Neuronal Communication Flashcards
what features are common to all sensory receptors
acts as energy transducers which establishes a generator potential
respond to specific stimuli
describe the basic structure of pacinian corpuscle
single nerve fibre surrounded by layers of connective tissue
stretch mediated NA+ channels on plasma membrane
capillary runs along base layer
what stimulus does a pacinian corpuscle respond to
pressure deforms membrane causing stretch mediated NA+ channels to open
if influx of sodium raises membrane to threshold potential then generator potential produced
action potential moves along sensory neurones
describe the features of all neurones
cell body-contains organelles and high proportion of RER
dendrons-branch into dendrites that carry impulses towards cell body axon-long, unbranched fibre carries nerve impulses away from cell body
describe additional features of myelinated neurones
schwann cells-wrap around axon many times
myelin sheath-made from myelin rich membranes of schwann cells
nodes of ranvier-very short gaps between neighbouring schwann cells where there is no myelin sheath
name 3 processes schwann cells are involved in
electrical insulation
phagosytosis
nerve regeneration
explain why myelinated axons conduct impulses quicker
saltatory conduction
impulses jump from one node to another as depolarisation cannot occur where myelin sheath acts as an electrical insulator
what is resting potential
potential difference across membrane when not stimulated-usually around -70mv
how is resting potential established
- membrane is more permeable to K+ than Na+
- sodium potassium pump actively pumps 3nA+ out of cell and 2K+ in
- establishes electrochemical gradient as cell content is more negative
what happens during depolarisation
- stimulus detected so facilitated diffusion of Na+ into cell down electrochemical gradient
- potential difference becomes more positive
- if membrane reaches threshold potential then sodium vg channel opens
- significant influx of sodium reverses potential difference to 40
what happens during repolarisation
- sodium channels close and potassium channels open
- faciliated diffusion of potassium out of cell down electrochemical gradient
3.potential difference becomes more negative
what happens during hyperpolarisation
- potassium ions diffuse out so potential difference becomes more negative than resting potential
- refractory period=no stimulus is large enough to raise membrane to threshold potential
- potassium channels close and active pump reestablishes resting potential
explain the importance of the refractory periods
unidirectional impulse
discrete impulses
limits frequency of impulse transmission
what is the function of synapses
electrical impulse cannot cross junction
neurotransmitters send impulses betwene neurones
