Cell-to-Cell communication

The human body is composed of ~75 trillion cells

• what are they trying to do? how?

about 60-70 trillion cells trying to live as a single organism

• to do so they must effectively communicate to coordinate function and maintain homeostasis

What are the three main ways of cell-to-cell communication?

1) direct cytoplasmic transfer: contact depended on direct transfer via gap junctions/connexons

2) local communication: through chemicals, NT, and graded potential vis DIFFUSION

3) Local distance signaling: chemicals vis hormones and electrical signals via neurons

1) direct cytoplasmic transfer

• what is it? what moves?

• characteristic of channel

Two cells directly communicating, done with protein channels (gap junctions/connexons). Since it is a channel, small molecules (ions) move through them.

Channels are selective and are regulated by gates (typically single)

2) Local communication

• what does it depend on

• what are some examples?

depends on the DIFFUSION of chemical signals

autocrines, paracrines, neurotransmitter, and graded potentials

Local communication: Autocrine

chemicals secreted by the cell that binds to the receptors of the cell it self (acts on self)

Local communication: Paracrine

Chemicals secreted by one cell and diffuse to neighboring cells, binding onto receptors and acting on them

Local communication: Neurotransmitters

released at the synapses and diffuses to neighboring cells, binding onto receptors and acting on them

• local communication depends on the diffusion of NT across the synaptic cleft

Local communication: Graded potentials

localized electrical event that decays with time and distance

• local communication from dendrites because as ions enter the cell they diffuse to the axon hillock, but decay with time and distance

Local communication: Graded potentials

• example

NT binds to ligand gated channels and open (or close) and ions go into the postsynaptic cells, creating either IPSP or EPSP

Long distance communication:

• what are the two types?

Neural, humoral, and neurohormones

Long distance communication: Humoral

endocrine cell secretes hormones that travel in blood to distant target cell that has receptors

• all cells are exposed to the hormone but ONLY the TARGET cell is affected

Long distance communication: Neural

neurons transmit electrical signals down (long) axons

Long distance communication: Neurohormones

• example

release “NT” that is carried by blood to target cells

• hormones are produced by the hypothalamus and released through neurons in the posterior pituitary as vesicles filled with oxytocin/antidiuretic

All types of communication or interconnected, explain

long distance communication can lead to local communication, and local communication can lead to long distance communication

• it does not have to be just one type

Each type of signal may cause another type of signal?

• explain

• what organ exhibits all?

one organ can doo call communication and one communication can lead to the next in order to synchronize function

• heart exhibits all

Heart exhibits all types of communication

• Local

• Direct cytoplasmic

• Long

SA node generates local graded potentials → local graded potentials can cause cardiac AP → AP is passed between cells via gap junctions (direct)

Heart responds to different autocrines and paracrines like histamine

Heart makes and responds to hormones

Responds to PSNS/SNS fibers

• long distance communication releasing NT, being local communication binding to the receptors, then generating IPSP or EPSP on the heart muscle