Quiz 4 (Section 2 Quiz 1) Flashcards
what are electrochemical gradients
-the driving force for ion movement across membranes
-due to concentration differences across a cell membrane
-due to potential differences across a membrane
which ion(s) are most important for establishing the normal resting membrane potential of a neuron?
-K+ and Na+
action potentials:
-conduct neural signals along the membrane
-are an all-or-none phenomenon
which of the following statements about the absolute refractory period are true?
-the absolute refractory period occurs when the inactivation gates of the voltage-gated sodium channels are closed.
electro-
potential difference between inside and outside of cell
-chemical
concentration difference between inside and outside of cell
concentration of potassium:
high inside (intracellular), low outside (extracellular)
concentration of sodium
low inside (intracellular), high outside (extracellular)
the equilibrium potential:
is the electrical potential that exactly opposes the net diffusion down the concentration gradient across the membrane. (Nernst/reversal potential) point where electrical and chemical forces cancel out
nernst equation:
EMF (V) = (RT/zF) * (log(conc out/conc in))
EMF in nernst equation:
the electromagnetic force (potential inside the membrane) in volts
R in nernst equation:
universal gas constant (8.314 J/K/mol)
T in nernst equation:
temperature in kelvin
z in nernst equation:
electrical charge of the ion
F in nernst equation:
Faraday’s constant (96,485 C/mol)
RT/F =
61
concentration of an ion is in:
mEq/L or mmol/L
potassium concentrations:
in: 140 mEq/L
out: 4 mEq/L
sodium concentrations:
in: 14 mEq/L
out: 142 mEq/L
calcium concentrations:
in: 0.00007 mEq/L
out: 2 mEq/L
chloride concentrations:
in: 10 mEq/L
out: 110 mEq/L
in the nernst equation, if you end with a positive number, it indicates
more positive inside the cell than outside
in the nernst equation, if you end with a negative number, it indicates
more negative inside the cell than outside
when do you use the Goldman Hodgkin Equation?
when the membrane is permeable to several different ions (MULTIPLE IONS)
ions most important for membrane potential:
Na+, K+, Cl-
what does membrane potential depend on?
-polarity of the electrical charge of each ion
-permeability of the membrane to each ion
-concentration of the respective ions on the inside and outside of the membrane
Goldman equation:
EMF (mv) = 61 * log( (PNa[Na]out + PK[K]out + Pcl[Cl]in)/(PNa[Na]in + PK[K]in + Pcl[Cl]out) )
if other concentrations are not permeable, they equal 0.
electrochemical driving force causes net movement of the ion across the membrane. equation is:
Vdf = Vm - Veq,X
Vdf is inside relative too outside:
-positive Vdf = positive ion moves out of the cell
-negative Vdf = positive ion moves into the cell
-opposite for negative ions
-positive Vdf = negative ion moves into the cell
-negative Vdf = negative ion moves out of the cell
when a cell in equilibrium what happens to the ions?
they are still moving
dendrites:
input
axon terminals:
Output. where the neuron connects to another neuron.
what is action potential?
rapid changes in membrane potential that spread rapidly along a nerve fiber membrane.
-all or none
-must pass threshold to happen
-propagate along a nerve fiber until it reaches the end (if it starts, it doesnt stop)
-conducts neural signals
-constant amplitude. cannot become greater. one or none (ex. if two collide, its not double, only amplitude of one of them)
action potential phases:
-resting: flat before and after peak
-depolarization: going up
-repolarization: going down
the threshold/overshoot is the max peak
voltage gated Na+ channel:
-2 gates (inactivation and activation)
-gate is closed when at rest. a certain voltage must come along to be opened.
voltage gated K+ channel:
1 gate
large anions:
-too big to cross through the membrane
-contribute to negative intracellular charge when K+ ions leave cell
-are anions of proteins, organic phosphates and sulfates
calcium ions:
-play a significant role in action potentials in cardiac cells and smooth muscle cells
-calcium pumps: establish calcium concentration gradient (higher out than in)
-voltage gated calcium channels: slower channels. contribute to sustained depolarization of some cells.
what does the speed of transmission depend on?
fiber size and whether it is meyelinated
Action potentials are sent from neurons to other tissues to:
initiate various cellular responses.
muscle contraction and secretion of glands
action potentials deliver sensory information to:
the central nervous system.
excitation:
-the process of elictiing an AP due to any process that leads to influx of Na+ ions.
-mechanical, chemical, and electrical stimuli
initiation:
occurs only after the threshold potential is reached.
-initial rise in potential die to one of the three stimuli.
-threshold = -55 mV. triggers posiitve feedback loop
positive feedback loop:
more and more voltage-gated Na+ channels open as a potential increases, until all Na+ channels are open
is unmyelinated or myelinated neurons larger?
unmyelinated
out to in:
epineurium
perineurium
endoneurium
how often are nodes of ranvier?
about every 1-3 mm
what happens in the nodes of ranvier?
there is no myelination so a lot of ions flow in this region.
myelin sheath:
the plasma membrane of a schwann cell. wraps arond neurons in the peripheral nervous system. on eneuron per wrap. hard for ions to flow through.
oligodendrocytes:
form myelin around neurons in the central nervous system- the brain and spinal cord. multiple neurons wrapped in one (opposite of myelin sheath in peripheral nervous system.
saltatory conduction:
process of AP progogation in myelinated axons
benefits of saltatory conduction:
-increases transmission velocity 5-50x because AP can now jump long places
-conserves energy because less energy expenditure by Na+/K+ pumps because fewer ions cross the membrane
refractory period:
the time in which a neuron is unable to fire another action potential
absolute refractory period:
the time in which neural excitability is zero, because the sodium channels are inactivated
relative refractory period:
interval following the absolute refractory period in which neural excitability is reduced and an AP can only be generated with a strong stimulus
typical action potential:
depolarization immediately followed by repolarization
action potentials with a plateau occur where?
cardiac muscle fibers
plateaus in action potential:
-membrane does not immediately repolarize after depolarization
-occurs in cardiac cell
what are some causes of a plateau?
voltage gated Ca+2 channels are slower to open that voltage gated Na+ channels- prolonged depolarization phase.
-voltage gated K+ channels are slower to open than usual-delayed repolarization
repetitive discharges:
-rhythmic, self-induced depolarizations
-occurs in the smooth muscle, regions of the heart, and some brain centers. rhythmic beating of the heart, peristalsis of the intestines, and control of breathing
-caused by: high membrane permeability to Na+ leading to leakage of Na+. these leakages lead to the channels opening by themselves.
skeletal muscle:
composed of muscle fascicles arranged in parallel
muscle fiber:
muscle cell 10-80 micro meters in diameter
muscle fascicles:
composed of muscle fibers arranged in parallel
sarcolemma:
plasma membrane of a muscle fiber and collagen coating that fuses with the tendon
sarcoplasm:
intracellular fluid in muscle cell. contains a lot of mitochondria
sarcoplasmic reticulum:
specialized reticulum important for muscle contraction
myofibrils:
-special organelle for muscle fiber contraction. arranged in parallel in muscle fiber.
-contractile organelle of the muscle. 100s to 100s in parallel within each muscle cell. extend the entire length of the muscle fiber. 1-2 micro meters in diameter. composed of repeating sacromeres arranged in series
sacromeres
functional unit of satiated muscle. composed mainly of actin and myosin proteins. causes muscle contraction
myosin:
thick filaments. main contractile machinery
actin:
thin filaments. protein that myosin walks along
z-disk:
forms the lateral boundaries of the sarcomere. attaches multiple actin filaments together. attaches myofibrils together across an entire muscle fiber
titin:
elastic molecule holding myosin and actin filaments in place
I band:
Region around a a disc where there are only thin filaments (actin)
M line:
Center of myosin tails
H zone:
Region around M line where there are thick filaments only (myosin)
A band:
Region that contains thick and thin filaments
