sensory, relay and motor neurons

• sensory neuron

  • carry messages from PNS (sense, organs, environment) to CNS
  • long dentrites, short axons

  
• relay neuron

  • connects sensory neurons to motor / other relay neurons
  • short dentrites, short axons

  
• motor neuron

  • connects CNS to effectors (muscles and glands)
  • short dentrites, long axons

  
• axon

  carries impulses away from the cell body down length of neuron
• cell body

  includes nucleus, holds genetic material of the cell
• dendrites

  carry nerve impulses from neighboring neurons towards the cell body
• myelin sheath

  fatty layer protecting axon and speeding up electrical transmission of impulse
• nodes of raviner

  speed up transmission of impulse by forcing it to jump across gaps in the axon
• reflex - reflex arc

  • stimulus (hammer) hits knee
  • detected by sense organs in PNS, which convey a message along a sensory neuron
  • message reaches the CNS, where it connects with a relay neuron
  • this transfers message to the motor neuron
  • this carries message to effector (like a muscle) which causes muscle to contract, and hence causes knee to move or jerk
• neurotransmitters

  • exitatory - make it more likely that the next neuron will fire an electrical impulse
  • inhibitory - make it less likely that the next neuron will fire
• neurotransmitters

  chemicals which diffuse across the synapse to the next neuron in the chain

  • each has own specific molecular structure that fits perfectly into the post synaptic receptor site
  • eg. acetylcholine is found at each point where a motor neuron meets muscle and upon its release will cause a muscle to contract
• step by step on synaptic transmission

  1. electrical impulse gets to synapse
  2. gets to the end of the neuron
  3. this makes the neurotransmitter go into the gap
  4. it locks onto the receptor on the next neuron
  5. causes a newer electrical impulse
  6. all old neurotransmitters are reabsorbed
• synaptic transmission

  1. synthesis and storage of neurotransmitter molecules in synaptic vesicles
  2. release of neurotransmitter molecules into synaptic left
  3. binding of neurotransmitters at receptor sites on postsynaptic membrane
  4. inactivation (by enzymes) or removal (drifting away of neurotransmitters)
  5. reuptake of neurotransmitters sponged up by the presynaptic neuron
• synaptic transmission

  the process by which neighbouring neurons communicate with eachother by sending chemical messages along the gap (the synapse) that separates them
• exitation

  neurotransmitters (eg. adrenaline) increases a positive charge of the postsynaptic neuron. this increases the likelihood that the neuron will fire and pass on the electrical impulse
• inhibition

  neurotransmitter (eg. seratonin) increases the negative charge of the postsynaptic neuron. this decreases the likelihood that the neuron will fire and pass on the electrical impulse