Neurophys Midterm 1 Flashcards
(159 cards)
1
Q
Stretching of muscle requires relatively little force until the PRELOAD reaches ___ μ
A
3.2 μ
2
Q
Compare Osmolarity with Tonicity
A
Osmolarity:
- A physiochemical property
- Is a way of expressing [] of particles in a solution
Tonicity:
- Is a property OF a certain solution
- Determines whether it will make a cell shrink, swell, or maintain its original size
3
Q
Water flux measured by diffusion of ______ed _____ (“___”) allows the diffusion coefficient of water to be measured
A
Water flux measured by diffusion of TRITIATED WATER (THO)
allows the diffusion coefficient of water to be measured
4
Q
[Na+] much higher in/outside?
A
Outside
5
Q
The means by which an AP “jumps” from one Node of Ranvier to the next is?
A
via Graded Potentials
6
Q
During an Iso_____ contraction, the muscle develops FORCE and SHORTENS
A
IsoTONIC contraction
7
Q
The distribution of proteins in a phospholipid bilayer is called…?
A
The Fluid Mosaic Model
8
Q
The nerve axon axial resistance (Rax) is much LESS than…?
A
The membrane resistance, Rm
9
Q
What happens to a RBC placed in a solution of 145 mM NaCl (σ<span>NaCl</span> = .9)?
A
ISOTONIC
(2 x 145= 290 mM)
10
Q
The gates of which channels (Na+ or K+) open faster?
A
Because K+ channel’s “N“gates OPEN MUCH MORE SLOWLY
than Na+ channel’s “M” gates
Thus, Na+ channels are open before the K+ channels are
11
Q
The density of capillaries in a tissue is dependent on what?
Give 2 examples
A
…the metabolic rate of the tissues
- Metabolic rate in heart is HIGH, therefore TONS of capillaries in myocardium
- Metabolic rate in SK muscle is LOW, therefore LOW density of capillaries
12
Q
What is the take-home message of the Time Course of Diffusion (the “Einstein relationship”)?
A
Diffusion is a FAST process over SHORT distances
Diffusion is a SLOW process over LONG distances
When a substance diffuses, the distance is NOT a LINEAR function of time
13
Q
In an Isotonic contraction, the load lifted by the muscle when it shortens is called the…?
A
“Afterload”
14
Q
What could happen if the membrane were impaired?
A
Equilibrium would be lost
Cell could BURST
15
Q
To what point do Graded Potentials have to depolarize the membrane above in order to generate an AP?
aka what is the Threshold Voltage?
A
Above -55 mV
16
Q
Graded Potentials: Describe EPSPs
A
Excitatory Postsynaptic Potential (EPSP)
Is the DE-polarization of a Graded Potential on the the post-synaptic membrane
17
Q
Define ELECTROLYTES
A
= Substances that dissociate into cations (+) and anions (-) when they dissolve in water
18
Q
What causes HYPERpolarization to occur?
A
K+ channels are open as long as the membrane is depolarized
Once membrane hits resting potential, K+ channels start to close, but do so SLOWLY
The extra K+ ions that sneak in before it closes cause the “undershoot“
When Na gate opens, K+ flows OUT of the cell, hyperpolarizing the membrane BACK to its resting potential
19
Q
The inside of the cell is usually ______ in relation to the outside
A
NEGATIVE
Inside (-)
Outside (+)
20
Q
Most cells are within ___μM of a capillary
A
100μM
21
Q
Increased stiffness of proteins like Titin & Nebulin helps, at high preloads, to prevent what?
A
Muscle overstretching
22
Q
Time course of diffusion (Einstein relationship) explains why animals require…?
A
a circulatory system
(diffusion is too slow over long distances)
23
Q
The duration of a “twitch” is greater than the duration of …?
A
An AP
24
Q
During an AP, the membrane potential in a neuron, Em, will always be between which two values?
A
Between -90mV and +60mV
25
_Ohm's Law during an AP_
\*Remember: During an AP, the cell is **_NOT_** in what?
**IK + INa ≠ ?**
NOT in **"steady state"**
**IK + INa ≠ 0**
26
Differentiate:
**Channel** proteins vs **Carrier** proteins
_**CHANNEL** proteins:_
* Create a water-filled **pore**
* Form an open "channel" b/t the two sides of the membrane
_**CARRIER** proteins:_
* **_NEVER_ FORM AN OPEN CHANNEL** b/t both sides of the membrane!!
27
What happens that causes the Na channel to **inactivate**?
**H gate closes**
| (Na channel is closed)
28
What is the typical Resting Membrane potential **NOT** equal to?
Resting membrane potential **(-70 mV)** is **NOT** equal to:
## Footnote
**EK or ENa**
29
If a solute (e.g. sucrose) is **IMPERMEABLE** to the cell membrane, ie σ = 1.0 :
## Footnote
*A solution that is **_hypo-osmotic_** to the cell contents will be...?*
**HYPOTONIC**
30
Formula for Fick's Law of Diffusion (**_WITH_** partitioning)
**J = Kp ⋅ D ⋅ ΔC / Δx**
* J = Flux
* Kp = partition coeff.
* ΔC = [] difference, C1-C2
* Δx = membrane thickness, usually 7.5nm
* D = diffusion coeff
31
Ions, **such as \_\_, \_\_, and \_\_,** can NOT diffuse through the plasma membrane
**Cl-, K+, Na+**
32
What are 3 common types of **Aquaporins**, and where are they found?
* AQP**1***
* AQP**4***
* AQP**9***
Found in the **_BRAIN_**
33
What happens to a RBC placed in a solution of **290 mM sucrose?**
## Footnote
**σsucrose = 1**
**Isotonic**
| (no net mvmt)
34
Van't Hoff formula for a **SINGLE** solution = ?
Solutions of **higher []** have higher/lower Posmotic?
**Δπ = nRTC**
(just using **"C"** instead of "ΔC")
∴ solutions of **HIGHER []** have **HIGHER Posmotic**
35
The brain has no ________ system, therefore **brain edema fluid** is eliminated how?
No **_LYMPHATIC_** system
Eliminated into the ventricular **CSF** and **through the BBB**
36
pH in ECF = ?
7.4
37
Define **"Eion"**
The membrane potential (Em) at which the sum of the **electrical** and **chemical** forces on an ion is **zero**
The Nernst equation solves for Eion
38
\_\_\_\_\_\_ potentials:
Depolarizations or hyperpolarizations whose
***Strength is proportional to the strength of the triggering event***
**Graded** potentials
| (not the case in AP's)
39
**INCREASED** _Unsaturated_ FA's = \_\_\_\_\_\_\_\_ed membrane **fluidity**
= **Increased** membrane fluidity
| (due to kinks in HC tail)
40
What type of fluid (hyper-, hypo-. hyper-) could **reduce the swelling** of the brain following traumatic injury?
**HYPERTONIC** fluid
41
*Strength-duration curve:*
What is the **Rheobase?**
The minimum **current** , ***I***, that can cause an AP
42
Large, UNcharged polar molecules, **such as _____ and \_\_\_\_\_,** can NOT diffuse across the membrane
**Glucose, Sucrose**
43
*Strength-duration curve:*
What is the **Chronaxie?**
The minimum stimulus **TIME**, T, that will cause an AP
## Footnote
*...using a current **2X** the value of the rheobase*
44
[K+] in ECF = ?
4 mM
45
In Iso**metric** contractions, contractions produced by successive \_\_\_\_'s can \_\_\_\_\_\_
contractions produced by **successive AP's** can **summate**
46
Resting membrane potential is a _____ state, but **NOT** an _______ state
Why is this?
_Resting membrane potential is a **STEADY** state, but **NOT** an **EQUILIBRIUM** state_
This is bc the cell can **only** remain at resting membrane potential because the **Na+/K+ pump is running** (this requires **energy!!!**)
*Hence, this is a steady state, **not** an equilibrium*
47
What's the main difference b/t a **PORE** and a **CHANNEL?**
Pores **AREN'T** regulated
Channels **ARE** regulated
48
If a solute (e.g. sucrose) is **IMPERMEABLE** to the cell membrane, ie σ = 1.0 :
## Footnote
*A solution that is **_isosmotic_** to the cell contents will be...?*
**ISOTONIC**
49
Describe **[] difference, ΔC, diffusion, and voltage difference, Em,** across the cell when:
## Footnote
*Cell (below) is **IMPERMEABLE** to both K+ and Cl-*
No [] difference, **ΔC = 0**
No diffusion of K+ **OR** Cl-
No potential (voltage) difference, **Em = 0**
50
During an Iso**TONIC** contraction, the ***_VELOCITY_*** of shortening is **inversely proportional** to what?
Inversely proportional to the **AFTERLOAD**
51
Both the ECF & ICF are **electrically...?**
...electrically **NEUTRAL**
52
What happens to a RBC placed in a solution of **580 mM sucrose?**
## Footnote
**σsucrose = 1**
**Hypertonic**
(water moves OUT of cell,
cell **shrinks**, ie is "crenated")
53
[K+] much higher **in/outside?**
Inside
54
If a solute (e.g. sucrose) is **IMPERMEABLE** to the cell membrane, ie σ = 1.0 :
## Footnote
*A solution that is **_hyper-osmotic_** to the cell contents will be...?*
**HYPERTONIC**
55
56
What is the **Chord Choductance** equation?
How does it relate to the **Transference** equation?
57
Define **"Tonicity"**
*= the [] of particles in a solution **OUTSIDE** the cell which **CANNOT CROSS** the membrane*
58
Do **ENa & EK change** during an AP?
Why/why not?
**_NO_**
## Footnote
*...because the number of ions which move are **so small** that **NO** concentration change can be detected*
59
The force produced during an Iso**metric** contraction (also) depends on the **# of what?**
Depends on the **# of muscle fibers activated**
60
A solution with **LESSER** osmolarity than another is said to be...?
"**Hypo**-osmolar"
61
What causes **potassium conductance, gK,** to change during an AP?
Changes because of **movement of the N gate**
62
When the Na channel is **closed and _NOT_ available for activation**,
what has to happen to make it **AVAILABLE** for activation?
What happens after that?
Membrane potential must **return to about -80 mV**
Then, **M** gate **closes**, and **H** gate **opens**
* Now, channel is **STILL CLOSED**, but **AVAILABLE** for activation*
* (same state it was in before the AP arrived)*
63
**TNa + TK = ?**
***TNa + TK = 1***
64
**gNa** and **gK** DO change during an AP,
therefore what **also** changes?
**TNa and TK**
65
Describe **[] difference, ΔC, diffusion, and voltage difference, Em,** across the cell when:
## Footnote
*Cell is **PERMEABLE to K+** but **_not_** to Cl-*
* [K+] difference exists
* **ΔC = ( .1 - .01) = .09**
* **K+ diffuses OUT of cell**, down [] gradient
* Extra **negative** charges (Cl-) **INSIDE**
* Extra **positive** charges (K+) **OUTSIDE**
* Potential difference forms
* Causes **interior** of cell to become **negative** wrt cell exterior
_EQUILIBRIUM HAS **NOT YET** BEEN REACHED_
66
An Iso**TONIC** contraction consists of what 3 phases?
1. It **contracts isoMETRICALLY**
* Until the force developed is equal to the "Afterload"
2. It **shortens isoTONICALLY**
* At a constant velocity
* Until it shortens as much as possible
3. It **contracts isoMETRICALLY**
* Until it begins to relax
67
On which part of the post-synaptic membrane do Graded Potentials summate?
The **Trigger** Zone
68
In **Diffusion**, how much of the random molecule mvmt is related to **HEAT** in the solution?
**_NONE!_**
69
What happens to a RBC placed in a solution of:
**145** **mM NaCl and 290 mM urea** **(σNaCl = .9 and σurea = .2 )?**
**ISOTONIC**
**(Both ≤ 290 mM)**
70
If there are **NO BARRIERS,** the process of diffusion results in what?
In **equilibrium**
[]s the same everywhere
71
Since **Van't Hoff equation** only solves for osmotic pressure of **IMPERMEABLE** membranes, what happens if you're given a question where the membrane is **PARTIALLY** permeable?
Here, the _actual_ Posmotic will be:
## Footnote
**BETWEEN ZERO & the Posmotic predicted by Van't Hoff's Law**
72
**CHO** composes ~\_\_\_% of all membrane lipid
What does it do to the membrane? (2)
CHO is **~19-50%** of all membrane lipid
## Footnote
1. It **stabilizes** the membrane
2. It **reduces the mobility of complex lipids** in the membrane
73
During an Iso**TONIC** contraction, the ***_AMOUNT_*** of shortening is **inversely proportional** to what?
Inversely proportional to the AFTERLOAD
74
Small, uncharged polar molecules, **such as \_\_\_\_, \_\_\_\_, and \_\_\_\_\_** can diffuse through the membrane
**H2O, Glycerol, Indole**
75
What would the osmolarity of a **.15 M NaCl** solution?
= **.15** \* **2** **molecules** (Na + Cl)
**= ~.3 osm**
76
What causes **excess urination** in diabetics?
***Excess glucose** in renal tubular fluid **DRAWS WATER OUT**,*
*into the tubules, and eventually into the urine*
(Osmotic balance of renal fluids)
77
What happens to a RBC placed in a solution of **145 mM sucrose?**
## Footnote
**σsucrose = 1**
**HypOtonic**
(Cell **swells**, but doesnt burst)
78
Hydro**philic** solutes require \_\_\_\_\_s or \_\_\_\_\_s, because they **CAN'T** diffuse across the phospholipid bilayer
**Channels** or **Pores**
79
*"**Osmotic pressure differences** cause water to move through **pores** in a membrane just like _______ \_\_\_\_\_\_\_\_ would"*
"...just like **HYDROSTATIC PRESSURE** would"
80
***_REGARDLESS_*** of the **osmolarity** of the solution,
if the reflection oefficient is **_LESS_ than 1 ( σ \< 1 )**, the cell will be...?
* **Why** is this the case?
* When is the only time you'd need to take into account if the solute is an **electrolyte** (and then **solve for osmolarity)**?
*If σ **ISOTONIC!!!***
* This is true because it will always **EVENTUALLY** reach equilibrium and thus be "isotonic"
* it is only when the solute is **_IMPERMEABLE_** (σ = 1) that you need to take into account if it is an electrolyte, and then solve for osmolarity
81
What is the tonicity of **SWEAT?**
Why?
**_HYPOTONIC_**
*Has a lower [] of electrolytes than the cells of sweat glands*
∴ WE become **hypertonic**; need **ISOTONIC** fluids (e.g. Gatorade) to **replenish the lost electrolytes**
82
In an **Iso\_\_\_\_\_ contraction,** the total length of the muscle does NOT change
Iso**METRIC** contraction
83
What does an AP in a neuron look like **graphically?**
## Footnote
***Include**: Resting potential, Threshold potential, Depolarization, Repolarization, Hyperpolarization, Refractory period*
84
**NaCl** is effectively **IMPERMEABLE** to RBCs (σ=1)
∴ an **ISOTONIC** solution of NaCl is \_\_\_\_mM (\_\_%)
**Isotonic** solution of NaCl=
**154 mM (.9%)**
85
Graded or Action Potential?
"Merge on a membrane and summate algebraically"
(Spatial & temportal summation)
= **Graded** Potentials
86
A solution with **GREATER** osmolarity than another is said to be...?
"**Hyper**osmolar"
87
Describe **Absolute Refractory Period**
*A second AP **cannot** be generated **no matter how strong** a stimulus is used*
* Not enough Na+ channels available to trigger another AP.
* They are either all already in use, or have been inactivated.
88
What is the formula for the **Nernst equation?**
What is it used to calculate?
**_Used to calculate the voltage where the ion is in equilibrium_**
## Footnote
**Solves for Eion**
*" used to calculate the membrane potential where the **electrochemical potential of an ion** will be the **same on both sides** of a membrane with the given concentrations"*
89
Formula for **Fick's Law of Diffusion** (**_WITHOUT_** partitioning)
**J = D ⋅ ΔC / Δx**
* J = Flux
* ΔC = [] difference, C1-C2
* Δx = membrane thickness, usually 7.5nm
* D = diffusion coeff
90
What types of fluids (hyper-, hypo-, or isotonic) should be consuded to **rehydrate** following aerobic exercise?
**ISOTONIC** fluids
e.g. Gatorade
91
How **thick** is the plasma membrane (in nm)?
Due to its thickness, the membrane is "mechanically \_\_\_\_"
**7.5 nm**
Hence, plasma membrane is "mechanically **weak**"
92
The contractile force produced by a **_SINGLE AP_** is called a...?
"Twitch contraction"
93
Can (non-water) solutes get through **Aquaporins?**
**NO!**
## Footnote
Aquaporins **extremely specific** for water-- water **ONLY** gets through
94
**NaCl** is effectively **IMPERMEABLE** to RBCs (σ=1)
∴ an **ISOTONIC** solution of NaCl is \_\_\_\_mM (\_\_%)
**Isotonic** solution of NaCl=
**154 mM (.9%)**
95
If a solute (e.g. Urea) is **PARTIALLY PERMEABLE** to the cell membrane, ie **σ \< 1:**
## Footnote
*A solution that is **_hypo-osmotic_** to the cell contents will be...?*
**HYPOTONIC**
96
What happens to a RBC placed in a solution of **290 mM urea** (σurea = .2)
**ISOTONIC**
(Urea can easily pass through membrane; won't be isotonic initially but will be within milliseconds)
97
AQP**2** is abundant where, and what **hormone** targets it?
AQP**2** found in collecting duct of **KIDNEYS**
Is the target of **ADH**
98
What causes **sodium conductance, gNa**, to change during an AP?
gNa changes **due to movement of M and H gates**
99
In an Isometric contraction, the initial length of the muscle **PRIOR** to contraction is called the...?
"Preload"
100
Channels can be regulated by what 2 things?
Voltage
Binding of certain small molecules
101
**K+** channels have how many **gates**?
Where will you find many K+ channels?
Just **one** gate, the **"N"** gate
102
What does the **Van't Hoff equation** solve ?
The osmotic pressure across a membrane **(Δπ)**
* ...when solutions are **dilute** and the membrane is*
* absolutely **IMPERMEABLE** to the solute*
**_"Van't Hoff equation quantifies osmotic pressure across a membrane"_**
103
**Efferent** neurons conduct APs down **what type of nerve**, **resulting in what?**
**Efferent** neurons conduct APs down **_motor nerves,_**
resulting in **_SK muscle contraction_**
104
What do Graded Potentials **precede?**
Action Potentials
105
Describe **[] difference, ΔC, diffusion, and voltage difference, Em,** across the cell when:
## Footnote
*Cell is **IMPERMEABLE** to both K+ and Cl-*
* [K+] difference!
* **ΔC = ( .1 - .01) = .09**
* **NO** diffusion of K+ **OR** Cl-
* Because membrane is impermeable to both
* No potential (voltage) difference, **Em = 0**
106
\_\_\_\_\_\_ potentials **decay spatially**
**Graded** potentials
| (AP's do **NOT** dimish spatially)
107
Fick's Law of Diffusion:
Equation using **PERMEABILITY** = ?
What do (+) values indicate wrt movement in/out of cell?
**J = P(Cin - Cout)**
**Positive** values mean there is a **net OUTWARD flux** of solute from a cell
108
What are the **2 "modulators" of cell excitability?**
* **Low extracellular Ca2+**
* Makes Na+ channels more easily activated
* THIS MAKES THE CELL **MORE** EXCITABLE
* **High extracellular K+**
* Depolarizes cell
* Inactivates Na+ channels
* Activates some K+ channels
* THESE CHANGES MAKE THE CELL **LESS** EXCITABLE
109
**Na+** channels have what **gates**?
What needs to happen for Na+ channels to be **open**?
**Activation** gate, **"M"** gate
**Inactivation** gate, **"H"** gate
The channel is open ***only if BOTH gates are open***
110
What does the Na+ channel's **M gate** require to open up?
a very tiny current, called the **_Gating Current_**
111
[Ca2+] much higher in/outside?
Outside
112
[Na+] in ECF = ?
142 mM
113
During "Solvent Drag," why dont the permeable solutes just cross the membrane on their own?
Solvent drag is **FASTER!**
114
Hydrophobic molecules, **such as \_\_\_, \_\_\_, and \_\_\_,** can diffuse through the membrane
**O2, CO2, and N2**
115
While it can vary according to cell type, the **voltage difference** is usually between what values?
Between **-50mV and -90mV**
116
If two solutions have the **SAME OSMOLARITY**, they are said to be...?
"Iso-osmolar"
117
What does the **Strength-Duration curve** of a nerve stimulus look like **graphically**?
What is the **formula** that explains this relationship?
*Hyperbolic curve*
**Q = IT**
* Q = **Charge** placed on membrane
* I = **Current** of stimulus
* T = **Duration** of stimulus
118
**NON**electrolytes are lipo\_\_\_\_\_
lipo**PHILIC**
119
Describe "Undershoot"
* Because so many K+ channels are open,*
* the **K+ transference, TK,** becomes **large enough** to make the membrane potential, Em, **even more negative** than the normal resting potential.*
* This **hyperpolarized** phase is called the "**undershoot"***
120
**Van't Hoff** formula = ?
Explain each component
**Δπ = nRTΔC**
## Footnote
* Δπ = Difference in Posmotic across an impermeable membrane
* n = **# of particles** the solute dissociates into
* 1 for **non**electrolytes
* 2 for NaCl
* 3 for MgCl2
* R = universal gas constant, .**0821**
* T = temperature, **273 + celsius temp**
* ΔC = difference in molar [], C2-C1
121
[Cl-] much higher in/outside?
outside
122
pH:
ECF vs ICF
**E**CF is slightly **ALKALINE (basic)**
while **I**CF is closer to **NEUTRAL**
123
[H+] in ECF = ?
40 **_n_**M
124
_Resting membrane potential:_
There can be **NO potential difference** ("voltage difference") unless....?
Unless the membrane is permeable TO AT LEAST **_ONE_** ION!
125
The force produced during an Iso**metric** contraction depends on what 3 things?
1. The Preload
* i.e. the **overlap** b/t thick & thin filaments
2. The # of muscle fibers activated
3. The frequency of APs generated
126
The phenomenon of **different solubility of a solute** in **OIL** as opposed to **WATER** is called...?
"Partitioning"
127
Graded Potentials: Describe **IPSPs**
*Inhibitory Postsynaptic Potential (IPSP)*
Is the **HYPER-polarization** of a Graded Potential on the the post-synaptic membrane
128
Where do Graded Potentials occur?
Occur in all tissues ***_which spontaneously generate or conduct APs_***
For example:
* In c**ell bodies** and **dendrites of neurons**
* In cells electrically coupled by **gap junctions** (e.g. **cardiac myocytes**)
* On **post-synaptic membranes**
129
How is **cell volume** regulated by movement of solutes across the membrane?
By the **transport of ions** (via active transport)
130
Define **"Solvent Drag"**
When water is moving across a multicellular "membrane" by osmosis,
**PERMEABLE solutes get caught up** in the flow and are swept along
131
**Kp** is equal to...?
Therefore, **Kp \> 1** indicates?
Kp = solubility in **OIL** / solubility in **WATER**
**Kp \> 1** means it's **_LIPOPHILIC/ HYDROPHOBIC_**
(diffuses across membrane **more quickly** **& easily**)
132
_Ohm's Law during an AP:_
What component of the formula **changes** during different phases of an AP?
**gNa & gK**
133
[Ca2+] in ECF = ?
1 mM
134
Why don't K+ channel **INACTIVATE**?
K+ channels are **open** as long as the membrane is \_\_\_\_\_\_\_\_\_?
Because they ***dont have any INACTIVATION gates*** (unlike Na channels)
K+ channels are open as long as the membrane is DEpolarized
135
[Cl-] in ECF = ?
105 mM
136
In Na+ channels, what determine the **inward Na+ current?**
_Determined by:_
the driving force on Na+, **(Em - ENa)**
the sodium conductance, **gNa**
137
What happens to a RBC placed in a solution of:
**580 mM urea** **(σurea = .2 )?**
**ISOTONIC (?)**
138
Compare osmolarity values for ECF & ICF
Usually **EQUAL** to e/o
139
**Channels** are made up of one or more of what?
**Integral membrane proteins**
140
What causes **TETANY** (intermittent muscular spasms) in muscles?
**_LOW_** extracellular Ca2+
141
Carriers for what type of carrier-mediated transport can **"come back empty?"**
What exactly does that mean?
**_FACILITATED DIFFUSION_**
* = Empty carriers can **REORIENT** themselves*
* from **ONE** face of the membrane to the **OTHER***
(e. g. extracellular face ⇋ cytosolic face)
142
The force produced during an Iso**metric** contraction depends on the...?
PRELOAD
143
Describe **Relative Refractory Period**
* A second AP **CAN** be generated but a **stronger** stimulus*
* (**greater** voltage) must be used.*
* There are not as many Na+ channels available as normal to trigger another AP because many are inactivated.
* Also, many more K+ channels are **open**, so it is more **difficult to depolarize** the membrane to threshold.
144
Describe IK and INa at **REST**
**IK + INa = 0**
## Footnote
At rest, both IK and INa are **small**
145
What happens to a RBC placed in a solution of **PURE WATER?**
***_VERY_* *HYPOTONIC***
(Water moves into cells, CELL **BURSTS!!**)
146
Osmolarity in ECF = ?
290 **mOsm/L**
| ("milliosmoles")
147
If a neuron has an **absolute refractory period of 1.25mS**,
what is the maximum firing rate (in Hz)?
Maximum firing rate = 1 S/ 1.25mS = 1000mS/1.25mS = **800 (Hz)**
(convert seconds to milliseconds, then divide)
148
What causes ankle edema (swollen ankles)?
What can pts do to relieve their symptoms?
**= EXCESS FLUID**
**Reducing the amount of SALT** in your food ofter relieves edema
149
What happens to a RBC placed in a solution of **290 mM NaCl** (σNaCl = .9)?
**HYPERTONIC**
| (2 x 290= 580 mM)
150
What is it called when **membrane potential, Em,** becomes **positive** and **approaches ENa?**
"Overshoot"
151
In AP conductance, the positive charge that enters the nerve cell is carried by ___ and is called the "\_\_\_\_\_\_\_\_ current"
Carried by **K+**
Called the **Axoplasmic current**, or **iax**
152
In AP conductance, the positive charge that LEAVES the nerve cell through membrane channels is called the ________ current, or ...?
**Membrane current**, or **im**
153
In both myelinated AND unmyelinated axons, increasing the ______ will leads to increased conduction velocity
Diameter
154
**Time constant, τ**, is the time at which...?
It is a measure of what?
Formula = ?
Time at which it reaches 63% of the final voltage
it is a measure of how rapidly a voltage disturbance SETTLES DOWN
**τ = Rm Cm**
155
Length constant, λ, is the distance where...?
What is it a measure of?
Is the distance where the voltage is only 37% of the voltage where x=0
It is a measure of HOW FAR ALONG the axon a voltage disturbance is felt
156
In a MYELINATED axon, the length constant, λ, and conduction velocity, V, are directly proportional to..?
Diameter
157
In an UNMYELINATED axon, the length constant, λ, and conduction velocity, V, are directly proportional to..?
**√** Diameter
158
Only the ____ channels at the nodes of ranvier need to be activated, which saves _____ and increases \_\_\_\_\_
Na channels
saves time
increases speed of propagation
159
Do myelinated or unmyelinated axons have more LOCAL CIRCUIT PATHS?
Unmyelinated
