Nerve, Endo, CNS

• Negative feedback acts to make the deviation smaller
• Positive feedback acts to make the deviation larger
• Feedforward systems


  A response to a change outside the body to prevent a change inside the body
• Ion concentrations

  • Na+, Cl- and Ca2+ are high outside the cell and low inside the cell
  • K+ is high inside the cell and low outside the cell
• Osmolarity

  Kept between 275-300 mosmol/L in ICF and ECF
• Total body water (TBW)

  60% of body mass in males, 55% of body mass in women
• ECF


  1/3 of TBW
• ICF


  2/3 of TBW
• Plasma


  1/5 of ECF
• ISF


  4/5 of ECF
• Water is always gained or lost from ECF first
• Membrane proteins

  • Integral membrane proteins
  • Peripheral membrane proteins
  • Transmembrane proteins
• Fick's Law of Diffusion

  J = PA∆C
• Osmolarity

  The total number of solute particles dissolved in the solution (mosmol/L)
• Hyposmotic solution


  Has less solute molecules per L than the cell
• Hyperosmotic solution


  Has more solute molecules per L than the cell
• Tonicity

  The effect a solution has on cell volume
• Cell volume in different solutions

  • Isotonic - stays the same size
  • Hypertonic - shrinks
  • Hypotonic - swells
• Pinocytosis

  Non-specific uptake of solutes and water from the ECF via vesicles
• Phagocytosis

  Phagocytes bring bacteria and debris into the cell to then fuse with lysosomes then destroy their contents
• Receptor-mediated endocytosis

  An extracellular molecule binds to a receptor on the cell surface, and the plasma membrane then folds and forms a vesicle around the receptor
• Exocytosis is generally triggered by an increased level of Ca2+ in the cytosol
• Nerve

  Made up of bundles of fascicles and blood vessels
• Fascicle


  Bundle of neurons
• Neuron types

  • Multipolar
  • Unipolar
  • Anaxonic
• Neuron signal integration

  1. Dendrites and soma receive input from local potentials

  2. Axon hillock summates the local potentials and fires an action potential down the axon

  3. Axon carries the action potential to the synaptic terminals

  4. Synaptic terminals release a neurotransmitter to initiate a response in a target cell
• Resting membrane potential

  The combined permeabilities and gradients of all ions involved in the cell, typically -70mV
• Local potentials


  Small potentials that can depolarise or hyperpolarise the membrane
• The amplitude of local potentials decreases with distance
• Action potential

  Will only occur if the membrane potential reaches -60mV
• The amplitude of action potentials is unaffected by distance
• Excitatory neurotransmitter


  Brings membrane potential closer to threshold by making it more positive and causing depolarisation, brings Na+ into the cell
• Inhibitory neurotransmitter


  Brings membrane potential further from threshold by making it more negative and causing hyperpolarisation, brings Cl- into the cell
• Types of summation

  • Spatial summation
  • Temporal summation
• Refractory period


  When the cell cannot generate another action potential because the voltage gated Na+ channels are either open or inactive
• Myelin

  Made from oligodendrocytes in the CNS, made from Schwann cells in the PNS
• Multiple sclerosis (MS)


  Caused by the demyelination of cells in the CNS, impairs impulse conduction
• Chemical synaptic transmission

  1. Depolarisation of the axon terminal causes voltage gated Ca2+ channels to open and Ca2+ to flow into the nerve terminal

  2. Increased Ca2+ level triggers the release of neurotransmitter from vesicles into the synaptic cleft

  3. Neurotransmitter diffuses across the synaptic cleft and binds to its receptor which is a chemically gated Na+ channel on the postsynaptic membrane

  4. Na+ then enters the postsynaptic cell and depolarises the cell
• Neurotransmitter types

  • Acetylcholine
  • Amino acids
  • Biogenic amines
  • Purines
  • Peptides
  • Gases
• Neurotransmitter receptor types

  • Ionotropic
  • Metabotropic