BIOPHYSICS N°14 (FILL)

Gradient potentials can be .............. or ................

depolarise, hyperpolaryse

The transient hyperpolarization, that arises from the summed activity of voltage gated

and non gated K+ channels, is called the after ...............

Hyperpolarisation

The period of time during which it is possible to elicit a new action potential, but it

requires a larger than normal stimulus is the ............... period

Relative refractive

The rapid repolarization of the membrane arises from two phenomena: 1. Inactivation

of .............. 2. Increase in .................

Na, K

Stimuli must be above ............... to set off an action potential.

Threshold

Excitable cells have special ............ and ............... channels with gates that open and close in

response to the membrane potential difference (.............. gated channels)

Na, K, Voltage

As the action potential travels along the ........... , it stays the same size

Axon

Many nerves have an insulating layer called the myelin sheath. Gaps are left every few

millimeters called ............

Node of Ranvier

If the stimulus is not strong enough for the membrane to reach the threshold, no action

potential will be fired. This stimulus is called ............... stimulus

Decremental

In a myelinated nerve, conduction velocity increases ............ times

10-100

Action potential is a .............. change in the membrane potential , which is

transmitted along the axon.

Temporary

If the membrane potential goes from -70 to 60 mV, this is called ............. because

it lessens the potential difference across the cell membrane.

Depolarisation

Propagating " without .............." means that the height of the action potential

remains the same as it travels along the fiber.

Decrement

The membrane potential at which the action potential occurs is called .............. for the nerve or muscle fiber.

Threshold

A stimulus either fails to elicit an action potential or produces a full strength action

potential. Such a phenomenon is called ..............

All or nothing

For some period during an action potential, a second action potential cannot be

elicited , no matter how strong the stimulus. This is ...............

Absolute refractory period

in the central nervous system most nerves are stimulated by chemical activity at ................

Synopses

Action potentials are triggered by a shift in the membrane potential to a less ............ value inside.

Negative

The importance of myelination is demonstrated by the demyelinating disease .............., in which the immune system attacks and destroys myelin sheaths in some regions

of CNS.

Multiple sclerosis

Axon can conduct action potentials in both directions, but .............. usually prevent

this.

Connections

Sensory neves respond to stimuli of many types: ..................

Chemical, light, touch, electrical

Very weak stimuli cause only a small .................

Disturbance

The membrane potential recovers by closing ............ channels and opening ............... channels.

Na, K

K channels are ............ than Na+ channels.

Slower

Conduction velocity for myelinated nerve is about ............

100 m/s

.............. are proteins which use the energy of ATP hydrolysis to produce and to maintain

concentration gradients of ions across cell membranes.

Carrier or channel proteins ?

The relationship between membrane potential, ................ and .............. is

one of a positive feedback.

I(Na) and g(Na)

Sodium channels activation means increase in ............. due to depolarization.

Sodium permeability

............. gate of Na+ channel is said to be opened by depolarization.

M

During the ............ refractory period, some Na+ channels are open.

Relative

The membrane potential difference is headed towards ............. when the action potential

begins to turn itself off.

Ek

Excitable cells generate action potentials by transiently increasing Na+ permeability

and thus driving membrane electrical potential difference in a positive direction toward

...............

Negative

The process of opening and closing of ion channels is called ................

Gating