Neurons and Synaptic Transmission

• Neurons

  Individual cells in the nervous system that receive, integrate, and transmit information.
• Sensory neurons


  Neurons that carry incoming information from the sensory receptors to the brain and spinal cord
• Relay neurons


  - These connect the sensory neurons to the motor or other relay neurons.

  - They have short dendrites and short axons.

  
• Motor neurons


  Neurons that carry outgoing information from the brain and spinal cord to the muscles and glands
• Cell body


  Largest part of a typical neuron; contains the nucleus and much of the cytoplasm

  
• Nucleus


  Control centre of the cell

  
• Dendrites


  Branchlike parts of a neuron that are specialized to receive information.

  
• Axon


  A threadlike extension of a neuron that carries nerve impulses away from the cell body.

  
• Myelin sheath


  A layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next.

  
• Nodes of Ranvier


  Gaps in the myelin sheath

  
• Terminal buttons


  Small knobs at the end of axons that secrete chemicals called neurotransmitters

  
• Synapse


  A junction where information is transmitted from one neuron to the next.

  
• Ganglia


  Collections of nerve cell bodies
• Action potential


  A neural impulse: a brief electrical charge that travels down an axon
• Synaptic transmission


  - When action potential reaches the presynaptic neuron, it triggers the synaptic vesicles to release neurotransmitters into the synaptic gap.

  - The neurotransmitters diffuse across the synaptic gap and bind to the postsynaptic receptors.

  - The neurotransmitters are now turned back into an electrical impulse.
• Neural networks


  - Interconnected neural cells.

  - With experience, networks can learn, as feedback strengthens or inhibits connections that produce certain results.

  - Computer simulations of neural networks show analogous learning.
• Neurotransmitter


  Chemical messengers that cross the synaptic gaps between neurons

  
• Synaptic vesicles


  Tiny pouches or sacs in the axon terminals that contain chemicals called neurotransmitters.

  
• Postsynaptic receptor site


  - A receptor on the neuron receiving the information at the synapse.

  - A neurotransmitter locks into a specific receptor on the receiving neuron - triggering an electrical signal in the receiving neuron.

  
• Excitation


  Increase in the activity of a neuron or brain area
• Inhibition


  A synaptic message that prevents a recipient neuron from firing.
• Serotonin


  Affects mood, hunger, sleep, and arousal
• Adrenaline


  A hormone released into the bloodstream in response to physical or mental stress
• Hormone


  Chemical messengers, mostly those manufactured by the endocrine glands, that are produced in one tissue and affect another