L13 Introduction

• What is a bilaterian?

  An animal with bilateral symmetry.
• What is cephalisation?


  Nervous tissue concentrated toward one end of an organism.
• Nervous system:

  • Central nervous system - the brain and spinal cord
  • Peripheral nervous system - NS other than brain and spinal cord
• What are glia cells?

  Supporting cells in the nervous system. They provide structure and insulate nerve cells with myelin sheaths.
• Glia functions pt 2:

  • Supply nutrients and oxygen to neurons (astrocytes)
  • Removal of dead neuronal tissue and immune defence of the CNS
  • Provide scaffolds for neurons to migrate to their final destinations
  • Modulate neurotransmission in the synapses.
• Soma (cell body)

  • Contains cell nucleus and ’machinery’
  • machinery:
  • Mitochondria - performs metabolic activities, extracts energy from nutrients
  • Ribosomes - protein production
  • Endoplasmic reticulum - transports proteins to other locations
• Afferent neurons - carry information from receptors
• Efferent neurons - carry signals away to the effectors i.e. muscles or glands
• Interneurons - connect other neurons
• What is resting polarization?

  The membrane of a neuron maintains an electrical gradient between the inside and outside of the cell. The electrical potential inside the neuron is slightly lower than outside.
• Excitation:

  • Dendrites - many postsyanptic potentials - changes in electrical potential moving towards the centre. Potentials from all dendrites sum up.
  • Cell's body - if the sum is strong enough the neuron fires
• Two types of summation:

  over space - from different dendrites

  over time - from the same dendrites
• Excitation:

  • In the cell body the free potential is formed and moves toward the proximal part of the axon.
  • If the free potential is low and does not reach the threshold level it dies.
  • If the free potential is high it provokes a sudden and massive electric excitation
  • The amplitude of an action potential is independent of the amount of current which produced it and is all or nothing (larger currents do not create larger action potentials)