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22 Cards in this Set

  • Front
  • Back
What are phasic and tonic receptors?
phasic - rapidly adapting
tonic - slowly adapting
What are the relative merits of phasic versus tonic receptors?
Adapting rapidly requires less energy than slowly adapting and continuing to analyze needless information.
Are somatosensory receptors actually neurons?
Do somatosensory receptors have dendrites?
Where are the cell bodies for somatosensory receptors and where do they make synapses?
Cell bodies are in the dorsal root ganglion. The first synapse is made by the terminals of the centrally projecting axons of dorsal root ganglion cells onto neurons in the brainstem nuclei (gracile and cuneate). The axons of these second-order neurons synapse on third-order neurons of the ventral posterior nuclear complex of the thalamus, which in turn send their axons to the primary somatic sensory cortex.
What are the main somatosensory sub modalities?
Mechanoreceptors, Thermoreceptors, Nociceptors, Proprioceptors
What form of chemical communication acts over a longer range than synaptic transmission and involves the secretion of chemical signals onto a group of nearby target cells?
paracrine signaling
Which form of chemical communication refers to the secretion of hormones into the bloodstream where they can affect targets throughout the body?
endocrine signaling
Chemical signaling of any sort requires what three components?
a molecular signal that transmits information from one cell to another, a receptor molecule that transduces the information provided by the signal, and a target molecule that mediates the cellular response
What part of chemical signaling takes place within the confines of the target cell?
intracellular signal transduction
Why does signal amplification occur?
Individual signaling reactions can produce a large number of products.
What does having multiple levels of molecular interactions facilitate?
The timing of returning the signal cascade to subthreshold values before the arrival of another stimulus and keeping the intermediates in a signaling pathway activated for a sustained response.
What three classes can signaling molecules be grouped into?
Cell-impermeant, cell-permeant, and cell-associated signaling molecules.
What are cell-impermeant signaling molecules?
Cell-impermeant signaling molecules typically bind to receptors associated with cell membranes. Hundreds of secreted molecules have now been identified, including the neurotransmitters discussed in Chapter 6, as well as proteins such as neurotrophic factors (see Chapter 23), and peptide hormones such as glucagon, insulin, and various reproductive hormones. These signaling molecules are typically short-lived, either because they are rapidly metabolized or because they are internalized by endocytosis once bound to their receptors.
What are cell-permeant signaling molecules?
Cell-permeant signaling molecules can cross the plasma membrane to directly act on receptors that are inside the cell. Examples include numerous steroid (glucocorticoids, estradiol, and testosterone) and thyroid (thyroxin) hormones, and retinoids. These signaling molecules are relatively insoluble in aqueous solutions and are often transported in blood and other extracellular fluids by binding to specific carrier proteins. In this form, they may persist in the bloodstream for hours or even days.
What are cell-associated signaling molecules?
Cell-associated signaling molecules are arrayed on the extracellular side of the plasma membrane. These molecules act only on cells physically in contact with the cell possessing such signals. Examples include proteins such as the integrins and neural cell adhesion molecules (NCAMs) that influence axonal growth (see Chapter 23). Membrane-bound signaling molecules are more difficult to study, but are clearly important in neuronal development and other circumstances where physical contact between cells provides information about cellular link
What are the three types of cell-impermeant molecule receptors?
Channel-linked receptors, enzyme-linked receptors, and G-protein linked receptors.
What are channel-linked receptors?
Channel-linked receptors (also called ligand-gated ion channels) have the receptor and transducing functions as part of the same protein molecule. Interaction of the chemical signal with the binding site of the receptor causes the opening or closing of an ion channel pore in another part of the same molecule. The resulting ion flux changes the membrane potential of the target cell and, in some cases, can also lead to entry of Ca2+ ions that serve as a second messenger signal within the cell.
What are enzyme-linked receptors?
Enzyme-linked receptors also have an extracellular binding site for chemical signals. The intracellular domain of such receptors is an enzyme whose catalytic activity is regulated by the binding of an extracellular signal. The great majority of these receptors are protein kinases, often tyrosine kinases, that phosphorylate intracellular target proteins, thereby changing the physiological function of the target cells. Noteworthy members of this group of receptors include the Trk family of neurotrophin receptors and other receptors for growth factors.
What are G-protein linked receptors?
G-protein-coupled receptors regulate intracellular reactions by an indirect mechanism involving an intermediate transducing molecule, called the GTP-binding proteins (or G-proteins). Because these receptors all share the structural feature of crossing the plasma membrane seven times, they are also referred to as 7-transmembrane receptors (or metabotropic receptors). Hundreds of different G-protein-linked receptors have been identified. Well-known examples include the β-adrenergic receptor, the muscarininc type of acetylcholine receptor, metabotropic glutamate receptors, receptors for odorants in the olfactory system, and many types of receptors for peptide hormones. Rhodopsin, a light-sensitive 7-transmembrane protein in retinal photoreceptors, is another form of G-protein-linked receptor.
How do intracellular receptors work?
Intracellular receptors are activated by cell-permeant or lipophilic signaling molecules. Many of these receptors lead to the activation of signaling cascades that produce new mRNA and protein within the target cell. Often such receptors comprise a receptor protein bound to an inhibitory protein complex. When the signaling molecule binds to the receptor, the inhibitory complex dissociates to expose a DNA-binding domain on the receptor. This activated form of the receptor can then move into the nucleus and directly interact with nuclear DNA, resulting in altered transcription. Some intracellular receptors are located primarily in the cytoplasm, while others are in the nucleus. In either case, once these receptors are activated they can affect gene expression by altering DNA transcription.
What is the difference between heterotrimeric G-proteins and monomeric G-proteins?
Heterotrimeric G-proteins are composed of three distinct subunits (α, β, and γ) and monomeric G-proteins are one molecule.