Cell-to-cell communication

Electrical signals

• changes in cell’s membrane potential

→ caused by ion flux —flow—(ex: depolarization, hyperpolarization, repolarization

Chemical signals

• molecules secreted by cells into the extracellular fluid

→ active process of secretion: exocytosis

What do we call the cells that create and release these signals to communicate information?

• They are called “signal generators”

• they control the function of other cells in he body

→ typically neurons, endocrine cells, or immune cells

What do we call the cells that receive or respond to these signals

• They are called “target cells”

• These could be any cell in your body that performs an action (ex: skeletal muscle cells, cardiac muscle cells, glandular cells, etc)

LOCAL cell to cell communication: Gap junctions

form direct cytoplasmic connections between adjacent cells

• NOT channels

• the fastest form of cell-to-cell communication, they work simultaneously

• There is a physical connection between the cytosol of adjacent cells through complexes of membrane-spanning proteins called connexins

• There can be a transfer of chemical and/or electrical connected cells

LOCAL cell to cell communication: Contact dependent signals

require interaction between membrane molecules on two cells

• via Cell-adhesion molecules (CAMs)

• Surface molecules on one bind to protein receptors on the other

• Transfers signals in both directions

→ both cells will change function in a specific way

~cells “kiss" and then go opposite directions lol

LOCAL cell to cell communication: Autocrine signals + Paracrine signals

Autocrine signals (“auto” = self)

• act on the same cell that secreted them

Paracrine signals (“para” = beside or nearby

• are secreted by one cell and diffuse to adjacent cells

→ Cells can also secrete signal molecules by exocytosis to affect the function of target cells

→ Paracrine and autocrine signal molecules exist throughout the body

LONG-DISTANCE cell-to-cell communication: Hormones

• released by specialized endocrine cells/glands

• Travel through blood to distant target cells

→ Target cell has receptor for the hormone

→ May take some time to get there; typically mediate slow changes in body function

LONG-DISTANCE cell-to-cell communication: Cytokines

are very similar to hormones, but since they are also released into the blood, but….

• They are made on demand (NOT stored in vesicles, like hormones)

• They are NOT released from specialized cells. Cytokines can be produced in and secreted from ANY nucleated cell in the body

LONG-DISTANCE cell-to-cell communication: Neurotransmitters (NT) and Neuromodulators

• released from an axon terminal of a neuron into a synaptic cleft

• Cross synapse to its target cell (only a few nanometers away)

→ Neurotransmitters (NT): have a very fast effect on the target cell’s function

→ Neuromodulators (NM): lead to longer-term changes inn target cell function

• Narrow synaptic cleft and length of axon allows for very fast, long-distance communication (ex: spinal cord to/from arm or leg muscles)

LONG-DISTANCE cell-to-cell communication: Neurohormone

• Longer distance, but slower than a NT or NM

→ Neuro = from neuron

→ hormone = signal molecule released into the blood

• binds to target cells with specific receptors and changes their function in specific ways