BIOMED SCIE Lecture 19 Synaptic comm CNS PNS

• Axon terminals


  Output Zone
• Dendrites and Cell body


  Input Zone
• Axon hillock


  Trigger Zone
• Neurons communicate with other cells at synapses
• At electrical synapses, the electrical current flows from one neuron to another
• At chemical synapses, a chemical neurotransmitter carries information across the gap junction
• Most synapses are chemical synapses
• Most neurons have many synapses on their dendrites and cell body
• Chemical Synaptic Transmission


  • Transmission can be only in one direction
  • The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal.
  • The action potential causes the release of the neurotransmitter
  • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
• The Generation of Postsynaptic Potentials


  Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell• a ligand is another term for a neurotransmitter• Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential
• Depolarizations - bring the membrane potential

  toward threshold
• Chemical transmitter binds to the post synaptic receptor and opens and ion channel which allows Na+ to enter the cell and a small amount of K+ can leave the cell via this channel.This causes the cell to become more depolarised (more positive in membrane potential), which moves the membrane potential at the axon hillock closer to the potential where an Action Potential will be generated
• Inhibitory postsynaptic potentials (


  Hyperpolarizations - move the membrane potential farther from the threshold potential where an action potential is generated. Chemical Neurotransmitter binds to receptors on the post synaptic cells and opens ion channels which make the cell more negative e.g. Chloride (Cl-) ions enter the cell. The inhibitory neurotransmitter Gamma Amino Butyric Acid (GABA) can open Cl- channel
• After release, the neurotransmitter


  May diffuse out of the synaptic cleft– May be taken up by surrounding cells– May be degraded by enzymes
• Neurotransmitters


  There are more than 100 neurotransmitters, belonging to five groups: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases• A single neurotransmitter may have more than a dozen different receptors
• Neuromuscular transmission

  • Action potential in presynaptic motor axon terminals.
  • Increase in Ca++ permeability and influx of Ca++ into axon terminal.
  • Release of acetylcholine from synaptic vesicles into the synaptic cleft
  • Diffusion of acetylcholine to postjunctional membrane
  • Combination of acetylcholine with specific receptors (nicotinic) on postjunctional membrane
  • Increase in permeability of postjunctional membrane to Na+ and K+ causes EPP.
  • Depolarisation of areas of muscle membrane adjacent to endplate and initiation of an AP.
• Some Disorders of Neuromuscular Junction


  Myasthenia Gravis

  Lambert Eaton Syndrome
• Lambert Eaton Syndrome


  •Presynaptic Autoimmune disease.•Antibodies to pre-synaptic Ca2+ channel, thus inhibiting transmitter release.•Detected by EMG
• Myasthenia Gravis


  •Autoimmune disease of ACh Receptor.• Amplitude of end plate potential is reduced to the point where it is barely above threshold to activate adjacent Na+ channels.• Can be detected by EMG
• Organophosphates (pesticide research


  Venomous Agent X (VX) agent (Kim Jong-nam)• Sarin• Novichok nerve agent (Sergei and Yulia Skripal)
• Command and Control Center


  The human brain contains about 100 billion neurons ,organized into circuits more complex than the most powerful supercomputers• A recent advance in brain exploration involves a method for expressing combinations of colored proteins in brain cells, a technique called “brain bow”• This may allow researchers to develop detailed maps of information transfer between regions of the brain
• Central nervous system


  Brain , Spinal cord
• Peripheral nervous system 


  Cranial nerves . Ganglia outside CNS. spinal nerves
• The brain and spinal cord contain


  Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons– White matter, which consists of bundles of myelinated axons
• Glia


  Glia have numerous functions to nourish, support, and regulate neurons:

  • Embryonic radial glia form tracks along which newly formed neurons migrate.
  • Astrocytes induce cells lining capillaries in the CNS to form tight junctions, resulting in a blood-brain barrier and restricting the entry of most substances into the brain
• The Peripheral Nervous System

  • The PNS has two efferent components: the motor system and the autonomic nervous system
  • The motor system carries signals to skeletal muscles and is voluntary.
  • The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary
• The Autonomic Nervous System


  • The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions
  • The sympathetic division regulates arousal and energy generation (“fight-or-flight” response)
  • The parasympathetic division has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions.
  • The enteric division controls activity of the digestive tract, pancreas, and gallbladder