PSL201Y1 Lecture Notes - Extracellular Fluid, Axon Terminal, Signal Transduction
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5 CHEMICAL MESSENGERS
Mechanisms of Intercellular Communication
DIRECT COMMUNICATION THROUGH GAP JUNCTIONS
Gap junctions link adjacent cells, and are formed by plasma membrane proteins, called
connexins, that form structures called connexons.
The movement of ions through gap junctions electrically couples the cells, such that electrical
signals in one cell are directly transmitted to the neighboring cells.
INDIRECT COMMUNICATION THROUGH CHEMICAL MESSENGERS
Ligands: chemical messengers, molecules that bind to proteins.
A target cell responds to the chemical messenger because it has certain proteins (receptors).
Signal transduction: the binding of messengers to receptors produces a responds in the target
cell through mechanisms.
The strength of the target cell response increases as the number of bound receptors increases.
Depends on concentration of messengers and receptors.
FUNCTIONAL CLASSIFICATION OF CHEMICAL MESSENGERS
Paracrine: chemicals that communicate with neighboring cells. Reach target cell by simple
diffusion; i.e. growth factors, clotting factors, and cytokines.
Growth factors: proteins that stimulate proliferation and differentiation.
Clotting factors: proteins that stimulate formation of a blood cot.
Cytokines: peptides, released from immune cells that function in coordinating the body’s defense
Autocrines: subclass of paracines that act on the same cell that secreted them.
Neurotransmitters: chemicals released into the interstitial fluid from nervous system cells called
neurons. Released from the axon terminal, which is closed to the target cell.
The juncture between the two cells is called a synapse, communication by neurotransmitters is
called synaptic signaling.
Presynaptic neuron: the cell that releases the neurotransmitter. Postsynaptic cell: the target cell.
Hormones: chemicals released from endocrine glands into the interstitial fluid., where they
diffuse into blood.
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