Lesson 13 Flashcards
electrical potential
difference in concentration of charged particles between two points
current
flow of charged particles from one point to another
resting membrane potential (RMP)
charge difference across plasma membrane
leak channels
membrane channels that are always open; are specific for one ion
gated channels
channels that are normally closed, but can be stimulated to open; specific to its ion
chemically-gated channel
binding of a chemical (hormone, neurotransmitter) causes the channel to open
- found on neuron cell body, dendrites
voltage-gated channel
channel opens due to a change in the membrane potential
- found on neuronal axon, skeletal/cardiac muscle
mechanically-gated channel
channel opens due to physical stress/deformation on the cells plasma membrane
- found on sensory receptors (touch)
three states of a gated channel
- closed - but capable of opening
- open - aka activated
- inactivated - ions cannot pass through, channel is not closed but ‘gated off’ by an inactivation gate
resting membrane potential results from these three things
- diffusion of ions down their concentration gradients through the membrane
- selective permeability of the membrane, allowing some inos to pass more easily than others
- electrical attraction of cations and anion to each other
what ion has the greatest influence on resting membrane potential?
potassium K+
Is sodium or potassium more abundant in the ECF?
sodium
What can sensory neurons be triggered by? (4)
chemicals, light, heat, or mechanical forces
characteristics of local potentials: graded
vary in magnitude with stimulus strength
- stronger stimuli will cause gated channels to remain open longer
characteristics of local potentials: decremental
get weaker the farther they spread from the point of stimulation
characteristics of local potentials: reversible
if stimulation ceases, membrane voltage quickly returns to normal resting potential
depolarization
is excitatory, makes a neuron more likely to fire an action potential
hyperpolarization
is inhibitory, makes a neuron less likely to produce an action potential
action potential
rapid up-and-down change in voltage produce by the coordinated opening and closing of voltage-gated ion channels
seven steps of an action potential
- local potential spreads to the axon hillock (must reach threshold potential)
- voltage-gated Na+ channels open quickly; depolarizing the cell
- when voltage reaches +35 mV, Na+ channels inactivate
- the voltage gated K+ channels are fully open, and K+ flows out of the cell membrane repolarizing it
- K+ continues to exit and produces a negative overshoot, aka hyperpolarization
- membrane potential returns back to normal as Na+ leaks into the cell
- cell is at resting potential
all-or-none law
if threshold is reached (-55mV), a neuron fires to maximum voltage; if threshold is not reached, it does not fire
characteristics of local potentials: nondecremental
does not get weaker with distance, the action potential is ‘regenerated’ as it travels along the axon
characteristics of local potentials: irreversible
once starts, an action potential travels all the way down the axon and cannot be stopped
refractory period
period of resistance to stimulation; has two phases
absolute refractory period
no stimulus of any strength will trigger another action potential
relative refractory period
an unusually strong stimulus is needed to trigger a new action potential
unmyelinated axons have ______ along their entire length
voltage-gated channels
continuous conduction
chain-reaction continuing down an axon
why can action potentials only be generated at the nodes of axons?
the voltage-gated ion channels are concentrated here
the speed at which a nerve signal travels down an axon depends on two factors…
- diameter of the neuron
- presence or absence of myelin
type A neuronal fibers
- myelinated, large diameter axons
- fast, carries info quickly
- high speed (120m/sec)
type B neuronal fibers
- myelinated, medium diameter axons
- carries intermediate info
- medium speed (18m/sec)
type C neuronal fibers
- unmyelinated, small diameter axons
- carries flow info
- slow speed (1m/s)
