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Lecture 11
Cellular communication part 1
| Question | Answer |
|---|---|
| cell to cell communication | coordinate physiological functions in multicellular orgnisms and to signal to other organisms and mechanisms of cellular regulation |
| cell signaling mechanisms | multiple cellular mechanisms for sending signals from one cell to another |
| type of cellular communication | 1. direct cell to cell signaling-direct contact 2. local signaling 3. long distance signaling |
| 2 main classes of signal mechanisms | 1. cehmical signaling 2. electrical signaling |
| chemical signals | endocrine, paracrine, autocrine |
| electrical signals | action potentials, receptor potencials |
| electrical signals in animals | 1.receive information via sensory receptors 2.integrate the sensory information for precessing 3. carry out a specific response by motor or efferent pathways |
| simple reflex through simple neural circuit (withdrawal reflex) | 1.afferent sensory pathway input 2. integration for processing 3. efferent motor pathway output |
| 2 main categories of cells in central nervous system | 1. Neurons 2. glial cells |
| neuron function | 1. sensory- to the CNS 2. interneurons-in the CNS 3. motor-away from CNS |
| glial cells | are supporting cell types: astocytes, oligodendrocytes, microlia |
| basic neuron types: | 1. bipolar interneuron 2. unipolar-sensory neuron 3. multipolar- motoneuron 4. pyrimidal cell |
| neuron structure | cell body, dendrites, axon and axon hillock, myelin sheath, terminal branches and bulbs |
| electrical signals and electrochemical properties of cells | due to an unequal distribution of ions across a cellular membrane each cell will have a resting membrane potential (Vm or Em) |
| Vm- resting membrane potential | is the quantitative electrical difference across that membrane and is measured as a voltage difference across the membrane |
| Vm | results form the separation of charged particles across the cell membrane |
| the resting membrane potential | is stored (potential) electrical energy, measured in volts |
| squid giant axon | stimulates muscles to contract to forcefully expel water and allow the squid to escape its prey |
| the membrane potential in neurons | is primarily determined by 3 ions (Na,K,Cl) and negatively charged impermeable ions that reside in the cell |
| how are resting membrane potentials generated | due to the combined effects of: diffusion, electroneutrality,semipermeable membranes, and Na/K ATPase pump |
| electrical potential voltage | the potential tendency for a charged ion to flow across a membrane (potential energy) |
| Nernst equation | calculates the equilibrium potential for each individual ion |
| goldman hodgkin katz | equation to calculate the steady state membrane potential |
| mammalian neuron at rest | is -70 to-80 mV at this state the membrane is said to be polarized |
| electrical events in neurons | 1. graded potentials 2. action potential |
| graded potentials | a transient electrical signal that occurs due to permeability changes across the membrane, that can be of varying magnitude; dissipates with distance and time |
| action potential | a transient electrical signal that occurs due to permeability changes across a membrane that has a magnitude that is essentially invariable; but does not dissipate with distance moved |
| depolarization | inside becomes more + |
| repolarization | inside returns to be more - |
| hyperpolarization | below resting potential |
| How do these electrical events occur? | there needs to be a change in conductance (movement) of some ion (Na, K,Cl,Ca), changes in ion conductance resulst from changes in permeability for that ion |
| ligand gated | will open in response to binding a specific ligand |
| voltage gated | will open in response to a change in membrane potential; ion specific |
| action potential | are rapid but large electrical depolarizations and repolarizations of the plasma membrane; result from the opening and closing of voltage gated Na and K channels |
| action potential phases | 1. depolarization-opening of Na channels"rising" 2. repolarization- opening of k channels "falling" 3. hyperpolarization "undershoot" due to prolonged opening of K channels |
| Na+ channel:4 main states | repol, depol, inactivated, inactivated and closed |
| Na channel: 2 gates | 1. activation gate 2. inactivation state |
| activation gate | closed at rest, open during depol, open during repol, closes at end of repolization |
| inactivation gate | open at rest, open during depolarization,closed during repolarization,opens during end of repolarization and hyperpolarization |
| what causes the gates to open and close? | depolarization causes activation gate to open quickly and inactivation gate to swing closed slowly |
| repolarization | causes both gates to reset~-40 to -60mV |
| absolute refractory period | Na channels are inactivated not just closed |
| what causes the voltage gated K channels to open? | depolarization but they open very slowly and achieve an open state at +30mV |
| hyperpolarization | occurs due to the elevated k conductance |
| relative refractory period | an AP can occur but it is more difficult due to the elevated K conductance |
| return to resting membrane potential | involves ionic movements and changes in gating status of the voltage gated Na and K channels |
| all or nothing | an AP is an all or nothing event if threshold is reached then an AP will fire the refractory period prevents AP from occurring too close channels are either open or closed |
| signaling | an action potential is essentially a signal that is carried from one part of an axon to another |
Created by:
aareynolds
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