nerves and synapses

• An introduction to the nerve and synapse
• Today's objectives are to describe the different levels of organization in the CNS, as well as the divisions of the nervous system, understand the different components that make up a neuron, understand the difference between excitation and inhibition in the brain, and describe the other cell types and their functions within the brain
• 1015 (1,000,000,000,000,000)
• Levels of organization in the CNS

  • Behavioural neuroscience
  • Systems neuroscience
  • Cellular neuroscience
  • Molecular neuroscience
• Divisions of the nervous system

  • Central (CNS) - Brain; spinal cord
  • Peripheral (PNS) - connections with e.g. muscles, glands, sensory organs
• Functional divisions of PNS

  • Autonomic - regulates viscera (gut, heart etc.)
  • Somatic - conveys sensory/motor signals
• Neuron


  Basic computational unit within the brain, Excitable, Highly interconnected
• Neuron


  • Needs to be irritable and conductive
• Soma

  Also called the cell body, this is the central region of the neuron which contains the nucleus
• Dendrite


  Receive synaptic input from other neurons which travels to the cell body
• Axon


  Carries signals to other cells via axon terminals. Most neurons have one axon
• Axon terminals


  Give rise to the synapse (Greek: to fasten together, synapsis)
• Presynaptic membrane is closely opposed to the postsynaptic cell
• Allows for interneuronal communication using specific proteins which enable neurotransmitter release
• Cytosol


  The salty, potassium rich solution inside the cell
• Organelles in the soma

  • Nucleus
  • Rough endoplasmic reticulum (aka Nissl bodies)
  • Smooth endoplasmic reticulum
  • Golgi apparatus
  • Mitochondria
• Rough ER


  1. Genetic information is used to synthesise proteins

  2. mRNA bind to the ribosomes, which translate instructions in RNA to assemble the protein

  3. Many ribosomes are attached to stacks of rough ER in neurons

  4. Usually involved in making proteins that will be inserted into the cell membrane or an organelle
• Smooth ER and Golgi apparatus


  1. Helps with protein folding

  2. Responsible for lipid synthesis

  3. Regulate internal concentrations of substances e.g. Ca2+

  4. Golgi apparatus is responsible for extensive post-translational chemical processing of proteins

  5. Sort proteins that are destined for different parts of the neuron
• Mitochondria


  Responsible for cellular respiration, Pulls in pyruvic acid and oxygen, Adds phosphate to adenosine diphosphate (ADP) to give adenosine triphosphate (ATP)
• 17 molecules of ATP are released for every molecule of pyruvic acid
• ATP is the energy source of the cell
• Dendrites


  Input from presynaptic cells can be either excitatory or inhibitory, Neurons integrate the signals received over time and will fire if they reach threshold
• Dendritic spines form the basis of synapses
• Neurotransmitter


  A chemical that is released from the presynaptic terminal upon stimulation and activates postsynaptic receptors
• Receptors


  A specialised protein that detects chemical signals and initiates a cellular response
• Types of neurons


  • Multipolar neurons
  • Pyramidal cells
  • Purkinje cells
  • Granule cells
• The hippocampus contains pyramidal cells and granule cells
• Inhibitory interneurons


  Lots of different types of GABAergic neurons, Can be classified by shape or by what genes are predominantly expressed, Synapse onto the cell they are inhibiting in different ways to create a nuanced control system
• Oscillations: waves in brain activity
• Cortical columns are a regular arrangement of cells throughout the cerebral cortex
• Glial cells


  • Astrocytes
  • Oligodendrocytes
  • Microglial
  • Ependymal cells
• Astrocytes


  Originally thought to be only support cells, More recently have been shown to be important in regulation of plasticity in the brain, Release gliotransmitters
• Oligodendrocytes


  Provide support and insulation to axons in CNS, Create the myelin sheath around axons, Injury can lead to demyelinating diseases
• Demyelinating diseases


  • Multiple sclerosis
  • Guillain-Barré syndrome
  • Charcot-Marie-Tooth disease
• Microglia


  Macrophage cell - the bin collectors of the brain, Always on the look out for plaques, damaged neurons, unused neurons and synapses and infectious substances, Very plastic - take on many forms (phenotypes) depending on the location and system needs
• Ependymal cells

  Line the ventricular system of the brain to form a thin neuroepithelial lining, Produce CSF