the nervous system

Question 1

Explain why there is a difference in colour between grey and white matter (1)

Answer 1

grey matter contains cell bodies

Question 2

What is the name given to the cells which partially cover neurones (1)

Answer 2

shwaan cell

Question 3

What is the name given to the material which the cells produce to cover the axon (1)

Answer 3

myelin

Question 4

What is the function of this material in the conduction of an action potential (2)

Answer 4

• insulates the axon
• allows saltatory conduction/ impulse jumps from node to nod
• so speeding up the transmission of the action potential/ increase speed of conduction

Question 5

Multiple scleropsis is a progressive, degenerative disease of the nervous system in which myelin sheath is destroyed. Symptoms include increasing muscle weakness and loss of vision suggest an explanation for these symptoms (2)

Answer 5

• impulses cannot jump from node to node/ saltatory conduction is stopped/ local circuits are too short/ voltage gate Na+ channels between nodes of ranvier
• so action potential cannot be generated/ speed of conduction is reduced/ action potential does not reach destination

Question 6

Suggest a possible medical treatment for multiple sclerosis (1)

Answer 6

• remyelinate the axon
• use of stem cells
• make the membrane add Na+ channels in bare areas
• prevet further ddemyelination
• immune suppressants/inhibitory frugs

Question 7

Give two ways in which the nerve net differes from the nervous system of a vertebrate (2)

Answer 7

• responds to limited number of stimuli
• cannot detect source of stimulus/ impulse passes in all directions
• number of effectors is mall
• no CNS
• action potential can be carried in more than one direction along a neurone
• one type of cell/ unmyelinatied / slower response

Question 8

Describe how the resting potential is maintained in the neurone (3)

Answer 8

• sodium potassium pump
• ATP/active transport
• 3Na+ out and 2K+ in
• organic anions negative charged molecules/ proteins
• -70mv potential difference across membrane
• membrane leakage more permeable to K+ than Na+

Question 9

What is taking place at -70mv
an at +40mv (5)

Answer 9

-70mv
* threshold reached
* sodium voltage gated channels open
* sodiums ion diffuse into cytoplam
* depolarised
+40mv
* sodium voltage gated channels close
* potassium voltage gated channels open
* potassium diffuses out
* sodium/ potassium pumps
* repolarised

Question 10

Multiple sclerosiss is caused by the immune system destroying th myelin sheath of nerones. Explain why this condiytion leads to the slowing down of the transmission of a nerve impulse (3)

Answer 10

• myelin sheath electrical insulation
• ions exchange only at nodes of ranvier/ depolarisation only at nodes
• action potential jumps from one node of ranvier to next
• saltatory conduction
• if no myelin sheath local circuits
• altatory conduction must faster than local circuits

Question 11

Suggest the ways in which chemicals could increase activity of the nervous system (2)

Answer 11

• mimic action of normal transmitters/ bind to receptors
• prevents breakdown of transmitter
• stimulate release of transmitters
• reduce threshold for excitation of posst synaptic membranes

Question 12

Suggest ways that chemical can decrease actviity in the nervous system (2)

Answer 12

• block receptors on posty synaptic membrane
• prevent Ca2+ being released
• prevent exocytosis
• prevents recycling of neurotransmitter /active tranport back across presynaptic membrane
• raises threshold
• changes shape of neurotransmitter

Question 13

Name the cell that forms myelin sheath (10

Answer 13

schwaan cell

Question 14

Explain in terms of movement of ions what causes the rise of membrane potential from -70mv to 40mv (2)

Answer 14

• voltage gated sodium channels open/ increase in sodium ion permeability
• sodium ions diffuse/flood/rush/sudden influx in

Question 15

state the name given to the name to the rapid fall in membrane potential (1)

Answer 15

repolarisation

Question 16

Suggest how cardiac muscle fibres would respond when the voltage across the membrane rises (1)

Answer 16

contraction

Question 17

The cardiac muscle fibres used to obtain the oscilloscope trace where obtained from a frogs heart. Consider the ethics of killing a frog to obtain cardica muscle fibre one argument in favour and one against (2)

Answer 17

• frog has a right to life / suffering/ pain/distres/ harm of frogs/ frogs are scarce in the wild
• benefits to medicine/ health of the heart

Question 18

What units is membrane potential (1)

Answer 18

mv

Question 19

What units is time (1)

Answer 19

ms

Question 20

What is represented by -55mv (1)

Answer 20

threshold potential

Question 21

When a person touches a hot object with their finger they will move away from the heat. State the advantage to humans of having this type of response to an external stimulus (1)

Answer 21

protecting/ prevents damage/injury/harm

Question 22

What is the name given to the type of nervous system in a cnidarian (1)

Answer 22

nerve net

Question 23

Explain why the non myelinated neurones of cnidarians result in slower impulses than mammals (2)

Answer 23

• impulse must pass along whole length of the neurone/membrane/axon
• mammals have meyli/nodes which cause saltatory conduction

Question 24

Explain the toxic effects of organophosphates (5)

Answer 24

• aceytlcholine is normally hydrolysed/ broken down by acetylcholinesterase
• organophosphates prevent the breakdown of acetylcholine
• acetylcholine remains bound to receptors on posty synaptic membrane
• so synaptic transmission/action potentials continue to be generated
• sustained contraciton of muscle
• uncontrolled ocntractions of diaphragm/intercostal muscles intefere with breathing

Question 25

psychoactive drugs can affect synaptic transmission in a number of different ways suggest some different mechanisms by which psychoactive drugs could decrease the rate of synaptic transmission (4)

Answer 25

* some drugs prevent synthesis/resynthesis of neurotransmitter * blocking Ca2+ uptake * some drugs inhibit release/exocytosis of neurootransmitters * some drug block receptors in post synaptic membrane preventing neurotransmitters biding to them * sodium ion channels change shape * faster reabsorption of neurotransmitter * hyperpolarisation of posty synaptic membrane

Question 26

Impulses are transmitted throguh the nuerone as a wave of action potentials. Explain how the movement of ions result in the generation of an action potential (4)

Answer 26

* sodium ions channels open * sodium ions (rusn in / influx) * threshold reached/ exceeded * charge changes to become positive inside axon and negative outside axon

Question 27

Give two reasons shown on the diagram whcih would prevent the nerve impulse travelling in the opposite direction (2)

Answer 27

* synaptic vesicles only on presynaptic membrane side of synapse * refractory period/ hyperpolarisation

Question 28

Explain what would happen to the rate of transmission of the never impulse if the myelin was damaged (2)

Answer 28

* slow down * saltatory conduction would ot take place/ local circuit shortened

Question 29

Curare is a poisonous plabts which causes muscle paralysis by acting on the post synaptic membrane preventing transmission fo the nerve impule across muscular joing suggest and explain how curare may prevent the transmission of the impulse across the neuromuscular junction (3)

Answer 29

* curare has a complementary shape binds to receptors of synaptic membrane * prevents transmitter substance / acetylcholine binding * Na+ gated channels remain close/no active potential/ Na+ oion do not move in

Question 30

Motor neurones have only a single dendrite true of false (1)

Answer 30

false

Question 31

Suggest why curare aplant poison causing muscle paralysis have no effect on the contraction of muscles of the heart (1)

Answer 31

different tranmitter used to trigger contraction of the heart / adrenalin used/ heart is myogenic

Question 32

Motor neuorne have many axons true or false

Answer 32

false

Question 33

dendrties recieve and intergrate impules true of false (1)

Answer 33

true

Question 34

dendrites of motor neurone are rarely myelinated true of false (1)

Answer 34

true

Question 35

What is a reflex actions (2)

Answer 35

* rapid reaction/ response to a stimulus * automatic/involuntary/not under concious control/brain not involved

Question 36

Describe how a resting potential is maintained in a neurone (2)

Answer 36

* Na+ sodium ions are activley removed / pumped out/ faster than K+ ions are moven in * K+ diffuse out more rapidly that Na+ * sodium potasssium pumps pump 3Na=out and 2K+ in

Question 37

Describe how the potential across the membrane is reversed when an action potential is produced (2)

Answer 37

* sudden change/increase in permeability of the membrane to Na+/ sodium gates/ channels open * sodium ions diffue in down a concentration gradient

Question 38

Suggest an explanation for the increase in speed of conduction as axon diameter increases (2)

Answer 38

* speed of transmission depends on resistane of axon * larger diameter of the axon the less the resistance * increased diameter increased surface area over which exchange of ions take place

Question 39

Explain wh a myelinated axon uses less ATP to transmit a nerve impulse than a non myelinate axon of the same diameter (2)

Answer 39

* ATP is required for active transport/ ref of sodium potassium pumps * Na+ ions activvley moved out only at nodes in myelinated * Na+ activley moved out along whole length of axon in nin myelinated

Question 40

Explain giving two reasons why nerve impulses can only travel in one directions (2)

Answer 40

* sensitvity of the nerrve membrane lost during depolarisation/refractory period * in synapses transmitter substances diffuse from knob to post synaptic membrane

Question 41

From which type of biological molecules are pumps and channels and the bilayer made up of (2)

Answer 41

* pumps and channels - proteins * bilayers - phospholipids

Question 42

How is the resting potential bought about (2)

Answer 42

* sodium and potassium pump * 3Na + out and 2K+ in * K channels open * less permebale to Na+

Question 43

How is depolarisation bought about (2)

Answer 43

* impulse opens Na+ channel * Na+ ions rush in / sudden increase in permeability to Na+

Question 44

Explaij how impulses are transmitted across a synapse (3)

Answer 44

* transmitter substances synthesised in synaptic knob * impulse causes secretory vesicle to migrate to presynaptic membrane / Ca2+ rush in * vesicle fuses with membrane discharges transmitter substance /exocytosis * diffusion of transmitter substance across cleft * transmitter binds to post synaptic membrane / stimulates depolarisation / reference to receptors

Question 45

Describe the function of acetylcholine at a synapse (5)

Answer 45

* acts as a neurotransmitter/ transmits impulse across synapse * synaptic vesicles fuse with pre synaptic membrane * released aceytlcholine diffuses across synpatic cleft * attatched to receptor sites on posty synaptic membrane * sodium channels open and Na+ ions diffuse in * membrane is depolarised * action potential is generated

Question 46

Explain how substance secreted by schwaan cells and their arrangement along the neurone affect the speed of transmission of a nerve impulse (4)

Answer 46

* myelin inhibits movement of ions from axon/insulates axon / prevent depolaisation * gaps between shwaan cells called nodes of ranvier * no myelin present in nodes * depolarisation only posible at nodes of ranvier / action potential can only form at nodes where there ins no myelin/ channels can only open/close in the nodes * action potential jumps from one node to next/saltatory conduction/lengthens local circuits * nerve impule transmission is faster