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Membrane and Action Potential
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Glecy Koline
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Steps in muscle contraction:
Initiated by a
depolarizing
stimulus opening voltage-gated
Na+
channels
Na+
influx depolarizes the membrane further, causing more
Na+
channels to open
Positive feedback loop
leads to rapid depolarization, the action potential
Terminated by inactivation of Na+ channels and opening of voltage-gated
K+
channels
K+ efflux
repolarizes the membrane, restoring the resting potential
Image of a
skeletal muscle fiber
, the
basic unit
of skeletal muscle, with
multiple nuclei
beneath the sarcolemma
Image of a skeletal muscle fiber seen with an
electron microscope
permit passage of certain ions
Integral proteins
An example of
voltage-gated
channel
Activation and Inactivation gate of
Sodium
channel
It balances the tendency for diffusion caused by
concentration difference
Equilibrium potential
generated across a membrane because of a concentration difference of an ion
potential difference
No
net diffusion
occurs in Nernst Potential
True
Value of Normal nerve RMP
-70mV
exhibited by all cells
RMP
Causes of occurrence of RMP
Nernst
potential of
Na
and
K
K
leak channels
Na K
ATPase
pump
Nerve membrane is more permeable to
K+
than
Na+
True
Why is nerve membrane more permeable to K+ than Na+?
High resting conductance to K
Exhibited only by
excitable
cells
AP
Characteristics of true Ap
Stereotypical
size and shape
Propagating
All
or
none
Each normal AP for a given cell type looks identical,
depolarizes
to the same potential and repolarizes to the same RMP
True
AP at one cell causes
depolarization
of adjacent cells in a nondecremental
manner
Propagating
If a threshold is reached, a full-sized AP will be produced, otherwise, none at all
All or none principle
Positive charges flow into the cell causing depolarization
Inward current
Positive charges flow out of the cell causing
hyperpolarization
Outward current
Make the MP more positive
Depolarization
Make the MP more negative
Hyperpolarization
Occurs during an AP when MP>0mV
Overshoot
Occurs during an AP when MP<RMP
Undershoot
Non-propagated local potential due to local change in ionic conductance
Electrotonic potential
the larger the nerve fiber, the
smaller
the internal resistance, and
the
faster
the conduction velocity
True
Where is conduction velocity is most dependent?
Nerve diameter
Where is AP is regenerated, which contains the highest concentration of Na+ channels per square micrometer of cell membrane?
Nodes of Ranvier
The basic working unit of CNS and PNS, and exhibits the characteristic of being electrically excitable
Neurons
Contains the
nucleus
, which is the neuron's metabolic center
Soma
bring signal away from the body (presynaptic terminal)
Axon
Brings and transmits signal towards the cell body
Dendrite
A protein-lipid complex that is wrapped around the axon
Myelin sheath
It is where action potentials cause the release of synaptic
transmitters
nerve endings
It transmits propagated impulses to the nerve endings
Axonal process
minimal intensity of stimulating current needed to produce an action potential
Threshold intesnsity
weak stimulus needs a long duration.
True
A strong stimulus is sufficient at a
short
duration
True
No action potential occurs if the stimulus is
subthreshold
in magnitude, and the
action potential has a
constant
amplitude and
form
at any stimulus
strength
above
the threshold
True
Associated with the immune system; scavenger cells that resemble tissue macrophages
Microglia
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