(15) Nervous coordination

Question 1

why are neurone cell membranes polarised at rest

Answer 1

in resting state the outside of the membrane is positively charged compared to the inside as there are more positive ions in the outside than inside. polarised means there is a voltage / potential diff across it

Question 2

what is the voltage across the membrane when it’s at rest (resting potential)

Answer 2

-70mV

Question 3

how is the resting potential created and maintained

Answer 3

sodium potassium pumps move sodium ions out of the neurone but membrane isn’t permeable to sodium ions so they can’t move back in
creates a sodium ion electrochemical gradient because there are more positive sodium ions outside than inside (positively charged)
potassium ions can move in and out

Question 4

how do neurone cell membranes become depolarised when stimulated

Answer 4

stimulus triggers sodium ion channels to open, membrane becomes more permeable, sodium ions diffuse in making inside of neurone less negative.
if P.D reaches -55mV more sodium channels open (depolarisation)
at +30mV sodium ion channels close and K ion channels open so K diffuses out (repolarisation) membrane returns to resting potential

Question 5

what is hyperpolarisation

Answer 5

K ion channels are slow to close so theres a slight overshoot where too many K diffuse out and the P.D becomes more negative than resting potential (-70mV)

Question 6

why can’t the neurone cell membrane be excited again straight away after an action potential

Answer 6

because the ion channels are recovering and can’t be made to open (refractory period)

Question 7

what is a wave of depolarisation

Answer 7

when an action potential happens some of the sodium ions diffuse sideways causing Na ion channels in the next region of the neurone to open and Na diffuses into that part causing wave of depolarisation

Question 8

what 3 things are as a result of the refractory period

Answer 8

1) action potentials don’t overlap but pass as separate impulses
2) theres a limit to teh freq at which nerve impulses can be transmitted
3) action potentials are unidirectional (only travel in one direction)

Question 9

what does it mean by the all or nothing nature of an action potential

Answer 9

1. action potential with the same change in voltage will always fire after the threshold is reached regardless of the stimulus
2. action potential wont fire unless the threshold is reached
3. bigger stimulus wont cause a bigger action potential only cause them to fire at a higher frequency

Question 10

why are axons with larger diameters advantageous

Answer 10

action potentials are conducted quicker as theres less resistance to the flow of ions so depolarisation reaches other parts of the neurone cell membrane quicker

Question 11

how is a higher temperature advantageous

Answer 11

speed of conduction increases with higher temp because ions start to diffuse faster. only up to 40c though as after that the proteins begin to denature

Question 12

what are the benefits of myelination

Answer 12

myelin sheath is made of schwann cells which have nodes of ranvier where the sodium ion channels are concentrated. impulse jumps from node to node (saltatory conduction) which is really fast

Question 13

how do impulses travel along non myelinated neurones

Answer 13

impulse travels as a wave along the whole length of the axon membrane so you get depolarisation along the whole length of the membrane (slower than saltatory conduction)

Question 14

how do impulses jump between nodes

Answer 14

neurones cytoplasm conducts enough electrical charge to depolarise the next node so impulse can jump

Question 15

what happens when an action potential reaches the end of a neurone

Answer 15

neurotransmitters are released into the synaptic cleft and diffuse across to the postsynaptic membrane where it binds to specific receptors

Question 16

what makes impulses unidirectional

Answer 16

receptors for neurotransmitters are only on the postsynaptic membrane

Question 17

how do excitatory neurotransmitters work

Answer 17

depolarise the postsynaptic membrane making it fire an action potential if the threshold is reached

Question 18

how do inhibitory neurotransmitters work

Answer 18

hyperpolarise the postsynaptic membrane (making PD more negative) preventing it from firing an action potential

Question 19

what is summation

Answer 19

the effect of neurotransmitter released from many neurones is added together

Question 20

what is spatial summation

Answer 20

many neurones connect to one neurone (small amount of neurotransmitter from each neurone is added together to reach the threshold in the postsynaptic neurone and trigger an action potential)

Question 21

when can spatial summation lead to no action potential

Answer 21

if more inhibitory neurotransmitters are released than excitatory

Question 22

what is temporal summation

Answer 22

2 or more nerve impulses arrive in quick succession from the same presynaptic neurone making an action potential more likely because more neurotransmitter is released

Question 23

what is a neuromuscular junction

Answer 23

synapse between a motor neurone and a muscle cell

Question 24

what are agonists

Answer 24

drugs that are the same shapes as neurotransmitters so they mimic their action at receptors so more receptors are activated

Question 25

what are antagonists

Answer 25

drugs that block receptors so they can’t be activated by neurotransmitters so fewer receptors are activated

Question 26

what are inhibitory drugs

Answer 26

inhibitory: inhibit the enzymes that break down neurotransmitters so there are more neurotransmitters to bind to receptors or some drugs inhibit the release of neurotransmitters from the presynaptic neurone

Question 27

what are stimulatory drugs

Answer 27

stimulate the release of neurotransmitters from presynaptic neurone so more receptors are activated

Question 28

what is skeletal muscle made up of

Answer 28

muscle fibres and sarcolemma that folds in and sticks into the sarcoplasm to help spread electrical impulses throughout the sarcoplasm
sarcoplasm reticulum stores and releases calcium ions needed for muscle contraction
lots of mitochondria
multinucleate

Question 29

what are myofibrils

Answer 29

long cylindrical organelles made of protein specialised for contraction. 
contain thick (myosin) and thin (actin) myofilaments that move past each other to make muscles contract

Question 30

what is the sliding filament theory

Answer 30

myosin and actin filaments slide over each other to make the sarcomeres contract. the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract as the muscle fibre relaxes the sarcomere returns to its original length

Question 31

adaptations of myosin filaments

Answer 31

globular heads that are hinged so they can move back and forth. each myosin head has a binding site for actin and a binding site for ATP

Question 32

adaptations of actin filaments

Answer 32

binding sites for myosin heads (actin-myosin binding sites)

tropomyosin (protein) found between actin filaments helps myofilaments move past each other

Question 33

what is the function of tropomyosin

Answer 33

in resting unstimulated muscle the actin myosin binding site is blocked by tropomyosin so myofilaments cant slide past each other because the myosin heads can’t bind to the actin-myosin binding sites

Question 34

what is the ATP-phosphocreatine system (PCr)

Answer 34

ATP is made by phosphorylating ADP (adding a phosphate group taken from PCr)
PCr is stored inside cells and the ATP-PCr system generates ATP quickly- used for short bursts of vigorous exercise eg a tennis serve
anaerobic and alactic

Question 35

what are the properties of slow twitch muscle fibres

Answer 35

1) contract slowly
2) used for posture eg in back
3) endurance activities
4) work for a long time without getting tired
5) energy released slowly by aerobic respiration (lots of mitochondria and blood vessels to supply oxygen)
6) reddish as rich in myoglobin

Question 36

what are the properties of fast twitch muscle fibres

Answer 36

1) contract very quickly
2) used for fast movement eg in eyes and legs
3) good for short bursts of speed and power
4) get tired very easily
5) energys released through anaerobic respiration using glycogen (few mitochondria or blood vessels)
6) whitish in colour as not much myoglobin