Section 9.2 ~ Summary

There are two ways in which cell communication occurs: 1. Intercellular signaling: between many cells

1. Intracellular signaling: within a singular cell

There are four main types of chemical signaling, differing in the relative distance of the signal cell to the target cell (Figure 9.2).

i. Autocrine: signaling cell & target cell are the same

ii. Across gap junction: signal between two connected cells * fastest signaling method

iii. Paracrine: signal between two nearby cells

iv. Endocrine: signal between cells at further distances using the bloodstream * slowest signaling method

Signals are transmitted through the interaction and subsequent binding of ligand molecules to receptors.

There are two types of cell receptors:

i. Internal: found within cytoplasm of cell<br /> * ligands bind inside cytoplasm * binds hydrophobic ligands (Figure 9.3)

ii. Cell-surface: integral proteins * ligands bind on surface * binds hydrophilic ligands

Cell-surface receptors can be further classified into three categories:

i. Ion channel-linked: binding of a ligand triggers the opening of a channel allowing for ion movement (Figure 9.5)

ii. G-protein-linked: the binding of a ligand activates g-protein (Figure 9.6) * g-protein activation opens ion channels or activates enzymes

iii. Enzyme-linked: the binding of a ligand activates an enzyme, triggering a cell response (Figure 9.7)

There are three types of ligands are explored within this section. Small hydrophobic (e.g. steroids, vitamin D) ligands are non-polar and bind to internal receptors. Water-soluble (e.g. peptides, proteins) ligands are polar and bind to cell-surface receptors. Nitric Oxide (NO) is a hydrophobic gas that binds to internal receptors in smooth muscle.

Work Cited

Hinic-Frlog, S., Hanley, J. and Laughton, S. (2020). Introductory Animal Physiology. Missausgua, CA: Pressbooks.

9.2 Key Concepts

Chemical Signaling: * Intracellular vs. Intercellular * types of chemical signaling

Receptors: * internal vs. surface-cell * categories of surface-cell receptors

Ligand Molecules: * hydrophobic * water-soluble * nitric oxide (NO)

Work Cited

Hinic-Frlog, S., Hanley, J. and Laughton, S. (2020). Introductory Animal Physiology. Missausgua, CA: Pressbooks.

Practise Question

Which of the following events does not occur after the binding of a ligand to an ion channel-linked receptor?

i. conformational change of the receptor

ii. movement of specific ions through the membrane

iii. closing of gated-ion channels

iv. all answers are correct

Answer: iii

Ligand binding to an ion channel-linked receptor triggers a conformational change in the receptor, leading to the opening of a gated-ion channel and allowing for the movement of ions through the membrane.

Work Cited

Hinic-Frlog, S., Hanley, J. and Laughton, S. (2020). Introductory Animal Physiology. Missausgua, CA: Pressbooks.

Practise Question

Recent experimentation has noted that gap junctions play a significant role in cardiac conduction. Identify and explain a potential reason why signaling across gap junctions is favoured within the heart.

Answer:

Signaling across gap junctions would be favoured in the heart because it is the fastest of the four chemical signaling types. Important signals will be able to travel from the signal cell to the target cell quickly, initiating a faster response.

Works Cited

Hinic-Frlog, S., Hanley, J. and Laughton, S. (2020). Introductory Animal Physiology. Missausgua, CA: Pressbooks.

Lo, C. W. (2000). Role of gap junctions in cardiac conduction and development: insights from the connexin knockout mice. Circ. Res. 87, 346–348.