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22 Cards in this Set

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Transduction of signals

Some kinds of sensory cells can transduce mechanical stimuli to electrical signals which can be conveyed along their surface for rapid spatial relay of the signal. At the end of the cell, the electrical signal is transduced to a chemical signal to convey the signal across the gap between the cells. The post-synaptic cell transduces this chemical signal back to an electrical signal.

Mechanical signals

Mechanical signaling requires close contact of cells and generally occurs through cell junctions. Mechanical force originates on filaments within cells that eventually connect to the extracellular matrix through cytoskeletal elements

Electrical signals

usually used within the cell, as part of a signaling pathway to communicate intracellularly, and most often to move the signal rapidly from one place in the cell to another

Chemical signals

do not require close contact.

contact-dependent signaling

In some cases the signaling molecule remains bound to the cell and so transmission of this signal requires contact between the signaling cell and its target. This is important in development and immune response.


Paracrine signals affect other types of cells located in the neighborhood of the signaling cell.


Autocrine signals have receptors on the signaling cell itself or others like it.


travels through the blood to act on remote targets

neuroendocrine signal

& neurotransmitter

When the neural chemical signal enters the blood and acts on distant targets. When it acts in the vicinity of its release site, it is a neurotransmitter.

The response of cells to signaling events include altered:

ion transport


gene expression or differentiation

shape, movement or force production

cell growth or cell division

Electrical signals and neurotransmitters are fastest; endocrine signals are slowest

Neurotransmitter signaling is the fastest response, followed by changes in cell shape or the development of force. Endocrine signals are slowest but last longer.

The effects of increasing cytoplasmic [Ca2+] include:

1. stimulus-secretion coupling

2. excitation-contraction couplin

3. calmodulin-dependent activation of enzymes

4. direct activation of enzymes

Three major classes of surface-membrane, ligand-gated ion channels have been identified

Pentameric Channels

Tetrameric Channels

Trimeric Channels

Pentameric Channels

acetylcholine, serotonin ( = 5 hydroxy tyrptamine), gamma amino butyric acid (GABA) and glycine all consist of five subunits

Tetrameric Channels


Trimeric Channels


G-protein coupled signaling pathways are versatile because of their modular structure

they consist of receptors, heterotrimeric G-proteins and effectors.

There are four class of G proteins

Gαs, Gαi /Gαo , Gαq and Gα12/Gα13

Beta adrenergic stimulation is an example of a Gαs mechanism

adenyly cyclase, that converts ATP into 3',5'cyclic AMP, or cAMP.

Increasing the concentration of cAMP activates protein kinase A (PKA) that phosphorylates (adds a phosphate to) a number of target proteins.

-cAMP is also broken down by phosphodiesterase (PDE) so that the increased [cAMP] is removed

Alpha2 adrenergic stimulation is an example of a Gαi / Gαo mechanism

Gi = inhibits adenylyl cyclase.

An example is epinephrine binding to α2 receptors on neurons.

Other members of this class achieve the same end - reduction in cAMP levels - by activating phosphodiesterase.

Still other ligands, such as acetylcholine, bind to M2 receptors that cause inhibition of adenyly cyclase and the βγ subunit activates a K+ channel

Gαq / Gα11 GPCR activate phospholipase C and releases Ca from intracellular stores

Activates phospholipase C on the surface membrane, which cleaves phosphatidyl inositol bisphosphate to produce diacylglycerol (DAG) and inositol tripohosphate (IP3). The IP3 releases Ca2+ from the endoplasmic reticulum, while the DAG activates protein kinase C (PKC).

Gα12 / Gα13 coupled receptors activate small monomeric GTPases

They are linked to GTP exchange factors (GEFs) that activate small monomeric G-proteins by exchanging their bound GDP with GTP. A second set of modulatory proteins, called2.8.9GAPs, for GTPase Activating Proteins, facilitate inactivation of these small monomeric GTPases.