Nervous system

• Central nervous system (CNS)


  The brain with the spinal cord
• Brain


  • Central organ of the nervous system
  • Constituted of nerve cells, glial cells, blood vessels and cerebrospinal fluid
  • Contains almost 98% of the body's neural tissue

  
• Average weight of a new-born human brain ~ 350-400 g, and adult human brain ~1300-1400 g
• Neurons


  • The primary constituents of the nervous system
  • Receive messages from other neurons through dendrites
  • Dendrites carry message to the neuron's cell body
  • Axon carries outgoing messages
• Terminology - Neurons


  • Nerve - group of axons bundled together in the PNS
  • Nerve fascicle/fasciculus - bundle of funiculi
  • Funiculus - bundle of axons
  • Tract - group of axons bundled together in the CNS
  • Nucleus - collection of neuron cell bodies in the CNS
  • Ganglion - collection of neuron cell bodies in the PNS (except, basal ganglia)

  
• The CNS underlie all the activity of the nervous system
• Functions of the CNS


  • Forms a communication network
  • Coordinates all the systems of the body and enables them to function
  • Integrates the information that it receives from all parts of the body
• Receptor


  A protein molecule that receives chemical signals from outside a cell
• Receptors


  • Same endogenous ligand leads to a large number of receptor subtypes
  • Receptor subtypes are widespread throughout the nervous system, providing diversity of functions
• Receptor type


  Ligand gated or G-protein coupled
• Ligand


  A substance that forms a complex with a biomolecule to serve a biological purpose
• Prodrug

  A chemical compound that must undergo chemical conversion by metabolic processes before becoming an active pharmacological agent
• Bioavailability


  The extent and rate at which the active drug or metabolite enters systemic circulation
• Nerves


  Categorized into 3 groups based on the direction of the signals

  
• Affinity


  How tightly a drug binds to its receptor
• Nerve groups


  • Afferent nerves: signals from sensory neurons to the CNS
  • Efferent nerves: signals from the CNS along motor neurons to their target muscles and glands
  • Mixed nerves: contain both afferent and efferent axons, and thus conduct both incoming sensory information and outgoing muscle commands in the same bundle

  
• Efficacy


  The capacity of a drug to produce a change in a target cell or organ after binding to its receptor
• Ascending or Afferent pathway


  Made of one or a series of neurons projecting from the periphery toward the brain

  
• Potency


  A measure of drug activity expressed in terms of the amount required to produce an effect of given intensity
• Descending or Efferent pathway


  Made of one or a series of neurons projecting from the brain toward the periphery

  
• A drug has varying degree of affinity and specificity


  This contributes to its side effects
• Dorsal root ganglia


  Contain the cell bodies of sensory neurons, located outside the spinal cord

  
• Dorsal horn


  The first point of synapse of sensory neurons, located inside the spinal cord
• Mirtazapine


  Tetracyclic antidepressant
• Cranial nerves


  Innervate parts of the head, and connect directly to the brain (especially to the brainstem)

  
• Mirtazapine


  • Potent antagonist or inverse agonist of the 2A-, 2B-, and 2C-adrenergic receptors, the serotonin 5-HT2A, 5-HT2C, and 5-HT3 receptors, and the histamine H1 receptor
• Side effects of Mirtazapine


  • Constipation, dry mouth, sleepiness, increased appetite and weight gain
• Cranial nerves are typically assigned Roman numerals from 1 to 12 and descriptive names
• Dorsal root ganglion


  Part of the spinal nerve that relays sensory information

  
• Agonist is a neurotransmitter or a drug that mimics the action of a neurotransmitter and binds to its cognate receptor
• Dorsal horn


  Part of the spinal cord that receives sensory information from the dorsal root ganglion
• Neurotransmitter


  Agonist, has high affinity for its own receptor
• Cranial nerves innervate parts of the head, and connect directly to the brain (especially to the brainstem)

  
• Agonist


  Can produce excitation or inhibition of the post-synaptic neuron
• Partial agonist


  An agonist ligand that produce a lower response than a full agonist after binding to the same number of receptors
• Spinal nerves

  There are 31 pairs in humans, arise from the spinal cord, supply the rest of the body, connect the CNS to the periphery

  
• Partial agonist

  Can act as competitive antagonist when in presence of a full agonist
• Spinal nerve designations

  Letter-number based on the vertebra through which they connect to the spinal column
• Inverse agonist

  A ligand that selectively binds to the inactive state of the receptor
• Spinal nerve branching


  1. Anterior/ventral root relays sensory information

  2. Posterior/dorsal root relays motor information