BVMS1

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mkusiak
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50705
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BVMS1
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2010-11-20 07:43:28
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Physiology
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Neurophysiology
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  1. the three communication systems w/in the body
    • Endocrine
    • neural
    • neuro-endocrine
  2. Endocrine communication system
    • rectpro message is blood borne message
    • integrating centre is hormone secreting gland
    • effector message is a hormone
  3. Neural communication system
    • receptor message is nerve impulses
    • integrating centre is central nervous system
    • effector message is a nerve impulse
  4. Neuro-endocrine communication system
    • rectpro message is nerve impulse
    • integrating centre is central nervous system
    • effector message is a hormone
    • (ex: lactation)
  5. Nervous system (general)
    peripheral nerve--> afferent neurone (into CNS)(sensory)--> interneurone-->efferent neurone (out of CNS)(motor)--> muscle gland
  6. Functional unit (the neuron)
    • Dendrites (recieve info)
    • cell body (organelles for most metabolic activity integration of incoming information)
    • axon (information transmission- long distance)
    • terminals (transfer of information)
    • synapse
  7. All cells have a potential difference across their cell membranes doe to...
    • unequal distribution of ions
    • (concentration of ions- mMol/L)
    • Na+ 150 extracellular 15 intracellular
    • Cl- 110 extracellular 10 intracellular
    • K+ 5 extracellular 150 intracellular
    • Ca2+ 1 extracellular 0.00007 intracellular
  8. Determinant of resting membrane potential
    • (- intracellular concentration, + extracellular concentration)
    • Na+/K+ pump (2 x K+ into cell, 3xNa+ out of cell- uses ATP)
    • Differential permeability (Na+ leaks into cell, K+ and Cl- rush out of cell)
    • Impermeable negatively charged molecules (positive out, neg in)
  9. IF the membrane was only permeable to K+
    • K+ ions move out of cell down concentration gradient until the electrical force opposing ion movement equals the force created by the concentration gradient
    • (membrane potential becomes more -)
    • (chemical is balanced by electrical gradient)
    • K+ ions move out of cell down concentration gradient until the electrical forces opposing ion movement equals the force created by the concentration gradient
  10. IF the membrane was only permeable to Na+
    membrane potential becomes more +
  11. Resting potential
    • the resting potential of a cell is determined by the relative permeability of the membrane to ALL ions
    • changes in the permeability of the membrane to any ion results in a change in membrane potenial of that cell
    • (adjusting the permeability to either K+ or Na+ will change the membrane potential)
  12. Side notes:
    • relative to the determination of membrane potential we have only discussed Na+ and K+ ion movement
    • reason- movement of Na+ and K+ ions can explain the changes in membrane potential seen in most nerves and in some but NOT all muscles
    • however, that doesn't mean that the movemet of other ions is not important...
  13. nerve/muscle communication systems
    • nerve and muscle cells are unique as their membrane potentials can be changed by a synaptic signal from an adjacent cell
    • signal transmission relies upon changes in the activity of both chemically gated ion channels and voltage gated ion channels
  14. graded/receptor potentials- short distance information transfer
    • resting membrane ~-70
    • if a stimulus does not created a graded potential to reach threshold- nothing will happen
    • *the farther from the point of stimulas= smaller change in potential.
    • the size of the respone is related to the size of the stimulus, in that it must reach threshold
    • * we can stimulate or inhibit the membrane potential
  15. Positive feedback
    • + feed back between membrane potential and Na+ permeability that leads to generation of an action potential:
    • stimulus--> increased membrane Na+--> increased flow of Na+ into cell-->membrane potential decreased to threshold-->opening of voltage gated Na+ channels in membrane--> (back to) increased membrane Na+ permeability...
    • **threshold movement of Na+ into cell exceeds movement of K+ out of cell
    • (moves away from initial start point... further away from resting membrane potential each time stimulus applied)
  16. Action Potentials
    • all or nothing response
    • information about stimulus size coded as frequency!!
    • **can NOT change the SIZE of the action potenital**
  17. Cellular events that occur during an action potential
    all channels are closed--> stimulus applied--> Na+ open quick, K+ open slow--> Na+ close (K+ are still open)--> K+ are slow to close

    • (RMP--> stimulus--> Action potential--> depolarization-->hyper polarization--> re polarization)
    • **remember bigger stimulus doesn't matter- only frequency**
  18. Absolute and Relative refractory period
    • Absolute refractory period: further stimulation cannot generate a new AP. Na channels are open, no further depolarisation can occur
    • relative refractory period: a larger change in the membrane potential is required to stimulate an AP. K channels open, any influx of Na+ is immediately balanced by movement of K+ (because it's hyperpolarized- it would need a greater stimulus to reach threshold)
  19. stages at level of Na and K receptrs during AP
    • at rest all are closed
    • activated (Na+ open)
    • inactivated (abs. ref)- "bottom" of Na+ close- K+ is partially open
    • At rest (closed)- "top" of Na+ closed, K+ is still open
    • (K+ is SLOW to open and close!!!)
  20. Action potentials- frequency coding
    • Graded potentials: stimulus size is directly related to the size of the response
    • action potentials: stimulus size is relative to action potential frequence
    • small stimulus: stimulus causes opening of chemically gated channels, that gives rise to a graded potential that just exceeds threshold. cells fires APs as long as the cell is above threshold
    • Larger stimuls: takes graded potentials much higher than threshold (reach threshold quicker), cells brought to threshold quicker after each AP thus frequency increased
  21. Accomodation
    a large abrupt stimulus is more likely to stimulate and AP than a stimulus of the same size applied slowly
  22. Local anaesthetics act by...
    blocking voltage gated Na+ channels
  23. Propagation of an action potential
    • time for gates to return to resting state cannot be stimulated! (ARP)
    • (RRP)- would need greater stimulus to hit AP
  24. AP transmission in a NON MYELINATED neurone
    • depolarized area (neg outside, pos inside) moves in all directions away from initial location- ('like a ripple')
    • *current loops*
    • the refractory period blocks the current loop from going back to polarized reigon- theis presence allows proper communication- not radical before movement
    • - actions potentials normally move in one direction down an axon as they start at one end of the axon
    • - APs normally begin at the axon hillock, move down the axon and sweep back over the cell
  25. AP transmission in a MYELINATED neurone
    • Have shwan cells= insulation
    • saltatory conductions: has advantages of speed and energy efficency (less na/k pumps)
    • exactly same process- bit only one place current loops at nodes of ranvier.
    • (used for fast info over long distance)
    • **larger diameter of fiber also increases speed of transmission**
  26. Communication between excitable cells
    • Convergent systems
    • divergent systems
    • synapses
  27. Convergent systems
    the activity of many cells influence the activity of ONE/few
  28. divergent systems
    the activity of ONE cell influences the activity of MANY
  29. synapses (electrical/chemical)
    • electrical- gap junctions- direct current flow
    • chemical- the MAJORITY- electrical signal-->chemical signal-->electrical signal
  30. Signal transmission (chemical) between 2 neurons
    • 1) AP- depolarizes membrane
    • 2) Ca2+ opens Ca2+ gated channels, Ca goes into cells= increase Ca concentration- migration of vesicles to synaptic clef
    • 3) bonds to P.S. cell- decode signal
    • 4) causes reaction in cell membrane (i.e- ion channels)
    • 5) remove Neurotransmitter by diffusion or repackaged or destruction

    • **always 1 direction!!, there are alot of Neurotransmitters some formed in body some formed in cell)
    • (there is a time lag b/c of clef)
  31. graded potentials/receptor potentials
    • (Post synaptic cell collects infor and decides what to use)
    • Excitatory post synaptic potential (EPSP): graded potential on post synaptic cell- open Na+ channels= depolarizing cell membrane
    • Inhibitory post synaptic potential (IPSP): open ion channels to make more permeable to K+ or less permiable to Na+
    • (**by opening more Cl- channels= membrane is more stable)
  32. Temporal and spatial summation of graded potentials
    • Temporal: same place on membrane over time
    • spatial: over distance
    • (see diagram)
  33. Synaptic effectiveness (presynaptic factors)
    • availability of NTs (if body or cell doesn't produce it- there will be no communication)
    • availability of enzymes (see above)
    • Ca2+ concentrations( if change extra cellular [Ca2+] increase = cell will be hyperactive)
    • presynaptic receptors
  34. Synaptic effectiveness (postsynaptic factors)
    • immediate history (IPSP, EPSP)
    • Drugs
    • disease
    • NT concentrations in cleft
    • NT agonist/antagonists
    • Receptor concentrations (no receptor= no signal can be transferred)
  35. How do you get information INTO the system
    • information comes in different forms: Touch, sound, light, pain, temperature, chemicals
    • but w/in the body information is all transmitted as APs
  36. Different types of receptors
    • mechanoreceptors
    • thermoreceptors
    • nociceptors
    • electromagnetic receptors
    • chemoreceptors
    • interpretation of the electrical signal occurs w/in the CNS
  37. Relationship between stimulus and changes in receptor potential
    Stimulus: change in membrane permeability--> graded potential--> AP ( the higher above threshold the greater the AP FREQUENCY)
  38. Pacinian corpuscle- mechanoreceptor (pressure)
    • membrane and fluid lamelli
    • when pressure- fluid displaces causeing receptor potential
    • after time- the membrane remains but fluid disperses so the receptor is no longer being stimulated until pressure is removed and fluid displaces once again
    • (displaced fluid causes the receptor membrane to displace/be triggered)
  39. Adaptation
    • Complete adaptation (fast and slow)- stimulus is constantly applied- but receptors stop triggering
    • incomplete adaptation (fast and slow)- stimulus is constantly applied but receptor information is reduced about half way
  40. Adaptation cont.
    • energy filtering: ex: pacinian corpuscle
    • Membrane effect: Ca2+ entry results in opening of K+ channels
    • efferent control: iris of eye (size)
    • slowly adapting receptors: infor about stimulus strength
    • rapidly adapting receptors- info about rate of change
  41. reflex arcs (monosynaptic)
    muslce (stretch receptor)-->AP (sensory neurone)-->dorsal roots (CNS)-->ventral roots--> AP (motor neurone)--> back to muscle
  42. reflex arcs (polysynaptic)
    stretch receptor--> sensory neurone-->dorsal roots--> ventral roots--> motor neurone--> different muscle
  43. Muscle spindle
    • nuclear bag fibre vs. nuclear chain fibre
    • efferent vs afferent
  44. Polysynaptic reflexes
    • more than one synapse in CNA
    • slower than monosynaptic reflexes
    • responses can be more prolonged due to variable number of synapses
  45. monosynaptic reflex w/ reciprocal inhibition
    when one muscle contracts antagonist muscle must relax

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