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58 Cards in this Set

  • Front
  • Back
The wolume of an axon is many times larger than that of the cell body.
Neurons are NOT post-mitotic.
False.They are.
Where is the majority of cell volume,membrane,protein and energy requirements found?
Outside cell body.
Is it true that the stock of neurones you are born with stays with you till you die?
At what age do you the max. no. of neurons?
1 year old.
What constitutes Nissl substance ?
Rough endoplasmic reticulum
Neurons are terminally differentiated.
What happens at the initial segment?
AP starts and axon leaves cell body.
Receive info and are numerous in numbers.
What is the equivalent of the BBB ,in the PNS?
Blood Nerve Barrier.
Can the brain use fats for energy?
NO.only glucose-ketones during fasting > 18 hours.
Where do heart cells get their energy from?
50 % from glc and 50 % from Fatty Acids.
Brain which is 1 % of body weight consumes
25 % of O2 and 2 % of blood flow AT REST.
Why does the brain have high energy requirements?
Area of cell membrane with numerous Na/K pumps
What is particularly significant about neurons?
No significant energy stores within them.
Does the brain have a good collateral circulation?
No-ischemic events.
Neurons are
Electrically active.
Talk to each other by chemical transmission but WITHIN neurons,signals transmitted electrically.
How is the depolarization signal transmitted along the axon?
Via AP.
Why does brain of a child increase in size?
Glial cells enlarge and proliferate.(NOT neurons)
Are neural circuits completely fixed ?
NO-ability to make/unmake synapses throughout life via :
-activity(protection v/s senile dementia)
-major culling during develop.
New synapses CANNOT be formed in the adult CNS.
Long term memory enhanced by
Adding new synapses.
Dendrites,being signal collectors, do not
Initiate APs.(they can have VASC)
Cell body
is the signal integrator.
Where do you have the highest density of VASC?
Axon hillock-AP initiator.
Can severe axons in the PNS regrow?
Severe axons in the CNS cannot regrow.
What are the 3 types of neurons in the PNS?
What happens during depolarisation to a neuron?
The -ve charge inside the cell become + ve due to Na mvt in(-80 to +30 mV)-amt of excess -ve charge inside cell is normally minute.
open at - 55 mV and close at -80mV.
Where are the most senstive VASCs?
At axon hillock.
Describe briefly what happens during depolar.
-VASCs open up and Na diffuse in
-Na outnumber -ve ions
-Excess + ve ions inside cells
-Na pumped out
Total driving force is based on
1.Concentration gradient
2. Voltage
What is the total driving force on Na and K ?
145 mV INWARDS for Na and 15 mV outwards for K.
What is the reversal potential?
Voltage equivalent to Conc. gradient.
What is the main INTRAcR ion in a neuron?
What is the main EXTRAcR ion?
Even if the no. of K+ channels > no. of Na+ channels,
no. of K+ out = no. of Na+ in.(no net movement of charges in a RESTING cell)
What happens at steady state?
Membrane V is constant with current flowing IN(Na+) exactly counterbalanced by current flowing OUT.(K+)
The resting K+ conductance is greater than the resting Na+ conductance.
True.From I.k= g.k x 15 mV and I. Na = g.Na x 145 mV
What does AP initiation require?
Inward current to depolarise a region of mb by about 25 mV.(VASCs stay open for abt 1-2 ms)---> large influx of Na ions and mb undergoes localised depol. and overshoots to + 30 mV.
What happens during AP termination?
-VASC close quickly as Na is pumped out.
-VA K+ channels open with K+ leaking out.
-Na/K keeps pumping the entire time.
Na and K channels are triggered by the same thing, at the same voltage but K+ channels respond slowly.
True-K+ channels open with a delay of 0.5-1 ms to speed up repolariz. and resume normal polarity.
AP spreads
Because neighbouring membrane becomes passively depolarised.
Depolar. of AP spreads passively with
distance-partial depol. infront of it.(threshold level)
Inward current spreads
Longitudinally but becomes weaker due to leakage.
What will be the state of the membrane at 2 lambda?
At threshold voltage.(-55mV)
Within 2 lambda(2 x length constant),
passive depolarization will reach threshold.(at or above threshold)
What does speed of depolarisation depend on?
1. how far the passive depol. spreads(varies between nerves)
2.delay between threshold voltage and reaching peak depolariz.
It takes 0.33 ms for AP to travel 2 lambda.
True-6000 lambda per sec(conduction velocity = 6000 lambda per sec)
The axon is depol. to threshold in advance of AP front, by a distance of 2 lambda.
What determines the length constant?
-The greater the mb's electrical resistance,the less leakage current.(how much of incoming charge can stay inside to neutralize inside -ve charge).
-the less the axon's internal resistance,the further the depol. current can spread.(lambda increases with axon diameter d)
Current leakage mainy determines
Length constant
-for myelinated fibres,lambda= d
-for unmyel. fibres,lambda=170 x square root of d.
Unmyelinated fibres
-Very fine: 0.5 micron diameter
-0.78 m/s
-VASCs and VAPCs located continuously throughout axons.
Myelinated fibres
-20 micron diameter
-Proprioceptive,motor fibres
-120 m/s
-VACs only at nodes of Ranvier(AP can jump more than one node at a time-like 5 nodes)
Name some EXCITATORY transmitters.
-ACh(neuromusc. junctions)
-Glu in CNS
---> increase g Na+
Name some INHIBITORY transmitters.
----> increase g Cl-