Lecture 6 Flashcards
what are the 4 primary categories of the CNS functions
sensory function
motor function
integrative
memory
what direction does all sensory information move?
move in one direction superiorly to the brain from the periphery
sensory information from receptors of the body surface and some internal structures
somatic
sensory CNS function includes ____.
somatic system and senses
Motor CNS function includes ?
effectors of body movement
In motor CNS the effectors of body movement signal move to the _____ of the brain and cause _____.
periphery
skeletal muscle
contraction of skeletal muscle can include ______ and ______
smooth muscle contraction of internal organs
exocrine and endocrine gland secretion
control of motor is not strictly from the brain, other sources of input control include_________.
spinal cord
midbrain reticular substances
basal ganglia
cerebellum
integrative function of CNS involve _____.
a lot of sensory information that is channeled to the region of brain most appropriate for it because most sensory information is irrelevant to function
for example a painful stimulus might go to the _________ is assessed and the _______ would decide to shift positions
cerebral cortex
motor cortex
an extremely painful stimulus would cause a _________
reflecting retraction of that limb thru reflex of motor neurons in the spinal cord (not go to brain first)
what determine the routing and sorting in the integrative functions of the CNS?
synapses either facilitate or inhibit signals
storage of information is primarily a process of ________
filling away sensory information
most storage of information in the CNS occurs in the ______, but many regions of the brain assist.
cerebral cortex
what makes storage of information more efficient over time and how?
synapses by retaining ability to send certain types of sensory signals
-repetition
there are _____ neurons in the CNS that move in _____ direction
the neurons inout into the _______ and the _____. They output into ______
100 billion
one direction only
dendrites and cell body
a single axon with branches to the rest of body
what is the structure of a typical synapse between two neurons?
presynaptic neuron - sends signal (bulb)
postsynaptic neuron - receiving signal (pit)
synaptic cleft - intercellular space between pre and post synaptic neurons over which electrical signal is passed
signal transmission from axon to dendrite
axodendritic
signal transmission from axon to cell body
axosomatic
signal transmission from axon to axon
axoaxonic
a synapse in which action potentials conduct directly between adjacent cells through structures called gap junctions
electrical synapses
electrical synapses are commonly found in ______?
smooth muscle
cardiac muscle
developing embryo
what are the advantages electrical synapses
faster communication due to direct communication through gap junctions.
have the ability to synchronize the activity of a group of neurons or muscle fibers
- can create action potentials in unison
- important in coordinated contraction
a synapse in which pre and postsynaptic membranes do not touch but are separated by a synaptic cleft
chemical synapse
how does chemical synapses work?
presynaptic neuron releases a chemical neurotransmitter that diffused through the synaptic cleft and binds to receptors in the plasma membrane of the postsynaptic neuron
the chemical signal in turn produces a postsynaptic potential
in chemical synapses, an ______ signal from presynaptic neuron is converted to a ______ signal which is converted back to an ______ signal by the postsynaptic cell.
this allows a synaptic delay of about ____.
electrical
chemical
electrical
0.5 msec
electrical potentials exist across the membranes of nearly all cells but there are differences in how these potential are used explain muscle and nerve cells vs glandular cells, macrophages, and ciliated cells?
excitable cells (muscle and nerve cells) - generate rapidly changing electrochemical impulses used to transmit electrical signals along their membranes
granular cells, macrophages, and ciliated cells
- generate local changes in membrane potential which activates many of their cell functions
membrane potential at their core are caused by ______
diffusion
- a concentration difference of ions across a selectively permeable membrane can create a membrane potential
example of membrane potentials caused by diffusion?
K concentration difference
- large K gradient from the inside toward the outside causes these ions to move from the inside to the outside carrying positive charge with them
- this creates electropositivity outside and electronegativity inside the membrane
the difference that is made from diffusion causing action potential is called _________
diffusion potential
the diffusion potential level that opposes the net diffusion of a particular ion through the membrane
Nernst potential
- also called equilibrium potential
what determines the magnitude of Nernst potential?
the ratio of concentration of that specific ion on the two sides of the membrane
the _____ the ratio the greater the tendency for the ion to diffuse in one direction, and the _____ the nernst potential requires to prevent additional net diffusion
greater
greater
what does the nernst equation measure
potential for any ion at normal body temp.
nernst equation
EMF (millivolts) = ±61 log (concentration inside/concentration outside)
- switch top and bottom for negative ions, that is for positive
for the nernst equation it is assumed that ECF remains at _____ potential and the nernt potential is the potential ____ the membrane.
zero
inside
for the nernst equation it is + if the diffusing ion is _____ and the sign is - if the diffusing ion is ______
negative
positive
when the membrane is permeable to several different ions we have to look at what three factors?
- polarity of the electrical charge of each ion
- permeability of the membrane (P)
- concentrations (C) of the respective ions on the inside (I) and outside (o) of the membrane
when looking at several different ions, what equation do we use
goldman-hodgkin-katz equation
equation that will give us the calculated membrane potential on the inside of the membrane when two univalent positive ions, ____ and ____ and the one enuvalent negative ion ____ are involved. these three ions are considered bc they are the most important ions involved in generating membrane potentials in nerve and muscle fibers. Whats this equation called?
Na K
Cl
goldman-hodgkin-katz equation
goldman-hodgkin-katz equation
EMF = -61 log [C(Na+i) P(Na+) ] + [C(K+i) P(K+)] + [C(Cl-o) P(Cl-) ]
_____________________________
[C(Na+o) P(Na+) ] + [C(K+o) P(K+)] + [C(Cl-i) P(Cl-) ]
resting membrane potential (RMP) for large nerve cells is about _______
what does this number mean?
The two ions that primarily contribute to the RMP are ___ and ___.
-90 mVs
potential inside the nerve fiber is about 90 mVs more negative than the potential in ECF
Na+ and K+
what are the three factors contributing to then origin of the RMP
contribution of the K+ diffusion potential
contribution of the Na+ diffusion potential
contribution of the Na+/K+ pump
typical concentrations of Na+ and K+
Na+ outside = 142 mEq/L
Na+ inside = 14 mEq/L
K+ outside = 4 mEq/L
K+ inside = 140 mEq/L
special ion channel (Na K pump) existing in the cell membrane are called ______
leak channels
in the sodium potassium pump, ____ is about 100 times more leaky/permeable than ____
K
Na
why is the potassium side more leaky
because the ratio of K ions inside to outside is high (35:1), so the tendency for potassium to leak out is high
what is the nernst potential corresponding to the ratio of potassium in the cell to out and calculate if they were the only ion
-94 mVs
log of 35=1.54
1.54 (-61) = -94
the ratio of Na ions from inside to outside is ____ which gives us nernst potential of ____
0.1
+61 mVs
if you condiser Na and potassium in goldman equation what do u get?
- 61 log (140)(100) + (14)(1)
(4) (100) + (142)(1)
= -86 mVs
so our Na+ K+ pump causes a loss of ____ charges from inside the membrane, and this creates an additional degree of _____ on the inside of the membrane. What is the final membrane potential
positive
negativity (-4 mVs)
-90 mVs
nerve action potentials are elicited when a stimulus causes a sudden change from normal ____ to a ______. how does it end?
RMP
Positive potential
almost equally rapid change back to RMP
what are the four stages of the action potential
- resting stage
- depolarization
- repolarization
- afterhyperpolarization
Resting stage
stage before action potential begins
RMP is polarized (-90 mVs)
voltage gated Na and K channels are closed
what happens in depolarization stage?
- stimulus causes membrane to depolarize to threshold (-65 mVs)
- triggers the rapid opening of Na channels
- membrane suddenly becomes very permeable to Na)
- large influx of positive charge diffuses into interior of axon
- RMP of -90 mVs by the infix of positive charge
in large nerve fibers, the large influx of positive charge is so great that it causes _____
overshoot beyond zero and membrane potential becomes positive
(usually around +35)
what happens in the repolarization stage?
within 10,000th of a second the Na channels close
K channels finally open but slowly (don’t open fully until Na channels are closing)
K rapidly flows outward and that makes inside more negative, reaching normal rmp
what is AfterHyperpolarization?
while K channels are still open, outflow may be large enough to cause afterhyperpolarization
RMP becomes more negative than its normal -90 mVs
gated channel close and RMP returns to normal value of -90
what is the role of impermeant negatively charged ions (anions) during action potentials
many anions inside the cell cannot pass through the membrane channels
this creates a deficit of positive ions inside the axon, and excess of impermeant negative ions
these ions are responsible for negative charge inside the fiber
what is important about calcium channels?
slightly permeable to Na as well as calcium and they flow into the fiber
Ca channels require 10-20x more time to activate than Na
Ca channels are numerous in cardiac and smooth muscle
calcium pumps so what? and where are they located?
pump calcium from interior to exterior or into the ER of the cell, creating an ion gradient and restoring normal levels
most all cells of the body on their membranes
how does action potential move from one area to the next?
positive electrical charges are carried inward by diffusing Na through the depolarized membrane for several millimeters in both directions along the axon core
The positive charges increase voltage for a distance of 1-3 mm inside the fiber to above the threshold voltage value for initiating an action potential
sodium channels in new adjacent areas open and an explosive action potential spreads
what is the all of nothing principle
once an action potential has been elicited at any point on the membrane there are two options : ALL or NOTHING
The ALL option in the all or nothing principle
the nerve fiber fires and the action potential spreads over the entire membrane under appropriate conditions
travels all directions away from the stimulus
The NOTHING option in the all or nothing principle
The nerve fiber does not fire and the action potential does not travel at all under inappropriate conditions
- insufficient voltage to stimulate the adjacent area of the membrane
applies to only excitable tissue (nerve and muscle)
The average nerve trunk contains _____ unmyelinated and _____ myelinated nerve fibers
twice as many unmyelinated than myelinated
what are myelinated nerve fibers?
axon membrane is covered with electrical insulator mmyelin
how does the myeline sheath get on myelinated fibers?
schwann cells rotate around axon laying down layers of shwann cell membrane
Their membrane includes a lipid sphingomyelin, which is n excellent electrical insulator
what does the myelin sheath do to the ion flow
decreases ion flow thru membrane 5000 fold
what is the node of ranvier?
the juncture between two successive shwann cells contains an unmyelinated region 2-3 micrometers in length
two different modes of action potential propagation?
what does it depend on?
continuous conduction
saltatory conduction
depends on myelination
what is continuous conduction?
occurs in unmyelinated fiber
step by step depolarization of each adjacent segment of the plasma membrane
this takes time therefore this ropagation is slower
what is saltatory conduction?
occurs in myelinated fibers
almost no ions can flow through the myelin sheath
ions flow through the nodes of ranvier which contain increased amounts of Na channels
the action potential occurring at one node of ranvier jumps to the next node and so forth until impulse travels all the way down the axon faster
what are some advantages of saltatory conduction?
velocity is 5-50 times faster than non myelinated fibers
conserved energy
period in which a new action potential cannot be elicited, even with a strong stimulus
absolute refractory period (ARP)
why does absolute refractory period happen?
shortly after the action potential has been initiated the Na channels become inactivated and no signals applied will re-open the gates
when does the absolute refractory period end?
when the membrane potential returns to ner RMP
