Neurons

• What is a cell?


  A small alive object that makes up all living things and is surrounded by a thin wall called a cell membrane.
• Different cells can have different functions, one important function is that cells can transmit information.
• Neuronal cells are cells that receive and transmit electrical signals. These electrical signals are called nerve impulses, or action potentials.
• What are the four main components of the neuron?

  dendrite, cell body, axon and axon terminal

  
• A nerve impulse is triggered at the cell of the body and travels in one direction from the dendrites down to the axon terminal.
• Nerve impulses occur if there is a big enough change in voltage at the cell body.
• The process through which nerve impulses are transmitted across the synapse is called synaptic transmission.
• The gap between the axon terminal of one neuron, and the dendrites of a second neuron is called the synapse.
• The part where the nerve impulse first arrives is called the pre-synaptic terminal and the membrane surrounding it is called the pre-synaptic membrane. The bit on the other side is the post-synaptic terminal, and the membrane around it is the post-synaptic membrane. The gap in the middle is the synaptic cleft.

  
• The little round bags in the pre-synaptic terminal are called synaptic vesicles, and they are filled with chemicals called neurotransmitters.
• What are the steps of synaptic transmission?

  1. Nerve impulse arrives at the pre-synaptic terminal causing synaptic vesicles to travel to the pre-synaptic membrane.
  2. Synaptic vesicle and pre-synaptic membrane fuse causing neurotransmitters to be released into the synaptic cleft.
  3. Neurotransmitters diffuse across the synaptic cleft towards the post-synaptic terminal.
  4. Neurotransmitters bind to receptors on the post-synaptic terminal allowing particles to flow into it.
  5. Neurotransmitters are released from receptors and are removed through the process of re-uptake (by re-uptake proteins)
• The more positively charged particles flow into the post-synaptic terminal the more likely it is that a nerve impulse is generated at the cell body.
• What is Re-uptake?

  The process of removing neurotransmitters from the synaptic cleft
• When can Summation occur?

  When multiple nerve impulses occur in the pre-synaptic neuron in close succession or when multiple nerve impulses occur at multiple synapses at the same time.
• What is summation?

  when multiple small changes in voltage add up together and make it more likely a nerve impulse will be triggered.
• Excitatory neurotransmitters cause positively charged particles to enter the post-synaptic neurons, and inhibitory neurotransmitters cause negatively charged particles to enter the post-synaptic neurons.
• Excitatory neurotransmitters make a nerve impulse more likely to occur where as inhibitory neurotransmitters make a nerve impulse less likely to occur.
• Excitatory neurotransmitters

  • cause positively charged particles to enter the post-synaptic neuron
  • make nerve impulses more likely to occur
  • creates excitatory post-synaptic potentials
• Inhibitory neurotransmitters

  • cause negatively charged particles to enter the post-synaptic neuron
  • create inhibitory posy-synaptic potentials
  • make nerve impulses less likely to occur
• For a nerve impulse to occur there need to be more excitatory post-synaptic potentials than inhibitory post-synaptic potentials, or there needs to be more excitatory neurotransmitter release than inhibitory neurotransmitter release.
• Excitatory posy-synaptic potentials and inhibitory post-synaptic potentials can summate, but inhibitory post-synaptic potentials cancel out the excitatory post-synaptic potentials.
• Whether a nerve impulse occurs, depends on the balance of excitatory and inhibitory neurotransmitters binding to post-synaptic receptors.
• What are the Types of Neurotransmitter?

  Excitatory neurotransmitters:

  • Acetylcholine,

  Inhibitory neurotransmitters:

  • GABA

  Both:

  • Dopamine
  • Serotonin
• What is Dopamine?

  Released between neurons that help control the brain's response to reward.

  • both Excitatory and Inhibitory.
• What is Serotonin?

  Released between neurons that help control mood

  • both Excitatory and Inhibitory
• What is GABA?

  Main inhibitory neurotransmitter used in the brain

  Makes nerve impulses less likely to happen
• What is Acetylcholine?

  Released by neurons controlling our muscles

  Makes nerve impulses more likely to happen.
• what are the 3 main types of neurons?

  • Sensory
  • Relay
  • Motor
• What are motor neurons?

  Neurons that carry information away from the brain and control muscle movement.
• What are relay neurons?

  Neurons that transform and process are located between sensory neurons and motor neurons within the central nervous system.
• What are Sensory neurons?

  Neurons that carry information towards the brain and react to sensory information

  
• What is different for a sensory neuron structure than a relay one?

  Sensory neurons have smaller dendrites due to having to connect to sensory receptors, not other axon terminals. It also has a cell body that sticks out of the axon and the axon is coated with a substance called the myelin sheath.
• What is the structural difference between a motor and a relay neuron?

  Motor neurons form synapses with muscle fibers at their axon terminals, and unlike motor neurons relay neurons do not have a myelin sheath.