Nervous system Flashcards
Resting membrane potential (Vr) is …..
It is caused by …..
the difference in potential between the inside and the outside of the cell at rest.
- Normal value is -60 mV, while for heart & skeletal muscles -90mV
- Caused by different distribution of ions and selective permeability of the cell membrane. The membrane is permeable to K, and impermeably to intracellular anions
Concentration gradient is …
the force that drives diffusion across a membrane so that the ions concentrations are equal on both sides of the membrane
Electrical gradient is …..
the force that drives diffusion across a membrane so that charges tend to equalize on both sides of the membrane
The Na-K pump maintains ….. & …..
low intracellular Na, High intracellular K
* For every 3 Na leaving the cell, 2 K enter. The result is +ve charge loss
Diffusion of an ion through a channel depends on ……. & ……
Ion size and charge,, and the channel size and charge
Ion channels are either ….. or ……
ligand gated, or voltage gated
* Voltage gated Ca channels are more abundant at axon terminals where Ca is needed for neurotransmitter release
Neurons possess the ability to …….
regulate their resistance because of their ion channels
A threshold potential (Vt) is …..
potential required to generate an action potential. It is about -50 mV
The all or none response means …….
any stimulus at or above the threshold intensity will generate the same action potential with constant amplitude
Axon hillock is ……
where the action potential starts and propagates in both directions.
* Most of the Na channels are located here, not at the soma
A hyperpolarizing pulse is ……, while a depolarizing pulse is ……..
- Hyperpolarizing pulse changes Vm so that the inside is more -ve. More intense stimuli is needed to generate AP
- Depolarizing pulse changes Vm so that the inside of the cell is less negative
When the tendency of K to leave is equal to the tendency of the membrane to pull back K, the membrane is ….
at rest (stable)
When the membrane reaches threshold, the magnitude of the response is greater because of …….
active participation of the membrane in which the inward movement of +ve ions overwhelms the repolarization process
The action of local anesthetic is by ……
blocking the Na influx, thereby inhibiting depolarization.
* LA affects smaller nerve fibers first (C fibers, small pain fibers, large A proprioceptive fibers)
Action potential continues ….. the stimuli discontiunues
after
After AP, the membrane is repolarized below ……
the resting potential
The absolute refractory period occurs ….., because ……
during the peak and first half of the falling phase of AP.
* No AP can be elicited at this period, because Na channels can not open and K is still elevated and flowing outward
The relative refractory period is ……
when the inactivation of Na channels is ending and the efflux of K is diminishing, here, a stronger than normal stimulus can initiate another AP
* This phase follows the absolute phase
The power of …….. is needed to re establish the resting potential
Na-K pump
Saltatory conduction is ……
the movement of AP from one node to another. It is much more faster than in unmyelinated axons
* Electrochemical basis behind saltatory conduction is ↓ membrane
capacitance (increase distance between charges; less charges necessary).
The greater the diameter of an axon, the ……
greater the speed of conduction
Why impulses are conducted in one direction only??
because:
- synapses permits transmission in one direction only
- The moving impulse doesn’t depolarize the spot behind it because it is either hyperpolarized or refractory
Orthodromic impulses are ….., while antidromic impulses are ……
- occur in normal direction of conduction
* occur in the opposing direction (only experimentally)
How is gradation of sensory impulse possible?
because many axons with different thresholds are present at the same sensory location