Neurons and synaptic transmission

• What is the structure and function of a sensory neuron?

  • Nerve cells that carry nerve impulses from sensory receptors towards CNS and brain
  • Carries messages from PNS (peripheral) to CNS
  • Long dendrites, short axons
• What is the structure and function of a relay neuron?

  • Connects sensory neuron to motor neurons
  • Short dendrites and short axons
  • No myelin sheath
• What is the structure and function of a motor neuron?

  • Connects CNS to effectors (muscles and glands)
  • Short dendrites, long axons
  • Lower motor neurons, travel from spinal cord to muscles of body
  • Upper motor neurons travel between brain and spinal cord
• What is the order of the reflex arc following the direction of conduction?

  • Sensory receptor -> Sensory neuron -> brain via PNS -> relay neuron -> motor neuron -> effector
• What is the function of a neuron?

  • Enables communication with the nervous system
• What is the cell body?

  • Sensory neuron has a cell body (soma)
  • Contains genetic material
• What are dendrites and what are their function?

  • Dendrites are branches that extend from the cell body
  • Carry functional information towards the cell body
  • Receive information from other neurons
• What are axons and what are their functions?

  • Carry messages away from cell body
  • If myelinated (have a myelin sheath) nerve transmission is sped up
• What are terminal buttons and their function?

  • Contain neurotransmitters
  • At the end of axons making synaptic connections with other cells
• Describe the process of synaptic transmission across two neurons

  • Electrical impulses (action potentials) reach the presynaptic terminal
  • electrical impulses (action potentials) trigger release of neurotransmitters (such as serotonin, GABA, noradrenaline)
  • Neurotransmitters cross the synapse from vesicles
  • Neurotransmitters bind with receptors on the postsynaptic membrane
  • Stimulation of postsynaptic receptors by neurotransmitters result in either:
  • excitation (depolarisation) or inhibition (hyperpolarisation) of the postsynaptic membrane, determines the likelihood another ap will be fired
• What is excitation? Give examples of 2 excitatory neurotransmitters

  • when a neurotransmitter increases the positive charge of the postsynaptic neuron
  • This increases the likelihood that the neuron will fire and pass on the electrical impulse.
  • (e.g. adrenaline/noradrenaline)
• What is inhibition? Give examples of 2 inhibitory neurotransmitters

  • When a neurotransmitter makes the charge of the postsynaptic neuron more negative
  • This decreases the likelihood that the neuron will fire and pass on the electrical impulse
  • (e.g. serotonin/GABA)
• What is summation

  • Whether a neuron does fire is decided by the process of summation.
• Process of summation

  • Neurotransmitters can be excitatory or inhibitory
  • E=excitation of the post-synaptic membrane, more likely to fire an electrical impulse.
  • I= inhibition of the post-synaptic membrane, less likely to fire an electrical impulse.
  • These influences are summed;
  • if the net effect on the post synaptic neuron is inhibitory, it will be less likely to fire. The opposite if its excitatory.
  • Therefore, the action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold.
• Strength of synaptic transmission

  • Research & Support: Foundational experiments by Loewi (chemical transmission) support synaptic approach. Modern scanning (e.g., PET, fMRI) confirm neural pathways.
  • Therapeutic Applications: Drugs targeting neurotransmitters, e.g., SSRIs for OCD, show real-life value as SSRIs act on blocking excessive serotonin reuptake reducing low levels of serotonin to decrease depressive symptoms
  • Similar for conditions such as SZ with dopamine
• Limitation of synaptic transmission

  • Biological Reductionism (levels of explanation): Explaining behaviour purely by neuronal activity might ignore environment, cognition
  • E.g. OCD does rely on serotonin levels but also is a result of trauma with 1/2 of patients establishing one (CROMER)
  • SZ as a result of poor family functioning, the schizophrenogenic mother and even a lack of central control