This document contains a summary of the lecture 5 and book of the course the adaptive brain. This summary is about chapter 7 in the book Neuroscience by Purves.
Molecular signalling within neurons chapter 7
Learning objectives: Cellular receptors
• Know how extracellular chemical signals work via different Cellular responses are determined by the presence of receptors
receptor classes that each initiate specific intracellular signalling that specifically bind to the signalling molecules. The binding of
pathways signal molecules causes a conformational change in the receptor
• Know the molecule life-cycle of different second messenger which triggers a signalling cascade within the cell.
molecules
• Know how intracellular signalling processes induce cellular Categories of cellular receptors:
responses via kinases/phosphatases and changes in gene 1) Channel-linked receptors, are also called ligand-gated ion
transcription channels. The receptor and transducing functions are part of the
same protein molecule. Interaction of the chemical signal with the
Chemical communication coordinates the behaviour of individual binding site of the receptor causes the opening or closing of an
nerve and glial cells in physiological processes that range from ion channel pore in another part of the molecule. This results in
neural differentiation to learning and memory. To carry out the an ion influx that changes the membrane potential of the target
communication a series of complex chemical signalling pathways cell. In some cases, this could lead to the entry of calcium ions
are involved. Chemical communication is not only limited to that serve as a second-messenger signal.
synapses, but also includes paracrine signalling, which acts over a 2) Enzyme-linked receptors also have an extracellular binding site
longer range than synaptic transmission and involves the for chemical signals. The binding of an extracellular signal results
secretion of chemical signals onto a group of nearby target cells, in catalytic activity. Example: protein kinases that phosphorylate
and also endocrine signalling, which refers to the secretion of intracellular target proteins.
hormones into the bloodstream where they can affect targets
throughout the body. Chemical signalling requires 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 an effector molecule that
mediates the cellular response.
3) G-protein coupled receptors, also called metabotropic receptors
regulate intracellular reactions by an indirect mechanism involving
an intermediate transducing molecule. This molecule is called a
Advantages of chemical signalling: GTP-binding protein (G-protein).
1) Amplification of the signal transduction pathways because 4) Intracellular receptors are activated by cell-permeant or
individual signalling reactions can generate a much larger number lipophilic signalling molecules. Many of these receptors lead to the
of molecular products than the number of molecules that initiate activation of signalling cascades that produce new mRNA and
the reaction. protein within the target cell. These receptors contain a receptor
2) Permit precise control of cell behaviour over a wide range of protein bound to an inhibitory protein complex. When the
times. Some molecular interactions allow information to be signalling molecule binds to the receptor, the inhibitory complex
transferred rapidly while others are slower and longer lasting. dissociates to expose a DNA-binding domain on the receptor. The
activated form of the receptor can then move into the nucleus
3 classes of cell signalling molecules and directly interact with nuclear DNA, resulting in altered
Secretion molecules that act on targets further away: transcription.
1) Cell-impermeant molecules, these cannot cross the plasma
membrane, but bind to receptors
2) Cell-permeant molecules, these can cross the plasma
membrane and bind to receptors inside. These molecules can last
for days
Molecules attached to the membrane (physical contact):
3) Cell-associated molecules (cell adhesion molecules that
influence axon growth) Effector pathways associated with G-protein coupled receptors
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