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ap bio


study guide


Unit 4

4.1 Cell Communication






written by

Annika Tekumulla

annika tekumulla

published on march 30, 2020

Last updated on July 1, 2020

available on hyper typer

The cells in your body communicate in many different ways. Cells must communicate with each other and the environment in order to complete tasks. They communicate through chemical signals. These signals are usually proteins. Multicellular organisms have trillions of cells that communicate in the following ways. 

Direct Contact

Direct contact is also called juxtacrine signaling. Direct contact occurs when the 2 cells are adjacent to another and occur in both plant and animal cells. In plant cells, the plasmodesmata connect one plant cell to another. In animal cells, gap junctions directly connect the cytoplasm of one animal cell to the cytoplasm of another animal cell. These junctions allow the passage of materials such as ions, signals, and molecules.

Memory Tip: Think of direct contact like a handshake because both people must have direct contact with each other during a handshake!

Image courtesy of Giphy.

Paracrine Signaling


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Another way that cells communicate is through paracrine signaling

Paracrine signaling is communication over short distances. Cell sends out signals to nearby cells which causes a change in the behavior of nearby cells. An example of paracrine signaling is contracting muscles. Chemical signals are sent from the nerve to the muscle. This causes the response of changes in the behavior of muscle so that the muscle contracts.

Memory Tip: Think of paracrine signaling as crossing the street. Crossing the street is a short distance and helps me remember that paracrine signaling is between nearby cells. Takes the “right down the street” phrase into a new perspective!

Image courtesy of Giphy.

Synaptic Signaling

Finally, there is synaptic signaling. Synaptic signaling involves a synapse which is the gap between 2 nerve cells. 

Signaling occurs when a neuron releases a neurotransmitter. Then, the neurotransmitter moves across the synapse. After it reaches the end of the gap, the neurotransmitter stimulates the adjacent neuron to fire.

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