Human Physiology-Chapter 6 (Cell Communication, Integration, and Homeostasis)

Gap junctions

form direct cytoplasmic connections between adjacent cells

Contact-dependent signals

require interaction between membrane molecules on two cells

Autocrine signals

act on the same cell that secretes them

Paracrine signals

are secreted by one cell and diffuse to adjacent cells

Long-distance signaling

may be electrical signals passing along neurons or chemical signals that travel through the circulatory system

Endocrine system

hormones are secreted by endocrine glands or cells into the blood. only target cells with receptors for the hormone respond to the signal

Nervous system (2)

-neurotransmitters: are chemicals secreted by neurons that diffuse across a small gap to the target cell

-neurohormones: are chemicals released by neurons into the blood for action at distant targets.

Lipophilic signal receptors

diffuse through the cell membrane -> binding to cytosolic or nuclear receptor triggers -> slower responses related to changes in gene activity

Extracellular signal molecule

binds to a cell membrane receptor -> binding triggers -> rapid cellular responses

4 Categories of membrane receptors

1. receptor-channel

2. G protein-coupled receptor

3. receptor-enzyme

4. integrin receptor

Receptor-Channel

ligand binding opens or closes the channel

G protein-coupled receptor

ligand binding to a G protein-coupled receptor opens an ion channel or alters enzyme activity

Receptor-enzyme

ligand binding to a receptor-enzyme activates an intracellular enzyme

Integrin receptor

ligand binding to integrin receptors alters enzymes or the cytoskeleton

Basic Signal Transduction

signal molecule > binds to membrane receptor protein > activates intracellular signal molecules > alter target proteins > create response

Signal transduction pathways form a...?

cascade

What does signal amplification allow?

Allows a small amount of signal to have a large effect.

Reflex steps

stimulus, sensor, input signal, integrating center, output signal, target, response