The Nervous System, Neurons and Synaptic Transmission

• Brain

  • the part of the central nervous system that is responsible for coordinating sensation, intellectual and nervous activity
• The nervous system

  • regulation of psychological processes
  • relays information to and from the brain from around the body
  • sympathetic nervous system helps us in emergencies (fight or flight) and spurs the body into action in preparation to deal with threats
  • parasympathetic nervous system works to calm the body back down after arousal from the sympathetic nervous system
• Brain - external

  • the cerebral cortex is the largest part and contains 4 lobes
  • frontal lobe - thought, planning, motivation and speech production
  • parietal lobe - motor movements and sensory information
  • temporal lobe - language comprehension, hearing and memory
  • occipital lobe - visual processing
  • brainstem - controls heart rate, blood pressure, swallowing and breathing
  • cerebellum - helps coordinate balance and fine muscle movements
• Brain - internal

  • thalamus - a relay station for nerve impulse from the sense
  • hypothalamus - regulation of body temperature, hunger and thirst, links endocrine and nervous system together, controls the release of hormones from the pituitary gland
  • hippocampus - hold short term memories and transfers these to the long-term memory storage
  • corpus collosum - responsible for transferring information from one hemisphere to the other
• Division of Peripheral Nervous System

  • somatic - 12 pairs of cranial nerves, 13 pairs of spinal nerves, sensory and relay neurons, sensory and relay messages to the CNS, motor neurons relay messages from the CNS to other areas of the body responsible for reflex actions
  • autonomic - sympathetic and parasympathetic, involuntary actions, unconscious decision making, heart beating/breathing/digesting
• Neurons

  • specialised cells that move electrical impulses to and from the CNS

  
• Branch

  • structures called dendrites protrude from the cell body, these carry nerve impulses from the neighbouring neurons towards the cell body
• Axon

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

  • protects the axon and speeds up electrical transmission of the impulse
  • if it was continuous, this has the revers effect and slow down the electrical transmission impulse
• Nodes of Ranvier

  • speed up the transmission of the impulse by forcing it to jump along the axon
• Terminal axon

  • communicate with the next neuron in the chain across a gap known as the synapse
• What initiates the release of neurotransmitters in synaptic transmission?

  Electrical signal reaching a threshold
• What happens when the action potential reaches the end of the axon?

  It transfers the signal to the next neuron
• How are signals transmitted between neurons?

  Chemically across the synapse
• What triggers the release of neurotransmitters from synaptic vesicles?

  Electrical impulses reaching the end of the neuron
• What happens to the neurotransmitter after it diffuses across the synapse?

  It is taken up by the postsynaptic receptor site
• How is the chemical message converted back into an electrical impulse?

  By binding to the postsynaptic receptor site
• What is the overall process of synaptic transmission?

  Electrical signal triggers neurotransmitter release, diffuses, and converts back
• What are the key steps in synaptic transmission?

  1. Electrical signal reaches threshold
  2. Signal opens vesicles to release neurotransmitter
  3. Neurotransmitter diffuses across synapse
  4. Neurotransmitter binds to postsynaptic receptor
  5. Chemical message converts back to electrical impulse
  6. Process repeats in the next neuron
• Excitation and Inhibition

  • neurotransmitters either have an excitatory or inhibitory effect on the neighbouring neuron
  • inhibition - the receiving neuron becoming negatively charges and less likely to fire (serotonin causes inhibition)
  • excitation - the receiving neuron becomes more positively charges making it more likely to fire (adrenaline causes excitation)
• What process decides if the post-synaptic neuron fires?

  Summation
• What happens to the excitatory and inhibitory influences during summation?

  They are summed together
• What is the effect of inhibitory signals on the postsynaptic neuron?

  It is less likely to fire
• What occurs if the net effect on the postsynaptic neuron is excitatory?

  It is more likely to fire
• What happens to the inside of the postsynaptic neuron when it fires?

  It becomes positively charged
• What occurs once the electrical impulse is created in the postsynaptic neuron?

  It travels down the neuron
• When is the action potential of the postsynaptic neuron triggered?

  If the sum of signals is excitatory
• What must occur for the postsynaptic neuron to fire?

  The sum of excitatory and inhibitory signals