Nervous Coordination (Topic 6B) Flashcards
what is the value for resting potential?
-70mV
how is resting potential established?
- 3 Na out 2 K in via Na/K pump
- more Na outside than K inside, creating chemical gradient
- Na try naturally diffuse in but most gates are closed so can’t and K diffuse out naturally
- generating further distance and charge & electro and chemical gradient
- equilibrium met between electric and chemical gradients
describe how the resting potential is established in an axon by the movement across the membrane
2 marks
pump of Na+ out the axon
diffusion of K+ out the axon
why can sodium and potassium ions can only cross the axon membrane through proteins?
2 marks
- cannot pass through phospholipid bilayer
- because the ions are water soluble
the membrane is depolarised at what value?
+ 40mV
what is a nerve impulse?
a self propagating wave of electrical disturbance
when the membrane is hyper polarised the value is?
below -70mV
how does the membrane go from depolarised to hyper polarised?
the voltage dependent Na channels close and voltage dependent K channels open and K+ leave axon repolarising membrane
how does the membrane go from hyper polarised to polarised?
voltage dependent K channels close and K+ diffuse back in
when a neurone transmits a series of impulses, why does its rate of oxygen consumption increase?
more respiration
more energy supplied
for active transport of ions
why does a myelinated axon conduct impulses faster than a non-myelinated axon?
3 marks
- in myelinated action potential only at nodes
- the sheath makes the impulse jump from node to node
- action potential doesn’t have to travel along the whole length
what factors affect the speed of nerve impulse conduction?
temperature
myelin sheath presence
axon diameter
pre synaptic neurones…
send messages
the post synaptic neurone…
recieves messages
cholinergic synapses use…
acetylcholine
the properties of an action potential are…
• have a threshold
• all or nothing
• all the same size
• have a refractory period
what is the refractory period?
where channels remain closed so no further depolarisation occurs which ensures they are separate and only go in one direction
describe what is meant by the all or nothing principle
once the threshold is reached an action potential will always fire with the same change in voltage no matter the size of the stimulus
how does action potential change for a bigger stimulus?
action potentials are fired more frequently
how does axon diameter affect speed of conduction? why?
the bigger the diameter the quicker they are conducted.
because there is less resistance to the flow of ions than in the cytoplasm of a smaller axon so reached other parts of the neurone quicker
how does temperature affect speed of conduction? why?
as temperature increases, speed of conduction increases
because ions diffuse faster
(until denaturing)
the synaptic knob contains….
synaptic vesicles filled with neurotransmitter
what are the 3 steps for a nerve impulse to travel across a synapse?
- arrival of an action potential
- fusion of the vesicles
- diffusion of acetylcholine
at cholinergic synapses,
when action potential arrives at the synaptic knob what happens?
stimulates voltage-gated calcium ion channels in the presynaptic neurone to open so Ca+ diffuse into the knob
at cholinergic synapses,
when fusion of the vesicles occurs what happens?
the influx of Ca+ into the knob causes synaptic vesicles fuse with the presynaptic neurone. the vesicles release acetylcholine into the synaptic cleft by exocytosis
at cholinergic synapses,
when acetylcholine diffuses what happens?
ACh diffuses across synapse and binds to specific cholinergic receptors on the post synaptic membrane causes sodium ion channels to open and move in causing depolarisation. an action potential is generated if the threshold is reached
what do exitatory neurotransmitters do?
depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached
what do inhibitory neurotransmitters do?
hyperpolarise the postsynaptic membrane, preventing it from firing action potential
an inhibitory synapse is…
a synapse where inhibitory neurotransmitters are released from the presynaptic neurone following an action potential
summation is…
where the sum total of lots of smaller impulses triggers an action potential
the two types of summation are…
spatial
temporal
spatial summation is…
where 2 or more presynaptic neurones release their neurotransmitters at the same time onto the same post synaptic neurone
temporal summation is….
where 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone
is action potential more likely with spatial or temporal summation?
temporal
a neuromuscular junction is…
a specialised cholinerguc synapse between a motor neurone and muscle cell
neuromuscular junstions use which neurotransmitter?
acetylcholine
how do nueromuscular junctions work?
4 marks
- ACh released from vesicles in presynaptic membrane
- ACh diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane
- this triggers an action potential if threshold is reached
- ACh is broken down in the synpatic cleft by acetylcholineesterase
what are the 3 differences between a neuromuscular junction and other synapses?
- the postsynaptic membrane has lots of folds that form clefts that store AChE
- postsynaptic membrane has more receptors than other synapses
- ACh is always exitatory, so a respinse is alomst always caused
some drugs are agonists and…
activate more receptors
some drugs are antagonists and…
block receptors so they can’t be activated by neurotransmitters. so fewer receptors can be activated
some drugs inhibit the enzyme that breaks down neurotransmitters means that there is…
more neurotransmitters in the synaptic cleft to bind to receptors and they’re there for longer
some drugs stimulate the release of neurotransmitter from the presynaptic neurone ….
so more receptors are activated
some drugs inhibit the release of neurotransmitters from the presynaptic neurone so…
fewer receptors are activated
the three types of muscle in the body are…
smooth muscle
cardiac muscle
skeletal muscle
the role of skeletal muscle is to…
produce movement
anatgonistic pairs are…
pairs of muscles that work together to move a bone. the agonist contract and the antagonist relaxes
one muscle fibre is made up of…
myofibrils
muscle fibres have lots of mitochondria to provide….
ATP for muscle contraction
muscles are made up of…
many muscle fibres
myofibrils contain bundles of…
thick and thin myofilaments
thick myofilaments are made of…
myosin
thin myofilaments are made of…
actin
dark bands in a myofibril are…
thick myosin filamnets and some overlapping thin actin filaments
light bands in a myofibril are…
actin filaments only
each myofibril is made up of…
sarcomeres
the ends of each sarcomere are marked with a..
Z line
in the middle of each sarcomere there in an…
M line
the M line is the middle of…
the myosin filaments
around the M line there is a…
H zone
the H zone only contains…
myosin filaments
the A band is the…
dark band - thick myosin filaments and some overlapping thin actin filaments
the I band is the..
light band - actin filaments only
what happens in the sliding filament theory?
myosin and actin filaments slide over each other to make the sarcomeres contract
after muscle contraction sarcomeres return…
to their original length
in the sliding filament theory of muscle contraction which band stays the same length?
A band
in the sliding filament theory of muscle contraction which band gets narrower?
I band
in the sliding filament theory of muscle contraction which zone gets narrower?
H zone
when muscles contract the Z lines…
get closer together meaning the sarcomeres get shorter
myosin filaments have…
globular heads that are hinged
myosin filaments are hinged so they…
can move back and forth
each myosin head has…
a binding site for actin and a binding sitefor ATP
actin filaments have…
binding sites for myosin heads called actin-myosin binding sites
what other protein is found between actin filaments?
tropomysoin
what does tropomyosin do?
helps myofilaments move past each other
the 4 stages in muscle contraction are….
- arrival of action potential
- movement of the actin filament
- breaking of cross bridge
- return to resting state
the bond formed when a myosin head bind to an actin filament is called….
actin-myosin cross bridge
slow twitch muscle fibres contract…
quickly
slow twitch muscle fibres can work for…
long periods of time
what are slow twitch muscle fibres used for?
long distance running
which type of respiration works alongside slow twitch fibres
aerobic
do slow twitch muscle fibres have lots of little mitochondria and blood vessels?
lots
why do slow twitch muscle fibres have lots of mitochondria and blood vessels?
to supply the muscles with oxygen
are slow twitch muscle fibres rich in myoglobin?
yes
fast twitch muscle fibres contract…
quickly
fast twitch muscle fibres work for…
short periods of time
what are fast twitch muscle fibres used for?
sprinting
do fast twitch muscle fibres have lots of little mitochondria and blood vessels?
little
do fast twitch fibres have lots of myoglobin?
no
give evidence for the sliding filament theory…
- distance between Z lines shortens
- I band gets narrower
- H zone becomes narrower
- distance between Z lines shortens
- I band gets narrower
- H zone becomes narrower
if a myosin molecule was unable to bind to another myosin molecule why would muscle contraction be prevented
3 marks
cannot form myosin
cannot move actin
can’t move actin towards each other
explain the role of ATPase during muscle contraction
2 marks
- ATPase breaks ATP down ATP to be used for energy
- (energy is) used to form actomyosin bridges
describe how stimulation by nerve impulse starts the movement of actin filament
(6 marks)
- calcium ions
- bond to tropomysin
- revealing binding site on actin
- myosin binds to exposed sites on actin
- cross bridges form between actin and myosin
- activates ATPase
after death cross bridges between actin and myosin remain firmly bonded, why?
2 marks
- no ATP produced
- to seperate actin and myosin
