Intracellular signalling refers to the communication between cells using signalling molecules and cellular pathways.
These signals allow cells to respond to their environment and coordinate their functions.
There are several forms of intracellular signalling, which can be classified based on the mode of signal transmission:
1. Contact-dependent signalling:
In this form of signalling, the signalling molecule remains attached to the surface of the signalling cell and directly interacts with receptors on the surface of the target cell.
This requires physical contact between the two cells, and the signal typically affects only the adjacent cells.
Examples of contact-dependent signalling include Notch-Delta signalling, which plays a crucial role in cell differentiation and development, and interactions between immune cells and their target cells.
2. Paracrine signalling:
In paracrine signalling, the signalling cell releases signalling molecules, such as growth factors or cytokines, which diffuse over a short distance through the extracellular space to affect neighbouring cells in close proximity.
The signalling molecules are often rapidly degraded or taken up by nearby cells, limiting their range of action.
Paracrine signalling plays essential roles in processes like wound healing, inflammation, and tissue repair.
3. Synaptic signalling:
Synaptic signalling is a specialized form of paracrine signalling that occurs at synapses between neurons in the nervous system.
When an electrical signal (action potential) reaches the synapse, neurotransmitter molecules are released from the presynaptic neuron and diffuse across the synaptic cleft.
These neurotransmitters bind to specific receptors on the postsynaptic neuron, either triggering or inhibiting an action potential in the target cell.
This precise, rapid form of signalling allows for the efficient transmission of information within the nervous system.
4. Endocrine signalling:
Endocrine signalling involves the release of hormones by specialized endocrine cells or glands into the bloodstream.
These hormones travel long distances through the circulatory system to reach their target cells, which may be located in distant parts of the body.
Hormone receptors are highly specific, ensuring that only the appropriate target cells respond to a particular hormone.
Endocrine signalling plays a crucial role in regulating various physiological processes, such as metabolism, growth, development, and reproduction.