11-3. Nerve Impulses Flashcards
resting neuron
not conducting an impulse
There is an ____ distribution of __ and ___ inside and outside the neuron.
unequal; Na+, K+
Na+ levels are higher ____; K+ levels are higher ___
outside; inside
Why is the distribution of ions unequal?
Na+/K+ Pump - uses ATP to actively transport Na+ out and K+ in (3 Na+ out for every 2 K+ in)
A resting neuron is 75x more permeable to ___.
K+ - greater number of + charges diffusing out
What other ions are found inside and outside the membrane?
large protein anions (A-) are trapped inside; negative Cl- ions outside
What causes the difference in charge across the membrane of a resting neuron?
more positive ions moving out of the neuron than into the neuron (Na+ is being pumped out, some K+ is also diffusing out)
resting potential
difference in charge across the resting membrane
A resting neuron is ___ charged inside, and is referred to as being ___.
negatively; polarized
The nerve impulse is also referred to as a(n) ____.
action potential
If a threshold stimulus is applied to the neuron, the membrane becomes 1000x more permeable to ___.
Na+
What happens to a neuron at the point of stimulation?
The sodium channels open and sodium rushes into the neuron by diffusion and attraction to negative charges inside
A stimulated neuron is ___ charged inside, and is referred to as being ___.
positively; depolarized
wave of depolarization
area of permeability to Na+ spreads down the neuron:
the local electrical current spreads to adjacent areas of the membrane, causing the Na+ channels to open > Na+ diffuses in > these areas are now also depolarized
The charge on a stimulated nerve membrane is called a(n) ___.
action potential
After the depolarization wave passes: ____.
Na+ channels close and K+ channels open, causing more K+ to diffuse outside the neuron
The outer surface of the neuron becomes ___ charged after the impulse passes, referred to as ___.
positively; repolarization
What happens after repolarization?
The Na+ that leaked in and the K+ that diffused out are returned to the original sides of the membrane by the Na+/K+ Pump.
How is an impulse conducted down a unmyelinated neuron?
continuous conduction
How is an impulse conducted down a myelinated neuron?
saltatory conduction
continuous conduction
step-by-step depolarization of each adjacent area of an axon in an unmyelinated neuron
myeline sheath
fatty insulated around some axons that doe snot conduct electrical current
node of Ranvier
unmyelinated gaps where depolarization can occur, and action potentials can be generated
saltatory conduction
the nerve impulse jumps from node to node along a myelinated axon - greatly increasing the speed of nerve impulse conduction
Speed is ___ stimulus strength
independant of
All-or-none Principle
an action potential either happens completely or not at all - if a stimulus is strong enough to cause an action potential, a stronger stimulus will not make it travel faster
What affects the speed of nerve impulses?
- temperature - warm neurons conduct at faster speed
- size of axon - larger diameters conduct impulses faster (less resistance)
- presence/absence of myelin - myelinated axons conduct faster (biggest effect on speed)
synapse
junction between two neurons - transfers information from one neuron to another
synaptic cleft
tiny space between the 2 neurons filled with ECF
presynaptic neuron
brings the nerve impulse to the synapse
postsynaptic neuron
carries the nerve impulse away from the synapse
When a wave of depolarization reaches the end of a presynaptic neuron: _____.
synaptic vesicles in the synaptic knobs fuse with the membrane and release their contents into the cleft
neurotransmitter
the chemical released from the synaptic vesicles in response to an action potential
Neurotransmitters ___ across the cleft and bind to ___ on the ____.
diffuse; receptors; postsynaptic membrane
Why does the synapse result in one-way impulse conduction?
only axon terminals have neurotransmitters - not in the cell body
Each neuron releases ___ of neurotransmitter.
one type
