5.1.3 Neuronal Communication

Question 1

What do neurones transmit

Answer 1

Nerve impulses rapidly around the body

These impulses are in a electric nature

Question 2

What is the function of a dendrite

Answer 2

Small extensions that carry impulses towards the cell body

Question 3

What’s the function of the cell body

Answer 3

Produced protein neurotransmitters and ATP, has nucleus cytoplasm rough ER and mitochondria

Question 4

What is the function of the myelin sheath

Answer 4

Lipid covering that insulated the axon speeding up nerve impulses by allowing Saltatory conduction

Question 5

What is the function of Schwann cells

Answer 5

Produce myelin sheath

Question 6

What is the function of node of ranvier

Answer 6

Gap between Schwann cells

No myelin sheath here

Question 7

What is the function of the axon

Answer 7

Carries nerve impulses away from cell body, thing long cytoplasm with plasma membrane

Question 8

What is the function of terminal end branches

Answer 8

Connect neurons to muscle

Question 9

What is the job of the sensory neurones

What is the structure like

Answer 9

Carries action potentials from sensory receptor cells to intermediate neurones/ brain

Cell body in middle of neurone
Shorter axon
Dendrons present
Dendrites do not connect directly to cell body

Question 10

What is the job of the motor neurones

What is the structure like

Answer 10

Carries action potentials from relay neurones to effector ( muscles or glands )

Cell body at end of neurone
Dendrites connect directly to cell body
Longer axon
No dendron

Question 11

What is the function of relay neurones

What is the structure

Answer 11

Transmit impulses between neurones like sensory to motor

Cell body central to neurone
Dendrites connect to directly to cell body
Many short axons
Dendron present

Question 12

Describe Schwann cells

Answer 12

Wraps around the axon except at the nodes of ranvier

Produces myelin sheath which insulates, this sheath is fatty and does not allow Na+ or K+ ions into or out of the axon

So depolarisation can only occur at the nodes

Hence action potential jumps from one node to the next

This is saltatory conduction

Question 13

What’s the benefit of myelin

Answer 13

Speeds up conduction of action potentials due to faster depolarisation

Question 14

What does polarised mean

Answer 14

Unequal distribution of

Charge

Question 15

What is the name for a concentration gradient when we are dealing with ions

Answer 15

Electrochemical gradient

Question 16

Describe the distribution of charge when at resting potential

Answer 16

Negative charge inside

Positive charge outside

Question 17

Describe the sodium potassium pump

Answer 17

Actively transports 2k+ in and 3Na+ out of the axon

Using ATP

Question 18

How is resting potential maintained

Answer 18

Sodium potassium pump used ATP to actively transport 3Na+ out and 2K+ in to the axon

Many K+ ion channels are open so K+ ions diffuse back out of the axon

Voltage gated Na+ ion channels are closed

Fewer Na+ ion channels are open, so fewer Na+ ions can diffuse back in

Question 19

What two things do all sensory receptors have in common

Answer 19

They are all specific to a single type of stimulus

They are all transducers- converts one form of energy into a different form of energy

Question 20

What are the 4 types of sensory receptors

Answer 20

Mechanoreceptor (stimulus is pressure and movement- eg pacinian corpuscle)

Chemoreceptor (stimulus is chemicals eg olfactory receptors in nose)

Thermoreceptors (stimulus is heat eg end-bulbs of Krause)

Photoreceptors (stimulus is light eg cone cell)

Question 21

What is pacinian corpuscle

Answer 21

A transducer- converts mechanical energy into electrical energy

A pressure receptor

Question 22

Describe how an action potential is generated in a pacinian corpuscle

Answer 22

Pressure ca sides the corpuscle to deform

Stretch mediated Na+ ion channels in the neurone membrane open

Na+ ions diffuse in

depolarising the membrane

if the threshold is reached an action potential is generated

Question 23

the greater the pressure, the greater…

Answer 23

the frequency of nerve impulses along the neurone

Question 24

what is the all or nothing law

Answer 24

if the stimulus is not strong enough, the generator potential does not reach the threshold value, depolarisation of membrane is inefficient, there is no action potential

Question 25

describe the distribution of charge when at action potential

Answer 25

negative outside | positive inside

Question 26

explain what happens sat resting potential -70mv

Answer 26

- sodium potassium ion pump uses ATP to actively transport 3 Na+ ions out and 2K+ ions into the axon - voltage gated sodium ion channels are closed - fewer Na+ diffuses in - K+ ion channels are open so K+ ions diffuse out of the axon

Question 27

what happens at depolarisation

Answer 27

- pressure applied to pacinian corpuscle - stretch mediated sodium ion channels open - sodium ions idffuse into the axon creating a generator potential - causes voltage gated sodium ion channels to open, Na+ move in - if it goes above -50mv threshold dit causes all sodium ion channels to open and more sodium infuses in (POSITIVE FEEDBACK) - until +40mv action potential is reached

Question 28

what happens during repolarisation

Answer 28

voltage gated sodium ion channels close - voltsage gated K+ ion channels open - K+ ions diffuse out of the axon

Question 29

what happens during hyperpolarisation

Answer 29

- very high rate of K+ ion diffusion out of the axon\ - voltage falls below resting potential - voltage gated K+ ion channels close - sodium potassium pump restores resting potential

Question 30

what is there function of a Schwann cell

Answer 30

wraps around the axon and produces myelin myelin provides electrical insulation prevents movement of ions into/out of neurone prevents depolarisation

Question 31

what does myelin prevent from entering the axon what does this mean

Answer 31

does not allow Na+ or K+ ions to pass through it depolarisation can only occur at the nodes of ranvier

Question 32

what is saltatory conduction what's the advantage of this

Answer 32

where the action potential jumps from one node to the next -advantage= conserves energy as sodium potassium pump (which uses ATP) can only operate at the nodes

Question 33

what do unmyelinated neurones have instead

Answer 33

voltage gated sodium ion channels along the whole length of the axon, all channels have to open as the impulse is transmitted down which takes time causes localised currents means the whole axon has to be depolarised

Question 34

describe multiple sclerosis

Answer 34

an autoimmune disease where the body own immune system recognises antigens on myelin sheath as non self this myelin is attacked by t killer cells and antibodies are produced prevents saltatory conduction so slows down conduction of action potentials

Question 35

what is the effect of increased temperature

Answer 35

higher temp= mol have more KE - faster diffusion rate of Na+ ions across axon - faster movement of vesicles and faster diffusion of neurotransmitter

Question 36

what happens if temperature gets too high

Answer 36

the sodium potassium pump is denatured ( as they are proteins) fluidity of the phospholipid bilayer is disrupted synaptic enzymes are denatured (acetylcholinesterase)

Question 37

what is the effect of as larger axon diameter

Answer 37

the wider the axon diameter, the faster the speed of conduction, less reistance to flow of ions in cytoplasm

Question 38

what does the refractory period prevent

Answer 38

the propagation of the action potential backwards - can only go forwards UNIDIRECTIONAL also means action potentials cannot overlap limits the frequency at which action potentials are generated

Question 39

where does the refractory period start

Answer 39

after depolarisation

Question 40

what is the effect of the puffer fish toxin

Answer 40

have a toxin called tetradotoxin this blocks the voltage gated sodium ion channels in human nerve cells preventing action potentials

Question 41

give an example of an excitatory neurotransmitter

Answer 41

acetylcholine

Question 42

give an example of an inhibitory neurotransmitter

Answer 42

GABA

Question 43

what do excitatory neurotransmitters cause

Answer 43

the depolarisation of the post synaptic membrane which if goes above threshold an action potential will be generated

Question 44

what do inhibitory neurotransmitters cuase

Answer 44

the hyperpolaraisation in the post synaptic membrane and prevention of action potentials

Question 45

how do synapses allow transmission in one direction

Answer 45

- only the presynaptic neurone releases neurotransmitter - only pre synaptic membrane has calcium ion channels - only post synaptic membrane has specific receptors

Question 46

why is there lots of mitochondria in neurones

Answer 46

produce ATP by aerobic respiration used to: recombine choline and ethnic acid into acetylcholine and to allow the movement of secretory vesicles along the cytoskeleton

Question 47

describe the process of synaptic transmission

Answer 47

1) Na+ moves along the axon and into the pre synaptic bulb causing action potential and depolarisation 2) voltage gated Ca2+ ion channels open 3) calcium ion diffuse into the neurone 4) vesicles containing neurotransmitter move along the cytoskeleton using ATP towards the presynaptic membrane 5) vesicles fuse with the membrane in a process named exocytosis and neurotransmitter is released into the synaptic cleft 6) neurotransmitter diffuses across the synaptic cleft and attaches to receptors on post-synaptic membrane 7) receptors on the sodium ion channels, causes these channels to open and Na+ moves in 8) acetylcholine is then broken down in the cleft by the enzyme acetylcholinesterase forming choline and ethnic acid which diffuses back into the presynaptic bulb 9) choline and ethnic acid recombine with ATP to form acetylcholine which is stored in vesicles in the presyntpic cell

Question 48

what is the name of the protein attached to vesicles

Answer 48

snare proteins that bind to snare protein receptors on the membrane

Question 49

what effect does toxins have on the vesicle proteins sometimes

Answer 49

change the structure or digest them so no exocytosis can take place

Question 50

define spatial summation

Answer 50

when a number of presynaptic neurones connect to one post-synaptic neurone this amplifies low level signals

Question 51

define temporal summation

Answer 51

when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period

Question 52

why are synapses important (4)

Answer 52

- allows neurones to communicate- cell signalling - ensure transmission of action potentials in one way - allows integration: 1) convergence- one neurone can receive impulses from many 2) divergence- one neurone can transmit impulse to many neurones

Question 53

what is the effect of amphetamines

Answer 53

trigger the presynaptic neurone to release more neurotransmitter means the user has to replenish it after using the drug

Question 54

what is the effect of nerve gas

Answer 54

inhibit the enzyme acetylcholineesterase which means continuous action potentials

Question 55

what is the effect of alcohol

Answer 55

ethanol binds to GABA receptors changing their shape so they can better transport GABA and so increase the effect of GABA in the post synaptic neurone

Question 56

what is the effect of the atropine toxin from nightshade

Answer 56

has similar shape to acetylcholine binds to receptors on post synaptic membrane blocking them so ACh cannot bind Na+ channels remain closed and cannot enter therefore no depolarisation

Question 57

could atropine be used as a antidote for nerve gas

Answer 57

yes atropine would compete for the ACh receptors so ACh cannot bind reducing depolarisation

Question 58

what is the purpose of reflex arcs

Answer 58

to protect the body from harmful stimuli and are innate

Question 59

why are reflex arcs so fast

Answer 59

because they are involuntary so do not use the brain they are fast because the pathway is short and only use a few synapses use myelinated neurones

Question 60

briefly describe a reflex arc

Answer 60

1. receptor 2. sensory neurone 3. intermediate neurone in the spinal chord 4. motor neurone 5. effector - -> response

Question 61

describe the reflex arc of the knee jerk

Answer 61

1) stimulus= hitting the patellar tendon 2) sensory neurone transmits impulse to spinal chord 3) impulse travels down the motor neurone to the extensor muscles, they contract, at the same time relay neurone inhibits the motor neurone to flexor muscle and so relaxes 4) response= knee jerk

Question 62

describe the blinking reflex ( cranial reflex)

Answer 62

1) cornea is touched 2) impulse transmits down sensory neurones 3) passes through relay muscle in lower brain stem 4) down motor neurone which branches to both eyes and to eyelid muscles.