Neuro

• water is polar because oxygen is partially negative and hydrogen is partially positive - opposites attract
• the charges of water molecules allow them to form a hydrogen bond
• ice can float because the density of ice is lower then water
• ions are charged substances that carry signals in the body and act as an energy store
• ion can interact biochemically as they interact with proteins and other molecules
• there are physiologically useful ions and biochemically useful ions
• calcium is both physiologically and biochemically useful
• in aqueous solutions ions attract each other and form a hydrogen bond due to the opposite charges
• smaller ions in radius have a bigger hydration shell due to higher charge density
• the hydration shell affects the mobility of ions in solution due to its size and interactions with proteins
• strokes law states ionic mobility is inversely proportional to the ions radius
• amphipathic nature drives the formation of bilayers, they have a hydrophobic head and hydrophilic tail
• cell membranes are constructed by lipid bilayers
• the main source of energy for the concentration of ions against the gradient in cells is hydrolysis of ATP
• pumps are a form of primary active transport
• Pumps, also called transporters, are transmembrane proteins that actively move ions and/or solutes against a concentration or electrochemical gradient across biological membranes.
• Pumps generate a membrane potential by creating an electrochemical gradient across the membrane.
• pump are fairly slow and nearly always move cations
• sodium-potassium ATPase pump - 2K+ in and 3 na+ out
• antiporter or exchanger is two ion in opposite direction
• sodium-calcium exchanger is 3Na+ in, 2 Ca2+ out
• ion gradients represent a source of energy and can be used to transmit information and used to power cellular processes
• ion channels are transmembrane proteins they are selectively permeable, there opening is controlled and they are diverse
• when sodium channels open it depolarises
• when potassium channels open it hyperpolarises
• when sodium and potassium channels open it depolarises
• when chlorine channels open it hyperpolarises
• when calcium channels open it is diverse
• examples of ligan-gated ion channels are cys loop receptors
• examples of cys loop receptors are

  • Nicotinic AChR. 
  • GABAa 
  • 5HT3 receptor. 
  • Inhibitory glycine receptor  
• Ach binding proteins are pentameric proteins with n terminal extracellular domains (when they are nicotinic receptors), they lost their transmembrane and intracellular domains
• Facilitated diffusion


  The process by which molecules or ions move across a cell membrane through specific transport proteins, down their concentration gradient
• Ions cannot cross lipid bilayers by simple diffusion
• Different concentrations between either side of the membrane causes a gradient
• Facilitated diffusion


  1. Ions flow down gradient

  2. Until concentrations equal on both sides

  3. Equilibrium is set up
• Molecules that punch holes in membranes

  Said to facilitate diffusion
• Facilitated diffusion mechanisms


  • Pumps
  • Carriers
  • Proteins
  • Channels
• 1D diffusion


  Movement along DNA
• 2D diffusion


  Movement in a membrane
• 3D diffusion


  Movement in liquid, cytosol, extracellular fluid