Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference? |
Resting Membrane Potential (RMP). Resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation |
Sodium and potassium ions can diffuse across the plasma membranes of all cells bc of the presence of what type of channel? |
Leak channels. ->Leak channels for NA+ and K+ are ubiquitous, and they allow for the diffusion of these ions across the plasma membrane |
On average the resting membrane potential is -70mV. What does the sign and magnitude of this value tell you? |
The inside surface of the plasma membrane is much more negatively charged than the outside surface. ->The inside surface of the plasma membrane accumulates more Negative charge bc of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na + and K+ |
The plasma membrane is much more permeable to K+ than to Na+. WHY? |
There are many more K+ leak channels than Na+ leak channels in the plasma membrane. -> More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+ |
The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors. |
The presence of concentration gradients and leak channels. -> concentration gradient and large # of K+ leak channels allow for robust K+ diffusion out of a cell ->the concentration gradient and relatively few Na+ leak channels allow for much less Na+ diffusion into a cell |
What prevents the Na+ and K+ gradients from dissipating? |
Na+-k+ATPase |
Where do most action potentials originate? |
Initial Segment ->The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hilock |
What opens first in response to a threshold stimulus? |
Voltage-gated Na+ channels. The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm. |
What characterizes depolarization, The first phase of the action potential? |
The membrane potential changes from a negative value to a positive value. -> The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value |
What characterizes repolarization, the second phase of action potential? |
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70mV. =>The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value |
What event triggers the generation of an action potential? |
-The membrane potential must depolarize from the resting voltage of -70mV to a threshold value of -55mV. -This is the minimum value required to open enough voltage-gated Na+channels so that depolarization is irreversible |
What is the first change to occur in response to a threshold stimulus? |
Voltage-gated Na+ channels change shape, and their activation gates open. ->The activation gates of voltage gated Na+channels open very rapidly in response to threshold stimuli ->The activation gates of voltage gated k+ channels are comparatively SLOW to open. |
What type of conduction takes place in unmyelinated axons? |
Continuous conduction. |
The action potential is self-regenerating bc |
Depolarizing currents established by the influx of Na+flow DOWN the axon and trigger an action potential at the next segment -> The Na+diffusing in to the axon during the first phase of the action potential creates a depolarizing current |
Why does regeneration of the action potential occur in one direction, rather than in two directions? |
The inactivation gates of voltage-gates Na+ channels close in the node, or segment, that has just fired an action potential ->At the PEAK of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels become absolutely refractory to another depolarizing stimulus |
What is the function of the myelin sheath? |
The myelin sheath INCREASES the speed of action potential conduction from the initial segment to the axon terminals. ->Myelin insulates the axon, reducing the loss of depolarizing current across the membrane ->second, allows the voltage across the membrane to change much faster. |
What changes occur to voltage-gated Na+and K+ channels at the peak of depolarization? |
Inactivation gates of voltage=gated Na+channels close, while activation gates of voltage-gated K+ channels open |
In which type of axon will velocity of action potential conduction be the fastest? |
->myelinated axons with the largest diameter |
Neurons that relay info WITHIN the CNS and are the location of info processing are called |
INterneurons |
What is the most abundant type of neuron |
Interneuron |
Sensory input is gathered by what division of the PNS |
Sensory, Or Afferent |
Sensory info is first detected by structures of the PNS called what?? |
Sensory receptors. |
Neurons that carry info AWAY from their cell bodies in the CNA to muscles and glants. |
Motor neurons |
One axon with 2 or more dendrites; typically have highly branched Dendritic tree |
MULTIpolar neurons |
One axon and one dendrite |
Bipolar neurons |
Pseudounipolar Neurons |
single short process that splits into two axons (no Dentrites) |
Motor (efferent) neurons, Interneurons |
Multipolar neurons |
Most neurons in the CNA, motor Neurons in the PNA |
Multipolar Neurons |
Special sense organs in the PNS, such as the retina and olfactory epithelium |
Bipolar neurons |
Sensory neurons in the PNS associated with touch, pain, and vibration sensations |
Pseudounipolar Neurons |
Mastering A and P homework #9
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