neurons etc

• Neurons

  Building blocks of nervous system. Nerve cells that process and transmit messages through electrical and chemical signals
• Neurotransmitters

  Brain chemicals released from synaptic vesicles. Relay signals across neurone through synapses (synaptic transmission). Can perform excitatory or inhibitory function
• neuron structure

  cell body contains nucleus and branch like structures called dendrites which carry impulses towards the cell body from neighbouring neurons. Axon is tube structure covered by myelin sheath (fatty layer) which carries impulses down length of neuron. Sheath speeds up transmission and gaps in it called nodes of ranvier - causes impulses to 'jump'. Terminal buttons at end.
• Types of neuron

  sensory - carry messages from sensory receptors along nerves in peripheral nervous system (PNS) to CNS

  motor - carry messages from CNS along PNS to effectors

  relay - connect sensory and motor neurons
• Excitation and inhibition

  Inhibition (eg serotonin) makes neuron more negatively charged and less likely to fire

  Excitation (eg dopamine) increases positive charge and makes it more likely to fire
• Summation

  Firing depends on summation (adding together of signals over time or space - temporal/spatial). If net effect is inhibitory then less likely to fire. If excitatory then postsynaptic neuron more likely to fire and momentarily becomes positively charged - depolarisation takes place and action potential travels down dendrite towards cell body.