nervous coordination

Question 1

resting potential

Answer 1

the difference between electrical charge inside and outside the axon when a neuron is not conducting an impulse
more positive ions outside axon than inside
inside the axon -70mV

Question 2

how is resting potential established

Answer 2

Sodium potassium pump actively transports 3 Na+ out of the axon, 2 K+ into the axon membrane more permeable to K+
K+ diffuses out down conc. gradient - facilitated diffusion
membrane less permeable to Na+ (closed Na+ channels)
higher conc. Na+ outside

Question 3

action potential

Answer 3

When the neuron’s voltage increases beyond the -55mV
threshold
nervous impulse generated
generated due to membrane
becoming more permeable to
Na+

Question 4

action potential stimulus

Answer 4

Voltage-gated Na+ channels open - membrane more permeable to Na+
Na+ diffuse (facilitated) into neuron down conc. gradient
voltage across membrane
increases

Question 5

action potential depolarisation

Answer 5

When a threshold potential is reached, an action potential is
generated
more voltage-gated Na+ channels open
Na+ move by facilitated diffusion down conc. gradient into axon
potential inside becomes more
positive

Question 6

action potential repolarisation

Answer 6

Na+ channels close, membrane less permeable it Na+
K+ voltage-gated channels open, membrane more permeable to K+
K+ diffuse out neuron down
conc. gradient
voltage rapidly decreases

Question 7

action potential hyperpolarisation

Answer 7

K+ channels slow to close -> overshoot in voltage
too many K+ diffuse out of neuron
potential difference decreases to
-80mV
sodium-potassium pump returns neuron to resting potential

Question 8

all or nothing principle

Answer 8

If depolarisation does not exceed -55 mV threshold, action potential is not produced
any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage

Question 9

importance of all or nothing principle

Answer 9

Makes sure animals only respond to large enough stimuli rather than responding to every small change in environment
(overwhelming)

Question 10

refractory period

Answer 10

After an action potential has been generated, the membrane enters a period where it cannot be stimulated
because Na+ channels are recovering and cannot be opened

Question 11

importance of refractory period

Answer 11

Ensures discrete impulses produced - action potentials separate and cannot be
generated immediately
unidirectional - cannot generate
action potential in refractory
region
limits number of impulse
transmissions - prevent
overwhelming

Question 12

factors affecting speed of conductance

Answer 12

Myelination (increases speed)
axon diameter (increases speed)
temperature (increases speed)

Question 13

how myelination affects speed

Answer 13

With myelination - depolarisation occurs at Nodes of Ranvier only -> saltatory conduction
impulse jumps from node-node
in non-myelinated neurones,
depolarisation occurs along full
length of axon - slower

Question 14

how axon diameter affects speed

Answer 14

increases speed of conductance
less leakage of ions

Question 15

how temperature affects speed

Answer 15

Increases speed of conductance
increases rate of movement of
ions as more kinetic energy
(active transport/diffusion)
higher rate of respiration as
enzyme activity faster so ATP is
produced faster - active
transport faster

Question 16

saltatory conduction

Answer 16

Gaps between myelin sheath are nodes of Ranvier
an action potential can “jump”
from node to node via saltatory
conduction - action potential
travels faster as depolarisation
across the whole length of the axon not required

Question 17

synapse

Answer 17

Gaps between end of axon of
one neurone and dendrite of
another
impulses are transmitted as
neurotransmitters

Question 18

why are synapses unidirectional

Answer 18

Receptors only present on the post-synaptic membrane
enzymes in the synaptic cleft break
down excess-unbound
neurotransmitter - concentration gradient
established from pre-post synaptic neurone
neurotransmitter only released from the pre-synaptic neurone

Question 19

cholinergic synapse

Answer 19

The neurotransmitter is acetylcholine
enzyme breaking down
acetylcholine = acetylcholine-esterase
breaks down acetylcholine to
acetate and choline to be
recycled in the pre-synaptic
neurone

Question 20

summation

Answer 20

Rapid build-up of neurotransmitters in the synapse to help generate an action potential by 2 methods:
spatial or temporal
required because some action
potentials do not result in
sufficient concentrations of
neurotransmitters released to
generate a new action potential

Question 21

spatial summation

Answer 21

Many different neurones collectively trigger a new action
potential by combining the
neurotransmitter they release
to exceed the threshold value
e.g., retinal convergence for
rod cells

Question 22

temporal summation

Answer 22

When one neurone releases
neurotransmitters repeatedly
over a short period of time to
exceed the threshold value
e.g., 1 cone cell signalling 1
image to the brain

Question 23

inhibitory synapses

Answer 23

Causes chloride ions (Cl-) to move into post-synaptic neuron and K+ to move out
makes membrane hyperpolarise
(more negative) so less likely an
action potential will be propagated

Question 24

neuromuscular junction

Answer 24

Synapse that occurs between a
motor neurone and a muscle
similar to synaptic junction

Question 25

neuromuscular junction vs cholinergic synapse

Answer 25

NMJ -
unidirectional
only excitatory
connects motor neurons to muscles
end point for action potential

CS-
unidirectional
excitatory or inhibitory
connects 2 neurons
new action potential generated in next neuron

Question 26

myofibril

Answer 26

Made up of fused cells that share nuclei/cytoplasm
(sarcoplasm) and many mitochondria
millions of muscle fibres make
myofibrils - bringing about movement

Question 27

role of Ca2+ in sliding filament theory

Answer 27

Ca2+ enters from sarcoplasmic
reticulum and causes tropomyosin to change shape
myosin heads attach to exposed
binding sites on actin forming
actin-myosin cross bridge
activates ATPase on myosin
ATP hydrolysed so energy for
myosin heads to be recocked

Question 28

role of tropomyosin in sliding filament theory

Answer 28

Tropomyosin covers binding site on actin filament
Ca2+ bind to tropomyosin on
actin so it changes shape exposes binding site
allows myosin to bind to actin,
forming cross bridge

Question 29

role of ATP in myofibril contraction

Answer 29

Hydrolysis of ATP -> ADP + Pi releases energy
movement of myosin heads pulls actin - power stroke
ATP binds to myosin head causing it to detach, breaking cross bridge
myosin heads recocked
active transport of Ca2+ back to
sarcoplasmic reticulum

Question 30

role of myosin in myofibril contraction

Answer 30

Myosin heads (with ADP attached) attach to binding sites on actin.
form actin-myosin cross bridge
power stroke - myosin heads
move pulling actin
requires ATP to release energy
ATP binds to myosin head to
break cross bridge so myosin
heads can move further along
actin

Question 31

phosphocreatine

Answer 31

A chemical which is stored in muscles
when ATP concentration is low,
this can rapidly regenerate ATP
from ADP by providing a Pi group.
for continued muscle contraction

Question 32

slow-twitch fibres

Answer 32

Specialised for slow, sustained contractions (endurance)
lots of myoglobin
many mitochondria - high rate
aerobic respiration to release
ATP
many capillaries - supply high
concentrations of glucose/O2 &
prevent build-up of lactic acid
e.g. thighs/calf

Question 33

fast-twitch fibres

Answer 33

Specialised in producing rapid,
intense contractions of short duration
glycogen -> hydrolysed to glucose -> glycolysis
higher concentration of enzymes involved in anaerobic
respiration - fast glycolysis phosphocreatine store
e.g., eyelids/biceps