A&P I Ch.10 & 12 Excitable Cells Flashcards
(106 cards)
1
Q
Excitability
A
the ability to send and receive electrical signals across the plasma membrane
2
Q
Concentration Gradient
A
difference in concentration of a substance between two compartments
3
Q
What are the ions?
A
-Potassium (K)
-Sodium (Na)
-Chloride (Cl)
-Calcium (Ca)
4
Q
What is the trend of Potassium?
A
higher inside
5
Q
What is the trend of Sodium?
A
higher outside
6
Q
What is the trend of Chloride?
A
higher outside
7
Q
What is the trend of Calcium?
A
higher outside
8
Q
Charge of Potassium
A
+1
9
Q
Charge of Sodium
A
+1
10
Q
Charge of Chloride
A
-1
11
Q
Charge of Calcium
A
+2
12
Q
General equation for calculating concentration gradients
A
Gradient= [Ion]out - [Ion]in
13
Q
What is the gradient of..
[Na+]out= 150mM
[Na+]in= 15mM
A
135mM
14
Q
What is the gradient of..
[Na+]out= 150mM
from: [Na+]in= 15mM to 50mM
A
from: 135mM to 100mM
when inside increases gradient decreases
15
Q
What is the gradient of..
[Na+]out= 150mM
from: [Na+]in= 15mM to 5mM
A
from: 135mM to 145mM
when inside decreases gradient increases
16
Q
What does it mean to move down a concentration gradient?
A
moving from HIGH to LOW concentration
17
Q
What does it mean to move up a concentration gradient?
A
moving from LOW to HIGH concentration
18
Q
Key points about ion channels
A
- Pumps only allow passive transport
-only allow ions to move DOWN their concentration gradient
-flux increases as concentration gradient increases
-active transport occurs via combination of transporters and pumps - Pumps are selective for specific ions
-Na+ channels only allow Na+
19
Q
Voltage-Gated
A
- binding
- gated by change in charge
20
Q
Ligand-Gated
A
- electricity
- gated by chemical messenger
21
Q
What do ion channels do and what are the two types?
A
- Transport ions across a membrane
- Ligand-Gated and Voltage-Gated
22
Q
Relative Concentrations During Homeostasis
A
-the millions of molecules moving across a concentration gradient represent only a TINY fraction of the molecules present in the interstital fluid and cytoplasm
-the concentration of sodium (for example) will ALWAYS be 10 times greater outside the cell than inside
23
Q
What is the relative concentration of a healthy person?
A
the relative concentration of any one ion is CONSTANT
24
Q
Neutral Atom
A
same # of protons and electrons
25
If the atom is negatively charged...
more electrons than protons
26
If the atom is positively charged...
more protons than electrons
27
Electrostatic Forces
-if ions are distributed unevenly across a membrane, then there is uneven distribution of charge across that membrane
-if ions are permeable and being transported across the membrane, then the charge distribution across the membrane is also changing
28
Membrane Potential
a form of potential energy created by a difference in charge between two environments
29
Membrane Potential Across the Plasma Membrane
-When ions move across the membrane, they change the electrochemical gradient
-allows cells to use the stored energy (membrane potential) for critical cellular processes
30
True or False? The concentration gradients for any one ion generally stay constant
True (if you are healthy conc. gradients barely change)
31
The concept of electrochemical equilibrium
-Electrostatic repulsion (flex outward)
-Equilibrium potential (no net flux)
-Concentration gradient (flux inward)
32
Electrostatic Repulsion (flex outward)
eg. Na+ is repulsed by the accumulation of positive charge inside the cell
33
Equilibrium Potential (no net flux)
BALANCE of forces inward versus outward
34
Concentration Gradient (flux inward)
e.g. Na+ flows from high concentration to low
35
Recoil
upward
36
Equilibrium
no movement
37
Gravity
downward
38
Nernest Equation
Eion= 61.5 mV/z * log10 [ion]out/ [ion]in
39
What does the Nernst equation calculate?
the electrochemical equilibrium point
40
What is Eion in the nernst equation?
the equilibrium potential for an ion
41
What is 61.5mV in the nernst equation?
a constant that assumes the cell is at 37 degrees celcius
42
log10[ion]out/ [ion]in
refers to the concentrations of the ion inside and outside of the cell
43
What is "z" in the nernst equation?
charge of the ion
44
Calculate the equilibrium potential of Chloride, when [Cl]out= 136mM and [Cl]in= 45mM
ECl= -29.52mV
45
Aside from constant values, what does the equilibrium potential of a given ion depend on? (What changes in the formula (DV)?)
Concentration of that ion inside and outside of the cell
46
If the concentration gradient is 0 what is the equilibrium potential?
It is also 0 (no concentration gradient -> no equilibrium)
47
True or false? Equilibrium is calculated together with each ion
FALSE; Equilibrium Potential is calculated SEPARATELY for each ion
48
True or false? Ion concentrations are regulated randomly, so equilibrium potentials generally change randomly
FALSE; Ion concentrations are regulated HOMEOSTATICALLY, so equilibrium potentials generally DO NOT change
49
Membrane potential depends on __________ _________
across the membrane
ION PERMEABILITY
50
Although cells are permeable to more than one ion, they are...
not equally permeable
51
What is the movement of ions at resting membrane potential?
the point where the movement of all ions is equal and opposite across the membrane (i.e., the net flux is zero); however, it is not a point where ions have stopped moving
52
At resting membrane potential: Net Flux=
0 (equal in and out)
53
Permeability of an ion increases ---->
Resting membrane potential moves TOWARDS that ion's equilibrium potential
54
Permeability of an ion decreases ---->
Resting membrane potential moves AWAY FROM that ion's equilibrium potential
55
The permeability of sodium were decreased, what would happen to the resting membrane potential?
It would decrease (become more negative)
56
What does the saying, "The Neuron is an excitable cell" mean?
the neuron detects a stimulus and transduces it into an electrical signal
57
Dendrites
- area where we receive signals from
- projections that extrude from the cell body
- site of signal input
-contain mainly ligand-gated channels
58
Axon
-"tail"
-sends signal
-long process extruding from soma
-where action potential travel
-contains voltage-gated channels that respond to local electrical changes
59
Axon Terminal
- distal portion of the axon
- site of signal output
- has synaptic cleft
60
Soma
-cell body
-contains nucleus, organelles, and majority of cytoplasm
61
Axon Hillock
- beginning of axon
- "trigger zone" where action potential is generated
62
What structure do neurons relay messages through?
- Synapses
-pre-synaptic cell
-synaptic cleft
-post-synaptic cell
63
Pre-Synaptic Cell
-neuron located before a synapse
-sends the signal
64
Synaptic Cleft
gap between two cells filled with interstitial fluid
65
Post-Synaptic Cell
-neuron located after a synapse
-receives the signal (receives neurotransmitters through dendrites)
66
Messages are sent as ____________
Neurotransmitters
67
Neurotransmitters
-molecules used by the body to carry signals
68
Popular Neurotransmitters
- Acetylcholine
- Glutamine
- Dopamine
- Serotonin
- Norepinephrine
69
Acetylcholine
responsible for stimulating muscle contraction
70
Neurotransmitters Target Destinations
- other neurons
- muscle cells
- glands
71
Which part of the neuron transmits the electrical signal from one end of the cell to the other?
Axon
72
What are the two major types of changes in membrane potential do neurons produce?
Graded and Action
73
Graded Potential
- produced when a ligand opens a ligand- gated channel in dendrites, allowing ions to enter or exit the cell
- transient change from resting membrane potential
- decreases in intensity over time and distance
74
Depolarization
membrane potential moves from rest to more positive value
75
EPSP
Excitatory Post Synaptic Potential
76
Repolarization
membrane potential moves back to resting value
77
Hyperpolarization
membrane potential moves from rest to a more negative value
78
What is the purpose of hyperpolarization?
-to maintain checks and balances
-gives cell time to rest
79
Graded potentials are ____________
decremental
80
Decremental
- changes in membrane potential are restricted to local area where ions are moving
81
No Summation
weak and unviable
82
Temporal Summation
-short period of time
-many signals received at the same time
83
Spatial Summation
-sent from same location
84
EPSP- IPSP Cancellation
alternating signals being sent out + bump and
- bump
85
Threshold Potential
must be reached for signal to be viable
86
An excitatory post synaptic potential (EPSP) is...
depolarizing (positive)
87
Action Potential always begins with _________
depolarization
88
The depolarization phase is characterized by ________ _________ ________
Rapid Sodium Entry
89
Rapid Sodium Entry
always begin with opening sodium channels so Sodium floods the cell which makes the cell more positive and voltage "shoots up"
90
What does a closed odium channel mean?
Resting
91
What does an opening sodium channel mean?
Subthreshold
92
What does an open sodium channel mean?
Depolarization
93
What does an inactivated sodium channel mean?
Repolarization
94
The Repolarization phase is accelerated by _______ _______
Potassium Efflux
95
Repolarization Phase
voltage gated potassium channels reach peak permeability
96
Hyperpolarization on Phase
- potassium channels still open
- inactivation gate on sodium channels opens
- relative refractory period- cell is hyper polarized, so requires greater stimulus to reach threshold
97
After- Hyperpolarization on Phase
- all channels close off
- potassium permeability reduced
- membrane potential goes back to resting value
98
True or False? Open sodium channels accelerate the repolarization phase of an action potential.
FALSE: Open potassium channels accelerate the repolarization phase of an action potential.
OR: Open sodium channels accelerate the depolarization phase of an action potential.
99
Action Potential Propagation
Action potential is "recharged" at each axon segment by fresh flow of Na+
100
Factors affecting action potential propagation
- Axon Diameter
- Myelination
101
Axon Diameter
- More space = more sodium channels = more depolarization
- Wider axons= faster action potential propagation
102
Myelination
-put myelin on the axon
-substance that coats (partially electrically insulates) axon
-produced by Schwann cells and oligodendrocytes
103
Nodes of Ranvier
where axons are refreshed
104
Axon Terminals
- goal is to make it to the bottom to open calcium channels
- when the action potential reaches the axon terminal, voltage-gated calcium channels are triggered to open, allowing calcium channels are triggered to open, allowing calcium influx into the axon terminal
-calcium allows membrane-bound vesicles, containing neurotransmitters produced by this neuron, to attach to the post-synaptic membrane and be released into the synapse
- If the post synaptic cell is a neuron, then the process will repeat when the neurotransmitter binds to ligand-gated ion channels on its dendrites
105
Electrical Synpases
-specialized gap junction
-current spreads passively across gap junction
-allows action potential from one cell to move rapidly into another
-avoids delay inherent in chemical synapses
-cannot be modulated
-e.g. cardiac cells
106
Graded Potential V.s. Action Potential
