5.1.3 Neuronal Communication Flashcards
What do neurones transmit
Nerve impulses rapidly around the body
These impulses are in a electric nature
What is the function of a dendrite
Small extensions that carry impulses towards the cell body
What’s the function of the cell body
Produced protein neurotransmitters and ATP, has nucleus cytoplasm rough ER and mitochondria
What is the function of the myelin sheath
Lipid covering that insulated the axon speeding up nerve impulses by allowing Saltatory conduction
What is the function of Schwann cells
Produce myelin sheath
What is the function of node of ranvier
Gap between Schwann cells
No myelin sheath here
What is the function of the axon
Carries nerve impulses away from cell body, thing long cytoplasm with plasma membrane
What is the function of terminal end branches
Connect neurons to muscle
What is the job of the sensory neurones
What is the structure like
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
What is the job of the motor neurones
What is the structure like
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
What is the function of relay neurones
What is the structure
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
Describe Schwann cells
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
What’s the benefit of myelin
Speeds up conduction of action potentials due to faster depolarisation
What does polarised mean
Unequal distribution of
Charge
What is the name for a concentration gradient when we are dealing with ions
Electrochemical gradient
Describe the distribution of charge when at resting potential
Negative charge inside
Positive charge outside
Describe the sodium potassium pump
Actively transports 2k+ in and 3Na+ out of the axon
Using ATP
How is resting potential maintained
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
What two things do all sensory receptors have in common
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
What are the 4 types of sensory receptors
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)
What is pacinian corpuscle
A transducer- converts mechanical energy into electrical energy
A pressure receptor
Describe how an action potential is generated in a pacinian corpuscle
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
the greater the pressure, the greater…
the frequency of nerve impulses along the neurone
what is the all or nothing law
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
describe the distribution of charge when at action potential
negative outside
positive inside
explain what happens sat resting potential -70mv
- 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
what happens at depolarisation
- 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
what happens during repolarisation
voltage gated sodium ion channels close
- voltsage gated K+ ion channels open
- K+ ions diffuse out of the axon
what happens during hyperpolarisation
- 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
what is there function of a Schwann cell
wraps around the axon and produces myelin
myelin provides electrical insulation
prevents movement of ions into/out of neurone
prevents depolarisation
what does myelin prevent from entering the axon
what does this mean
does not allow Na+ or K+ ions to pass through it
depolarisation can only occur at the nodes of ranvier
what is saltatory conduction
what’s the advantage of this
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
what do unmyelinated neurones have instead
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
describe multiple sclerosis
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
what is the effect of increased temperature
higher temp= mol have more KE
- faster diffusion rate of Na+ ions across axon
- faster movement of vesicles and faster diffusion of neurotransmitter
what happens if temperature gets too high
the sodium potassium pump is denatured ( as they are proteins)
fluidity of the phospholipid bilayer is disrupted
synaptic enzymes are denatured (acetylcholinesterase)
what is the effect of as larger axon diameter
the wider the axon diameter, the faster the speed of conduction, less reistance to flow of ions in cytoplasm
what does the refractory period prevent
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
where does the refractory period start
after depolarisation
what is the effect of the puffer fish toxin
have a toxin called tetradotoxin
this blocks the voltage gated sodium ion channels in human nerve cells
preventing action potentials
give an example of an excitatory neurotransmitter
acetylcholine
give an example of an inhibitory neurotransmitter
GABA
what do excitatory neurotransmitters cause
the depolarisation of the post synaptic membrane which if goes above threshold an action potential will be generated
what do inhibitory neurotransmitters cuase
the hyperpolaraisation in the post synaptic membrane and prevention of action potentials
how do synapses allow transmission in one direction
- only the presynaptic neurone releases neurotransmitter
- only pre synaptic membrane has calcium ion channels
- only post synaptic membrane has specific receptors
why is there lots of mitochondria in neurones
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
describe the process of synaptic transmission
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
what is the name of the protein attached to vesicles
snare proteins that bind to snare protein receptors on the membrane
what effect does toxins have on the vesicle proteins sometimes
change the structure or digest them so no exocytosis can take place
define spatial summation
when a number of presynaptic neurones connect to one post-synaptic neurone
this amplifies low level signals
define temporal summation
when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period
why are synapses important (4)
- 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
what is the effect of amphetamines
trigger the presynaptic neurone to release more neurotransmitter
means the user has to replenish it after using the drug
what is the effect of nerve gas
inhibit the enzyme acetylcholineesterase which means continuous action potentials
what is the effect of alcohol
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
what is the effect of the atropine toxin from nightshade
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
could atropine be used as a antidote for nerve gas
yes atropine would compete for the ACh receptors so ACh cannot bind reducing depolarisation
what is the purpose of reflex arcs
to protect the body from harmful stimuli and are innate
why are reflex arcs so fast
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
briefly describe a reflex arc
- receptor
- sensory neurone
- intermediate neurone in the spinal chord
- motor neurone
- effector
- -> response
describe the reflex arc of the knee jerk
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
describe the blinking reflex ( cranial reflex)
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.
