Lecture 4

Question 1

why do more complex organisms need a NS

Answer 1

• cells on the inside of the body are not in direct contact with the outside world
• cells live in diff environments
• cells have become specialised

Question 2

what do the cells need to do for the organisms to function ?

Answer 2

coordinate

Question 3

endocrine system do what ?

Answer 3

specialised to secrete chemicals ( hormones ) into bloodstream

slow

long term

not specific

Question 4

nervous system

Answer 4

specialised to transmit electrical impulses between 2+ cells

fast

precise co-ordination + communication

specific

Question 5

neural impulses

Answer 5

basis for constant and rapid communication between cells

( constant and rapid control and adjustment of ongoing cell activities)

Question 6

what do neurones do

Answer 6

• generate and transmit electrical impulses over great distances
• rapidly

Question 7

where do electrical impulses reach

Answer 7

specific target cells
- modifies the activity of this cell

• allows selective control of specific target structures

Question 8

how does the NS have a structured communication system

Answer 8

combination and integration of signals from diff sources
- structured communication
- input used to adjust output

Question 9

special requirements of neurone - to do with energy

Answer 9

no possibility to store energy
so glucose ( sugar ) and oxygen must be constantly supplied

Question 10

without glucose being provided for the neurone, what happens

Answer 10

it stops working within seconds
dies within minutes

Question 11

where do neurones come from

Answer 11

neural stem cells ( they do not divide )

Question 12

neurogenesis

Answer 12

generation of new neurones - 5 months after conception : after this, dead neurones usually replaced

Question 13

how many neurones die during maturation

Answer 13

20-80%

Question 14

Glia cells

Answer 14

provide protected environment for neurones to survive
develop like neurones - from neural stem cells
- as many glia as neurones in brain ( but 10th of a size of neurone )

Question 15

Astrocytes

Answer 15

star shaped

physical, nutritional support for neurone ( blood brain barrier )
transport nutrients from blood vessels to neurones

waste products away from neurones

hold neurones in place

Question 16

Microglia

Answer 16

small

mobile for defensive function

produce chemicals that aid repair of damaged neurones

digest dead neurones ( phagocytosis )

Question 17

Oliogendrogia

Answer 17

large

flat branches

wrap around axons

fatty substance ( myelin sheath ) insulating axon

Question 18

draw parts of neurone - look at diagram

Answer 18

dendrites
main input area
axon hillock
axon terminals
axon collaterals ( axon split into many branches )

Question 19

resting potential

Answer 19

ion conc differ between inside and outside of cell

if membrane was non-permeable, electrical potential would remain static

protein channels in cell membrane allow ions to enter / leave cell

if membrane channels were just passive ‘holes’, membrane would depolarise ( electrical potential dissapears )

-70mV

Question 20

sodium potassium pump + membrane potential - resting potential

Answer 20

active channels work against equilibrium

neurone need energy to maintain their resting potential

3 Na+ out
2 K+ in

Question 21

conc gradient + electrical gradient try to push in our push out K+ ( resting potential )

Answer 21

concentration gradient : push out

electrical gradient : push in

Question 22

conc gradient + electrical gradient try to push in our push out Na+ and Cl- ( resting potential )

Answer 22

Na+
conc grad = pull in
electrical grad = pull in

Cl-
conc grad = pull in
electrical grad = push out

Question 23

ion specific channels can do what? and when ?

Answer 23

open - by chance or response to stimulus

Question 24

depolarisation happens when

Answer 24

if + ions enter ( or - ions leave ), membrane depolarises
- inside less negative than usual

Question 25

membrane hyperpolarisation when

Answer 25

if negative ions enter ( positive leave ) inside more negative than usual

Question 26

electronic transmission happens where

Answer 26

soma and dendrites

Question 27

electronic transmission

Answer 27

electrical and concentration gradients sweep ions along the membrane passive and graded ( of diff magnitude - strength ) --> some ions get lost on their way eg. drift out of membrane so signal decays

Question 28

action potential - explain what is

Answer 28

electrical and concentration gradients push/pull ions across membrane active and not graded ( always same magnitude / strength of signal) self-replicating (signal replicates itself to same strength ) constant magnitude so no decay

Question 29

action potential process

Answer 29

sodium channels open or close in response to electrical changes at membrane membrane depolarises ( more negative ) sodium channels open if threshold reached ( -50mV) sodium ions enter cell membrane depolarises further all nearby sodium channels open membrane fully depolarises total sodium permeability enough positive ions enter that it becomes more positive inside than outside ( complete depolarisation) sodium channels close, no more sodium ions enter potassium channels open potassium ions rush OUT

Question 30

threshold potential is also called

Answer 30

Hodgkin-Huxley cycle

Question 31

Hodgkin-huxley cycle

Answer 31

IF membrane potential at axon hillock remains below -50mV = resting potential returns + signal decays IF membrane potential at axon hillock depolarises above -50mV - all sodium channels open - action potential generated

Question 32

repolarisation

Answer 32

enough positive ions enter that it becomes more positive inside than outside ( complete depolarisation) sodium channels close, no more sodium ions enter potassium channels open potassium ions rush OUT membrane repolarises

Question 33

hyper polarisation

Answer 33

potassium channels close when resting potential is restored fewer potassium ions inside than out cell = membrane hyper polarises

Question 34

conduction of action potential

Answer 34

starts from axon hillock and goes down axon each burst of depolarisation triggers sodium channels in adjacent sections of the membrane of the axon to open

Question 35

why does AP not travel backwards ?

Answer 35

during hyperpolarisation - (after AP has just passed through) the membrane is difficult to depolarise BUT membrane in front of AP is still at resting potential and so more easy to depolarise

Question 36

properties of AP

Answer 36

doesn't decay during transmission always strong enough to depolarise next area of membrane all-or-nothing phenomenon : either generated or not ( and at same intensities ) cannot be produced continuously - minimum Time of 2-5 ms between each AP fast

Question 37

all-or-nothing phenomenon

Answer 37

either generated or not ( and at same intensities ) but can be diff frequencies

Question 38

can an AP be produced continuously ?

Answer 38

no 2-5 ms between each AP

Question 39

In mammals, how do the signals travel so fast ?

Answer 39

because sensory and motor neurones are myelinated

Question 40

what does myelin prevent ?

Answer 40

inflow and outflow of ions because it electrically insulates electrical charges are transported inside the axon - without need to produce AP

Question 41

nodes of ranvier

Answer 41

every 1-2mm, myelin sheath has gaps called nodes of ranvier

Question 42

what happens at the nodes ?

Answer 42

new AP is generated - action potential jumps from node to node ( saltatory conduction )

Question 43

qualitative - types of info coded how

Answer 43

place in brain where signal received

Question 44

quantitative - how strong a stimulus is how detected ?

Answer 44

firing rate - how many AP's within given time a strong input will cause neurone to send out signals more quickly

Question 45

weak stimulus

Answer 45

low frequency of AP

Question 46

strong stimulus

Answer 46

higher frequency of AP's