Forms of intracellular signaling

• 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:

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.

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.

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.

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.

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