3. Neurons + Synaptic Transmission

• 1. Neurons + Synaptic Transmission

  Neurons:

  • transmit chemical/electrical signals around body (communication).

  
  

  Synaptic Transmission:

  • neighbouring neurons communicate by sending chemical messages across gap/synaptic cleft.
• 2. Neurons + Synaptic Transmission

  Types of Neurons - Sensory Neuron:

  • collect/process info from senses; carry message to CNS.
  • long dendrites, short axons.
• 2a. Neurons + Synaptic Transmission

  Types of Neurons - Relay Neurons:

  • connect sensory + motor.
  • short dendrites, short axons.
• 2b. Neurons + Synaptic Transmission

  Types of Neurons - Motor Neurons:

  • carry info away from CNS, to rest of body.
  • short dendrites, long axons.
• 3. Neurons + Synaptic Transmission

  Structure of Neuron:

  • cell body = nucleus (genetic material).
  • dendrites carry nerve impulses from neurons to cell body.
  • axon, carry impulses away from cell body.
  • axon covered in fatty layer of myelin sheath; protect axon + speed electrical transmission.
  • myelin sheath split into gaps = nodes of Ranvier; speeds up transmission by forcing to jump across gaps.
  • end of axon = terminal buttons; communicate w/ next neurons in synapse.
• 4. Neurons + Synaptic Transmission

  Action Potential:

  • when info from sensory receptors/neurons passed onto dendrites of another neuron, it’s passed down cell body onto axon.
  • at axon, info travels down length in form of electrical signal = ‘action potential’.
  • a.p. reaches terminal buttons, needs be transferred to another neuron = cross the synapse.
• 4a. Neurons + Synaptic Transmission

  Synaptic Transmission - Process:

  • action potential travels through axon.
  • vesicle fuse w/ membrane, release NT into synapse.
  • neurotransmitters bind to receptor; increase/decrease chance of post-synaptic neuron firing action potential.
  • if NT not bind to receptor then drift away (diffusion), or reuptake process (recycle), or enzyme breaks them down + sends back into pre-synaptic neuron.
  • chemical signals passed through synaptic cleft.
• 4b. Neurons + Synaptic Transmission

  Action potentials only travel in one direction because…

  • vesicles w/ NTs inside only in pre-synaptic neuron.
  • NT receptors only on post-synaptic membrane.
  • binding of NT to receptors allows info transmitted.
  • dendrites carry info to cell body; axon carries away.
• 5. Neurons + Synaptic Transmission

  Neurotransmitters (NT):

  • chemicals released from vesicles, relay signals across synapse from one neuron to another.
  • instruct nervous + endocrine system perform psychological responses.
  • when NT crosses gap, taken up by postsynaptic receptors (or dendrites of next neuron).
  • chemical msg converted back into electrical impulse, process of transmission begins in new neuron.
• 6. Neurons + Synaptic Transmission

  NTs have excitatory or inhibitory effect on next neuron:

  Excitatory…

  • NT increases positive charge of postsynaptic neuron, increasing chance of neuron firing + passing along action p. (electrical impulse).
  • excite effect.
  • e.g. adrenaline (F/F, stress response) + ACTH (muscle function).
• 6a. Neurons + Synaptic Transmission

  NTs have excitatory or inhibitory effect on next neuron:

  Inhibitory…

  • NT makes charge of postsynaptic neuron negative, decreasing chance neuron firing/passing along action p. (electrical impulse).
  • calming effect.
  • e.g. serotonin (mood regulator) + GABA (calming).
• 7. Neurons + Synaptic Transmission

  Summation:

  • when excitatory NT binds to postsynaptic receptor (dendrite) = ‘excitatory postsynaptic potential‘ (EPSP); more likely fire.
  • when inhibitory NT binds to postsynaptic receptor (dendrite) = ‘inhibitory postsynaptic potential‘ (IPSP); less likely fire.
  • if both EPSP + IPSP arrive at cell, calculation made to determine if presynaptic n. fires or not = summation.
  • if more excitatory, fires + postsynaptic n. sends impulse down dendrites to build new a.p. (if inhibitory, not fire).
• 8. Neurons + Synaptic Transmission


  Nervous System + Endocrine System:

  1. NS (brain/spinal cord), electrical impulses send info through nerves to move muscles/glands secrete hormones.
  2. sensory neurons process info; relay n. pass info to motor n, which shares w/ muscles/glands.
  3. NTs pass between synapse of neurones = synaptic transmission.
  4. more excitatory NT, neuron fire (opposite for inhib).
  5. alongside NS process, ES; glands + secretion of hormones into blood creates psychological responses.
  6. NS + ES process = fight/flight and rest/digest.