Download steps in nerve impulse transmission

NERVE IMPULSE TRANSMISSION
I. Transmission Along a Neuron
1. RESTING POTENTIAL
 Na K pump moves 3 Na out for every 2 K in
 ( -70mV)
2.
THE ACTION POTENTIAL
Triggered by a stimulus strong enough to produce a
depolarization through a special phenomenon
ALL OR NOTHING PHENOMENON
Increasing the intensity of the stimuli above threshold will
not produce an increased response.
Neurons either fire maximally
or not at all.
STAGES OF THE ACTION POTENTIAL
A. DEPOLARIZATION PHASE
 Na channels open to let Na rush in
 K channels stay closed (+30mV)
B. REPOLARIZATION PHASE
 K channels open and let K rush out
 Na stays in since gate is closed (down to -80mV)
(extra dip is refractory period)
3. UNDERSHOOT (AKA REFRACTORY PERIOD)
 Na and K channels close but NaK pump restores order
(-70mV) after hyperpolarization
II. Transmission Between Neurons
Communication between neurons is accomplished by moving
across a small gap called the synapse.
Synapse: space between two neurons or between a neuron
and an effector.
Presynaptic neuron: carries impulse toward synapse.
Postsynaptic neuron: carries impulse away from synapse.
1. Neurotransmitters (NT) are chemicals released from one
neuron at the presynaptic nerve terminal.
2. NT then cross the synapse where they may be accepted by
the next neuron at a specialized site called a receptor
3. The action that follows activation of a receptor site may be
either depolarization or hyperpolarization
EXAMPLES OF NEUROTRANSMITTERS
Acetylcholine (Ach)
GABA
Serotonin Dopamine
Neurotransmitters can be destroyed in different ways if they
are no longer needed
Example-enzymatic degradation
Acetylcholinesterase breaks Ach into choline
Summation: Effect produced by the accumulation of NTs
from two or more neurons.
a. Excitatory postsynaptic potential (EPSP)
Depolarization makes it MORE likely that an action potential will
fire
b. Inhibitory postsynaptic potential (IPSP)
Hyperpolarization makes it LESS likely that an action potential
will fire.