Post by skyship on Jul 8, 2009 2:12:42 GMT -5
Memory
In every animal that has been studied, including
* the sea slug Aplysia
* Drosophila
* mice
* ourselves,
the acquisition of a memory occurs in two phases:
* Short-Term Memory
As its name suggests, this only lasts for a short period. It involves an increase in the efficiency with which nerve impulses pass across synapses. It does not require any protein synthesis or remodeling of the synapse.
* Long-Term Memory
This lasts for a long period. It involves the formation of new synaptic connections. These require new gene expression; that is, gene transcription and protein synthesis (translation).
tinyurl.com/kqhg4e
users.rcn.com/jkimball.ma.ultranet/BiologyPages/
M/Memory.html#The_Long-Term_Response
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Excitable cells are those that can be stimulated to create a tiny electric current.
Links to
* muscle fibers
* types of neurons
* Muscle cells and
* nerve cells (neurons)are excitable.
The color photo (courtesy of Julie H. Sandell and Richard H. Masland) is of a single interneuron in the retina of a rabbit. The cell has been injected with a fluorescent dye to reveal all its branches. Each of the small knobs at the tips of the branches makes a synapse with another cell in the retina.
The electric current
* in neurons is used to rapidly transmit signals through the animal.
* in muscles is used to initiate contraction.
The Resting Potential
All cells (not just excitable cells) have a resting potential: an electrical charge across the plasma membrane, with the interior of the cell negative with respect to the exterior. The size of the resting potential varies, but in excitable cells runs about -70 millivolts (mv).
The resting potential arises from two activities:
* The sodium/potassium ATPase. This pump pushes only two potassium ions (K+) into the cell for every three sodium ions (Na+) it pumps out of the cell so its activity results in a net loss of positive charges within the cell.
* Some potassium channels in the plasma membrane are "leaky" allowing a slow facilitated diffusion of K+ out of the cell (red arrow).
Ionic Relations in the Cell
The sodium/potassium ATPase produces........
tinyurl.com/nuy3fp
users.rcn.com/jkimball.ma.ultranet/BiologyPages/
E/ExcitableCells.html
Skyship