Neurons

• What are neurons?

  Highly specialised cells that carry neural info throughout the body
• What are the three types of neurons?

  Sensory, relay, motor
• What are dendrites?

  Receive initial signal from another neuron / sensory receptors
• What is the cell body?

  Control center of the cell that receives info from dendrites and passes it to the axon
• What is the axon?

  Carries electrical impulse (action potential) along neuron
• What is the myelin sheath?

  Insulating layer surrounding axon to help impulses travel faster
• What are neurotransmitters?

  • chemical messengers
  • Either excitatory or inhibitory
• What are excitatory neurotransmitters?

  • ‘on switch’ in the nervous system
  • Make us alert
  • Increased likelihood of signal being sent to postsynaptic cell
  • Increased firing of neurotransmitters = excitatory post-synaptic potential (EPSP)
  • Dopamine, adrenaline
• What are inhibitory neurotransmitters?

  • ‘off switch’ of the nervous system
  • Return the body to calm
  • Decreased likelihood of signal being sent to postsynaptic cell
  • Decreased firing of neurotransmitters = inhibitory post-synaptic potential (IPSP)
  • Serotonin, GABA
• What is the gap between the presynaptic and postsynaptic neuron called?

  Cleft
• In which neuron are vesicles found (post / pre)

  Presynaptic neuron
• What do vesicles contain?

  Neurotransmitters
• In which neuron are receptor cells found? (post / pre)

  Postsynaptic neuron
• What is the pathways between presynaptic and post synaptic neurons?

  Electrical -> chemical -> electrical (by diffusion)
• What happens to left over neurotransmitters during synaptic transmission?

  Can get broken down by enzymes
• What is the role of the sensory neuron?

  Carry nerve impulses from sensory organs to the CNS (brain and spinal cord)
• Location of the sensory neuron?

  PNS (all nerve tissue outside brain and spinal cord) -> transmits info to CNS
• Dendrites of a sensory neuron:

  Dendrites are the receptors. No cell body in dendrites.
• Axon description of sensory neuron?

  • Has myelin sheath.
  • Cell body lies off to the side of it, around halfway down.
• Sensory neuron :

  • Convert info from sensory receptors →neural impulses
  • Impulses reach brain and become sensations
  • Some neurons terminate in the spinal cord (not all info reaches brain) → quick reflex actions
• Role of the relay neuron?

  Between sensory and motor neurons, allowing them to communicate
• Where are relay neurons found?

  Brain and spinal cord only (CNS)
• Relay neurons dendrites:

  Long projections branching off the top of the cell body
• Relay neurons axon:

  No myelin sheath
• Relay neuron:

  • Lie between sensory input and motor output (bridge the gap)
  • Sometimes called an interneuron
• Role of motor neuron:

  Conduct signals from CNS to effector organs (e.g. Muscles) to trigger movement
• Location of motor neurons :

  The cell body is found in the CNS while the axon is in the PNS
• Motor neuron dendrites:

  Long projections centered around a large cell body
• Motor neuron axon:

  Has myelin sheath
• Motor neuron :

  • Release neurotransmitters that bind to muscle receptors
  • Strength of the muscle response (contraction) depends on the firing rate of the motor neuron axon
  • Inhibition = muscle relaxation