neurons and synaptic transmission

• sensory neurons


  carry nerve impulses from sensory receptors in the PNS to the spinal cord and the brain

  they convert info from these sensory receptors into neutral impulses, when they reach the brain they are translated into sensation

  some sensory information only travels as far as the spinal cord in order to allow for reflex reactions which are much quicker
• relay neurons 


  allow sensory and motor neurons to communicate with each other , found within brain and spinal cord and sometimes referred to as interneurons
• motor neuron's 


  neurons that connect the CNS to muscles and glands , they form synapses with muscles to control heir contractions

  when stimulated motor neurons release neurotransmitters that bind to receptors on the muscle and trigger a response
• structure - cell body

  includes nucleus which contains the genetic material of the cell
• structure - dendrites 


  branch like structures that protrude from the cell body, they carry nerve impulses from neighboring neurons towards the cell body
• structure - axon 


  carries the impulses away from the cell body down the length of the neuron
• structure - myelin sheath 


  fatty layer that protects the axon and speeds up electrical transmission of the impulse
• structure - nodes of Ranvier 


  gas on the myelin sheath that seeds up transmission of the impulse by forcing it to jump across the gaps along the axon
• structure - axon terminal 


  allows communication with the next neurons in the chain across a gap called the synapse
• the firing of a neuron - action potential 


  when a neuron is activated the inside of the cell becomes positively charged for a split second - causes an action potential to occur , this creates an electrical impulses that travels drown that axon toward the end of the neuron
• actional potential 


  when a neuron is activated the inside of the cell becomes positively charged for a split second

  this causes an action potential to occur

  this creates an electrical impulse that travels down the axon towards the end of the neuron
• synaptic transmission 


  each neuron is separated from the next by a tiny gap called the synapse

  signals within neurons are transmitted electrically (action potentials) but signals between neurons are transmitted chemically across the synapse

  when the electricals impulse reaches the end of the neuron it triggers the release of neurotransmitters from tiny sacs called vesicles
• neurotransmitters 


  after diffusing across the synapse the neurotransmitter will be taken u by the post synaptic receptor site (on the dendrites of the next neuron) it is converted back into an electrical impulse (because it triggers an action potential) therefore the process of transmission starts again with the next neuron
• some neurotransmitters trigger nerve impulses in the receiving neuron ad stimulate the brain into action - these are called excitatory neurotransmitters

  others inhibit nerve impulses in order to calm the brain and balance mood - these are called inhibitory neurotransmitters
• excitatory and inhibitory neurotransmitters

  a nerve cell can receive both types of neurotransmitters at the same time

  likelihood of the cell firing is determined by adding the excitatory and inhibitory input
• excitatory neurotransmitters 


  if excitatory synapses are more active, the cell fires at a high rate (more action potential)
• inhibitory neurotransmitters 


  inhibitory synapses are more active, the cell fires at a much lower rate, if at all (less action potential)