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)
What are the different passages of neuronal communication through the plasma membrane?
- simple diffusion
- facilitated diffusion
- active transport
What is another name for simple diffusion?
movement of ions (K+, Na+, Cl-) from high concentration to low concentration, establishing a resting membrane potential and action potential
Diffusion is referred to as:
conductance from high concentration to low
passive movement of ions
Where do molecules want to go?
where there is less energy to reach equilibrium
What 3 types of channels may simple diffusion occur in?
- non-gated channels
- voltage-gated channels
- ligand-gated channels
What are the 3 types of simple diffusion channels referred to as?
Where are the non-gated channels?
protein molecules embedded in the cell membrane
Are non-gated channels open or closed?
When can ions pass through a non-gated channel?
What controls which ion can go through?
chemical nature (i.e., Na+ channel only allows Na+ to go through)
Where are voltage-gated channels?
embedded in the cell membrane
Are voltage-gated channels open or closed?
always closed in resting membrane
What allows a voltage-gated channel to open?
change in voltage (the action potential moving through a membrane creates a voltage difference)
What happens to protein molecules in response to voltage change?
undergo conformational change (changes its shape on a molecular level)
Are ligand-gated channels open or closed?
How do ligand-gated channels undergo a conformational change?
by interacting w/ ligand
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
What do ligand-gated channels respond to?
presence of molecule or chemical(neurotransmitters/neuromodulators)
Ions can go through each type of channel, it just depends on:
movement of water through semipermeable membrane (since the water can diffuse, but other molecules can't)
What are the 2 biological fluids?
- intracellular compartment
- extracellular compartment
Where is the intracellular compartment?
w/in confines of the cell membrane
Where is the extracellular compartment?
outside cell membrane
What are the two sub-sections of the extracellular compartment?
confines of vessels
- tissue fluid
- outside vessels, but b/w cells
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
movement of ions (or molecules) from high concentration to low concentration, but faster than simple diffusion b/c it utilizes carrier molecules
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)
movement of ions or molecules against concentration gradient (uphill/backwards)
What does active transport require?
energy expenditure that comes from hydrolysis of ATP (ATP->ADP+P)
What does the active transport system use?
transporter molecules (protein molecules) embedded in cell membrane that are specific for what they transport
Under certain conditions, active transport can maintain:
ionic differences b/w intracellular and extracellular fluid (concentration gradient w/in cells)
- 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
- 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
Resting membrane Potential:
neurons are charged, but not conducting AP
What causes the resting membrane potential?
a potential electrical difference (voltage), which exists across a cell membrane, causing excitability of muscle cells and neurons
At resting membrane potential, what is the charge outside of the cell?
At resting membrane potential, what is the charge inside the cell?
What accounts for the potential difference inside and outside of the cell?
- physiological factors
- biological factors
What physiological factors account for the potential difference between the inside and outside of a cell?
diffusion of ions through cell membrane
What biological factors account for the potential difference b/w the inside and outside of a cell?
membranes relative (selectively) permeability to various ions
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
There is a tendency fo ions to go from:
high concentration to low concentration to diffuse across concentration gradient to reach equilibrium
Diffusion of Na+ is high on the:
outside and low on the inside
Na+ and Cl- diffuse...
into the cell
outside the cell
What do ions use to reach equilibrium?
non-gated specific pores
Anions don't go through based on concentration gradients b/c:
they are too big to go through the pores
A membrane at rest is not conducting an AP, so it is:
50-100x more permeable to K+ than Na+ (biological factor)
Is it easy or difficult for Na+ to get into the cell?
Is it easy or difficult for K+ to get out of the cell?
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
Migration of K+ continues until:
excess of negativity inside and additional K+ outside of the cell restrains continued K+ diffusion (K+ ions reach equilibrium)
There is a limited diffusion of Na+ into the cell because:
the membrane is not very permeable to it (more permeable to K+)
Does Na+ play a major role in establishing resting membrane potential?
Does K+ play a major role in establishing resting membrane potential?
Due to the dynamics of Na+/K+, there is a __ charge on the outside and a ___ charge inside.
- positive outside
- negative inside
What is the nernst equation used for?
used to calculate equilibrium potential for ions (used for each ion involved)
What does the Nernst equation take into account?
- charge of ion
- ratio of interval/external [ion]
What does the K+ value establish?
RMP driving force that sets the value of RMP for normal human neuron (-70mV)
What is the threshold of activation for a neuron according to the Nernst equation?
What does the Goldman equation find?
- RMP value for normal human neuron (-70mV)
- value at which a neuron rests
What is the goldman equation based on?
all the individual ion equilibrium potentials
What is the driving force that determines RMP?
the K+ ion
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
In the Na/K pump for each ATP how many Na are out per K into the neuron to maintain concentration gradient?
Why does the Na/K pump maintain the concentration gradient?
to allow an AP
- 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