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Neurons
100 billion, are the functional units of cognition
diameter of a neuron
4 micron to 100 micron (motor neuron in cord)
number of synapses for a "typical" neuron
1,00 to 10,000
Conduction velocity of action potential
.6-120 m/s
connectional specificity:
Neurons pass info through specific circuit but the circuits are not touching. (a few exceptions)
Dynamic polarization
some structures in the neuron are for taking info in and others are for sending info
Postsynaptic is to .... as pre synaptic is too...
dendrites and axons
Support cells (Neural Glia..glia means glue)
CNS= astrocyte oligodendrocyte (produce Myelin) microglial cell PNS= schwann cell (produce myelin)
Difference between the Schwann Cell and the Oligodendrocyte
Schwann Cell = Peripheral Nervous System (PNS) number of axons myelinated by one cell is ONE Oligodendrocyte= central nervous system (CNS) the number of axons myelinated by one cell is MANY
Rostral =
Anterior (like forehead)
Current flow
is mediated by ionic current which is diff from the flow of electrons in copper wires
ions
are charged ions in a solution
the spike triggering zone on the neuron is the
region the integrates (sums) currents from many synaptic inputs or from stimulation of a sensory receptor.
difference between neurons and other cells
the neuronal membrane has transmembrane proteins (specialized structures such as passive ion channels and active transporters or pumps)
lipid bilayer
forms neuronal membrane like the orange peel thing in bio i learned or oil and water. lipid is not water soluble
The restin membrand potential
at rest the membrane is more pereable to some ions. that is SELEVTIVE PERMEABILITY. and is more permeable to k + (there are more non gated k+ selevtive channels than non gated Na+ channels) this means there is more K+ inside the cell than outside
Active Transporter during rest
there are active transporter pumps that pump out 3 Na+ ions and admits 2 K+ ions (concentration gradient is formed in which there is higher concentration of NA+ outside the neuron and higher concentration of K+ inside the neuron)
Ions always want to go where?
the concentration is lowest , where there is less crowding
the concentration gradient and the electrical gradient are in
opposition to each other with respect to K+
the neuron at rest is at
-40 to -90 millivoltz or -70 on avg
how far a passive current will go depends on the...
amplitude of the original current, resistandce, and conductivity of the intracellular fluid
if there is enough currents the neuron will
fire (an action potential)
the neuron must be depolarized enough to meet a threshold and when it does the ion chnnels open, what enters and what exits?
Na+ enters and K+ exits the cell (hodgkin-huxley cycle)
after a neuron is depolarized it is followed by a refractory period in which the cell....
is hyperpolarized becaus og too much K+ entering. (happens in milliseconds)
when the Na+ are closed, there is the
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