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Chapter 6
Communication, Integration, & Homeostasis
55
Physiology
Undergraduate 3
09/08/2015

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Term
electrical signals
Definition
changes in a cell's membrane potential
Term
chemical signals
Definition
molecules secreted by cells into the ECF
Term
target cells/targets
Definition
cells that respond to electrical or chemical signals
Term
3 types of local communication
Definition
1. gap junctions (direct cytoplasmic transfer of electrical & chemical signals between adjacent cells)
2. contact-dependent signals (surface molecules on one cell membrane bind to surface molecules on another cell's membrane)
3. chemicals that diffuse through the ECF to act on cells close by
Term
long-distance communication
Definition
uses a combination of chemical & electrical signals carried by nerve cells & chemical signals transported in the blood
Term
cell adhesion molecules/CAMs
Definition
first known for cell-to-cell adhesion, now known to act as receptors in cell-to-cell signaling; linked to the cytoskeleton or intracellular enzymes; transfer signals in both directions across cell membranes
Term
paracrine signal
Definition
acts on cells in the immediate vicinity of the cell that secreted the signal
Term
autocrine signal
Definition
a chemical signal that acts on the cell that secreted it
Term
hormones
Definition
chemical signals that are secreted into the blood & distributed all over the body by the circulation; how the endocrine system communicates
Term
neurocrine molecules
Definition
chemicals secreted by neurons
Term
neurotransmitter
Definition
a neurocrine molecule that diffuses from the neuron across a narrow extracellular space to a target cell & has a rapid-onset effect
Term
neuromodulator
Definition
a neurocrine that acts more slowly as an autocrine or paracrine signal
Term
neurohormone
Definition
a neurocrine molecule that diffuses into the blood for body-wide distribution
Term
A cell can respond to a particular chemical signal only if the cell _____
Definition
has the appropriate receptor protein to bind that signal
Term
4 features shared by all signal pathways
Definition
1. the signal molecule is a ligand that binds to a protein receptor
2. ligand-receptor binding activates the receptor
3. the receptor in turn activates one or more intracellular signal molecules
4. the last signal molecule in the pathway creates a response by modifying existing proteins or initiating the synthesis of new proteins
Term
signal transduction
Definition
the process by which an extracellular signal molecule activates a membrane receptor that in turn alters intracellular molecules that create a response
Term
transducer
Definition
a devices that converts a signal from one form into a different form
Term
3 steps of biological signal transduction
Definition
1. an extracellular molecule binds to & activates a membrane receptor
2. the activated membrane receptor turns on its associated proteins & starts an intracellular cascade of second messengers
3. the last second messenger in the cascade acts on intracellular targets to create a response
Term
2 things that membrane receptors & their associated proteins can do
Definition
1. activate protein kinases (enzymes that transfer a phosphate group from ATP to a protein)
2. activate amplifier enzymes that create intracellular second messengers
Term
3 things second messenger molecules can do
Definition
1. alter the gating of ion channels
2. increase intracellular calcium
3. change enzyme activity, especially of protein kinases or protein phosphatases (enzymes that remove a phosphate group)
Term
The steps of a signal transduction pathway form a _____
Definition
cascade
Term
signal amplification
Definition
turning one signal molecule into multiple second messenger molecules
Term
amplifier enzyme
Definition
turned on by the receptor-ligand complex; activates several molecules which in turn each activate several more molecules as the cascade proceeds
Term
The activation of _____ initiates the most rapid intracellular responses of all receptors
Definition
receptor-channels
Term
The _____ are a large & complex family of membrane-spanning proteins that cross the phospholipid bilayer 7 times
Definition
G protein-coupled receptors (GPCRs)
Term
G protein
Definition
a three-part membrane molecule to which the cytoplasmic tail of GPCRs are linked
Term
What was the first identified signal transduction pathway?
Definition
G protein-coupled adenylyl cyclase-cAMP system
Term
phospholipase C (PLC)
Definition
converts a membrane phospholipid into two lipid-derived second messenger molecules (diacylglycerol & inositol triphosphate) when a signal molecule activates the "phospholipase C" G-protein coupled pathway
Term
diacylglycerol (DAG)
Definition
a nonpolar diglyceride that remains in the lipid portion of the membrane & interacts with protein kinase C (PKC)
Term
protein kinase C (PKC)
Definition
a Ca2+-activated enzyme associated with the cytoplasmic face of the cell membrane
Term
inositol triphosphate (IP3)
Definition
a water-soluble messenger molecule that leaves the membrane & enters the cytoplasm
Term
2 regions on a receptor-enzyme
Definition
1. a receptor region on the extracellular side of the cell membrane
2. an enzyme region on the cytoplasmic side
Term
Guanylyl cyclase is the amplifier enzyme that converts GTP to _____
Definition
cyclic GMP (cGMP)
Term
4 types of modified proteins that control cell responses
Definition
1. metabolic enzymes
2. motor proteins for muscle contraction & cytoskeletal movement
3. proteins that regulate gene activity & protein synthesis
4. membrane transport & receptor proteins
Term
5 types of calcium-dependent events that occur in the cell
Definition
1. Ca2+ binds to the protein calmodulin
2. calcium binds to other regulator proteins & alters movement of contractile or cytoskeletal proteins such as microtubules
3. Ca2+ binds to regulatory proteins to trigger exocytosis of secretory vesicles
4. Ca2+ binds directly to ion channels to alter their gating state
5. Ca2+ entry into a fertilized egg initiates development of the embryo
Term
The best-known gaseous signaling molecule is _____
Definition
nitric oxide (NO)
Term
_____, a gas known mostly for its toxic effects, is also a signal molecule produced in minute amounts by certain cells
Definition
carbon monoxide (CO)
Term
The newest gaseous signal molecule to be described is _____
Definition
hydrogen sulfide (H2S)
Term
phospholipase A2 (PLA2)
Definition
an enzyme that produces arachidonic acid from membrane phospholipids
Term
2 major groups of arachidonic acid-derived paracrine molecules
Definition
1. leukotrienes (produced by the action of the enzyme lipoxygenase on arachidonic acid)
2. prostanoids (produced when the enzyme cyclooxygenase acts on arachidonic acid)
Term
2 types of prostanoids
Definition
1. prostaglandins
2. thromboxanes
Term
agonist
Definition
a competing ligand to a primary ligand that binds & elicits a response
Term
antagonist
Definition
a competing ligand to a primary ligand that binds & blocks receptor activity
Term
down-regulation
Definition
a decrease in receptor number
Term
up-regulation
Definition
when the target cell inserts more receptors into its membrane
Term
Cannon's 4 postulates
Definition
1. the nervous system has a role in preserving the "fitness" of the internal environment
2. some systems of the body are under tonic control
3. some systems of the body are under antagonistic control
4. one chemical signal can have different effects in different tissues
Term
parameter
Definition
a regulated variable
Term
stimulus
Definition
the disturbance or change that sets the reflex pathway in motion
Term
sensor
Definition
AKA sensory receptor; continuously monitors its environment for a particular variable
Term
When activated by a change, the sensor sends an _____ to the integrating center for the reflex
Definition
input (afferent) signal
Term
integrating center
Definition
part of a reflex pathway that compares the input signal with the setpoint
Term
setpoint
Definition
the desired value of a given variable
Term
output (efferent) signal
Definition
an electrical and/or chemical signal that travels to the target
Term
target/effector
Definition
the cell or tissue that carries out the appropriate response to bring the variable back within normal limits
Term
threshold
Definition
the minimum stimulus needed to set the reflex response in motion
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