • Action Potential skips over large sections of neurone= faster conduction 120m s-1
                • Features of a neurone
                  • Long- can carry action potential over long distance
                  • Gated ion channels on cell surface membrane
                  • Na+/K+ ion pumps using ATP
                  • Fatty myelin sheath (schwann cells) insulate neurone from electrical activity
                    • Nodes of Ranvier= gaps for saltatory conduction
                  • Motor neurones= cell body in CNS and long axon to carry action potential to effector
                  • Sensory Neurones have long dendron (receptor to cell body) and short axon (to CNS)
                  • Dendrites for connecting to other neurones
                • Nerve Junctions
                  • SYNAPSE- junction between two or more neurones
                    • One neurone can communicate with another
                      • Synaptic cleft= 20nm wide
                        • Presynaptic neurone releases neurotransmitter (cholinergic = acetylcholine)

              Comments

              No comments have yet been made

              Similar Biology resources:

              See all Biology resources »See all Human, animal and plant physiology resources »