Sem 4 Week 1 Lecture 1

Front 1

The wolume of an axon is many times larger than that of the cell body.

Back 1

True

Front 2

Neurons are NOT post-mitotic.

Back 2

False.They are.

Front 3

Where is the majority of cell volume,membrane,protein and energy requirements found?

Back 3

Outside cell body.

Front 4

Is it true that the stock of neurones you are born with stays with you till you die?

Back 4

Yes!

Front 5

At what age do you the max. no. of neurons?

Back 5

1 year old.

Front 6

What constitutes Nissl substance ?

Back 6

Rough endoplasmic reticulum

Front 7

Neurons are terminally differentiated.

Back 7

True

Front 8

What happens at the initial segment?

Back 8

AP starts and axon leaves cell body.

Front 9

Dendrites

Back 9

Receive info and are numerous in numbers.

Front 10

What is the equivalent of the BBB ,in the PNS?

Back 10

Blood Nerve Barrier.

Front 11

Can the brain use fats for energy?

Back 11

NO.only glucose-ketones during fasting > 18 hours.

Front 12

Where do heart cells get their energy from?

Back 12

50 % from glc and 50 % from Fatty Acids.

Front 13

Brain which is 1 % of body weight consumes

Back 13

25 % of O2 and 2 % of blood flow AT REST.

Front 14

Why does the brain have high energy requirements?

Back 14

Area of cell membrane with numerous Na/K pumps

Front 15

What is particularly significant about neurons?

Back 15

No significant energy stores within them.

Front 16

Does the brain have a good collateral circulation?

Back 16

No-ischemic events.

Front 17

Neurons are

Back 17

Electrically active.

Front 18

Neurons

Back 18

Talk to each other by chemical transmission but WITHIN neurons,signals transmitted electrically.

Front 19

How is the depolarization signal transmitted along the axon?

Back 19

Via AP.

Front 20

Why does brain of a child increase in size?

Back 20

Glial cells enlarge and proliferate.(NOT neurons)

Front 21

Are neural circuits completely fixed ?

Back 21

NO-ability to make/unmake synapses throughout life via :
-activity(protection v/s senile dementia)
-neutrophin
-major culling during develop.

Front 22

New synapses CANNOT be formed in the adult CNS.

Back 22

False

Front 23

Long term memory enhanced by

Back 23

Adding new synapses.

Front 24

Dendrites,being signal collectors, do not

Back 24

Initiate APs.(they can have VASC)

Front 25

Cell body

Back 25

is the signal integrator.

Front 26

Where do you have the highest density of VASC?

Back 26

Axon hillock-AP initiator.

Front 27

Can severe axons in the PNS regrow?

Back 27

YES.

Front 28

Severe axons in the CNS cannot regrow.

Back 28

True.

Front 29

What are the 3 types of neurons in the PNS?

Back 29

-Sensory
-Motor
-Autonomic

Front 30

What happens during depolarisation to a neuron?

Back 30

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.

Front 31

VASCs

Back 31

open at - 55 mV and close at -80mV.

Front 32

Where are the most senstive VASCs?

Back 32

At axon hillock.

Front 33

Describe briefly what happens during depolar.

Back 33

-VASCs open up and Na diffuse in
-Na outnumber -ve ions
-Excess + ve ions inside cells
-Na pumped out

Front 34

Total driving force is based on

Back 34

1.Concentration gradient
2. Voltage

Front 35

What is the total driving force on Na and K ?

Back 35

145 mV INWARDS for Na and 15 mV outwards for K.

Front 36

What is the reversal potential?

Back 36

Voltage equivalent to Conc. gradient.

Front 37

What is the main INTRAcR ion in a neuron?

Back 37

K+

Front 38

What is the main EXTRAcR ion?

Back 38

Na+

Front 39

Even if the no. of K+ channels > no. of Na+ channels,

Back 39

no. of K+ out = no. of Na+ in.(no net movement of charges in a RESTING cell)

Front 40

What happens at steady state?

Back 40

Membrane V is constant with current flowing IN(Na+) exactly counterbalanced by current flowing OUT.(K+)

Front 41

The resting K+ conductance is greater than the resting Na+ conductance.

Back 41

True.From I.k= g.k x 15 mV and I. Na = g.Na x 145 mV

Front 42

What does AP initiation require?

Back 42

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.

Front 43

What happens during AP termination?

Back 43

-VASC close quickly as Na is pumped out.
-VA K+ channels open with K+ leaking out.
-Na/K keeps pumping the entire time.

Front 44

Na and K channels are triggered by the same thing, at the same voltage but K+ channels respond slowly.

Back 44

True-K+ channels open with a delay of 0.5-1 ms to speed up repolariz. and resume normal polarity.

Front 45

AP spreads

Back 45

Because neighbouring membrane becomes passively depolarised.

Front 46

Depolar. of AP spreads passively with

Back 46

distance-partial depol. infront of it.(threshold level)

Front 47

Inward current spreads

Back 47

Longitudinally but becomes weaker due to leakage.

Front 48

What will be the state of the membrane at 2 lambda?

Back 48

At threshold voltage.(-55mV)

Front 49

Within 2 lambda(2 x length constant),

Back 49

passive depolarization will reach threshold.(at or above threshold)

Front 50

What does speed of depolarisation depend on?

Back 50

1. how far the passive depol. spreads(varies between nerves)
2.delay between threshold voltage and reaching peak depolariz.

Front 51

It takes 0.33 ms for AP to travel 2 lambda.

Back 51

True-6000 lambda per sec(conduction velocity = 6000 lambda per sec)

Front 52

The axon is depol. to threshold in advance of AP front, by a distance of 2 lambda.

Back 52

True

Front 53

What determines the length constant?

Back 53

-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)

Front 54

Current leakage mainy determines

Back 54

Length constant
-for myelinated fibres,lambda= d
-for unmyel. fibres,lambda=170 x square root of d.

Front 55

Unmyelinated fibres

Back 55

-Very fine: 0.5 micron diameter
-Olfaction,nociception,temp.
-0.78 m/s
-VASCs and VAPCs located continuously throughout axons.

Front 56

Myelinated fibres

Back 56

-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)

Front 57

Name some EXCITATORY transmitters.

Back 57

-ACh(neuromusc. junctions)
-Glu in CNS
---> increase g Na+

Front 58

Name some INHIBITORY transmitters.

Back 58

-GABA
-Glycine
----> increase g Cl-