THE NERVOUS SYSTEM

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  • THE NERVOUS SYSTEM
    • REFLEX ARC
      • reflex arc = response to a change in environment; it is rapid, involuntary & protective
      • refractory period = prevents a backward travel of impulse (area around the impulse is hyperpolarised) to prevent any further action potentials being propagated
      • overcome pathway by ascending nervous fibres to direct the impulse to the brain
      • A Reflex Arc
    • NEURONES
      • neurones = antagonistic, highly specialised cells that generate & transmit the impulse signal
      • sensory neurones relay the impulse from the organs to the Central Nervous System
      • relay neurones relay the impulse from the sensory neurone to the motor neurone
      • motor neurones relay the impulse from the Central Nervous System to the effector (muscle or gland)
      • dendrites = LARGE surface area & carry the impulse to the cell body
      • axon = carry the impulse from the cell body to the synapse
      • ganglion = cell body in the axon
      • Schwann cells (myelin sheath) around the neurone insulate & help with impulse transmission
      • node of Ranvier allow for the impulse to jump from node to node
    • NERVE NETS OF HYDRA
      • simple nervous systems
        • invertebrate phyla (jelly fish, coral)
        • chemical synapse
        • epithelial receptors
        • contractile effector cells
      • complex nervous system
        • more complex hydra nets
          • more diverse behaviours
      • Comparison between Simple & Complex Hydra Nets
    • NERVE IMPULSE
      • use a microelectrode to measure
      • resting potential = -70mV lower in neurone than outside
      • The Nerve Impulse Initiation
    • ACTION POTENTIAL
      • action potential = results in a change in membrane permeability to ions
      • phospholipids will isolate the impulse
      • threshold potential = minimum mV of impulse needed to initiate an action potential
      • propagation = an action potential will cause sodium channels on adjacent neurone to open
      • An Action Potential
    • SYNAPSE
      • synapse = a junction between neurones which slow down the impulse
      • The Synaptic Transmission
      • a stronger stimulus will cause an increase in action potential frequency
      • speed of impulse is effected by
        • myelin sheaths
          • increases speed as impulse can jump from node to node
        • wider axon diameter
          • increases speed as less phospholipid contact
        • higher temperature
          • increases speed as increase in energy & faster
      • function
        • convey action potential between neurones, unidirectional
        • filters out low-level stimuli for protection
        • summation = added effect of more than one action potential
          • spacial summation = action potentials from many neurones
          • temporal summation = many action potentials from one neurone
        • excitatory synapses = sodium ions cause polarisation
        • inhibitory synapses = chloride ions cause depolarisation
      • neurotransmitters
        • noradrenaline will increase heart rate
        • acetylcholine will decrease heart rate
    • THE EFFECT OF DRUGS
      • agonist = mimic to increase metabolism
        • mimic neurotransmitters
        • block enzymes
        • release neurotransmitters
        • e.g. cocaine
      • antagonist = block to slow down metabolism
        • block neuroreceptor
        • e.g. curare
    • PHOTOPERIODISM
      • plants have a slow response rate as the co-ordination is caused by chemicals
      • photoperiodism = response to light by leaves
      • photochrome = photoreceptors with will absorb light & change light pigments
        • when light, 660Pr is converted in 730Pfr (which is unstable)
        • when dark 730Pfr is converted into 660Pr
      • a normal day will have no effect on flowering
      • on a long-day light will influence flowering
      • on a short-day dark will induce flowering

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