Mastering A And P Homework #9

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

Leak channels. ->Leak channels for NA+ and K+ are ubiquitous, and they allow for the diffusion of these ions across the plasma membrane

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+

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 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

Na+-k+ATPase

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

Voltage-gated Na+ channels. The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm.

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

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

-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

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.

Continuous conduction.

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

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

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.

Inactivation gates of voltage=gated Na+channels close, while activation gates of voltage-gated K+ channels open

->myelinated axons with the largest diameter

INterneurons

Interneuron

Sensory, Or Afferent

Sensory receptors.

Motor neurons

MULTIpolar neurons

Bipolar neurons

single short process that splits into two axons (no Dentrites)

Multipolar neurons

Multipolar Neurons

Bipolar neurons

Pseudounipolar Neurons