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Neural tissue (neurons) activities (graded potential (a.k.a local…
Neural tissue (neurons) activities
graded potential
a.k.a local potentials
changes in the transmembrane potential cannot spread far from the stimulus site
any stimulus that opens a chemically-gated channel
intracellular Na+ concentration tapers off from the stimulation site
effect is either depolarization (Na+ or Ca++) or hyperpolarization (K+ or Cl-) depending on the property of the membrane channel involved
the effect is passive
action potential
depolarization
initiated by a graded depolarization at the axon hillock (a chemically-gated channel) large enough to move that section of membrane to negative 55 mv
transmembrane potential (
at rest
)
maintained by the Na+/K+ pump (
needs ATP
)
pumps 3 Na+ out of the cell for every 2K+ pumped into the cell
negative 70 mV
large negatively charged protein groups at the intracellular side of the membrane contribute to the resting potential
exists because the membrane is selectively permeable to ions
all or nothing (binary) threshold
propagation
saltatory propogation
FAST (help from myelin)
continuous propogation
SLOW (no myelin :cry:)
types of neuron membrane channels
voltage-gated
ex:
sodium channels
found:
neural axons, skeletal muscle sarcolemma, cardiac muscle
threshold for initiating opening = neg 60 to 55 mV
mechanically gated
found:
in sensory receptors
chemically gated
neurotransmitters such as ACh bind to the channel protein which then open to let ions through
found:
neuron cell body & dendrites
synapses
chemical (use neurotransmitters) = no cell 2 cell contact