C2.2 Neural Signalling

• Neuron

  specially adapted cells that can carry electrical impulses
• nerve impulse

  electrical signals passed between two cells
• Nerve impulses can go

  1. neuron to neuron
  2. neuron to muscle
  3. neuron to gland
• what is the function of the neuron part: dendrites

  Receive signals from other cells
• what is the function of the neuron part: cell body

  Organizes and keeps the cell functional
• what is the function of the neuron part: Cell membrane

  Protects the cell
• what is the function of the neuron part: Nucleus

  Contains the genetic material (chromosomes) of the neuron cell, as well as controls the entire neuron.
• what is the function of the neuron part: Axon hillock

  Generates impulse in the neuron
• what is the function of the neuron part: Axon

  Transfers signals to other cells and organs
• what is the function of the neuron part: Node of Ranvier

  Allows diffusion of ions
• What is the function of the neuron part: Myelin sheath

  Increases the speed of the signal
• What is the function of the neuron part: Schwann cell

  Produces the myelin sheath
• What is the function of the neuron part: Axon terminal

  Forms junctions with other cells
• Membrane potential

  • refers to the difference in eclectic charge between the interior and exterior of a cell membrane 
• Resting potential

   is the membrane potential of a neuron when it is not being stimulated.
• Steps of sodium-potassium pump action:

  1. Binding of cytoplasmic sodium ions 
  2. Phosphorylation by ATP 
  3. Release of sodium ions outside the cell 
  4. Binding of extracellular potassium ions. 
  5. Dephosphorylation 
  6. Release of potassium ions inside the cell 
• Action potential

  is a rapid change in the membrane potential that allows for the transmission of nerve impulses.

  •  that occurs when a neuron is conducting a signal. It arises from the transport of prively charged ions 
  • It occurs due ‘flip-flopping’ the charge acts in the axon.
• DEPOLARIZATION

  membrane potential goes from negative to positive
• REPOLARIZATION

   membrane potential goes from positive back to negative
• STEPS for polarization

  1. Voltage-gated sodium ion channels open 
  2. Sodium ions diffuse into the cell (facilitated diffusion)
  3. DEPOLARIZATION - to +
  4. Voltage gated sodium ion channels close, and voltage gated potassium ions channels open
  5. Potassium ions diffuse out of the cell (facilitated diffusion)
  6. REPOLARIZATION + to -
  7. Sodium-potassium pump re-establishes resting potential by actively pumping sodium ions out and potassium ions in 
• Self-propagating

   depolarization in one part triggers depolarization in the next part due to the opening of voltage gated channels.
• nerve impulses: how do we increase speed

  • increase diameter = decreases the resistance
  • increase myleination =
  • size of animal = larger animals tend to have faster conduction speeds
• Synapse

   is a junction between two neurons or between a neuron and an effector cell.

  Gap between cells through which signals are passed by neurotransmitters
• Synaptic cleft

   is the gap between the presynaptic and postsynaptic membranes
• Effector

  is a muscle or gland that responds to stimulation
• Examples of effector cells

  muscle cells and glandular cells
• Role of neurotransmitters

   transmit signals across synapses.
• Release of neurotransmitters from a presynaptic membrane - mechanisms

  • Depolarization of the presynaptic membrane leads to the opening of calcium channels
  • Calcium ions influx triggers exocytosis of neurotransmitter vesicles 
  • Neurotransmitters diffuse across the synaptic cleft 
• Steps for Release of neurotransmitters from a presynaptic membrane.

  1. ACTION POTENTIAL reaches the end of the presynaptic neuron
  2. VOLTAGE GATED calcium ions channels open 
  3. CALCIUM IONS enter the PRESYNAPTIC neurons (facilitated diffusion)
  4. CALCIUM IONS force VESICLES with NEUROTRANSMITTERS to fuse with the membrane 
  5. NEUROTRANSMITTERS are released into the SYNAPSE (Exocytosis)
• Generation of an excitatory postsynaptic potential.

  1. NEUROTRANSMITTERS diffuse across the SYNAPSE
  2. Bind to RECEPTORS on the POSTSYNAPTIC membrane 
  3. ION CHANNELS open 
  4. If enough lows enter the POSTSYNAPTIC cell, that generates an action potential 
  5. NEUROTRANSMITTER is removed from synapse 
  6. Either pumped back into or an enzyme destroys it 
• ACETYLCHOLINE


  NEUROTRANSMITTER, NEURON→MUSCLE