2.2.1 The Nerve Impulse 2 Flashcards
By increasing a negative charge within a neuron we see a change called ____, which means increased polarisation.
hyperpolarisation
Reducing the negative charge with a neuron towards zero is called ____.
depolarisation
Stimulation beyond the ____ of ____ produces a massive depolarisation of the membrane. When the potential reaches the threshold, the membrane opens the sodium channels and permits sodium to flow into the cell.
threshold of excitation
Any stimulation beyond the threshold, regardless of how far beyond, produces a big response. That response, a rapid depolarisation and then reversal of the usual polarisation, is the ____ ____.
action potential
The action potential always starts in an ____ and propagates without loss along the ____.
axon
For a given neuron, all action potentials are approximately equal in ____ and ____.
amplitude and velocity
According to the ____ law, the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold.
all-or-none
To signal the difference between a weak and a strong stimulus the axon sends more ____ action potentials to signal ____ ____ of stimulus.
frequent : greater intensity
Immediately after an action potential, the cell is in a ____ ____ during which it resists the production of further action potentials.
refractory period
In the first part of the refractory period, the ____ ____ ____, the membrane cannot produce an action potential, regardless of the stimulation.
absolute refractory period
During the second part, the ____ ____ ____, a stronger tun usual stimulus is necessary to initiate and action potential.
reflective refractory period
The refractory period has two mechanisms. The ____ channels are closed, and ____ is flowing out of the cell at a faster than usual rate.
sodium : potassium
It is important for axons to convey impulses without any loss of ____ over distance.
strength
In a motor neuron, an action potential begins on the ____ ____, a swelling where the axon meets the soma.
axon hillock
During the action potential, sodium ions enter a point on the axon. Temporarily, that spot is positively charged in comparison with neighbouring areas along the axon. The positive ion flows within the axon to neighbouring ____. The positive charges slightly ____ the next area of the membrane, causing it to reach its threshold and open its voltage-gated sodium channels. Therefore, the membrane ____ the action potential at that point. In this manner, the action potential travels along the axon.
regions : depolarise : regenerates
The term ____ of the ____ ____ describes the transmission of action potential down an axon.
propagation of the action potential
Myelinated axons are those covered with a ____ ____.
myelin sheath
Myelinated axons, found only in vertebrates, are covered with layers of ____ and ____.
fats and proteins
The myelin sheath is interrupted periodically by short sections of axon called ____ of ____, each one about one micrometer wide.
nodes of Ranvier
The jumping of action potentials from node to node is referred to as ____ ____.
saltatory conduction
In addition to providing rapid conduction of impulses, saltatory conduction conserves energy: instead of admitting sodium ions at every point along the axon and then having to pump them out via the sodium-potassium pump, a myelinated axon admits sodium only at its ____.
nodes
An axon that never had a myelin sheath conducts impulses ____ but steadily.
slowly
In axon that has lost its myelin is not the same. After myelin forms along an axon, the axon loses its sodium channels under the myelin. If the axon later loses it’s myelin, it still lacks sodium channels in the areas previously covered with myelin, and most action potentials die out between one node and the next. Associated with _____ ____.
Multiple sclerosis
Many small neurons have no axon. Neurons without an axon exchange information with only their closest neighbours. We therefore call them ____ ____.
local neurons
When a local neuron receives information from other neurons, it has a ____ ____, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus.
graded potential
In a graded potential, the change in the membrane potential is conducted to adjacent areas of the cell, in all directions, gradually decaying as it travels. Those various areas of the cell contact other neurons, which they excite or inhibit through ____.
synapses
