BIOL 1102 Study Guide part 1

Study Guide for Midterm 3

Electrical Signaling

  • Rules for ion movement
    • Higher to lower concentration
    • Away from like chargers, towards the opposite charge
    • Depends on the membrane permeability
  • Membranes Can be depolarized or hyperpolarized by the opening and closing of different ion channels
    • Resting potential= only K+ channels are open
    • Depolarized= voltage gated Na+ channels open
    • Hyperpolarized= chemically gated K+ channel open
  • Production of Action Potentials
    • Most neurons depolarization is graded only up to a certain membrane voltage called the threshold potential
    • Stimulus strong enough to produce a depolarization that depolarization that reaches the threshold potential triggers a different response= action potential
    • Action potential is a all or none thing= once it is triggered it has a magnitude that is independent of the strength of the triggering stimulus
    • Action potentials are signals that carry information from axons
    • Most are very brief which allows for the production of high frequency signals
    • Neurons generally encode information in action potential frequency and not amplitude
      • Frequency= how many occur per unit of time
      • amplitude= amount of voltage change per action potential
      • Refractory period= a state in which the no signal can be sent because the ions are deactivated
  • Myelination by Glia Speeds Signal Transmissions
    • The electrical charge jumps from space to space in the Nodes of Ranvier.
    • Layers of myelin insulate the axon. As a result, action potentials “jump” from node to node increasing the speed of conduction
    • At nodes of Ranvier there is a buildup of + charges and inside and - charges outside the axon.
    • Known as salutary action potentials.
  • Neurons communicate with other cells
    • Synapse= two neurons get together in order to transmit info from the presynaptic cell to the postsynaptic neuron
    • Given condition, should we go under an action potential or not
  • Events in a Chemical synapse
    • Blue arrow= showing that the presynaptic cell just had an action potential
    • When calcium voltage channels reach a certain voltage they open up and make vesicles that contain neurotransmitters and bind to the pre synaptic membrane at the axon terminal
    • On the postsynaptic membrane there are chemically gated channels that bid into the chemically gated channels. Allows sodium to come in and can cause depolarization.
    • Neurotransmitters can be repacked into vesicles and brought back to the presynaptic cell, degraded naturally or degraded by enzymes
  • Synapses can be;
    • excitatory= result in depolarization (open sodium channels)
    • inhibitory= result in hyperpolarization (open chloride channels)
  • Postsynaptic cells sums excitatory and inhibitory inputs
    • Spatial summation
    • Temporal summation
    • Inputs are integrated at the axon hillock= takes all of the inputs together and decide if an action potential is going to happen
      • Small changes (gradient potential→ excitatory and inhibitory)
      • Gradient change potential= graded change in postsynaptic cell= moderate change in the membrane potential of the postsynaptic cell. However if the depolarization passes the threshold an action potential can still occur.
      • Excitatory post synaptic potentials (EPSPs)= depolarize the post synaptic neuron. Binding of neurotransmitters to the postsynaptic receptors opens gated channels that allow Na+ to diffuse into the cells.
      • Inhibitory postsynaptic potentials (IPSPs) = hyperpolarize the postsynaptic neuron= binding of neurotransmitter to postsynaptic receptors opens gated channels that allow K+ to diffuse out of the cell or Cl- to diffuse into the cell

Summed EPSPs and IPsps

  • No summation= multiple EPSPs widely space din time do not set off an action potential
  • Temporal summation= multiple EPSPs arrive quickie at a synapse to set off an action potential
  • Spatial summation= single EPSPs at two or more different synapses set off an action potential
  • Cancellation= an EPSP and an IPSP may cancel each other so no action potential is set off
  • Refractory period= while the inactivation gate Na+ channel is closed the membrane is in its absolute refractory period, during which time the membrane is unresponsive to another stimulus. A change in voltage will not open these channels
  • Once te voltage gated Na channels change to the closed state, but while the voltage gated K+ channels are stiled channels are still open the membrane enters a brief relative refractory period
  • A new action potential may be generated but only in response to a really large stimulus

Sensory Systems Eye and Ear

  • All sensory information arrives in the central nervous system (CNS) and brain and spinal cord as action potentials
  • Sensory reception
    • Arrival of stimulus energy ay specialized sensory receptor cells
  • Sensory transduction/ amplification
    • Conversion of stimulus energy into a change in receptor cell membrane potential: receptor potential
    • Integration of stimulus information received by cells of the sensory organ and associated neurons
    • Amplification of stimulus into a sufficiently strong signal to be transmitted to CNS
  • Interpretation
    • Action potentials sent to the CNS are recognized as sensory information of a specific type of circuits in the CNS
  • Sensory receptor- proteins are found in the membranes of sensory receptor cells and respond to stimuli by opening or closing ion channels
    • Ionotropic receptors= open and close due to direct response to a stimulus
      • Mechanoreceptor
    • Metabotropic receptors= open or close ion channels indirectly via a signaling cascade
      • Chemoreceptor
      • Photoreceptor
    • Sound waves are the stimuli for hearing
      • Amplitude= sound wave corresponds to its volume
      • Frequency= refers to how frequently a sound wave oscillates per second
        • A sound wave that oscillates very quickly will produce a higher pitch while a sound wave that oscillates very slowly will produce a lower pitch
      • Process of hearing
        • The tympanic membrane mechanically transmits these pressure waves into movementsof the ossicles in the middle ear
        • The ossices transmit their movement into pressure waves in the fluid of the cochlea at the oval window
        • The cochlea is divided into fluid filled chambers; pressure waves from the ossicles cause the membrane to flex.
        • Flexing of the basilar membrane bends stereocilia on hair cells in the organ of Corti
        • The hair cells have mechanoreceptors on their stereocilia
          • The steocillia project into the middle canal which contains a fluid high in K+ and low in Na+. When K+ opens, the K+ enters and depolarizes the cell
          • Membrane depolarization opens voltage gated Ca 2+ channels causing neurotransmitter release
          • Low pitch= travel far down the vestibular canal and flex the basilar membrane activating the potentials in low frequency senors
          • Medium pitch= pressure waves travel only part way down the upper canal before flexing the basilar membrane and activating mid frequency sensors
          • High pitch= pressure waves travel short distance before flexing the basilar membrane and activating high frequency sensors
          • Elephants make sounds to be able to travel long distances
    • Process of sight
      • Sight is based off of opsin which contain photopigments known as retinal
      • Wavelengths of light determine color
      • Amplitude of light determine brightness
      • In the vertebrae retina light is absorbed by photoreceptor cells which have opsin in their membrane.
      • Rhodopsin= a form of opsin embedded in membranes within photoreceptor cells called rods which sense black and white. Light makes the photopigment in the retina change shape
      • Causes a G protein signaling cascade that changes the membrane potential
        • Cis retinal is sensitive to light
        • And when it absorbs the photon it becomes all trans retinal. Which signals a g protein cascade
        • Trans retinal returns to 11 cis conformation, it is photoresponsive again
        • Light absorption closed sodium channels
          • Tod and cone cells are naturally depolarized and become hyperpolarized with light so with stronger light more hyperpolatrization
          • Bipolar cells= synapse with rod or cone cells and relay responses to ganglion cells
          • Ganglion cells= send their axons out of the eye in the optic nerve
          • Amacrine and horizontal cells= modify electrical signals as they pass fromphotoreceptors to ganglion cells

Defies boundaries within images and increase the sensitivity of the eye moving images

Why hyperpolarized?

        • Watch ear video

Muscles and movement

  • skeleton= a structure or structures that serve functions for support and movement
    • Types
    • Hydrostatic= consist of fluid filled body compartments
      • Soft body invertebrates use this for support and movement
      • Combination of muscles anf fluid
      • Water is incompressible so pushing against it allows the invertebrate to move
    • Exoskeleton= hard substance outside of the body
      • External that surrounds and protect most of the body surface
      • Provides support and protection from the external environment and predators
      • Have to be regrown and shet
      • E.g.
        • Earwing, beetle, spider, shrimp, etc.
    • endoskeleton= hard substance inside the body
      • Provide support and protection for some internal organs but do not protect the body surface.
      • Found in some species of sponges all echinoderms like starfish and vertebranes
        • Hardened by calcium, magnesium phosphate and carbonate
      • Tendon and ligaments= made from collagen
        • Tendon= muscle to bone, muscle to muscle
        • ligaments= bones to bones
      • Order of organization
        • Myofibril gives rise to muscle fibers which are surrounded by connective tissue. Fibers then give rise to muscles.
        • Z discs= area where to actin filaments connect
        • Sarcomere= basic unit of a muscle cell
        • Myofibril= long contractile units
        • Muscle fiber= muscle cells
      • Filaments within muscle
        • Thin filament= two actin filaments twisted together
          • Tropomyosin runs through the grooved formed by actin helices
        • Each myosin molecule consists of two long polypeptide chains coiled together each ending with a globular head
        • Myosin molecules are arranged in parallel to form a thick filament, with myosin heads peeking out from the necks along the filament.
        • Actin and Myosin= overlap to form myofibrils
          • Tropomyosin and troponin are proteins that block myosin binding sites on monomers of actin filaments
          • While Ca2+ binds to troponin, it causes the troposomyosin to move and expose myosin binding sites

Titin acts like a spring and is a giant protein greater than 1 um in length

          • 1) Calcium is released from the sarcoplasmic reticulum
          • 2) Ca2+ in the sarcoplasm binds to troponin and exposes myosin-binding sites on the actin filaments
          • 3) Myosin heads bind to actin release Pi initiates power stroke
          • 4) In the power stroke, the myosin head changes conformation, filaments slide past one another
          • 5) ADP is released; ATP binds to myosin, causing it to release actin
          • 6) ATP is hydrolyzed. The myosin head returns to its extend conformation
          • 7) if Ca2+ is returned to the sarcoplasmic reticulum, the muscle relaxes
          • 8) If Ca2+ remains available, the cycle repeats and muscle contraction continues.
          • Watch sarcomere shortening and cross bridge cycle
        • Neurons communicate with muscle cells at neuromuscular synapses
          • 1) Action potential arrives at axon terminal
          • 2) Na+ channels open; depolarization causes voltage gated Ca2+ channels to open
          • 3) Ca2+ enters the cells and triggers fusion of acetylcholine (neurotransmitter) vesicles with the presynaptic membrane
          • 4) Acetylcholine molecules diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane
          • 5) When receptors bind acetycholine, they open their cation channels and depolarize the postsynaptic membrane
          • 6) The spreading depolarization fires an action potential in the postsynaptic membrane
          • 7) Acetylcholine is broken down and the components and the components are taken back up by the presynaptic cell. Acetylcholine and vesicles are recycled.
        • Actional potential to muscle contraction (look on slide)