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How does neuronal communication occur?
- passage through the plasma membrane
- -glucose and its derivatives involved w/ ATP production
- -growth hormone/regular hormones to produce protein (insulin to transport glucose, metabolic rate-thyroxin)
- -gases (CO2, O2)
- -insulin
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What are the different passages of neuronal communication through the plasma membrane?
- simple diffusion
- osmosis
- facilitated diffusion
- active transport
- exocytosis
- endocytosis
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What is another name for simple diffusion?
passive transport
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Simple diffusion:
movement of ions (K+, Na+, Cl-) from high concentration to low concentration, establishing a resting membrane potential and action potential
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Diffusion is referred to as:
conductance from high concentration to low
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Concentration gradient:
passive movement of ions
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Where do molecules want to go?
where there is less energy to reach equilibrium
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What 3 types of channels may simple diffusion occur in?
- non-gated channels
- voltage-gated channels
- ligand-gated channels
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What are the 3 types of simple diffusion channels referred to as?
ionophores (pores)
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Where are the non-gated channels?
protein molecules embedded in the cell membrane
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Are non-gated channels open or closed?
always open
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When can ions pass through a non-gated channel?
always
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What controls which ion can go through?
chemical nature (i.e., Na+ channel only allows Na+ to go through)
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Where are voltage-gated channels?
embedded in the cell membrane
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Are voltage-gated channels open or closed?
always closed in resting membrane
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What allows a voltage-gated channel to open?
change in voltage (the action potential moving through a membrane creates a voltage difference)
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What happens to protein molecules in response to voltage change?
undergo conformational change (changes its shape on a molecular level)
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Are ligand-gated channels open or closed?
normally closed
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How do ligand-gated channels undergo a conformational change?
by interacting w/ ligand
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What do ligands contain?
chemicals (neurotransmitters or neuromodulators) that attach to receptor site on protein pore and cause a conformational change to open the channel
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What do ligand-gated channels respond to?
presence of molecule or chemical(neurotransmitters/neuromodulators)
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Ions can go through each type of channel, it just depends on:
the circumstances
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Osmosis:
movement of water through semipermeable membrane (since the water can diffuse, but other molecules can't)
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What are the 2 biological fluids?
- intracellular compartment
- extracellular compartment
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Where is the intracellular compartment?
w/in confines of the cell membrane
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Where is the extracellular compartment?
outside cell membrane
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What are the two sub-sections of the extracellular compartment?
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intervascular
confines of vessels
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interstitial:
- tissue fluid
- outside vessels, but b/w cells
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Osmosis is the tendency of water to move outside the cell to area of what?
high concentration of solute. Water moves w/ concentration gradient to try and achieve equilibrium
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Facilitated Diffusion:
movement of ions (or molecules) from high concentration to low concentration, but faster than simple diffusion b/c it utilizes carrier molecules
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What are carrier molecules?
- protein molecules embedded in cell membrane
- movement is bi-directional (inside->outside; outside->inside)
- concentration gradient provides energy for movement
- in order for it to open, there must be a conformational change)
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Active transport:
movement of ions or molecules against concentration gradient (uphill/backwards)
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What does active transport require?
energy expenditure that comes from hydrolysis of ATP (ATP->ADP+P)
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What does the active transport system use?
transporter molecules (protein molecules) embedded in cell membrane that are specific for what they transport
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Under certain conditions, active transport can maintain:
ionic differences b/w intracellular and extracellular fluid (concentration gradient w/in cells)
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Exocytosis:
- neuron releases macromolecules (neurotransmittors and neuromodulators) by diffusion of vesicles w/in plasma membrane
- vesicles form a fusion pore complex on membrane
- when Ca+ influx in, pores open and release chemicals into synaptic cleft
- chemicals function as NTM/neuromodulators
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Endocytosis:
- engulfment process
- plasma membrane surrounds and engulfs materials into plasma membrane as vesicles
- preserves some of NTM dumped into synaptic cleft to recycle them
- don't have to continually process NTM
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Resting membrane Potential:
neurons are charged, but not conducting AP
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What causes the resting membrane potential?
a potential electrical difference (voltage), which exists across a cell membrane, causing excitability of muscle cells and neurons
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At resting membrane potential, what is the charge outside of the cell?
positive
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At resting membrane potential, what is the charge inside the cell?
negative
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What accounts for the potential difference inside and outside of the cell?
- physiological factors
- biological factors
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What physiological factors account for the potential difference between the inside and outside of a cell?
diffusion of ions through cell membrane
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What biological factors account for the potential difference b/w the inside and outside of a cell?
membranes relative (selectively) permeability to various ions
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Equilibrium of a cell is reached when:
more Na+ (inside or outside)
more Cl- (inside or outside)
more K+ (inside or outside)?
- more (x10) Na+ outside
- more (x14) Cl- outside
- more (x30) K+ inside
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There is a tendency fo ions to go from:
high concentration to low concentration to diffuse across concentration gradient to reach equilibrium
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Diffusion of Na+ is high on the:
outside and low on the inside
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Na+ and Cl- diffuse...
into the cell
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K+ diffuses...
outside the cell
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What do ions use to reach equilibrium?
non-gated specific pores
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Anions don't go through based on concentration gradients b/c:
they are too big to go through the pores
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A membrane at rest is not conducting an AP, so it is:
50-100x more permeable to K+ than Na+ (biological factor)
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Is it easy or difficult for Na+ to get into the cell?
difficult
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Is it easy or difficult for K+ to get out of the cell?
easy
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As K+ diffuses outside of the cells:
excessive negative ions (albumin) are left behind, inside the cell, maintaining negativity due to loss of positive ions
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Migration of K+ continues until:
excess of negativity inside and additional K+ outside of the cell restrains continued K+ diffusion (K+ ions reach equilibrium)
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There is a limited diffusion of Na+ into the cell because:
the membrane is not very permeable to it (more permeable to K+)
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Does Na+ play a major role in establishing resting membrane potential?
no
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Does K+ play a major role in establishing resting membrane potential?
yes
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Due to the dynamics of Na+/K+, there is a __ charge on the outside and a ___ charge inside.
- positive outside
- negative inside
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What is the nernst equation used for?
used to calculate equilibrium potential for ions (used for each ion involved)
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What does the Nernst equation take into account?
- charge of ion
- temperature
- ratio of interval/external [ion]
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Nernst equation
K+= ?
Na+= ?
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What does the K+ value establish?
RMP driving force that sets the value of RMP for normal human neuron (-70mV)
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What is the threshold of activation for a neuron according to the Nernst equation?
-60mV
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What does the Goldman equation find?
- RMP value for normal human neuron (-70mV)
- value at which a neuron rests
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What is the goldman equation based on?
all the individual ion equilibrium potentials
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What is the driving force that determines RMP?
the K+ ion
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If conductance of ions naturally takes place through pores, why is there a need for concentration gradient?
- due to active transport system
- Na/K pump is active transport that occurs against the concentration gradient
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In the Na/K pump for each ATP how many Na are out per K into the neuron to maintain concentration gradient?
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Why does the Na/K pump maintain the concentration gradient?
to allow an AP
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RMP Review:
- requires semipermeable membrane
- certain ions passively pass (conductance) along a concentration gradient in non-gated channels (Na, K, Cl)
- K is principle ion due to its significant permeability as compared to Na and Cl
- Presence of Na/K pump maintains the concentration gradient of Na/K
- Nernst equation calculates the equilibrium potential for each ion
- sum of equilibrium potentials=RMP (-70mV)--Goldman's formula
- when a neuron reaches a resting charged state, it is polarized
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